@article {1191, title = {Comparison of the dynamics of the primary events of bacteriorhodopsin in its trimeric and monomeric states}, journal = {Biophysical Journal}, volume = {83}, number = {3}, year = {2002}, note = {Wang, JP Link, S Heyes, CD El-Sayed, MA}, month = {Sep}, pages = {1557-1566}, abstract = {In this paper, femtosecond pump-probe spectroscopy in the visible region of the spectrum has been used to examine the ultrafast dynamics of the retinal excited state in both the native trimeric state and the monomeric state of bacteriorhodopsin (bR). It is found that the excited state lifetime (probed at 490 nm) increases only slightly upon the monomerization of bR. No significant kinetic difference is observed in the recovery process of the bR ground state probed at 570 nm nor in the fluorescent state observed at 850 nm. However, an increase in the relative amplitude of the slow component of bR excited state decay is observed in the monomer, which is due to the increase in the concentration of the 13-cis retinal isomer in the ground state of the light-adapted bR monomer. Our data indicate that when the protein packing around the retinal is changed upon bR monomerization, there is only a subtle change in the retinal potential surface, which is dependent on the charge distribution and the dipoles within the retinal-binding cavity. In addition, our results show that 40\% of the excited state bR molecules return to the ground state on three different time scales: one-half-picosecond component during the relaxation of the excited state and the formation of the J intermediate, a 3-ps component as the J changes to the K intermediate where retinal photoisomerization occurs, and a subnanosecond component during the photocycle.}, isbn = {0006-3495}, author = {Wang, Jianping and Link, Stephan and Heyes, C D and El-Sayed, Mostafa A} } @article {853, title = {The correlation between emission in freshly prepared porous silicon and the carrier density in silicon water}, journal = {Asian Journal of Spectroscopy}, volume = {6}, year = {2002}, author = {Zou, Bingsuo and Wang, Jianping and El-Sayed, Mostafa A} } @article {1236, title = {Comparison between the polarized Fourier-transform infrared spectra of aged porous silicon and amorphous silicon dioxide films on Si (100) surface}, journal = {Journal of Molecular Structure}, volume = {508}, number = {1-3}, year = {1999}, note = {Wang, JP Zou, BS El-Sayed, MA}, month = {Sep}, pages = {87-96}, abstract = {The s- and p-polarized Fourier transform infrared spectra were measured for an aged porous silicon (PS) film on Si (100) surface. The asymmetric stretching and symmetric stretching modes as well as the bending or rocking mode of the Si-O-Si group are studied. The deconvoluted spectra in Si-O-Si asymmetric stretching frequency region at different polarization directions show two pairs of vibrational modes, and can be assigned to the longitudinal-optic (LO) and transverse-optic (TO) pair of the corresponding vibrational modes. The smaller LO-TO pair splitting, the broader bandwidth, and the lower polarization ratio of the PS vibration bands as compared with those observed in an a-SiO2 film on Si wafer, suggest a less ordered SiO2 structure and a shorter range of coulombic interaction in PS. (C) 1999 Elsevier Science B.V. All rights reserved.}, isbn = {0022-2860}, doi = {10.1016/s0022-2860(99)00003-4}, author = {Wang, Jianping and Zou, Bingsuo and El-Sayed, Mostafa A} } @article {1259, title = {A Comparison of the Photoelectric Current Responses Resulting from the Proton Pumping Process of Bacteriorhodopsin under Pulsed and CW Laser Excitations}, journal = {The Journal of Physical Chemistry B}, volume = {101}, year = {1997}, note = {doi: 10.1021/jp972475r}, month = {1997}, pages = {10599 - 10604}, publisher = {American Chemical Society}, abstract = {When excited with a pulsed laser, an electric field-oriented bacteriorhodopsin (bR) film on an indium-tin oxide (ITO) conductive electrode generates a photocurrent composed of at least three different components: B1 (<100 ps), B2 (60 μs), and B3 (ms). When excited with an electronic shutter modulated CW light pulse (>200 ms in duration), a differential photocurrent (components D1 and D2 with decay times in milliseconds) is observed from the bR film. D1 is observed when the CW light is turned on, and D2 is observed when the CW light is turned off. In this paper, we compare the amplitudes and lifetimes of B2, B3, and D1 at various values of pH and ionic strength of the electrolyte solution in which the photocurrent is measured. It is found that changing the film orientation changes the polarity (sign) of B1 and B2, while it does not affect the polarity of B3 and D1. It is also found that B3 and D1 change their polarity upon changing the pH of electrolyte solution, whereas B1 and B2 do not. These results suggest that the origin of B3 and D1 is different from that of B1 and B2. Our results suggest that B3 and D1 are due to the formation of a transient proton capacitor between the two ITO electrodes resulting from the proton pumping in bR. The magnitude and sign of B3 and D1 are determined by the transient proton concentration change (accumulation or disappearance) occurring near the bR-modified ITO electrode interface on the millisecond time scale. The change of sign in B3 and D1 as a function of pH is due to the sequence of proton release/uptake in the bR photocycle: It first releases protons into the aqueous solution at high pH, while it first takes up protons from the aqueous solution at low pH. The effects of buffer and ionic strength on B3 and D1 are discussed in terms of the kinetics of proton release/uptake and of the transportation of positive and negative ions in the electrolyte solution.}, isbn = {1520-6106}, url = {http://dx.doi.org/10.1021/jp972475r}, author = {Wang, Jianping and Song, Li and Yoo, Seoung-Kyo and El-Sayed, Mostafa A} }