Accurate redetermination of the X-ray structure and electronic bonding in adenosylcobalamin

The electronic structure of adenosylcobalamin (B12 coenzyme, AdoCbl) has been calculated by a density functional method, using the orthogonalized linear combination of the atomic orbital method (OLCAO). Since a fixed accurately determined geometry was needed in such calculations, the crystal structure of adenosylcobalamin has been redone and refined to R = 0.065, using synchrotron diffraction data. Comparison with the recently reported electronic structures of cyano- (CNCbl) and methylcobalamin (MeCbl) shows that the net charges and bond orders vary only on the axial donors. The values in the three cobalamins suggest that the Co-C bond in MeCbl has a strength similar to that in AdoCbl, but it is significantly weaker that that in CNCbl. Present results are compared with those previously reported for the analogous corrin derivatives; i.e., simplified cobalamins with the side chains a-f replaced by H atoms. Despite a qualitative agreement, a discrepancy in the calculated HOMO-LUMO gap is found.     

间硝基苯胺的同步辐射光电离研究

利用同步辐射光电质谱法对间硝基苯脘进行了研究，测得了其电离势ＩＰ为９．６６０．０５ｅＶ，以及一些碎片离子出现势ＡＰ，计算出离解能Ｄ０（Ｎ２Ｏ－Ｃ６Ｈ６Ｎ＾＋）和离子生成焓ΔＨｆ（Ｃ６Ｈ６Ｎ＾＋）。给出了间硝基苯胺的同步辐射同离质谱图，并对主要碎片离子的产生过程进行了初步分析。     

Spectrophotometric determination of nicoumalone, acebutolol hydrochloride and procainamide hydrochloride

A sensitive spectrophotometric method is described for the determination of nicoumalone (NIC), acebutolol hydrochloride (ACBH) or procainamide hydrochloride (PAH) either in pure form or in pharmaceutical formulations. The method is based on the oxidative coupling reaction through the involvement of an aromatic primary amino group (released through reduction in NIC or hydrolysis in ACBH or existing free in PAH) in the drug with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of ferric chloride [Fe(III)]. The resulting chromophores are measured at 620 nm for NIC and ACBH and 580 nm for PAH. The concentration measurements are reproducible within a relative standard deviation of 1%.