Structure and properties of silicified purple membrane thin films

Electrodeposited or evaporated thin films of purple membrane (PM) sheets comprising close packed arrays of bacteriorhodopsin demonstrate enhanced chemical stability and retention of photochromic and photovoltaic behavior when periodically intercalated with nanothin layers of aminopropyl-functionalized silica. In contrast, hybrid composites prepared from PM films infiltrated with nonorgano-functionalized silica are structurally nonintegrated, prone to cracking, and exhibit no photochromic or photoelectric properties. The results indicate that the presence of the aminopropyl functionality in the silica matrix facilitates formation of the intercalated nanostructure, increases the rates of B-state recovery and M-state decay in the photocycle, and enhances the photovoltage response. Changes in photoactivity suggest that the aminopropyl moiety acts as a strong proton donor/acceptor when intercalated between PM sheets. The ability to fabricate hybrid thin films of electrophoretically oriented PM sheets with enhanced physical and chemical properties could be important in the design of novel components for bacteriorhodopsin-based applications.