POLARIZED MICRO-RAMAN SPECTROSCOPIC STUDIES OF NUCLEIC-ACID - LOCAL RAMAN TENSORS IN INOSINE-5'-MONOPHOSPHORIC ACID AND THE ORIENTATION OF HYPOXANTHINE RESIDUE IN POLY(RI)CENTER-DOT-POLY(RC) FIBER

The polarized Raman spectra of a single crystal of the barium salt of inosine monophosphoric acid hexahydrate (Ba-IMP . 6H(2)O) have been ob served with 488.0 nm excitation. For each Raman band, the relative int ensities of aa, bb, cc, ab and be tensor components have been determin ed. The tensor quotients from the crystal were augmented with measured depolarization ratios in solution. From these experimental data, the shape and orientation of the localized Raman scattering tensor were de duced for each of the normal modes of the hypoxanthine residue, phosph ate moiety and ribose portion. The hypoxanthine residue gives a strong Raman band around 1553 cm(-1), which shows rather large depolarizatio n ratio, rho = 0.32, in aqueous solution, and shows a great scattering anisotropy in the single crystal of IMP. The shape and orientation of the Raman tensor associated to this 1553 cm(-1) vibration have been d etermined: one of its principal axes (gamma-axis) is directed along th e long axis (N1-N7) of the hypoxanthine residue and the relative magni tudes of its components are given as r(1) = alpha(xx)/alpha(zz) = -1, r(2) = alpha(yy)/alpha(zz) = 12. Next, a general relation has been sho wn between the orientation angles (theta and chi) of such a local Rama n tensor in a uniaxial biological fiber and the anisotropy of Raman sc attering intensities from the fiber. By the use of this relation, a di scussion has been made of the orientation of the hypoxanthine residue in a poly(rI). poly(rC) duplex fiber.