A stable anionic N-heterocyclic carbene and its zwitterionic complexes

Pyrimidinium beta?nes (1), readily accessible via a straightforward modular synthesis from a formamidine and a monosubstituted malonic acid, are readily deprotonated by nBuLi (or KHMDS) to give the stable carbene species [2]Li+ (abbreviated as maloNHC). The latter represents the archetype of a subgroup of N-heterocyclic carbenes incorporating a malonate as remote anionic functional group within their heterocyclic backbone. While playing the dual role of monodentate 2 e- L type donor and noncoordinating charge carrier X, such ligands are seen to provide a rational route to zwitterionic complexes, as illustrated here by three examples (Rh, Fe, Ag). In particular, the reaction of [2]Li+ with [RhCl(1,5-COD)]2 produces the neutral 14 e- complex Rh(maloNHC)(COD) (3) in which coordinative unsaturation at the metal is relieved in the solid state by an uncommon labile bonding interaction between the Cipso of one of the mesityl arms and the Rh center.     

Multi-layered analyses using directed partitioning to identify and discriminate between biogenic amines

Multiple layers of statistical analyses were used to decipher the response from a single, cross-reactive conjugated polymer (1) providing enhanced classification accuracies over traditional multivariate statistical approaches. This analysis was demonstrated by classifying a series of seven biologically relevant, nonvolatile amines (i.e. biogenic amines). If only a single layer of analysis was employed (linear discriminant analysis), 89% classification accuracy was achieved lacking any concentration information. However, using this multi-layered, group-ungroup method, the analytes were first categorized based on general class of molecule (directed partitioning), i.e. aromatic, aliphatic, polyamines, with 98% accuracy. In a second analysis layer, these sub-groups were broken down into the individual molecular components, with the aliphatic and aromatic amines classifying near 99%, while the polyamine identification accuracy approached 90%. In the third layer of analysis, the concentration of the analytes in question was determined in the biologically relevant range within approximately 10% accuracy by following trends in the principle component analysis output.     

Oxidation of 2'-deoxycytidine to four interconverting diastereomers of N1-carbamoyl-4,5-dihydroxy-2-oxoimidazolidine nucleosides

Modification of 2'-deoxycytidine (dCyd) by hydroxyl radicals and direct ionization leads to the formation of various oxidation products, including dCyd 5,6-glycols, 5-hydroxy-2'-deoxycytidine, and ring fragmentation products. The mechanism of oxidation is complex and poorly understood. In the present work, we have prepared four cis- and trans-diastereomers of N1-(2-deoxy-beta-D-erythro-pentofuranosyl)-1-carbamoyl-2-oxo-4,5-dihydroxyimidazolidine by bromination of dCyd followed by peroxidation of the resulting dCyd bromohydrins. The structure and stereochemistry of each product were determined by 1H NMR, 13C NMR, and 2D NOE analyses. The formation of imidazolidine products involves rearrangement of initial 5(6)-hydroxy-6(5)-hydroperoxides to C6-C2 endoperoxides, which subsequently decompose by a concerted pathway to imidazolidine products. A remarkable feature of the four diastereomers was their ability to interconvert via single and successive cycles of ring-chain tautomerism at N1-C5 and N3-C4, leading to epimerization of C5 and C4, respectively. The rate of isomerization was greater for cis-diastereomers compared to trans-diastereomers, and the rate sharply increased with pH (pH 9.0>7.0>5.5).     

螺旋波激发甲烷等离子体光谱诊断

利用螺旋波激发等离子体化学气相沉积(LPP-CVD)技术,以甲烷和氦气为反应气体产生等离子体.通过采集到甲烷的可见光到紫外发射光谱,对甲烷等离子体进行原位诊断,发现存在CH、Ha及Hβ等碎片粒子的光辐射,同时,分析了不同入射功率、气压下CH粒子以及Hβ、Hγ的相对强度变化情况.结果表明:CH粒子的相对强度随着射频功率是先增大而后减小,随工作气压的增大而逐渐减小;随气压及功率的增加,Hβ、Hγ相对强度变化的总体趋势都是先增加而后减小的.