@article {872, title = {Photoisomerization Quantum Yield and Apparent Energy Content of the K Intermediate in the Photocycles of Bacteriorhodopsin, Its Mutants D85N, R82Q, and D212N, and Deionized Blue Bacteriorhodopsin}, journal = {The Journal of Physical Chemistry}, volume = {100}, year = {1996}, note = {doi: 10.1021/jp9515242}, month = {1996}, pages = {2391 - 2398}, publisher = {American Chemical Society}, abstract = {The quantum yield of photoisomerization and the energy content of the K intermediate in the photocycle of bacteriorhodopsin and its mutants D85N, R82Q, and D212N and deionized blue bR were measured. Transient optical absorption and photoacoustic spectroscopy with excitation using 400 fs laser pulse were combined to obtain results. The spectroscopic characteristics of the excited state, the J and K intermediates in the photocycle of the mutants, and deionized blue bR were determined. The presence of both 13-cis and all-trans isomers in the ground state of light-adapted D85N, R82Q, and D212N and deionized blue bR makes extraction of the quantum yield for each isomer difficult. Thus, only average values of the quantum yield for these samples were determined. The replacement of charged groups in the vicinity of the retinal Schiff base was found to decrease the rate of the photoisomerization by up to 30 times, but with no signficant change in either the apparent quantum yield of the photoisomerization or the energy stored in the K intermediate. The results are discussed in terms of the different models for the excited and ground state potential surfaces of the retinal configuration in bacteriorhodopsin.The quantum yield of photoisomerization and the energy content of the K intermediate in the photocycle of bacteriorhodopsin and its mutants D85N, R82Q, and D212N and deionized blue bR were measured. Transient optical absorption and photoacoustic spectroscopy with excitation using 400 fs laser pulse were combined to obtain results. The spectroscopic characteristics of the excited state, the J and K intermediates in the photocycle of the mutants, and deionized blue bR were determined. The presence of both 13-cis and all-trans isomers in the ground state of light-adapted D85N, R82Q, and D212N and deionized blue bR makes extraction of the quantum yield for each isomer difficult. Thus, only average values of the quantum yield for these samples were determined. The replacement of charged groups in the vicinity of the retinal Schiff base was found to decrease the rate of the photoisomerization by up to 30 times, but with no signficant change in either the apparent quantum yield of the photoisomerization or the energy stored in the K intermediate. The results are discussed in terms of the different models for the excited and ground state potential surfaces of the retinal configuration in bacteriorhodopsin.}, isbn = {0022-3654}, url = {http://dx.doi.org/10.1021/jp9515242}, author = {Logunov, Stephan L. and El-Sayed, Mostafa A and Song, Li and Lanyi, Janos K.} } @article {867, title = {Picosecond Dynamics of Colloidal Gold Nanoparticles}, journal = {The Journal of Physical Chemistry}, volume = {100}, year = {1996}, note = {doi: 10.1021/jp960484e}, month = {1996}, pages = {8053 - 8056}, publisher = {American Chemical Society}, abstract = {Colloidal gold nanoparticles with an average radius of 15 nm have a surface plasmon absorption band at 530 nm. Excitation by laser pulses of 450 fs duration, and wavelength of 600 or 380 nm ?bleached? the plasmon band and produced a transient absorption at the wings of the ?bleach? spectrum. The transient absorption was found to have a similar temporal behavior at different wavelengths. Analysis of their temporal behavior showed two time constants:? 2.5 ps, and a slower component of >50 ps. Laser excitation close to the plasmon band at 600 nm leads to the formation of ?hot? non-Fermi electronic distribution within the colloidal particles. Transient absorption from these ?hot? electrons led to different absorptions from that of the plasmon absorption of ?cold? electrons. The ?hot? electrons relax via electron?phonon coupling in 2.5 ps, and the phonon?phonon relaxation of the lattice occurs in >50 ps. At 380 nm excitation, the amplitude of the blue wing becomes smaller, and the slow component becomes longer, which could be due to possible excitation of the d-band electrons. These results are discussed in terms of Mie theory and a two-temperature model (TTM), and their consequences on the optical absorption spectrum.Colloidal gold nanoparticles with an average radius of 15 nm have a surface plasmon absorption band at 530 nm. Excitation by laser pulses of 450 fs duration, and wavelength of 600 or 380 nm ?bleached? the plasmon band and produced a transient absorption at the wings of the ?bleach? spectrum. The transient absorption was found to have a similar temporal behavior at different wavelengths. Analysis of their temporal behavior showed two time constants:? 2.5 ps, and a slower component of >50 ps. Laser excitation close to the plasmon band at 600 nm leads to the formation of ?hot? non-Fermi electronic distribution within the colloidal particles. Transient absorption from these ?hot? electrons led to different absorptions from that of the plasmon absorption of ?cold? electrons. The ?hot? electrons relax via electron?phonon coupling in 2.5 ps, and the phonon?phonon relaxation of the lattice occurs in >50 ps. At 380 nm excitation, the amplitude of the blue wing becomes smaller, and the slow component becomes longer, which could be due to possible excitation of the d-band electrons. These results are discussed in terms of Mie theory and a two-temperature model (TTM), and their consequences on the optical absorption spectrum.}, isbn = {0022-3654}, url = {http://dx.doi.org/10.1021/jp960484e}, author = {Ahmadi, Temer S. and Logunov, Stephan L. and El-Sayed, Mostafa A} } @article {873, title = {Picosecond Electronic Relaxation in CdS/HgS/CdS Quantum Dot Quantum Well Semiconductor Nanoparticles}, journal = {The Journal of Physical Chemistry }, volume = {100}, year = {1996}, note = {doi: 10.1021/jp953708m}, month = {1996}, pages = {6381 - 6384}, publisher = {American Chemical Society}, abstract = {Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.}, isbn = {0022-3654}, url = {http://dx.doi.org/10.1021/jp953708m}, author = {Kamalov, Valey F. and Little, Reginald and Logunov, Stephan L. and El-Sayed, Mostafa A} } @article {1277, title = {pH Dependence of the Rate and Quantum Yield of the Retinal Photoisomerization in Bacteriorhodopsin}, journal = {The Journal of Physical Chemistry}, volume = {98}, year = {1994}, note = {doi: 10.1021/j100093a003}, month = {1994}, pages = {10674 - 10677}, publisher = {American Chemical Society}, abstract = {View http://dx.doi.org/10.1021/j100093a003 for article{\textquoteright}s front page in lieu of an abstract}, isbn = {0022-3654}, doi = {doi: 10.1021/j100093a003}, url = {http://dx.doi.org/10.1021/j100093a003}, author = {Logunov, Stephan L. and Song, Li and El-Sayed, Mostafa A} } @article {859, title = {The pH dependence of the subpicosecond retinal photoisomerization process in bacteriorhodopsin: evidence for parallel photocycles.}, journal = {Biophysical journal}, volume = {67}, year = {1994}, month = {1994 Nov}, pages = {2008-12}, abstract = {The pH dependence of the subpicosecond decay of the retinal photoexcited state in bacteriorhodopsin (bR) is determined in the pH range 6.8-11.3. A rapid change in the decay rate of the retinal photoexcited state is observed in the pH range 9-10, the same pH range in which a rapid change in the M412 formation kinetics was observed. This observation supports the previously proposed heterogeneity model in which parallel photocycles contribute to the observed pH dependence of the M412 formation kinetics in bR.}, keywords = {Bacteriorhodopsins, Biophysical Phenomena, Biophysics, Hydrogen-Ion Concentration, Isomerism, Kinetics, Molecular Structure, Photochemistry, Retinaldehyde}, issn = {0006-3495}, doi = {10.1016/S0006-3495(94)80684-8}, author = {Song, Li and Logunov, Stephan L. and Yang, Difei and El-Sayed, Mostafa A} }