The rate of O2 and CO binding to a copper complex, determined by a "flash-and-trap" technique, exceeds that for hemes |
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Authors: | Fry H Christopher Scaltrito Donald V Karlin Kenneth D Meyer Gerald J |
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Institution: | Johns Hopkins University, Department of Chemistry, 3400 N. Charles Street, Baltimore, Maryland 21218, USA. |
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Abstract: | The observation and fast time-scale kinetic determination of a primary dioxygen-copper interaction have been studied. The ability to photorelease carbon monoxide from Cu(I)(tmpa)(CO)](+) in mixtures of CO and O(2) in tetrahydrofuran (THF) between 188 and 218 K results in the observable formation of a copper-superoxide species, Cu(II)(tmpa)(O(2)(-))](+) lambda(max) = 425 nm. Via this "flash-and-trap" technique, temperature-dependent kinetic studies on the forward reaction between dioxygen and Cu(I)(tmpa)(thf)](+) afford activation parameters DeltaH = 7.62 kJ/mol and DeltaS = -45.1 J/mol K. The corresponding reverse reaction proceeds with DeltaH = 58.0 kJ/mol and DeltaS = 105 J/mol K. Overall thermodynamic parameters are DeltaH degrees = -48.5 kJ/mol and DeltaS degrees = -140 J/mol K. The temperature-dependent data allowed us to determine the room-temperature second-order rate constant, k(O2) = 1.3 x 10(9) M(-1) s(-1). Comparisons to copper and heme proteins and synthetic complexes are discussed. |
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