Metal cation assisted protonation of retinylidene Schiff base in aqueous acetonitrile and in reverse micelles
Abstract
Metal cations (Ca2+, Mg2+, Zn2+) cause water to protonate all-trans-N-retinylidenebutylamine when solubilised in (i) acetonitrile containing aqueous MgBr2 and (ii) CaA2, MgA2 and ZnA2[where A = bis(2-ethylhexyl) sulfosuccinate anion] solubilised water pools in heptane. The results are discussed in terms of the role of metal cations and water in wavelength regulation in the opsin family of proteins.