Crystals

15 pages, 1400 KiB

Open AccessEditor’s ChoiceReview

A Review of the Latest Developments in the Field of Refractory High-Entropy Alloys

by Muthe Srikanth, A. Raja Annamalai, A. Muthuchamy and Chun-Ping Jen

Crystals 2021, 11(6), 612; https://doi.org/10.3390/cryst11060612 - 28 May 2021

Cited by 69 | Viewed by 9900

This review paper provides insight into current developments in refractory high-entropy alloys (RHEAs) based on previous and currently available literature. High-temperature strength, high-temperature oxidation resistance, and corrosion resistance properties make RHEAs unique and stand out from other materials. RHEAs mainly contain refractory elements [...] Read more.

This review paper provides insight into current developments in refractory high-entropy alloys (RHEAs) based on previous and currently available literature. High-temperature strength, high-temperature oxidation resistance, and corrosion resistance properties make RHEAs unique and stand out from other materials. RHEAs mainly contain refractory elements like W, Ta, Mo, Zr, Hf, V, and Nb (each in the 5–35 at% range), and some low melting elements like Al and Cr at less than 5 at%, which were already developed and in use for the past two decades. These alloys show promise in replacing Ni-based superalloys. In this paper, various manufacturing processes like casting, powder metallurgy, metal forming, thin-film, and coating, as well as the effect of different alloying elements on the microstructure, phase formation, mechanical properties and strengthening mechanism, oxidation resistance, and corrosion resistance, of RHEAs are reviewed. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

► Show Figures

Figure 1

10 pages, 5710 KiB

Open AccessEditor’s ChoiceArticle

Template Effect of Multi-Phase Liquid Crystals

by Yao Gao, Tengfei Huang and Jiangang Lu

Crystals 2021, 11(6), 602; https://doi.org/10.3390/cryst11060602 - 27 May 2021

Cited by 5 | Viewed by 2942

Abstract

The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, [...] Read more.

The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, which includes the refilling CLC and intrinsic template BPLC or SPLC, can be fabricated. By refilling a CLC of different chiral pitch into a CLC template, a multi-pitch CLC that includes the refilling CLC and intrinsic CLC, can be fabricated. Twist structure LC devices with multi-phase and multi-pitch show great potential for applications in optical communication, displays, and LC lasing. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

► Show Figures

Figure 1

16 pages, 2044 KiB

Open AccessEditor’s ChoiceReview

Interplay between Vortex Dynamics and Superconducting Gap Structure in Layered Organic Superconductors

by Syuma Yasuzuka

Crystals 2021, 11(6), 600; https://doi.org/10.3390/cryst11060600 - 26 May 2021

Cited by 2 | Viewed by 4679

Abstract

Layered organic superconductors motivate intense investigations because they provide various unexpected issues associated with their low dimensionality and the strong electron correlation. Since layered organic superconductors possess simple Fermi surface geometry and they often share similarities to the high temperature oxide superconductors and [...] Read more.

Layered organic superconductors motivate intense investigations because they provide various unexpected issues associated with their low dimensionality and the strong electron correlation. Since layered organic superconductors possess simple Fermi surface geometry and they often share similarities to the high temperature oxide superconductors and heavy fermion compounds, research on layered organic superconductors is suitable for understanding the essence and nature of strongly correlated electron systems. In strongly correlated electron systems, one of the central problems concerning the superconducting (SC) state is the symmetry of the SC gap, which is closely related to the paring mechanism. Thus, experimental determination of the SC gap structure is of essential importance. In this review, we present the experimental results for the in-plane angular variation of the flux-flow resistance in layered organic superconductors k-(ET)₂Cu(NCS)₂, β″-(ET)₂SF₅CH₂CF₂SO₃, and λ-(BETS)₂GaCl₄. The interplay between the vortex dynamics and nodal structures is discussed for these superconductors. Full article

(This article belongs to the Special Issue Organic Conductors)

► Show Figures

Figure 1

13 pages, 1813 KiB

Open AccessEditor’s ChoiceArticle

Comparative Hybrid Hartree-Fock-DFT Calculations of WO₂-Terminated Cubic WO₃ as Well as SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) Surfaces

by R. I. Eglitis, Juris Purans and Ran Jia

Crystals 2021, 11(4), 455; https://doi.org/10.3390/cryst11040455 - 20 Apr 2021

Cited by 51 | Viewed by 5296

Abstract

We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO₂-terminated cubic WO₃ (001) surface and analyzed the systematic trends in the WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO [...] Read more.

We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO₂-terminated cubic WO₃ (001) surface and analyzed the systematic trends in the WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) surface ab initio calculations. According to our first principles calculations, all WO₂ or TiO₂-terminated WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaZrO₃ (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO₂ and TiO₂-terminated WO₃ and PbTiO₃ (001) surface O atoms. The WO₂ or TiO₂-terminated WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ bulk are smaller than those near the TiO₂-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO₃ bulk is larger than near the WO₂-terminated WO₃ (001) surface. Full article

(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)

► Show Figures

Figure 1

13 pages, 3121 KiB

Open AccessEditor’s ChoiceArticle

Extraction–Pyrolytic Method for TiO₂ Polymorphs Production

by Vera Serga, Regina Burve, Aija Krumina, Marina Romanova, Eugene A. Kotomin and Anatoli I. Popov

Crystals 2021, 11(4), 431; https://doi.org/10.3390/cryst11040431 - 16 Apr 2021

Cited by 51 | Viewed by 4380

Abstract

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO₂) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) [...] Read more.

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO₂) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) for the production of nanocrystalline TiO₂ powders. A titanium-containing precursor (extract) was prepared by liquid–liquid extraction using valeric acid C₄H₉COOH without diluent as an extractant. Simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC), as well as the Fourier-transform infrared (FTIR) spectroscopy were used to determine the temperature conditions to fabricate TiO₂ powders free of organic impurities. The produced materials were also characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The results showed the possibility of the fabrication of storage-stable liquid titanium (IV)-containing precursor, which provided nanocrystalline TiO₂ powders. It was established that the EPM permits the production of both monophase (anatase polymorph or rutile polymorph) and biphase (mixed anatase–rutile polymorphs), impurity-free nanocrystalline TiO₂ powders. For comparison, TiO₂ powders were also produced by the precipitation method. The results presented in this study could serve as a solid basis for further developing the EPM for the cheap and simple production of nanocrystalline TiO₂-based materials in the form of doped nanocrystalline powders, thin films, and composite materials. Full article

(This article belongs to the Special Issue Advances in Functional Inorganic Materials Prepared by Wet Chemical Methods)

► Show Figures

Graphical abstract

22 pages, 1998 KiB

Open AccessEditor’s ChoiceReview

State-of-the-Art Review of the Applicability and Challenges of Microbial-Induced Calcite Precipitation (MICP) and Enzyme-Induced Calcite Precipitation (EICP) Techniques for Geotechnical and Geoenvironmental Applications

by Abdullah Almajed, Mohammed Abdul Lateef, Arif Ali Baig Moghal and Kehinde Lemboye

Crystals 2021, 11(4), 370; https://doi.org/10.3390/cryst11040370 - 1 Apr 2021

Cited by 129 | Viewed by 11377

Abstract

The development of alternatives to soil stabilization through mechanical and chemical stabilization has paved the way for the development of biostabilization methods. Since its development, researchers have used different bacteria species for soil treatment. Soil treatment through bioremediation techniques has been used to [...] Read more.

The development of alternatives to soil stabilization through mechanical and chemical stabilization has paved the way for the development of biostabilization methods. Since its development, researchers have used different bacteria species for soil treatment. Soil treatment through bioremediation techniques has been used to understand its effect on strength parameters and contaminant remediation. Using a living organism for binding the soil grains to make the soil mass dense and durable is the basic idea of soil biotreatment. Bacteria and enzymes are commonly utilized in biostabilization, which is a common method to encourage ureolysis, leading to calcite precipitation in the soil mass. Microbial-induced calcite precipitation (MICP) and enzyme-induced calcite precipitation (EICP) techniques are emerging trends in soil stabilization. Unlike conventional methods, these techniques are environmentally friendly and sustainable. This review determines the challenges, applicability, advantages, and disadvantages of MICP and EICP in soil treatment and their role in the improvement of the geotechnical and geoenvironmental properties of soil. It further elaborates on their probable mechanism in improving the soil properties in the natural and lab environments. Moreover, it looks into the effectiveness of biostabilization as a remediation of soil contamination. This review intends to present a hands-on adoptable treatment method for in situ implementation depending on specific site conditions. Full article

(This article belongs to the Special Issue New Frontiers in Cementitious and Lime-Based Materials and Composites)

► Show Figures

Figure 1

17 pages, 4293 KiB

Open AccessEditor’s ChoiceArticle

Combinatorial Materials Design Approach to Investigate Adhesion Layer Chemistry for Optimal Interfacial Adhesion Strength

by Rachel L. Schoeppner, Barbara Putz, Aidan A. Taylor, Laszlo Pethö, Keith Thomas, Olivier Antonin, Thomas Nelis and Johann Michler

Crystals 2021, 11(4), 357; https://doi.org/10.3390/cryst11040357 - 30 Mar 2021

Cited by 3 | Viewed by 3922

Abstract

A combinatorial material adhesion study was used to optimize the composition of an adhesion promoting layer for a nanocrystalline diamond (NCD) coating on silicon. Three different adhesion promoting metals, namely W, Cr, and Ta, were selected to fabricate arrays of co-sputtered binary alloy [...] Read more.

A combinatorial material adhesion study was used to optimize the composition of an adhesion promoting layer for a nanocrystalline diamond (NCD) coating on silicon. Three different adhesion promoting metals, namely W, Cr, and Ta, were selected to fabricate arrays of co-sputtered binary alloy films, with patches of seven different, distinct alloy compositions for each combination, and single element reference films on a single Si wafer (three wafers in total; W–Cr, Cr–Ta, Ta–W). Scratch testing was used to determine the critical failure load and practical work of adhesion for the NCD coatings as a function of adhesion layer chemistry. All tested samples eventually exhibit delamination of the NCD coating, with buckles radiating perpendicularly away from the scratch track. Application of any of the presented adhesion layers yields an increase of the critical failure load for delamination as compared to NCD on Si. While the influence of adhesion layers on the maximum buckle length is less pronounced, shorter buckles are obtained with pure W and Cr–Ta alloy layers. As a general rule, the addition of an adhesion layer showed a 75% improvement in the measured adhesion energies of the NCD films compared to the NCD coating without an adhesion layer, with specific alloys and compositions showing up to 125% increase in calculated practical work of adhesion. Full article

(This article belongs to the Special Issue Advanced Nanoindentation in Materials)

► Show Figures

Figure 1

15 pages, 7701 KiB

Open AccessEditor’s ChoiceArticle

Light Extraction Enhancement Techniques for Inorganic Scintillators

by Francesco Gramuglia, Simone Frasca, Emanuele Ripiccini, Esteban Venialgo, Valentin Gâté, Hind Kadiri, Nicolas Descharmes, Daniel Turover, Edoardo Charbon and Claudio Bruschini

Crystals 2021, 11(4), 362; https://doi.org/10.3390/cryst11040362 - 30 Mar 2021

Cited by 17 | Viewed by 5315

Abstract

Scintillators play a key role in the detection chain of several applications which rely on the use of ionizing radiation, and it is often mandatory to extract and detect the generated scintillation light as efficiently as possible. Typical inorganic scintillators do however feature [...] Read more.

Scintillators play a key role in the detection chain of several applications which rely on the use of ionizing radiation, and it is often mandatory to extract and detect the generated scintillation light as efficiently as possible. Typical inorganic scintillators do however feature a high index of refraction, which impacts light extraction efficiency in a negative way. Furthermore, several applications such as preclinical Positron Emission Tomography (PET) rely on pixelated scintillators with small pitch. In this case, applying reflectors on the crystal pixel surface, as done conventionally, can have a dramatic impact of the packing fraction and thus the overall system sensitivity. This paper presents a study on light extraction techniques, as well as combinations thereof, for two of the most used inorganic scintillators (LYSO and BGO). Novel approaches, employing Distributed Bragg Reflectors (DBRs), metal coatings, and a modified Photonic Crystal (PhC) structure, are described in detail and compared with commonly used techniques. The nanostructure of the PhC is surrounded by a hybrid organic/inorganic silica sol-gel buffer layer which ensures robustness while maintaining its performance unchanged. We observed in particular a maximum light gain of about 41% on light extraction and 21% on energy resolution for BGO, a scintillator which has gained interest in the recent past due to its prompt Cherenkov component and lower cost. Full article

(This article belongs to the Special Issue Scintillator & Phosphor Materials)

► Show Figures

Figure 1

12 pages, 3279 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Physiological Metals Can Induce Conformational Changes in Transthyretin Structure: Neuroprotection or Misfolding Induction?

by Lidia Ciccone, Nicolò Tonali, William Shepard, Susanna Nencetti and Elisabetta Orlandini

Crystals 2021, 11(4), 354; https://doi.org/10.3390/cryst11040354 - 29 Mar 2021

Cited by 12 | Viewed by 3480

Abstract

Transthyretin (TTR) is a plasma homotetrameric protein that transports thyroxine and retinol. TTR itself, under pathological conditions, dissociates into partially unfolded monomers that aggregate and form fibrils. Metal ions such as Zn²⁺, Cu²⁺, Fe²⁺, Mn²⁺ and [...] Read more.

Transthyretin (TTR) is a plasma homotetrameric protein that transports thyroxine and retinol. TTR itself, under pathological conditions, dissociates into partially unfolded monomers that aggregate and form fibrils. Metal ions such as Zn²⁺, Cu²⁺, Fe²⁺, Mn²⁺ and Ca²⁺ play a controversial role in the TTR amyloidogenic pathway. TTR is also present in cerebrospinal fluid (CSF), where it behaves as one of the major Aβ-binding-proteins. The interaction between TTR and Aβ is stronger in the presence of high concentrations of Cu²⁺. Crystals of TTR, soaked in solutions of physiological metals such as Cu²⁺ and Fe²⁺, but not Mn²⁺, Zn²⁺, Fe³⁺, Al³⁺, Ni²⁺, revealed an unusual conformational change. Here, we investigate the effects that physiological metals have on TTR, in order to understand if metals can induce a specific and active conformation of TTR that guides its Aβ-scavenging role. The capability of certain metals to induce and accelerate its amyloidogenic process is also discussed. Full article

► Show Figures

Graphical abstract

12 pages, 5293 KiB

Open AccessEditor’s ChoiceArticle

1,4-Dibromo-2,5-bis(phenylalkoxy)benzene Derivatives: C–Br...π(arene) Versus C–H...Br and Br...Br Interactions in the Solid State

by Giacomo Manfroni, Alessandro Prescimone, Edwin C. Constable and Catherine E. Housecroft

Crystals 2021, 11(4), 325; https://doi.org/10.3390/cryst11040325 - 25 Mar 2021

Cited by 5 | Viewed by 3080

Abstract

We have prepared and characterized 1,4-dibromo-2,5-bis(2-phenylethoxy)benzene (1) and 1,4-dibromo-2,5-bis(3-phenylpropoxy)benzene (2). Their single-crystal structures confirm that, at the molecular level, they are similar with the phenylalkoxy chains in extended conformations. However, there are significant differences in packing interactions. The packing [...] Read more.

We have prepared and characterized 1,4-dibromo-2,5-bis(2-phenylethoxy)benzene (1) and 1,4-dibromo-2,5-bis(3-phenylpropoxy)benzene (2). Their single-crystal structures confirm that, at the molecular level, they are similar with the phenylalkoxy chains in extended conformations. However, there are significant differences in packing interactions. The packing in 1 is dominated by C–Br...π(arene) interactions, with each Br located over one C–C bond of the central arene ring of an adjacent molecule. In contrast, the packing of molecules of 2 involves a combination of C–H...Br hydrogen bonds, Br...Br interactions, and arene–arene π-stacking. The single-crystal structures of both orthorhombic and triclinic polymorphs of 1 have been determined and the packing interactions are shown to be essentially identical. Full article

(This article belongs to the Special Issue Advanced Research in Halogen Bonding)

► Show Figures

Graphical abstract

22 pages, 7115 KiB

Open AccessEditor’s ChoiceArticle

Weak Interactions in Cocrystals of Isoniazid with Glycolic and Mandelic Acids

by Raquel Álvarez-Vidaurre, Alfonso Castiñeiras, Antonio Frontera, Isabel García-Santos, Diego M. Gil, Josefa M. González-Pérez, Juan Niclós-Gutiérrez and Rocío Torres-Iglesias

Crystals 2021, 11(4), 328; https://doi.org/10.3390/cryst11040328 - 25 Mar 2021

Cited by 11 | Viewed by 3825

Abstract

This work deals with the preparation of pyridine-3-carbohydrazide (isoniazid, inh) cocrystals with two α-hydroxycarboxylic acids. The interaction of glycolic acid (H₂ga) or d,l-mandelic acid (H₂ma) resulted in the formation of cocrystals or salts of composition (inh)·(H₂ga) ( [...] Read more.

This work deals with the preparation of pyridine-3-carbohydrazide (isoniazid, inh) cocrystals with two α-hydroxycarboxylic acids. The interaction of glycolic acid (H₂ga) or d,l-mandelic acid (H₂ma) resulted in the formation of cocrystals or salts of composition (inh)·(H₂ga) (1) and [Hinh]⁺[Hma]^–·(H₂ma) (2) when reacted with isoniazid. An N′-(propan-2-ylidene)isonicotinic hydrazide hemihydrate, (pinh)·1/2(H₂O) (3), was also prepared by condensation of isoniazid with acetone in the presence of glycolic acid. These prepared compounds were well characterized by elemental analysis, and spectroscopic methods, and their three-dimensional molecular structure was determined by single crystal X-ray crystallography. Hydrogen bonds involving the carboxylic acid occur consistently with the pyridine ring N atom of the isoniazid and its derivatives. The remaining hydrogen-bonding sites on the isoniazid backbone vary based on the steric influences of the derivative group. These are contrasted in each of the molecular systems. Finally, Hirshfeld surface analysis and Density-functional theory (DFT) calculations (including NCIplot and QTAIM analyses) have been performed to further characterize and rationalize the non-covalent interactions. Full article

(This article belongs to the Special Issue σ- and π-Hole Interactions (Volume II))

► Show Figures

Figure 1

10 pages, 4426 KiB

Open AccessEditor’s ChoiceArticle

Electro-Optic Control of Lithium Niobate Bulk Whispering Gallery Resonators: Analysis of the Distribution of Externally Applied Electric Fields

by Yannick Minet, Hans Zappe, Ingo Breunig and Karsten Buse

Crystals 2021, 11(3), 298; https://doi.org/10.3390/cryst11030298 - 17 Mar 2021

Cited by 8 | Viewed by 4045

Abstract

Whispering gallery resonators made out of lithium niobate allow for optical parametric oscillation and frequency comb generation employing the outstanding second-order nonlinear-optical properties of this material. An important knob to tune and control these processes is, e.g., the linear electro-optic effect, the Pockels [...] Read more.

Whispering gallery resonators made out of lithium niobate allow for optical parametric oscillation and frequency comb generation employing the outstanding second-order nonlinear-optical properties of this material. An important knob to tune and control these processes is, e.g., the linear electro-optic effect, the Pockels effect via externally applied electric fields. Due to the shape of the resonators a precise prediction of the electric field strength that affects the optical mode is non-trivial. Here, we study the average strength of the electric field in z-direction in the region of the optical mode for different configurations and geometries of lithium niobate whispering gallery resonators with the help of the finite element method. We find that in some configurations almost 100% is present in the cavity compared to the ideal case of a cylindrical resonator. Even in the case of a few-mode resonator with a very thin rim we find a strength of 90%. Our results give useful design considerations for future arrangements that may benefit from the strong electro-optic effect in bulk whispering gallery resonators made out of lithium niobate. Full article

(This article belongs to the Special Issue New Trends in Lithium Niobate: From Bulk to Nanocrystals)

► Show Figures

Figure 1

23 pages, 5139 KiB

Open AccessEditor’s ChoiceArticle

Affinity and Structural Analysis of the U1A RNA Recognition Motif with Engineered Methionines to Improve Experimental Phasing

by Yoshita Srivastava, Rachel Bonn-Breach, Sai Shashank Chavali, Geoffrey M. Lippa, Jermaine L. Jenkins and Joseph E. Wedekind

Crystals 2021, 11(3), 273; https://doi.org/10.3390/cryst11030273 - 10 Mar 2021

Cited by 4 | Viewed by 3987

Abstract

RNA plays a central role in all organisms and can fold into complex structures to orchestrate function. Visualization of such structures often requires crystallization, which can be a bottleneck in the structure-determination process. To promote crystallization, an RNA-recognition motif (RRM) of the U1A [...] Read more.

RNA plays a central role in all organisms and can fold into complex structures to orchestrate function. Visualization of such structures often requires crystallization, which can be a bottleneck in the structure-determination process. To promote crystallization, an RNA-recognition motif (RRM) of the U1A spliceosomal protein has been co-opted as a crystallization module. Specifically, the U1-snRNA hairpin II (hpII) single-stranded loop recognized by U1A can be transplanted into an RNA target to promote crystal contacts and to attain phase information via molecular replacement or anomalous diffraction methods using selenomethionine. Herein, we produced the F37M/F77M mutant of U1A to augment the phasing capability of this powerful crystallization module. Selenomethionine-substituted U1A(F37M/F77M) retains high affinity for hpII (K_D of 59.7 ± 11.4 nM). The 2.20 Å resolution crystal structure reveals that the mutated sidechains make new S-π interactions in the hydrophobic core and are useful for single-wavelength anomalous diffraction. Crystals were also attained of U1A(F37M/F77M) in complex with a bacterial preQ₁-II riboswitch. The F34M/F37M/F77M mutant was introduced similarly into a lab-evolved U1A variant (TBP6.9) that recognizes the internal bulged loop of HIV-1 TAR RNA. We envision that this short RNA sequence can be placed into non-essential duplex regions to promote crystallization and phasing of target RNAs. We show that selenomethionine-substituted TBP6.9(F34M/F37M/F77M) binds a TAR variant wherein the apical loop was replaced with a GNRA tetraloop (K_D of 69.8 ± 2.9 nM), laying the groundwork for use of TBP6.9(F34M/F37M/F77M) as a crystallization module. These new tools are available to the research community. Full article

(This article belongs to the Special Issue Nucleic Acid Crystallography)

► Show Figures

Graphical abstract

27 pages, 5851 KiB

Open AccessEditor’s ChoiceArticle

Boundary Conditions for Simulations of Fluid Flow and Temperature Field during Ammonothermal Crystal Growth—A Machine-Learning Assisted Study of Autoclave Wall Temperature Distribution

by Saskia Schimmel, Daisuke Tomida, Makoto Saito, Quanxi Bao, Toru Ishiguro, Yoshio Honda, Shigefusa Chichibu and Hiroshi Amano

Crystals 2021, 11(3), 254; https://doi.org/10.3390/cryst11030254 - 4 Mar 2021

Cited by 10 | Viewed by 4349

Abstract

Thermal boundary conditions for numerical simulations of ammonothermal GaN crystal growth are investigated. A global heat transfer model that includes the furnace and its surroundings is presented, in which fluid flow and thermal field are treated as conjugate in order to fully account [...] Read more.

Thermal boundary conditions for numerical simulations of ammonothermal GaN crystal growth are investigated. A global heat transfer model that includes the furnace and its surroundings is presented, in which fluid flow and thermal field are treated as conjugate in order to fully account for convective heat transfer. The effects of laminar and turbulent flow are analyzed, as well as those of typically simultaneously present solids inside the autoclave (nutrient, baffle, and multiple seeds). This model uses heater powers as a boundary condition. Machine learning is applied to efficiently determine the power boundary conditions needed to obtain set temperatures at specified locations. Typical thermal losses are analyzed regarding their effects on the temperature distribution inside the autoclave and within the autoclave walls. This is of relevance because autoclave wall temperatures are a convenient choice for setting boundary conditions for simulations of reduced domain size. Based on the determined outer wall temperature distribution, a simplified model containing only the autoclave is also presented. The results are compared to those observed using heater-long fixed temperatures as boundary condition. Significant deviations are found especially in the upper zone of the autoclave due to the important role of heat losses through the autoclave head. Full article

(This article belongs to the Special Issue Artificial Intelligence for Crystal Growth and Characterization)

► Show Figures

Figure 1

9 pages, 1694 KiB

Open AccessEditor’s ChoiceArticle

Helimagnetism in MnBi₂Se₄ Driven by Spin-Frustrating Interactions Between Antiferromagnetic Chains

by Judith K. Clark, Chongin Pak, Huibo Cao and Michael Shatruk

Crystals 2021, 11(3), 242; https://doi.org/10.3390/cryst11030242 - 27 Feb 2021

Cited by 11 | Viewed by 4754

Abstract

We report the magnetic properties and magnetic structure determination for a linear-chain antiferromagnet, MnBi₂Se₄. The crystal structure of this material contains chains of edge-sharing MnSe₆ octahedra separated by Bi atoms. The magnetic behavior is dominated by intrachain antiferromagnetic [...] Read more.

We report the magnetic properties and magnetic structure determination for a linear-chain antiferromagnet, MnBi₂Se₄. The crystal structure of this material contains chains of edge-sharing MnSe₆ octahedra separated by Bi atoms. The magnetic behavior is dominated by intrachain antiferromagnetic (AFM) interactions, as demonstrated by the negative Weiss constant of −74 K obtained by the Curie–Weiss fit of the paramagnetic susceptibility measured along the easy-axis magnetization direction. The relative shift of adjacent chains by one-half of the chain period causes spin frustration due to interchain AFM coupling, which leads to AFM ordering at T_N = 15 K. Neutron diffraction studies reveal that the AFM ordered state exhibits an incommensurate helimagnetic structure with the propagation vector k = (0, 0.356, 0). The Mn moments are arranged perpendicular to the chain propagation direction (the crystallographic b axis), and the turn angle around the helix is 128°. The magnetic properties of MnBi₂Se₄ are discussed in comparison to other linear-chain antiferromagnets based on ternary mixed-metal halides and chalcogenides. Full article

(This article belongs to the Special Issue Intermetallic)

► Show Figures

Graphical abstract

12 pages, 2225 KiB

Open AccessEditor’s ChoiceArticle

Modeling of the Resonant X-ray Response of a Chiral Cubic Phase

by Timon Grabovac, Ewa Gorecka, Damian Pociecha and Nataša Vaupotič

Crystals 2021, 11(2), 214; https://doi.org/10.3390/cryst11020214 - 21 Feb 2021

Cited by 2 | Viewed by 2647

Abstract

The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation [...] Read more.

The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation in the unit cell, could be applied to select the most appropriate model. We modeled the RXS response for the recently proposed chiral cubic phase structure with an all-hexagon chiral continuous grid. A tensor form factor of a unit cell is constructed, which enables calculation of intensities of peaks for all Miller indices. We find that all the symmetry allowed peaks are resonantly enhanced, and their intensity is much stronger than the intensity of the symmetry forbidden (resonant) peaks. In particular, we predict that a strong resonant enhancement of the symmetry allowed peaks (011) and (002), not observed in a nonresonant scattering, could be observed by RXS at the carbon absorption edge. By RXS at the sulfur absorption edge, one might observe a resonant peak (113) and resonantly enhanced peak (233), and resonant enhancement of all the peaks that are observed in a nonresonant scattering, which probably hide the rest of the predicted resonant peaks. Full article

(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)

► Show Figures

Figure 1

16 pages, 3848 KiB

Open AccessEditor’s ChoiceArticle

Extending Libraries of Extremely Localized Molecular Orbitals to Metal Organic Frameworks: A Preliminary Investigation

by Erna K. Wieduwilt, Giovanni Macetti, Rebecca Scatena, Piero Macchi and Alessandro Genoni

Crystals 2021, 11(2), 207; https://doi.org/10.3390/cryst11020207 - 20 Feb 2021

Cited by 5 | Viewed by 4919

Abstract

Libraries of extremely localized molecular orbitals (ELMOs) have been recently assembled to reconstruct approximate wavefunctions of very large biological systems, such as polypeptides and proteins. In this paper, we investigate for the first time the possibility of using ELMO transferability to also quickly [...] Read more.

Libraries of extremely localized molecular orbitals (ELMOs) have been recently assembled to reconstruct approximate wavefunctions of very large biological systems, such as polypeptides and proteins. In this paper, we investigate for the first time the possibility of using ELMO transferability to also quickly obtain wavefunctions, electron densities, and electrostatic potentials of three-dimensional coordination polymers such as metal organic frameworks (MOFs). To accomplish this task, we propose a protocol that, in addition to exploiting the usual exportability of extremely localized molecular orbitals, also takes advantage of the novel QM/ELMO (quantum mechanics/extremely localized molecular orbital) approach to properly describe the secondary building units of MOFs. As a benchmark test, our technique has been applied to the well-known metal organic framework HKUST-1 ({Cu₃(BTC)₂}_n, with BTC=1,3,5-benzenetricarboxylate) to quickly calculate electrostatic potential maps in the small and large cavities inside the network. On the basis of the obtained results, we envisage further improvements and applications of this strategy, which can be also seen as a starting point to perform less computationally expensive quantum mechanical calculations on metal organic frameworks with the goal of investigating transformation phenomena such as chemisorption. Full article

► Show Figures

Figure 1

16 pages, 3210 KiB

Open AccessEditor’s ChoiceReview

Insights into Solution Structures of Photosynthetic Protein Complexes from Small-Angle Scattering Methods

by Maksym Golub, Adrian Kölsch, Artem Feoktystov, Athina Zouni and Jörg Pieper

Crystals 2021, 11(2), 203; https://doi.org/10.3390/cryst11020203 - 19 Feb 2021

Cited by 12 | Viewed by 3304

Abstract

High-resolution structures of photosynthetic pigment–protein complexes are often determined using crystallography or cryo-electron microscopy (cryo-EM), which are restricted to the use of protein crystals or to low temperatures, respectively. However, functional studies and biotechnological applications of photosystems necessitate the use of proteins isolated [...] Read more.

High-resolution structures of photosynthetic pigment–protein complexes are often determined using crystallography or cryo-electron microscopy (cryo-EM), which are restricted to the use of protein crystals or to low temperatures, respectively. However, functional studies and biotechnological applications of photosystems necessitate the use of proteins isolated in aqueous solution, so that the relevance of high-resolution structures has to be independently verified. In this regard, small-angle neutron and X-ray scattering (SANS and SAXS, respectively) can serve as the missing link because of their capability to provide structural information for proteins in aqueous solution at physiological temperatures. In the present review, we discuss the principles and prototypical applications of SANS and SAXS using the photosynthetic pigment–protein complexes phycocyanin (PC) and Photosystem I (PSI) as model systems for a water-soluble and for a membrane protein, respectively. For example, the solution structure of PSI was studied using SAXS and SANS with contrast matching. A Guinier analysis reveals that PSI in solution is virtually free of aggregation and characterized by a radius of gyration of about 75 Å. The latter value is about 10% larger than expected from the crystal structure. This is corroborated by an ab initio structure reconstitution, which also shows a slight expansion of Photosystem I in buffer solution at room temperature. In part, this may be due to conformational states accessible by thermally activated protein dynamics in solution at physiological temperatures. The size of the detergent belt is derived by comparison with SANS measurements without detergent match, revealing a monolayer of detergent molecules under proper solubilization conditions. Full article

(This article belongs to the Special Issue Macromolecular Serial Crystallography (Volume II))

► Show Figures

Graphical abstract

8 pages, 2986 KiB

Open AccessEditor’s ChoiceArticle

Enlarging the Eyebox of Maxwellian Displays with a Customized Liquid Crystal Dammann Grating

by Ziqian He, Kun Yin, Kuan-Hsu Fan-Chiang and Shin-Tson Wu

Crystals 2021, 11(2), 195; https://doi.org/10.3390/cryst11020195 - 17 Feb 2021

Cited by 19 | Viewed by 4694

Abstract

The Maxwellian view offers a promising approach to overcome the vergence-accommodation conflict in near-eye displays, however, its pinhole-like imaging naturally limits the eyebox size. Here, a liquid crystal polymer-based Dammann grating with evenly distributed energy among different diffraction orders is developed to enlarge [...] Read more.

The Maxwellian view offers a promising approach to overcome the vergence-accommodation conflict in near-eye displays, however, its pinhole-like imaging naturally limits the eyebox size. Here, a liquid crystal polymer-based Dammann grating with evenly distributed energy among different diffraction orders is developed to enlarge the eyebox of Maxwellian view displays via pupil replication. In the experiment, a 3-by-3 Dammann grating is designed and fabricated, which exhibits good efficiency and high brightness uniformity. We further construct a proof-of-concept Maxwellian view display breadboard by inserting the Dammann grating into the optical system. The prototype successfully demonstrates the enlarged eyebox and full-color operation. Our work provides a promising route of eyebox expansion in Maxwellian view displays while maintaining full-color operation, simple system configuration, compactness, and lightweight. Full article

(This article belongs to the Special Issue Patterned-Liquid-Crystal for Novel Displays)

► Show Figures

Figure 1

15 pages, 5020 KiB

Open AccessEditor’s ChoiceArticle

Heteroleptic [Cu(P^P)(N^N)][PF₆] Complexes: Effects of Isomer Switching from 2,2′-biquinoline to 1,1′-biisoquinoline

by Nina Arnosti, Marco Meyer, Alessandro Prescimone, Edwin C. Constable and Catherine E. Housecroft

Crystals 2021, 11(2), 185; https://doi.org/10.3390/cryst11020185 - 13 Feb 2021

Cited by 6 | Viewed by 3109

Abstract

The preparation and characterization of [Cu(POP)(biq)][PF₆] and [Cu(xantphos)(biq)][PF₆] are reported (biq = 1,1′-biisoquinoline, POP = bis(2-(diphenylphosphanyl)phenyl)ether, and xantphos = (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane). The single crystal structure of [Cu(POP)(biq)][PF₆] 0.5Et₂O was determined and compared to that [...] Read more.

The preparation and characterization of [Cu(POP)(biq)][PF₆] and [Cu(xantphos)(biq)][PF₆] are reported (biq = 1,1′-biisoquinoline, POP = bis(2-(diphenylphosphanyl)phenyl)ether, and xantphos = (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane). The single crystal structure of [Cu(POP)(biq)][PF₆] 0.5Et₂O was determined and compared to that in three salts of [Cu(POP)(bq)]⁺ in which bq = 2,2′-biquinoline. The P–C–P angle is 114.456(19)^o in [Cu(POP)(biq)]⁺ compared to a range of 118.29(3)–119.60(3)^o [Cu(POP)(bq)]⁺. There is a change from an intra-POP PPh₂-phenyl/(C₆H₄)₂O-arene π-stacking in [Cu(POP)(biq)]⁺ to a π-stacking contact between the POP and bq ligands in [Cu(POP)(bq)]⁺. In solution and at ambient temperatures, the [Cu(POP)(biq)][PF₆]⁺ and [Cu(xantphos)(biq)]⁺ cations undergo several concurrent dynamic processes, as evidenced in their multinuclear NMR spectra. The photophysical and electrochemical behaviors of the heteroleptic copper (I) complexes were investigated, and the effects of changing from bq to biq are described. Short Cu···O distances within the [Cu(POP)(biq)]⁺ and [Cu(xantphos)(biq)]⁺ cations may contribute to their very low photoluminescent quantum yields. Full article

(This article belongs to the Special Issue Self-Assembled Complexes: “Love at First Sight”)

► Show Figures

Graphical abstract

14 pages, 3511 KiB

Open AccessEditor’s ChoiceArticle

Weak Interactions in the Structures of Newly Synthesized (–)-Cytisine Amino Acid Derivatives

by Anna K. Przybył, Anita M. Grzeskiewicz and Maciej Kubicki

Crystals 2021, 11(2), 146; https://doi.org/10.3390/cryst11020146 - 30 Jan 2021

Cited by 2 | Viewed by 2472

Abstract

Eight new (–)-(N-[(AA)-(N-phtaloyl)]cytisines (where AA is amino acid: glycine, β-alanine, D,L-valine, L-valine, L-isoleucine, L-leucine, D-leucine and D,L-phenyloalanine), were synthesized and fully spectroscopically characterized (NMR, FTIR and MS). For two [...] Read more.

Eight new (–)-(N-[(AA)-(N-phtaloyl)]cytisines (where AA is amino acid: glycine, β-alanine, D,L-valine, L-valine, L-isoleucine, L-leucine, D-leucine and D,L-phenyloalanine), were synthesized and fully spectroscopically characterized (NMR, FTIR and MS). For two of these compounds, N-[glycine-(N-phtaloyl)]cytisine and N-[L-isoleucine-(N-phtaloyl)]cytisine, X-ray crystal structures were obtained and used as the basis for an in-depth analysis of intermolecular interactions and packing energies. The structural geometrical data (weak hydrogen bonds, π···π interactions, etc.) were compared with the energies of interactions and the topological characteristics (electron density, Laplacian at the appropriate critical point) based on the atoms-in-molecules theory. The results suggest that there is no straightforward connection between the geometry of point-to-point interactions and the molecule-to-molecule energies. Additionally, the usefulness of the transfer of multipolar parameters in estimating of critical points’ characteristics have been confirmed. Full article

(This article belongs to the Special Issue Hydrogen Bonds in Crystals)

► Show Figures

Figure 1

10 pages, 2126 KiB

Open AccessEditor’s ChoiceCommunication

Role of Halogen Substituents on Halogen Bonding in 4,5-DiBromohexahydro-3a,6-Epoxyisoindol-1(4H)-ones

by Atash V. Gurbanov, Dmitriy F. Mertsalov, Fedor I. Zubkov, Maryana A. Nadirova, Eugeniya V. Nikitina, Hieu H. Truong, Mikhail S. Grigoriev, Vladimir P. Zaytsev, Kamran T. Mahmudov and Armando J. L. Pombeiro

Crystals 2021, 11(2), 112; https://doi.org/10.3390/cryst11020112 - 26 Jan 2021

Cited by 17 | Viewed by 2699

Abstract

A series of 4,5-dibromo-2-(4-substituted phenyl)hexahydro-3a,6-epoxyisoindol-1(4H)-ones were synthesized by reaction of the corresponding 2-(4-substituted phenyl)-2,3,7,7a-tetrahydro-3a,6-epoxyisoindol-1(6H)-ones with [(Me₂NCOMe)₂H]Br₃ in dry chloroform under reflux for 3−5 h. In contrast to the 4-F and 4-Cl substituents, one of [...] Read more.

A series of 4,5-dibromo-2-(4-substituted phenyl)hexahydro-3a,6-epoxyisoindol-1(4H)-ones were synthesized by reaction of the corresponding 2-(4-substituted phenyl)-2,3,7,7a-tetrahydro-3a,6-epoxyisoindol-1(6H)-ones with [(Me₂NCOMe)₂H]Br₃ in dry chloroform under reflux for 3−5 h. In contrast to the 4-F and 4-Cl substituents, one of the bromine atoms of the isoindole moiety behaves as a halogen bond donor in the formation of intermolecular halogen bonding in the 4-H, 4-Br and 4-I analogues. Not only intermolecular hydrogen bonds, but also Ha⋯Ha and Ha⋯π types of halogen bonds in the 4-H, 4-Br, and 4-I compounds, contribute to the formation of supramolecular architectures leading to 2D or 3D structures. Full article

(This article belongs to the Special Issue Advanced Research in Halogen Bonding)

► Show Figures

Graphical abstract

15 pages, 4052 KiB

Open AccessEditor’s ChoiceArticle

H-Bonds, π-Stacking and (Water)O-H/π Interactions in (µ₄-EDTA)Bis(Imidazole) Dicopper(II) Dihydrate

by Jeannette Carolina Belmont-Sánchez, María Eugenia García-Rubiño, Antonio Frontera, Josefa María González-Pérez, Alfonso Castiñeiras and Juan Niclós-Gutiérrez

Crystals 2021, 11(1), 48; https://doi.org/10.3390/cryst11010048 - 8 Jan 2021

Cited by 5 | Viewed by 3599

Abstract

We synthesized and studied the polymeric compound {[Cu₂(µ₄-EDTA)(Him)₂] 2H₂O}_n (1). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), [...] Read more.

We synthesized and studied the polymeric compound {[Cu₂(µ₄-EDTA)(Him)₂] 2H₂O}_n (1). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), and magnetic behavior. The crystal consists of infinite 2D-networks built by centrosymmetric dinuclear motifs, constructed by means of a bridging anti,syn-carboxylate group from each asymmetric unit. Each layer guides Him ligands toward their external faces. They are connected by intermolecular (Him)N-H···O(carboxylate) bonds and antiparallel π–π stacking between symmetry related pairs of Him ligands, and then pillared in a 3D-network with parallel channels, where disordered water molecules are guested. About half of the labile water is lost from these channels over a wide temperature range (r.t. to 210 °C) before the other one, most strongly retained by the cooperating action of (water)O1-H(1A)···O(carboxylate) and (water) O1-H(1B)···π(Him) interactions. The latter is lost when organic ligands start to burn. ESR spectra and magnetic measurements indicated that symmetry related Cu(II) centers connected by the bridging carboxylate groups behave magnetically not equivalently, enabling an exchange interaction larger than their individual Zeeman energies. Full article

(This article belongs to the Special Issue σ- and π-Hole Interactions (Volume II))

► Show Figures

Graphical abstract

11 pages, 3686 KiB

Open AccessEditor’s ChoiceArticle

Effect of Laser Beam Profile on Rotating Lattice Single Crystal Growth in Sb₂S₃ Model Glass

by Courtney Au-Yeung, Dmytro Savytskii, Keith Veenhuizen, Volkmar Dierolf and Himanshu Jain

Crystals 2021, 11(1), 36; https://doi.org/10.3390/cryst11010036 - 31 Dec 2020

Cited by 3 | Viewed by 3241

Abstract

Laser heating of chalcogenide glasses has successfully produced rotating lattice single crystals through a solid-solid transformation. To better understand the nature of complex, orientation-dependent lattice rotation, we designed heat profiles of the continuous wave laser by beam shaping, fabricated larger Sb₂S [...] Read more.

Laser heating of chalcogenide glasses has successfully produced rotating lattice single crystals through a solid-solid transformation. To better understand the nature of complex, orientation-dependent lattice rotation, we designed heat profiles of the continuous wave laser by beam shaping, fabricated larger Sb₂S₃ crystal dots in Sb₂S₃ glass, and investigated the lattice rotation where the crystal could grow in all radial directions under a circular thermal gradient. The results show that the rate of lattice rotation is highly anisotropic and depends on crystallographic direction. The nature of this rotation is the same in crystals of different orientation relative to the surface. The growth directions that align with the slip planes show the highest rate of rotation and the rotation rate gradually decreases away from this direction. Additionally, the presence of multiple growth directions results in a complicated rotation system. We suggest that the growth front influences the density of dislocations introduced during growth under confinement and thus affects the lattice rotation rate in these crystals. Full article

(This article belongs to the Special Issue Laser-Induced Crystallization)

► Show Figures

Figure 1

11 pages, 21949 KiB

Open AccessEditor’s ChoiceArticle

High-Pressure Spectroscopy Study of Zn(IO₃)₂ Using Far-Infrared Synchrotron Radiation

by Akun Liang, Robin Turnbull, Enrico Bandiello, Ibraheem Yousef, Catalin Popescu, Zoulikha Hebboul and Daniel Errandonea

Crystals 2021, 11(1), 34; https://doi.org/10.3390/cryst11010034 - 30 Dec 2020

Cited by 12 | Viewed by 3343

Abstract

We report the first high-pressure spectroscopy study on Zn(IO₃)₂ using synchrotron far-infrared radiation. Spectroscopy was conducted up to pressures of 17 GPa at room temperature. Twenty-five phonons were identified below 600 cm⁻¹ for the initial monoclinic low-pressure polymorph of [...] Read more.

We report the first high-pressure spectroscopy study on Zn(IO₃)₂ using synchrotron far-infrared radiation. Spectroscopy was conducted up to pressures of 17 GPa at room temperature. Twenty-five phonons were identified below 600 cm⁻¹ for the initial monoclinic low-pressure polymorph of Zn(IO₃)₂. The pressure response of the modes with wavenumbers above 150 cm⁻¹ has been characterized, with modes exhibiting non-linear responses and frequency discontinuities that have been proposed to be related to the existence of phase transitions. Analysis of the high-pressure spectra acquired on compression indicates that Zn(IO₃)₂ undergoes subtle phase transitions around 3 and 8 GPa, followed by a more drastic transition around 13 GPa. Full article

(This article belongs to the Special Issue Properties of Transition Metals and Their Compounds at Extreme Conditions)

► Show Figures

Figure 1

21 pages, 2457 KiB

Open AccessEditor’s ChoiceArticle

Intramolecular Hydrogen Bond Energy and Its Decomposition—O–H∙∙∙O Interactions

by Sławomir J. Grabowski

Crystals 2021, 11(1), 5; https://doi.org/10.3390/cryst11010005 - 23 Dec 2020

Cited by 37 | Viewed by 7382

Abstract

The method to calculate the energy of intramolecular hydrogen bond is proposed and tested for a sample of malonaldehyde and its fluorine derivatives; the corresponding calculations were performed at the ωB97XD/aug-cc-pVTZ level. This method based on relationships found for related intermolecular hydrogen bonds [...] Read more.

The method to calculate the energy of intramolecular hydrogen bond is proposed and tested for a sample of malonaldehyde and its fluorine derivatives; the corresponding calculations were performed at the ωB97XD/aug-cc-pVTZ level. This method based on relationships found for related intermolecular hydrogen bonds is compared with other approaches which may be applied to estimate the intramolecular hydrogen bond energy. Particularly, methods based on the comparison of the system that contains the intramolecular hydrogen bond compared with corresponding conformations where such interaction does not occur are discussed. The function-based energy decomposition analysis, FB-EDA, of the intramolecular hydrogen bonds is also proposed here. Full article

(This article belongs to the Special Issue Hydrogen Bonds in Crystals)

► Show Figures

Graphical abstract

18 pages, 21908 KiB

Open AccessEditor’s ChoiceArticle

Dynamics of Quasiperiodic Beams

by Mohit Gupta and Massimo Ruzzene

Crystals 2020, 10(12), 1144; https://doi.org/10.3390/cryst10121144 - 16 Dec 2020

Cited by 17 | Viewed by 4404

Abstract

Quasiperiodic metastrucures are characterized by edge localized modes of topological nature, which can be of significant technological interest. We here investigate such topological modes for stiffened and sandwich beams, which can be employed as structural members with inherent vibration localization capabilities. Quasiperiodicity is [...] Read more.

Quasiperiodic metastrucures are characterized by edge localized modes of topological nature, which can be of significant technological interest. We here investigate such topological modes for stiffened and sandwich beams, which can be employed as structural members with inherent vibration localization capabilities. Quasiperiodicity is achieved by altering the geometric properties and material properties of the beams. Specifically, in the stiffened beams, the geometric location of stiffeners is modulated to quasiperiodic patterns, while, in the sandwich beams, the core’s material properties are varied in a step-wise manner to generate such patterns. The families of periodic and quasiperiodic beams for both stiffened and sandwich-type are obtained by varying a projection parameter that governs the location of the center of the stiffener or the alternating core, respectively. The dynamics of stiffened quasiperiodic beams is investigated through 3-D finite element simulations, which leads to the observation of the fractal nature of the bulk spectrum and the illustration of topological edge modes that populate bulk spectral bandgaps. The frequency spectrum is further elucidated by employing polarization factors that distinguish multiple contributing modes. The frequency response of the finite stiffened cantilever beams confirms the presence of modes in the non-trivial bandgaps and further demonstrates that those modes are localized at the free edge. A similar analysis is conducted for the analysis of sandwich composite beams, for which computations rely on a dynamic stiffness matrix approach. This work motivates the use of quasiperiodic beams in the design of stiffened and sandwich structures as structural members in applications where vibration isolation is combined with load-carrying functions. Full article

(This article belongs to the Special Issue Emerging Trends in Phononic Crystals)

► Show Figures

Graphical abstract

12 pages, 1556 KiB

Open AccessEditor’s ChoiceArticle

Shock Damage Analysis in Serial Femtosecond Crystallography Data Collected at MHz X-ray Free-Electron Lasers

by Alexander Gorel, Marie Luise Grünbein, Richard Bean, Johan Bielecki, Mario Hilpert, Michele Cascella, Jacques-Philippe Colletier, Hans Fangohr, Lutz Foucar, Elisabeth Hartmann, Mark S. Hunter, Henry Kirkwood, Marco Kloos, Romain Letrun, Thomas Michelat, Robert L. Shoeman, Jolanta Sztuk-Dambietz, Guillaume Tetreau, Herbert Zimmermann, Adrian P. Mancuso, Thomas R.M. Barends, R. Bruce Doak, Claudiu Andrei Stan and Ilme Schlichting Show full author list Hide full author list

Crystals 2020, 10(12), 1145; https://doi.org/10.3390/cryst10121145 - 16 Dec 2020

Cited by 6 | Viewed by 4044

Abstract

Serial femtosecond crystallography (SFX) data were recorded at the European X-ray free-electron laser facility (EuXFEL) with protein microcrystals delivered via a microscopic liquid jet. An XFEL beam striking such a jet may launch supersonic shock waves up the jet, compromising the oncoming sample. [...] Read more.

Serial femtosecond crystallography (SFX) data were recorded at the European X-ray free-electron laser facility (EuXFEL) with protein microcrystals delivered via a microscopic liquid jet. An XFEL beam striking such a jet may launch supersonic shock waves up the jet, compromising the oncoming sample. To investigate this efficiently, we employed a novel XFEL pulse pattern to nominally expose the sample to between zero and four shock waves before being probed. Analyzing hit rate, indexing rate, and resolution for diffraction data recorded at MHz pulse rates, we found no evidence of damage. Notably, however, this conclusion could only be drawn after careful identification and assimilation of numerous interrelated experimental factors, which we describe in detail. Failure to do so would have led to an erroneous conclusion. Femtosecond photography of the sample-carrying jet revealed critically different jet behavior from that of all homogeneous liquid jets studied to date in this manner. Full article

(This article belongs to the Special Issue Approach of Serial Crystallography)

► Show Figures

Graphical abstract

9 pages, 16822 KiB

Open AccessEditor’s ChoiceArticle

Sildenafil–Resorcinol Cocrystal: XRPD Structure and DFT Calculations

by Rafael Barbas, Vineet Kumar, Oriol Vallcorba, Rafel Prohens and Antonio Frontera

Crystals 2020, 10(12), 1126; https://doi.org/10.3390/cryst10121126 - 10 Dec 2020

Cited by 18 | Viewed by 3922

Abstract

Herein, the X-ray powder diffraction (XRPD) crystal structure of a new Sildenafil cocrystal is reported, where resorcinol has been used as the coformer. The crystal structure has been solved by means of direct space methods used in combination with density functional theory (DFT) [...] Read more.

Herein, the X-ray powder diffraction (XRPD) crystal structure of a new Sildenafil cocrystal is reported, where resorcinol has been used as the coformer. The crystal structure has been solved by means of direct space methods used in combination with density functional theory (DFT) calculations. In the structure, the Sildenafil and resorcinol molecules form cooperative hydrogen bond (HB) and π-stacking interactions that have been analyzed using DFT calculations, the molecular electrostatic potential (MEP) surface, and noncovalent interaction plot (NCI plot). The formation of O–H⋯N H-bonds between resorcinol and Sildenafil increases the dipole moment and enhances the antiparallel π-stacking interaction. Full article

(This article belongs to the Special Issue σ- and π-Hole Interactions (Volume II))

► Show Figures

Figure 1

12 pages, 3005 KiB

Open AccessEditor’s ChoiceCommunication

Impact of the Co/Ni-Ratio on Microstructure, Thermophysical Properties and Creep Performance of Multi-Component γ′-Strengthened Superalloys

by Christopher H. Zenk, Nicklas Volz, Carolin Zenk, Peter J. Felfer and Steffen Neumeier

Crystals 2020, 10(11), 1058; https://doi.org/10.3390/cryst10111058 - 21 Nov 2020

Cited by 17 | Viewed by 3715

Abstract

The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio [...] Read more.

The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio in the more advanced nine-component superalloy ERBOCo-1: exchanging Co and Ni in this Co/Ni-based superalloy while keeping the other alloying elements constants has a big influence on a variety of material properties. The elemental segregation after casting is slightly more pronounced in the alloy with higher Ni-content. Microstructural characterization of this alloy termed ERBOCo-1X after heat-treatment reveals that the precipitates are cuboidal in the Co- and spherical in the Ni-rich alloy, indicating a decrease in the γ/γ′ lattice misfit. Analyzing the elemental partitioning behavior by atom probe tomography suggests that the partitioning behavior of W is responsible for that. Furthermore, it is found that even though Ni exhibits the highest overall concentration, the γ matrix phase is still Co-based, because Ni is strongly enriched in the γ′ precipitates. Creep tests at 900 °C reveal that even though the microstructure looks less favorable, the creep resistance of the Ni-rich alloy is slightly superior to the Co-rich variant. Full article

(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)

► Show Figures

Graphical abstract

12 pages, 8106 KiB

Open AccessEditor’s ChoiceArticle

Parity-Time Symmetry and Exceptional Points for Flexural-Gravity Waves in Buoyant Thin-Plates

by Mohamed Farhat, Sebastien Guenneau, Pai-Yen Chen and Ying Wu

Crystals 2020, 10(11), 1039; https://doi.org/10.3390/cryst10111039 - 16 Nov 2020

Cited by 4 | Viewed by 3090

Abstract

We derive and apply a transfer matrix method (M-matrix) coupling liquid surface waves and flexural-gravity waves in buoyant thin elastic plates. We analyze the scattering matrix (S-matrix) formalism for such waves propagating within a Fabry-Perot like system, which are [...] Read more.

We derive and apply a transfer matrix method (M-matrix) coupling liquid surface waves and flexural-gravity waves in buoyant thin elastic plates. We analyze the scattering matrix (S-matrix) formalism for such waves propagating within a Fabry-Perot like system, which are solutions of a sixth order partial differential equation (PDE) supplied with adequate boundary conditions. We develop a parity-time (

PT

)-symmetry theory and its applications to thin elastic floating plates. The sixth order PDE governing the propagation of these waves leads to six by six M and S matrices, and results in specific physical properties of the

PT

-symmetric elastic plate systems. We show the effect of geometry and gain/loss on the asymmetric propagation of flexural-gravity waves, as well as a Fano-like line-shape of the reflection signature. Importantly, we show the possibility of obtaining coherent perfect absorber-laser (CPAL) using simple thin structures. Full article

(This article belongs to the Special Issue Emerging Trends in Phononic Crystals)

► Show Figures

Figure 1

14 pages, 4302 KiB

Open AccessEditor’s ChoiceArticle

Photosensitive Bent-Core Compounds with Azo-Group Attached to the Central Ring

by Martin Cigl, Věra Hamplová, Damian Pociecha and Vladimíra Novotná

Crystals 2020, 10(11), 1030; https://doi.org/10.3390/cryst10111030 - 11 Nov 2020

Cited by 5 | Viewed by 2673

Abstract

We prepared and studied bent-core liquid crystalline (LC) compounds based on 1,3-disubstituted benzene in a central part and azo-linkage attached directly to this bent core. We designed three structures and checked their mesogenic properties, as well as photosensitivity. We found that two studied [...] Read more.

We prepared and studied bent-core liquid crystalline (LC) compounds based on 1,3-disubstituted benzene in a central part and azo-linkage attached directly to this bent core. We designed three structures and checked their mesogenic properties, as well as photosensitivity. We found that two studied compounds revealed columnar LC mesophases, which we transformed to the isotropic phase under the illumination of UV light. We concluded that only one type of structural motif was not mesogenic. For LC compounds, we established phases and phase transition temperatures based on differential scanning calorimetry (DSC) measurements and observations in a polarizing microscope. To confirm phase identification, X-ray studies were performed and structural parameters describing the columnar phases supplied. Full article

(This article belongs to the Special Issue Photosensitive Liquid Crystals)

► Show Figures

Graphical abstract

14 pages, 5661 KiB

Open AccessEditor’s ChoiceArticle

The Na_2−nH_n[Zr(Si₂O₇)]∙mH₂O Minerals and Related Compounds (n = 0–0.5; m = 0.1): Structure Refinement, Framework Topology, and Possible Na⁺-Ion Migration Paths

by Natalya A. Kabanova, Taras L. Panikorovskii, Vladimir V. Shilovskikh, Natalya S. Vlasenko, Victor N. Yakovenchuk, Sergey M. Aksenov, Vladimir N. Bocharov and Sergey V. Krivovichev

Crystals 2020, 10(11), 1016; https://doi.org/10.3390/cryst10111016 - 9 Nov 2020

Cited by 10 | Viewed by 4082

Abstract

The Na_2−nH_n[Zr(Si₂O₇)]∙mH₂O family of minerals and related compounds (n = 0–0.5; m = 0.1) consist of keldyshite, Na₃H[Zr₂(Si₂O₇)₂], and parakeldyshite, Na₂ [...] Read more.

The Na_2−nH_n[Zr(Si₂O₇)]∙mH₂O family of minerals and related compounds (n = 0–0.5; m = 0.1) consist of keldyshite, Na₃H[Zr₂(Si₂O₇)₂], and parakeldyshite, Na₂[Zr(Si₂O₇)], and synthetic Na₂[Zr(Si₂O₇)]∙H₂O. The crystal structures of these materials are based upon microporous heteropolyhedral frameworks formed by linkage of Si₂O₇ groups and ZrO₆ octahedra with internal channels occupied by Na⁺ cations and H₂O molecules. The members of the family have been studied by the combination of theoretical (geometrical–topological analysis, Voronoi migration map calculation, structural complexity calculation), and empirical methods (single-crystal X-ray diffraction, microprobe analysis, and Raman spectroscopy for parakeldyshite). It was found that keldyshite and parakeldyshite have the same fsh topology, while Na₂ZrSi₂O₇∙H₂O is different and has the xat topology. The microporous heteropolyhedral frameworks in these materials have a 2-D system of channels suitable for the Na⁺-ion migration. The crystal structure of keldyshite can be derived from that of parakeldyshite by the Na⁺ + O²⁻ ↔ OH⁻ + □ substitution mechanism, widespread in the postcrystallization processes in hyperagpaitic rocks. Full article

(This article belongs to the Special Issue Crystal Chemistry and Properties of Minerals)

► Show Figures

Graphical abstract

12 pages, 2825 KiB

Open AccessEditor’s ChoiceArticle

A New Modification of Rb[Al(NH₂)₄] and Condensation in Solid State

by Christian Bäucker and Rainer Niewa

Crystals 2020, 10(11), 1018; https://doi.org/10.3390/cryst10111018 - 9 Nov 2020

Cited by 3 | Viewed by 1983

Abstract

A new modification of Rb[Al(NH₂)₄] in space group C2/c, which differs from the known structural modification in the way the [Al(NH₂)₄]⁻-tetrahedra are arranged in the surrounding area of the rubidium [...] Read more.

A new modification of Rb[Al(NH₂)₄] in space group C2/c, which differs from the known structural modification in the way the [Al(NH₂)₄]⁻-tetrahedra are arranged in the surrounding area of the rubidium cation, was obtained from ammonothermal synthesis at 673 K and 680 bar. The crystal structure was determined by Rietveld refinements and further investigated by infrared and Raman spectroscopy. Thermal gravimetric investigations indicate two decomposition steps up to 450 °C, which can be assigned to ammonia leaving the material while the sample liquefies. During the third and final step, volatile rubidium amide is released, leaving nano-scaled cubic AlN behind. Investigating differently aged samples implies decomposition and condensation of amidoaluminate ions already at ambient temperature, which is supported by refinements of single crystal X-ray diffraction data, revealing lower nitrogen amounts than expected. The observed single crystal also exhibits a significantly smaller volume than the reported structures, further supporting the decomposition–condensation mechanism. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

► Show Figures

Graphical abstract

26 pages, 11525 KiB

Open AccessEditor’s ChoiceArticle

Identification of Local Structure in 2-D and 3-D Atomic Systems through Crystallographic Analysis

by Pablo Miguel Ramos, Miguel Herranz, Katerina Foteinopoulou, Nikos Ch. Karayiannis and Manuel Laso

Crystals 2020, 10(11), 1008; https://doi.org/10.3390/cryst10111008 - 5 Nov 2020

Cited by 15 | Viewed by 4196

Abstract

In the present work, we revise and extend the Characteristic Crystallographic Element (CCE) norm, an algorithm used to simultaneously detect radial and orientational similarity of computer-generated structures with respect to specific reference crystals and local symmetries. Based on the identification of point group [...] Read more.

In the present work, we revise and extend the Characteristic Crystallographic Element (CCE) norm, an algorithm used to simultaneously detect radial and orientational similarity of computer-generated structures with respect to specific reference crystals and local symmetries. Based on the identification of point group symmetry elements, the CCE descriptor is able to gauge local structure with high precision and finely distinguish between competing morphologies. As test cases we use computer-generated monomeric and polymer systems of spherical particles interacting with the hard-sphere and square-well attractive potentials. We demonstrate that the CCE norm is able to detect and differentiate, between others, among: hexagonal close packed (HCP), face centered cubic (FCC), hexagonal (HEX) and body centered cubic (BCC) crystals as well as non-crystallographic fivefold (FIV) local symmetry in bulk 3-D systems; triangular (TRI), square (SQU) and honeycomb (HON) crystals, as well as pentagonal (PEN) local symmetry in thin films of one-layer thickness (2-D systems). The descriptor is general and can be applied to identify the symmetry elements of any point group for arbitrary atomic or particulate system in two or three dimensions, in the bulk or under confinement. Full article

(This article belongs to the Section Macromolecular Crystals)

► Show Figures

Graphical abstract

14 pages, 4813 KiB

Open AccessEditor’s ChoiceArticle

Direct Observation of Molecular Orbitals Using Synchrotron X-ray Diffraction

by Shunsuke Kitou, Yuto Hosogi, Ryo Kitaura, Toshio Naito, Toshikazu Nakamura and Hiroshi Sawa

Crystals 2020, 10(11), 998; https://doi.org/10.3390/cryst10110998 - 3 Nov 2020

Cited by 10 | Viewed by 5368

Abstract

The physical properties of molecular crystals are governed by the frontier orbitals of molecules. A molecular orbital, which is formed by superposing the atomic orbitals of constituent elements, has complicated degrees of freedom in the crystal because of the influence of electron correlation [...] Read more.

The physical properties of molecular crystals are governed by the frontier orbitals of molecules. A molecular orbital, which is formed by superposing the atomic orbitals of constituent elements, has complicated degrees of freedom in the crystal because of the influence of electron correlation and crystal field. Therefore, in general, it is difficult to experimentally observe the whole picture of a frontier orbital. Here, we introduce a new method called “core differential Fourier synthesis” (CDFS) using synchrotron X-ray diffraction to observe the valence electron density in materials. By observing the valence electrons occupied in molecular orbitals, the orbital state can be directly determined in a real space. In this study, we applied the CDFS method to molecular materials such as diamond, C₆₀ fullerene, (MV)I₂, and (TMTTF)₂X. Our results not only demonstrate the typical orbital states in some materials, but also provide a new method for studying intramolecular degrees of freedom. Full article

(This article belongs to the Special Issue Organic Conductors)

► Show Figures

Graphical abstract

13 pages, 4524 KiB

Open AccessEditor’s ChoiceArticle

5-Fluorocytosine/Isocytosine Monohydrate. The First Example of Isomorphic and Isostructural Co-Crystal of Pyrimidine Nucleobases

by Gustavo Portalone

Crystals 2020, 10(11), 999; https://doi.org/10.3390/cryst10110999 - 3 Nov 2020

Cited by 8 | Viewed by 3202

Abstract

To date, despite the crucial role played by cytosine, uracil, and thymine in the DNA/RNA replication process, no examples showing isomorphic and isostructural behavior among binary co-crystals of natural or modified pyrimidine nucleobases have been so far reported in the literature. In view [...] Read more.

To date, despite the crucial role played by cytosine, uracil, and thymine in the DNA/RNA replication process, no examples showing isomorphic and isostructural behavior among binary co-crystals of natural or modified pyrimidine nucleobases have been so far reported in the literature. In view of the relevance of biochemical and pharmaceutical compounds such as pyrimidine nucleobases and their 5-fluoroderivatives, co-crystals of the molecular complex formed by 5-fluorocytosine and isocytosine monohydrate, C₄H₄FN₃O·C₄H₅N₃O·H₂O, have been synthesized by a reaction between 5-fluorocytosine and isocytosine. They represent the first example of isomorphic and isostructural binary co-crystals of pyrimidine nucleobases, as X-ray diffraction analysis shows structural similarities in the solid-state organization of molecules with that of the (1:1) 5-fluorocytosine/5-fluoroisocytosine monohydrate molecular complex, which differs solely in the H/F substitution at the C5 position of isocytosine. Molecules of 5-fluorocytosine and isocytosine are present in the crystal as 1H and 3H-ketoamino tautomers, respectively. They form almost coplanar WC base pairs through nucleobase-to-nucleobase DAA/ADD hydrogen bonding interactions, demonstrating that complementary binding enables the crystallization of specific tautomers. Additional peripheral hydrogen bonds involving all available H atom donor and acceptor sites of the water molecule give a three-dimensional polymeric structure. In the absence of H⋯F hydrogen-bonding interactions, the robustness of the supramolecular architectures based on three-point recognition synthons is responsible for the existence of isostructurality between the two molecular complexes. Full article

(This article belongs to the Special Issue Design, Synthesis, and Structures of Modified RNA/DNA Bases)

► Show Figures

Figure 1

9 pages, 2233 KiB

Open AccessEditor’s ChoiceArticle

Preparation of Cellulose Nanocrystal-Reinforced Physical Hydrogels for Actuator Application

by Jaehwan Kim, Tippabattini Jayaramudu, Lindong Zhai, Hyun Chan Kim and Dickens Owino Agumba

Crystals 2020, 10(11), 969; https://doi.org/10.3390/cryst10110969 - 26 Oct 2020

Cited by 16 | Viewed by 4407

Abstract

In the present investigation, we prepared cellulose nanocrystal (CNC)-reinforced polyvinyl alcohol-cellulose (PVA-Cell) physical hydrogels using a simple blending method for actuator application. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and the surface and cross-section were studied by scanning [...] Read more.

In the present investigation, we prepared cellulose nanocrystal (CNC)-reinforced polyvinyl alcohol-cellulose (PVA-Cell) physical hydrogels using a simple blending method for actuator application. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and the surface and cross-section were studied by scanning electron microscopy. CNCs were well dispersed in the PVA-Cell hydrogel. In the preparation process, surface hydroxyl groups of the CNC and PVA-Cell matrix hydroxyl groups were interacted to produce uniform dispersion of CNCs in the hydrogels. Swelling behavior and compression studies revealed that the increase of the CNCs reinforced the crosslinking. The actuation test of the prepared hydrogels showed that the displacement linearly increased with the voltage, and the immense output displacement was observed at low CNC concentration. The prepared hydrogels are applicable for soft robot actuators and active lens. Full article

(This article belongs to the Special Issue New Composite Hydrogels)

► Show Figures

Graphical abstract

15 pages, 5080 KiB

Open AccessEditor’s ChoiceArticle

Formation Process of Columnar Grown (101)-Oriented Silicalite-1 Membrane and Its Separation Property for Xylene Isomer

by Motomu Sakai, Takuya Kaneko, Yukichi Sasaki, Miyuki Sekigawa and Masahiko Matsukata

Crystals 2020, 10(10), 949; https://doi.org/10.3390/cryst10100949 - 17 Oct 2020

Cited by 13 | Viewed by 3497

Abstract

Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. [...] Read more.

Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. The silicalite-1 membrane became (h0l)-orientation with increasing membrane thickness, possibly because the orientation was attributable to “evolutionally selection”. The (h0l)-oriented silicalite-1 membrane showed high p-xylene separation performance for a xylene isomer mixture (o-/m-/p-xylene = 0.4/0.4/0.4 kPa). The p-xylene permeance through the membrane was 6.52 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ with separation factors α_p/o, α_p/m of more than 100 at 373 K. As a result of microscopic analysis, it was suggested that a very thin part in the vicinity of surface played as effective separation layer and could contribute to high permeation performance. Full article

(This article belongs to the Special Issue Zeolites)

► Show Figures

Graphical abstract

10 pages, 1880 KiB

Open AccessEditor’s ChoiceArticle

Structural Variations in Manganese Halide Chain Compounds Mediated by Methylimidazolium Isomers

by Ceng Han, David B. Cordes, Alexandra M. Z. Slawin and Philip Lightfoot

Crystals 2020, 10(10), 930; https://doi.org/10.3390/cryst10100930 - 13 Oct 2020

Cited by 9 | Viewed by 3479

Abstract

The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl₃(H₂O) and [4MiH]MnCl₃(H₂O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl₃ [...] Read more.

The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl₃(H₂O) and [4MiH]MnCl₃(H₂O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl₃(H₂O)]_n⁻ edge-sharing octahedral chains. The structures are compared to the previously reported isomeric analogue [2MiH]MnCl₃(H₂O) ([2MiH] = 2-methylimidazolium), and three closely related compounds. The variations in packing of the inorganic chains are shown to be influenced by hydrogen bonding abilities of the imidazolium or related moieties. Both new compounds show intense red luminescence at ambient temperature under UV irradiation. Full article

(This article belongs to the Special Issue Coordination Polymers: Structure, Bonding and Applications)

► Show Figures

Figure 1

17 pages, 3418 KiB

Open AccessEditor’s ChoiceArticle

Effect of Process Conditions on Particle Size and Shape in Continuous Antisolvent Crystallisation of Lovastatin

by John McGinty, Magdalene W. S. Chong, Andrew Manson, Cameron J. Brown, Alison Nordon and Jan Sefcik

Crystals 2020, 10(10), 925; https://doi.org/10.3390/cryst10100925 - 12 Oct 2020

Cited by 31 | Viewed by 6041

Abstract

Lovastatin crystals often exhibit an undesirable needle-like morphology. Several studies have shown how a needle-like morphology can be modified in antisolvent crystallisation with the use of additives, but there is much less experimental work demonstrating crystal shape modification without the use of additives. [...] Read more.

Lovastatin crystals often exhibit an undesirable needle-like morphology. Several studies have shown how a needle-like morphology can be modified in antisolvent crystallisation with the use of additives, but there is much less experimental work demonstrating crystal shape modification without the use of additives. In this study, a series of unseeded continuous antisolvent crystallisation experiments were conducted with the process conditions of supersaturation, total flow rate, and ultrasound level being varied to determine their effects on crystal size and shape. This experimental work involved identifying acetone/water as the most suitable solvent/antisolvent system, assessing lovastatin nucleation behaviour by means of induction time measurements, and then designing and implementing the continuous antisolvent crystallisation experiments. It was found that in order to produce the smallest and least needle-like particles, the maximum total flow rate and supersaturation had to be combined with the application of ultrasound. These results should aid development of pharmaceutical manufacturing processes where the ability to control particle size and shape would allow for optimisation of crystal isolation and more efficient downstream processing. Full article

(This article belongs to the Special Issue Crystallization Processes: Food and Pharmaceutical Crystals)

► Show Figures

Graphical abstract

12 pages, 1302 KiB

Open AccessEditor’s ChoiceArticle

Influence of Alumina Air-Abrasion on Flexural and Shear Bond Strengths of CAD/CAM Composite

by Pirat Karntiang, Hiroshi Ikeda, Yuki Nagamatsu and Hiroshi Shimizu

Crystals 2020, 10(10), 927; https://doi.org/10.3390/cryst10100927 - 12 Oct 2020

Viewed by 2703

Abstract

The purpose of this study was to clarify the influence of alumina air-abrasion on flexural and bond strengths of CAD/CAM composites. The flexural strength (FS) of two brands of commercial CAD/CAM composites was investigated by the three-point bending test using two specimen designs: [...] Read more.

The purpose of this study was to clarify the influence of alumina air-abrasion on flexural and bond strengths of CAD/CAM composites. The flexural strength (FS) of two brands of commercial CAD/CAM composites was investigated by the three-point bending test using two specimen designs: the single-bar according to the ISO standard and the bonded-double-bar fabricated by bonding two bars with a resin cement. The bond strength between the composites and the resin cement was measured by a conventional shear bond strength (SBS) test. The FS of single-bar specimens was significantly decreased by the air-abrasion. For the FS of the bonded-double-bar specimen, on the other hand, there was no significant difference between the specimens with/without air-abrasion. The SBS for the composites was significantly increased by air-abrasion. The results suggest that alumina air-abrasion improves the SBS of the composites while weakening its FS. Contrarily, the FS of the air-abraded composite did not decrease when the composites were bonded with the resin cement. Full article

(This article belongs to the Special Issue Resin Ceramics Composite)

► Show Figures

Figure 1

15 pages, 2950 KiB

Open AccessEditor’s ChoiceArticle

Crystallization of ApoA1 and ApoE4 Nanolipoprotein Particles and Initial XFEL-Based Structural Studies

by Megan L. Shelby, Deepshika Gilbile, Thomas D. Grant, William J. Bauer, Brent Segelke, Wei He, Angela C. Evans, Natalia Crespo, Pontus Fischer, Tim Pakendorf, Vincent Hennicke, Mark S. Hunter, Alex Batyuk, Miriam Barthelmess, Alke Meents, Tonya L. Kuhl, Matthias Frank and Matthew A. Coleman

Crystals 2020, 10(10), 886; https://doi.org/10.3390/cryst10100886 - 1 Oct 2020

Cited by 6 | Viewed by 4775

Abstract

Nanolipoprotein particles (NLPs), also called “nanodiscs”, are discoidal particles with a patch of lipid bilayer corralled by apolipoproteins. NLPs have long been of interest due to both their utility as membrane-model systems into which membrane proteins can be inserted and solubilized and their [...] Read more.

Nanolipoprotein particles (NLPs), also called “nanodiscs”, are discoidal particles with a patch of lipid bilayer corralled by apolipoproteins. NLPs have long been of interest due to both their utility as membrane-model systems into which membrane proteins can be inserted and solubilized and their physiological role in lipid and cholesterol transport via high-density lipoprotein (HDL) and low-density lipoprotein (LDL) maturation, which are important for human health. Serial femtosecond crystallography (SFX) at X-ray free electron lasers (XFELs) is a powerful approach for structural biology of membrane proteins, which are traditionally difficult to crystallize as large single crystals capable of producing high-quality diffraction suitable for structure determination. To facilitate understanding of the specific role of two apolipoprotein/lipid complexes, ApoA1 and ApoE4, in lipid binding and HDL/LDL particle maturation dynamics, and to develop new SFX methods involving NLP membrane protein encapsulation, we have prepared and crystallized homogeneous populations of ApoA1 and ApoE4 NLPs. Crystallization of empty NLPs yields semi-ordered objects that appear crystalline and give highly anisotropic and diffuse X-ray diffraction, similar to fiber diffraction. Several unit cell parameters were approximately determined for both NLPs from these measurements. Thus, low-background, sample conservative methods of delivery are critical. Here we implemented a fixed target sample delivery scheme utilizing the Roadrunner fast-scanning system and ultra-thin polymer/graphene support films, providing a low-volume, low-background approach to membrane protein SFX. This study represents initial steps in obtaining structural information for ApoA1 and ApoE4 NLPs and developing this system as a supporting scaffold for future structural studies of membrane proteins crystalized in a native lipid environment. Full article

(This article belongs to the Special Issue Macromolecular Serial Crystallography (Volume II))

► Show Figures

Figure 1

24 pages, 5443 KiB

Open AccessEditor’s ChoiceArticle

Anatomical Variation of Human Bone Bioapatite Crystallography

by Brittany Foley, Martina Greiner, George McGlynn and Wolfgang W. Schmahl

Crystals 2020, 10(10), 859; https://doi.org/10.3390/cryst10100859 - 24 Sep 2020

Cited by 17 | Viewed by 4778

Abstract

This systematic investigation of bioapatite, the mineral component of human bone, aims to characterize its crystallographic state, including lattice parameters and average crystallite size, and correlate these values with respect to anatomical position (bone function), physicality, and bone chemical composition. In sample sets [...] Read more.

This systematic investigation of bioapatite, the mineral component of human bone, aims to characterize its crystallographic state, including lattice parameters and average crystallite size, and correlate these values with respect to anatomical position (bone function), physicality, and bone chemical composition. In sample sets of buried bone from three different human adult skeletons, anatomical variation of crystallographic parameters and correlation to chemical composition were indeed observed. In general, the observed bioapatite a unit-cell edge-length among all analyzed human bones in this study was larger by 0.1–0.2% compared to that of stoichiometric hydroxylapatite (HAp), and substantially larger than that of fluorapatite (FAp). Across all analyzed samples, the a (=b) lattice parameter (unit cell edge-length) varies more than does the c lattice parameter. Average crystallite size (average coherent diffracting domain size) in the c-direction was equal to approximately 25 nm, ranging among the analyzed 18 bone samples from about 20–32 nm, and varying more than crystallite size in the a,b-direction (~8–10 nm). Neither lattice parameters nor average bioapatite crystallite sizes appeared to be correlated with bone mechanical function. The relative chemical composition of the bone material, however, was shown to correlate with the a (=b) lattice parameter. To our knowledge, this research provides, for the first time, the systematic study of the crystallographic parameters of human bone bioapatite in the context of anatomical position, physical constitution, and bone chemical composition using X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FTIR). Full article

(This article belongs to the Special Issue Biominerals: Formation, Function, Properties)

► Show Figures

Figure 1

7 pages, 2374 KiB

Open AccessEditor’s ChoiceArticle

Shear Induced TiO₂ Nano Structure Using Brush-Coating for Liquid Crystal Alignment

by Jong In Jang and Hae-Chang Jeong

Crystals 2020, 10(10), 860; https://doi.org/10.3390/cryst10100860 - 24 Sep 2020

Cited by 5 | Viewed by 3237

Abstract

We have developed a very useful and cost-effective liquid crystal (LC) alignment layer of brush-coated TiO₂ that is solution-processable for twisted nematic (TN) LC cells. TiO₂ was prepared via the sol-gel method. The TiO₂ solution was brush-coated on the substrate, [...] Read more.

We have developed a very useful and cost-effective liquid crystal (LC) alignment layer of brush-coated TiO₂ that is solution-processable for twisted nematic (TN) LC cells. TiO₂ was prepared via the sol-gel method. The TiO₂ solution was brush-coated on the substrate, followed by an annealing process. During the brush-coating process, a retracting force is generated on the deposited TiO solutions along the coating direction. The annealing process hardens the TiO₂ and generates shearing stress arising from the retracting force along the brush-coating direction. The shearing stress created highly oriented nano/microstructure and uniformly aligned LCs with a stable pretilt angle of 0.6°. TN mode LC cells based on brush-coated TiO₂ exhibited a performance of 12.5 ms of response and a threshold voltage of 1.8 V. Our brush-coated TiO₂ incorporates two steps of the film deposition and alignment process into one step. Full article

(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment (Volume II))

► Show Figures

Graphical abstract

17 pages, 1373 KiB

Open AccessEditor’s ChoiceArticle

Electric Transport of Nodal Line Semimetals in Single-Component Molecular Conductors

by Yoshikazu Suzumura, Reizo Kato and Masao Ogata

Crystals 2020, 10(10), 862; https://doi.org/10.3390/cryst10100862 - 24 Sep 2020

Cited by 5 | Viewed by 2919

Abstract

We examine an effect of acoustic phonon scattering on the electric conductivity of a single-component molecular conductor [Pd(dddt)

_{2}

] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) with a half-filled band by applying the previous calculation in a two-dimensional model with Dirac cone [Phys. Rev. B. 98, [...] Read more.

We examine an effect of acoustic phonon scattering on the electric conductivity of a single-component molecular conductor [Pd(dddt)

_{2}

] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) with a half-filled band by applying the previous calculation in a two-dimensional model with Dirac cone [Phys. Rev. B. 98, 161205 (2018)], wherethe electric transport by the impurity scattering exhibits a noticeable interplay of the Dirac cone and the phonon scattering, resulting in maximum of the conductivity with increasing temperature. The conductor shows a nodal line semimetal, where the band crossing of HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) provides a loop of Dirac points located close to the Fermi energy followed by the density of states (DOS) similar to that of a two-dimensional Dirac cone. Using a tight-binding (TB) model [arXiv:2008.09277], which was obtained using the crystal structure observed from a recent X ray diffraction experiment under pressure, it is shown that the obtained conductivity explains reasonably the anomalous behavior in [Pd(dddt)

_{2}

] exhibiting temperature-independent resistivity at finite temperatures. This paper demonstrates a crucial role of the acoustic phonon scattering at finite temperatures in the electric conductivity of Dirac electrons. The present theoretical results of conductivity are compared with those of the experiments. Full article

(This article belongs to the Special Issue Organic Conductors)

► Show Figures

Figure 1

16 pages, 3409 KiB

Open AccessEditor’s ChoiceArticle

Depth Profile Analysis of Deep Level Defects in 4H-SiC Introduced by Radiation

by Tomislav Brodar, Luka Bakrač, Ivana Capan, Takeshi Ohshima, Luka Snoj, Vladimir Radulović and Željko Pastuović

Crystals 2020, 10(9), 845; https://doi.org/10.3390/cryst10090845 - 22 Sep 2020

Cited by 10 | Viewed by 6013

Abstract

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below [...] Read more.

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below the conduction band minimum are created in either ion implanted and neutron irradiated material beside carbon vacancies (Z_1/2). In our study, we analyze components of EH1 and EH3 deep levels based on their concentration depth profiles, in addition to (−3/=) and (=/−) transition levels of silicon vacancy. A higher EH3 deep level concentration compared to the EH1 deep level concentration and a slight shift of the EH3 concentration depth profile to larger depths indicate that an additional deep level contributes to the DLTS signal of the EH3 deep level, most probably the defect complex involving interstitials. We report on the introduction of metastable M-center by light/medium heavy ion implantation and neutron irradiation, previously reported in cases of proton and electron irradiation. Contribution of M-center to the EH1 concentration profile is presented. Full article

(This article belongs to the Special Issue Crystalline Materials for Radiation Detection: A New Perspectives)

► Show Figures

Figure 1

11 pages, 1393 KiB

Open AccessEditor’s ChoiceReview

Glycosylation: A “Last Word” in the Protein-Mediated Biomineralization Process

by John Spencer Evans

Crystals 2020, 10(9), 818; https://doi.org/10.3390/cryst10090818 - 16 Sep 2020

Cited by 5 | Viewed by 3085

Abstract

Post-translational modifications are one way that biomineral-associated cells control the function and fate of proteins. Of the ten different types of post-translational modifications, one of the most interesting and complex is glycosylation, or the covalent attachment of carbohydrates to amino acid sidechains Asn, [...] Read more.

Post-translational modifications are one way that biomineral-associated cells control the function and fate of proteins. Of the ten different types of post-translational modifications, one of the most interesting and complex is glycosylation, or the covalent attachment of carbohydrates to amino acid sidechains Asn, Ser, and Thr of proteins. In this review the author surveys some of the known biomineral-associated glycoproteins and summarizes recent in vitro recombinant protein experiments which test the impact of glycosylation on biomineralization protein functions, such as nucleation, crystal growth, and matrix assembly. These in vitro studies show that glycosylation does not alter the inherent function of the polypeptide chain; rather, it either accentuates or attenuates functionality. In essence, glycosylation gives the cell the “last word” as to what degree a biomineralization protein will participate in the biomineralization process. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

► Show Figures

Graphical abstract

14 pages, 2945 KiB

Open AccessEditor’s ChoiceArticle

Large Angle Forward Diffraction by Chiral Liquid Crystal Gratings with Inclined Helical Axis

by Migle Stebryte, Inge Nys, Yera Ye. Ussembayev, Jeroen Beeckman and Kristiaan Neyts

Crystals 2020, 10(9), 807; https://doi.org/10.3390/cryst10090807 - 12 Sep 2020

Cited by 27 | Viewed by 5630

Abstract

A layer of chiral liquid crystal (CLC) with a photonic bandgap in the visible range has excellent reflective properties. Recently, two director configurations have been proposed in the literature for CLC between two substrates with periodic photo-alignment: one with the director parallel to [...] Read more.

A layer of chiral liquid crystal (CLC) with a photonic bandgap in the visible range has excellent reflective properties. Recently, two director configurations have been proposed in the literature for CLC between two substrates with periodic photo-alignment: one with the director parallel to the substrates and one with the director in the bulk parallel to the tilted plane. The transmission experiments under large angles of incidence (AOI) presented in this work prove that, in the bulk, the director does not remain parallel with the substrates. Because of the inclined helical axis, the full reflection band can be observed at a smaller AOI than in planar CLC. For sufficiently large AOI, the reflection of diffracted light is prohibited by total internal reflection and efficient diffraction occurs in the forward direction. Full article

(This article belongs to the Special Issue Nematic Liquid Crystals)

► Show Figures

Graphical abstract

15 pages, 2643 KiB

Open AccessEditor’s ChoiceArticle

Microplates for Crystal Growth and in situ Data Collection at a Synchrotron Beamline

by Miao Liang, Zhijun Wang, Hai Wu, Li Yu, Bo Sun, Huan Zhou, Feng Yu, Qisheng Wang and Jianhua He

Crystals 2020, 10(9), 798; https://doi.org/10.3390/cryst10090798 - 9 Sep 2020

Cited by 6 | Viewed by 3187

Abstract

An efficient data collection method is important for microcrystals, because microcrystals are sensitive to radiation damage. Moreover, microcrystals are difficult to harvest and locate owing to refraction effects from the surface of the liquid drop or optically invisible, owing to their small size. [...] Read more.

An efficient data collection method is important for microcrystals, because microcrystals are sensitive to radiation damage. Moreover, microcrystals are difficult to harvest and locate owing to refraction effects from the surface of the liquid drop or optically invisible, owing to their small size. Collecting X-ray diffraction data directly from the crystallization devices to completely eliminate the crystal harvesting step is of particular interest. To address these needs, novel microplates combining crystal growth and data collection have been designed for efficient in situ data collection and fully tested at Shanghai Synchrotron Radiation Facility (SSRF) crystallography beamlines. The design of the novel microplates fully adapts the advantage of in situ technology. Thin Kapton membranes were selected to seal the microplate for crystal growth, the crystallization plates can support hanging drop and setting drop vapor diffusion crystallization experiments. Then, the microplate was fixed on a magnetic base and mounted on the goniometer head for in situ data collection. Automatic grid scanning was applied for crystal location with a Blu-Ice data collection system and then in situ data collection was performed. The microcrystals of lysozyme were selected as the testing samples for diffraction data collection using the novel microplates. The results show that this method can achieve comparable data quality to that of the traditional method using the nylon loop. In addition, our method can efficiently and diversely perform data acquisition experiments, and be especially suitable for solving structures of multiple crystals at room temperature or cryogenic temperature. Full article

(This article belongs to the Special Issue Advances in Industrial Crystallization)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI