Title

The development, characterization and applications of polymeric films containing bacteriorhodopsin

Date of Award

1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Robert Birge

Keywords

Biophysics, Chemistry

Subject Categories

Biological and Chemical Physics

Abstract

The procedures for fabricating homogeneous thin films containing the protein bacteriorhodopsin doped in poly(vinylalcohol) and poly(acrylamide) are developed and discussed. Both polymers maintain the structural stability of the protein and the native photochemical properties of the protein for periods of years. Increasing the initial film solution pH, adding the chemical compounds guanidine hydrochloride or diaminopropane to the film solution, or decreasing the humidity of the film, increase the lifetime of the M-thermal intermediate in the bacteriorhodopsin photocycle and decrease the reciprocal sensitivity. Measurement of the photodiffractive properties of these films in the Raman-Nath diffraction regime indicate significant high order diffraction at an interbeam recording angle of 0.8$\sp\circ$. Diffraction measurements in the volume holographic regime showed approximately 0.4% diffraction efficiency per unit protein optical density at 570 nm. Increasing the initial film solution pH lead to a concomitant decrease in the reciprocal sensitivity of the film but had no notable effect on the maximum steady state diffraction efficiency of the film. The reciprocal sensitivities ranged from $\sim$10 mJ/cm$\sp2$ to 30mJ/cm$\sp2$. Higher initial film optical densities lead to higher diffraction efficiencies, but the maximum efficiency is found to be less than that of similar optical density films containing the mutant protein D96 $\to$ N. The measured values of the diffraction efficiency from each diffraction regime are found to be consistent with the predictions made using physical theories that describe the diffraction phenomenon in each regime. The resolution of the films as measured by varying the spatial frequency of the grating was found to vary little in the range of spatial frequency from 25 to 1500 mm$\sp{-1}$. BR films developed in this work are shown to be suitable in potentially useful applications such as optical correlation, incoherent to coherent light conversion, and a real-time holographic recording material in a pulsed double-exposure interferometer. The intensity dependent refractive index change of a PVA/BR film is also characterized over a wide range of intensities. Our interpretation of the results suggests that, at high laser intensities, strong self-defocusing effects dominate the refractive index process in thin films of the protein. Lastly, the refractive index change associated with the blue to pink photochemical transformation in the blue membrane form of bacteriorhodopsin is measured using a modified Mach-Zehnder interferometer. The sign and magnitude of the index change is measured to be approximately 0.00025 at 647 nm for a 3.5 OD$\sb{603}$ film sample. The results are consistent with the theoretical predictions from the Kramers-Kronig relation.

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