The Rate of O₂and CO Binding to a Copper Complex, Determined by a “Flash-and-Trap” Technique, Exceeds that for Hemes

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.

Homogeneous catalytic O 2 reduction to water by a cytochrome c oxidase model with trapping of intermediates and mechanistic insights

“…5B) also starts via fast electron transfer from Fc* to the heme, forming 6 LFe II . In the absence of the Cu, however, as discussed, the subsequent O 2 -binding is slower than that observed for ½ In fact, this conclusion about the role of Cu agrees with other notable findings: (i) O 2 -binding to copper complexes can occur at near diffusion-controlled rates (26,27), (ii) CcO enzyme studies in fact implicate Cu B as the entry point for O 2 during catalysis (28)(29)(30).…”

Pseudoazurin Dramatically Enhances the Reaction Profile of Nitrite Reduction by Paracoccus pantotrophus Cytochrome cd1 and Facilitates Release of Product Nitric Oxide

“…2) (18). Photolysis is a well known method of dissociating ligands such as CO and NO from heme (29), and the fact that the products of photocatalyzed dissociation and that dependent on pseudoazurin are essentially identical (Fig. 2) provides strong evidence to suggest that pseudoazurin causes NO release from the enzyme.…”

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

“…[75] Extrapolating k 1 to 25°C, the rate constant of O 2 binding is 1.3 × 10 9 M −1 s −1 , which is nearly 10 to 100 times faster than myoglobin and hemoglobin, k 1 = 1.4–25 × 10 7 M −1 s −1 and 2.9–22 × 10 7 M −1 s −1 , respectively. [76] …”