SPECTROSCOPIC MIMICRY FOR THE PROTONATED RETINAL SCHIFF-BASE IN-VIVO WITH MODIFIED AMPHIPHILIC CLAY INTERLAYERS AS A POSSIBLE MODEL OF OPSIN ENVIRONMENT

We have found that clay acts as a novel model matrix for the amphiphil ic protein-opsin to mimic the visible absorption spectrum of a protona ted retinal Schiff base (RSB) in vivo. Without strong acids at ambient temperature, a visible broad absorption spectrum with a lambda(max) a t 530 mn covering the range from 400 to 680 nn was achieved for the pr otonated RSB with cationic surfactant-modified montmorillonite clay. T he interlayers of the dimethyloctadecylamine (DOA) modified clay were found to pro,ide amphiphilic space allowing the amphiphilic RSB to be intercalated easily and sequentially and protonated by the DOA. It is proposed that the visible absorption spectrum at lambda(max) 530 mn wa s attributable to electrostatic effects, permitting the appropriate di stance between the nitrogen of the protonated RSB and the negatively c harged clay interlayers and also to the anisotropic orientation of the RSB molecules in the interlayers.