Models for Terminal Ni(S-Cysteine) Modification in [NiFe]Hydrogenases by Iodoacetamide and Iodoacetate

Abstract

The cis-dithiolate complex [N,N′-bis(2-mercaptoethyl-2-methylpropyl)-1,5-diazacyclooctane]nickel(II) (Ni-1*) reacts with stoichiometric amounts of iodoacetamide to yield S-alkylated, mono- and diacetamide complexes, [(AA)Ni-1*][I] and [(AA)2Ni-1*][I]2. Their molecular structures are established by X-ray crystallography and find the former in pseudo-square planar geometry with no additional coordination of the amide functionality, while the latter is an octahedral N2S2O2NiII complex. The assignment of the axial coordination ligands as amide oxygen atoms is consistent with IR-spectroscopic ν(C=O) results both in the solid and solution states. The complexes are further characterized by UV/Vis spectroscopy, conductance measurements, and electrochemical studies. Comparisons are drawn between the alkylation of these simple dithiolate complexes and the loss of [NiFe]hydrogenase activity upon addition of alkylating agents.