Stereochemistry of nucleic acids and polynucleotides. II. Allowed conformations of the monomer unit for different ribose puckerings

Abstract

The allowed conformations of a monomer unit of a polynucleotide chain are worked out for different puckerings of the ribose moiety, based on the criteria of minimal contact distances developed in this laboratory. The allowed ranges for the conformational angles θ1, θ2, θ3 and χ thus obtained are found, to a large extent, to be independent of the puckering of the ribose, and are valid for both ribo-and deoxyribonucleosides and nucleotides. Observations on the conformations of nucleosides and nucleotides in the solid state confirm the predictions made on the basis of the hardsphere approximation. It appears from this study that the monomer unit has only a limited range of conformations centered around the values θ1=180°, θ2=±60°, 180°; θ3=210-270° and χ=30°, 220°.