Oxygen versus nitrogen co-ordination in complexes of MoVI and hydroxamate derivatives of α-amino acids: equilibrium, structural and theoretical studies †
作者:Etelka Farkas、Hajnalka Csóka、Gareth Bell、David A. Brown、Laurence P. Cuffe、Noel J. Fitzpatrick、William K. Glass、William Errington、Terence J. Kemp
DOI:10.1039/a902572c
日期:——
Equilibrium and spectroscopic studies showed that MoVI (MoO42â) reacts with α-aminohydroxamic acids (glycine-, sarcosine-, α-alanine-hydroxamic acids, Glyha, Sarha and α-Alaha) in the acidic pH range to give species involving O,O co-ordination whereas, as the pH is raised, species involving N,N co-ordination are formed. The crystal structure of [MoO2(Glyha)2] confirmed formation of an O,O co-ordination isomer. Theoretical studies of the O,O and N,N isomers of [MoO2(Glyha)2] and [MoO2(Sarha)2] showed the former to be the more stable but the relative closeness of the calculated energies of the isomers is in accord with the solution studies. Histidine hydroxamic acid (Hisha) forms O,O isomers in the acidic pH range but as the pH is raised forms two new isomers, one containing the amino nitrogen protonated and co-ordinated in a tridentate manner using the two hydroxamate oxygen atoms and the imidazole N while the other probably contains protonated imidazole N and is co-ordinated via the amino and hydroxamate nitrogens.
平衡和光谱研究表明,MoVI(MoO42â)与δ-氨基羟肟酸(甘氨酸、肌氨酸、δ-丙氨酸羟肟酸、Glyha、Sarha 和 δ-Alaha)在酸性 pH 值范围内发生反应,生成涉及 O,O 配位的物种,而随着 pH 值的升高,则形成涉及 N,N 配位的物种。MoO2(Glyha)2] 的晶体结构证实了 O,O 配位异构体的形成。对[MoO2(Glyha)2]和[MoO2(Sarha)2]的 O,O 和 N,N 异构体进行的理论研究表明,前者更为稳定,但这两种异构体的计算能量相对接近,这与溶液研究结果一致。组氨酸羟肟酸(Hisha)在酸性 pH 值范围内形成 O,O 异构体,但随着 pH 值的升高会形成两种新的异构体,一种含有质子化的氨基氮,并通过两个羟肟酸氧原子和咪唑 N 以三叉方式配位,而另一种可能含有质子化的咪唑 N,并通过氨基和羟肟酸硝基配位。