A pressure- and temperature-controlled electrochemical cell for investigating biological electron transfer reactions.

The construction and operation of a cell for pressure- and temperature-controlled direct electrochemical studies of oxygen-sensitive biological materials is described. The stainless steel electrochemical cell, which contains a pyrolytic graphite working electrode, and Ag/AgCl counter and reference electrodes in an isolated compartment, easily maintains pressures between 1 and 2000 atm, and temperatures between 4 degrees C and at least 100 degrees C. The utility of the cell was demonstrated by determining the reduction potential of a redox dye, phenol red, by square wave voltammetry as a function of pressure and temperature. Thermodynamic parameters associated with electron transfer (delta V degree, delta beta, delta S degree, and delta H degree) were determined from the pressure and temperature/reduction potential profiles. Both pressure- and temperature-dependent reduction potentials of phenol red were attributed to differences in solvent interactions between its oxidation states. A discussion regarding the analysis of electrostatic interaction energies of biomolecules through pressure- and temperature-controlled electrochemical studies is presented.