Replacement of sodium ions by cryptate (C222) complexed barium ions in sodium dodecyl sulfate micelles studied by electron spin resonance and electron spin-echo modulation of 5-doxylstearic acid and N,N,N',N'-tetramethylbenzidine photoionization and by viscosity measurements

Abstract

Ultraviolet irradiation of solubilized N,N,N{prime},N{prime}-tetramethylbenzidine (TMB) and viscosity measurements have been carried out at room temperature in mixed micellar solutions of sodium dodecyl sulfate (SDS) and barium dodecyl sulfate (Ba(DS){sub 2}). The barium ions were complexed by the macrocyclic cryptate C222. The irradiations did not lead to constant photoionization yields in the barium/C222-containing solutions because of secondary reactions. The viscosity as a function of the Ba{sup 2+}/2 mole fraction (X) changed from 1.47 mPa s at X = 0 to 1.33 mPa s at X = 1, passing through a maximum at X = 0.2. At 77 K in frozen solutions the TMB photoionization yield as measured by electron spin resonance increased by a factor of 1.8 in the range X = 0-0.2 and leveled off at larger X. Deuterium modulation depths of electron spin-echo decay curves measured at 4.2 K for TMB{sup +} and 5-doxylstearic acid increase as a function of X in a similar way as the photoionization yields. The results indicate a higher local concentration of water molecules in the micellar surface region when the C222-complexed barium ions are present.