Photoreductive self-assembly from [MoVI7O 24]6- to Anti-Tumoral [H2Mov12O28(OH)12(MoVIO3) 4]6- in aqueous media

Abstract

The long-term photolysis of [iPrNH3] 6[Mo7O24]·3H2O in aqueous solutions at pH 5-6 is found to provide the formation of anti-tumoral [H 2MoV12O28(OH)12(Mo VIO3)4]6- species (1a), the core of which is a well-known ε-isomer ({ε-MoV12}) of the Keggin anion showing edge-shared MoVO6 octahedra in the arrangement of six diamagnetic MoV2-pairs with a MoV-MoV bond distance of 2.6 Å. To obtain structural insight of la in aqueous solutions from a viewpoint of the pharmaceutical mechanism, 95Mo NMR, electronic absorption, IR, and electrospray ionization mass (ESI-MS) spectrometries of 1a are investigated and indicate that the {ε-MoV12} core remains intact at pH 5-9 and that a detachment of the MoVIO3 unit from la proceeds at high pH level with an accompanying increase in the electronic transition of the MoV2 pairs. Highly positive and negative potentials (0.8-0.9 and -1.1- 1.2 V) of oxidation and reduction current peaks for the MoV2 pairs of 1a assist the structural stability of the ε-Keggin {MoV12} framework in aerobic solutions. A plausible mechanism of the photo-reductive self-assembly of [Mo VI7O24]6- to la through two- and four-electron reduction species, [MoV2Mo5O 22(OH)2]6- ({MoV2Mo VI5}) and [MoV4Mo3O 20(OH)4]6- ({MoV4Mo VI3}), is proposed in terms of the formation of a half molecule ([HMoV6O18(OH)6(Mo VIO3)2]11-) of 1a, which is suggested by ESI-MS spectrometry of the photolytes. © 2008 The Chemical Society of Japan.