strongly by solvents (1). The effect is ascribed to the solva-Electroreflectance (ER), ellipsometry, and surface-enhanced tion shell which surrounds the organic solute molecule and Raman spectroscopy (SERS) measurements were performed for whose properties depend on interactions between the solvent immobilized tryptamine on polycrystalline gold electrodes. SERS and solute molecules. In aqueous solutions there are strong study indicates that the indole ring does not interact directly with interactions between the water electric dipole and residual the gold surface. Ellipsometric measurements yielded a thickness charges on the solute molecule. The net result of the interacof the tryptamine layer of (1.98 { 0.05) nm and an inferred surface tions is that the electronic transitions of organic molecules concentration of 3.3 1 10 06 mol/m 2 . ER measurements were perin aqueous solution have to be viewed as occurring between formed in the wavelength region 200-300 nm using the NIST states of a system composed of the solute molecule and its synchrotron ultraviolet radiation facility (SURF). The ER resolvation shell. This is the main reason why purely spectrosponse was interpreted as a Stark shift in the tryptamine absorption line at 218 nm. Assuming that the tryptamine layer consists scopic studies are performed with vapor samples (2). In the of two stacked tryptamine molecules associated at the indole rings, case of tryptamine immobilized on an electrode, the charges a unified analysis of ER and ellipsometric data gave the difference associated with the electrode will exert a strong influence between the static dipole moments of the solvated ground and on the solvation shell of the immobilized tryptamine moleexcited states of 0.65 1 10 030 C m in low ionic strength buffer cule and hence on the electronic absorption bands. In the (0.01 M PBS) and 0.25 1 10 030 C m in high ionic strength buffer following, we will attempt to make plausible that the ER (0.01 M PBS / 1.0 M NaClO 4 ). The results point to the imporand ellipsometric measurements can be interpreted in terms tance of the composition of the solvation shell. Semiempirical of potential induced shift in the tryptamine absorption band quantum chemistry calculations of tryptamine molecules gave a where the shift depends on the difference in the static dipole qualitative explanation of the ER response in the low ionic buffer.
moments of the ground and excited states of the solvated
The large ER response suggests that the method could be applied tryptamine molecule. The interpretation will be in the conto the study of the tryptophan environment in adsorbed proteins.
text of an assumed model of the structure of the tryptamine α§ 1998 Academic Press layer.
ER has been used to study metal centers of proteins undergoing electron transfer (ET) with the electrode (3, 4). The