Next Issue
Volume 11, March
Previous Issue
Volume 11, January

Crystals, Volume 11, Issue 2 (February 2021) – 143 articles

Cover Story (view full-size image): 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. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Order results
Result details
Select all
Export citation of selected articles as:
Open AccessArticle
Design and Realization of a Compact Efficient Beam Combiner, Based on Liquid Crystal Pancharatnam–Berry Phase Gratings
Crystals 2021, 11(2), 220; https://doi.org/10.3390/cryst11020220 - 23 Feb 2021
Viewed by 196
Abstract
We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the [...] Read more.
We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the layer is controlled by spacers. The beam combiner can bring two parallel laser beams closer to each other while remaining parallel. This work shows the potential to realize components based on flat optical LC devices. Full article
(This article belongs to the Special Issue Liquid-Crystal Polarization Gratings)
Show Figures

Graphical abstract

Open AccessArticle
Experimental and Numerical Study of Lattice Girder Composite Slabs with Monolithic Joint
Crystals 2021, 11(2), 219; https://doi.org/10.3390/cryst11020219 - 23 Feb 2021
Viewed by 257
Abstract
This paper studies the behavior of lattice girder composite slabs with monolithic joint under bending. A full-scale experiment is performed to investigate the overall bending resistance, deflection and the final crack distribution of latticed girder composite slab under uniformly distributed load. A finite [...] Read more.
This paper studies the behavior of lattice girder composite slabs with monolithic joint under bending. A full-scale experiment is performed to investigate the overall bending resistance, deflection and the final crack distribution of latticed girder composite slab under uniformly distributed load. A finite element model is given for the analysis of the latticed girder composite slabs. The effectiveness and correctness of the numerical simulations are verified against experimental results. The experimental and numerical studies conclude that the lattice girder composite slabs conform to the requirement of existing design codes. A parametric study is provided to investigate the effects of lattice girder with following conclusions: (a) the lattice girder significantly increases the stiffness of the slab when comparing with the precast slab without reinforcement crossing the interface; (b) the additional reinforcement near the joint slightly increases the stiffness and resistance, while it prevents damage near the joint. Full article
(This article belongs to the Special Issue Advances in Sustainable Concrete System)
Show Figures

Figure 1

Open AccessArticle
First Report on the Geologic Occurrence of Natural Na–A Zeolite and Associated Minerals in Cretaceous Mudstones of the Paja Formation of Vélez (Santander), Colombia
Crystals 2021, 11(2), 218; https://doi.org/10.3390/cryst11020218 - 22 Feb 2021
Viewed by 184
Abstract
This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, [...] Read more.
This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world. Full article
(This article belongs to the Special Issue Zeolites)
Show Figures

Figure 1

Open AccessReview
Theoretical and Experimental Aspects of Current and Future Research on NbO2 Thin Film Devices
Crystals 2021, 11(2), 217; https://doi.org/10.3390/cryst11020217 - 22 Feb 2021
Viewed by 195
Abstract
The present research front of NbO2 based memory, energy generation, and storage thin film devices is reviewed. Sputtering plasmas contain NbO, NbO2, and NbO3 clusters, affecting nucleation and growth of NbO2, often leading to a formation of [...] Read more.
The present research front of NbO2 based memory, energy generation, and storage thin film devices is reviewed. Sputtering plasmas contain NbO, NbO2, and NbO3 clusters, affecting nucleation and growth of NbO2, often leading to a formation of nanorods and nanoslices. NbO2 (I41/a) undergoes the Mott topological transition at 1081 K to rutile (P42/mnm), yielding changes in the electronic structure, which is primarily utilized in memristors. The Seebeck coefficient is a key physical parameter governing the performance of thermoelectric devices, but its temperature behavior is still controversial. Nonetheless, they perform efficiently above 900 K. There is a great potential to improve NbO2 batteries since the theoretical capacity has not been reached, which may be addressed by future diffusion studies. Thermal management of functional materials, comprising thermal stress, thermal fatigue, and thermal shock, is often overlooked even though it can lead to failure. NbO2 exhibits relatively low thermal expansion and high elastic modulus. The future for NbO2 thin film devices looks promising, but there are issues that need to be tackled, such as dependence of properties on strain and grain size, multiple interfaces with point and extended defects, and interaction with various natural and artificial environments, enabling multifunctional applications and durable performance. Full article
(This article belongs to the Special Issue Thin Films and Coatings: Modeling Meets Experiment)
Show Figures

Graphical abstract

Open AccessArticle
Characterization of Failure Strain In Fiber Reinforced Composites: Under On-Axis and Off-Axis Loading
Crystals 2021, 11(2), 216; https://doi.org/10.3390/cryst11020216 - 22 Feb 2021
Viewed by 211
Abstract
Metals are known for high ductility and have, been used to design and fabricate structural components for many years. However, composite materials are taking over traditional materials owing to their significant mechanical properties. Fiber-reinforced composites exhibit lower ductility and failure strain, resulting in [...] Read more.
Metals are known for high ductility and have, been used to design and fabricate structural components for many years. However, composite materials are taking over traditional materials owing to their significant mechanical properties. Fiber-reinforced composites exhibit lower ductility and failure strain, resulting in brittle failure, limiting their application where high ductility is desired. In this study, an effort has been made to design, fabricate, and test continuous fiber-reinforced composites with improved ductility. A comparative analysis was performed for optimizing the failure strain of different woven fiber-reinforced composite materials under both on-axis (0°/90°) and off-axis (±45°) loading. The materials include carbon/epoxy, E-glass/epoxy, and jute/epoxy composite. The tests were performed according to ASTM D3039 standard. The strength of all tested composites in on-axis and off-axis loading was obtained from tensile test results. But failure strain was limited in on-axis loading. Interestingly, glass/epoxy composite showed improved failure strain, by 90%, without much loss in tensile strength in off-axis loading than on-axis loading. The jute fiber revealed limited tensile strength and failure strain in both loading conditions. Full article
(This article belongs to the Special Issue Dynamic Behavior of Carbon Fiber Related Materials)
Show Figures

Figure 1

Open AccessArticle
Photocatalytic Decolorization of Methyl Red on Nanoporous Anodic ZrO2 of Different Crystal Structures
Crystals 2021, 11(2), 215; https://doi.org/10.3390/cryst11020215 - 21 Feb 2021
Viewed by 177
Abstract
High surface area, self-organized nanoporous ZrO2 arrays with perfect adhesion to the Zr substrate were synthesized by anodization in an aqueous electrolyte containing (NH4)2SO4 and NH4F. The obtained semiconductor materials were tested as photocatalysts for [...] Read more.
High surface area, self-organized nanoporous ZrO2 arrays with perfect adhesion to the Zr substrate were synthesized by anodization in an aqueous electrolyte containing (NH4)2SO4 and NH4F. The obtained semiconductor materials were tested as photocatalysts for decolorization of the methyl red (MR) as a model azo dye pollutant. It was demonstrated that as-synthesized anodic ZrO2 anodic layers are already crystalline and, therefore, do not require further thermal treatment to provide a high photocatalytic performance. However, photocatalytic efficiency could be improved by annealing at a relatively low-temperature of 350 °C. Higher annealing temperatures caused a gradual drop of photocatalytic activity. The photocatalytic behavior was correlated with the crystal phase transformation in anodic ZrO2. It was found that higher photocatalytic activity was observed for the tetragonal phase over the monoclinic phase (predominant at elevated temperatures). It results from the optimal and complex electronic structure of annealed ZrO2 with three different energy states having absorption edges at 2.0, 4.01 and 5.28 eV. Full article
(This article belongs to the Special Issue Nanostructured Crystalline Materials)
Show Figures

Figure 1

Open AccessArticle
Modeling of the Resonant X-ray Response of a Chiral Cubic Phase
Crystals 2021, 11(2), 214; https://doi.org/10.3390/cryst11020214 - 21 Feb 2021
Viewed by 214
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

Open AccessArticle
Elucidation of the Mechanism of Phase Transition in a Zinc Formate Framework Templated by a Diammonium Cation—Structural, Phonon and Dielectric Studies
Crystals 2021, 11(2), 213; https://doi.org/10.3390/cryst11020213 - 21 Feb 2021
Viewed by 162
Abstract
In this paper we present the synthesis method and a detailed description of the crystal structure, as well as thermal, dielectric and phonon properties, of the [CH3NH2CH2CH2NH2CH3][Zn2(HCOO)6] [...] Read more.
In this paper we present the synthesis method and a detailed description of the crystal structure, as well as thermal, dielectric and phonon properties, of the [CH3NH2CH2CH2NH2CH3][Zn2(HCOO)6] (dmenH2-Zn) metal organic framework. The negative charge of the anionic framework ([Zn2(HCOO)6]2-) is balanced by N,N′-dimethylethylenediamine (dmenH22+) ions located in the voids of the framework. Thermal analysis revealed that dmenH2-Zn underwent a reversible structural phase transition at around room temperature (Tc~300 K). The single-crystal X-ray diffraction showed that dmenH22+ templates were dynamically disordered at 295 K, since N-HO bonds were too weak to surmount their thermally activated motions. Reduction in the temperature resulted in ordering of the dmenH22+ cations as a consequence of freezing of their reorientational movements. This behavior caused a symmetry change from P-31c (trigonal) to C 2/c (monoclinic). The mechanism of the observed phase transition of dmenH2-Zn compound was also investigated by temperature-dependent IR measurements. These spectroscopic studies showed that the ordering of the dmenH22+ ions also resulted in the distortion of the anionic framework. Dielectric investigations revealed the occurrence of the dipolar relaxation process clearly defined in the monoclinic phase. The asymmetric shape of the studied process, which indicated a non-Debye-like relaxation, was analyzed using the Havriliak–Negami relaxation function, leading to an Ea value of approximately 0.36 eV. Full article
(This article belongs to the Special Issue Crystallography on Metal-Organic Frameworks and Beyond)
Show Figures

Figure 1

Open AccessArticle
Biodiesel Purification via Ultrasonic-Assisted Solvent-Aided Crystallization
Crystals 2021, 11(2), 212; https://doi.org/10.3390/cryst11020212 - 20 Feb 2021
Viewed by 139
Abstract
Wet washing is a widely used method for biodiesel purification. However, this technique generates a large amount of wastewater that needs to be treated afterward, which is costly and time-consuming. Thus, solvent-aided crystallization (SAC) with ultrasonic irradiation as solution movement assistance was introduced. [...] Read more.
Wet washing is a widely used method for biodiesel purification. However, this technique generates a large amount of wastewater that needs to be treated afterward, which is costly and time-consuming. Thus, solvent-aided crystallization (SAC) with ultrasonic irradiation as solution movement assistance was introduced. This technique is based on the addition of 1-butanol to biodiesel to enhance purification via crystallization. During crystallization, two phases are formed, where glycerol solidifies (solid phase) and pure biodiesel remains (liquid phase). Technically, the implementation of ultrasonic technology can optimize laboratory work by saving time, as no cleaning or washing of the propeller is needed. Biodiesel purity was analyzed using gas chromatography-mass spectroscopy (GC-MS), where a purity of 99% was achieved. The optimum parameters in achieving higher purity fatty acid methyl ester (FAME) were a 1-butanol concentration of 1 wt.%, a coolant temperature of 9 °C, and a crystallization time of 40 min. Full article
Show Figures

Figure 1

Open AccessArticle
Computational Study of Structural, Molecular Orbitals, Optical and Thermodynamic Parameters of Thiophene Sulfonamide Derivatives
Crystals 2021, 11(2), 211; https://doi.org/10.3390/cryst11020211 - 20 Feb 2021
Viewed by 288
Abstract
Thiophene and sulfonamide derivatives serve as biologically active compounds, used for the manufacture of large numbers of new drugs. In this study, 11 selected derivatives of thiophene sulfonamide were computed for their geometric parameters, such as hyperpolarizability, chemical hardness (ƞ), electronic chemical potential [...] Read more.
Thiophene and sulfonamide derivatives serve as biologically active compounds, used for the manufacture of large numbers of new drugs. In this study, 11 selected derivatives of thiophene sulfonamide were computed for their geometric parameters, such as hyperpolarizability, chemical hardness (ƞ), electronic chemical potential (μ), electrophilicity index (ω), ionization potential (I), and electron affinity (A). In addition, FT-IR and UV-Vis spectra were also simulated through theoretical calculations. The geometrical parameters and vibrational frequencies with assignments of the vibrational spectra strongly resemble the experimentally calculated values. Besides, the frontier molecular orbitals were also determined for various intramolecular interactions that are responsible for the stability of the compounds. The isodensity surfaces of the frontier molecular orbitals (FMOs) are the same pattern in most of the compounds, but in some compounds are disturbed due to the presence of highly electronegative hetero-atoms. In this series of compounds, 3 shows the highest HOMO–LUMO energy gap and lowest hyperpolarizability, which leads to the most stable compound and less response to nonlinear optical (NLO), while 7 shows the lowest HOMO–LUMO energy gap and highest hyperpolarizability, which leads to a less stable compound and a high NLO response. All compounds have their extended three-dimensional p-electronic delocalization which plays an important role in studying NLO responses. Full article
(This article belongs to the Special Issue New Trends in King Saud University in Crystals)
Show Figures

Figure 1

Open AccessArticle
Prediction of Neutralization Depth of R.C. Bridges Using Machine Learning Methods
Crystals 2021, 11(2), 210; https://doi.org/10.3390/cryst11020210 - 20 Feb 2021
Viewed by 144
Abstract
Machine learning techniques have become a popular solution to prediction problems. These approaches show excellent performance without being explicitly programmed. In this paper, 448 sets of data were collected to predict the neutralization depth of concrete bridges in China. Random forest was used [...] Read more.
Machine learning techniques have become a popular solution to prediction problems. These approaches show excellent performance without being explicitly programmed. In this paper, 448 sets of data were collected to predict the neutralization depth of concrete bridges in China. Random forest was used for parameter selection. Besides this, four machine learning methods, such as support vector machine (SVM), k-nearest neighbor (KNN) and XGBoost, were adopted to develop models. The results show that machine learning models obtain a high accuracy (>80%) and an acceptable macro recall rate (>80%) even with only four parameters. For SVM models, the radial basis function has a better performance than other kernel functions. The radial basis kernel SVM method has the highest verification accuracy (91%) and the highest macro recall rate (86%). Besides this, the preference of different methods is revealed in this study. Full article
Show Figures

Figure 1

Open AccessArticle
Characterisation and Life Cycle Assessment of Pervious Concrete with Recycled Concrete Aggregates
Crystals 2021, 11(2), 209; https://doi.org/10.3390/cryst11020209 - 20 Feb 2021
Viewed by 347
Abstract
The search for environmental preservation and conservation of natural resources gives rise to new concepts and viable technical solutions on the path to sustainable development. In this context, this study’s main objective is to analyse the influence of recycled concrete aggregates (RCAs) on [...] Read more.
The search for environmental preservation and conservation of natural resources gives rise to new concepts and viable technical solutions on the path to sustainable development. In this context, this study’s main objective is to analyse the influence of recycled concrete aggregates (RCAs) on the development of pervious concrete, whose use as a floor covering represents an excellent device to mitigate the urban soil sealing phenomena. For this, mechanical and hydraulic tests were carried out, in addition to microstructural analyses and the assessment of its environmental performance. The results obtained were compared to reference studies also involving the incorporation of recycled aggregates. A pilot-scale case study was conducted, involving a parking space lined with pervious concrete moulded “in situ”. In laboratory tests, permeability coefficients and mechanical strengths compatible with the literature and above the normative limit for light traffic were found. The case study demonstrated higher permeability than in the laboratory, but the flexural strength was lower, being indicated only for pedestrian traffic. The environmental assessment showed that the RCA represents a positive contribution to the environmental performance of pervious concrete. Still, attention should be given to the recycled aggregate transport distance between the concrete plant and the RCA treatment plant. Full article
Show Figures

Graphical abstract

Open AccessArticle
Bis (Diamines) Cu and Zn Complexes of Flurbiprofen as Potential Cholinesterase Inhibitors: In Vitro Studies and Docking Simulations
Crystals 2021, 11(2), 208; https://doi.org/10.3390/cryst11020208 - 20 Feb 2021
Viewed by 191
Abstract
Alzheimer’s disease (AD) causes dementia and continuous damage to brain cells. Cholinesterase inhibitors can alleviate the condition by increasing communication between the nerve cells and reducing the risk of dementia. In an effort to treat Alzheimer’s disease, we synthesized flurbiprofen-based diamines (1,2 diaminoethane [...] Read more.
Alzheimer’s disease (AD) causes dementia and continuous damage to brain cells. Cholinesterase inhibitors can alleviate the condition by increasing communication between the nerve cells and reducing the risk of dementia. In an effort to treat Alzheimer’s disease, we synthesized flurbiprofen-based diamines (1,2 diaminoethane and 1,3 diaminopropane) Zn(II), Cu(II) metal complexes and characterized them by single-crystal X-ray analysis, NMR, (FT)-IR, UV-Vis, magnetic susceptibility, elemental analysis and conductivities measurements. Synthesized diamine metal complexes appeared in ionic forms and have distorted octahedral geometry based on conductivity studies, magnetic susceptibility and electronic studies. Single crystal X-ray diffraction analysis confirmed (2b) Cu(H2O)2(L1)2(L2)2 complex formation. Moreover, we tested all synthesized metal complexes against the cholinesterase enzyme that showed higher inhibition potential. In general, copper metal complexes showed higher inhibitory activities than simple metal complexes with flurbiprofen. These synthesized metal complexes may derive more effective and safe inhibitors for cholinesterases. Full article
Show Figures

Figure 1

Open AccessArticle
Extending Libraries of Extremely Localized Molecular Orbitals to Metal Organic Frameworks: A Preliminary Investigation
Crystals 2021, 11(2), 207; https://doi.org/10.3390/cryst11020207 - 20 Feb 2021
Viewed by 184
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
(This article belongs to the Special Issue Charge Density for Physical Properties in Crystals)
Show Figures

Figure 1

Open AccessArticle
Ultrahigh Ballistic Resistance of Twisted Bilayer Graphene
Crystals 2021, 11(2), 206; https://doi.org/10.3390/cryst11020206 - 20 Feb 2021
Viewed by 201
Abstract
Graphene is a good candidate for protective material owing to its extremely high stiffness and high strength-to-weight ratio. However, the impact performance of twisted bilayer graphene is still obscure. Herein we have investigated the ballistic resistance capacity of twisted bilayer graphene compared to [...] Read more.
Graphene is a good candidate for protective material owing to its extremely high stiffness and high strength-to-weight ratio. However, the impact performance of twisted bilayer graphene is still obscure. Herein we have investigated the ballistic resistance capacity of twisted bilayer graphene compared to that of AA-stacked bilayer graphene using molecular dynamic simulations. The energy propagation processes are identical, while the ballistic resistance capacity of the twisted bilayer graphene is almost two times larger than the AA-bilayer graphene. The enhanced capacity of the twisted bilayer graphene is assumed to be caused by the mismatch between the two sheets of graphene, which results in earlier fracture of the first graphene layer and reduces the possibility of penetration. Full article
(This article belongs to the Special Issue Graphene Mechanics (Volume II))
Show Figures

Figure 1

Open AccessArticle
Evolution Mechanism of Transient Strain and Residual Stress Distribution in Al 6061 Laser Welding
Crystals 2021, 11(2), 205; https://doi.org/10.3390/cryst11020205 - 19 Feb 2021
Viewed by 239
Abstract
Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are [...] Read more.
Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa). Full article
(This article belongs to the Special Issue Non-Traditional Machining of Crystal Materials)
Show Figures

Figure 1

Open AccessArticle
Effect of Fe on the Microstructure and Mechanical Properties of Fe/FeAl2O4 Cermet Prepared by Hot Press Sintering
Crystals 2021, 11(2), 204; https://doi.org/10.3390/cryst11020204 - 19 Feb 2021
Viewed by 168
Abstract
The Fe/FeAl2O4 cermet was prepared with Fe-Fe2O3-Al2O3 powder by a hot press sintering method at 1400 °C. The raw materials for the powder particles were respectively 2 µm (Fe), 0.5 µm (Fe2 [...] Read more.
The Fe/FeAl2O4 cermet was prepared with Fe-Fe2O3-Al2O3 powder by a hot press sintering method at 1400 °C. The raw materials for the powder particles were respectively 2 µm (Fe), 0.5 µm (Fe2O3), and 0.5 µm (Al2O3) in diameter, the sintering pressure was 30 MPa, and the holding time was 120 min. The effects of different Fe mass ratios on the microstructure and mechanical properties of Fe/FeAl2O4 cermet were studied. The results showed that a new ceramic phase FeAl2O4 could be formed by an in situ reaction during the hot press sintering. When the Fe mass ratio was increased, the microstructure and mechanical properties of the Fe/FeAl2O4 cermet showed a change law that initially became better and then became worse. The best microstructure and mechanical properties were obtained in the S2 sample, where the mass ratio of Fe-Fe2O3-Al2O3 was 6:1:2. In this Fe mass ratio, the relative density was about 94%, and the Vickers hardness and bending strength were 1.21 GPa and 210.0 MPa, respectively. The reaction mechanism of Fe in the preparation process was the in situ synthesis reaction of FeAl2O4 and the diffusion reaction of Fe to FeAl2O4 grains. The increase of the Fe mass ratio improved the wettability of Fe and FeAl2O4, which increased the diffusion rate of Fe to FeAl2O4 grains, which increased the influence on the structure of FeAl2O4. Full article
(This article belongs to the Special Issue Metallurgical Slag)
Show Figures

Graphical abstract

Open AccessReview
Insights into Solution Structures of Photosynthetic Protein Complexes from Small-Angle Scattering Methods
Crystals 2021, 11(2), 203; https://doi.org/10.3390/cryst11020203 - 19 Feb 2021
Viewed by 174
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 Crystallography at X-ray Free-Electron Lasers (XFELs))
Show Figures

Graphical abstract

Open AccessArticle
Influence of HAP on the Morpho-Structural Properties and Corrosion Resistance of ZrO2-Based Composites for Biomedical Applications
Crystals 2021, 11(2), 202; https://doi.org/10.3390/cryst11020202 - 19 Feb 2021
Viewed by 246
Abstract
In the present work, ZrO2-based composites were prepared by adding different amounts of antibacterial magnesium oxide and bioactive and biocompatible hydroxyapatite (HAP) to the inert zirconia. The composites were synthesized by the conventional ceramic processing route and morpho-structurally analyzed by X-ray [...] Read more.
In the present work, ZrO2-based composites were prepared by adding different amounts of antibacterial magnesium oxide and bioactive and biocompatible hydroxyapatite (HAP) to the inert zirconia. The composites were synthesized by the conventional ceramic processing route and morpho-structurally analyzed by X-ray powder diffraction (XRPD) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). Two metallic dental alloys (i.e., Ni–Cr and Co–Cr) coated with a chitosan (Chit) membrane containing the prepared composites were exposed to aerated artificial saliva solutions of different pHs (i.e., 4.3, 5, 6) and the corrosion resistances were investigated by electrochemical impedance spectroscopy technique. The obtained results using the two investigated metallic dental alloys shown quasi-similar anticorrosive properties, having quasi-similar charge transfer resistance, when coated with different ZrO2-based composites. This behavior could be explained by the synergetic effect between the diffusion process through the Chit-composite layer and the roughness of the metallic electrode surface. Full article
(This article belongs to the Special Issue Hydroxyapatite Base Nanocomposites)
Show Figures

Figure 1

Open AccessArticle
Phase Behaviour of Methane Hydrates in Confined Media
Crystals 2021, 11(2), 201; https://doi.org/10.3390/cryst11020201 - 18 Feb 2021
Viewed by 247
Abstract
In a study designed to investigate the melting behaviour of natural gas hydrates which are usually formed in porous mineral sediments rather than in bulk, hydrate phase equilibria for binary methane and water mixtures were studied using high-pressure differential scanning calorimetry in mesoporous [...] Read more.
In a study designed to investigate the melting behaviour of natural gas hydrates which are usually formed in porous mineral sediments rather than in bulk, hydrate phase equilibria for binary methane and water mixtures were studied using high-pressure differential scanning calorimetry in mesoporous and macroporous silica particles having controlled pore sizes ranging from 8.5 nm to 195.7 nm. A dynamic oscillating temperature method was used to form methane hydrates reproducibly and then determine their decomposition behaviour—melting points and enthalpies of melting. Significant decreases in dissociation temperature were observed as the pore size decreased (over 6 K for 8.5 nm pores). This behaviour is consistent with the Gibbs–Thomson equation, which was used to determine hydrate–water interfacial energies. The melting data up to 50 MPa indicated a strong, essentially logarithmic, dependence on pressure, which here has been ascribed to the pressure dependence of the interfacial energy in the confined media. An empirical modification of the Gibbs–Thomson equation is proposed to include this effect. Full article
(This article belongs to the Special Issue Membrane Technology for Solid Particles Production)
Show Figures

Figure 1

Open AccessArticle
Effect of the Dimensions of Coplanar Inner Floating Ring Electrode on the Performance of Liquid Crystal Lenses
Crystals 2021, 11(2), 200; https://doi.org/10.3390/cryst11020200 - 18 Feb 2021
Viewed by 181
Abstract
In this study, we mainly investigated the effect of the dimensions of a coplanar inner floating ring (CIFR) on the lens performance in CIFR–hole-patterned electrode liquid crystal lenses (HPELCLs) at 100 Hz of the electrical driving frequency. The operation and threshold voltages in [...] Read more.
In this study, we mainly investigated the effect of the dimensions of a coplanar inner floating ring (CIFR) on the lens performance in CIFR–hole-patterned electrode liquid crystal lenses (HPELCLs) at 100 Hz of the electrical driving frequency. The operation and threshold voltages in CIFR–HPELCLs are approximately 76% compared with those of the conventional HPELCL. The diameter of the CIFR with 360 μm in relation to imaging capabilities and those of the conventional glass lens and HPELCL were analyzed via the modulation transfer function. The relative mechanisms of the CIFR dimensions and the lens performance were also examined. An electric circuit model was used to analyze and illustrate the experimental results. Full article
Show Figures

Figure 1

Open AccessReview
Encapsulation of Calcium Phosphates on Electrospun Nanofibers for Tissue Engineering Applications
Crystals 2021, 11(2), 199; https://doi.org/10.3390/cryst11020199 - 18 Feb 2021
Viewed by 302
Abstract
In the field of tissue engineering, electrospinning is a versatile technique that provides nanofibers with structure similar to that of the extracellular matrix owing to their flexible functionalization. Considerable developments in electrospinning have been made to produce engineered electrospun nanofibers for different biomedical [...] Read more.
In the field of tissue engineering, electrospinning is a versatile technique that provides nanofibers with structure similar to that of the extracellular matrix owing to their flexible functionalization. Considerable developments in electrospinning have been made to produce engineered electrospun nanofibers for different biomedical applications. Various biopolymers possess good biocompatibility and biodegradability and are nontoxic in nature. Modification of these biopolymers can enhance or elicit certain properties. One technique of modification is the incorporation of certain inorganic ions or components that can enhance its specific functional characteristics such as mineralization, osseointegration, and bioactivity. Incidentally, calcium phosphate (CaP) materials have proven to be suitable and versatile for biopolymer incorporation and exploration because of their inherent bioactivity and being key mineral constituents of bone and teeth. The addition of CaP materials to polymers enhances cell infiltration, differentiation, and biomineralization. We aim to provide a broad overview of CaP material (particularly hydroxyapatite (HA))-incorporated electrospun nanocomposite fibers and their possible applications in tissue engineering. Some key polymer/HA composites were discussed in detail, and a brief discussion on other polymer/HA composites was also provided. Finally, we discussed the future perspectives of this interesting and emerging composite material fabricated via electrospinning. Full article
(This article belongs to the Special Issue Hydroxyapatite Base Nanocomposites)
Show Figures

Graphical abstract

Open AccessArticle
Halogen-Bonding-Driven Self-Assembly of Solvates of Tetrabromoterephthalic Acid
Crystals 2021, 11(2), 198; https://doi.org/10.3390/cryst11020198 - 18 Feb 2021
Viewed by 432
Abstract
Halogen bonding is one of the most interesting noncovalent attractions capable of self-assembly and recognition processes in both solution and solid phase. In this contribution, we report on the formation of two solvates of tetrabromoterephthalic acid (H2Br4tp) with acetonitrile [...] Read more.
Halogen bonding is one of the most interesting noncovalent attractions capable of self-assembly and recognition processes in both solution and solid phase. In this contribution, we report on the formation of two solvates of tetrabromoterephthalic acid (H2Br4tp) with acetonitrile (MeCN) and methanol (MeOH) viz. H2Br4tp·2MeCN (1MeCN) and H2Br4tp·2MeOH (2MeOH). The host structures of both 1MeCN and 2MeOH are assembled via the occurrence of simultaneous Br···Br, Br···O, and Br···π halogen bonding interactions, existing between the H2Br4tp molecular tectons. Among them, the cooperative effect of the dominant halogen bond in combination with hydrogen bonding interactions gave rise to different supramolecular assemblies, whereas the strength of the halogen bond depends on the type of hydrogen bond between the molecules of H2Br4tp and the solvents. These materials show a reversible release/resorption of solvent molecules accompanied by evident crystallographic phase transitions. Full article
(This article belongs to the Special Issue Advanced Research in Halogen Bonding)
Show Figures

Figure 1

Open AccessArticle
Ultrafast Laser-Induced Crystallization of Lead Germanate Glass
Crystals 2021, 11(2), 193; https://doi.org/10.3390/cryst11020193 - 18 Feb 2021
Viewed by 273
Abstract
Laser-induced space-selective crystallization of glass enabling the growth of continuous crystal-in-glass architectures consisting of non-centrosymmetric phases with functional properties is promising, including single-crystal waveguides for the development of integrated optical circuits. In this study, femtosecond laser direct writing of crystalline lines inside lead [...] Read more.
Laser-induced space-selective crystallization of glass enabling the growth of continuous crystal-in-glass architectures consisting of non-centrosymmetric phases with functional properties is promising, including single-crystal waveguides for the development of integrated optical circuits. In this study, femtosecond laser direct writing of crystalline lines inside lead germanate glass with the composition close to Pb5Ge3O11 has been demonstrated. The growth of crystalline lines by the .moving focused laser beam required the preliminary growth of a seed crystal by the fixed beam. Confocal Raman spectroscopy revealed the precipitation of ferroelectric Pb5Ge3O11, which, under certain exposure conditions, could be accompanied by precipitation of the metastable lead germanate phase. Depending on the laser beam parameters, either bilateral growth providing split, horseshoe-shaped morphology of the crystal cross-section, or centered growth resulting in elongated, elliptical cross-section shape occurred. The obtained results are of interest for the fabrication of ferroelectric Pb5Ge3O11-based crystal-in-glass waveguides. Full article
(This article belongs to the Special Issue Laser-Induced Crystallization)
Show Figures

Figure 1

Open AccessArticle
Ultrasound-Assisted Synthesis and Crystal Structure of Novel 2D Cd (II) Metal–Organic Coordination Polymer with Nitrite End Stop Ligand as a Precursor for Preparation of CdO Nanoparticles
Crystals 2021, 11(2), 197; https://doi.org/10.3390/cryst11020197 - 17 Feb 2021
Viewed by 235
Abstract
In the present research, a sonochemical approach was applied to prepare new cadmium(II) coordination 2D polymer, [Cd(L)(NO2)2]n (L = 1,2-bis(1-(pyridin-3-yl)ethylidene)hydrazine) and structurally characterized with various spectroscopic techniques including XRD, elemental analysis, SEM, and IR spectroscopy. The coordination number [...] Read more.
In the present research, a sonochemical approach was applied to prepare new cadmium(II) coordination 2D polymer, [Cd(L)(NO2)2]n (L = 1,2-bis(1-(pyridin-3-yl)ethylidene)hydrazine) and structurally characterized with various spectroscopic techniques including XRD, elemental analysis, SEM, and IR spectroscopy. The coordination number of cadmium (II) ions is seven (CdN2O5) by two nitrogen atoms from two organic Schiff base ligand and five oxygen of nitrite anions. The 2D sheet structures ended by nitrite anions and the nitrite anion displayed the end-stop role. The comprehensive system showed a three-dimensional structure with several weak interactions. The high-intensity ultrasound is regarded as an easy, environmentally-friendly, and flexible synthetic instrument for the compounds of coordination. CdO NPs was obtained by thermolysing 1 at 180 °C with oleic acid (as a surfactant). Further, the size and morphology of the produced CdO nanoparticles were investigated through SEM. Full article
Show Figures

Figure 1

Open AccessArticle
High-Durability Concrete with Supplementary Cementitious Admixtures Used in Corrosive Environments
Crystals 2021, 11(2), 196; https://doi.org/10.3390/cryst11020196 - 17 Feb 2021
Viewed by 389
Abstract
Durability of concrete is of great significance to prolong the service life of concrete structures in corrosive environments. Aiming at the economical and environment-friendly production of concrete by comprehensive utilization of the supplementary cementitious materials made of industrial byproducts, the resistances to chloride [...] Read more.
Durability of concrete is of great significance to prolong the service life of concrete structures in corrosive environments. Aiming at the economical and environment-friendly production of concrete by comprehensive utilization of the supplementary cementitious materials made of industrial byproducts, the resistances to chloride penetration, sulfate attack, and frost of high-performance concrete were studied in this paper. Fifteen concretes were designed at different water–binder ratio with the changes of contents of fly ash (FA), silica fume (SF), ground granulated blast-furnace slag (GGBS), and admixture of sulfate corrosion-resistance (AS). The compressive strength, the total electric flux of chloride penetrability, the sulfate resistance coefficient, and the indices of freezing and thawing were measured. Results indicate that, depending on the chemical composition, fineness, and pozzolanic activity, the supplementary cementitious admixtures had different effects on the compressive strength and the durability of concrete; despite having a higher fineness and pozzolanic activity, the GGBS gave out a negative effect on concrete due to a similar chemical composition with cement; the SF and FA presented beneficial effects on concrete whether they were used singly with GGBS or jointly with GGBS; the AS improved the compressive strength and the sulfate corrosion resistance of concrete. In general, the grade of durability was positively related to the compressive strength of concrete. Except for the concretes admixed only with GGBS or with GGBS and FA, others had super durability with the compressive strength varying from 70 MPa to 113 MPa. The concretes with water to binder ratio of 0.29 and total binders of 500 kg/m3 admixed with 7% FA + 8% SF + 8% GGBS or 7% FA + 8% SF + 8% GGBS + (10~12)% AS presented the highest grades of resistances specified in China codes to chloride penetration, sulfate corrosion, and frost, while the compressive strength was about 100 MPa. Full article
(This article belongs to the Special Issue Properties and Performance of Concrete Materials and Structures)
Show Figures

Figure 1

Open AccessArticle
Enlarging the Eyebox of Maxwellian Displays with a Customized Liquid Crystal Dammann Grating
Crystals 2021, 11(2), 195; https://doi.org/10.3390/cryst11020195 - 17 Feb 2021
Viewed by 265
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

Open AccessArticle
Mechanical Behavior of Al–Al2Cu–Si and Al–Al2Cu Eutectic Alloys
Crystals 2021, 11(2), 194; https://doi.org/10.3390/cryst11020194 - 16 Feb 2021
Viewed by 187
Abstract
In this study, laser rapid solidification technique was used to refine the microstructure of ternary Al–Cu–Si and binary Al–Cu eutectic alloys to nanoscales. Micropillar compression testing was performed to measure the stress–strain response of the samples with characteristic microstructure in the melt pool [...] Read more.
In this study, laser rapid solidification technique was used to refine the microstructure of ternary Al–Cu–Si and binary Al–Cu eutectic alloys to nanoscales. Micropillar compression testing was performed to measure the stress–strain response of the samples with characteristic microstructure in the melt pool regions. The laser-remelted Al–Al2Cu–Si ternary alloy was observed to reach the compressive strength of 1.59 GPa before failure at a strain of 28.5%, which is significantly better than the as-cast alloy with a maximum strength of 0.48 GPa at a failure strain of 4.8%. The laser-remelted Al–Cu binary alloy was observed to reach the compressive strength of 2.07 GPa before failure at a strain of 26.5%, which is significantly better than the as-cast alloy with maximum strength of 0.74 GPa at a failure strain of 3.3%. The enhanced compressive strength and improved compressive plasticity were interpreted in terms of microstructural refinement and hierarchical eutectic morphology. Full article
(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)
Show Figures

Figure 1

Open AccessArticle
Electrorheological Effect of Gold Nanoparticles Coated with Fluorescent Mesogenic Groups Dispersed in Nematic Liquid Crystal
Crystals 2021, 11(2), 192; https://doi.org/10.3390/cryst11020192 - 16 Feb 2021
Viewed by 204
Abstract
The electrorheological (ER) properties of composite materials consisting of a nematic liquid crystal (LC) and gold nanoparticles (GNPs) coated with bistolane-based mesogenic groups were studied. The GNPs were coated by normal alkyl chains and the fluorescent LC compounds, of which the molecular structure [...] Read more.
The electrorheological (ER) properties of composite materials consisting of a nematic liquid crystal (LC) and gold nanoparticles (GNPs) coated with bistolane-based mesogenic groups were studied. The GNPs were coated by normal alkyl chains and the fluorescent LC compounds, of which the molecular structure was similar to that of the LC matrix. The dispersity of the GNPs in the nematic LC was investigated by polarizing optical microscopy (POM). In order to improve the ER effect of the composite, a simple strategy was investigated from the viewpoint of a material design in surface-modified GNPs by lateral substitution of the mesogenic groups. The presence of the GNPs in the nematic LC led to a slightly enhanced ER effect compared to that observed for only the nematic LC. This study demonstrates the potential of a hybrid system consisting of LCs and GNPs to yield a larger ER effect. Full article
Show Figures

Figure 1

Open AccessArticle
Cocrystals Based on 4,4’-bipyridine: Influence of Crystal Packing on Melting Point
Crystals 2021, 11(2), 191; https://doi.org/10.3390/cryst11020191 - 16 Feb 2021
Viewed by 187
Abstract
The reactions of piperonylic acid (HPip) and cinnamic acid (HCinn) with 4,4’-bipyridine (4,4’-bipy) have been assayed using the same synthetic methodology, yielding two binary cocrystals with different acid:4,4’-bipy molar ratios, (HPip)(4,4’-bipy) (1) and (HCinn)2(4,4’-bipy) (2). The melting [...] Read more.
The reactions of piperonylic acid (HPip) and cinnamic acid (HCinn) with 4,4’-bipyridine (4,4’-bipy) have been assayed using the same synthetic methodology, yielding two binary cocrystals with different acid:4,4’-bipy molar ratios, (HPip)(4,4’-bipy) (1) and (HCinn)2(4,4’-bipy) (2). The melting point (m.p.) of these cocrystals have been measured and a remarkable difference (ΔT ≈ 78 °C) between them was observed. Moreover, the two cocrystals have been characterized by powder X-ray diffraction (PXRD), elemental analysis (EA), FTIR-ATR, 1H NMR spectroscopies, and single-crystal X-ray diffraction. The study of their structural packings via Hirshfeld surface analysis and energy frameworks revealed the important contribution of the π···π and C-H···π interactions to the formation of different structural packing motifs, this being the main reason for the difference of m.p. between them. Moreover, it has been observed that 1 and 2 presented the same packing motifs as the crystal structure of their corresponding carboxylic acids, but 1 and 2 showed lower m.p. than those of the carboxylic acids, which could be related to the lower strength of the acid-pyridine heterosynthons respect to the acid-acid homosynthons in the crystal structures. Full article
Show Figures

Graphical abstract

Previous Issue
Next Issue
Back to TopTop