Chemical Tools for the Temporal Control of Water Solution pH and Applications in Dissipative Systems

The chemical reagents used to achieve a predictable and programmable time control of the pH of water solutions are reviewed with the purpose to present a toolbox of instruments to be used when a precise pH vs time profile is needed. These tools are particularly useful in view of the growing interest on dissipative systems, many of which operate in water solutions, under the action of reagents (chemical fuels) that allow for programmed pH evolution. After a brief introduction describing the importance of such tools for the operation of dissipative systems in water, five sections follow, which illustrate the different method used so far to temporally control the pH of a water solution. In particular, time-programmable pH variations based on: 1) bubbling of gases (CO2, N-2, Air), 2) hydrolysis of esters, lactones and sultones, 3) enzymatic and biocatalytic networks, 4) decarboxylation reaction of activated carboxylic acids, and 5) pH-oscillators are described together with selected examples of application.