RELATIVE INTENSITIES IN SURFACE-ENHANCED RAMAN-SPECTRA OF 9-METHOXY-2-N-METHYLELLIPTICINIUM CHLORIDE STUDIED BY POTENTIAL-ENERGY DISTRIBUTION OF THE VIBRATIONAL-MODES

Near-infrared Fourier transform (NIR-FT) Raman and surface-enhanced Ra man spectroscopic (SERS) techniques were used in studies of the vibrat ional spectrum of 9-methoxy-2-N-methylellipticinium chloride. NIR-FT-R aman spectra were obtained on the powder and SER spectra were measured in silver colloids using dilute aqueous solutions of the drug (2 x 10 (-6) M, pH 7.5). Some Raman bands in the SER spectrum show increased r elative intensities compared with the corresponding bands in the NIR-F T-Raman spectrum, whereas other bands show decreased relative intensit ies. A general valence force field was used in the calculation of the potential energy distribution of the vibrational modes. This calculati on reveals that bands from the indole moiety of the molecule show inte nsity enhancements, whereas bands arising from modes localized in the isoquinolinium part of the molecule show decreasing intensities in the SER spectra. These results strongly indicate that the indole part of the molecule is close to or attached to the silver surface.