“NMR invisible” aluminum species in dealuminated mordenite zeolite: a1H/27 AI TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced¹H/²⁷ AI TRAPWR method as well as²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0± 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH) _n , respectively. The source of the “invisible Al” is discussed on the basis of the NMR experimental results.     

A density functional theory study on boundary of “superreduced” transition metal carbonyl anions [M(CO)n](M=Cr, n=5, 4, 3, z=2, 4, 6; M=Mn, n=5, 4, 3, z=1, 3, 5; M=Fe, n=4, 3, 2, z=2, 4, 6; M=Co, n=4, 3, 2, z=1, 3, 5)

A nonlocal density functional theory (DFT) method has been applied to the calculations on optimized geometry, Mulliken atomic net charges and interatomic Mulliken bond orders as well as total bonding energies (E) in the binary transition metal carbonyl anions with different reduced states [M(CO)_n]^z− (M=Cr, n=5, 4, 3, z=2, 4, 6; M=Mn, n=5, 4, 3, z=1, 3, 5; M=Fe, n=4, 3, 2, z=2, 4, 6; M=Co, n=4, 3, 2, z=1, 3, 5). For comparison of relative stability, a relative stabilization energy D is defined as D=E([M(CO)_n]^z−)−nE(CO). The calculated C–O distances are lengthened monotonously with the increase of the anionic charge, but the M–C distances are significantly lengthened only in the higher reduced states. The relative stabilization energy calculated is a considerable negative value in the lower reduced states, but a larger positive value in the higher reduced states. The DFT calculations show that with the increase of the anionic charge, the Mulliken net charges on the M, C, and O atoms all increase, however, an excess of the anionic charge is mainly located at the central metal atom. The calculated C–O Mulliken bond orders decrease consistently with the increase of the anionic charge, but the M–C bond orders exhibit an irregular behavior. However, the total bond orders calculated clearly explain the higher reduced states to be considerably unstable. From analysis of the calculated results, it is deduced that the stability of the binary transition metal carbonyl anions [M(CO)_n]^z− studied are associated with the coordination number n and the anionic charge z, further, it is possible for the anions studied to be stable if n≥z, conversely, it is impossible when n<z.     

Copper‐Bismuth Bimetallic Microspheres for Selective Electrocatalytic Reduction of CO2 to Formate

Electrocatalytic carbon dioxide reduction holds great promise for reducing the atmospheric CO₂ level and alleviating the energy crisis. High‐performance electrocatalysts are often required in order to lower the high overpotential and expedite the sluggish reaction kinetics of CO₂ electroreduction. Copper is a promising candidate metal. However, it usually suffers from the issues of poor stability and low product selectivity. In this work, bimetallic Cu‐Bi is obtained by reducing the microspherical copper bismuthate (CuBi₂O₄) for selectively catalyzing the CO₂ reduction to formate (HCOO^–). The bimetallic Cu‐Bi electrocatalyst exhibits high activity and selectivity with the Faradic efficiency over 90% in a wide potential window. A maximum Faradaic efficiency of ~95% is obtained at –0.93 V versus reversible hydrogen electrode. Furthermore, the catalyst shows high stability over 6 h with Faradaic efficiency of ~95%. This study provides an important clue in designing new functional materials for CO₂ electroreduction with high activity and selectivity.     

火焰原子吸收光谱法测定茶叶中的锰

介绍悬浮液进样-次灵敏线火焰原子吸收光谱法测定茶叶中的锰的方法。以琼脂为悬浮剂，将茶叶样品均匀、稳定地悬浮于琼脂溶胶中，直接喷入空气-乙炔火焰中，利用锰280.1nm次灵敏线，以工作曲线或标准加入法测定锰的含量，方法简便、快速，用于测定茶叶和桃叶样品中的锰，结果准确。     

Electron impact mass spectral fragmentation of chiral bisbenzoxazole,bisbenzothiazole and biscarbamide derivatives of 2,2-dimethyl-1,3-dioxolane

The mass spectrometric fragmentation behaviour of five pairs of (R,R)- and (S,S)-4,5-bis(benzoxazol-2-yl)-2,2-dimethyl-1,3-dioxolane derivatives, one pair of (R,R)- and (S,S)-4,5-bis(benzothiazol-2-yl)-2,2-dimethyl-1,3-dioxolanes, and three pairs of (R,R)- and (S,S)-N,N'-bis(2-hydroxyaryl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamides, all important compounds for asymmetric catalysis (P. Jiao et al., Tetrahedron Asymmetry 2001; 12: 3081), has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization conditions. The spectral observations have been rationalized in terms of fragment ion structures and fragmentation mechanisms that will provide an aid to spectral interpretation for new compounds of this type.     

乙二醇在电解银表面的氧化

用超高真空程序升温反应谱和瞬时应答方法研究了乙二醇在电解银表面的氧化，实验表明，室温下乙二醇吸附在电解银表面，并在３４３Ｋ分解给出一组产物群，预吸附氧与乙二醇反应时，在３４３Ｋ，４３３Ｋ和６１２Ｋ处给出三组产物群，它们分别对应于不同的表面反应，并给出了电解银催化乙二醇制乙二醛的活性结果。     

邻苯二酚的高效液相色谱分析

本文提出了邻苯二酚成品质量的高效液相色谱分析方法。     

喹乙醇的合成

喹乙醇的合成张维汉，李瑞声，李开颜，邓一军，谭桂利（中山大学化学系，广州，５１０２７５）关键词：喹乙醇，合成，相转移催化使用含有饲料添加剂的混合饲料，既节省粮食，又能提高畜牧产品的质量，因此发展高效无毒的多功能饲料添加剂很有意义。喹乙醇（Ｏｌａｑｕｉ...     

Electrophoretic separation of DNA using a new matrix in uncoated capillaries

A new separation matrix, consisting of polymer poly(N-isopropylacrylamide) (PNIPAM) and small molecule additive mannitol, was used for double-stranded (ds) DNA and plasmid DNA separation by capillary electrophoresis. The matrix had a low viscosity, which made it very easy to handle. The additive mannitol dramatically enhanced the sieving performance of PNIPAM in TBE buffer. The optimal mannitol concentration 6% in polymer solution, was determined with the consideration of both speed and resolution. A resolution of 0.95 was achieved on the separation of 271/281 bp in the phiX174/HaeIII digest by using 1.5% PNIPAM + 6% mannitol, while the supercoiled, linear and nicked conformers of lambda plasmid were separated in 1% PNIPAM + 6% mannitol, demonstrating the potential use of this new matrix for effective DNA separations. The dramatic impact of mannitol on sieving performance of PNIPAM solution was investigated. pH dependent self-coating ability of PNIPAM was revealed. The presence of mannitol in TBE buffer decreased the pH of the buffer, which led to more efficient self-coating ability of PNIPAM probable due to the formation of hydrogen bonds between PNIPAM molecules and silanol groups at the silica wall.     

新显色剂4,4′-二偶氮苯重氮氨基偶氮苯测定水中微量锌的研究

本文报告在四硼酸钠体系中和Triton X-100存在下,锌与新显色剂4,4′-二偶氮苯重氮氨基偶氮苯有灵敏的显色反应。红色络合物在525nm处摩尔吸光系数为1.63×10~5L·mol~(-1)·cm~(-1),并研究了测定锌的各种条件和40余种共存离子对测定的影响。