@article {1254,
	title = {Low-temperature retinal photoisomerization dynamics in bacteriorhodopsin},
	journal = {Journal of Physical Chemistry B},
	volume = {102},
	number = {13},
	year = {1998},
	note = {Logunov, SL Masciangioli, TM Kamalov, VF El-Sayed, MA},
	month = {Mar},
	pages = {2303-2306},
	abstract = {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.},
	isbn = {1089-5647},
	doi = {10.1021/jp972921a},
	author = {Logunov, Stephan L. and Masciangioli, Tina M. and Kamalov, Valey F. and El-Sayed, Mostafa A}
}
@article {1255,
	title = {Quantitative determination of the protein catalytic efficiency for the retinal excited-state decay in bacteriorhodopsin},
	journal = {Journal of Physical Chemistry B},
	volume = {102},
	number = {41},
	year = {1998},
	note = {Logunov, SL Masciangioli, TM El-Sayed, MA},
	month = {Oct},
	pages = {8109-8112},
	abstract = {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\%.},
	isbn = {1089-5647},
	doi = {10.1021/jp9813600},
	author = {Logunov, Stephan L. and Masciangioli, Tina M. and El-Sayed, Mostafa A}
}
@article {1269,
	title = {Homogeneous Line Width of the Different Vibronic Bands of Retinal Absorption in Bacteriorhodopsin by the Hole-Burning Technique},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp952971k},
	month = {1996},
	pages = {2762 - 2765},
	publisher = {American Chemical Society},
	abstract = {Using the hole-burning technique, resolved vibrational structure was observed in the retinal absorption spectrum of bacteriorhodopsin (bR) in poly(vinyl alcohol) (PVA) film at 10 K with 556 and 632 nm irradiation. The homogeneous line widths of v = 1 and v = 2 vibronic bands are estimated from the deconvolution of the observed spectrum. The absorption maximum is found to shift by 100?200 cm-1 by using the two excitation wavelengths; resulting from partial site selection due to the contribution of inhomogeneous broadening. The hole width produced by excitation near the zero-phonon band is found to be ?1250 cm-1, which corresponds to a homogeneous width of ?600 cm-1, and the low limit of dephasing time can be estimated as 20 fs. This width is found to be independent of the vibronic band observed.Using the hole-burning technique, resolved vibrational structure was observed in the retinal absorption spectrum of bacteriorhodopsin (bR) in poly(vinyl alcohol) (PVA) film at 10 K with 556 and 632 nm irradiation. The homogeneous line widths of v = 1 and v = 2 vibronic bands are estimated from the deconvolution of the observed spectrum. The absorption maximum is found to shift by 100?200 cm-1 by using the two excitation wavelengths; resulting from partial site selection due to the contribution of inhomogeneous broadening. The hole width produced by excitation near the zero-phonon band is found to be ?1250 cm-1, which corresponds to a homogeneous width of ?600 cm-1, and the low limit of dephasing time can be estimated as 20 fs. This width is found to be independent of the vibronic band observed.},
	isbn = {0022-3654},
	doi = {doi: 10.1021/jp952971k},
	url = {http://dx.doi.org/10.1021/jp952971k},
	author = {Kamalov, Valey F. and Masciangioli, Tina M. and El-Sayed, Mostafa A}
}
@article {1271,
	title = {Monodentate vs Bidentate Binding of Lanthanide Cations to PO2- in Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp9533279},
	month = {1996},
	pages = {6863 - 6866},
	publisher = {American Chemical Society},
	abstract = {The frequency difference between the symmetric and antisymmetric stretching vibration of PO2- in phosphatidylglycerol phospate (PGP) is used to differentiate between monodentate and bidentate binding of these groups to metal cations in the membrane of bacteriorhodopsin (bR) and phosphatidylglycerol phospate. The binding of Ca2+ to PGP is found to have a frequency difference corresponding to monodentate binding. The symmetric and antisymmetric PO2- bands in bR show similar frequency shifts upon Ca2+ binding, which is independent of pH. This suggests that Ca2+ has a monodentate type binding with the PO2- in bR. In contrast, the PO2- symmetric and antisymmetric frequencies of PGP complexes with trivalent lanthanide cations with higher charge density (Ho3+ and Dy3+) are observed to have smaller separations and to increase their separation with increasing pH toward the value observed for Ca2+ binding. Lanthanide cations (Ho3+, Dy3+, Eu3+, Nd3+, and La3+) binding in bR at pH 4 show small frequency separations that are observed to have similar frequency shifts with pH, the magnitude of which is dependent on the cation. It is proposed that at low pH the lanthanide cations with higher charge density have bidentate binding to bR, while at high pH, complexation with the OH- competes with one of the oxygens of the PO2- for the binding of the lanthanide ion thus changing the bidentate to monodentate type binding.The frequency difference between the symmetric and antisymmetric stretching vibration of PO2- in phosphatidylglycerol phospate (PGP) is used to differentiate between monodentate and bidentate binding of these groups to metal cations in the membrane of bacteriorhodopsin (bR) and phosphatidylglycerol phospate. The binding of Ca2+ to PGP is found to have a frequency difference corresponding to monodentate binding. The symmetric and antisymmetric PO2- bands in bR show similar frequency shifts upon Ca2+ binding, which is independent of pH. This suggests that Ca2+ has a monodentate type binding with the PO2- in bR. In contrast, the PO2- symmetric and antisymmetric frequencies of PGP complexes with trivalent lanthanide cations with higher charge density (Ho3+ and Dy3+) are observed to have smaller separations and to increase their separation with increasing pH toward the value observed for Ca2+ binding. Lanthanide cations (Ho3+, Dy3+, Eu3+, Nd3+, and La3+) binding in bR at pH 4 show small frequency separations that are observed to have similar frequency shifts with pH, the magnitude of which is dependent on the cation. It is proposed that at low pH the lanthanide cations with higher charge density have bidentate binding to bR, while at high pH, complexation with the OH- competes with one of the oxygens of the PO2- for the binding of the lanthanide ion thus changing the bidentate to monodentate type binding.},
	isbn = {0022-3654},
	doi = {doi: 10.1021/jp9533279},
	url = {http://dx.doi.org/10.1021/jp9533279},
	author = {Griffiths, Jennifer A. and Masciangioli, Tina M. and Roselli, Cecile and El-Sayed, Mostafa A}
}
