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R.B. King 《Israel journal of chemistry》1990,30(4):315-325
Ideas derived from topology and graph theory can be used to model the skeletal chemical bonding in metal carbonyl clusters as well as boranes and carboranes. In such molecules delocalized skeletal bonding occurs when there is a mismatch between the number of internal orbitals provided by a vertex atom and the number of polyhedral edges meeting at that vertex. Such global delocalization in deltahedral metal clusters may be regarded as a three-dimensional analogue of the aromaticity in planar polygonal molecules such as benzene. Elementary graph-theoretical considerations provide a basis for the 2n+2 skeletal electrons normally observed in n vertex delocalized deltahedral metal clusters lacking tetrahedral chambers. Electron-rich n-vertex metal clusters have more than 2n + 2 skeletal electrons and form polyhedra having at least one face with at least 4 edges. Electron-poor n-vertex metal clusters have less than 2n + 2 skeletal electrons and form deltahedra having at least one tetrahedral chamber. Ideas derived from group theory and graph theory can be used to analyze molecular orbital energy parameters for the most symmetrical deltahedral borane anions BnHn2− (particularly n = 6 and 12) computed using either semiempirical extended Hückel methods or ab initio methods based on Gaussian orbitals. Some of the fundamental aspects of the graph-theory derived models for skeletal bonding in delocalized deltahedral metal clusters are closely related to the tensor surface harmonic theory of Stone. 相似文献
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Oxides and carbon are commonly used as supports for gold nanoparticles, but metal salts are barely considered as suitable supports. Our group recently communicated that gold nanoparticles supported on nanosized LaPO4 (6–8 nm) are active for CO oxidation (Yan et al., Angew Chem Int Ed 45:3614, 2006). In the current work, we systematically developed an array of Au/M–P–O catalysts and tested them for catalytic activity and stability. It was found that 200 °C-pretreated Au/M–P–O (M = Ca, Fe, Co, Y, La, Pr, Nd, Sm, Eu, Ho, Er) show high CO conversions below 50 °C, and 500 °C-pretreated Au/M–P–O (M = Ca, Y, La, Pr, Nd, Sm, Eu, Ho, Er) show high CO conversions below 100 °C. These samples were characterized by ICP-OES, BET, XRD, TEM, SEM, and H2-TPR. The stability of selected catalysts was studied as a function of time on stream. This work furnishes a new catalyst system for further fundamental and applied research. 相似文献
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Cis and trans stilbene, styrene, 1-decene and 6-dodecene adsorbed on silica gel were reacted with oxygen atoms produced by microwave discharge of O2 and CO2. At 0°C these compounds gave mainly epoxides and carbonyl compounds as in neat liquid reactions. Below — 60°C ozonolysis products were formed; cis and trans stilbene and styrene gave benzaldehyde while 1-decene and 6-dodecene resulted mainly in ozonides. 相似文献
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Harshada Kotrange Agnieszka Najda Aarti Bains Robert Gruszecki Prince Chawla Mansuri M. Tosif 《International journal of molecular sciences》2021,22(17)
In addition to the benefits, increasing the constant need for antibiotics has resulted in the development of antibiotic bacterial resistance over time. Antibiotic tolerance mainly evolves in these bacteria through efflux pumps and biofilms. Leading to its modern and profitable uses, emerging nanotechnology is a significant field of research that is considered as the most important scientific breakthrough in recent years. Metal nanoparticles as nanocarriers are currently attracting a lot of interest from scientists, because of their wide range of applications and higher compatibility with bioactive components. As a consequence of their ability to inhibit the growth of bacteria, nanoparticles have been shown to have significant antibacterial, antifungal, antiviral, and antiparasitic efficacy in the battle against antibiotic resistance in microorganisms. As a result, this study covers bacterial tolerance to antibiotics, the antibacterial properties of various metal nanoparticles, their mechanisms, and the use of various metal and metal oxide nanoparticles as novel antibiotic carriers for direct antibiotic delivery. 相似文献
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Studies have been performed on the photochemical transformations of perylene adsorbed on non-activated silica gel of different pore sizes and alumina used as models of atmospheric particulate matter. Fluorescence, diffuse reflectance and EPR techniques have been used to study the effect of coadsorbed gases (O2 and Ar), H2O, time of storage in the dark, and loading on the photodegradation rates and on the formation of intermediate products. Oxygen quenches significantly the fluorescence and accelerates the photodegradation rate, suggesting the participation of O2 reactive species in the degradation reactions. The formation of photoproducts emitting and absorbing at longer wavelengths than the original compound is observed. It is suggested that oxygen participates in the destruction pathways since in an argon atmosphere these bands do not appear. Adsorbed H2O induces the formation of absorbing and emitting complexes with perylene or of aggregates of it formed by its displacement from the adsorption sites. New emitting intermediate products are observed in the presence of H2O. The pore sizes and the loading influence the rate of product formation. The EPR spectra of irradiated samples confirm the presence of the radical cation and the photoionization of Per into Per+ on the silica gel. 相似文献
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Meryem Hrimla Lahoucine Bahsis My Rachid Laamari Miguel Julve Salah-Eddine Stiriba 《International journal of molecular sciences》2022,23(1)
This review accounts for the most recent and significant research results from the literature on the design and synthesis of 1,2,3-triazole compounds and their usefulness as molecular well-defined corrosion inhibitors for steels, copper, iron, aluminum, and their alloys in several aggressive media. Of particular interest are the 1,4-disubstituted 1,2,3-triazole derivatives prepared in a regioselective manner under copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reactions. They are easily and straightforwardly prepared compounds, non-toxic, environmentally friendly, and stable products to the hydrolysis under acidic conditions. Moreover, they have shown a good efficiency as corrosion inhibitors for metals and their alloys in different acidic media. The inhibition efficiencies (IEs) are evaluated from electrochemical impedance spectroscopy (EIS) parameters with different concentrations and environmental conditions. Mechanistic aspects of the 1,2,3-triazoles mediated corrosion inhibition in metals and metal alloy materials are also overviewed. 相似文献
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过渡金属羰基簇合物常具有新颖的几何构型和多样化的成键方式。它们不仅扩展了配位化学的研究范畴和深度 ,更在工业催化〔1〕和分子材料〔2〕领域显示出重要的科学意义和广泛的应用前景〔3〕。而如何合成出具有新奇结构的过渡金属羰基簇合物便成为不少化学工作者所感兴趣的研究方向。本文通过实例阐述了二 - (三苯基膦 )铵盐 (简称PPN)在过渡金属羰合物合成及表征等方面中的应用。1 用PPN合成的过渡金属羰基簇合物PPN常被用于制备含填隙、半填隙配原子的过渡金属羰基簇合物。合成此类化合物大体有两种方法 :一是用过渡金属二元羰合物与… 相似文献
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制备了不同载体、不同金属助剂及不同贵金属Pt含量的蜂窝催化氧化催化剂,并评价了催化剂催化氧化含丙烷有机废气的活性:通过表面结构表征和活性评价实验,发现r-氧化铝作为载体时催化剂活性比分子筛和二氧化钛好;随着Pt含量的增加,催化剂的活性先升高后降低,Pt质量分数为0.2%时催化剂的活性最高;分别制备Pt/MO_x/Al_2O_3(M为铜、锰、钨、铈、锆、镧中的一种),在催化剂表面发现Pt聚集的颗粒,CeO_x的加入可改善贵金属的分布,Pt/CeO_x/Al_2O_3活性最佳,在400℃条件下,丙烷转化率达到95%以上,此时CeO_x的质量分数为1.0%。 相似文献
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A hardwood kraft lignin (obtained by precipitating an industrial black liquor with a solution of calcium salt in alcohol) was oxidized in alkaline medium to obtain phenolic compounds (syringaldehyde, vanillin, syringic acid and vanillic acid). Nitrobenzene and copper (II) oxide were the oxidants employed. Influence of temperature, reaction time and oxidant concentration on yield and product distribution were studied. The results show that nitrobenzene is a more effective oxidant (15–18 % of aldehydes on kraft lignin) than copper (II) oxide (7–8 %). Product distribution showed the highest aldehyde selectivity for nitrobenzene, due to the presence of two additional oxidation products in the copper oxide oxidations. In the oxidation to aldehydes, the alcohol-calcium precipitated kraft lignin is a better raw material than other precipitated kraft lignin. 相似文献
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