Cystine peptides. Disulfide conformations in fourteen membered loops investigated by Raman spectroscopy and circular dichroism

NHCH3 (X = Gly 1, Ala 2, Aib 3, Leu 4 and D-Ala 5), have been investigated by Raman and circular dichroism (CD) spectroscopy. Solid state Raman spectra are consistent with β-turn conformations in all five peptides. These peptides exhibit similar conformations of the disulfide segment in the solid state with a characteristic disulfide stretching frequency at 519 ± 3 cm-1, indicative of a trans-gauche-gauche arrangement about the Cα—Cβ—S—S—Cβ—Cα bonds. The results correlate well with the solid state conformations determined by X-ray diffraction for peptides 3 and 4. CD studies in chloroform and dimethylsulfoxide establish solvent dependent conformational changes for peptides 1, 3 and 5. Disulfide chirality has been derived using the quadrant rule. CD results together with previously reported nuclear magnetic resonance (n.m.r.) data suggest a conformational coupling between the peptide backbone and the disulfide segment

Time-Resolved Resonance Raman Studies on Proton-Induced Electron-Transfer Reaction from Triplet Excited State of 2-Methoxynaphthalene to Decafluorobenzophenone

In this paper time-resolved resonance Raman (TR3) spectra of intermediates generated by proton induced electron-transfer reaction between triplet 2-methoxynaphthalene ((ROMe)-R-3) and decafluorobenzophenone (DFBP) are presented The TR3 vibrational spectra and structure of 2-methoxynaphthalene cation radical (ROMe+) have been analyzed by density functional theory (DFT) calculation It is observed that the structure of naphthalene ring of ROMe+ deviates from the structure of cation radical of naphthalene

Raman induced phase conjugation spectroscopy

Raman induced phase conjugation (RIPC) spectroscopy is a relatively new coherent Raman spectroscopic (CRS) technique using optical phase conjugation (OPC), with which complete Raman spectra of transparent media can be obtained. It is a non-degenerate four-wave mixing technique in which two pulsed laser beams at Ω1 and Ω1 ± Δ where A corresponds to a vibrational frequency of a nonlinear medium mix with a third laser beam at Ω1 to generate a fourth beam Ω1 ± Δ, which is nearly phase conjugate to one of the beams at Ω1. With this technique one can measure the ratio of the resonant and nonresonant components of the third-order nonlinear susceptibilities of the nonlinear media. We have used this technique to get Raman spectra of well-known organic solvents like benzene etc., using pulsed Nd: YAG -dye laser systems. We have also studied the effect of delaying one of the interacting beams with respect to the others and the phase conjugate property of RIPC signals.

Influence of Raman scattering on the cross phase modulation in optical fibers

The effect of Raman scattering on co-propagation of two short optical pulses is considered. The intra pulse Raman scattering causes the self-frequency shift of each pulse. The effect of the inter pulse Raman scattering is to enhance the frequency shift while the stimulated Raman scattering (SRS) term suppresses (enhances) the frequency shift if the center frequency difference between the optical pulses falls to the right (left) of the Raman gain peak. An expression for the frequency shift as a function of the propagation distance is obtained.

Orientational phase transitions in C70: A Raman spectroscopic investigation

Raman investigations of C70 films in the 14-370-K range show significant changes across the orientational phase transitions around 270 and 330 K. Seven of the Raman modes of C70 soften smoothly across the transitions, the magnitude of the decrease in frequencies being in the range of 2-5 cm-1. Linewidths of the bands increase in the transition region over and above the anharmonic contributions.

Polarization Changes of Radiation through Stimulated Raman Scattering

We study change in the polarization of electromagnetic waves due to the stimulated Raman scattering in a plasma. In this process an electromagnetic wave undergoes coherent scattering off an electron plasma wave. It is found that some of the observed polarization properties such as the rapid temporal variations, sense reversal, rotation of the plane of polarization, and change of nature of polarization in the case of pulsars and quasars could be accounted for through stimulated Raman scattering.