Determination of the Effective Charge Density of pH‐Responsive Keplerate Polyoxometalate Clusters by Means of Agarose Gel Electrophoresis

Abstract

Keywords: Polyoxometalates / Self-assembly / Electrophoresis / Charge density / AnionsThe effective (net) charge densities of the Keplerate {Mo 72 Fe 30 }, {Mo 72 V 30 }, and {W 72 Mo 30 } macroanions in dilute aqueous solution were determined from electrophoresis measurements, which provided direct, quantitative evidence of the counterion association behavior around macroions. The latter two clusters are strong electrolytes, and their charge [a] 1854 densities show no clear pH dependence. The surface charge density of {Mo 72 Fe 30 } increased with increasing solution pH owing to the partial deprotonation of the weak acid {Mo 72 Fe 30 } macroions. A close connection between the surface charge density of {Mo 72 Fe 30 } and their assembled blackberry structure sizes was observed.

Isolation of Blackberry-Shaped Nanoparticles of a Giant {Mo72Fe30} Cluster and Their Transformation to a Crystalline Nanoferric Molybdate

“…The importance of this particular compound is reflected in the fact that more than 80 research articles based on only this compound have been published to date . This compound has attracted immense interest and attention because of its importance in diverse disciplines, e.g., chemical science, molecular physics, magnetochemistry, biological sciences, materials science, and even mathematics. − The stability of this compound has extensively been studied in its solid state as well as in its solution. , An amorphous form of this cluster-containing compound was recently reported by the pioneering group of Müller and co-workers . The synthetic procedure for this amorphous {Mo 72 Fe 30 } compound is quite comparable to that of ferrimolybdite, synthesized by Kerr et al., who also isolated a yellow amorphous substance in the course of synthesizing a yellow coating mineral (ferrimolybdite) frequently found on ores of molybdenum .…”