Photochromic polymer films based on a 14-F bacteriorhodopsin derivative

Spectral and kinetic characteristics were measured for polymer (gelatin) films based on 14-F bacteriorhodopsin (BR), both wild-type (WT) and D96N mutant, to study the peculiarities of photo-induced transformation of the samples. It was demonstrated earlier that incorporation of 14-F retinal into the apomembrane of both 14-F WT and 14-F D96N produces pigments with drastically different photo-induced behavior, regarding the formation and decay of a red-shifted species at 660 nm. However, similar fundamental differences between 14-F WT and 14-F D96N, if embedded into gelatin matrix, were not observed. Results are discussed in the frame of the relationship between the kinetic rates of two photo-induced processes that occur in suspensions and gelatin films of corresponding pigments. These experimental results can possibly be explained by the difference in kinetics for gelatin films and water suspensions. The main factor in altering the kinetics is the relative humidity of gelatin samples. Therefore, the effect of relative humidity on performance of 14-F BR gelatin films, both WT and D96N, was studied. A range of humidity has been defined for each pigment, in which spectral and kinetic characteristics were changed in the desired direction. It was shown that 14-F WT gelatin films may offer a technological advantage relative to those based on 14-F D96N.