Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals

The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts.     

Efficient Synthesis of Bi-butenolides Derivatives through Oxidative Dimeric Cyclizing-Coupling Reaction of 2,3-Allenoic Acids

Allenes are three carbon functional groups possessing two perpendicular π-orbitals. Their unique reaction be havior is spread over three carbon atoms, which shows great potential in organic synthesis in terms of chirality transfer and diversity, as a result of the axial chirality as well as the substituent-loading capability. Recently, we devoted ourselves to establish a new area of oxidative cyclization-dimerization reactions between two functionalized allenes to give interesting bicyclic compounds in a single step. The formidable challenges are to match the reactivities of two allenes, and regenerate the catalyst, which would be reduced after reductive-elimination. In this paper we wish to disclose our recent studies on the synthesis of bi-butenolides from oxidative cyclization self-coupling reaction of 2,3 allenoic acids, in which a new system (PdCl2/RI/air) for regeneration of the palladium(Ⅱ) species was observed.     

Formation of spatially patterned colloidal photonic crystals through the control of capillary forces and template recognition

We report the formation of microscopic patterns of substrate-supported, 3D planar colloidal crystals using physical confinement in conjunction with surfaces displaying predetermined binary patterns of hydropholicity. The formation process involves a primary self-assembly wherein nano- and microscale colloids order into a photonic fcc lattice via capillary interactions followed by a secondary template-induced crystal cleavage step. Following this method, arbitrary arrays of pattern elements, which preserve structural and orientational properties of the parent crystal, can be easily obtained.     

离子抑制反相高效液相色谱法测定槐米中芦丁含量的研究

1 引言 芦丁是植物界广泛存在的一种重要的黄酮类化合物,在临床上可用作治疗毛细血管病的药物和治疗高血压病的辅助药物。因此,定量分析植物样品中的芦丁含量具有一定的现实意义。目前,国内有关这方面的工作多采用薄层色谱-紫外分光光度法,本文首次在国内报道采用离子抑制RP-HPLC法测定中草药槐米中     

催化光度返滴定法测定微量锰的研究

本文研究了催化光度反滴定法测定微量锰的原理，找到最佳实验条件，确立了实验方法，测定波长６２２ｎｍ；反应时间１ｍｉｎ４０ｓ；活化剂ＮＴＡ用量０．６０ｍＬ，ＫＩＯ４与孔雀石绿用量比为１．００：０．３５，室温下滴定；用ｐＨ＝５．４的乙酸－乙酸钠缓冲溶液控制溶液酸度；测定Ｍｎ＾２＋的浓度范围为１×１０＾－７～１×１０＾－５ｍｏｌ／Ｌ，Ｃｏ＾２＋，Ｂｉ＾３＋，Ｃａ＾２＋，Ａｌ＾３＋，Ｐｂ＾２＋，Ｃｕ＾２＋，     

Total Synthesis of (-)-Tetrahydropalmatine via Chiral Formamidine Carbanions: Unexpected Behavior with Certain Ortho-Substituted Electrophiles

A method has been developed by alkylation of chiral lithioformamidines to construct protoberberine alkaloids with a C(9) and C(10) D-ring substitution pattern. This ring pattern was established using an ortho-substituted hydroxymethylbenzene electrophile protected as a silyl ether to ultimately provide (-)-tetrahydropalmatine in 88% ee. Additionally, we have discovered limitations with ortho-substituted electrophiles in the asymmetric formamidine alkylation. These electrophiles have the potential to disrupt the lithium formamidine chelate and cause the selectivity in the alkylation to be uncharacteristically low. The total synthesis of (+/-)-canadine and (-)-tetrahydropalmatine along with the limitations to the formamidine alkylation technology are delineated herein.     

CCR5 antagonists: 3-(pyrrolidin-1-yl)propionic acid analogues with potent anti-HIV activity

[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1.     

Initial evaluation of quantitative performance of chromatographic methods using replicates at multiple concentrations

The introduction of a novel analytical method must be supported by consistent information about its quantitative potentialities; this is critical for whoever considers its utilization for an specific application. Unfortunately, literature abounds in papers proposing excellent chromatographic methods of analysis that have been subjected to comparatively poor quantitative evaluation. The methodology proposed in the present work makes use of some of the performance characteristics whose measurement is recommended in validation protocols; pertinent to this stage of method development are the detection and quantitation limits, the linear range and the repeatability. All this information can be calculated from the results of a calibration with several replicates at each analyte level. Replicates enable the calculation of reproducibility at several analyte levels and the estimation of the linear range; more important, replicates are necessary to detect changes in peak area standard deviation with analyte amount. Regression of calibration data by means of unweighted least-squares (ULSR) can only be performed in those cases in which homoscedasticity has been previously verified; heteroscedastic calibration data demand regression by means of weighted least-squares (WLSR), since ULSR results in gross overestimation of prediction limits at low analyte concentration. The proposal is used for the preliminary quantitative evaluation of a method for the determination of nine biogenic amines by means of pre-column derivatization with dabsyl chloride and separation of derivatives by RPLC. Limits of detection are calculated by a regression approach and by the classical signal-to-noise ratio method (S/N approach). No significant difference was detected for the amines limits of detection estimated by WLSR and by the S/N approach; ULSR estimated limits of detection are between 7 and 78 times larger than those obtained by the other two methods, as a consequence of the heteroscedasticity of calibration data.     

二氧化氮分子中的化学键

二氧化氮分子中的化学键张小平李夏＊邹应泉（北京铁路师范学校１０００３１）（首都师范大学化学系１０００３７）（北京师范大学化学系１００８７５）我们曾经利用半经验方法讨论过Ｎ２Ｏ４的结构问题［１］。最近，具有奇数电子的角形结构的ＮＯ２分子又引起了我们极大...