title: pH and solvent H/D isotope effects on the thermodynamics and kinetics of electron transfer for electrode-immobilized native and urea-unfolded stellacyanin.
abstract: The thermodynamics of Cu(II) to Cu(I) reduction and the kinetics of the electron transfer (ET) process for  Rhus vernicifera  stellacyanin (STC) immobilized on a decane-1-thiol coated gold electrode have been measured through cyclic voltammetry at varying pH and temperature, in the presence of urea and in D(2)O. Immobilized STC undergoes a limited conformational change that mainly results in an enhanced exposure of one or both copper binding histidines to solvent which slightly stabilizes the cupric state and increases histidine basicity. The large immobilization-induced increase in the pK(a) for the acid transition (from 4.5 to 6.3) makes this electrode-SAM-protein construct an attractive candidate as a biomolecular ET switch operating near neutral pH in molecular electronics. Such a potential interest is increased by the robustness of this interface against chemical unfolding as it undergoes only moderate changes in the reduction thermodynamics and in the ET rate in the presence of up to 8 M urea. The sensitivity of these parameters to solvent H/D isotope effects testifies to the role of protein solvation as effector of the thermodynamics and kinetics of ET.
authors.affiliation: Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Ranieri
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Marco
authors.initials: M
authors.lastname: Borsari
authors.forename: Carlo Augusto
authors.initials: CA
authors.lastname: Bortolotti
authors.forename: Giulia
authors.initials: G
authors.lastname: Di Rocco
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
mesh_terms: D041961:Deuterium Exchange Measurement; D055664:Electrochemical Techniques; D004566:Electrodes; D004579:Electron Transport; D006046:Gold / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D010940:Plant Proteins / Q000737:chemistry*; D058767:Protein Unfolding; D029045:Rhus / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry*
chemical_list: D008667:Metalloproteins; D010940:Plant Proteins; D012997:Solvents; C003343:stellacyanin protein, plant; D006046:Gold; D014508:Urea