Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

The coordination ability of the [(ppy)Au(IPr)]²⁺ fragment [ppy = 2-phenylpyridine, IPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl⁻, BF₄⁻, OTf⁻, H₂O, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF₄⁻ and OTf⁻ have very similar coordination ability towards [(ppy)Au(IPr)]²⁺ and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)]²⁺ fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)]²⁺ (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf⁻ and BF₄⁻, in agreement with experiment. Effect of the ancillary ligand substitution demonstrates that the coordination ability of Au(III) is quantitatively strongly affected by the nature of the ligands (even more than the net charge of the complex) and that all the investigated gold fragments coordinate to alkynes more strongly than H₂O. Remarkably, a stabilization of the water-coordinating species with respect to the alkyne-coordinating one can only be achieved within a microsolvation model, which reconciles theory with experiment. All the results reported here suggest that both the Au(III) fragment coordination ability and its proper computational modelling in the experimental conditions are fundamental issues for the design of efficient catalysts.     

A Combined Experimental and Computational Study of Chrysanthemin as a Pigment for Dye-Sensitized Solar Cells

The theoretical study of chrysanthemin (cyanidin 3-glucoside) as a pigment for TiO₂-based dye-sensitized solar cells (DSSCs) was performed with the GAUSSSIAN 09 simulation. The electronic spectra of neutral and anionic chrysanthemin molecules were calculated by density functional theory with B3LYP functional and DGDZVP basis set. A better energy level alignment was found for partially deprotonated molecules of chrysanthemin, with the excited photoelectron having enough energy in order to be transferred to the conduction band of TiO₂ semiconductor in DSSCs. In addition, we used the raw aqueous extracts of roselle (Hibiscus sabdariffa) calyces as the source of chrysanthemin and the extracts with various pH values were tested in DSSCs. The extracts and photosensitized semiconductor layers were characterized by UV-Vis spectroscopy, and DSSCs based on raw extracts were characterized by current density-voltage measurements.     

Synthesis of a Novel Chitosan/Basil Oil Blend and Development of Novel Low Density Poly Ethylene/Chitosan/Basil Oil Active Packaging Films Following a Melt-Extrusion Process for Enhancing Chicken Breast Fillets Shelf-Life

An innovative process for the adsorption of the hydrophobic Basil-Oil (BO) into the hydrophilic food byproduct chitosan (CS) and the development of an advanced low-density polyethylene/chitosan/basil-oil (LDPE/CS_BO) active packaging film was investigated in this work. The idea of this study was the use of the BO as both a bioactive agent and a compatibilizer. The CS was modified to a CS_BO hydrophobic blend via a green evaporation/adsorption process. This blend was incorporated directly in the LDPE to produce films with advanced properties. All the obtained composite films exhibited improved packaging properties. The film with 10% CS_BO content exhibited the best packaging properties, i.e., 33.0% higher tensile stress, 31.0% higher water barrier, 54.3% higher oxygen barrier, and 12.3% higher antioxidant activity values compared to the corresponding values of the LDPE films. The lipid oxidation values of chicken breast fillets which were packaged under vacuum using this film were measured after seven and after fourteen days of storage. These values were found to be lower by around 41% and 45%, respectively, compared with the corresponding lipid oxidation values of pure LDPE film.     

Redox Modulation of the Reactivity and Regioselectivity in Diels–Alder Reaction of Metallofullerene La@C82 with Cyclopentadiene

Modulation of the reactivity of metallofullerenes is critical for production of metallofullerene derivatives with desired properties and functionalities. In this study, we investigate the effects of reduction and oxidation on the reactivity and regioselectivity in Diels–Alder reaction of metallofullerene La@C₈₂ by means of density functional theory calculations. Because of the enhanced electron-deficiency characteristic upon oxidation, the oxidized metallofullerene exhibits higher thermodynamic and kinetic reactivity as compared with neutral La@C₈₂. The regioselectivity in the reaction of La@C₈₂ with cylcopentadiene is remarkably changed after oxidation of the metallofullerene, which is explained in terms of the changes in the geometrical structure and the electronic structure of the metallofullerene. Quantitative analysis based on the activation-strain model demonstrates that the low activation energy barrier for the reaction of the cation La@C₈₂⁺ with cyclopentadiene originates from small strain energy and large interaction energy between the reactants. Energy decomposition analysis on the transition states of the reactions reveals that the exchange-repulsion interaction energy is one of the critical factors that determine the kinetic reactivity of the metallofullerene. This study not only provides new theoretical insights on how to modulate the reactivity of metallofullerenes, but also offers guideline for future experimental synthesis of new metallofullerene derivatives.     

Computational studies on two novel energetic nitrogen‐rich compounds based on tetrazolone

Two novel energetic nitrogen‐rich compounds 1,4‐diaminotetrazol‐5‐one ( DATO ) and 1,4‐dinitrotetrazol‐5‐one ( DNTO ) were proposed first and studied by quantum chemistry method with B3LYP/6‐31G* level of theory. The optimized geometry, IR predicted spectrum and thermochemical parameters, frontier molecular orbitals and molecular electrostatic potential were calculated for inspecting the electronic structure, molecular stability and chemical reactivity. The important macroscopic properties including density, enthalpy of formation, detonation parameters and impact sensitivity have been predicted as well. As a result, two designed compounds DATO and DNTO possess positive enthalpy of formation (395.79 and 342.77 kJ/mol), impressive detonation parameters (D = 8.80 km/s, P = 33.69 GPa; D = 8.89 km/s, P = 34.98 GPa) superior to the remarkable explosive RDX, acceptable sensitivities and might be promising candidates of energetic materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Transient spectroscopic characterization of the ring‐opening reaction of tetrahydrochromeno[2,3‐dimethyl]indole

Tetrahydrochromeno is a structural variant of spiropyran that undergoes a reversible ring‐opening to generate a colored nitrophenolate intermediate. Earlier work confirmed this intermediate through trimethylsilyl cyanide trapping under continuous irradiation. We have performed transient absorption spectroscopy to further characterize the mechanism of the ring‐opening reaction. Excitation at 355 nm produced a transient species with an absorption maximum at 445 nm, which we assign to the nitrophenolate unit of the ring‐opened product. The transient absorption decays after ~970 ns with small optical density changes corresponding to a 0.15 quantum yield. Exposure to oxygen did not exhibit a significant deleterious effect on the photoisomerization of the chromeno dye. Time‐dependent density functional theory corroborated spectroscopic assignments of the starting chromeno and the putative ring‐opened intermediate. The excited state behavior of this system parallels the structurally similar oxazine system reported by Raymo and coworkers. The one significant difference is the longer lifetime of the photochemically generated intermediate from chromeno. Copyright © 2015 John Wiley & Sons, Ltd.     

Excited‐state hydrogen bond strengthening of coumarin 153 in ethanol solvent: a TDDFT study

So far, coumarin dyes have been extensively studied with various means to understand their photophysical behaviors and photochemical properties. Here, our performing time‐dependent density functional theory calculation is aimed at exploring the excited‐state hydrogen bonding dynamics of coumarin 153 (C153) in protic ethanol (EtOH) solvent. The calculated results suggest that the excited‐state hydrogen bond C?O?H?O between C?O group and O?H group in the C153‐EtOH complex is strengthened, and the S₀ → S₁ transition of the complex corresponds to the highest occupied molecular orbital (HOMO) hopping to the lowest unoccupied molecular orbital (LUMO). The excited‐state hydrogen bond strengthening has been further confirmed by its larger binding energy in the S₁ state than in the S₀ state. In addition, because of the formation of the hydrogen bond C?O?H?O, a red shift of about 7 nm occurs in the electronic spectra of the C153‐EtOH complex, which is in good accordance with the experiment result. Copyright © 2016 John Wiley & Sons, Ltd.     

基于临界电子密度的多载波微放电全局阈值分析

多载波微放电即发生在宽带、大功率真空无源微波部件中的二次电子倍增放电现象, 是影响空间和加速器应用中无源微波部件长期可靠性的主要隐患. 多载波微放电全局阈值功率的预测对于工作在真空环境中的微波部件至关重要, 但迄今尚无有效方法进行上述阈值的准确分析. 本文将微放电发生过程中二次电子分布区域等效为等离子体, 通过在理论上建立微波部件的电磁特性和电子密度间的对应关系, 提出了一种基于测试系统可检测水平的多载波微放电全局阈值功率分析方法. 为了能够通过蒙特卡罗优化方法得到全局阈值, 进一步基于电子加速的类半正弦等效, 提出了微放电演化过程中电子数涨落的快速计算方法. 基于以上两种方法得到的针对实际微波部件的全局阈值分析结果与实验结果相符合. 不同于传统基于多载波信号功率分析的经验方法, 本文基于临界电子密度判断依据和电子数涨落快速计算, 为多载波微放电全局阈值的准确预测提供了一种高效的分析方法.     

富勒烯C20四聚体的结构与性能研究

采用密度泛函理论(DFT)中的杂化密度泛函(B3LYP)方法, 在6-31 G基组水平上对C₂₀四聚体进行了几何参数全优化, 得到了基态构型, 并对其稳定性、电子结构、极化率和芳香性进行了计算研究. 结果表明: C₂₀碳笼以[2+2]加成方式结合形成C₂₀四聚体, 具有良好的热力学稳定性; C原子内部以sp²的方式杂化, C原子之间有少量电荷转移; C₂₀ 四聚体的IR和Raman光谱都有较多的振动峰; 随碳笼数的增加, C₂₀聚合物中原子间的成键相互作用随之增强; C₂₀四聚体具有芳香性.