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Selected Papers from the 2nd International Online Conference on Crystals

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A special issue of Crystals (ISSN 2073-4352).

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 27544

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Prof. Dr. Reshef Tenne

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Department of Materials and Interfaces, Weizmann Institute, Rehovot 76100, Israel
Interests: nanoparticles synthesis; solid state chemistry; characterization of nanoparticles
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Prof. Zoran Radić

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Skaggs School of Pharmacy and Pharmaceutical Sciences, UC San Diego, La Jolla, CA 92093, USA
Interests: Enzyme kinetics, catalytic mechanisms, protein structure, cholinesterase structure/activity, acetylcholinesterase, butyrylcholinesterase, cholinesterase inhibition, cholinesterase reactivation, antidotes against organophosphate intoxication, structure-based antidote design

Dr. Anna Moliterni

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Institute of Crystallography (IC), CNR (National Research Council), 700185 Roma, Italy
Interests: Ab-initio structure determination by powder diffraction data; computational crystallography; qualitative phase analysis; quantitative phase analysis; Rietveld refinement; structure determination and refinement by single crystal diffraction data; data collection and processing

Prof. Dr. Robert F. Klie

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Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
Interests: transmission electron microscopy; scanning transmission electron microscopy; electron energy-loss spectroscopy; correlated oxides; molecular beam epitaxy; electron beam diffraction; magnetism
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Dr. Rocco Caliandro

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Institute of Crystallography, National Research Council of Italy, Via Amendola 122/O, 70126 Bari, Italy
Interests: protein crystallography; phasing methods; modulated enhanced diffraction; multivariate analysis
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Dr. Dritan Siliqi

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Institute of Crystallography- CNR, Via G. Amendola, 122/O, 70126 Bari, Italy
Interests: protein crystallography; small and wide angle X-ray scattering (SAXS and WAXS); BioSAXS; biological molecules; rare diseases; phasing algorithm; nano- and bio-materials; X-ray imaging
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue comprises selected papers from the Proceedings of the 2nd International Online Conference on Crystals (Crystals 2020), 10–20 November, 2020, held on sciforum.net, an online platform for hosting scholarly e-conferences and discussion groups.

After the 1st Electronic Conference on Crystals, held in 2018, which offered the opportunity for researchers engaged in the study of crystalline materials to present their research and exchange ideas with their colleagues by taking full advantage of the Internet, removing the need to travel and participation expenses, we found it appropriate to renew the experience to gather contributions from more significant advances made in the last two years. These stems from advances in experimental (both diffractometric and spectroscopic) and computational techniques for research in many different areas, from pharmaceutical, to materials and biomolecular science. The second conference will be organized around the following topics and related themes.

Liquid Crystals
Crystalline Materials
Crystal Engineering
Biomolecular Crystals
Crystalline Minerals and Biominerals
Phase Transformations in Crystalline Materials
Small and Wide Angle X-ray Scattering Applied to Nano- and Biomaterials
Software/Tools to Deal with Crystal and Crystallographic Issues & Teaching Crystallography
Structure of Cholinesterases

Selected papers that attract the most interest on the web or that provide a particularly innovative contribution will be selected for publication. These papers will be subjected to peer review and published with the aim of rapid and wide dissemination of research results, developments, and applications. We hope this Conference Series will continue to grow in acceptance and recognition by potential participants, contributors, experts who want to disseminate their latest findings, and readers who seek for information on relevant water science topics.

Prof. Dr. Reshef Tenne
Prof. Zoran Radić
Dr. Anna Moliterni
Prof. Dr. Robert Klie
Dr. Rocco Caliandro
Dr. Dritan Siliqi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (12 papers)

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Research

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9 pages, 3834 KiB

Open AccessArticle

The Interaction of the 2D MoP₂ and NbP₂ Surfaces with Carbon Dioxide and Carbon Monoxide and Changes in Their Optical Properties

by Osiris Salas, Eric Garcés and Luis Fernando Magana

Crystals 2022, 12(1), 45; https://doi.org/10.3390/cryst12010045 - 29 Dec 2021

Cited by 1 | Viewed by 1329

Abstract

Using first-principles molecular dynamics (FPMD) simulations at atmospheric pressure and 300 K, we investigated the adsorption of the molecules CO and CO₂ on each of the surfaces of the 2D materials MoP₂ and NbP₂. We found that both surfaces adsorbed the carbon monoxide molecule but not the carbon dioxide. The adsorption energy on the MoP₂ surface was −0.9398 eV, and on the NbP₂ surface, −0.9017 eV. Furthermore, we obtained substantial changes in the optical properties of each 2D material after the CO adsorption. For the two materials, the optical absorption shows significant changes in the ultraviolet region. Furthermore, the two surfaces present essential changes in the ultraviolet range in the case of reflectivity. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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13 pages, 8440 KiB

Open AccessArticle

Effects of theTiB₂-SiC Volume Ratio and Spark Plasma Sintering Temperature on the Properties and Microstructure of TiB₂-BN-SiC Composite Ceramics

by Shi Tian, Zelin Liao, Wenchao Guo, Qianglong He, Heng Wang and Weimin Wang

Crystals 2022, 12(1), 29; https://doi.org/10.3390/cryst12010029 - 25 Dec 2021

Cited by 4 | Viewed by 2170

Abstract

TiB₂-BN composite ceramics combine excellent electrical conductivity, thermal shock resistance, high-temperature resistance, corrosion resistance, and easy processing of TiB₂ and BN. However, in practical applications, their high-temperature oxidation resistance is poor and the resistivity distribution is uneven and changes substantially with temperature. A TiB₂-BN-SiC composite ceramic with stable and controllable resistivity was prepared by introducing SiC into the TiB₂-BN composite ceramics. In this work, spark plasma sintering (SPS) technology was used to prepare TiB₂-BN-SiC composite ceramics with various TiB₂-SiC ratios and sintering temperatures. The samples were tested by XRD, SEM, and thermal and mechanical analysis. The results show that as the volume ratio of TiB₂-SiC was increased from 3:1 to 12:1, the resistivity of the sample decreased from 8053.3 to 4923.3 μΩ·cm, the thermal conductivity increased from 24.89 to 34.15 W/(m k), and the thermal expansion rate increased from 7.49 (10⁻⁶/K) to 10.81 (10⁻⁶/K). As the sintering temperature was increased from 1650 to 1950 °C, the density of the sample increased, the mechanical properties were slightly improved, and the resistivity, thermal expansion rate, and thermal conductivity changed substantially. The volume ratio and sintering temperature are the key factors that control the resistivity and thermal characteristics of TiB₂-SiC-BN composite ceramics, and the in situ from liquid phases of FeB and FeO also promotes the sintering of the TiB₂-BN-SiC ceramics. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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11 pages, 1358 KiB

Open AccessEditor’s ChoiceArticle

Statistical Theory of Helical Twisting in Nematic Liquid Crystals Doped with Chiral Nanoparticles

by Mikhail A. Osipov, Alexey S. Merekalov and Alexander A. Ezhov

Crystals 2021, 11(11), 1432; https://doi.org/10.3390/cryst11111432 - 22 Nov 2021

Viewed by 2003

Abstract

A molecular field theory of the cholesteric ordering in nematic nanocomposites doped with chiral nanoparticles was developed taking into consideration chiral dispersion interaction between rod-like nanoparticles. It was shown that the inverse pitch of the cholesteric helical structure is proportional to the anisotropy of the effective polarizability and the anisotropy of the effective gyration tensor of a nanoparticle in the nematic host. The theory enables one to predict the helical sense inversion induced by a change of the low-frequency dielectric susceptibility of the nematic host phase. The components of the high-frequency effective polarizability and the effective optical activity of a gold rod-like nanoparticle in a particular nematic solvent were calculated numerically. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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8 pages, 2426 KiB

Open AccessArticle

M-Center in Neutron-Irradiated 4H-SiC

by Ivana Capan, Tomislav Brodar, Takahiro Makino, Vladimir Radulovic and Luka Snoj

Crystals 2021, 11(11), 1404; https://doi.org/10.3390/cryst11111404 - 18 Nov 2021

Cited by 6 | Viewed by 1766

Abstract

We report on the metastable defects introduced in the n-type 4H-SiC material by epithermal and fast neutron irradiation. The epithermal and fast neutron irradiation defects in 4H-SiC are much less explored compared to electron or proton irradiation-induced defects. In addition to the carbon vacancy (Vc), silicon vacancy (Vsi) and carbon antisite-carbon vacancy (CAV) complex, the neutron irradiation has introduced four deep-level defects, all arising from the metastable defect, the M-center. The metastable deep-level defects were investigated by deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and isothermal DLTS. The existence of the fourth deep-level defect, M₄, recently observed in ion-implanted 4H-SiC, has been additionally confirmed in neutron-irradiated samples. The isothermal DLTS technique has been proven as a useful tool for studying the metastable defects. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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13 pages, 4149 KiB

Open AccessArticle

Backbone Conformation Shifts in X-ray Structures of Human Acetylcholinesterase upon Covalent Organophosphate Inhibition

by Stephanie Luedtke, Celine Bojo, Yunshen Li, Emilio Luna, Bianca Pomar and Zoran Radić

Crystals 2021, 11(11), 1270; https://doi.org/10.3390/cryst11111270 - 20 Oct 2021

Cited by 5 | Viewed by 2991

Abstract

Conformations of Cα backbones in X-ray structures of most organophosphate (OP)-inhibited human acetylcholinesterases (hAChEs) have been previously shown to be similar to that of the native hAChE. One of the exceptions is the structure of the diethylphosphoryl-hAChE conjugate, where stabilization of a large ethoxy group into the acyl pocket (AP) of hAChE-triggered notable loop distortions and consequential dissociation of the hAChE homodimer. Recently, six X-ray structures of hAChE conjugated with large OP nerve agents of the A-type, Novichoks, have been deposited to PDB. In this study we analyzed backbone conformation shifts in those structures, as well as in OP-hAChE conjugates formed by Paraoxon, Soman, Tabun, and VX. A Java-based pairwise alpha carbon comparison tool (PACCT 3) was used for analysis. Surprisingly, despite the snug fit of large substituents on phosphorus, inside Novichok-conjugated hAChEs only minor conformational changes were detected in their backbones. Small magnitudes of observed changes were due to a 1.2–2.4 Å shift of the entire conjugated OP away from the AP. It thus appears that the small AP of AChEs can accommodate, without distortion, substituents of the size of ethoxy or butyryl groups, provided that conjugated OP is “pulled” away from the AP. This observation has practical consequences in the structure-based design of nucleophilic reactivation antidotes as well as in the definition of the AChE specificity that relies on the size of its AP. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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14 pages, 3374 KiB

Open AccessArticle

Spectroscopic and Structural Properties of β-Tricalcium Phosphates Ca₉RE(PO₄)₇ (RE = Nd, Gd, Dy)

by Veronica Paterlini, Asmaa El Khouri, Marco Bettinelli, Daniele Maria Trucchi and Francesco Capitelli

Crystals 2021, 11(10), 1269; https://doi.org/10.3390/cryst11101269 - 19 Oct 2021

Cited by 2 | Viewed by 1689

Abstract

Rare-earth-based Ca₉RE(PO₄)₇ (RE = Nd, Gd, Dy) materials were synthesized by solid-state reaction at T = 1200 °C. The obtained tricalcium phosphate (TCP) materials are efficient light emitters due to the presence of RE³⁺ ions, although these ions are present at high concentrations. Moreover, in these host structures, these ions can be used as optical probes to study their local environments. Thus, photoluminescence (PL) emission spectra of the powder samples clearly indicated, for Dy³⁺ and Gd³⁺ ions, the presence of the RE³⁺ ion in low-symmetry sites with some local structural disorder, and the spectra show the presence of vibrational features (in the case of Gd³⁺). For the Nd³⁺ phase, emission bands are present around 900, 1050, and 1330 nm, originating from the ⁴F_3/2 level. In general, these RE-TCP samples are interesting luminescent materials in the visible (Dy), UV (Gd), and NIR (Nd) regions, due to weak concentration quenching even for high concentrations of the emitting ion. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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11 pages, 2099 KiB

Open AccessEditor’s ChoiceArticle

Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

by Fabrizio Ciciulla, Annamaria Zaltron, Riccardo Zamboni, Cinzia Sada, Francesco Simoni, Victor Yu. Reshetnyak and Liana Lucchetti

Crystals 2021, 11(8), 908; https://doi.org/10.3390/cryst11080908 - 02 Aug 2021

Cited by 7 | Viewed by 2249

Abstract

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 10⁷ W/m². Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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17 pages, 1394 KiB

Open AccessArticle

Int3D: A Data Reduction Software for Single Crystal Neutron Diffraction

by Nebil A. Katcho, Laura Cañadillas-Delgado, Oscar Fabelo, María Teresa Fernández-Díaz and Juan Rodríguez-Carvajal

Crystals 2021, 11(8), 897; https://doi.org/10.3390/cryst11080897 - 31 Jul 2021

Cited by 5 | Viewed by 2396

Abstract

We describe a new software package for the data reduction of single crystal neutron diffraction using large 2D detectors. The software consists of a graphical user interface from which the user can visualize, interact with and process the data. The data reduction is achieved by sequentially executing a series of programs designed for performing the following tasks: peak detection, indexing, refinement of the orientation matrix and motor offsets, and integration. The graphical tools of the software allow visualization of and interaction with the data in two and three dimensions, both in direct and reciprocal spaces. They make it easy to validate the different steps of the data reduction and will be of great help in the treatment of complex problems involving incommensurate structures, twins or diffuse scattering. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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13 pages, 3983 KiB

Open AccessArticle

Dynamic and Photonic Properties of Field-Induced Gratings in Flexoelectric LC Layers

by Serguei P. Palto

Crystals 2021, 11(8), 894; https://doi.org/10.3390/cryst11080894 - 30 Jul 2021

Cited by 1 | Viewed by 1426

Abstract

For LCs with a non-zero flexoelectric coefficient difference (e₁–e₃) and low dielectric anisotropy, electric fields exceeding certain threshold values result in transitions from the homogeneous planarly aligned state to the spatially periodic one. Field-induced grating is characterized by rotation of the LC director about the alignment axis with the wavevector of the grating oriented perpendicular to the initial alignment direction. The rotation sign is defined by both the electric field vector and the sign of the (e₁–e₃) difference. The wavenumber characterizing the field-induced periodicity is increased linearly with the applied voltage starting from a threshold value of about π/d, where d is the thickness of the layer. Two sets of properties of the field-induced gratings are studied in this paper using numerical simulations: (i) the dynamics of the grating appearance and relaxation; (ii) the transmittance and reflectance spectra, showing photonic stop bands in the waveguide mode. It is shown that under ideal conditions, the characteristic time of formation for a spatially limited grating is determined by the amplitude of the electric voltage and the size of the grating itself in the direction of the wave vector. For large gratings, this time can be drastically reduced via spatial modulation of the LC anchoring on one of the alignment surfaces. In the last case, the time is defined not by the grating size, but the period of the spatial modulation of the anchoring. The spectral structure of the field-induced stop bands and their use in LC photonics are also discussed. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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9 pages, 14985 KiB

Open AccessArticle

Phase Stability and Transport Properties of (ZrO₂)_0.91−x(Sc₂O₃)_0.09(Yb₂O₃)_x Crystals (x = 0–0.01)

by Mikhail Borik, Galina Korableva, Alexey Kulebyakin, Irina Kuritsyna, Nataliya Larina, Elena Lomonova, Filipp Milovich, Valentina Myzina, Polina Ryabochkina, Nataliya Sidorova, Nataliya Tabachkova and Tatyana Volkova

Crystals 2021, 11(2), 83; https://doi.org/10.3390/cryst11020083 - 21 Jan 2021

Cited by 1 | Viewed by 1712

Abstract

Phase stability and transport properties of (ZrO₂)_0.91−x(Sc₂O₃)_0.09(Yb₂O₃)_x crystals (x = 0–0.01) have been studied before and after air annealing at 1000 °C for 400 h. The crystals have been grown by radio frequency (RF) heating in a cold crucible. The microstructure, phase composition, and electrical conductivity of the crystals have been studied using optical microscopy, X-ray diffraction, Raman spectroscopy, and impedance spectroscopy. Phase stability and degradation of ionic conductivity of the crystals upon long-term high-temperature heat treatment have been discussed. We show that the stabilization of ZrO₂ co-doped with 9 mol.% Sc₂O₃ and 1 mol.% Yb₂O₃ provides transparent uniform crystals with the pseudocubic t″ phase structure having high phase stability. Crystals of this composition had the highest conductivity in the entire temperature range. Long-term high-temperature annealing of these crystals did not lead to conductivity degradation. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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Review

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13 pages, 3043 KiB

Open AccessReview

Interplay of Nanoparticle Properties during Endocytosis

by Xiaohuan Wang, Long Li, Long Li, Fan Song and Fan Song

Crystals 2021, 11(7), 728; https://doi.org/10.3390/cryst11070728 - 24 Jun 2021

Cited by 13 | Viewed by 2876

Abstract

Nanoparticles (NPs) have been widely applied as drug carriers in drug delivery, due to their unique physical and structural properties. To achieve the drug delivery purpose, receptor-mediated endocytosis is a primary explored mechanism to internalize NPs into tumor cells. During the endocytosis process, properties of NPs, including size, shape, and surface functionality, play an important role in determining the final drug delivery efficacy. Many of these NP properties have been extensively explored individually. However, the multiple NP properties naturally interplay with each other in the endocytosis process to determine the internalization efficiency together. Therefore, it is significantly important to understand the interplay of different NP properties to improve the NP’s final delivery efficacy. In this review, we focus on the interplay of NPs properties on the endocytosis process to summarize the relevant experimental observations and physical mechanisms. Particularly, three different aspects are discussed in detail, including the interplay between size and shape; size and elasticity; shape and elasticity. We have summarized the most recent works and highlighted that building up systematic understandings for the complex interplay between NP properties can greatly help a better design of NP platforms for drug delivery. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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16 pages, 8479 KiB

Open AccessReview

Patterned Photoalignment in Thin Films: Physics and Applications

by Vladimir Chigrinov, Aleksey Kudreyko and Qi Guo

Crystals 2021, 11(2), 84; https://doi.org/10.3390/cryst11020084 - 21 Jan 2021

Cited by 13 | Viewed by 3381

Abstract

Photoalignment of liquid crystals by using azo dye molecules is a commonly proposed alternative to traditional rubbing alignment methods. Photoalignment mechanism can be well described in terms of rotational diffusion of azo dye molecules exposed by ultraviolet polarized light. A specific feature of the irradiated light is the intensity dependent change of azimuthal anchoring of liquid crystals. While there are various mechanisms of azo dye photoalignment, photo-reorientation occurs when dye molecules orient themselves perpendicular to the polarization of incident light. In this review, we describe both recent achievements in applications of photoaligned liquid crystal cells and its simulation. A variety of display and photonic devices with azo dye aligned nematic and ferroelectric liquid crystals are presented: q-plates, optically rewritable flexible e-paper (monochromatic and color), and Dammann gratings. Some theoretical aspects of the alignment process and display simulation are also considered. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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