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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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19 pages, 1077 KB  
Article
Some Issues on Crystal Plasticity Models Formulation: Motion Decomposition and Constitutive Law Variants
by Peter Trusov, Alexey Shveykin and Nikita Kondratev
Crystals 2021, 11(11), 1392; https://doi.org/10.3390/cryst11111392 - 15 Nov 2021
Cited by 12 | Viewed by 3161
Abstract
In this paper, kinematic relations and constitutive laws in crystal plasticity are analyzed in the context of geometric nonlinearity description and fulfillment of thermodynamic requirements in the case of elastic deformation. We consider the most popular relations: in finite form, written in terms [...] Read more.
In this paper, kinematic relations and constitutive laws in crystal plasticity are analyzed in the context of geometric nonlinearity description and fulfillment of thermodynamic requirements in the case of elastic deformation. We consider the most popular relations: in finite form, written in terms of the unloaded configuration, and in rate form, written in terms of the current configuration. The presence of a corotational derivative in the relations formulated in terms of the current configuration testifies to the fact that the model is based on the decomposition of motion into the deformation motion and the rigid motion of a moving coordinate system, and precisely the stress rate with respect to this coordinate system is associated with the strain rate. We also examine the relations of the mesolevel model with an explicit separation of a moving coordinate system and the elastic distortion of crystallites relative to it in the deformation gradient. These relations are compared with the above formulations, which makes it possible to determine how close they are. The results of the performed analytical calculations show the equivalence or similarity (in the sense of the response determined under the same influences) of the formulation and are supported by the results of numerical calculation. It is shown that the formulation based on the decomposition of motion with an explicit separation of the moving coordinate system motion provides a theoretical framework for the transition to a similar formulation in rate form written in terms of the current configuration. The formulation of this kind is preferable for the numerical solution of boundary value problems (in a case when the current configuration and, consequently, contact boundaries, are not known a priori) used to model the technological treatment processes. Full article
(This article belongs to the Special Issue Crystal Plasticity (Volume II))
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19 pages, 4026 KB  
Article
Strain-Gradient Crystal Plasticity Finite Element Modeling of Slip Band Formation in α-Zirconium
by Omid Sedaghat and Hamidreza Abdolvand
Crystals 2021, 11(11), 1382; https://doi.org/10.3390/cryst11111382 - 12 Nov 2021
Cited by 13 | Viewed by 3642
Abstract
Two methods for the determination of geometrically necessary dislocation (GND) densities are implemented in a lower-order strain-gradient crystal plasticity finite element model. The equations are implemented in user material (UMAT) subroutines. Method I has a direct and unique solution for the density of [...] Read more.
Two methods for the determination of geometrically necessary dislocation (GND) densities are implemented in a lower-order strain-gradient crystal plasticity finite element model. The equations are implemented in user material (UMAT) subroutines. Method I has a direct and unique solution for the density of GNDs, while Method II has unlimited solutions, where an optimization technique is used to determine GND densities. The performance of each method for capturing the formation of slip bands based on the calculated GND maps is critically analyzed. First, the model parameters are identified using single crystal simulations. This is followed by importing the as-measured microstructure for a deformed α-zirconium specimen into the finite element solver to compare the numerical results obtained from the models to those measured experimentally using the high angular resolution electron backscatter diffraction technique. It is shown that both methods are capable of modeling the formation of slip bands that are parallel to those observed experimentally. Formation of such bands is observed in both GND maps and plastic shear strain maps without pre-determining the slip band domain. Further, there is a negligible difference between the calculated grain-scale stresses and elastic lattice rotations from the two methods, where the modeling results are close to the measured ones. However, the magnitudes and distributions of calculated GND densities from the two methods are very different. Full article
(This article belongs to the Special Issue Crystal Plasticity (Volume II))
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11 pages, 3379 KB  
Article
Crystal Structures, Thermal and Luminescent Properties of Gadolinium(III) Trans-1,4-cyclohexanedicarboxylate Metal-Organic Frameworks
by Pavel A. Demakov, Alena A. Vasileva, Vladimir A. Lazarenko, Alexey A. Ryadun and Vladimir P. Fedin
Crystals 2021, 11(11), 1375; https://doi.org/10.3390/cryst11111375 - 11 Nov 2021
Cited by 12 | Viewed by 3565
Abstract
Four new gadolinium(III) metal-organic frameworks containing 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) chelate ligands and trans-1,4-cyclohexanedicarboxylate (chdc2−) were synthesized. Their crystal structures were determined by single-crystal X-ray diffraction analysis. All four coordination frameworks are based on the binuclear carboxylate building units. [...] Read more.
Four new gadolinium(III) metal-organic frameworks containing 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) chelate ligands and trans-1,4-cyclohexanedicarboxylate (chdc2−) were synthesized. Their crystal structures were determined by single-crystal X-ray diffraction analysis. All four coordination frameworks are based on the binuclear carboxylate building units. In the compounds [Gd2(bpy)2(chdc)3]·H2O (1) and [Gd2(phen)2(chdc)3]·0.5DMF (2), the six-connected {Ln2(L)2(OOCR)6} blocks form a 3D network with the primitive cubic (pcu) topology. In the compounds [Gd2(NO3)2(phen)2(chdc)2]·2DMF (3) and [Gd2Cl2(phen)2(chdc)2]·0.3DMF·2.2dioxane (4), the four-connected {Ln2(L)2(X)2OOCR)4} units (where X = NO3− for 3 or Cl− for 4) form a 2D square-grid (sql) network. The solid-state luminescent properties were investigated for the synthesized frameworks. Bpy-containing compound 1 shows no luminescence, possibly due to the paramagnetic quenching by Gd3+ cation. In contrast, the phenathroline-containing MOFs 2–4 possess yellow emission under visible excitation (λex = 460 nm) with the tuning of the characteristic wavelength by the coordination environment of the metal center. Full article
(This article belongs to the Special Issue Hybrid Organic-Inorganic Materials Used to Improve the Environment and Human Health)
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17 pages, 4976 KB  
Article
Porosity Distribution Simulation and Impure Inclusion Analysis of Porous Crystal Layer Formed via Polythermal Process
by Yingshuang Meng, Zhonghua Li, Xiangcun Li, Wu Xiao, Gaohong He, Xuemei Wu and Xiaobin Jiang
Crystals 2021, 11(11), 1347; https://doi.org/10.3390/cryst11111347 - 5 Nov 2021
Cited by 2 | Viewed by 2638
Abstract
In this work, we investigated the porosity distribution and separation property of the porous crystal layer formed via the polythermal process. The proposed porosity distribution model, considering both the cooling profile and the crystal settling effect, provided simulative results that met the MRI [...] Read more.
In this work, we investigated the porosity distribution and separation property of the porous crystal layer formed via the polythermal process. The proposed porosity distribution model, considering both the cooling profile and the crystal settling effect, provided simulative results that met the MRI analysis experimental results with suitable agreement. Significant porosity variation from the top to the bottom of the crystal layer (ϕ from 0.75 to 0.55 under rapid cooling profile) was detected. Meanwhile, the vertical supersaturation degree gradient induced by the fluid fluctuation could impact nucleation and crystal growth kinetic along with crystal particle settling. The resulting crystal layer possessed various impurity inclusion conditions. Under a moderate cooling profile (0.4 K·min−1), the volume fraction of closed pores against overall pores decreased from 0.75 to 0.36. The proposed model and experimental analysis approach were demonstrated to be helpful for porosity distribution simulation and impure inclusion analysis of layer crystallization. Full article
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9 pages, 3062 KB  
Article
Surface Porosity of Natural Diamond Crystals after the Catalytic Hydrogenation
by Aleksei Chepurov, Valeri Sonin, Dmitry Shcheglov, Egor Zhimulev, Sergey Sitnikov, Alexander Yelisseyev and Anatoly Chepurov
Crystals 2021, 11(11), 1341; https://doi.org/10.3390/cryst11111341 - 3 Nov 2021
Cited by 4 | Viewed by 2822
Abstract
The study of diamond surfaces is traditionally undertaken in geology and materials science. As a sample material, two natural diamond crystals of type Ia were selected, and their luminescence and nitrogen state was characterized. In order to etch the surface catalytic hydrogenation was [...] Read more.
The study of diamond surfaces is traditionally undertaken in geology and materials science. As a sample material, two natural diamond crystals of type Ia were selected, and their luminescence and nitrogen state was characterized. In order to etch the surface catalytic hydrogenation was performed using Fe particles as an etchant. Micromorphology of the surface was investigated by scanning electron and laser confocal microscopy. It was demonstrated that etching occurred perpendicular to the crystal surface, with no signs of tangential etching. The average depth of caverns did not exceed 20–25 μm with a maximal depth of 40 μm. It is concluded that catalytic hydrogenation of natural type Ia diamonds is effective to produce a porous surface that can be used in composites or as a substrate material. Additionally, the comparison of results with porous microsculptures observed on natural impact diamond crystals from the Popigai astrobleme revealed a strong resemblance. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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37 pages, 12641 KB  
Review
Advances in Diffraction Studies of Light-Induced Transient Species in Molecular Crystals and Selected Complementary Techniques
by Krystyna A. Deresz, Piotr Łaski, Radosław Kamiński and Katarzyna N. Jarzembska
Crystals 2021, 11(11), 1345; https://doi.org/10.3390/cryst11111345 - 3 Nov 2021
Cited by 11 | Viewed by 3815
Abstract
The review provides a summary of the current methods of tracing photoexcitation processes and structural dynamics in the solid state, putting major emphasis on the X-ray diffraction techniques (time-resolved Laue diffraction on synchrotron sources and time-resolved serial femtosecond crystallography on X-ray free-electron lasers). [...] Read more.
The review provides a summary of the current methods of tracing photoexcitation processes and structural dynamics in the solid state, putting major emphasis on the X-ray diffraction techniques (time-resolved Laue diffraction on synchrotron sources and time-resolved serial femtosecond crystallography on X-ray free-electron lasers). The recent developments and nowadays experimental possibilities in the field are discussed along with the data processing and analysis approaches, and illustrated with some striking literature examples of the respective successful studies. Selected complementary methods, such as ultrafast electron diffraction or time-resolved X-ray absorption spectroscopy, are briefly presented. Full article
(This article belongs to the Special Issue Time-Resolved X-ray Diffraction and Scattering Techniques Applied to Dynamical Processes)
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6 pages, 2298 KB  
Communication
Liquid Crystalline Cholesteric Reflective Layers for Colored Silicon-Based Solar Cells
by Sangwok Bae, Dong-Sun Park and Suk-Won Choi
Crystals 2021, 11(11), 1336; https://doi.org/10.3390/cryst11111336 - 1 Nov 2021
Cited by 1 | Viewed by 3007
Abstract
The performance of a prototype opaque-type colored silicon-based solar cell integrated with liquid crystalline cholesteric layers is investigated. These devices were developed using only organic components and wet processes, without complicated vacuum processes. The evaluated performances of the prototype solar cells were inferior [...] Read more.
The performance of a prototype opaque-type colored silicon-based solar cell integrated with liquid crystalline cholesteric layers is investigated. These devices were developed using only organic components and wet processes, without complicated vacuum processes. The evaluated performances of the prototype solar cells were inferior to those of the other types of previously reported colored solar cells because of the inherent limitations of the cholesteric layers, such as the limited reflectance (~50%), narrow color gamut, and viewing angle-dependent color changes. We propose effective strategies for improving the performance of colored solar cell modules integrated with cholesteric layers. Full article
(This article belongs to the Section Organic Crystalline Materials)
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20 pages, 3408 KB  
Review
Liquid Crystal Thermography in Gas Turbine Heat Transfer: A Review on Measurement Techniques and Recent Investigations
by Srinath V. Ekkad and Prashant Singh
Crystals 2021, 11(11), 1332; https://doi.org/10.3390/cryst11111332 - 31 Oct 2021
Cited by 22 | Viewed by 4691
Abstract
Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to [...] Read more.
Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to design hot gas path components that can meet the modern-day engine performance and emission goals. LCT provides valuable information on the local surface temperature, which is used in different experimental methods to arrive at the local h and η. The detailed nature of h and η through LCT sets it apart from conventional thermocouple-based measurements and provides valuable insights into cooling designers for concept development and its further iterations. This article presents a comprehensive review of the state-of-the-art experimental methods employing LCT, where a critical analysis is presented for each, as well as some recent investigations (2016–present) where LCT was used. The goal of this article is to familiarize researchers with the evolving nature of LCT given the advancements in instrumentation and computing capabilities, and its relevance in turbine heat transfer problems in current times. Full article
(This article belongs to the Special Issue Liquid Crystal Thermography for Gas Turbine Heat Transfer Measurements)
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9 pages, 1755 KB  
Article
Potential of Sub-THz-Wave Generation in Li2B4O7 Nonlinear Crystal at Room and Cryogenic Temperatures
by Dmitry Ezhov, Snezhana Turgeneva, Nazar Nikolaev, Alexander Mamrashev, Sergei Mikerin, Fedor Minakov, Andrey Simanchuk, Valery Antsygin, Valery Svetlichnyi, Valery Losev and Yury Andreev
Crystals 2021, 11(11), 1321; https://doi.org/10.3390/cryst11111321 - 29 Oct 2021
Cited by 3 | Viewed by 2694
Abstract
Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz [...] Read more.
Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li2B4O7; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o − e → o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o − o → e and e − e → e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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14 pages, 5993 KB  
Article
Novel Device and Strategy for Growing Large, High-Quality Protein Crystals by Controlling Crystallization Conditions
by Naoki Tanigawa, Sachiko Takahashi, Bin Yan, Masayuki Kamo, Naoki Furubayashi, Koji Kubota, Koji Inaka and Hiroaki Tanaka
Crystals 2021, 11(11), 1311; https://doi.org/10.3390/cryst11111311 - 27 Oct 2021
Cited by 1 | Viewed by 2904
Abstract
Neutron diffraction experiments are informative for determining the locations of hydrogen atoms in protein molecules; however, much larger crystals are needed than those required for X-ray diffraction. Thus, additional techniques are required to grow larger crystals. Here, a unique crystallization device and strategy [...] Read more.
Neutron diffraction experiments are informative for determining the locations of hydrogen atoms in protein molecules; however, much larger crystals are needed than those required for X-ray diffraction. Thus, additional techniques are required to grow larger crystals. Here, a unique crystallization device and strategy for growing large protein crystals are introduced. The device uses two micropumps to control crystal growth by altering the precipitant concentration and regulating the pinpoint injection of dry air flow to the crystallization cell. Furthermore, the crystal growth can be observed in real time. Preliminary microbatch crystallization experiments at various concentration ranges of polyethylene glycol (PEG) 4000 and sodium chloride were first performed to elucidate optimized crystallization conditions. Based on these results, a device to precisely control the sodium chloride and PEG concentrations and the supply of dry air to the crystallization cell was used, and 1.8 mm lysozyme and 1.5 mm alpha-amylase crystals with good reproducibility were obtained. X-ray data sets of both crystals were collected at room temperature at BL2S1 of the Aichi Synchrotron Radiation Center and confirmed that these crystals were of high quality. Therefore, this crystallization device and strategy were effective for growing large, high-quality protein crystals. Full article
(This article belongs to the Special Issue Protein Crystallography: Achievements and Challenges)
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10 pages, 3711 KB  
Article
Synthesis, Crystal Structure, and Luminescent Properties of a New Holmium(III) Coordination Polymer Involving 2,5-Dihydroxy-1,4-terephthalic Acid Dianion as Ligand
by Jiaqi Li, Linan Dun, Fanming Zeng, Chun Li and Zhongmin Su
Crystals 2021, 11(11), 1294; https://doi.org/10.3390/cryst11111294 - 26 Oct 2021
Cited by 2 | Viewed by 3030
Abstract
A novel coordination polymer {[Ho2(DHTA)3(H2O)5]·H2O}n (1) was synthesized by hydrothermal synthesis (DHTA = 2,5-dihydroxy-1,4-terephthalic acid anion). The crystallographic data show that complex 1 crystallizes in a triclinic system with space group P [...] Read more.
A novel coordination polymer {[Ho2(DHTA)3(H2O)5]·H2O}n (1) was synthesized by hydrothermal synthesis (DHTA = 2,5-dihydroxy-1,4-terephthalic acid anion). The crystallographic data show that complex 1 crystallizes in a triclinic system with space group P1¯, with a = 9.6617(17) Å, b = 11.902(2) Å, c = 13.284(2) Å, α = 100.617(3)°, β = 92.765(2)°, γ = 106.715(2)°, V = 1429.6(4) Å3, Z = 2, C24H24O24Ho2, and Mr = 1026.290. Complex 1 contains two eight-coordinated metal centers Ho(III). The TGA results show that the weight loss can be ascribed to the removal of the organic component from 400 to 650 °C. At the temperature above 650 °C, the residue is Holmium(III) oxide (Ho2O3). The luminescent results reveal that the complex has potential application as a new green luminescence material. Full article
(This article belongs to the Special Issue Self-Assembled Complexes: “Love at First Sight”)
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14 pages, 3843 KB  
Article
Photosensitive Bent-Core Liquid Crystals with Laterally Substituted Azobenzene Unit
by Diana Jágerová, Michal Šmahel, Anna Poryvai, Jan Macháček, Vladimíra Novotná and Michal Kohout
Crystals 2021, 11(10), 1265; https://doi.org/10.3390/cryst11101265 - 18 Oct 2021
Cited by 7 | Viewed by 3394
Abstract
Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables [...] Read more.
Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables fast (E)-to-(Z)-isomerization upon irradiation with UV-light and visible light, while the substitution facilitates the high stability of the photochemically formed (Z)-isomer. The effectiveness of the irradiation and the composition of photostationary states was determined by UV/Vis and 1H NMR spectroscopy. A nematic phase formed by the materials was characterized by differential scanning calorimetry and optical polarizing microscopy. We show that the materials easily change their relative configuration of the N=N double bond not only in solution, but also in the mesophase, which leads to fast isothermal phase transition from the nematic phase to isotropic liquid. Full article
(This article belongs to the Special Issue Photosensitive Liquid Crystals)
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9 pages, 7986 KB  
Article
The Curled Up Dimension in Quasicrystals
by Fang Fang, Richard Clawson and Klee Irwin
Crystals 2021, 11(10), 1238; https://doi.org/10.3390/cryst11101238 - 14 Oct 2021
Viewed by 3955
Abstract
Most quasicrystals can be generated by the cut-and-project method from higher dimensional parent lattices. In doing so they lose the periodic order their parent lattice possess, replaced with aperiodic order, due to the irrationality of the projection. However, perfect periodic order is discovered [...] Read more.
Most quasicrystals can be generated by the cut-and-project method from higher dimensional parent lattices. In doing so they lose the periodic order their parent lattice possess, replaced with aperiodic order, due to the irrationality of the projection. However, perfect periodic order is discovered in the perpendicular space when gluing the cut window boundaries together to form a curved loop. In the case of a 1D quasicrystal projected from a 2D lattice, the irrationally sloped cut region is bounded by two parallel lines. When it is extrinsically curved into a cylinder, a line defect is found on the cylinder. Resolving this geometrical frustration removes the line defect to preserve helical paths on the cylinder. The degree of frustration is determined by the thickness of the cut window or the selected pitch of the helical paths. The frustration can be resolved by applying a shear strain to the cut-region before curving into a cylinder. This demonstrates that resolving the geometrical frustration of a topological change to a cut window can lead to preserved periodic order. Full article
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29 pages, 24863 KB  
Article
Strain Localization Modes within Single Crystals Using Finite Deformation Strain Gradient Crystal Plasticity
by Lei Cai, Mohamed Jebahi and Farid Abed-Meraim
Crystals 2021, 11(10), 1235; https://doi.org/10.3390/cryst11101235 - 13 Oct 2021
Cited by 6 | Viewed by 2967
Abstract
The present paper aims at providing a comprehensive investigation of the abilities and limitations of strain gradient crystal plasticity (SGCP) theories in capturing different kinds of localization modes in single crystals. To this end, the small deformation Gurtin-type SGCP model recently proposed by [...] Read more.
The present paper aims at providing a comprehensive investigation of the abilities and limitations of strain gradient crystal plasticity (SGCP) theories in capturing different kinds of localization modes in single crystals. To this end, the small deformation Gurtin-type SGCP model recently proposed by the authors, based on non-quadratic defect energy and the uncoupled dissipation assumption, is extended to finite deformation. The extended model is then applied to simulate several single crystal localization problems with different slip system configurations. These configurations are chosen in such a way as to obtain idealized slip and kink bands as well as general localization bands, i.e., with no particular orientation with respect to the initial crystallographic directions. The obtained results show the good abilities of the applied model in regularizing various kinds of localization bands, except for idealized slip bands. Finally, the model is applied to reproduce the complex localization behavior of single crystals undergoing single slip, where competition between kink and slip bands can take place. Both higher-order energetic and dissipative effects are considered in this investigation. For both effects, mesh-independent results are obtained, proving the good capabilities of SGCP theories in regularizing complex localization behaviors. The results associated with higher-order energetic effects are in close agreement with those obtained using a micromorphic crystal plasticity approach. Higher-order dissipative effects led to different results with dominant slip banding. Full article
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15 pages, 7375 KB  
Article
Mesomorphic and Thermal Behavior of Symmetric Bent-Core Liquid Crystal Compounds Derived from Resorcinol and Isophthalic Acid
by Catalina Ionica Ciobanu, Iulian Berladean, Elena-Luiza Epure, Aurel Simion, Gabriela Lisa, Yahia Boussoualem and Irina Carlescu
Crystals 2021, 11(10), 1215; https://doi.org/10.3390/cryst11101215 - 8 Oct 2021
Cited by 4 | Viewed by 2864
Abstract
Bent-core liquid crystals (BCLC) have been widely studied as a result of their unusual polar and chiral properties. Similar to calamitic and discotic molecules, BCLC molecules also exhibit nematic phases, besides other higher order mesophases. The aim of this work is to comparatively [...] Read more.
Bent-core liquid crystals (BCLC) have been widely studied as a result of their unusual polar and chiral properties. Similar to calamitic and discotic molecules, BCLC molecules also exhibit nematic phases, besides other higher order mesophases. The aim of this work is to comparatively analyze the mesomorphic behavior of some bent-core 1,3-disubstituted benzene core compounds derived from resorcinol and isophthalic acid. Thus, the two classes of compounds differ in the nature of the orientation of the ester bond between the benzene central core and the two branches attached to the core. The mesomorphic behavior was elucidated by polarized light optical microscopy and differential calorimetry. Given the relatively high isotropic points of the compounds, confirmation of the thermal stability in the domains manifesting liquid crystalline properties was performed by thermogravimetric studies. The theoretical explanation of the difference in mesomorphic behavior for the two classes was based on molecular modeling studies. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-Emitting Liquid Crystals (Volume II))
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22 pages, 3834 KB  
Review
On the Importance of σ–Hole Interactions in Crystal Structures
by Antonio Frontera and Antonio Bauzá
Crystals 2021, 11(10), 1205; https://doi.org/10.3390/cryst11101205 - 7 Oct 2021
Cited by 71 | Viewed by 7120
Abstract
Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF4−, [...] Read more.
Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF4−, PF6−, ClO4−, etc.). Moreover, elements of groups 15 to 17 are also able to act as Lewis bases (from one to three available lone pairs, respectively), thus presenting a dual character. These emerging NCIs where the main group element behaves as Lewis base, belong to the σ–hole family of interactions. Particularly (i) tetrel bonding for elements belonging to group 14, (ii) pnictogen bonding for group 15, (iii) chalcogen bonding for group 16, (iv) halogen bonding for group 17, and (v) noble gas bondings for group 18. In general, σ–hole interactions exhibit different features when moving along the same group (offering larger and more positive σ–holes) or the same row (presenting a different number of available σ–holes and directionality) of the periodic table. This is illustrated in this review by using several examples retrieved from the Cambridge Structural Database (CSD), especially focused on σ–hole interactions, complemented with molecular electrostatic potential surfaces of model systems. Full article
(This article belongs to the Special Issue Advanced Research in Halogen Bonding)
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14 pages, 4212 KB  
Article
DFT Calculation, Hirshfeld Analysis and X-Ray Crystal Structure of Some Synthesized N-alkylated(S-alkylated)-[1,2,4]triazolo[1,5-a]quinazolines
by Hatem A. Abuelizz, Saied M. Soliman, Hazem A. Ghabbour, Mohamed Marzouk, Mohamed M. Abdellatif and Rashad Al-Salahi
Crystals 2021, 11(10), 1195; https://doi.org/10.3390/cryst11101195 - 30 Sep 2021
Cited by 3 | Viewed by 2799
Abstract
The present work aimed to synthesize 2-methylthio-triazoloquinazoline derivatives and study their X-ray, NMR, DFT and Hirshfeld characteristics. The cyclocondensation of dimethyl-N-cyanodithiocarbonate with 2-hydrazinobenzoic acid hydrochloride resulted in an intermediate, 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (A), which upon treatment with phosphorus pentasulfide, [...] Read more.
The present work aimed to synthesize 2-methylthio-triazoloquinazoline derivatives and study their X-ray, NMR, DFT and Hirshfeld characteristics. The cyclocondensation of dimethyl-N-cyanodithiocarbonate with 2-hydrazinobenzoic acid hydrochloride resulted in an intermediate, 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (A), which upon treatment with phosphorus pentasulfide, transformed into the 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-thione (B). Reaction of 2-methylthio-triazoloquinazolines (A&B) with alkyl halides (allyl bromide and ethyl iodide) in basic medium afforded 4-allyl-2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (1; N-alkylated) and 5-ethylthio-2-methylthio-[1,2,4]triazolo[1,5-a]quinazoline (2; S-alkylated), respectively. Their molecular and supramolecular structures were presented. Unambiguously, the molecular structures of 1 and 2 were confirmed via NMR and single-crystal X-ray diffraction. The resulting findings confirmed the structures of 1 and 2 and determined their crystalized system (monoclinic system; P21/n space group). Hirshfeld analysis of 1 revealed the importance of the significantly short O···H (6.7%), S···S (1.2%) and C···C (2.8%); however, the short H···H (42.6%), S···H (16.3%) and C···C (4.3%) were showed in 2 by intermolecular interactions in the molecular packing. The 1,2,4-triazoloquinzolines (1&2) were anticipated to be relatively polar compounds with net dipole moments of 2.9284 and 4.2127 Debye, respectively. The molecular electrostatic potential, atomic charge distribution maps and reactivity descriptors for 1 and 2 were also determined. The calculated nuclear magnetic resonance spectra of the targets 1 and 2 were well correlated with the experimental data. Full article
(This article belongs to the Special Issue Crystal Engineering: From Molecules to Crystals to Functional Materials)
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13 pages, 6799 KB  
Article
Impact of a Partial Solid Solution and Water Molecules on the Formation of Fibrous Crystals and Fluid Inclusions
by Laureline Marc, Chrystal Lopes, Jean-Marie Schneider, Morgane Sanselme and Gérard Coquerel
Crystals 2021, 11(10), 1188; https://doi.org/10.3390/cryst11101188 - 29 Sep 2021
Cited by 8 | Viewed by 3332
Abstract
Resolution of (±)ibuprofen using S-α-Methylbenzylamine in pure ethanol leads to the enriched S-IBU/S-αMBA diastereomeric salt which crystallizes as very fine needles. In order to improve the filterability and processability of the solid phase, water can be added to the medium and lead to [...] Read more.
Resolution of (±)ibuprofen using S-α-Methylbenzylamine in pure ethanol leads to the enriched S-IBU/S-αMBA diastereomeric salt which crystallizes as very fine needles. In order to improve the filterability and processability of the solid phase, water can be added to the medium and lead to more equant particles that are still elongated. A high fraction of the resulting platelets display on both ends a fluid inclusion containing both liquid and a large bubble of gas. A detailed analysis of the particles reveals that they are not really single crystals but more an ordered association of fibers defined as fibrous crystal. A domain of partial solid solution is evidenced near the pure less soluble diastereomer and its impact on the formation of fibrous crystals is demonstrated. When pure S-IBU/S-αMBA diastereomeric salt is recrystallized in the same medium (e.g., ethanol–water) the crystallinity is improved, but fluid inclusions can still be observed. Full article
(This article belongs to the Special Issue Crystal Nucleation and Growth Kinetics)
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12 pages, 5203 KB  
Article
Ferroelectric Properties and Spectroscopic Characterization of Pb(Mg1/3Nb2/3)O3-32PbTiO3:Er3+/Sc3+ Crystal
by Jin Zhang, Zengzhe Xi, Xinzhe Wang, Hao Feng, Wei Long and Aiguo He
Crystals 2021, 11(10), 1155; https://doi.org/10.3390/cryst11101155 - 23 Sep 2021
Cited by 3 | Viewed by 2750
Abstract
An Er3+/Sc3+ co-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm2 and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. [...] Read more.
An Er3+/Sc3+ co-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm2 and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. Green (524 and 551 nm) and red (654 nm) emission bands are generated at the 980 nm excitation, which corresponds to the 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions of Er3+, respectively. Judd–Ofelt theory has been applied to predict the spectroscopic characteristics of the as-grown crystals. The obtained J–O intensity parameters Ωt (t = 2, 4 and 6) are Ω2 = 0.76 × 10−20 cm2, Ω4 = 1.0 × 10−20 cm2, Ω6 = 0.55 × 10−20 cm2. Spectroscopic characteristics, including optical transition probabilities, branching ratio, and radiative lifetime of Er3+ in the crystal, are determined. The calculated radiative lifetimes of 4I13/2 and 4I11/2 energy levels are 2.82 ms and 2.61 ms, respectively. These investigations provide possibilities for the crystal Pb(Mg1/3Nb2/3)O3-0.32PbTiO3:Er3+/Sc3+ to be a new type of multifunctional crystal integrating electricity-luminescence. Full article
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8 pages, 2171 KB  
Article
Multi-Component Crystals of 2,2′-Bipyridine with Aliphatic Dicarboxylic Acids: Melting Point-Structure Relations
by Vhukhudo Nethanani and Eustina Batisai
Crystals 2021, 11(10), 1151; https://doi.org/10.3390/cryst11101151 - 22 Sep 2021
Viewed by 2855
Abstract
The aim of the study was to investigate the relationship between the melting point and the supramolecular structure of three multi-component crystals of aliphatic dicarboxylic acids with 2,2′-bipyridine and to investigate the conformations of 2,2′-bipyridine in published multi-component crystals. The crystals were prepared [...] Read more.
The aim of the study was to investigate the relationship between the melting point and the supramolecular structure of three multi-component crystals of aliphatic dicarboxylic acids with 2,2′-bipyridine and to investigate the conformations of 2,2′-bipyridine in published multi-component crystals. The crystals were prepared using the solvent evaporation method and were characterized using single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). The crystal structures were further analyzed using CrystalExplorer, and the results were correlated with the melting points. The results of the conformation analysis of the reported multi-component crystals of 2,2′-bipyridine are also presented. Full article
(This article belongs to the Section Crystal Engineering)
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18 pages, 3542 KB  
Review
Advances of Yb:CALGO Laser Crystals
by Hao Wang, Jing Pan, Yuan Meng, Qiang Liu and Yijie Shen
Crystals 2021, 11(9), 1131; https://doi.org/10.3390/cryst11091131 - 17 Sep 2021
Cited by 17 | Viewed by 7806
Abstract
Yb:CaGdAlO4, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses [...] Read more.
Yb:CaGdAlO4, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses with ever short durations. More specifically, its remarkable thermal-optic property and its high conversion efficiency allow high-power operation. Its high nonlinear coefficient facilitates study of optimized mode locking lasers. Besides, its ultrabroad and flat-top emission band benefits the generation of complex structured light with outstanding tunability. In this paper, we review the recent advances in the study of Yb:CALGO, covering its physical properties as well as its growing applications in various fields and prospect for future development. Full article
(This article belongs to the Special Issue Advanced Laser Technology and Applications)
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10 pages, 3112 KB  
Article
Bandgap and Carrier Dynamic Controls in CsPbBr3 Nanocrystals Encapsulated in Polydimethylsiloxane
by Lianxing Liao, Kunhua Quan, Xiangshi Bin, Ruosheng Zeng and Tao Lin
Crystals 2021, 11(9), 1132; https://doi.org/10.3390/cryst11091132 - 17 Sep 2021
Cited by 5 | Viewed by 4184
Abstract
Bandgap tunability through ion substitution is a key feature of lead halide perovskite nanocrystals (LHP-NCs). However, the low stability and low luminescent performance of CsPbCl3 hinder their full-color applications. In this work, quantum confinement effect (QCE) was utilized to control the bandgap [...] Read more.
Bandgap tunability through ion substitution is a key feature of lead halide perovskite nanocrystals (LHP-NCs). However, the low stability and low luminescent performance of CsPbCl3 hinder their full-color applications. In this work, quantum confinement effect (QCE) was utilized to control the bandgap of CsPbBr3 NCs instead of using unstable CsPbCl3, which possess much higher emission efficiency in blue spectra region. Studies of microstructures, optical spectra and carrier dynamics revealed that tuning the reaction temperature was an effective way of controlling the NC sizes as well as QCE. Furthermore, the obtained CsPbBr3 NCs were encapsulated in a PDMS matrix while maintaining their size distribution and quantum-confined optoelectronic properties. The encapsulated samples showed long-term air and water stability. These results provide valuable guidance for both applications of LHP-NCs and principal investigation related to the carrier transition in LHP-NCs. Full article
(This article belongs to the Section Materials for Energy Applications)
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12 pages, 5334 KB  
Article
Comparison of Spatial Structures and Packaging of Phosphorybosil Pyrophosphate Synthetase 2 from Thermus thermophilus HB27 in Rhombohedral and Tetragonal Crystals
by Yulia Abramchik, Evgeniy Zayats, Maria Kostromina, Dmitry Lykoshin, Ilya Fateev, Irina Konstantinova, Nadezda Zhukhlistova, Vladimir Timofeev, Inna Kuranova and Roman Esipov
Crystals 2021, 11(9), 1128; https://doi.org/10.3390/cryst11091128 - 16 Sep 2021
Cited by 1 | Viewed by 2550
Abstract
We report the spatial structure of phosphoribosyl pyrophosphate synthetase 2 from the thermophilic bacterium Thermus thermophilus HB27 (TthPRPPS2) obtained at a 1.85 Å resolution using a diffraction set collected from rhombohedral crystals (space group R32-h), grown with lithium sulfate as [...] Read more.
We report the spatial structure of phosphoribosyl pyrophosphate synthetase 2 from the thermophilic bacterium Thermus thermophilus HB27 (TthPRPPS2) obtained at a 1.85 Å resolution using a diffraction set collected from rhombohedral crystals (space group R32-h), grown with lithium sulfate as a precipitant. This crystal structure was compared with the structure of TthPRPPS2, previously obtained at a 2.2 Å resolution using diffraction sets from the tetragonal crystals (space group P41212), grown with ammonium sulfate as a precipitant. The comparison of these structures allows the study of the differences between protein molecules in both crystalline structures, as well as the packaging of enzyme molecules in crystals of both spatial groups. Our results may contribute to the research of the structural basis of catalytic activity and substrate specificity of this enzyme. Full article
(This article belongs to the Section Biomolecular Crystals)
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9 pages, 2340 KB  
Article
Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers
by Yi-Hong Shih, Xin-Yu Lin, Harry Miyosi Silalahi, Chia-Rong Lee and Chia-Yi Huang
Crystals 2021, 11(9), 1100; https://doi.org/10.3390/cryst11091100 - 10 Sep 2021
Cited by 11 | Viewed by 3748
Abstract
An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with [...] Read more.
An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging. Full article
(This article belongs to the Special Issue Liquid Crystal Optics for Applications)
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15 pages, 8295 KB  
Article
Thermal Deformations of Crystal Structures in the L-Aspartic Acid/L-Glutamic Acid System and DL-Aspartic Acid
by Roman Sadovnichii, Elena Kotelnikova and Heike Lorenz
Crystals 2021, 11(9), 1102; https://doi.org/10.3390/cryst11091102 - 10 Sep 2021
Cited by 5 | Viewed by 3202
Abstract
The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp0.25,L-glu0.75 solid solution. These amino acids were not found to undergo any [...] Read more.
The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp0.25,L-glu0.75 solid solution. These amino acids were not found to undergo any solid-phase (polymorph) transformations. When heated, they all experienced only thermal deformations. The corresponding parameters of the monoclinic cells of L-asp and DL-asp, and the orthorhombic cells of L-glu and L-asp0.25,L-glu0.75, were calculated for the entire range of studied temperatures (up to 220 °C). The data obtained were used to calculate the parameters of the thermal deformation tensors, and to plot the figures of their thermal expansion coefficients. A correlation between the maximum and minimum values of thermal expansion coefficients and the length, type, direction, and number of hydrogen bonds in the crystal structures of the investigated amino acids was established. The observed negative thermal expansion (contraction) of crystal structures of L-asp and DL-asp along the ac plane can be explained as a result of shear deformations occurring in monoclinic crystals with a non-fixed angle β. The studies were related to the presence of amino acids in various natural and technological processes occurring at different temperatures. Full article
(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)
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12 pages, 596 KB  
Article
The Refraction Indices and Brewster Law in Stressed Isotropic Materials and Cubic Crystals
by Daniele Rinaldi, Pier Paolo Natali, Luigi Montalto and Fabrizio Davì
Crystals 2021, 11(9), 1104; https://doi.org/10.3390/cryst11091104 - 10 Sep 2021
Cited by 2 | Viewed by 2530
Abstract
We study the elasto-optic behavior of stressed cubic crystals (all classes) and isotropic materials (like e.g., glasses). We obtain the explicit dependence of the refraction indices on the stress (either applied or residual), as well as a mild generalization of the Brewster law [...] Read more.
We study the elasto-optic behavior of stressed cubic crystals (all classes) and isotropic materials (like e.g., glasses). We obtain the explicit dependence of the refraction indices on the stress (either applied or residual), as well as a mild generalization of the Brewster law for cubic crystals. We show also that the optic indicatrix and the stress ellipsoid are coaxial only in the isotropic case. This theory allows the improvement of the measurement techniques, as photoelasticity, on cubic crystals and optically isotropic materials. Full article
(This article belongs to the Special Issue Photoelasticity in Optical Media from Crystals to Amorphous Materials)
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13 pages, 2827 KB  
Article
Remarkable Increase of Fluorescence Quantum Efficiency by Cyano Substitution on an ESIPT Molecule 2-(2-Hydroxyphenyl)benzothiazole: A Highly Photoluminescent Liquid Crystal Dopant
by Tsuneaki Sakurai, Masaya Kobayashi, Hiroyuki Yoshida and Masaki Shimizu
Crystals 2021, 11(9), 1105; https://doi.org/10.3390/cryst11091105 - 10 Sep 2021
Cited by 19 | Viewed by 5059
Abstract
Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (ΦFL) in [...] Read more.
Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (ΦFL) in the solution or viscous media, due to their structural relaxations in the excited state to reach the S0/S1 conical intersection, shackle further applications of ESIPT-active luminophores. Here we report that the introduction of a cyano group (-CN) into the phenyl group of 2-(2-hydroxyphenyl)benzothiazole (HBT), a representative ESIPT compound, remarkably increase its fluorescence quantum yield (ΦFL) from 0.01 (without -CN) to 0.49 (with -CN) in CH2Cl2, without disturbing its high ΦFL (=0.52) in the solid state. The large increase of the solution-state ΦFL of the cyano-substituted HBT (CN-HBT) is remarkable, comparing with our previously reported ΦFL values of 0.05 (with 4-pentylphenyl), 0.07 (with 1-hexynyl), and 0.15 (with 4-pentylphenylethynyl). Of interest, the newly-synthesized compound, CN-HBT, is miscible in a conventional room-temperature nematic liquid crystal (LC), 4-pentyl-4′-cyano biphenyl (5CB), up to 1 wt% (~1 mol%), and exhibits a large ΦFL of 0.57 in the viscous LC medium. A similar ΦFL value of ΦFL = 0.53 was also recorded in another room-temperature LC, trans-4-(4-pentylcyclohexyl)benzonitrile (PCH5), with a doping ratio of 0.5 wt% (~0.5 mol%). These 5CB/CN-HBT and PCH5/CN-HBT mixtures serve as light-emitting room-temperature LCs, and show anisotropic fluorescence with the dichroic ratio of 3.1 upon polarized excitation, as well as electric field response of luminescence intensity changes. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-Emitting Liquid Crystals (Volume II))
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14 pages, 921 KB  
Article
Photoelastic Properties of Trigonal Crystals
by Bohdan Mytsyk, Nataliya Demyanyshyn, Anatoliy Andrushchak and Oleh Buryy
Crystals 2021, 11(9), 1095; https://doi.org/10.3390/cryst11091095 - 8 Sep 2021
Cited by 8 | Viewed by 3485
Abstract
All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) πim and some sums of πim based on experimental [...] Read more.
All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) πim and some sums of πim based on experimental data obtained from the samples of direct and X/45°-cuts are given. The reliability of the values of POCs is proven by the convergence of πim obtained from different experimental geometries as well as by the convergence of some sums of POCs. Because both the signs and the absolute values of POCs π14 and π41 are defined by the choice of the right crystal-physics coordinate system, we here use the system whereby the condition S14 > 0 is fulfilled (S14 is an elastic compliance coefficient). The absolute value and the sign of S14 are determined by piezo-optic interferometric method from two experimental geometries. The errors of POCs are calculated as mean square values of the errors of the half-wave stresses and the elastic term. All components of the matrix of elasto-optic coefficients pin are calculated based on POCs and elastic stiffness coefficients. The technique is tested on LiTaO3 crystal. The obtained results are compared with the corresponding data for trigonal LiNbO3 and Ca3TaGa3Si2O14 crystals. Full article
(This article belongs to the Special Issue Photoelasticity in Optical Media from Crystals to Amorphous Materials)
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19 pages, 3321 KB  
Article
Synthesis, Crystal Structure, Inhibitory Activity and Molecular Docking of Coumarins/Sulfonamides Containing Triazolyl Pyridine Moiety as Potent Selective Carbonic Anhydrase IX and XII Inhibitors
by Yassine Aimene, Romain Eychenne, Frédéric Rodriguez, Sonia Mallet-Ladeira, Nathalie Saffon-Merceron, Jean-Yves Winum, Alessio Nocentini, Claudiu T. Supuran, Eric Benoist and Achour Seridi
Crystals 2021, 11(9), 1076; https://doi.org/10.3390/cryst11091076 - 6 Sep 2021
Cited by 17 | Viewed by 5058
Abstract
In this work, two classes of Carbonic Anhydrase (CA) inhibitors, sulfonamide and coumarin derivatives linked to pyta moiety (2a-b) and their corresponding rhenium complexes (3a-b), were designed. These compounds were synthesized and fully characterized by classical analytical methods and [...] Read more.
In this work, two classes of Carbonic Anhydrase (CA) inhibitors, sulfonamide and coumarin derivatives linked to pyta moiety (2a-b) and their corresponding rhenium complexes (3a-b), were designed. These compounds were synthesized and fully characterized by classical analytical methods and X-ray diffraction. All the synthesized compounds were evaluated for their inhibitory activity against the hCA isoforms I, II, IX and XII. They exhibited high inhibitory activities in the range of nanomolar for both hCA IX and hCA XII isoforms. The sulfonamide compound 2a showed the strongest inhibition against the tumour-associated hCA IX isoform with a Ki of 11.7 nM. The tumour-associated isoforms hCA IX and hCA XII were selectively inhibited by all the coumarin derivatives, with inhibition constants ranging from 12.7 nM (2b) to 44.5 nM (3b), while the hCA I and II isoforms were slightly inhibited (in the micromolar range), as expected. In terms of selectivity, compared to previously published rhenium complex-based CA inhibitors, complex 3b showed one of the highest selectivities against hCA IX and hCA XII compared to the off-target isoforms hCA I and hCA II, making it a potential anti-cancer drug candidate. Molecular docking calculations were performed to investigate the inhibition profiles of the investigated compounds at the tumour-associated hCA IX active site and to rationalize our results. Full article
(This article belongs to the Special Issue Discovery, Modeling, Synthesis and Performance Evaluation of Enzyme Inhibitors)
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12 pages, 2687 KB  
Article
Scanning Electron Microscopy Investigation of Surface Acoustic Wave Propagation in a 41° YX-Cut of a LiNbO3 Crystal/Si Layered Structure
by Dmitry Roshchupkin, Evgenii Emelin, Olga Plotitcina, Anatoly Mololkin and Oleg Telminov
Crystals 2021, 11(9), 1082; https://doi.org/10.3390/cryst11091082 - 6 Sep 2021
Cited by 6 | Viewed by 3241
Abstract
The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO3 crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration [...] Read more.
The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO3 crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration mode, made it possible to visualize the SAW and PSAW in the LiNbO3/Si layered structure. The process of the SAW and PSAW propagation in a LiNbO3/Si layered structure and in a bulk 41° YX-cut of a LiNbO3 crystal were compared. It was demonstrated that the SAW velocities in the layered LiNbO3/Si structure exceed the typical SAW velocities for LiNbO3 and Si single crystals. In the layered structure, the SAW and PSAW velocities were 4062 m/s, 4731 m/s, and 5871 m/s. It was also demonstrated that the PSAW velocities are the same in the LiNbO3/Si layered structure and in the bulk 41° YX-cut of a LiNbO3 crystal. Full article
(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)
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12 pages, 1855 KB  
Article
Growth of Acetaminophen Polymorphic Crystals and Solution-Mediated Phase Transition from Trihydrate to Form II in Agarose Gel
by Akari Nishigaki, Mihoko Maruyama, Shun-ichi Tanaka, Hiroshi Y. Yoshikawa, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori and Kazufumi Takano
Crystals 2021, 11(9), 1069; https://doi.org/10.3390/cryst11091069 - 5 Sep 2021
Cited by 2 | Viewed by 3807
Abstract
The growth of acetaminophen polymorphic crystals and the solution-mediated phase transition from trihydrate to form II in agarose gel were investigated. The form II crystals grown in gels, presumably because of the agarose content, dissolved less rapidly at high temperatures and were more [...] Read more.
The growth of acetaminophen polymorphic crystals and the solution-mediated phase transition from trihydrate to form II in agarose gel were investigated. The form II crystals grown in gels, presumably because of the agarose content, dissolved less rapidly at high temperatures and were more stable than in water. The trihydrate crystals in the gel were also expected to be stabilized by containing agarose, but in fact the fine morphology resulted in reduced stability. The solution-mediated phase transition from trihydrate to form II via form II seeding took longer in the gel because the gel slowed down the dissolution of the trihydrate by hindering the dispersion of the form II seeds and delayed the growth of form II by reducing the diffusion rate of the molecules dissolved from the trihydrate. Delays in solution-mediated phase transition and changes in stability for crystals grown in gels indicate the effectiveness of gels in controlling polymorphisms in pharmaceutical compounds. Full article
(This article belongs to the Special Issue Crystallization Processes: Food and Pharmaceutical Crystals)
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12 pages, 4047 KB  
Article
Control of Crystallographic Texture and Mechanical Properties of Hastelloy-X via Laser Powder Bed Fusion
by Shinya Hibino, Tsubasa Todo, Takuya Ishimoto, Ozkan Gokcekaya, Yuichiro Koizumi, Kenichiroh Igashira and Takayoshi Nakano
Crystals 2021, 11(9), 1064; https://doi.org/10.3390/cryst11091064 - 3 Sep 2021
Cited by 40 | Viewed by 5251
Abstract
The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like [...] Read more.
The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with <100>//build direction (BD) (<100>-SCM), single crystalline-like microstructure with <110>//BD (<110>-SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the <110>//BD oriented main layers and the <100>//BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior. Full article
(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)
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10 pages, 2592 KB  
Review
Optically Rewritable Liquid Crystal Displays: Characteristics and Performance
by Vladimir G. Chigrinov, Aleksey A. Kudreyko and Fedor V. Podgornov
Crystals 2021, 11(9), 1053; https://doi.org/10.3390/cryst11091053 - 1 Sep 2021
Cited by 7 | Viewed by 3226
Abstract
Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing [...] Read more.
Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing studies do not include sufficient analysis on how to achieve acceptable reflective characteristics within short exposure time. In order to achieve this goal, we have applied the rotational diffusion model. We find that the parameters of the diffusion model can be adjusted to get acceptable light-reflecting characteristics within 10 s of exposure. In comparison with the long-time exposure, the reflectance coefficient reduces by 24%. The route to material improvements for optimized e-paper device is discussed. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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7 pages, 676 KB  
Communication
Using DFT to Calculate the Parameters of the Crystal Field in Mn2+ Doped Hydroxyapatite Crystals
by Daria Vladimirovna Shurtakova, Peter Olegovich Grishin, Marat Revgerovich Gafurov and Georgy Vladimirovich Mamin
Crystals 2021, 11(9), 1050; https://doi.org/10.3390/cryst11091050 - 31 Aug 2021
Cited by 10 | Viewed by 3987
Abstract
Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized [...] Read more.
Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized Mn-HAp powders Ca9.995Mn0.005(PO4)6(OH)2. It is found that in the investigated species, the manganese is redistributed between both calcium sites with prevalence in Ca (I). Agreement between the calculated and experimental data proves that crystal field parameters in HAp can be calculated in the classical DFT model using the distributed electron density. Full article
(This article belongs to the Special Issue Hydroxyapatite Base Nanocomposites (Volume II))
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16 pages, 2644 KB  
Article
Crystal-Site-Based Artificial Neural Networks for Material Classification
by Juan I. Gómez-Peralta, Nidia G. García-Peña and Xim Bokhimi
Crystals 2021, 11(9), 1039; https://doi.org/10.3390/cryst11091039 - 29 Aug 2021
Cited by 5 | Viewed by 5874
Abstract
In materials science, crystal structures are the cornerstone in the structure–property paradigm. The description of crystal compounds may be ascribed to the number of different atomic chemical environments, which are related to the Wyckoff sites. Hence, a set of features related to the [...] Read more.
In materials science, crystal structures are the cornerstone in the structure–property paradigm. The description of crystal compounds may be ascribed to the number of different atomic chemical environments, which are related to the Wyckoff sites. Hence, a set of features related to the different atomic environments in a crystal compound can be constructed as input data for artificial neural networks (ANNs). In this article, we show the performance of a series of ANNs developed using crystal-site-based features. These ANNs were developed to classify compounds into halite, garnet, fluorite, hexagonal perovskite, ilmenite, layered perovskite, -o-tp- perovskite, perovskite, and spinel structures. Using crystal-site-based features, the ANNs were able to classify the crystal compounds with a 93.72% average precision. Furthermore, the ANNs were able to retrieve missing compounds with one of these archetypical structure types from a database. Finally, we showed that the developed ANNs were also suitable for a multitask learning paradigm, since the extracted information in the hidden layers linearly correlated with lattice parameters of the crystal structures. Full article
(This article belongs to the Special Issue Applications of Machine Learning to the Study of Crystalline Materials)
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25 pages, 8705 KB  
Article
Crystal Structure, Vibrational, Spectroscopic and Thermochemical Properties of Double Sulfate Crystalline Hydrate [CsEu(H2O)3(SO4)2]·H2O and Its Thermal Dehydration Product CsEu(SO4)2
by Yuriy G. Denisenko, Maxim S. Molokeev, Aleksandr S. Oreshonkov, Alexander S. Krylov, Aleksandr S. Aleksandrovsky, Nikita O. Azarapin, Oleg V. Andreev, Illaria A. Razumkova and Victor V. Atuchin
Crystals 2021, 11(9), 1027; https://doi.org/10.3390/cryst11091027 - 26 Aug 2021
Cited by 79 | Viewed by 5506
Abstract
Crystalline hydrate of double cesium europium sulfate [CsEu(H2O)3(SO4)2]·H2O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs+:1Eu3+:2SO42− ions. Anhydrous salt CsEu(SO4 [...] Read more.
Crystalline hydrate of double cesium europium sulfate [CsEu(H2O)3(SO4)2]·H2O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs+:1Eu3+:2SO42− ions. Anhydrous salt CsEu(SO4)2 was formed as a result of the thermal dehydration of the crystallohydrate. The unusual effects observed during the thermal dehydration were attributed to the specific coordination of water molecules in the [CsEu(H2O)3(SO4)2]·H2O structure. The crystal structure of [CsEu(H2O)3(SO4)2]·H2O was determined by a single crystal X-ray diffraction analysis, and the crystal structure of CsEu(SO4)2 was obtained by the Rietveld method. [CsEu(H2O)3(SO4)2]·H2O crystallizes in the monoclinic system, space group P21/c (a = 6.5574(1) Å, b = 19.0733(3) Å, c = 8.8364(2) Å, β = 93.931(1)°, V = 1102.58(3) Å3). The anhydrous sulfate CsEu(SO4)2 formed as a result of the thermal destruction crystallizes in the monoclinic system, space group C2/c (a = 14.327(1) Å, b = 5.3838(4) Å, c = 9.5104(6) Å, β = 101.979(3) °, V = 717.58(9) Å3). The vibration properties of the compounds are fully consistent with the structural models and are mainly determined by the deformation of non-rigid structural elements, such as H2O and SO42−. As shown by the diffused reflection spectra measurements and DFT calculations, the structural transformation from [CsEu(H2O)3(SO4)2]·H2O to CsEu(SO4)2 induced a significant band gap reduction. A noticeable difference of the luminescence spectra between cesium europium sulfate and cesium europium sulfate hydrate is detected and explained by the variation of the extent of local symmetry violation at the crystallographic sites occupied by Eu3+ ions, namely, by the increase in inversion asymmetry in [CsEu(H2O)3(SO4)2]·H2O and the increase in mirror asymmetry in CsEu(SO4)2. The chemical shift of the 5D0 energy level in cesium europium sulfate hydrate, with respect to cesium europium sulfate, is associated with the presence of H2O molecules in the vicinity of Eu3+ ion. Full article
(This article belongs to the Special Issue Raman Spectroscopy of Crystals Volume II)
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12 pages, 895 KB  
Article
Tunable Bandgaps in Phononic Crystal Microbeams Based on Microstructure, Piezo and Temperature Effects
by Jun Hong, Zhuangzhuang He, Gongye Zhang and Changwen Mi
Crystals 2021, 11(9), 1029; https://doi.org/10.3390/cryst11091029 - 26 Aug 2021
Cited by 15 | Viewed by 2807
Abstract
A new model of non-classical phononic crystal (PC) microbeam for the elastic wave bandgap generation is provided, incorporating microstructure, piezomagnetism, piezoelectricity and temperature effects. The wave equation of a general magneto–electro–elastic (MEE) phononic crystal microbeam is derived, which recovers piezoelectric- and piezomagnetic-based counterparts [...] Read more.
A new model of non-classical phononic crystal (PC) microbeam for the elastic wave bandgap generation is provided, incorporating microstructure, piezomagnetism, piezoelectricity and temperature effects. The wave equation of a general magneto–electro–elastic (MEE) phononic crystal microbeam is derived, which recovers piezoelectric- and piezomagnetic-based counterparts as special cases. The piezomagnetic and piezoelectric materials are periodically combined to construct the PC microbeam and corresponding bandgaps are obtained by using the plane wave expansion (PWE) method. The effects of the piezomagnetism, piezoelectricity, microstructure, geometrical parameters and applied multi-fields (e.g., external electric potential, external magnetic potential, temperature change) on the bandgaps are discussed. The numerical results reveal that the bandgap frequency is raised with the presence of piezo and microstructure effects. In addition, the geometry parameters play an important role on the bandgap. Furthermore, large bandgaps can be realized by adjusting the external electric and magnetic potentials at micron scale, and lower bandgap frequency can be realized through the temperature rise at all length scales. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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16 pages, 8742 KB  
Review
A Review of Two-Dimensional Liquid Crystal Polarization Gratings
by Kai Zuo, Yue Shi and Dan Luo
Crystals 2021, 11(9), 1015; https://doi.org/10.3390/cryst11091015 - 25 Aug 2021
Cited by 14 | Viewed by 5565
Abstract
In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal [...] Read more.
In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal manipulation stimulates the development of multibeam optical devices. Therefore, the development of two-dimensional (2D) PGs is in demand. This review summarizes the research progress of 2D PGs. Different designs and fabrication methods are summarized, including assembling two 1D polarization patterns, a 2D holographic lithography by polarization interference and a micro-pixelated electric field stimulated 2D liquid crystal (LC) structure. Both experiments and analyses are included. The design strategy, diffraction property, merits and demerits are discussed and summarized for the different methods. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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11 pages, 4302 KB  
Article
Crystalline Silicon Spalling as a Direct Application of Temperature Effect on Semiconductors’ Indentation
by Maha M. Khayyat
Crystals 2021, 11(9), 1020; https://doi.org/10.3390/cryst11091020 - 25 Aug 2021
Cited by 1 | Viewed by 3021
Abstract
Kerf-less removal of surface layers of photovoltaic materials including silicon is an emerging technology by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to [...] Read more.
Kerf-less removal of surface layers of photovoltaic materials including silicon is an emerging technology by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to be deposited on the surface of a brittle material; then, the controlled removal of a continuous surface layer can be performed at a predetermined depth by manipulating the thickness and stress of the Ni layer, introducing a crack near the edge of the substrate, and mechanically guiding the crack as a single fracture front across the surface. However, spalling Si(100) at 300 K (room temperature RT) introduced many cracks and rough regions within the spalled layer. These mechanical issues make it difficult to process these layers of Si(100) for PV, and in other advanced applications, Si does not undergo phase transformations at 77 K (Liquid Nitrogen Temperature, LNT); based on this fact, spalling of Si(100) has been carried out. Spalling of Si(100) at LNT improved material quality for further designed applications. Mechanical flexibility is achieved by employing controlled spalling technology, enabling the large-area transfer of ultrathin body silicon devices to a plastic substrate at room temperature. Full article
(This article belongs to the Special Issue Fabrication of Carbon and Related Materials/Metal Hybrids and Composites)
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12 pages, 3580 KB  
Article
Crystal Plasticity with Micromorphic Regularization in Assessing Scale Dependent Deformation of Polycrystalline Doped Copper Alloys
by Matti Lindroos, Tom Andersson, Jarkko Metsäjoki and Anssi Laukkanen
Crystals 2021, 11(8), 994; https://doi.org/10.3390/cryst11080994 - 21 Aug 2021
Cited by 2 | Viewed by 2707
Abstract
It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects [...] Read more.
It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects in microstructure are relevant in terms of susceptibility to creep and damage from the loading evolution imposed by its operating environment. This work focuses on studying the microstructure level length-scale dependent deformation behavior of the material, of particular significance with respect to accumulation of plasticity over the extensive operational period of the overpacks. The reduced micromorphic crystal plasticity model, which is similar to strain gradient models, is used in this investigation. Firstly, the model’s size dependent plasticity effects are evaluated. Secondly, different microstructural aggregates presenting overpack sections are analyzed. Grain size dependent hardening responses, i.e., Hall-Petch like behavior, can be achieved with the enhanced hardening associated with the micromorphic model at polycrystalline level. It was found that the nominally large grain size in the base material of the overpack shows lower strain hardening potential than the fine grained region of the welded microstructure with stronger strain gradient related hardening effects. Size dependent regularization of strain localization networks is indicated as a desired characteristic of the model. The findings can be utilized to provide an improved basis for modeling the viscoplastic deformation behavior of the studied copper alloy and to assess the microstructural origins of any integrity concerns explicitly by way of full field modeling. Full article
(This article belongs to the Special Issue Micromechanical Modelling and Its Applications to Polycrystals)
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13 pages, 17495 KB  
Article
Growth of SrB4O7 Crystal Fibers along the c-Axis by Micro-Pulling-Down Method
by Ryouta Ishibashi, Harutoshi Asakawa and Ryuichi Komatsu
Crystals 2021, 11(8), 987; https://doi.org/10.3390/cryst11080987 - 20 Aug 2021
Cited by 2 | Viewed by 3597
Abstract
SrB4O7 (SBO) receives much attention as solid-state ultraviolet lasers for micro-machining, photochemical synthesis, and laser spectroscopy. For the application of SBO, the SBO crystals require the control of twinning to amplify the conversion light. We also expected that the inhibitation [...] Read more.
SrB4O7 (SBO) receives much attention as solid-state ultraviolet lasers for micro-machining, photochemical synthesis, and laser spectroscopy. For the application of SBO, the SBO crystals require the control of twinning to amplify the conversion light. We also expected that the inhibitation of the SrB2O4 appearance was essential. Here, we show the growth of SBO crystals along the c-axis through the micro-pulling-down method while alternating the application of electric fields (E). Without the application, single crystals were grown. At E ≧ 400 V/cm no needle domains of SrB2O4 inside SBO crystals existed; however, composition planes were formed and twin boundaries did not appear. In contrast, the inversion of surface morphology emerged, and the convex size was especially large at 1000 V/cm. These results demonstrate that convection is generated perpendicular to the growth front by alternating the application of electric fields. This surface morphological change contradicts the conventional concept of growth through the micro-pulling-down method. The distance from seed crystals vs. grain density plot also showed that the density did not decrease with a sufficient slope. Consequently, we concluded that the selection of the c-axis as growth faces is not fruitful to fabricate twins, and the selection of the growth condition, under which geometrical selection strongly affects, is the key. Full article
(This article belongs to the Special Issue New Trends in Growth Technique of Micro-Pulling-Down Method)
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19 pages, 21632 KB  
Article
Influences of Chemical Functionalities on Crystal Structures and Electrochemical Properties of Dihydro-benzoxazine Dimer Derivatives
by Natapol Suetrong, Kantapat Chansaenpak, Sarawoot Impeng, Piyanut Pinyou, Vincent Blay, Rubén Blay-Roger, Sireerat Lisnund, Pongsakorn Kanjanaboos, Yuranan Hanlumyuang, Suttipong Wannapaiboon and Worawat Wattanathana
Crystals 2021, 11(8), 979; https://doi.org/10.3390/cryst11080979 - 18 Aug 2021
Cited by 7 | Viewed by 5133
Abstract
Dihydro-1,3,2H-benzoxazine dimer derivatives or dihydro-benzoxazine dimers are a class of compounds typically prepared by ring-opening reactions between dihydro-benzoxazines and phenols. Dihydro-benzoxazine dimers act as chelating agents for several transition and rare-earth cations. To better understand the chelating properties, it is necessary [...] Read more.
Dihydro-1,3,2H-benzoxazine dimer derivatives or dihydro-benzoxazine dimers are a class of compounds typically prepared by ring-opening reactions between dihydro-benzoxazines and phenols. Dihydro-benzoxazine dimers act as chelating agents for several transition and rare-earth cations. To better understand the chelating properties, it is necessary to examine their structural features and electrochemical characteristics thoroughly. However, the electrochemical properties of dihydro-benzoxazine dimers have not been tremendously examined. Herein, eight derivatives of dihydro-benzoxazine dimers possessing different substituents on the benzene ring and the tertiary-amine nitrogen were synthesized as model compounds to investigate their influences on crystal structures and electrochemical properties. The crystal structure of the dihydro-benzoxazine dimer, namely 2,2′-(cyclohexylazanediyl)bis(methylene)bis(4-methoxyphenol) (7), is identified for the first time and further used to compare with the crystal structures of other derivatives reported previously. For all the derivatives, intermolecular O–H⋅⋅⋅O hydrogen bonds are the significant interactions to hold the crystal packing of (7) and also the other derivatives. Hirshfeld surface analyses confirm the presence of intermolecular O–H⋅⋅⋅O hydrogen bonds. Redox behavior of the eight dihydro-benzoxazine dimers was studied by cyclic voltammetry. An oxidation peak observed at 0.25–0.47 V corresponds to the oxidation of the phenolic –OH group to the phenoxonium intermediate. The shift in the electrochemical peak positions is due to the different abilities of the substituents to stabilize the phenoxonium cation intermediate. The stabilizing power is ranged in the following order: methoxy > dimethyl > ethyl ≈ methyl, and N-cyclohexyl > N-methyl. Thus, the derivative (7), which contains both the methoxy and N-cyclohexyl groups, has the lowest oxidation potential. Our work elucidates the effect of the substituents on the crystal structures and electrochemical properties of the dihydro-benzoxazine dimers. Full article
(This article belongs to the Section Organic Crystalline Materials)
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14 pages, 3732 KB  
Article
Mesomorphic Behaviour and DFT Insight of Arylidene Schiff Base Liquid Crystals and Their Pyridine Impact Investigation
by Mohamed A. Zakaria, Mohammed Alazmi, Kanubhai D. Katariya, Yeldez El Kilany, El Sayed H. El Ashry, Mariusz Jaremko, Mohamed Hagar and Sayed Z. Mohammady
Crystals 2021, 11(8), 978; https://doi.org/10.3390/cryst11080978 - 18 Aug 2021
Cited by 15 | Viewed by 3524
Abstract
A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of [...] Read more.
A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of the compounds were elucidated by 1H NMR and 13C NMR. The mesomorphic thermal and optical characteristics of the samples were determined via differential thermal analysis (DSC) and polarization optical microscopy (POM). All compounds exhibit enantiotropic dimorphic mesophase behaviour, referred to as smectic X1 (SmX1) and smectic X2 (Sm A). Experimental results obtained for the mesophases were correlated with density functional theory (DFT) theoretical calculations. The results of the new series are further compared to two series of compounds bearing pyridine (two ring Schiff bases) and biphenyl, respectively, in their mesogens. The series of compounds of one pyridine ring are generally not mesomorphic. The results indicate that the alkyl chain length has a strong impact on the mesomorphic characteristics and thermal stabilities of the different mesophases. As a trend, the temperature ranges of both of smectic mesophases of all compounds are higher in new compounds bearing the 4-phenyl pyridine moiety. In addition, the total mesophase range is generally higher in the new compounds when compared to their biphenyl analogues. Finally, theoretical DFT calculations were performed to illustrate the experimental finding of the mesomorphic behaviour in terms of the molecular geometry and aromaticity, π–π stacking and LOL-π. Full article
(This article belongs to the Special Issue Smectic Liquid Crystals)
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14 pages, 4924 KB  
Article
Transfer of a Rational Crystal Contact Engineering Strategy between Diverse Alcohol Dehydrogenases
by Brigitte Walla, Daniel Bischoff, Robert Janowski, Nikolas von den Eichen, Dierk Niessing and Dirk Weuster-Botz
Crystals 2021, 11(8), 975; https://doi.org/10.3390/cryst11080975 - 17 Aug 2021
Cited by 8 | Viewed by 4544
Abstract
Protein crystallization can serve as a purification step in biotechnological processes but is often limited by the non-crystallizability of proteins. Enabling or improving crystallization is mostly achieved by high-throughput screening of crystallization conditions and, more recently, by rational crystal contact engineering. Two selected [...] Read more.
Protein crystallization can serve as a purification step in biotechnological processes but is often limited by the non-crystallizability of proteins. Enabling or improving crystallization is mostly achieved by high-throughput screening of crystallization conditions and, more recently, by rational crystal contact engineering. Two selected rational crystal contact mutations, Q126K and T102E, were transferred from the alcohol dehydrogenases of Lactobacillus brevis (LbADH) to Lactobacillus kefir (LkADH). Proteins were expressed in E. coli and batch protein crystallization was performed in stirred crystallizers. Highly similar crystal packing of LkADH wild type compared to LbADH, which is necessary for the transfer of crystal contact engineering strategies, was achieved by aligning purification tag and crystallization conditions, as shown by X-ray diffraction. After comparing the crystal sizes after crystallization of LkADH mutants with the wild type, the mean protein crystal size of LkADH mutants was reduced by 40–70% in length with a concomitant increase in the total amount of crystals (higher number of nucleation events). Applying this measure to the LkADH variants studied results in an order of crystallizability T102E > Q126K > LkADH wild type, which corresponds to the results with LbADH mutants and shows, for the first time, the successful transfer of crystal contact engineering strategies. Full article
(This article belongs to the Special Issue Bulk Protein Crystallization)
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16 pages, 876 KB  
Review
Engineering Crystal Packing in RNA Structures I: Past and Future Strategies for Engineering RNA Packing in Crystals
by Narsimha Pujari, Stephanie L. Saundh, Francis A. Acquah, Blaine H. M. Mooers, Adrian R. Ferré-D’Amaré and Adelaine Kwun-Wai Leung
Crystals 2021, 11(8), 952; https://doi.org/10.3390/cryst11080952 - 15 Aug 2021
Cited by 12 | Viewed by 5166
Abstract
X-ray crystallography remains a powerful method to gain atomistic insights into the catalytic and regulatory functions of RNA molecules. However, the technique requires the preparation of diffraction-quality crystals. This is often a resource- and time-consuming venture because RNA crystallization is hindered by the [...] Read more.
X-ray crystallography remains a powerful method to gain atomistic insights into the catalytic and regulatory functions of RNA molecules. However, the technique requires the preparation of diffraction-quality crystals. This is often a resource- and time-consuming venture because RNA crystallization is hindered by the conformational heterogeneity of RNA, as well as the limited opportunities for stereospecific intermolecular interactions between RNA molecules. The limited success at crystallization explains in part the smaller number of RNA-only structures in the Protein Data Bank. Several approaches have been developed to aid the formation of well-ordered RNA crystals. The majority of these are construct-engineering techniques that aim to introduce crystal contacts to favor the formation of well-diffracting crystals. A typical example is the insertion of tetraloop–tetraloop receptor pairs into non-essential RNA segments to promote intermolecular association. Other methods of promoting crystallization involve chaperones and crystallization-friendly molecules that increase RNA stability and improve crystal packing. In this review, we discuss the various techniques that have been successfully used to facilitate crystal packing of RNA molecules, recent advances in construct engineering, and directions for future research in this vital aspect of RNA crystallography. Full article
(This article belongs to the Special Issue Nucleic Acid Crystallography)
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10 pages, 3191 KB  
Communication
Investigation on the Effects of Grain Boundary on Deformation Behavior of Bicrystalline Pillar by Crystal Plasticity Finite Element Method
by Hui Zhou, Pei Wang and Shanping Lu
Crystals 2021, 11(8), 923; https://doi.org/10.3390/cryst11080923 - 9 Aug 2021
Cited by 7 | Viewed by 2914
Abstract
A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found [...] Read more.
A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found that the angle between the activated slip systems, which is determined by the crystal orientations, rather than the grain boundary misorientation angle, influences the interactions between the plastic slip and the grain boundary, which further influence the heterogeneous deformation of bicrystalline specimens. Full article
(This article belongs to the Special Issue Crystal Plasticity (Volume II))
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13 pages, 31239 KB  
Article
Heterogeneous Crystal Nucleation from the Melt in Polyethylene Oxide Droplets on Graphite: Kinetics and Microscopic Structure
by Muhammad Tariq, Thomas Thurn-Albrecht and Oleksandr Dolynchuk
Crystals 2021, 11(8), 924; https://doi.org/10.3390/cryst11080924 - 9 Aug 2021
Cited by 9 | Viewed by 3485
Abstract
It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation [...] Read more.
It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation in an ensemble of polyethylene oxide (PEO) droplets on graphite and on amorphous polystyrene (PS). The optical microscopy measurements during cooling with a constant rate explicitly evidenced that the graphite substrate enhances the nucleation kinetics, as crystallization occurred at approximately an 11 °C higher temperature than on PS due to changes in the interactions at the solid interface. This observation allowed us to conclude that graphite induces heterogeneous nucleation in PEO. By employing the classical nucleation theory for analysis of the data with reference to the amorphous PS substrate, the obtained results indicated that the crystal nuclei with contact angles in the range of 100–117° were formed at the graphite interface. Furthermore, we show that heterogeneous nucleation led to a preferred orientation of PEO crystals on graphite, whereas PEO crystals on PS had isotropic orientation. The difference in crystal orientations on the two substrates was also confirmed with AFM, which showed only edge-on lamellae in PEO droplets on graphite compared to unoriented lamellae on PS. Full article
(This article belongs to the Topic Polymer Crystallization)
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22 pages, 7297 KB  
Article
Investigation of Mid-Infrared Broadband Second-Harmonic Generation in Non-Oxide Nonlinear Optic Crystals
by Ilhwan Kim, Donghwa Lee and Kwang Jo Lee
Crystals 2021, 11(8), 921; https://doi.org/10.3390/cryst11080921 - 8 Aug 2021
Cited by 7 | Viewed by 4173
Abstract
The mid-infrared (mid-IR) continuum generation based on broadband second harmonic generation (SHG) (or difference frequency generation) is of great interest in a wide range of applications such as free space communications, environmental monitoring, thermal imaging, high-sensitivity metrology, gas sensing, and molecular fingerprint spectroscopy. [...] Read more.
The mid-infrared (mid-IR) continuum generation based on broadband second harmonic generation (SHG) (or difference frequency generation) is of great interest in a wide range of applications such as free space communications, environmental monitoring, thermal imaging, high-sensitivity metrology, gas sensing, and molecular fingerprint spectroscopy. The second-order nonlinear optic (NLO) crystals have been spotlighted as a material platform for converting the wavelengths of existing lasers into the mid-IR spectral region or for realizing tunable lasers. In particular, the spectral coverage could be extended to ~19 µm with non-oxide NLO crystals. In this paper, we theoretically and numerically investigated the broadband SHG properties of non-oxide mid-IR crystals in three categories: chalcopyrite semiconductors, defect chalcopyrite, and orthorhombic ternary chalcogenides. The technique is based on group velocity matching between interacting waves in addition to birefringent phase matching. We will describe broadband SHG characteristics in terms of beam propagation directions, spectral positions of resonance, effective nonlinearities, spatial walk-offs between interacting beams, and spectral bandwidths. The results will show that the spectral bandwidths of the fundamental wave allowed for broadband SHG to reach several hundreds of nm. The corresponding SH spectral range spans from 1758.58 to 4737.18 nm in the non-oxide crystals considered in this study. Such broadband SHG using short pulse trains can potentially be applied to frequency up-conversion imaging in the mid-IR region, in information transmission, and in nonlinear optical signal processing. Full article
(This article belongs to the Special Issue Advances in Middle Infrared Laser Crystals and Its Applications)
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16 pages, 4246 KB  
Article
Crystal Growth on Cenospheres from High-Calcium Fly Ash
by Sorachon Yoriya and Phattarathicha Tepsri
Crystals 2021, 11(8), 919; https://doi.org/10.3390/cryst11080919 - 7 Aug 2021
Cited by 8 | Viewed by 3212
Abstract
This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on [...] Read more.
This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on cenosphere yield and properties were investigated. Those properties include physical properties, morphology, chemical composition, and mineral phases. The recovery yields are in the range of 0.34–0.64%, approximately one third of the yield obtained from the general gravity settling method. Density, particle size, and morphology of the collected cenospheres appeared to be independent of sequence of the applied speeds and times. Interrelation of chemical composition and mineral phases was established, with the focus on calcium carbonate formation on cenosphere surface and crystallite size study. The study has revealed the preferential formation of calcite–(104) peak is observed–by cenospheres, with stable growth behavior of crystallite sizes obtained from all the centrifugal conditions. The result was compared to that obtained from the sink-float method for a better insight. The influence and limitation of the centrifugal method, the varied parameters, and the relevant reaction pathways on crystal growth process in terms of important dissolving species (i.e., Ca2+ and CO32−) behavior in the ash suspension were discussed. Full article
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13 pages, 2901 KB  
Article
Topological Defect-Guided Regular Stacking of Focal Conic Domains in Hybrid-Aligned Smectic Liquid Crystal Shells
by JungHyun Noh and Jan P. F. Lagerwall
Crystals 2021, 11(8), 913; https://doi.org/10.3390/cryst11080913 - 4 Aug 2021
Cited by 7 | Viewed by 3569
Abstract
We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at [...] Read more.
We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at the thinnest and thickest points, respectively. On cooling from N to SmA, the symmetry axis connecting the defects gradually reorients from along gravity to perpendicular to it, reversibly and continuously, if the LC and aqueous phase are density matched at the N-SmA transition. This suggests reduced density near the defects—reflecting a local reduction in order—under the strong confinement with antagonistic boundary conditions. In the SmA phase, a regular array of focal conic domains (FCDs) develops, templated in position and orientation by the +1 defect at the thinnest point. Around this defect, a single complete toroidal FCD always develops, surrounded by incomplete FCDs. In contrast to similar FCD arrangements on flat aqueous interfaces, this is a stable situation, since the two +1 defects are required by the spherical topology. Our results demonstrate how the topological defects of LC shells can be used to template complex self-organized structures. With a suitable adaption of the LC chemistry, shells might serve as a basis for producing solid particles with complex yet highly regular morphologies. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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