| Ultraviolet resonance Raman (UVRR) spectra are reported for several synthetic polynucleotides containing A-U and A-T base pairs. Spectral signatures of Watson-Crick base pairing, especially for the exocyclic frequencies, have been documented. Raman hypochromic ratios appear to be indicative of purine-purine or purine-pyrimidine stacking interactions.;Similar analyses have been performed on the triplex structures poly(rU)-poly(rA)-poly(rU) and poly(rA)-poly(rA)-poly(rU), where Hoogsteen hydrogen bonding becomes important. The base pairing scheme for the latter is confirmed to be via the N1 and N6 of the additional adenine to the uracil C4=O and adenine N6 positions of the core A-U duplex.;The minor groove binding drug, distamycin, interacts analogously with alternating and non-alternating A-T sequences of DNA, as shown by changes in its UVRR spectra upon complexation. Characteristic changes in amide vibrational frequencies are consistent with crystal structure data, where H-bond donation occurs from amide protons to adenine and thymine groups.;By monitoring signals from the aromatic amino acids, tripeptides of the form lys-X-lys, where X=Trp, Tyr, Phe, are shown to bind to single stranded poly(rA) and poly(rU) by stacking of the aromatic against the planar nucleic acid bases. The effect is most pronounced for tyrosine and tryptophan and the polynucleotide structure is not significantly perturbed.;UVRR data for Fe(II) and Fe(III) cytochrome c are presented as a function of ionic strength. Evidence is provided for a weakening of the H-bond between Tyr-48 and the heme propionate in the oxidized protein at low ionic strength. Red-shifted tryptophan excitation profiles are seen for both oxidation states and result from the H-bonded, hydrophobic environment of the indole side chain. The indole H/D exchange rate is significantly affected by both oxidation state and ionic strength; the most rapid exchange occurring for the Fe(III) form at low ionic strength.;Finally, Raman excitation profiles for aqueous solutions of the aromatic amino acids are reported and enhancement mechanisms discussed. |
