A. Voroshilov

Secondary Structure of Bovine Albumin as Studied by Polarization-Sensitive Multiplex CARS Spectroscopy

The first application of polarization-sensitive multiplex coherent anti-Stokes Raman spectroscopy (MCARS) in the absence of resonance enhancement to the resolution of the secondary structure of a protein in solution is reported. Polarization MCARS spectra of bovine albumin in D2O were obtained in the range 1370 to 1730 cm−1 with the aid of the background suppression technique. The spectra were fitted simultaneously with a single set of parameters (band positions, bandwidths, amplitudes, and depolarization ratios). Polarized Raman spectra simulated with these parameters revealed a good correspondence with the spontaneous Raman spectra measured. The broad amide I′ band was decomposed assuming the three major secondary conformations of protein, of which the contribution of β-sheet structure was found to be negligible. Relative weights of α-helix and random coil conformations agree well with the estimates obtained with Raman and circular dichroism (CD) spectroscopies.

On the coherent vibrational phase in polarization sensitive resonance CARS spectroscopy of copper tetraphenylporphyrin

Polarization sensitive multiplex spectroscopy of resonance coherent anti-Stokes Raman scattering (CARS) of copper(II)-tetraphenylporphyrin in solution (CH2Cl2) is reported. The measurements were performed in the Q band range of the porphyrin electronic absorption. Four polarized CARS spectra were resolved in 1300–1650 cm−1 Raman range and were simultaneously fitted with a single set of vibrational parameters (band positions, bandwidths, amplitudes, depolarization ratios, and phases). The obtained coherent vibrational phases of A1g, A2g, and B1g skeletal modes of the porphyrin macrocycle appeared to correlate strongly with the mode vibrational symmetry. The origin of such correlation is analyzed within a model of the third-order nonlinear electric susceptibility χ(3). The proposed model is based on multidimensional displaced harmonic oscillator in the Herzberg–Teller expansion of Raman polarizability. The coherent vibrational phases of modes of different symmetry classes are directly affected by the symmet...

Polarization properties of v10, v11, and v19 modes of (de)oxyheme of hemoglobin as obtained from three-color CSRS

We report polarization sensitive coherent Stokes Raman scattering (CSRS) measurements of oxy- and deoxyhemoglobin in aqueous solutions that were carried out under electronic resonance with the Q absorption bands. All independent susceptibility (Chi) (3) components as well as anisotropic and anti-symmetric scattering contributions were resolved within frequency nondegenerate CSRS scheme. Eight bands of oxy- and five of deoxyhemoglobin were observed in the range 1500 - 1680 cm-1. Each set of dispersion profiles was simultaneously fitted with a set of parameters including band positions, widths, amplitudes, phases and, importantly, all the CSRS depolarization ratios. On this basis the major bands were assigned to non-totally symmetric (nu) 10, (nu) 11, and (nu) 19 modes of the porphyrin macrocycle. These displayed a clear correlation of vibrational phase with the mode symmetry. Of eight bands resolved in oxyHb spectra three were attributed to features of intermediate deoxyHb, caused by a partial photolysis of oxyhemes. On a nanosecond time scale they were found essentially similar to those found for stable deoxyHb. A detectable isotropy was observed for all non-totally symmetric modes of both oxy- and deoxyhemes. The (nu) 10 and (nu) 11 modes were found to exhibit anti-symmetry as well. The decrease in depolarization ratio (rho) 1212R of anomalously polarized (nu) 19 mode from 7.7 (oxyheme) to 4.3 (deoxyheme) was detected. The latter evidenced heme deformation related with a further doming that occurs upon release of oxygen.