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Editor’s Choice Articles

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

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8 pages, 1858 KiB  
Article
Optical Transport Properties of Graphene Surface Plasmon Polaritons in Mid-Infrared Band
by Yindi Wang, Hongxia Liu, Shulong Wang, Ming Cai and Lan Ma
Crystals 2019, 9(7), 354; https://doi.org/10.3390/cryst9070354 - 12 Jul 2019
Cited by 25 | Viewed by 3855
Abstract
The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation [...] Read more.
The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation results indicate that graphene SPPs show unique properties in the mid-infrared region including ultra-compact mode confinement and dynamic tunability, which allow these SPPs to overcome the defects of metal SPPs and traditional silicon-based optoelectronic devices. Thus, they can be used to manufacture subwavelength devices. The work in this paper lays a theoretical foundation for the application of graphene SPPs in the mid-infrared region. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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14 pages, 3033 KiB  
Article
The Fabrication of Calcium Alginate Beads as a Green Sorbent for Selective Recovery of Cu(Ⅱ) from Metal Mixtures
by Niannian Yang, Runkai Wang, Pinhua Rao, Lili Yan, Wenqi Zhang, Jincheng Wang and Fei Chai
Crystals 2019, 9(5), 255; https://doi.org/10.3390/cryst9050255 - 17 May 2019
Cited by 61 | Viewed by 6388
Abstract
Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl2, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted [...] Read more.
Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl2, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted on Cu(II), Cd(II), Ni(II) and Zn(II) as the model heavy metals and the concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The characterization and sorption behavior of the CA beads were analyzed in detail via using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption experiments demonstrated that the CA beads exhibited a high removal efficiency for the selective adsorption of Cu(II) from the tetra metallic mixture solution and an excellent adsorption capacity of the heavy metals separately. According to the isotherm studies, the maximum uptake of Cu(II) could reach 107.53 mg/g, which was significantly higher than the other three heavy metal ions in the tetra metallic mixture solution. Additionally, after five cycles of adsorption and desorption, the uptake rate of Cu(II) on CA beads was maintained at 92%. According to the properties mentioned above, this material was assumed to be applied to reduce heavy metal pollution or recover valuable metals from waste water. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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15 pages, 1497 KiB  
Article
Van der Waals Density Functional Theory vdW-DFq for Semihard Materials
by Qing Peng, Guangyu Wang, Gui-Rong Liu and Suvranu De
Crystals 2019, 9(5), 243; https://doi.org/10.3390/cryst9050243 - 8 May 2019
Cited by 22 | Viewed by 5318
Abstract
There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability [...] Read more.
There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability are mainly determined by the interactions between instantaneously induced dipoles, the so called London dispersion force or van der Waals force. It is challenging to accurately model the structural and mechanical properties of these semihard materials in the frame of density functional theory where the non-local correlation functionals are not well known. Here, we propose a van der Waals density functional named vdW-DFq to accurately model the density and geometry of semihard materials. Using β -cyclotetramethylene tetranitramine as a prototype, we adjust the enhancement factor of the exchange energy functional with generalized gradient approximations. We find this method to be simple and robust over a wide tuning range when calibrating the functional on-demand with experimental data. With a calibrated value q = 1.05 , the proposed vdW-DFq method shows good performance in predicting the geometries of 11 common energetic material molecular crystals and three typical layered van der Waals crystals. This success could be attributed to the similar electronic charge density gradients, suggesting a wide use in modeling semihard materials. This method could be useful in developing non-empirical density functional theories for semihard and soft materials. Full article
(This article belongs to the Special Issue First-Principles Prediction of Structures and Properties in Crystals)
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11 pages, 4319 KiB  
Article
Dielectric and Piezoelectric Properties of Textured Lead-Free Na0.5Bi0.5TiO3-Based Ceramics
by Nannan Dong, Xiaoyi Gao, Fangquan Xia, Hanxing Liu, Hua Hao and Shujun Zhang
Crystals 2019, 9(4), 206; https://doi.org/10.3390/cryst9040206 - 14 Apr 2019
Cited by 24 | Viewed by 4097
Abstract
This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na0.5Bi0.5TiO3-0.08K0.5Bi0.5TiO3-0.04BaTiO3 (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method [...] Read more.
This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na0.5Bi0.5TiO3-0.08K0.5Bi0.5TiO3-0.04BaTiO3 (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method using NaNbO3 (NN) for templates. For textured ceramics with 4 wt% NN templates, a Lotgering factor of 96% and piezoelectric coefficient d33 of 185 pC/N were obtained. Compared to the randomly oriented ceramics, textured ceramics show lower strain hysteresis (H = 7.6%), higher unipolar strain of 0.041% with corresponding large signal piezoelectric coefficient d33* of 200 pm/V at applied field of 2 kV/mm. This enhancement can be explained by the grain orientation along <001> direction by texturing, where an engineered domain configuration is formed after polarization, leading to decreased hysteresis and increased piezoelectric property. Full article
(This article belongs to the Section Crystalline Materials)
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12 pages, 604 KiB  
Review
Prospective of (BaCa)(ZrTi)O3 Lead-free Piezoelectric Ceramics
by Wenfeng Liu, Lu Cheng and Shengtao Li
Crystals 2019, 9(3), 179; https://doi.org/10.3390/cryst9030179 - 26 Mar 2019
Cited by 31 | Viewed by 5163
Abstract
Piezoelectric ceramics is a functional material that can convert mechanical energy into electrical energy and vice versa. It can find wide applications ranging from our daily life to high-end techniques and dominates a billion-dollar market. For half a century, the working horse of [...] Read more.
Piezoelectric ceramics is a functional material that can convert mechanical energy into electrical energy and vice versa. It can find wide applications ranging from our daily life to high-end techniques and dominates a billion-dollar market. For half a century, the working horse of the field has been the polycrystalline PbZr1−xTixO3 (PZT), which is now globally resisted for containing the toxic element lead. In 2009, our group discovered a non-Pb piezoelectric material, (BaCa)(ZrTi)O3 ceramics (BZT-BCT), which exhibits an ultrahigh piezoelectric coefficient d33 of 560–620 pC/N. This result brought extensive interest in the research field and important consequences for the piezoelectric industry that has relied on PZT. In the present paper, we review the recent progress, both experimental and theoretical, in the BZT-BCT ceramics. Full article
(This article belongs to the Special Issue Synthesis and Characterization of Ferroelectrics)
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8 pages, 2170 KiB  
Communication
Hybrid Biomimetic Materials from Silica/Carbonate Biomorphs
by Julian Opel, Niklas Unglaube, Melissa Wörner, Matthias Kellermeier, Helmut Cölfen and Juan-Manuel García-Ruiz
Crystals 2019, 9(3), 157; https://doi.org/10.3390/cryst9030157 - 18 Mar 2019
Cited by 10 | Viewed by 4118
Abstract
The formation of a polymer protection layer around fragile mineral architectures ensures that structures stay intact even after treatments that would normally destroy them going along with a total loss of textural information. Here we present a strategy to preserve the shape of [...] Read more.
The formation of a polymer protection layer around fragile mineral architectures ensures that structures stay intact even after treatments that would normally destroy them going along with a total loss of textural information. Here we present a strategy to preserve the shape of silica-carbonate biomorphs with polymers. This method converts non-hybrid inorganic-inorganic composite materials such a silica/carbonate biomorphs into hybrid organic/carbonate composite materials similar to biominerals. Full article
(This article belongs to the Special Issue Biological Crystallization)
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49 pages, 9954 KiB  
Review
Crystallochemical Design of Huntite-Family Compounds
by Galina M. Kuz’micheva, Irina A. Kaurova, Victor B. Rybakov and Vadim V. Podbel’skiy
Crystals 2019, 9(2), 100; https://doi.org/10.3390/cryst9020100 - 15 Feb 2019
Cited by 24 | Viewed by 5194
Abstract
Huntite-family nominally-pure and activated/co-activated LnM3(BO3)4 (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties [...] Read more.
Huntite-family nominally-pure and activated/co-activated LnM3(BO3)4 (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties depending on a composition and crystal structure. The purpose of the work is to establish stability regions for the rare-earth orthoborates in crystallochemical coordinates (sizes of Ln and M ions) based on their real compositions and space symmetry depending on thermodynamic, kinetic, and crystallochemical factors. The use of diffraction structural techniques to study single crystals with a detailed analysis of diffraction patterns, refinement of crystallographic site occupancies (real composition), and determination of structure–composition correlations is the most efficient and effective option to achieve the purpose. This approach is applied and shown primarily for the rare-earth scandium borates having interesting structural features compared with the other orthoborates. Visualization of structures allowed to establish features of formation of phases with different compositions, to classify and systematize huntite-family compounds using crystallochemical concepts (structure and superstructure, ordering and disordering, isostructural and isotype compounds) and phenomena (isomorphism, morphotropism, polymorphism, polytypism). Particular attention is paid to methods and conditions for crystal growth, affecting a crystal real composition and symmetry. A critical analysis of literature data made it possible to formulate unsolved problems in materials science of rare-earth orthoborates, mainly scandium borates, which are distinguished by an ability to form internal and substitutional (Ln and Sc atoms), unlimited and limited solid solutions depending on the geometric factor. Full article
(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)
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16 pages, 3290 KiB  
Review
Recent Advances on Carrier and Exciton Self-Trapping in Strontium Titanate: Understanding the Luminescence Emissions
by Miguel L. Crespillo, Joseph T. Graham, Fernando Agulló-López, Yanwen Zhang and William J. Weber
Crystals 2019, 9(2), 95; https://doi.org/10.3390/cryst9020095 - 13 Feb 2019
Cited by 35 | Viewed by 6108
Abstract
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and [...] Read more.
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and exciton self-trapping on the luminescence emissions under a variety of excitation sources with special emphasis on experiments with laser pulses and energetic ion-beams. In spite of the extensive research effort, a definitive identification of such localized states, as well as a suitable understanding of their operative light emission mechanisms, has remained lacking or controversial. However, promising advances have been recently achieved and are the objective of the present review. In particular, significant theoretical advances in the understanding of electron and hole self-trapping are discussed. Also, relevant experimental advances in the kinetics of light emission associated with electron-hole recombination have been obtained through time-resolved experiments using picosecond (ps) laser pulses. The luminescence emission mechanisms and the light decay processes from the self-trapped excitons are also reviewed. Recent results suggest that the blue emission at 2.8 eV, often associated with oxygen vacancies, is related to a transition from unbound conduction levels to the ground singlet state of the STE. The stabilization of small electron polarons by oxygen vacancies and its connection with luminescence emission are discussed in detail. Through ion-beam irradiation experiments, it has recently been established that the electrons associated with the vacancy constitute electron polaron states (Ti3+) trapped in the close vicinity of the empty oxygen sites. These experimental results have allowed for the optical identification of the oxygen vacancy center through a red luminescence emission centered at 2.0 eV. Ab-initio calculations have provided strong support for those experimental findings. Finally, the use of Cr-doped STO has offered a way to monitor the interplay between the chromium centers and oxygen vacancies as trapping sites for the electron and hole partners resulting from the electronic excitation. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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29 pages, 9219 KiB  
Review
Inorganic, Organic, and Perovskite Halides with Nanotechnology for High–Light Yield X- and γ-ray Scintillators
by Francesco Maddalena, Liliana Tjahjana, Aozhen Xie, Arramel, Shuwen Zeng, Hong Wang, Philippe Coquet, Winicjusz Drozdowski, Christophe Dujardin, Cuong Dang and Muhammad Danang Birowosuto
Crystals 2019, 9(2), 88; https://doi.org/10.3390/cryst9020088 - 8 Feb 2019
Cited by 165 | Viewed by 17609
Abstract
Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The [...] Read more.
Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The combination of high–light yield and fast response can be found in Ce 3 + , Pr 3 + and Nd 3 + lanthanide-doped scintillators while the maximum light yield conversion of 100,000 photons/MeV can be found in Eu 3 + doped SrI 2 . However, the fabrication of those lanthanide-doped scintillators is inefficient and expensive as it requires high-temperature furnaces. A self-grown single crystal using solution processes is already introduced in perovskite photovoltaic technology and it can be the key for low-cost scintillators. A novel class of materials in scintillation includes lead halide perovskites. These materials were explored decades ago due to the large X-ray absorption cross section. However, lately lead halide perovskites have become a focus of interest due to recently reported very high photoluminescence quantum yield and light yield conversion at low temperatures. In principle, 150,000–300,000 photons/MeV light yields can be proportional to the small energy bandgap of these materials, which is below 2 eV. Finally, we discuss the extraction efficiency improvements through the fabrication of the nanostructure in scintillators, which can be implemented in perovskite materials. The recent technology involving quantum dots and nanocrystals may also improve light conversion in perovskite scintillators. Full article
(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Models for Better Performances)
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18 pages, 6120 KiB  
Article
Critical Evaluation of Organic Thin-Film Transistor Models
by Markus Krammer, James W. Borchert, Andreas Petritz, Esther Karner-Petritz, Gerburg Schider, Barbara Stadlober, Hagen Klauk and Karin Zojer
Crystals 2019, 9(2), 85; https://doi.org/10.3390/cryst9020085 - 6 Feb 2019
Cited by 20 | Viewed by 6016
Abstract
The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters [...] Read more.
The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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9 pages, 3228 KiB  
Article
Liquid-Phase Epitaxial Growth and Characterization of Nd:YAl3(BO3)4 Optical Waveguides
by Yi Lu, Peter Dekker and Judith M. Dawes
Crystals 2019, 9(2), 79; https://doi.org/10.3390/cryst9020079 - 1 Feb 2019
Cited by 5 | Viewed by 3700
Abstract
We investigated the fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched, un-doped yttrium aluminum borate substrates. We observed the [...] Read more.
We investigated the fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched, un-doped yttrium aluminum borate substrates. We observed the refractive index contrast of the doped and un-doped crystal layers via differential interference contrast microscopy. In addition, characterization by X-ray powder diffraction, optical absorption and luminescence spectra demonstrated the crystal quality, uniformity and optical guiding of the resulting thin films. Full article
(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)
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18 pages, 18471 KiB  
Review
Emerging Perovskite Nanocrystals-Enhanced Solid-State Lighting and Liquid-Crystal Displays
by Ziqian He, Caicai Zhang, Yajie Dong and Shin-Tson Wu
Crystals 2019, 9(2), 59; https://doi.org/10.3390/cryst9020059 - 22 Jan 2019
Cited by 54 | Viewed by 8393
Abstract
Recent advances in perovskite nanocrystals-enhanced solid-state lighting (SSL) and liquid-crystal displays (LCDs) are reviewed. We first discuss the development, optical properties, and stability issue of materials, and then we evaluate the performance of SSL and LCDs with perovskite downconverters adopted. In SSL performance [...] Read more.
Recent advances in perovskite nanocrystals-enhanced solid-state lighting (SSL) and liquid-crystal displays (LCDs) are reviewed. We first discuss the development, optical properties, and stability issue of materials, and then we evaluate the performance of SSL and LCDs with perovskite downconverters adopted. In SSL performance evaluation, we investigate the fitting-curve effect in calculations and optimizations where simple Gaussian fitting and precise fitting are compared in detail, and we further optimize for highly efficient, good color-rendering, and human-healthy SSL sources. For LCD performance evaluation, we study the intrinsic tradeoffs between total light efficiency and color gamut coverage. Through optimizations using real line shapes, Rec. 2020 standard coverage as large as 92.8% can be achieved through hybrid integration. Finally, we briefly discuss two future challenges: materials development and device integration. We believe the emerging perovskite nanocrystals are highly promising for next-generation SSL and LCDs. Full article
(This article belongs to the Special Issue Advanced LED Solid-State Lighting Optics)
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18 pages, 3517 KiB  
Article
Spatio-temporal Investigations of the Incomplete Spin Transition in a Single Crystal of [Fe(2-pytrz)2{Pt(CN)4}]·3H2O: Experiment and Theory
by Houcem Fourati, Guillaume Bouchez, Miguel Paez-Espejo, Smail Triki and Kamel Boukheddaden
Crystals 2019, 9(1), 46; https://doi.org/10.3390/cryst9010046 - 16 Jan 2019
Cited by 15 | Viewed by 3998
Abstract
Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz) 2 {Pt(CN) 4 }]·3H 2 O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, [...] Read more.
Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz) 2 {Pt(CN) 4 }]·3H 2 O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, high-spin low-spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete spin transition, the present transformation involves smaller volume changes at the transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this spin transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this spin transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations. Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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10 pages, 3859 KiB  
Article
Tripling the Optical Efficiency of Color-Converted Micro-LED Displays with Funnel-Tube Array
by Fangwang Gou, En-Lin Hsiang, Guanjun Tan, Yi-Fen Lan, Cheng-Yeh Tsai and Shin-Tson Wu
Crystals 2019, 9(1), 39; https://doi.org/10.3390/cryst9010039 - 14 Jan 2019
Cited by 54 | Viewed by 10382
Abstract
Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density [...] Read more.
Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density of color conversion materials. With funnel-tube array, the optical efficiency of the color-converted micro-LED display can be improved by ~3X, while the crosstalk is eliminated. After optimization of the tapper angle, the ambient contrast ratio is also improved due to higher light intensity. Full article
(This article belongs to the Special Issue Advanced LED Solid-State Lighting Optics)
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16 pages, 667 KiB  
Review
Peculiarities of Protein Crystal Nucleation and Growth
by Christo N. Nanev
Crystals 2018, 8(11), 422; https://doi.org/10.3390/cryst8110422 - 8 Nov 2018
Cited by 11 | Viewed by 4992
Abstract
This paper reviews investigations on protein crystallization. It aims to present a comprehensive rather than complete account of recent studies and efforts to elucidate the most intimate mechanisms of protein crystal nucleation. It is emphasized that both physical and biochemical factors are at [...] Read more.
This paper reviews investigations on protein crystallization. It aims to present a comprehensive rather than complete account of recent studies and efforts to elucidate the most intimate mechanisms of protein crystal nucleation. It is emphasized that both physical and biochemical factors are at play during this process. Recently-discovered molecular scale pathways for protein crystal nucleation are considered first. The bond selection during protein crystal lattice formation, which is a typical biochemically-conditioned peculiarity of the crystallization process, is revisited. Novel approaches allow us to quantitatively describe some protein crystallization cases. Additional light is shed on the protein crystal nucleation in pores and crevices by employing the so-called EBDE method (equilibration between crystal bond and destructive energies). Also, protein crystal nucleation in solution flow is considered. Full article
(This article belongs to the Special Issue Biological Crystallization)
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14 pages, 2116 KiB  
Article
NMR Crystallography of the Polymorphs of Metergoline
by Jiri Czernek, Martina Urbanova and Jiri Brus
Crystals 2018, 8(10), 378; https://doi.org/10.3390/cryst8100378 - 25 Sep 2018
Cited by 16 | Viewed by 4352
Abstract
Two polymorphs of the drug compound metergoline (C25H29N3O2) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum [...] Read more.
Two polymorphs of the drug compound metergoline (C25H29N3O2) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum chemical calculations that were performed for molecular crystals. In this way, it was possible to assign the total of 40 1H–13C correlation pairs in a highly complex system, namely, in the dynamically disordered polymorph with two independent molecules in the unit cell of a large volume of 4234 Å3. For the simpler polymorph, which exhibits only small-amplitude motions and has just one molecule in the unit cell with a volume of 529.0 Å3, the values of the principal elements of the 13C chemical shift tensors were measured. Additionally, for this polymorph, a set of crystal structure predictions were generated, and the {13C, 1H} isotropic and 13C anisotropic chemical shielding data were computed while using the gauge-including projector augmented-wave approach combined with the “revised Perdew-Burke-Ernzerhof“ exchange-correlation functional (GIPAW-RPBE). The experimental and theoretical results were combined in an application of the newly developed strategy to polymorph discrimination. This research thus opens up new routes towards more accurate characterization of the polymorphism of drug formulations. Full article
(This article belongs to the Special Issue NMR Crystallography)
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26 pages, 4591 KiB  
Review
The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds
by Simon Steinberg and Richard Dronskowski
Crystals 2018, 8(5), 225; https://doi.org/10.3390/cryst8050225 - 18 May 2018
Cited by 227 | Viewed by 17247
Abstract
Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the [...] Read more.
Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the Crystal Orbital Hamilton Population (COHP) method has been established as an efficient and reliable tool to extract the chemical-bonding information based on electronic-structure calculations of various quantum-chemical types. In this review, we present a brief introduction into the theoretical background of the COHP method and illustrate the latter by diverse applications, in particular by looking at representatives of the class of (polar) intermetallic compounds, usually considered as “black sheep” in the light of valence-electron counting schemes. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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19 pages, 44833 KiB  
Article
Tuning of Luminescent and Magnetic Properties via Metal Doping of Zn-BTC Systems
by Taoguang Qu, Qiang Wei, Carlos Ordonez, Jennifer Lindline, Michael Petronis, Marina S. Fonari and Tatiana Timofeeva
Crystals 2018, 8(4), 162; https://doi.org/10.3390/cryst8040162 - 8 Apr 2018
Cited by 7 | Viewed by 6071
Abstract
In order to assess how metal doping affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me2NH2+} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M [...] Read more.
In order to assess how metal doping affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me2NH2+} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M1-M2-BTC}{Me2NH2+} (M1 = Co, Cu; M2 = Ni, Co) were synthesized. Trace amounts of different metals were doped via addition of another metal salt during the synthetic process. All compounds retained the same crystal structure as that of the parent {Zn-BTC}{Me2NH2+} MOF, which was supported by single crystal and powder X-ray diffraction studies. Thermal Gravimetric Analysis (TGA) of these compounds also revealed that all MOFs had similar stability up to ~450 °C. Solid state photoluminescent studies indicated that {Zn-Mn-BTC}{Me2NH2+}, {Zn-Cd-BTC}{Me2NH2+}, and {Zn-Ca-BTC}{Me2NH2+} had a significant red shifting effect compared to the original {Zn-BTC}{Me2NH2+} MOF. Applications of this doping method to other MOF systems can provide an efficient way to tune the luminescence of such systems, and to obtain a desired wavelength for several applications such as sensors and white light LED materials. Because Zn, Co, Cu, Ni, Mg have magnetic properties, the effect of the doping metal atom on the magnetism of the {Zn-BTC}{Me2NH2+} networks was also studied. To characterize the magnetic behavior of the synthesized MOFs, we conducted low-temperature (10 K) saturation remanence experiments in a 3 Tesla applied field, with the principal goal of identifying the domain state of the synthesized materials (Zn, Zn-Co, Zn-Cu-Co, Zn-Cu-Ni, Zn-Mg, Zn-Mn, Zn-Ni-Co, Zn-Ni). During room/low temperature saturation magnetization experiments, Zn, Zn-Co, Zn-Cu-Co, and Zn-Cu-Ni systems yielded data indicative of superparamagnetic behavior, yet during zero field and field cooled experiments Zn-Co showed a slight paramagnetic effect, Zn showed no temperature dependence on warming and Zn-Cu-Co and Zn-Cu-Ni demonstrated only a slight temperature dependence on warming. These behaviors are consistent with ferromagnetic ordering. Zero field and field cooled experiments indicate that Zn-Mg and Zn-Ni have a ferromagnetic ordering and Zn-Mn and Zn-Ni-Co show paramagnetic ordering behavior. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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13 pages, 14797 KiB  
Review
Radiation Damage in Macromolecular Crystallography—An Experimentalist’s View
by Helena Taberman
Crystals 2018, 8(4), 157; https://doi.org/10.3390/cryst8040157 - 4 Apr 2018
Cited by 15 | Viewed by 8072
Abstract
Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K), [...] Read more.
Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K), which can lead to incorrect biological conclusions being drawn from the resulting structure, or even prevent structure solution entirely. Investigation of mitigation strategies and the effects caused by radiation damage has been extensive over the past fifteen years. Here, recent understanding of the physical and chemical phenomena of radiation damage is described, along with the global effects inflicted on the collected data and the specific effects observed in the solved structure. Furthermore, this review aims to summarise the progress made in radiation damage studies in macromolecular crystallography from the experimentalist’s point of view and to give an introduction to the current literature. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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15 pages, 3401 KiB  
Article
Intra-/Intermolecular Bifurcated Chalcogen Bonding in Crystal Structure of Thiazole/Thiadiazole Derived Binuclear (Diaminocarbene)PdII Complexes
by Alexander S. Mikherdov, Alexander S. Novikov, Mikhail A. Kinzhalov, Andrey A. Zolotarev and Vadim P. Boyarskiy
Crystals 2018, 8(3), 112; https://doi.org/10.3390/cryst8030112 - 27 Feb 2018
Cited by 49 | Viewed by 5563
Abstract
The coupling of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with 4-phenylthiazol-2-amine in molar ratio 2:3 at RT in CH2Cl2 leads to binuclear (diaminocarbene)PdII complex 3c. The complex was characterized by HRESI+-MS, 1H NMR spectroscopy, and its structure was elucidated by single-crystal XRD. Inspection of [...] Read more.
The coupling of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with 4-phenylthiazol-2-amine in molar ratio 2:3 at RT in CH2Cl2 leads to binuclear (diaminocarbene)PdII complex 3c. The complex was characterized by HRESI+-MS, 1H NMR spectroscopy, and its structure was elucidated by single-crystal XRD. Inspection of the XRD data for 3c and for three relevant earlier obtained thiazole/thiadiazole derived binuclear diaminocarbene complexes (3a EYOVIZ; 3b: EYOWAS; 3d: EYOVOF) suggests that the structures of all these species exhibit intra-/intermolecular bifurcated chalcogen bonding (BCB). The obtained data indicate the presence of intramolecular S•••Cl chalcogen bonds in all of the structures, whereas varying of substituent in the 4th and 5th positions of the thiazaheterocyclic fragment leads to changes of the intermolecular chalcogen bonding type, viz. S•••π in 3a,b, S•••S in 3c, and S•••O in 3d. At the same time, the change of heterocyclic system (from 1,3-thiazole to 1,3,4-thiadiazole) does not affect the pattern of non-covalent interactions. Presence of such intermolecular chalcogen bonding leads to the formation of one-dimensional (1D) polymeric chains (for 3a,b), dimeric associates (for 3c), or the fixation of an acetone molecule in the hollow between two diaminocarbene complexes (for 3d) in the solid state. The Hirshfeld surface analysis for the studied X-ray structures estimated the contributions of intermolecular chalcogen bonds in crystal packing of 3a–d: S•••π (3a: 2.4%; 3b: 2.4%), S•••S (3c: less 1%), S•••O (3d: less 1%). The additionally performed DFT calculations, followed by the topological analysis of the electron density distribution within the framework of Bader’s theory (AIM method), confirm the presence of intra-/intermolecular BCB S•••Cl/S•••S in dimer of 3c taken as a model system (solid state geometry). The AIM analysis demonstrates the presence of appropriate bond critical points for these interactions and defines their strength from 0.9 to 2.8 kcal/mol indicating their attractive nature. Full article
(This article belongs to the Special Issue Chalcogen Bonding in Crystalline and Catalyst Materials)
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16 pages, 9480 KiB  
Review
Multifunctional Aromatic Carboxylic Acids as Versatile Building Blocks for Hydrothermal Design of Coordination Polymers
by Jinzhong Gu, Min Wen, Xiaoxiao Liang, Zifa Shi, Marina V. Kirillova and Alexander M. Kirillov
Crystals 2018, 8(2), 83; https://doi.org/10.3390/cryst8020083 - 3 Feb 2018
Cited by 105 | Viewed by 8225
Abstract
Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile [...] Read more.
Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile carboxylic acid building blocks have become very promising toward the hydrothermal synthesis of metal-organic architectures possessing distinct structural features, topologies, and functional properties. Thus, the main aim of this mini-review has been to motivate further research toward the synthesis and application of coordination polymers assembled from polycarboxylic acids with phenyl-pyridine or biphenyl cores. The importance of different reaction parameters and hydrothermal conditions on the generation and structural types of CPs or MOFs has also been highlighted. The influence of the type of main di- or tricarboxylate ligand, nature of metal node, stoichiometry and molar ratio of reagents, temperature, and presence of auxiliary ligands or templates has been showcased. Selected examples of highly porous or luminescent CPs, compounds with unusual magnetic properties, and frameworks for selective sensing applications have been described. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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12 pages, 3731 KiB  
Article
A Graphene-Based Microfluidic Platform for Electrocrystallization and In Situ X-ray Diffraction
by Shuo Sui, Yuxi Wang, Christos Dimitrakopoulos and Sarah L. Perry
Crystals 2018, 8(2), 76; https://doi.org/10.3390/cryst8020076 - 1 Feb 2018
Cited by 13 | Viewed by 6505
Abstract
Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a [...] Read more.
Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a stable sample environment over time. We characterize different methods for fabricating graphene electrodes, and validate the electrical capabilities of our device through the use of methyl viologen, a redox-sensitive dye. Proof-of-concept electrocrystallization experiments using an internal electric field at constant potential were performed using hen egg-white lysozyme (HEWL) as a model system. We observed faster nucleation and crystal growth, as well as a higher signal-to-noise for diffraction data obtained from crystals prepared in the presence of an applied electric field. Although this work is focused on the electrocrystallization of proteins for structural biology, we anticipate that this technology should also find utility in a broad range of both X-ray technologies and other applications of microfluidic technology. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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14 pages, 4990 KiB  
Article
Prussian Blue Analogue Mesoframes for Enhanced Aqueous Sodium-ion Storage
by Huiyun Sun, Wei Zhang and Ming Hu
Crystals 2018, 8(1), 23; https://doi.org/10.3390/cryst8010023 - 7 Jan 2018
Cited by 19 | Viewed by 8085
Abstract
Mesostructure engineering is a potential avenue towards the property control of coordination polymers in addition to the traditional structure design on an atomic/molecular scale. Mesoframes, as a class of mesostructures, have short diffusion pathways for guest species and thus can be an ideal [...] Read more.
Mesostructure engineering is a potential avenue towards the property control of coordination polymers in addition to the traditional structure design on an atomic/molecular scale. Mesoframes, as a class of mesostructures, have short diffusion pathways for guest species and thus can be an ideal platform for fast storage of guest ions. We report a synthesis of Prussian Blue analogue mesoframes by top-down etching of cubic crystals. Scanning and transmission electron microscopy revealed that the surfaces of the cubic crystals were selectively removed by HCl, leaving the corners, edges, and the cores connected together. The mesoframes were used as a host for the reversible insertion of sodium ions with the help of electrochemistry. The electrochemical intercalation/de-intercalation of Na+ ions in the mesoframes was highly reversible even at a high rate (166.7 C), suggesting that the mesoframes could be a promising cathode material for aqueous sodium ion batteries with excellent rate performance and cycling stability. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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