Rate Parameters for the Quenching of Singlet Oxygen by Water‐soluble and Lipid‐soluble Substrates in Aqueous and Micellar Systems

Abstract

Abstract— The laser flash photolysis method has been used to determine the bimolecular rate constants for the reaction between O2(1Δ9) and several lipid‐soluble and water‐soluble substrates. Values for lipid‐soluble substrates have been obtained using aqueous dispersions of surfactants above the critical micelle concentration with 1,3 diphenylisobenzofuran as monitor of singlet oxygen. Under these conditions the hydrophobic substances are solubilized by the micellar phase. For substrates which are water‐soluble, 9,10‐anthracene dipropionic acid disodium salt was used as singlet oxygen monitor. For several substances, the values obtained are comparable to the values found in homogeneous nonaqueous solutions. In cases where significant differences have been found these have been rationalized according to the individual case. The only major unexpected result concerned β‐carotene which, in micellar dispersion, failed to react at all with O2(1Δ9) This may be due to multi‐molecular aggregations occurring in the polar medium. The work described herein shows clearly that, under appropriate conditions, singlet oxygen kinetics can be effectively followed in aqueous solutions by time resolved methods. The indiscriminate use of β‐carotene as a quencher of O2(1Δ9)in mainly aqueous media is questioned.

Photomodification of Biological Membranes With Emphasis on Singlet Oxygen Mechanisms

“…For example furans bleach when they react with singlet oxygen and the kinetics of bleaching can be used to determine the kinetics of singlet oxygen production. Because furans are not very water soluble they must be used in organic solvents, or in micelles (Lindig and Rodgers, 1981). Thus the applicability to a biological system is questionable, although micelle results appear promising.…”

“…Since excited intermediates generated by the sensitizer can diffuse a finite distance within their lifetime in solution, action at a distance is theoretically possible. For singlet oxygen, with a 3 to 4 microsecond lifetime in aqueous solution (Lindig and Rodgers, 1979;Rodgers and Snowden, 1982;Parker and Stanbro, 1984), the mean diffusion distance before solvent quenching occurs is about 0.06 microns (from a surface source: Pooler and Valenzeno, 1979b) to 0.1 microns (from a point source : Grossweiner, 1977;Lindig and Rodgers, 1981) or about twenty times the thickness of a cell membrane. The first demonstration of photomodification by sensitizer restricted to the external medium was provided by Bezman et al (1978) studying inactivation of E. coli with rose bengal bound to polystyrene beads.…”

“…This method has been used in a number of studies, but has caused some problems also (Blum and Grossweiner, 1985). A second 'reasonably water soluble' reactant, 9,lO-anthracene dipropionic acid, has also been used (Lindig and Rodgers, 1981). Detection of the characteristic oxidation product of cholesterol, 5 alpha cholesterol hydroperoxide, is also evidence of the action of singlet oxygen (see below; Lamola, 1977).…”

“…Membrane photomodification has been included in a number of more general reviews which may be of interest to the reader including reviews of mechanisms of photosensitization (Girotti, 1983), photosensitizers in cell biology (Ito, 1983), mammalian cell photomodification (Spikes, 1983a), porphyrins in model cell systems (Spikes, 1983b), photodynamic cell killing (Pooler and Valenzeno, 1981), chlorpromazine photosensitized damage (Kochevar, 1981) and a review of molecular excited states in micellar systems (Lindig and Rodgers, 1980).…”

Effects of solar ultraviolet radiation on biogeochemical dynamics in aquatic environments : report of a workshop, Marine Biological Laboratory, Woods Hole, Massachusetts, October 23-26, 1989

“…Preliminary data with pure 102 exposures of murine hepatocytes demonstrate the potent cytotoxicity of this toxicant in these mammalian cells; 90% kiling was achieved with only 40% of the 102 needed for the same response in gram-negative bacteria (unpublished data; see accompanying poster). Because uf its short lifetime (aqueous = 2 tLs), 102 has a limited diffusion radius (100-200 nm in pure water; Lindig and Rogers, 1981). Other reactive species generated from photosensitization have lifetimes just fractions of this.…”