Interaction between molybdate and histidine and its reduction to molybdenum(V) dimer

Temperature-dependent reactions of molybdates with histidine in weak acidic solution resulted in the isolations of coordinated and uncoordinated products Na[MoAO3(S-His)]center dot H2O (1) (HHis = histidine, C6H9N3O2) and K-4(S-H(2)His)(2)(Mo7O24)center dot 16H(2)O (2) respectively. The former 1 can be reduced by hydrazine hydrochloride for the preparation of molybdenum(V) histidine [Mo2O4(S-His)(2)]center dot 3H(2)O (3) with dinuclear [Mo2O4](2+) core. The complex 2 shows strong hydrogen bonds between molybdate and histidine. The solution behaviors of the complexes were probed and compared between solid and solution H-1 and C-13 NMR spectra. Obvious dissociation of histidine in 1 has been observed for 35%, showing the equilibrium between the coordinated and free histidine groups. This may support the liability of coordinated imidazole in histidine with iron-molybdenum cofactor. Furthermore, solid CD spectra show 1 and 3 with positive and negative Cotton effects respectively. (C) 2015 Elsevier Ltd. All rights reserved.