| 1. |
- Halldin Stenlid, Joakim, 1987-, et al.
(författare)
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σ-Holes on Transition Metal Nanoclusters and Their Influence on the Local Lewis Acidity
- 2017
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the molecular interaction behavior of transition metal nanoclusters lies at the heart of their efficient use in, e.g., heterogeneous catalysis, medical therapy and solar energy harvesting. For this purpose, we have evaluated the applicability of the surface electrostatic potential [VS(r)] and the local surface electron attachment energy [ES(r)] properties for characterizing the local Lewis acidity of a series of low-energy TM13 transition metal nanoclusters (TM = Au, Cu, Ru, Rh, Pd, Ir, Pt, Co), including also Pt7Cu6. The clusters have been studied using hybrid Kohn–Sham density functional theory (DFT) calculations. The VS(r) and ES(r), evaluated at 0.001 a.u. isodensity contours, are used to analyze the interactions with H2O. We find that the maxima of VS(r), σ-holes, are either localized or diffuse. This is rationalized in terms of the nanocluster geometry and occupation of the clusters’s, p and d valence orbitals. Our findings motivate a new scheme for characterizing σ-holes as σs (diffuse), σp (localized) or σd (localized) depending on their electronic origin. The positions of the maxima in VS(r) (and minima in ES(r)) are found to coincide with O-down adsorption sites of H2O, whereas minima in VS(r) leads to H-down adsorption. Linear relationships between VS,max (and ES,min) and H2O interaction energies are further discussed.
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| 2. |
- Jha, Piyush Kumar, et al.
(författare)
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An Overview on Magnetic Field and Electric Field interactions with Ice crystalization; Application in case of frozen food
- 2017
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 7:10
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Forskningsöversikt (refereegranskat)abstract
- Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however, this is still under debate in the literature. Static electric field (SEF) has a significant effect on crystallisation; this has been evidenced experimentally and confirmed by the theory. Oscillating magnetic field induces an oscillating electric field and is also expected to interact with water crystallisation. Oscillating electromagnetic fields interact with water, perturb and even disrupt hydrogen bonds, which in turn are thought to increase the degree of supercooling and to generate numerous fine ice crystals. Based on the literature, it seems that the frequency has an influence on the above-mentioned phenomena. This review article summarizes the fundamentals of freezing under magnetic, electric and electromagnetic fields, as well as their applicability and potentials within the food industry.
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| 3. |
- Ali, Sk Imran, et al.
(författare)
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Crystal Structure of the Disordered Non-Centrosymmetric Compound Fe0.43Mo2.56SbO9.5
- 2019
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 degrees C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) angstrom, b = 7.3355(3) angstrom, c = 12.6985(6) angstrom, = 90 degrees. The crystal structure comprises five crystallographically independent M atoms and one Sb3+ atom, M atoms are of two kinds of partially occupied sites Mo6+ and Fe3+. The building blocks consist of [SbO3O0.5O0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O-6] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo-Fe distances. Six (Mo/Fe)O-6 octahedra are connected to form a pseudohexagonal channel. The Sb3+ atom is displaced from the pseudo-six-fold axis.
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| 4. |
- B. Brant Carvalho, Paulo H., et al.
(författare)
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Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures
- 2022
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The high pressure structural behavior of H-2 and Ne clathrate hydrates with approximate composition H-2/Ne center dot~4H(2)O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C-1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C-2 phase (H-2 center dot H2O, filled ice I-c) and ice VIII' takes place. Upon heating to 200 K the CS-II to C-1 transition completes instantly whereas C-1 decomposition appears sluggish also at 200 K. C-1 was observed metastably up to 8 GPa. At 95 K C-1 and C-2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice I-c, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C-2 hydrate and ice VIII'.
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| 5. |
- Bikondoa, Oier, et al.
(författare)
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X-ray photon correlation spectroscopy with coherent nanobeams : A numerical study
- 2020
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photon correlation spectroscopy accesses a wide variety of dynamic phenomena at the nanoscale by studying the temporal correlations among photons that are scattered by a material in dynamical equilibrium when it is illuminated with a coherent X-ray beam. The information that is obtained is averaged over the illuminated area, which is generally of the order of several square microns. We propose here that more local information can be obtained by using nanobeams with great potential for the study of heterogeneous systems and show the feasibility of this approach with the support of numerical simulations.
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| 6. |
- Bildirir, Hakan, 1985
(författare)
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Have covalent organic framework films revealed their full potential?
- 2021
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 11:7
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Forskningsöversikt (refereegranskat)abstract
- Porous organic polymers provide high accessible surface areas, which make them attrac-tive for gas storage, separation, and catalysis. In addition to those classical usage areas, such compounds are particularly interesting for electronic applications since their high dimensional, electron-rich backbone provides advanced electronic and photophysical properties. However, their non-sol-uble nature is a challenge for their processability, especially in the case of film formation, hence their limited utilization in organic electronic devices so far. Nevertheless, there are several techniques presented in the literature to overcome that issue, most of which were on the crystalline porous organic polymers, namely covalent organic frameworks (COFs). In this perspective, the develop-ments on COF film formation and prospects for the improvements are discussed with suggestions to further their performances in organic electronics.
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| 7. |
- Caleman, Carl, et al.
(författare)
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A Perspective on Molecular Structure and Bond-Breaking in Radiation Damage in Serial Femtosecond Crystallography
- 2020
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Ingår i: Crystals. - : MDPI. - 2073-4352. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers (XFELs) have a unique capability for time-resolved studies of protein dynamics and conformational changes on femto- and pico-second time scales. The extreme intensity of X-ray pulses can potentially cause significant modifications to the sample structure during exposure. Successful time-resolved XFEL crystallography depends on the unambiguous interpretation of the protein dynamics of interest from the effects of radiation damage. Proteins containing relatively heavy elements, such as sulfur or metals, have a higher risk for radiation damage. In metaloenzymes, for example, the dynamics of interest usually occur at the metal centers, which are also hotspots for damage due to the higher atomic number of the elements they contain. An ongoing challenge with such local damage is to understand the residual bonding in these locally ionized systems and bond-breaking dynamics. Here, we present a perspective on radiation damage in XFEL experiments with a particular focus on the impacts for time-resolved protein crystallography. We discuss recent experimental and modelling results of bond-breaking and ion motion at disulfide bonding sites in protein crystals.
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| 8. |
- Chayanun, Lert, et al.
(författare)
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Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline
- 2019
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 9:8
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Tidskriftsartikel (refereegranskat)abstract
- The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can be achieved by combining these techniques with simultaneous electrical measurements. Here, we present a system for electrical biasing and current measurement of single nanostructure devices, which has been developed for the NanoMAX beamline at the fourth-generation synchrotron, MAX IV, Sweden. The system was tested on single InP nanowire devices. The mechanical stability was sufficient to collect scanning XRD and XRF maps with a 50 nm diameter focus. The dark noise of the current measurement system was about 3 fA, which allowed fly scan measurements of X-ray beam induced current (XBIC) in single nanowire devices.
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| 9. |
- Dai, Jing, et al.
(författare)
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Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal
- 2019
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Ingår i: Crystals. - : MDPI. - 2073-4352. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution C-13 nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each C-13 spin to its H-1 neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C-H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals.
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| 10. |
- Dai, Jing, et al.
(författare)
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NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals
- 2019
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Ingår i: Crystals. - : MDPI. - 2073-4352. ; 9:10
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Tidskriftsartikel (refereegranskat)abstract
- We report on molecular and local orientational order of a series of imidazolium-based ionic liquid crystals exhibiting layered smectic A mesophase. Materials constituting of 1-dodecyl-3-methylimidazolium cation, and different counter-ions, were investigated. We apply two-dimensional C-13-H-1 dipolar NMR spectroscopy to quantify orientational order of C-H bonds of the organic cation. The experimental data supported the structural model of the interdigitated chains aligned with the smectic layer normal. Molecular order parameter S was found to increase in the anion sequence BF4- < I- < Br- < Cl-. This trend correlates well with ionic radius, negative charge delocalization, and hydrogen-bonding properties of the anions.
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