Polarized Micro Raman Spectroscopic Studies of Nucleic Acid: Local Raman Tensors in Inosine-5′-monophosphoric Acid and the Orientation of Ekypoxanthine Residue in Poly(rI). Poly(rC) Fiber

Abstract

The polarized Raman spectra of a single crystal of the barium salt of inosine monophosphoric acid hexahydratc (Ba-IMP.6H₂O) have been observed with 488.0 nm excitation. For each Raman band, the relative intensities of aa, bb, cc, ab and bc tensor components have been determined. 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 deduced for each of the normal modes of the hypoxanthine residue, phosphate moiety and ribose portion. The hypoxanthine residue gives a strong Raman band around 1553 cm⁻¹, which shows rather large depolarization ratio, p = 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 determined: one of its principal axes (y-axis) is directed along the long axis (N1-N7) of the hypoxanthine residue and the relative magnitudes of its components are given as r ₁ = α_xx/α_zz = −1, r ₂ = α_yy/α_zz = 12. Next, a general relation has been shown between the orientation angles (θ and χ) of such a local Raman tensor in a uniaxial biological fiber and the anisotropy of Raman scattering intensities from the fiber. By the use of this relation, a discussion has been made of the orientation of the hypoxanthine residue in a poly(r1). poly(rC) duplex fiber.

^‡This paper is dedicated to Professor Yoshihisa Mizuno on the occasion of his 75th birthday.

Notes

^‡This paper is dedicated to Professor Yoshihisa Mizuno on the occasion of his 75th birthday.