Rau Tobias, Alsfasser Ralf, Zahl Achim, van Eldik Rudi
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Inorg Chem. 1998 Aug 24;37(17):4223-4230. doi: 10.1021/ic9711574.
Complex-formation reactions of the L-cysteine-derived ligands (alpha)N-acetyl-S-methylene-(2'-pyridine)-L-cysteine (py-CH(2)-accys) and (alpha)N-acetyl-S-ethylene-2-(2'-pyridine)-L-cysteine (py-C(2)H(4)-accys) with Pt(en)(H(2)O)(2) and Pd(en)(H(2)O)(2) were investigated structurally by NMR spectroscopy and kinetically by UV-vis and stopped-flow spectrophotometry. The complexes Pt(en)(py-CH(2)-accys-S,N)(2) (1) and Pt(en)(py-C(2)H(4)-accys-S,N)(2) (2) were isolated and purified by reversed-phase HPLC. NMR spectroscopy revealed an S-thioether, N-pyridyl chelation mode with five- and six-membered chelate rings for 1 and 2 and their Pd(II) analogues 3 and 4. The amino acid functional group is not involved in coordination. Comparison of the second-order rate constants for the complex-formation reactions resulted in k(Pd(II))/k(Pt(II)) ratios of 3.7 x 10(4) for py-CH(2)-accys and 2.4 x 10(4) for py-C(2)H(4)-accys. In the presence of excess ligand, the trans effect of the Pd-coordinated sulfur donor induced labilization of the coordinated en ligand with successive displacement to give [Pd(py-CH(2)-accys)(2)] and [Pd(py-C(2)H(4)-accys)(2)]. The displacement reactions were shown to be in accordance with a preequilibrium behavior consisting of reversible formation of the ring-opened intermediate followed by successive irreversible ring closure. The results are discussed in reference to available literature data for related systems.
通过核磁共振光谱对L-半胱氨酸衍生配体（α）N-乙酰基-S-亚甲基-（2'-吡啶基）-L-半胱氨酸（py-CH₂-accys）和（α）N-乙酰基-S-乙烯基-2-（2'-吡啶基）-L-半胱氨酸（py-C₂H₄-accys）与[Pt（en）（H₂O）₂]²⁺和[Pd（en）（H₂O）₂]²⁺的络合形成反应进行了结构研究，并通过紫外可见光谱和停流分光光度法进行了动力学研究。通过反相高效液相色谱法分离并纯化了配合物Pt（en）（py-CH₂-accys-S，N）₂（1）和Pt（en）（py-C₂H₄-accys-S，N）₂（2）。核磁共振光谱显示，对于1和2及其Pd（II）类似物3和4，存在S-硫醚、N-吡啶基螯合模式，具有五元环和六元螯合环。氨基酸官能团不参与配位。络合形成反应的二级速率常数比较结果表明，py-CH₂-accys的k（Pd（II））/k（Pt（II））比值为3.7×10⁴，py-C₂H₄-accys的k（Pd（II））/k（Pt（II））比值为2.4×10⁴。在过量配体存在下，Pd配位的硫供体的反位效应导致配位的en配体不稳定，随后相继发生取代，生成[Pd（py-CH₂-accys）₂]和[Pd（py-C₂H₄-accys）₂]。取代反应显示符合一种预平衡行为，该行为由开环中间体的可逆形成，随后是相继的不可逆闭环组成。参考相关体系的现有文献数据对结果进行了讨论。
