title: Redox thermodynamics of the Fe(3+)/Fe(2+) couple in horseradish peroxidase and its cyanide complex.
abstract: The thermodynamics of Fe3+ to Fe2+ reduction for the five-coordinate high-spin native form of horseradish peroxidase and for its six-coordinate low-spin cyanide adduct have been determined from variable-temperature UV-vis spectroelectrochemical experiments. In both cases, the DeltaH degrees 'rc and DeltaS degrees 'rc values are positive. Hence, the negative reduction potentials turn out to be the result of two opposing and partially compensating contributions: a large enthalpic term, which is the determinant of the negative E degrees ' values for both species, and a smaller, yet relevant, entropic contribution. The decrease in E degrees ' of the Fe3+/Fe2+ couple on cyanide binding turns out to be a fully entropic effect, unequivocally demonstrating the importance of entropic effects in determining the E degrees ' values of redox metal centers.
authors.affiliation: Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Marco
authors.initials: M
authors.lastname: Borsari
authors.forename: Antonio
authors.initials: A
authors.lastname: Ranieri
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
mesh_terms: D003486:Cyanides / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D006735:Horseradish Peroxidase / Q000737:chemistry*; D010084:Oxidation-Reduction; D013816:Thermodynamics
chemical_list: D003486:Cyanides; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006735:Horseradish Peroxidase