Circular dichroism of nucleoside derivatives. VIII. Coupled oscillator calculations of molecules with fixed structure

Abstract

A method of calculating rotational strengths by a bond-bond coupled oscillatory theory is described. The technique is applied to a variety of specially chosen molecules to check the theory at various levels of approximation. Good agreement with experiment, particularly in the case of the cyclonucleosides, suggests that coupled oscillator theory accounts for most of the observed optical activity in the pyrimidine nucleosides. The calculation is particularly useful for structure determination because of its simplicity and complete dependency on bond orientations within a molecule.

Impact of phosphorylation on the encapsulation of nucleoside analogues within porous iron(iii) metal–organic framework MIL-100(Fe) nanoparticles

“…furanose unit and/or the torsion angle between the sugar and the thymine base may change leading an increased fraction of molecules to the syn range. 31 The effect is reasonably inuenced by the specic interactions of each molecule with the MOF frame. In the case of the AZT-MOF system, no change in the CD intensity was observed, in agreement with the lack of a strong interaction between AZT and MOF.…”

“…Both the sign and the magnitude of a CD band depend on the nature and orientation of the sugar moieties relative to the transition dipole moment which pertains to the optical transition under consideration. 31,32 In particular, the molecular ellipticity of the B 2u Cotton effect is a function of the F CN torsion angle and the conformation of the sugar ring. 31 Structural and solvent effects determine the equilibrium of all the nucleoside conformations.…”

“…31,32 In particular, the molecular ellipticity of the B 2u Cotton effect is a function of the F CN torsion angle and the conformation of the sugar ring. 31 Structural and solvent effects determine the equilibrium of all the nucleoside conformations. In the case of the pyrimidine nucleosides, the CD signal in the region of 270 nm depends on the ratio between the anti and syn conformations: a positive signal demonstrates the prevalence of the anti conformations, a negative band the prevalence of the syn conformations.…”

Optical activity and electronic absorption spectra of some simple nucleosides related to cytidine and uridine: all-valence-shell molecular orbital calculations.

“…Calculations of the rotational strengths ofpyrimidine nucleosides have previously been based on models in which the molecule is partitioned into spatially separated groups (30)(31)(32)(33)(34)(35)(36)(37)(38)(39) (71) with spectroscopic parameterization (CNDO/S) is used without modification except for changes designed to enhance the efficiency of the computation. The Nishimoto-Magata approximation was used to represent the two-center Coulomb repulsion integrals, and excited states were generated from configuration interaction between the 120 lowest energy one-electron excitations.…”

“…Along with difficulties associated with treating the weak perturbation effects of the nonchromophoric sugar, this incomplete knowledge has hindered the development of theoretical models for calculating the rotatory parameters and extracting stereochemical information from them. In spite of these problems, CD studies of nucleosides have produced some useful rules and diagrams relating the sign of the first CD band to anomeric configuration and to conformation (10,(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61).…”