Inhibitory effect of water on the oxygen reduction catalyzed by cobalt(II) tetraphenylporphyrin.

Stopped-flow kinetic measurements, UV-vis spectroscopy, rotating disk voltammetry, and quantum chemical calculations are used to clarify the role of water in the homogeneous two-electron reduction of O2 to H2O2 in 1,2-dichloroethane (DCE) using ferrocene (Fc) as an electron donor, tetrakis(pentafluorophenyl)boric acid (HTB) as a proton donor, and [5,10,15,20-tetraphenyl-21H,23H-porphine]cobalt(II) (Co(II)TTP) as a catalyst. Kinetic analysis suggests that the reaction is controlled by the intramolecular proton coupled electron transfer to the O2 molecule coordinated to the metal center producing the O2H(•) radical. This rate-determining step is common to both the O2 reduction by Fc catalyzed by Co(II)TPP and the O2 reduction by Co(II)TPP itself.

Competitive inhibition of a metal-free porphyrin oxygen-reduction catalyst by water.

A stopped-flow method is used to study the effects of water and reactant acid anion TB(-) = tetrakis(pentafluorophenyl)borate on the homogeneous oxygen reduction catalyzed by the protonated tetraphenylporphyrin. Observed competitive inhibition of the catalyst is linked to the DFT free energy of extraction of O(2), water, and TB(-) from the porphyrin complex.

Fine tuning of the catalytic effect of a metal-free porphyrin on the homogeneous oxygen reduction.

The catalytic effect of tetraphenylporphyrin on the oxygen reduction with ferrocene in 1,2-dichloroethane can be finely tuned by varying the molar ratio of the acid to the catalyst present in the solution. The mechanism involves binding of molecular oxygen to the protonated free porphyrin base, in competition with ion pairing between the protonated base and the acid anion present.

Molecular electrocatalysis for oxygen reduction by cobalt porphyrins adsorbed at liquid/liquid interfaces.

Molecular electrocatalysis for oxygen reduction at a polarized water/1,2-dichloroethane (DCE) interface was studied, involving aqueous protons, ferrocene (Fc) in DCE and amphiphilic cobalt porphyrin catalysts adsorbed at the interface. The catalyst, (2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-5-p-amino-phenylporphyrin) cobalt(II) (CoAP), functions like conventional cobalt porphyrins, activating O(2) via coordination by the formation of a superoxide structure. Furthermore, due to the hydrophilic nature of the aminophenyl group, CoAP has a strong affinity for the water/DCE interface as evidenced by lipophilicity mapping calculations and surface tension measurements, facilitating the protonation of the CoAP-O(2) complex and its reduction by ferrocene.

Dynamics of phospholipid monolayers on polarised liquid-liquid interfaces.

Quasi-elastic laser light scattering (QELS) is used to investigate dynamics of the polarised water/1,2-dichloroethane (DCE) interface in the presence of adsorbed DL-alpha-dipalmitoylphosphatidylcholine (DPPC) over a range of the interfacial potential differences (+/-0.3 V) and DPPC concentrations (0-20 microM). An analysis of the frequency of thermally excited capillary waves reveals some novel features in the adsorption of DPPC.