@article {1103, title = {Bacteriorhodopsin O-state Photocycle Kinetics: A Surfactant Study}, journal = {Photochemistry and Photobiology}, volume = {86}, number = {1}, year = {2010}, note = {Chu, Li-Kang El-Sayed, Mostafa A.}, month = {Jan-Feb}, pages = {70-76}, abstract = {The spectroscopy and dynamics of interaction between the O intermediate of bacteriorhodopsin (bR) and several surfactants (cetrimonium bromide [CTAB], sodium dodecyl sulfate [SDS] and diethylene glycol mono-n-hexyl ether [C6E2]) were investigated using steady-state UV-VIS spectrometry, circular dichroism spectroscopy and time-resolved absorption techniques. The steady-state spectral results show that bR can retain its trimeric state without severe damage in the molar concentration ratio of C6E2/bR ranging up to 4000. Time-resolved observations indicate that the rise and decay rates and transient populations of the O state can be increased in the presence of nonionic surfactant C6E2; however, these studies indicate the opposite phenomenon in the presence of the ionic surfactants CTAB and SDS. The observed 40\% enhancement in the transient population of the O intermediate state that results from treatment of C6E2 is proposed to result from an expanding bR structure, which leads to more effective proton pumping efficiency in the photosynthetic system of bR.}, isbn = {0031-8655}, doi = {10.1111/j.1751-1097.2009.00629.x}, author = {Chu, L. K. and El-Sayed, Mostafa A} } @article {1101, title = {Bacteriorhodopsin-based photo-electrochemical cell}, journal = {Biosensors \& Bioelectronics}, volume = {26}, number = {2}, year = {2010}, note = {Chu, Li-Kang Yen, Chun-Wan El-Sayed, Mostafa A.}, month = {Oct}, pages = {620-626}, abstract = {A simple solution-based electrochemical cell has been constructed and successfully employed in the detection of the photoelectric response upon photoexcitation of bacteriorhodopsin (bR) without external bias. Commercially-available indium tin oxide (ITO) glasses served as the optical windows and electrodes. Small amounts of bR suspensions (similar to 100 mu L) were utilized as the photovoltaic medium to generate the proton gradient between two half-cells separated by a molecular porous membrane. Continuous broadband visible light (lambda >380 nm) and a short-pulse 532-nm laser were employed for the photoexcitation of bR. Upon the modulated cw broadband irradiation, an instantaneous rise and decay of the current was observed. Our observations of the pH-dependent photocurrent are consistent with previous reports in a bR thin film configuration, which also showed a polarity inversion at pH 5-6. This is due to the change of the priority of the proton release and proton uptake in the photocycle of bR. Studies on the ionic strength effect were also carried out at different KC1 concentrations, which resulted in the acceleration of the rise and decay of the photoelectric response. This was accompanied by a decrease in the stationary photocurrent at higher KC1 concentrations in the broadband excitation experiments. The solution-based electrochemical cell uses aqueous medium, which is required for the completion of the bR proton pumping function. Due to the generation of the stationary current, it is advantageous to convert solar energy into electricity without the need of film-based photovoltaic devices with external bias. (C) 2010 Elsevier B.V. All rights reserved.}, isbn = {0956-5663}, doi = {10.1016/j.bios.2010.07.013}, author = {Chu, L. K. and Yen, C. W. and El-Sayed, Mostafa A} }