%0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 2001 %T The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies %A Logunov, Stephan L. %A Volkov, V. V. %A Braun, Markus %A El-Sayed, Mostafa A %X We present the results of two-pump and probe femtosecond experiments designed to follow the relaxation dynamics of the lowest excited state (S-1) populated by different modes. In the first mode, a direct (S-0 --> S-1) radiative excitation of the ground state is used. In the second mode, an indirect excitation is used where the S-1 state is populated by the use of two femtosecond laser pulses with different colors and delay times between them. The first pulse excites the S-0 --> S-1 transition whereas the second pulse excites the S-1 --> S-n transition. The nonradiative relaxation from the S-n state populates the lowest excited state. Our results suggest that the S1 state relaxes faster when populated nonradiatively from the S-n state than when pumped directly by the S-0 --> S-1 excitation. Additionally, the S-n --> S-1 nonradiative relaxation time is found to change by varying the delay time between the two pump pulses. The observed dependence of the lowest excited state population as well as its dependence on the delay between the two pump pulses are found to fit a kinetic model in which the S-n state populates a different surface (called Si) than the one being directly excited (S-1). The possible involvement of the A(g) type states, the J intermediate, and the conical intersection leading to the S-0 or to the isomerization product (K intermediate) are discussed in the framework of the proposed model. %B Proceedings of the National Academy of Sciences of the United States of America %V 98 %P 8475-8479 %8 Jul %@ 0027-8424 %G eng %M WOS:000169967000050 %R 10.1073/pnas.141220198 %0 Journal Article %J Journal of Physical Chemistry A %D 1998 %T Charge separation effects on the rate of nonradiative relaxation processes in quantum dots quantum well heteronanostructures %A Little, Reginald %A Burda, Clemens %A Link, Stephan %A Logunov, Stephan L. %A El-Sayed, Mostafa A %X Using time-resolved optical hole (oh)-burning techniques with femtosecond lasers, the time dependence of the spectral diffusion of the oh is examined for both the CdS quantum dot (QD) and the CdS/HgS/CdS quantum dot quantum well (QDQW) nanoparticles. It is found that the nonradiative relaxation of the optical hole is at least 3 orders of magnitude slower in the QDQW than in the QD system. Analysis of the second derivative of the broad transient bleach spectrum of the QDQW system in the 1.6-2.5 eV energy region at 50 fs delay time is found to have a minimum at 2.1 eV, corresponding to a minimum in the radiative probability. Around this energy, the rise and decay times of the transient bleach in the spectrum an found to change greatly. These results suggest that spectral diffusion in the QDQW is a result of relaxation from high- to low-energy exciton states, involving an intervening dark state at an energy of similar to 2.0 eV. The energies of the maxima and minimum of the second-derivative curve are found to be in good agreement with recent theoretical calculations by Jaskolski and Bryant(1) of the energies of the radiative and dark charge-separated state, respectively. In the latter, the hole is in the CdS clad and the electron is in the HgS well. The slow nonradiative relaxation processes involving this state are expected to be slow owing to the large change in the charge carrier effective masses as they cross from the CdS clad to the HgS well. %B Journal of Physical Chemistry A %V 102 %P 6581-6584 %8 Aug %@ 1089-5639 %G eng %M WOS:000075509700001 %R 10.1021/jp9822687 %0 Journal Article %J Journal of Physical Chemistry A %D 1998 %T Interfacial carriers dynamics of CdS nanoparticles %A Logunov, Stephan L. %A Green, T.C. %A Marguet, S. %A El-Sayed, Mostafa A %X The relaxation dynamics of charge carriers in 4 nm CdS colloidal quantum dots are studied by means of picosecond time-resolved fluorescence and femtosecond transient absorption experiments. We also studied the effects of the adsorption of viologen derivatives as electron accepters on the surface of these particles. From these experimental measurements, we reached a model of the electron-hole dynamics in these nanoparticles consistent with previous proposals. In particular, we have confirmed that the electron trapping in these particles is slower than the hole trapping (30 ps versus a few picoseconds). After excitation, rapid formation of an optical hole (bleach) within the lowest energy exciton (band gap) absorption region appears. The maximum of the bleaching band is red-shifted by 20 meV in 2.5 ps, and the bleach intensity recovers in 30 ps. Upon the adsorption of electron accepters, the rate of the red shift of the optical hole is not affected while the bleach recovery time is reduced to a few picoseconds. This leads to the following conclusions: (1) the shift in the bleach band results from hole trapping dynamics, and (2) the bleach recovery is rate limited by the electron trapping process in the CdS nanoparticles (30 ps) or by the hole trapping process (a few picoseconds) in the presence of the electron accepters. The latter conclusion supports a previous proposal by Klimov et al., that the rate of the recovery in CdS nanoparticles is determined by the electron surface trapping process. The electron transfer to the viologen accepters is found to be very efficient and takes place in 200-300 fs, which efficiently competes with surface trapping and electron-hole recombination processes and thus quenches both the band gap and the deep trap emissions. %B Journal of Physical Chemistry A %V 102 %P 5652-5658 %8 Jul %@ 1089-5639 %G eng %M WOS:000074751500050 %R 10.1021/jp980387g %0 Journal Article %J Journal of Physical Chemistry B %D 1998 %T Low-temperature retinal photoisomerization dynamics in bacteriorhodopsin %A Logunov, Stephan L. %A Masciangioli, Tina M. %A Kamalov, Valey F. %A El-Sayed, Mostafa A %X Retinal photoisomerization dynamics are studied at both room temperature and 20 K in wild-type bacteriorhodopsin using femtosecond pulses. We were able to resolve the decay at 20 K into two components with the dominant component having a similar lifetime to that observed at room temperature. This strongly suggests that the retinal lifetime at physiological temperature is barrierless. The minor, low-temperature long-lived component is discussed in terms of previous results obtained for fluorescence and transient absorption with lower time resolution, and the origin of this component is discussed in terms of low-temperature glass heterogeneity. %B Journal of Physical Chemistry B %V 102 %P 2303-2306 %8 Mar %@ 1089-5647 %G eng %M WOS:000072904200001 %R 10.1021/jp972921a %0 Journal Article %J Journal of Physical Chemistry B %D 1998 %T Quantitative determination of the protein catalytic efficiency for the retinal excited-state decay in bacteriorhodopsin %A Logunov, Stephan L. %A Masciangioli, Tina M. %A El-Sayed, Mostafa A %X It was previously found that by removing the negative charge of Asp85 in bacteriorhodopsin (bR), either by protonating it (as in deionized bR) or by mutation to Asn, the decay time of the retinal excited state increases from 0.5 ps to either 1.5 or 10 ps. The two decay components result from the presence of all-trans and 13-cis,15-syn (13-cis) retinal isomers in the modified retinal protein. To quantitatively determine the protein catalysis for the primary process in native bR, we need to determine which decay component results from the excited state of the all-trans isomer (present in the native bR). It is known that the all-trans isomer absorbs at longer wavelength than the 13-cis isomer in blue bR. In this communication, we report the results of pump-probe experiments using 100 fs laser pulses. Probing is carried out at 490 nm, where the excited state in both isomers absorbs. It is found that the ratio of the amplitudes of the two decay components in blue bR changes with variation of the excitation wavelength. The shorter-lived component is found to increase in amplitude as the excitation wavelength increases, i.e., as we excite more of the all-trans isomer. This leads to the conclusion that the short-lived component (1.5 ps) is for the decay of the all-trans excited state while the long-lived component (10 ps) is for the 13-cis retinal excited-state decay. Thus, the presence of the negative charge of Asp85 in native bR catalyzes the rate of the excited-state decay of the all-trans retinal by 300% and that of the 13-cis isomer by >2000%. %B Journal of Physical Chemistry B %V 102 %P 8109-8112 %8 Oct %@ 1089-5647 %G eng %M WOS:000076617100024 %R 10.1021/jp9813600 %0 Journal Article %J The Journal of Physical Chemistry B %D 1997 %T Electron Dynamics of Passivated Gold Nanocrystals Probed by Subpicosecond Transient Absorption Spectroscopy %A Logunov, Stephan L. %A Ahmadi, Temer S. %A El-Sayed, Mostafa A %A Khoury, J. T. %A Whetten, R. L. %X The electronic dynamics of gold nanocrystals, passivated by a monolayer of alkylthiol(ate) groups, were studied by transient spectroscopy after excitation with subpicosecond laser pulses. Three solution-phase gold samples with average particle size of 1.9, 2.6, and 3.2 nm with size distribution less than 10% were used. The photoexcitation in the intraband (surface plasmon region) leads to the heating of the conduction electron gas and its subsequent thermalization through electron?electron and electron?phonon interaction. The results are analyzed in terms of the contribution of the equilibrated ?hot? electrons to the surface plasmon resonance of gold. A different spectral response was observed for different sizes of gold nanoparticles. The results were compared to the dynamics of the large (30 nm diameter) gold nanocrystals colloidal solution. The size-dependent spectral changes are attributed to the reduction of the density of states for small nanoparticles. The observed variation in the kinetics of the cooling process in gold nanoparticles with changing the laser intensity is attributed to the temperature dependence of the heat capacity of the electron gas.The electronic dynamics of gold nanocrystals, passivated by a monolayer of alkylthiol(ate) groups, were studied by transient spectroscopy after excitation with subpicosecond laser pulses. Three solution-phase gold samples with average particle size of 1.9, 2.6, and 3.2 nm with size distribution less than 10% were used. The photoexcitation in the intraband (surface plasmon region) leads to the heating of the conduction electron gas and its subsequent thermalization through electron?electron and electron?phonon interaction. The results are analyzed in terms of the contribution of the equilibrated ?hot? electrons to the surface plasmon resonance of gold. A different spectral response was observed for different sizes of gold nanoparticles. The results were compared to the dynamics of the large (30 nm diameter) gold nanocrystals colloidal solution. The size-dependent spectral changes are attributed to the reduction of the density of states for small nanoparticles. The observed variation in the kinetics of the cooling process in gold nanoparticles with changing the laser intensity is attributed to the temperature dependence of the heat capacity of the electron gas. %B The Journal of Physical Chemistry B %I American Chemical Society %V 101 %P 3713 - 3719 %8 1997 %@ 1520-6106 %G eng %U http://dx.doi.org/10.1021/jp962923f %N 19 %! J. Phys. Chem. B %0 Journal Article %J Pure and Applied Chemistry %D 1997 %T On the molecular origin of the protein catalysis of the primary process in bacteriorhodopsin photosynthesis: Retinal photoisomerization %A El-Sayed, Mostafa A %A Logunov, Stephan L. %X Using subpicosecond transient optical absorption spectroscopic techniques, the photoisomerization rates and quantum yields were determined for. bacteriorhodopsin, its relevant mutants, its dionized form and at different pH and Cl- concentrations. It is found that the rate is catalyzed and made highly specific around the C-13-C-14 bond by the presence of negative charges within the retinal cavity (e.g., Asp85 and Asp 212). Any perturbation that genetically removes, acid neutralizes, or changes the geometry of these negative charges is found to decrease the tate of photoisomerization, but does not greatly change its quantum yield. These results sue discussed in terms of the changes in the electronic structure of the retinal as well as in the anisotropic charge distribution within the cavity that result from the photoexcitation process. The different potential energy surfaces proposed to explain the dynamics of the photoisomerization process are examined in terms of our observed results. %B Pure and Applied Chemistry %V 69 %P 749-754 %8 Apr %@ 0033-4545 %G eng %M WOS:A1997XH29600016 %R 10.1351/pac199769040749 %0 Journal Article %J The Journal of Physical Chemistry B %D 1997 %T Redetermination of the Quantum Yield of Photoisomerization and Energy Content in the K-Intermediate of Bacteriorhodopsin Photocycle and Its Mutants by the Photoacoustic Technique %A Logunov, Stephan L. %A El-Sayed, Mostafa A %X Data obtained previously in our lab for the quantum yield retinal photoisomerization and the energy content of the K-intermediate formed in the bacteriorhodopsin and its mutants (bR) photocycle are reexamined using time-resolved transient spectroscopy and laser-induced photoacoustic spectroscopy. In the present experiment both nanosecond and subpicosecond laser pulses are used for excitation, with different reference compounds. From these new results it can be concluded that using CoCl2 as a reference compound in the photoacoustic experiment with subpicosecond laser pulses gives a large amount of prompt heat release resulting from multiphoton absorption processes. This results in an overestimated energy content of the K-intermediate of bR and its mutants. Using different reference compounds, the corrected values are 40 ± 10 kJ/mol, which is in agreement with previously reported values. The apparent quantum yield and energy content values (for each of the isomeric compositions) of the mutants D212N, D85N, R82Q, A53G, W182F, V49A, deionized blue bR, and acid purple bR are also recalculated using bR as a reference compound and are similar to those of bR. (Φ is in the range 0.55?0.65, and EK is in the range 40?50 kJ/mol.) The relative insensitivity of the apparent average quantum yield value is discussed.Data obtained previously in our lab for the quantum yield retinal photoisomerization and the energy content of the K-intermediate formed in the bacteriorhodopsin and its mutants (bR) photocycle are reexamined using time-resolved transient spectroscopy and laser-induced photoacoustic spectroscopy. In the present experiment both nanosecond and subpicosecond laser pulses are used for excitation, with different reference compounds. From these new results it can be concluded that using CoCl2 as a reference compound in the photoacoustic experiment with subpicosecond laser pulses gives a large amount of prompt heat release resulting from multiphoton absorption processes. This results in an overestimated energy content of the K-intermediate of bR and its mutants. Using different reference compounds, the corrected values are 40 ± 10 kJ/mol, which is in agreement with previously reported values. The apparent quantum yield and energy content values (for each of the isomeric compositions) of the mutants D212N, D85N, R82Q, A53G, W182F, V49A, deionized blue bR, and acid purple bR are also recalculated using bR as a reference compound and are similar to those of bR. (Φ is in the range 0.55?0.65, and EK is in the range 40?50 kJ/mol.) The relative insensitivity of the apparent average quantum yield value is discussed. %B The Journal of Physical Chemistry B %I American Chemical Society %V 101 %P 6629 - 6633 %8 1997 %@ 1520-6106 %G eng %U http://dx.doi.org/10.1021/jp970955c %N 33 %! J. Phys. Chem. B %0 Journal Article %J Biophysical journal %D 1996 %T Catalysis of the retinal subpicosecond photoisomerization process in acid purple bacteriorhodopsin and some bacteriorhodopsin mutants by chloride ions. %A Logunov, Stephan L. %A El-Sayed, Mostafa A %A Lanyi, Janos K. %K Acoustics %K Anions %K Bacteriorhodopsins %K Biophysical Phenomena %K Biophysics %K Catalysis %K Chlorides %K Halobacterium salinarum %K Hydrogen-Ion Concentration %K Kinetics %K Photochemistry %K Point Mutation %K Retinaldehyde %K Spectrophotometry %X The dynamics and the spectra of the excited state of the retinal in bacteriorhodopsin (bR) and its K-intermediate at pH 0 was compared with that of bR and halorhodopsin at pH 6.5. The quantum yield of photoisomerization in acid purple bR was estimated to be at least 0.5. The change of pH from 6.5 to 2 causes a shift of the absorption maximum from 568 to 600 nm (acid blue bR) and decreases the rate of photoisomerization. A further decrease in pH from 2 to 0 shifts the absorption maximum back to 575 nm when HCl is used (acid purple bR). We found that the rate of photoisomerization increases when the pH decreases from 2 to 0. The effect of chloride anions on the dynamics of the retinal photoisomerization of acid bR (pH 2 and 0) and some mutants (D85N, D212N, and R82Q) was also studied. The addition of 1 M HCl (to make acid purple bR, pH 0) or 1 M NaCl to acid blue bR (pH 2) was found to catalyze the rate of the retinal photoisomerization process. Similarly, the addition of 1 M NaCl to the solution of some bR mutants that have a reduced rate of retinal photoisomerization (D85N, D212N, and R82Q) was found to catalyze the rate of their retinal photoisomerization process up to the value observed in wild-type bR. These results are explained by proposing that the bound Cl- compensates for the loss of the negative charges of the COO- groups of Asp85 and/or Asp212 either by neutralization at low pH or by residue replacement in D85N and D212N mutants. %B Biophysical journal %V 71 %P 1545-53 %8 1996 Sep %G eng %N 3 %1 http://www.ncbi.nlm.nih.gov/pubmed/8874028?dopt=Abstract %R 10.1016/S0006-3495(96)79357-8 %0 Journal Article %J The Journal of Physical Chemistry %D 1996 %T Excited-State Dynamics of a Protonated Retinal Schiff Base in Solution %A Logunov, Stephan L. %A Song, Li %A El-Sayed, Mostafa A %X The dynamics of all-trans and 13-cis retinal protonated Schiff base (RPSB) were studied in different solvents by means of picosecond transient spectroscopy. The decay time of the excited state absorption was found to be wavelength dependent due to the contribution of the faster decay of stimulated emission. The stimulated emission has a lifetime of a 2.5−4 ps while the excited state absorption decay is biexponential with lifetimes of 2.5−4 and 10−12 ps. The fluorescence quantum yield is strongly temperature dependent, but viscosity has a small effect on both excited-state lifetime and fluorescence quantum yield. This leads to the conclusion that there is a 600 cm-1 barrier in the excited-state which results from intramolecular electronic factors and not from the solvent viscosity. The comparison of these results with those for the retinal in rhodopsin and bacteriorhodopsin is discussed in terms of the protein catalysis for the retinal photoisomerization. %B The Journal of Physical Chemistry %I American Chemical Society %V 100 %P 18586 - 18591 %8 1996 %@ 0022-3654 %G eng %U http://dx.doi.org/10.1021/jp962046d %N 47 %! J. Phys. Chem. %0 Journal Article %J The Journal of Physical Chemistry %D 1996 %T 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 %A Logunov, Stephan L. %A El-Sayed, Mostafa A %A Song, Li %A Lanyi, Janos K. %X 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. %B The Journal of Physical Chemistry %I American Chemical Society %V 100 %P 2391 - 2398 %8 1996 %@ 0022-3654 %G eng %U http://dx.doi.org/10.1021/jp9515242 %N 6 %! J. Phys. Chem. %0 Journal Article %J The Journal of Physical Chemistry %D 1996 %T Picosecond Dynamics of Colloidal Gold Nanoparticles %A Ahmadi, Temer S. %A Logunov, Stephan L. %A El-Sayed, Mostafa A %X 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. %B The Journal of Physical Chemistry %I American Chemical Society %V 100 %P 8053 - 8056 %8 1996 %@ 0022-3654 %G eng %U http://dx.doi.org/10.1021/jp960484e %N 20 %! J. Phys. Chem. %0 Journal Article %J The Journal of Physical Chemistry %D 1996 %T Picosecond Electronic Relaxation in CdS/HgS/CdS Quantum Dot Quantum Well Semiconductor Nanoparticles %A Kamalov, Valey F. %A Little, Reginald %A Logunov, Stephan L. %A El-Sayed, Mostafa A %X 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. %B The Journal of Physical Chemistry %I American Chemical Society %V 100 %P 6381 - 6384 %8 1996 %@ 0022-3654 %G eng %U http://dx.doi.org/10.1021/jp953708m %N 16 %! J. Phys. Chem. %0 Journal Article %J Biophysical journal %D 1996 %T Replacement effects of neutral amino acid residues of different molecular volumes in the retinal binding cavity of bacteriorhodopsin on the dynamics of its primary process. %A Logunov, Stephan L. %A El-Sayed, Mostafa A %A Lanyi, Janos K. %K Bacteriorhodopsins %K Binding Sites %K Biophysical Phenomena %K Biophysics %K Halobacterium salinarum %K Kinetics %K Mutagenesis, Site-Directed %K Photochemistry %K Quantum Theory %K Retinaldehyde %K Schiff Bases %X We have determined the rate and quantum yield of retinal photoisomerization, the spectra of the primary transients, and the energy stored in the K intermediate in the photocycle of some bacteriorhodopsin mutants (V49A, A53G, and W182F) in which residue replacements are found to change the Schiff base deprotonation kinetics (and thus the protein-retinal interaction). Because of their change in the local volume resulting from these individual replacements, these substitutions perturb the proton donor-acceptor relative orientation change and thus the Schiff base deprotonation kinetics. These replacements are thus expected to change the charge distribution around the retinal, which controls its photoisomerization dynamics. Subpicosecond transient spectroscopy as well as photoacoustic technique are used to determine the retinal photoisomerization rate, quantum yield, and the energy stored in the K-intermediate for these mutants. The results are compared with those obtained for wild-type bacteriorhodopsin and other mutants in which charged residues in the cavity are replaced by neutral ones. In some of the mutants the rate of photoisomerization is changed, but in none is the quantum yield or the energy stored in the K intermediate altered from that in the wild type. These results are discussed in terms of the shapes of the potential energy surfaces of the excited and ground states of retinal in the perpendicular configuration within the protein and the stabilization of the positive charge in the ground and the excited state of the electronic system of retinal. %B Biophysical journal %V 70 %P 2875-81 %8 1996 Jun %G eng %N 6 %1 http://www.ncbi.nlm.nih.gov/pubmed/8744325?dopt=Abstract %R 10.1016/S0006-3495(96)79857-0 %0 Journal Article %J The Journal of Physical Chemistry %D 1994 %T pH Dependence of the Rate and Quantum Yield of the Retinal Photoisomerization in Bacteriorhodopsin %A Logunov, Stephan L. %A Song, Li %A El-Sayed, Mostafa A %X View http://dx.doi.org/10.1021/j100093a003 for article's front page in lieu of an abstract %B The Journal of Physical Chemistry %I American Chemical Society %V 98 %P 10674 - 10677 %8 1994 %@ 0022-3654 %G eng %U http://dx.doi.org/10.1021/j100093a003 %N 42 %! J. Phys. Chem. %R doi: 10.1021/j100093a003 %0 Journal Article %J Biophysical journal %D 1994 %T The pH dependence of the subpicosecond retinal photoisomerization process in bacteriorhodopsin: evidence for parallel photocycles. %A Song, Li %A Logunov, Stephan L. %A Yang, Difei %A El-Sayed, Mostafa A %K Bacteriorhodopsins %K Biophysical Phenomena %K Biophysics %K Hydrogen-Ion Concentration %K Isomerism %K Kinetics %K Molecular Structure %K Photochemistry %K Retinaldehyde %X 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. %B Biophysical journal %V 67 %P 2008-12 %8 1994 Nov %G eng %N 5 %1 http://www.ncbi.nlm.nih.gov/pubmed/7858138?dopt=Abstract %R 10.1016/S0006-3495(94)80684-8