Laser photolysis studies of singlet molecular oxygen in aqueous micellar dispersions

Abstract

The kinetics of singlet oxygen in aqueous (D20 and H20) micellar systems were examined using laser flash photolysis with 1,3-diphenylisobenzofuran (DPBF) as the reactive monitor. The use of two different sensitizer types (2-acetonaphthone, solubilized in the interior of the micelles, and methylene blue, present in bulk aqueous phase) demonstrated that both the natural decay rate of J02* and its bimolecular rate constant for reaction with DPBF are insensitive to the site of singlet oxygen production in the micellar solution. Singlet oxygen lifetimes in solutions of ionic surfactant (sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB), and sodium laurate) were longer than any values previously reported in D20: 53 ± 5 ps. This value is proposed as a minimum value of the singlet oxygen lifetime in D20. Lifetimes measured in nonionic surfactant solutions (Brij 35, Igepal CO 630, and Igepal CO 660) were considerably shorter: 21-26 ps. This effect is probably due to the loss of electronic excitation of x02* ^Ag) to vibrational modes of the terminal hydroxyl groups of these nonionic surfactants. This quenching action appears to be related to the aggregation of the surfactant in aqueous media, since quenching by these surfactants was not observed in organic solvents. The bimolecular rate constant for reaction of singlet oxygen with DPBF (kr) was approximately 6.5 X 108 L mol-1 s"1 for the cationic surfactant CTAB and the three nonionic surfactants. However, kT was found to be approximately 60% higher in the two anionic surfactants SDS and sodium laurate. The lifetime of singlet oxygen in surfactant-H20 solution was estimated by extrapolation from H20-D20 mixtures. The values obtained for two surfactants were 4.0 (CTAB) and 3.5 ps (Igepal CO 630).

Photomodification of Biological Membranes With Emphasis on Singlet Oxygen Mechanisms

“…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.…”

“…The lifetime of singlet oxygen in aqueous solution is 3 to 4 microseconds (Lindig and Rodgers, 1979;Rodgers and Snowden, 1982;Parker and Stanbro, 1984). The hydroxyl bonds in water molecules act as quenchers for singlet oxygen (Merkel and Kearns, 1972), so that in D 2 0 , which quenches less efficiently, the lifetime is significantly extended.…”

“…The lifetime normally measured in such a suspension reflects the overall lifetime of singlet oxygen in both the solvent and the micelle. Under normal conditions the solvent dominates due to its much larger volume fraction and overall lifetimes in micellar suspensions in D 2 0 approximate those in pure D 2 0 (Lindig and Rodgers, 1979;Rodgers and Bates, 1982;Rodgers, 1983). In some instances, however, there is a significant reaction of the singlet oxygen with the micelle resulting in a lifetime reduction (Lindig and Rodgers.…”

Photoinactivation of acetylcholinesterase by erythrosin B and related compounds

“…Two commonly used diagnostics of '02 participation are based on the large deuterium solvent effect on the lifetime of '02 in solution ( T~ = 53-68 ps (26,27); r,,o = 4-5 ps (28)) and the efficient quenching of ' 0 2 by N3- (29). Table 2 lists the observed rate constants of photoinactivation in H20 and D20 under aerobic and anaerobic conditions, and the effects of azide thereon.…”

Lifetime of Singlet Oxygen and Quenching by NaN3 in Mixed Solvents

“…The lifetime of singlet oxygen is an important factor to clarify the reaction mechanism of the photooxidation, and it has been studied by many workers (Long et al [4]; Young et al [5]; Linding and Rodgers [6]) with laser flash photolysis. However, the lifetime was indirectly estimated.…”