Absorption spectra, environmental effects

However Smith and Symons (43, 44, 45) found that the theory of Franck and Platzman did not account for environmental (temperature, solvents, added salts) effects on the spectrum. They proposed instead a theory based on an electron in a box of radius r. Absorption of hv causes the resulting atom to contract, the electron preserving its radius as in the ground state. Environmental effects change this radius. 

Kronman et al. (1965) and Kronman and Holmes (1965) appear to be the first to have studied the effects of acid on a-lactalbumin and report that this protein, adjusted to pH values below its isoelectric point, exhibits a hypsochromic shift in its absorption spectrum between 270 and 300 nm. Spectral shifts in this region usually reflect changes in the environment of Trp and Tyr residues. The conformational change is a complex one, involving a series of steps. Because of the nature of the shift, the numbers of Trp and Tyr residues present, and the relative magnitudes of e for Trp and Tyr, Kronman and co-workers concluded that the shift results from environmental alterations for more than one of the buried Trp residues. (At the time of this study, three Trp residues were considered to be buried in bovine a-lactalbumin.) There appears to be no corresponding effect for hen egg-white lysozyme. [However, note the effect of acetic acid studied by Kato et al. (1984).]... 

Both ORD and CD are sensitive to conformational changes and chemical transformation. ORD has the following advantages over CD (1) It is easier to visualize the Cotton effect with ORD because of the three distinct points in the ORD curve the peak, the crossover, and the trough (in that order or in reverse order). (2) An optically active compound that does not show the band in the wavelength range of interest in the absorption spectrum will not show a CD curve but will show a plain ORD curve. CD, on the other hand, possesses an intrinsic discreteness and is a more sensitive tool in examining the environmental effect on the conformation of macromolecules. 

---