Kinetics and mechanism of the reduction of horse heart ferricytochrome c by chromium(II) at low pH

Journal Article · Wed Jan 01 04:00:00 EST 1975 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic50151a017· OSTI ID:7196871

Przystas, T J; Sutin, N

The rate constant for the reduction of ferricytochrome c by chromium (II) at 25/sup 0/ is (40/(H/sup +/) + 3.6 x 10/sup 2/ + 4.7 x 10/sup 3/(H/sup +/)) M/sup -1/ sec/sup -1/ in 1.0 M chloride at (H/sup +/) = 0.003-0.20 M and (3.2/(H/sup +/) + 10) M/sup -1/ sec/sup -1/ in 0.1 M perchlorate at (H/sup +/) = 0.006-0.08 M. The addition of thiocyanate ions to the reactant solutions markedly increases the reaction rate, and the third-order rate constant for the thiocyanate-assisted reaction at (H/sup +/) = 0.006-0.05 M is (1.1 +- 0.2) x 10/sup 6/ M/sup -2/ sec/sup -1/ in 1.0 M chloride and (2.3 +- 0.4) x 10/sup 6/ M/sup -2/ sec/sup -1/ in 0.1 M chloride. The reaction in chloride media is postulated to occur by an inner-sphere mechanism with a transition state (Fe-Cl-Cr). The thiocyanate-assisted reaction is thought to occur mainly by an outer-sphere mechanism, with electron transfer taking place through the porphyrin ring system. However, the detection of an unstable chromium (III) product containing thiocyanate bound to the chromium through the sulfur indicates that part of the thiocyanate-assisted reaction proceeds through an inner-sphere mechanism with a transition state (Fe-NCS-Cr). The same unstable chromium (III) product is formed in the reaction of chromium (II) with tetrakis(4-pyridyl) porphineiron (III) chloride in chloride or perchlorate media containing added thiocyanate. (auth)

• Research Organization: Brookhaven National Lab., Upton, NY
• OSTI ID: 7196871
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 14:9; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
550500 -- Metabolism
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BIOCHEMICAL REACTION KINETICS
BODY
CARBONIC ACID DERIVATIVES
CARDIOVASCULAR SYSTEM
CHEMICAL REACTIONS
CHROMIUM
CYTOCHROMES
ELECTRON TRANSFER
ELEMENTS
HEART
HORSES
IRON COMPOUNDS
KINETICS
MAMMALS
METALS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANS
PIGMENTS
REACTION KINETICS
REDUCTION
THIOCYANATES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VERTEBRATES