The long term objective is to study the chemistry of the prosthetic group of visual pigments. For, although the spectroscopy of retinal, N-retinylidene n-butylamine (NRBA) and related polyenes has been examined in some detail, knowledge of the relationship between the chemistry and spectroscopy is not clearly understood. In order to correctly deduce the chemical role of the prosthetic group within the environment of the pigment protein, the chemistry of the prosthetic group in chemically defined experimental systems must first be probed. In this work, the hydrogen bonding (H-bond) and proton transferring reactions of CH3(CH=CH)5C=NC4H9 (compound I) and NRBA are to be studied both qualitatively and quantitatively. Some of the experimental variables to be studied are: i) donor reagents such as phenol, substituted phenols, acetic acid and chloro substituted acetic acids, ii) selected solvents such as hydrocarbons and chlorohydrocarbons, and iii) changing temperature. It was learned in prior studies that, in hydrocarbon solvents, when I is treated with a weak acid such as phenol, and when the temperature is progressively lowered, three separate spectra sequentially appear. These spectra belong to respectively: compound I, H-bonded I, and proton transferred I. This entire process can be placed in the formal framework of acid-base equilibria studies. The degree of conversion from one species to another will be obtained from changes in absorbance that will be used to find equilibrium constants. The resulting values will be used to determine the temperature dependent thermodynamic constants deltaH, deltaS. Compound I and NRBA undergo proton transfer with certain weak acids, and these reactions will be examined quantitatively in the same manner. The obtained thermodynamic constants for both reaction steps and the three excitation energies will link the three species together in a relative energy state diagram. From these results, it will be possible to measure the relative stability contributed to each ground and excited state by the selected donors and solvents.
| Blatz, P E; Tompkins, J A (1993) Relative ground and excited state energies of CH3(CH = CH)5CH = NC4H9, its hydrogen-bonded and proton-transferred species, and charge partitioning and distribution in the protonated Schiff base of retinal. Photochem Photobiol 58:400-8 |
| Baumgartner, N R; Blatz, P E (1991) Wavelength dependency of the rate of iodine catalyzed photoisomerization of retinol and retinal. Photochem Photobiol 54:805-10 |
| Blatz, P E; Mohler, J H; Ahmed, W (1991) Spectroscopic observation of solvent interaction with selected retinal Schiff bases. Photochem Photobiol 54:255-64 |
