Light triggered dioxygen complexation by CoII-meso-tetraphenylporphyrin and long chain derivatives in aqueous micellar solutions

Abstract

The complexation of dioxygen, triggered by a photodeligandation of Co(II)TPP and long chain substituted derivatives, is shown to be a general reaction in aqueous micellar solutions. A very interesting feature exhibited by some of these systems is the room temperature reversibility of dioxygen complexation even in dilute solutions of a detergent in water. Dioxygen binding is induced by irradiation in the Soret band as well as in the visible absorption band. An explanation of this reaction, based on the initial binding on the fifth and sixth axial co-ordination sites of the cobalt atom, of either an ether oxygen of Triton or of a water molecule, or of both of them, is proposed. Visible irradiation would eject one of these ligands, leaving room for an incoming dioxygen. It is also shown that although these results may explain the mechanism, other elements are needed to explain the stability and the reversibility of these systems. In this respect, it is shown that the existence of a liquid interface, with its directional and polar character, is essential. Other regioselective interactions between solvent molecules, or specific parts of the detergent molecule, and the cobalt porphyrins come into play. Quantum yields for the photo-processes and thermodynamic data are given for ionic and non-ionic micellar solutions.

These results show that most of the conditions required for cobalt-reconstituted biological dioxygen carriers to be as functional as natural carriers, can be met in some of these simple models.