Keplerate cluster (Mo-132) mediated electrostatic assembly of nanoparticles

The electrostatic assembly between a series of differently charged Mo-132-type Keplerates present in the compounds (NH4)(42)[{(Mo-VI)(Mo5O21)-O-VI(H2O)(6)}(12) {(MO2O4)-O-V(CH3COO)}(30)].ca. {300 H2O + 10 CH3COONH4} (Mo-132a), (NH4)(72-n)[{(H2O)(81-n) + (NH4)(n)} {(Mo-VI)(Mo5O21)-O-VI(H2O)(6)}(12) {(Mo2O4)-O-V(SO4)}(30)].ca. 200 H2O (Mo-132b), and Na-10(NH4)(62)[{(Mo-VI)(Mo5O21)-O-VI(H2O2)(6)}(12) {(Mo2O4)-O-V(HPO4)}(30). ca. {300H(2)O + 2Na(+) + 2NH(4)(+) + 4H(2)PO(4)(-)) (Mo-132c) with cationic gold nanoparticles (AuNPs) was investigated for the first time. The rapid electrostatic assembly from nanoscopic entities to micron scale aggregates was observed upon precipitation, which closely matched the point of aggregate electroneutrality. Successful assembly was demonstrated using UV-vis, DLS, TEM, and zeta-potential analysis. Results indicate that the point at which precipitation occurs is related to charge balance or electroneutrality, and that counterions at both the Mo-132 and AuNP play a significant role in assembly. (C) 2014 Elsevier Inc. All rights reserved.