固体核磁共振结合密度泛函理论计算研究SSZ-39分子筛的钠离子落位与铝分布

具有AEI结构的SSZ-39分子筛的骨架外阳离子落位和铝分布对其催化性能影响显著.AEI笼中有三个结晶学不等价位，且铝取代T位具有一定的倾向性.本文结合固体核磁共振（NMR）技术（²⁷Al/²³Na MQ MAS NMR），以及密度泛函理论（DFT）计算，研究了不同硅铝比Na-SSZ-39分子筛中的Na⁺落位和铝分布.在孤立铝分布的情况下，铝原子优先占据于T3位，Na⁺主要落位于AEI笼中的SIIa0和SIII'a0位点上，其中SIII'a0位点的优先度较高，此外少部分Na⁺还落位于六棱柱内部的SIa0.当铝对存在时，AlSiSiAl分布的铝对占据六元环的对位（T3-T3），对应的Na⁺分别落位于SIIa1和SⅢ'a1位点.随着分子筛结构的部分破坏，游离的Na⁺可能形成明显的SIII'b位点.本文可加深对SSZ-39分子筛构效关系的理解，为更好地调控催化性能奠定基础.     

单斜ZnP2负极材料的锂化机理及性能

过渡金属磷化物电位低且比容量高, 是有发展前景的锂离子电池(LIBs)负极材料. 其中, ZnP₂属于双活性负极材料, Zn与P都能与Li⁺发生反应, 储Li⁺性能更具有竞争力. 但是, 对于ZnP₂的锂化机理及产物尚不明确. 采用第一性原理计算和电化学测试方法研究了ZnP₂的电子性质和电化学性能, 通过理论计算和实验测试相结合阐述了ZnP₂的锂化机制. 首先, 以密度泛函理论(DFT)计算揭示了ZnP₂的锂化机理、Li⁺扩散路径、势垒和理论比容量(1477 mAh/g). 其次, 通过直流电弧等离子体法及固相烧结法合成ZnP₂, 并测试其首圈放电曲线, 显示放电容量为1439 mAh/g, 与理论计算结果相近. 此外, 薄膜X射线衍射(XRD)检测最终产物成分为LiZn和Li₃P, 与DFT计算结果一致.     

The Decisive Role of Spin States and Spin Coupling in Dictating Selective O2 Adsorption in Chromium(II) Metal–Organic Frameworks**

The coordinatively unsaturated chromium(II)-based Cr₃[(Cr₄Cl)₃(BTT)₈]₂ (Cr−BTT; BTT³⁻=1,3,5-benzenetristetrazolate) metal–organic framework (MOF) has been shown to exhibit exceptional selectivity towards adsorption of O₂ over N₂/H₂. Using periodic density functional theory (DFT) calculations, we attempted to decipher the origin of this puzzling selectivity. By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas-bound MOFs [(Cr₄(X)₄Cl)₃(BTT)₈]³⁻ (X=O₂, N₂, and H₂), we unequivocally established the role of spin states and spin coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The binding of O₂ to the MOF follows an electron-transfer mechanism resulting in a Cr^III superoxo species (O₂^.−) with a very strong antiferromagnetic coupling between the two centers, whereas N₂/H₂ are found to weakly interact with the metal center and hence only slightly perturb the associated coupling constants. Although the gas-bound and unbound MOFs have an S=0 ground state (GS), the nature of spin the configurations and the associated magnetic exchanges are dramatically different. The binding energy and the number of oxygen molecules that can favorably bind to the Cr center were found to vary with respect to the spin state, with a significant energy margin (47.6 kJ mol⁻¹). This study offers a hitherto unknown strategy of using spin state/spin couplings to control gas adsorption selectivity in MOFs.     

Key Role of a-Top CO on Terrace Sites of Metallic Pd Clusters for CO Oxidation

Pd-based catalysts are the most widely used for CO oxidation because of their outstanding catalytic activity and thermal stability. However, fundamental understanding of the detailed catalytic processes occurring on Pd-based catalysts under realistic conditions is still lacking. In this study, we investigated CO oxidation on metallic Pd clusters supported on Al₂O₃ and SiO₂. High-angle annular dark-field scanning transmission electron microscopy revealed the formation of similar-sized Pd clusters on Al₂O₃ and SiO₂. In contrast, CO chemisorption analysis indicated a gradual change in the dispersion of Pd (from 0.79 to 0.2) on Pd/Al₂O₃ and a marginal change in the dispersion (from 0.4 to 0.24) on Pd/SiO₂ as the Pd loading increased from 0.27 to 5.5 wt %; these changes were attributed to differences in the metal-support interactions. Diffuse reflectance infrared Fourier-transform spectroscopy revealed that fewer a-top CO species were present in Pd supported on Al₂O₃ than those in Pd supported on SiO₂, which is related to the morphological differences in the metallic Pd clusters on these two supports. Despite the different dispersion profiles and surface characteristics of Pd, O₂ titration demonstrated that linearly bound CO (with an infrared signal at 2090 cm⁻¹) reacted first with oxygen in the case of CO-saturated Pd on Al₂O₃ and SiO₂, which suggests that a-top CO on the terrace site plays an important role in CO oxidation. The experimental observations were corroborated by periodic density functional calculations, which confirmed that CO oxidation on the (111) terrace sites is most plausible, both kinetically and thermodynamically, compared to that on the edge or corner sites. This study will deepen the fundamental understanding of the effect of Pd clusters on CO oxidation under reaction conditions.     

Density functional theory study on sensing properties of g-C3N4 sheet to atmospheric gasses: Role of zigzag and armchair edges

The ability of the polymer-based graphitic carbon nitride (g-C₃N₄) as a gas sensor toward NO, NO₂, CO, CO₂, SO₂, SO₃, and O₂ gasses is assessed using density functional theory (DFT) calculations in terms of energetic and electronic transport characteristics. In particular, this study is aimed to explore the role of zigzag and armchair edges of the g-C₃N₄ sheet on sensing performances. The electronic properties of adsorption systems, such as Bader charge analysis, band gaps, work function, and density of states (DOS), are used to understand the interaction between the adsorbed gas molecules and the g-C₃N₄ sheet. Our calculated results indicate that SOx (SO₃ and SO₂) gasses have higher adsorption energies on the g-C₃N₄ sheet than other gasses. Furthermore, the transport properties, such as current–voltage (I-V) and resistance-voltage (R-V) curves along the zigzag and armchair directions are calculated using the non-equilibrium Green's function (NEGF) method to understand the performance of the g-C₃N₄ sheet as a prominent conductive/resistive sensor. The I-V/R-V results indicate that the zigzag g-C₃N₄ sheet has excellent sensing ability toward SOx gasses at low applied voltages. However, the presence of H₂O degrades the sensing performance of the armchair g-C₃N₄ sheet. Theoretical recovery time has also been calculated to evaluate the reusability of g-C₃N₄ sheet-based gas sensors. Our results reveal that the zigzag g-C₃N₄ sheet-based sensing device has a remarkably high sensitivity (>300%) and selectivity toward SOx gasses and has the potential to work in a complex environment.     

Structure determination and magnetic studies of triazole chelated Co(II) coordination polymers

Two cobalt(II) halide complexes with 1,2,4-triazole as a ligand were synthesized. Their structures were determined by extended x-ray absorption fine structure (EXAFS) and powder x-ray diffraction (XRD). Both complexes [Co(Htrz)Cl₂]_n ( 1 ) and {[Co(Htrz)₂(trz)]BF₄}_n ( 2 ) form one-dimensional polymeric chain and the distances of Co⋯Co are 3.3521(2) Å and 3.8629(2) Å, respectively. The Htrz and Cl⁻ are bridging ligands to connect two Co(II) ions in 1 , and the local environment of Co site is in a distorted octahedron with {CoN₂Cl₄} core. In complex 2 , two Htrz and one trz are bridging ligands to connect two Co(II) ions, and the local geometry of Co is in a pseudo octahedron with {CoN₆} core. The analysis of Co L_II,III-edge XAS indicates that the Co(II) of both complexes are at high spin state with t_2g⁵e_g² configuration and the crystal field strength (10Dq) is about 1.2 eV. The broken-symmetry DFT calculations indicate that antiferromagnetic coupling state of Co⋯Co is the most stable state in both complexes; and the coupling constants of 1 and 2 are −0.32 cm⁻¹ and −3.70 cm⁻¹, respectively. Based on the distances of Co⋯Co and coupling constants, such antiferromagnetic interaction is achieved through triazole ligands.     

Boron-Cluster Embedded Necklace-Shaped Nanohoops

The combination of carbon-based nanohoops with other functional organic molecular structures should lead to the design of new molecular configurations with interesting properties. Here, necklace-like nanohoops embedded with carborane were synthesized for the first time. The unique deboronization of o-carborane has led to the facile preparation of ionic nanohoop compounds. Nanohoops functionalized by nido-o-carborane show excellent fluorescence emission, with a solution quantum yield of up to 90.0 % in THF and a solid-state quantum efficiency of 87.3 %, which opens an avenue for the applications of the nanohoops in OLEDs and bioimaging.     

Effect of solvation on the molecular structure,vibrational assignment,nature of bonding,and the antiviral drug-like potential of troxerutin against HBV proteins

Drugs used in the management of Hepatitis B virus (HBV) infection are largely based on nucleosides or their analogues and these have several side-effects. These drugs only inhibit viral replication, cannot eliminate cccDNA and present with serious long-term effects. Hence, researchers are now searching for potential targets that present with less side-effect and are more effective. The study was aimed at evaluating and comparing the antiviral drug-like potential of troxerutin against various HBV proteins and entecavir. In this study, troxerutin was purified, synthesized and characterized using ¹H NMR, ¹³C NMR and FT-IR. In addition, detailed investigation using density functional theory (DFT), and in-silico molecular docking of troxerutin and entecavir against various HBV proteins were conducted. The spectral analysis (NMR and FT-IR) confirmed the presence of characteristic functional groups with the presence of C–H, C–C and OH bonds/vibrations. Docking result showed excellent binding affinities across all four HBV proteins with the bindings scores for troxerutin (−6.3 to −7.1 kcal/mol) that was similar to those of entecavir (−6.2 to −7.8 kcal/mol). Unlike entecavir, troxerutin did not show any predicted hepatotoxicity but appears to be immunotoxic with an LD₅₀ value of 1000 mg/kg. Given the anti-HBV potential of troxerutin this study has revealed, further in-vivo and in-vitro studies are needed to validate these findings.     

Computational design of rasagiline derivatives: Searching for enhanced antioxidant capability

A set of new rasagiline derivatives is presented. They were designed to be antioxidant compounds with the potential to be used for treating neurodegenerative disorders. They are expected to be multifunctional molecules that can help reduce oxidative stress, which is thought to contribute to neurodegenerative disorders. The CADMA-Chem computational protocol was used to produce rasagiline derivatives and to evaluate their likeliness as oral drugs and antioxidants. Three of them were identified as the most promising ones. They are proposed to be better free radical scavengers than rasagiline. In addition, they are expected to keep the parent's molecule neuroprotective capability. Hopefully, the results presented here would promote further experimental and theoretical investigations on these compounds.