Variation of alkylmethylviologen radical cation-water interactions in micelles and vesicles from ESEM spectroscopy: effect of alkyl chain length

The variation in alkylmethylviologen radical cation-water interactions with the alkyl chain length in frozen sodium dodecyl sulfate (SDS) micelles and dihexadecyl phosphate (DHP) vesicles were investigated by electron spin echo modulation spectroscopy. In the DHP vesicle system, the measured deuterium modulation depth associated with deuteriated water indicated a significant decrease in the magnitude of these interactions with an increase in the alkyl chainlength of the viologen. However, a comparable trend was absent in the SDS micelle system. In addition, the strength of the dimethylviologen radical cation-water interactions in SDS micelles was much weaker than those measured for any of the viologen radicals in the vesicle system. These observations were found to be in qualitative agreement with currently proposed models of the binding characteristics of alkylmethylviologens to DHP vesicles and SDS micelles and may also reflect structural differences between these two types of assemblies.