VIBRATIONAL ANALYSIS OF NUCLEIC ACIDS .4. NORMAL MODES OF THE DNA PHOSPHODIESTER STRUCTURE MODELED BY DIETHYL PHOSPHATE

摘要

Raman and ir spectra ale reported for diethyl phosphate [(CH3CH2O)(2)PO2-] and diethylphosphate isotopomers incorporating carbon-13 at methylene group sites [((CH3CH2O)-C-13)(2)PO2-] and deuterium substituents on methyl and methylene carbons [(CH3CD2O)(2)PO2-, (CD3CH2O)(2)PO2-, (CD3CD2O)(2)PO2-]. The vibrational spectra are analyzed to develop a consistent set of assignments for the C-C-O-P(O-2(-))-O-C-C network, which series as a model for the nucleic acid phosphodiester backbone. The present study resolves previously conflicting vibrational assignments for the phosphodiester skeleton and provides a firm empirical basis for interpreting conformationally sensitive modes of DNA and RNA. Ab initio vibrational analyses have also been conducted on the above isotopomers of diethyl phosphate in the trans-gauche-gauche-trans conformation, optimized using the 3-21+G* basis set at the restricted Hartree-Fock level. The ab initio calculations are in good agreement with the empirical results, thus strengthening the proposed assignment scheme for Raman and infrared spectra. The present study provides a basis for improvement of empirical force fields utilized in previous normal coordinate analyses of the nucleic acid phosphodiester group. (C) 1996 John Wiley & Sons, Inc. [References: 48]