Effect of h-BN Support on Photoluminescence of ZnO Nanoparticles: Experimental and Theoretical Insight

Herein we report a simple and easily scalable method for fabricating ZnO/h-BN composites with tunable photoluminescence (PL) characteristics. The h-BN support significantly enhances the ultraviolet (UV) emission of ZnO nanoparticles (NPs), which is explained by the ZnO/h-BN interaction and the change in the electronic structure of the ZnO surface. When h-BN NPs are replaced with h-BN microparticles, the PL in the UV region increases, which is accompanied by a decrease in visible light emission. The dependence of the PL properties of ZnO NPs on the thickness of h-BN carriers, observed for the first time, is explained by a change in the dielectric constant of the support. A quantum chemical analysis of the influence of the h-BN thickness on the electron density redistribution at the wZnO/h-BN interface and on the optical properties of the wZnO/h-BN composites was carried out. Density functional theory (DFT) calculations show the appearance of hybridization at the h-BN/wZnO interface and an increase in the intensity of absorption peaks with an increase in the number of h-BN layers. The obtained results open new possibilities for controlling the properties of ZnO/h-BN heterostructures for various optical applications.     

Investigation of PbSnTeSe High-Entropy Thermoelectric Alloy: A DFT Approach

Thermoelectric materials have attracted extensive attention because they can directly convert waste heat into electric energy. As a brand-new method of alloying, high-entropy alloys (HEAs) have attracted much attention in the fields of materials science and engineering. Recent researches have found that HEAs could be potentially good thermoelectric (TE) materials. In this study, special quasi-random structures (SQS) of PbSnTeSe high-entropy alloys consisting of 64 atoms have been generated. The thermoelectric transport properties of the highest-entropy PbSnTeSe-optimized structure were investigated by combining calculations from first-principles density-functional theory and on-the-fly machine learning with the semiclassical Boltzmann transport theory and Green–Kubo theory. The results demonstrate that PbSnTeSe HEA has a very low lattice thermal conductivity. The electrical conductivity, thermal electronic conductivity and Seebeck coefficient have been evaluated for both n-type and p-type doping. N-type PbSnTeSe exhibits better power factor (PF = S²σ) than p-type PbSnTeSe because of larger electrical conductivity for n-type doping. Despite high electrical thermal conductivities, the calculated ZT are satisfactory. The maximum ZT (about 1.1) is found at 500 K for n-type doping. These results confirm that PbSnTeSe HEA is a promising thermoelectric material.     

Molecular Dynamic in Ethosuximide Glass Forming Pharmaceutical as Studied by Dielectric Relaxation Spectroscopy

Polymorphism and molecular dynamics of ethosuximide with molecules of left- and right-handed chirality have been studied in detail using dielectric spectroscopy. Density functional theory calculations of molecular conformations and dimer formation were performed to aid the interpretation of measurements. Moving window correlation analysis of the imaginary part of dielectric permittivity spectra allowed us to complete the monotropic system of phases found by the differential scanning calorimetry method. Extra transition connected with freezing-in/activation of slow molecular motions was identified in partially ordered crystal CrI phase. In high-temperature orientationally disordered CrI_h and in low-temperature conformationally disordered CrI_l phases, 2 relaxation processes were detected at frequency range below 10⁵ Hz. In glass of CONDIS CrI_l, β-relaxation was identified.     

Electrochemical and surface studies on chemically modified glucose derivatives as environmentally benign corrosion inhibitors

Three glucose derivatives, namely Ethylenediamine-modified glucose, Tetramethylenediamine-modified glucose, and Hexamethylenediamine-modified glucose with three different carbon chain lengths were synthesized using environmentally benign and low-cost reactants at ambient temperature. The synthesized derivatives were evaluated as inhibitors for mild steel corrosion in 1 M HCl using electrochemical, surface analysis (XPS, AFM and contact angle), as well as computational (DFT) techniques. The obtained results suggest that the synthesized glucose derivatives significantly mitigate the corrosion of mild steel and show a rise in the inhibition efficiency with increasing inhibitor dosage. The inhibitor adsorption obeyed the Langmuir isotherm. The XPS analyses provided an elucidation on the interaction of the inhibitors with the steel substrate. The DFT studies showed that the protonated forms of the inhibitors act more prominently compared to the neutral form. The inhibitor HMG having the alkyl chain with six carbon atoms exhibited the highest inhibition performance of >95% at 22.71 × 10^?5 mol L^?1.     

晶习对辛伐他汀氧化稳定性的影响

目的 分析晶习对辛伐他汀氧化稳定性的影响。方法 将辛伐他汀从不同极性的溶剂混合物中重结晶,制备辛伐他汀的不同晶习,使用电子顺磁共振波谱仪(EPR)表征氧化稳定性,采用密度泛函理论(DFT)方法计算分析氧化位点,使用多晶X射线衍射仪(PXRD)进行晶面检测分析。结果 制备得到辛伐他汀I晶型的薄片状和棒状两种晶习,EPR结果显示棒状晶习氧化稳定性更好,DFT计算显示辛伐他汀氧化位点在辛伐他汀六氢萘片段上,PXRD结果显示薄片状晶习比棒状晶习暴露的氧化位点更多。辛伐他汀晶习不同导致各晶面占比不同,活泼氧化位点的暴露比例不同,活泼氧化位点暴露越多的晶习越不稳定,而将活泼位点更多保护在晶体内部的晶习更加稳定。结论 开发了一种高效、无损的氧化稳定性EPR检测方法,为药物晶习的相关研究提供了新思路和新方法。     

The influence of NH3-attaching on the NMR and NQR parameters in the (6,0) zigzag single-walled BPNTs: a density functional study

The structural properties, NMR and NQR parameters in the pristine and NH₃-attached (6,0) zigzag BPNTs model were calculated using DFT methods in order to evaluate the influence of NH₃-attached on the (6,0) zigzag BPNTs for the first time. Geometry optimizations were carried out at the BLYP, B3LYP/6-31G^* levels of theory using the Gaussian 03 program suites. The chemical shielding (CS) parameters for the sites of various ¹¹B and ³¹P atoms and quadrupole coupling constant (C_Q), and asymmetry parameter (η_Q) at the sites of various ¹¹B nuclei were calculated in the pristine and the NH₃-attached (6,0) zigzag BPNTs model. The values of dipole moments detect notable changes due to direct effect of the NH₃-attached on the BPNTs; however, the tip diameters are slightly significant changed in comparison to the pristine models and the gap energies of the NH₃-attached BPNT do not detect any changes in comparison to the pristine model. For the NH₃-attached BPNT, the NMR values for the ¹¹B₁₄ atom which is directly bonded to the NH₃ molecule and the ³¹P atoms that directly bonded to the ¹¹B₁₄ atom in the BPNT are significantly changed. CS^I parameters of the atoms are increased whereas CS^A parameters of the atoms are decreased. The NQR results showed that in BPNTs, the B atoms at the edges of nanotubes play dominant roles in determining the electronic behaviors of BPNTs and the average value of C_Q (¹¹B) and η_Q for the NH₃-attached (6,0) zigzag BPNTs is further in comparison to the pristine model.     

A cysteine-selective fluorescent probe for the cellular detection of cysteine

A series of coumarin fluorophores (1-3), each bearing a double bond conjugated quinoline unit that can undergo a Michael-type reaction with thiol-containing compounds, is reported. These systems, designed to provide so-called turn-on changes in fluorescence response when exposed to thiols, act as fluorescent chemical sensors for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). In the case of 1, selectivity for Cys over Hcy and GSH is observed, both in terms of analyte-induced signal enhancement and response time. On the basis of fluorescence spectroscopic analyses, DFT calculations, and pH dependent studies this substrate selectivity is ascribed to steric interactions between the substituents on the quinolone units present in 1 and the targeted thiols, as well as to the comparatively lower pK_a value of Cys relative to Hcy and GSH. In aqueous solution, probe 1 was found capable of detecting Cys with a detection limit of 10⁻⁷ m. This system was successfully applied to the fluorescence imaging of intracellular Cys in HepG2 cells.     

Successful prediction of a model pharmaceutical in the fifth blind test of crystal structure prediction

The range of target structures in the fifth international blind test of crystal structure prediction was extended to include a highly flexible molecule, (benzyl-(4-(4-methyl-5-(p-tolylsulfonyl)-1,3-thiazol-2-yl)phenyl)carbamate, as a challenge representative of modern pharmaceuticals. Two of the groups participating in the blind test independently predicted the correct structure. The methods they used are described and contrasted, and the implications of the capability to tackle molecules of this complexity are discussed.