Zinkkomplexe von Aminosäuren und Peptiden, 2^[1]. Koordination einfacher Histidin‐Derivate an Zink

Abstract

Zinc Complexes of Amino Acids and Peptides, 2 [1] . – Coordination of Simple Histidine Derivatives to Zinc The bis( L ‐histidine)ZnCl 2 complex 1 is likely to have tetrahedral ZnN 2 Cl 2 coordination. For the compound ( L ‐histidine)‐ZnCl 2 · HCl ( 2 ) a structure determination has revealed a tetrahedral ZnOCl 3 coordination. Of the C ‐protected histidine derivatives His‐OMe and His‐NH 2 and zinc salts of non‐coordinating anions the complexes (His‐OMe) 2 ZnX 2 ( 3 ) and (His‐NH 2 ) 2 Zn(ClO 4 ) 2 ( 4 ) were obtained. A structure determination of (His‐OMe) 2 Zn(BPh 4 ) 2 · H 2 O has revealed a ZnN 4 coordination with chelating histidine units. Of the N ‐protected histidine derivative N α ‐acetylhistidine the complexes (Ac‐His)ZnX · H 2 O ( 5 , X = ClO 4 , BF 4 ) have been isolated which are coordination polymers in the solid state. From pH‐dependent 13 C‐NMR studies it is concluced that in solution the imidazole N and carboxyl O are coordinated to zinc in (Ac‐His)Zn and (Ac‐His) 2 Zn units. The doubly protected histidine derivative Bz‐His‐OMe acts as a monodentate ligand forming the tetrahedral complexes (Bz‐His‐OMe) 4 Zn(ClO 4 ) 2 ( 6 ) and [(Bz‐His‐OMe) 2 Zn(2,9‐dimethyl‐ o ‐phenanthroline)](ClO 4 ) 2 ( 7 ).