Homo- and Heteronuclear Group 12 Metallothionein Type B Cluster Analogs: Synthesis, Structure, 1 H NMR and ESI-MS.

Metallothioneins (MTs) are a ubiquitous class of small cysteine-rich metal-binding proteins involved in metal homeostasis and detoxification with highly versatile metal binding properties. Despite the long-standing association of MT with M 3 S 3 and M 4 S 5 metal clusters, synthetic complexes with these core architectures are exceptionally rare. Here, we demonstrate an approach to synthesizing and characterizing aggregates of group 12 metal ions with monocyclic M 3 S 3 cores in acetonitrile solution without the protection of a protein. Multidentate monothiol ligand N , N -bis(2-pyridylmethyl)-2-aminoethanethiol ( L1H ) provided [Cd 3 ( L1 ) 3 ](ClO 4 ) 3 ( 1 ), the first structurally characterized nonproteinaceous aggregate with a metallothionein-like monocyclic Cd 3 S 3 core. In addition, [Zn 3 ( L1 ) 3 ](ClO 4 ) 3 ·4CH 3 CN ( 2 ·4CH 3 CN) was characterized by X-ray crystallography. The complex cations of 1 and 2 had comparable structures despite being nonisomorphic. Variable temperature and concentration 1 H NMR were used to investigate aggregation equilibria of 1 , 2 , and a precipitate with composition "Hg( L1 )(ClO 4 )" ( 3 ). Cryogenic 1 H NMR studies of 3 revealed a J ( 199 Hg 1 H) coupling constant pattern consistent with an aggregate possessing a cyclic core. ESI-MS was used for gas-phase characterization of 1 - 3 , as well as mixed-metal [M 2 M'( L1 ) 3 (ClO 4 ) 2 ] + ions prepared in situ by pairwise acetonitrile solution combinations of the group 12 complexes of L1 . Access to synthetic variants of metallothionein-like group 12 aggregates provides an additional approach to understanding their behavior.