Chiral and supramolecular model complexes for vanadium haloperoxidases: Host–guest systems and hydrogen bonding relays for vanadate species

Supramolecular interactions and hydrogen bonding play a fundamental role in determining both structure and function of vanadate in enzymatic systems and in particular for the active site of vanadium haloperoxidases. Vanadium complexes with N-salicylidene hydrazide ligands provide a versatile approach towards molecular model systems with hydrogen bonding interactions. The variation of the side chains within these hydrazone ligands provides the ability to introduce chirality in molecular model complexes by the utilization of appropriate carbohydrate fragments. Moreover, the synthetic potential and the transformation reactions found for dioxidovanadium(V) complexes with N-salicylidene hydrazide ligands are reminiscent of what is usually observed for carboxylates and can therefore be regarded as their inorganic counterpart. The anisotropy effect of the oxido groups in vanadium complexes is a valuable tool that allows for the configurational and conformational analysis of structures with corresponding chelate rings. Utilizing appropriate vanadium complexes it is possible to generate inclusion compounds with cyclodextrins. The dependence of solid state and solution structures on the ring size of the cyclodextrin is discussed.