title: Influence of terminal 3' phosphates or 2',3'-cyclic phosphates on the conformations of oligoriboadenylates, oligoribocytidylates, and the corresponding monomers.
abstract: The circular dichroism spectra of chemically synthesized adenylate and cytidylate dinucleotides and trinucleotides bearing terminal 3' phosphates have been compared under a variety of conditions with the spectra obtained from the corresponding oligomers with 2',3'-terminal cyclic phosphate groups. Similar comparisons for the mononucleotides are also presented. Although the base stacking of an oligomer with a terminal cyclic phosphate might be expected to be greater than that of the corresponding oligomer with a 3' phosphate from charge repulsion considerations, the magnitudes of the Cotton effects in the former class are always considerably smaller than those in the latter class. This suggests a decreased stacking. The implications of these observations are discussed in light of the compelling crystallographic evidence that cytidine 2',3'-cyclic phosphate adopts an unusual sugar puckering and the syn conformation.
mesh_terms: D000249:Adenosine Monophosphate; D002942:Circular Dichroism; D003568:Cytidine Monophosphate; D008968:Molecular Conformation; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides; D009843:Oligoribonucleotides
chemical_list: D009841:Oligonucleotides; D009843:Oligoribonucleotides; D000249:Adenosine Monophosphate; D003568:Cytidine Monophosphate