蛋氨酸稀土配合物构象的^(13)C NMR研究

^(13)C-NMR STUDY ON CONFORMATION OF LANTHANIDE COMPLEXES WITH METHIONINE

本文测量了在7种不同稀土离子(La^(3+)、Pr^(3+)、Nd^(3+)、Dy^(3+)、Ho^(3+)、Er^(3+)和Tm^(3+))的水溶液中蛋氨酸^(13)C稀土诱导位移。利用稀土诱导位移对蛋氨酸稀土配合物构象的模拟结果表明,蛋氨酸通过离子化的羧基与稀土离子配位,Ln^(3+)—O长度为2.7A在配合物中,蛋氨酸以伸展状态存在,C_0-C_α-C_β-C_γ和C_α-C_β-C_γ-S成反式构象,C_β-C_γ-S-C_δ成旁式构象。根据稀土诱导位移方法建立的构象模型符合~1H邻位质子偶合常数和^(13)C顺磁弛豫速率的结果。

Lanthanide-induced shifts have been measured for ^(13)C nuclei of methionine in thepresence of seven lanthanide cations (La, P_1, Nd, Dy, Ho,Er, Tm) in aqueous solution.The simulation for conformation of lanthanide complexes with methionine shows that theligand is coordinated to lanthanide ion through oxygen atoms of carboxyl group and thebend length of Ln-O is 2.7A. In the complexes,methionine is in extended state,the favor- able conformation of C_ο-C_α-C_β-C_γ-S and C_α-C_β-C_γ-S is in trans, while that of C_β-C_γ-S-C_δin gauche. The conformation established for methionine complex by lanthanide-inducedshift method is in agreement with the results of vicinyl proton coupling constants and ^(13)Cparamagnetic relaxation rate determinations.