Quadratic electro-optic effects in bacteriorhodopsin: Measurement of γ(−ω;0,0,ω) in dried gelatin thin films

Abstract

Quadratic electro-optic effect in a nano-optical material based on the nonconjugated conductive polymer, poly( β -pinene)Quadratic electro-optic effects ͑dc or low frequency Kerr effect͒ of bacteriorhodopsin dispersed in dried gelatin thin films are examined in the near resonance region at three wavelengths: 633, 647, and 676 nm. The films show relatively large quadratic electro-optic effects compared to other molecular dispersed systems. The purple membrane is fixed within the polymerized gelatin matrix, and we show that the electronic contribution to ␥ dominates over possible orientational contributions. At 676 nm, the quadratic electro-optic coefficient s 1133 (Ϫ;0,0,) is 6.7 ϫ10 Ϫ20 m 2 /V 2 and the third order nonlinear susceptibility 1133 (3) (Ϫ;0,0,) is 7.0 ϫ10 Ϫ13 cm 4 statCoulomb Ϫ2 , with both values obtained for a protein concentration of 6.9ϫ10 18 cm Ϫ3 . The orientationally averaged second molecular hyperpolarizability ͗␥(Ϫ;0,0,)͘ determined from the quadratic electro-optic coefficients at 676 nm assuming an Onsager ellipsoidal local field factor is (10.8Ϯ5.1)ϫ10 Ϫ32 cm 7 statCoulomb Ϫ2 ͓(1.34Ϯ0.63)ϫ10 Ϫ56 F 3 m 4 C Ϫ2 ͔. The ͗␥(Ϫ;0,0,)͘ value increases roughly tenfold when the probe wavelength is decreased to 633 nm.The behavior of ␥(Ϫ;0,0,), when fit to a two-state model, predicts that ␥(Ϫ;0,0,) is strongly enhanced via type III processes. Thus, the magnitude of ␥(Ϫ;0,0,) is dominated by a term (⌬ 10 2 ϫ 10 2 )/( 10 Ϫ) 3 , where ⌬ 10 is the change in dipole moment, 10 is the transition moment, and 10 is the transition energy of the lowest-lying allowed 1 B u * ϩ -like ,* state. We calculate that ⌬ 10 is 12.8Ϯ1.2 D, in good agreement with previous Stark and two-photon experimental values. Time-dependent Hartree-Fock methods based on the MNDO Hamiltonian yield reasonable agreement with experiment, underestimating ␥(Ϫ;0,0,) by factors of only 2-4, with the error increasing as the frequency approaches resonance.

Counterion-controlled spectral tuning of the protonated Schiff-base retinal

“…The CT nature of the excitation in RPSB is well known but hard to quantify [16][17][18][19][20]. For this purpose we have carried out a wave function analysis for 1 + proposed by Plasser and coworkers [38].…”

“…1. The extent of CT in RPSB has been studied theoretically [14,15] and experimentally through indirect optical measurements [16][17][18][19][20]. Here we present a study of the color tuning of the RPSB due to electrostatic interaction through a combination of gas-phase measurements and quantum chemical calculations.…”

Angular Orientation of the Retinyl Chromophore of Bacteriorhodopsin: Reconciliation of 2H NMR and Optical Measurements

“…(As noted above, our calculation does not include the dispersion interactions between the chromophore and nearby amino acids.) To make this condensed-phase correction, we use the method based on the considerations of ref and the arguments as to the effective cavity shape and refractive index given in ref . Because of the very approximate nature of this local field cavity correction procedure and because of the gross approximations utilized in its implementation (i.e., deciding what cavity dimension to use for the chromophore in the interior of the protein), we do not give the details of this calculation here but rather calculate extreme limits.…”

Light-Induced Hydrolysis and Rebinding of Nonisomerizable Bacteriorhodopsin Pigment

“…Reorientation of the protein dipoles induces conformational alterations, which may persist longer than the chromophore excited state lifetime. In support of this mechanism, it is a well-established fact that light excitation of bR initiates a large, induced electron redistribution in the polyene (Huang et al, 1989;Yamazaki et al, 1998).…”