Dioxygen binding rates

Dioxygen binding rates to diiron-carboxylate cores can be retarded and oxygenated intermediate can be trapped by embedding the metal complex into dendrimers.96 A third-generation dendrimer assembled around a paddlewheel diiron complex with 02CArTo1 reacts with 02 300 times slower than its nondendritic counterpart. 

The possible applications of the models include blood substitutes for clinical use in humans [274]. An important recent advance was made by Tsuchida et al. [291,292], who prepared membrane-bound picket-fence iron porphyrins for in vivo testing. The dioxygen binding rate and affinity were found to be similar to those of red blood cells [293] or erythrocytes in suspension [294]. 

Rate and equilibrium constants for O2 and CO binding to Fe hemes have been measured in various solvents and at various temperatures. Dioxygen binding to Fe porphyrins can be studied at low temperatures by a variety of spectroscopic techniques, where reactions that lead to irreversible autoxidation are suppressed. However, at higher temperatures (above 0°C) fast Kinetic... 

The differences in oxygen affinities are determined by the rates of O2 binding rather than O2 dissociation (Figure 4.11, Table 4.3). For a reversible dioxygen binding process depicted in Equation 4.5, the observed oxygenation rate constant depends linearly on the concentration of O2 ... 

Mechanisms and rates of dioxygen binding to copper(I) were determined for a series of tripodal complexes that afford end-on superoxo intermediates. Kinetic parameters for a these complexes proved to be rather similar, with activation enthalpies ranging about 3(MK) k.l/mol for reactions in coordinating solvents (nitriles). Activation entropies were relatively small for these processes both small positive and small negative values have been reported.40 This behavior is indicative of... 

Steric effects also play a role in thermodynamics and kinetics of dioxygen binding to Vaska-type complexes. For example, ort/zo-substituents on arylphosphine ligands significantly decrease the oxygenation rate or even completely shut down the... 

With very few exceptions, side-on peroxo bis-ji-oxo rearrangement occurs very rapidly, so 02 binding to copper(I) complexes affords the most stable isomer (or their mixture in cases of their similar stabilities). When two isomers are in a rapid equilibrium, they appear to form from Cu(I) precursors and 02 with equal rates. When dicopper(III) bis- i-oxo form is favored, it forms directly from two molecules of copper(I) complex and a molecule of 02 (or, in some cases, from one molecule of dicopper(I) complex with a dicompartmental ligand and a molecule of 02). As usual, oxygenation rates are fast, even at low temperatures, and activation barriers are low.40 The overall dioxygen binding process can be described by Equation 4.30 ... 

---