pH and Solvent H/D IsotopeEffects on the Thermodynamicsand Kinetics of Electron Transfer for Electrode-Immobilized Nativeand Urea-Unfolded Stellacyanin.

The thermodynamics of Cu(II) to Cu(I) reduction and thekineticsof the electron transfer (ET) process for Rhus verniciferastellacyanin (STC) immobilized on a decane-1-thiol coated gold electrodehave been measured through cyclic voltammetry at varying pH and temperature,in the presence of urea and in D2O. Immobilized STC undergoesa limited conformational change that mainly results in an enhancedexposure of one or both copper binding histidines to solvent whichslightly stabilizes the cupric state and increases histidine basicity.The large immobilization-induced increase in the pKafor the acid transition (from 4.5 to 6.3) makes thiselectrode–SAM–protein construct an attractive candidateas a biomolecular ET switch operating near neutral pH in molecularelectronics. Such a potential interest is increased by the robustnessof this interface against chemical unfolding as it undergoes onlymoderate changes in the reduction thermodynamics and in the ET ratein the presence of up to 8 M urea. The sensitivity of these parametersto solvent H/D isotope effects testifies to the role of protein solvationas effector of the thermodynamics and kinetics of ET. [ABSTRACT FROM AUTHOR]