(ii) Water solubility is significantly affected by the net charge of organic molecules. A prototypical example is methyl viologen dication , which exhibits a solubility of 1.5 M in aqueous solutions. As electrons are transferred through reduction reactions, the solubility decreases, until the neutral molecule becomes practically insoluble. It can therefore be argued that the solubility of neutral molecules involved in the redox processes may represent a critical bottleneck. Only three records were excluded after filtering out charged molecules.