Raman Spectroscopic Studies Of Flavins, Catecholamines And Psoralens.

Surface enhanced resonance Raman scattering (SERRS) of free flavins and flavoproteins on colloidal silver has been studied with 488 nm excitation. The fluorescence arising from the flavin 480 nm (pi) (--->) (pi)* electronic transition is completely quenched. At concentrations as low as 1 x 10('-9) M, free flavins give good Raman spectra, with evidence for strong adsorption at the silver surface. The active species on the surface has been identified. The several strong SERRS bands known to be ring III modes are perturbed from their frequencies in resonance Raman spectra. N(3) deuterated species give SERRS at the same or slightly shifted frequencies. N(3) substituted flavins do not give any SERRS. The pH dependence of SERRS intensity confirms the N(3) anion as the active species. The active species on the silver sol is the flavin N(3) anion, and it is coordinated to the silver surface through N(3) and the oxygen of C(4)=O. We have attempted to study flavoproteins by SERRS. No frequency differences are observed in the spectra of riboflavin binding protein (RBP), glucose oxidase (GO), flavodoxin (FD), lactate oxidase (LO), p-hydroxybenzoate hydroxylase (PHBH), and Old yellow enzyme (OYE). The resonance Raman spectra of the same flavoproteins are quite different. The SERRS intensities are 5% or less than those of equi-molar free flavins. The SERRS of any flavoprotein disappears on addition of excess apo-RBP. Control experiments demonstrate that SERRS intensities increase with laser exposure. The observed spectra are from dissociated free flavin, not from the intact flavoproteins. In exploratory experiments, the SERS of the neurotransmitters dopamine, epinephrine and norepinephrine have been obtained at a silver electrode. Dopamine gives intense SERS. Similar but weaker SERS is obtained for norepinephrine. Epinephrine gives very weak SERS. Good dopamine SERS is observed at 1(mu)M, and the strong bands are detectable at 0.1(mu)M. There is no interference from ascorbic acid, acetylcholine or glutamic acid. SERS is proposed as a useful technique in neurochemistry. Inverse Raman spectroscopy has been used to obtain the triplet state Raman spectra of 8-methoxypsoralen (8-MOP) and 3-carbethoxypsoralen (3-CP). The furan C=C stretch of 3-CP is perturbed in the triplet state, whereas the pyrone C=C stretch of 8-MOP is perturbed in the triplet state. Spontaneous Raman scattering has been applied to low temperature psoralen systems. The results confirm the inverse Raman findings.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127972/2/8702772.pd