title: Bond order and charge localization in nucleoside phosphorothioates.
abstract: In the recent literature on nucleoside phosphorothioate anions the structural formulas show a double bond between phosphorus and sulfur and a single bond between phosphorus and oxygen with a negative charge localized on oxygen. However, a review of physical data on these compounds shows the reverse to be the case; that is, in phosphorothioate anions the P-S bond is a single bond with a negative charge localized on sulfur, while the P-O bond order for exocyclic and nonbridging oxygens is greater than 1, approaching 2 in O-alkyl phosphorothioate monoanions and O,O-dialkyl phosphorothioates. The P-O bond orders in phosphorothioate dianions and trianions approach 1 1/2 and 1 1/3, respectively, owing to delocalization of negative charge among two or three oxygens. These conclusions are based on bond lengths obtained from x-ray crystallographic data and electron diffraction, the magnitudes of the effects of 18O on the 31P-nuclear magnetic resonance chemical shifts of phosphorus in nucleoside [18O]phosphorothioates, the pH-dependence of 17O-NMR chemical shifts in [17O]phosphate and [17O]thiophosphate, the vibrational spectra of thiophosphate di- and trianions, and the pKa (dissociation constant) values for phosphoric and thiophosphoric acids.
authors.forename: P A
authors.initials: PA
authors.lastname: Frey
authors.forename: R D
authors.initials: RD
authors.lastname: Sammons
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002627:Chemistry, Physical; D000242:Cyclic AMP / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D010710:Phosphates / Q000378:metabolism; D010756:Phosphoric Acids / Q000378:metabolism; D013873:Thionucleotides / Q000378:metabolism
chemical_list: D010710:Phosphates; D010756:Phosphoric Acids; D013873:Thionucleotides; D000242:Cyclic AMP; C030242:phosphoric acid; C035638:thiophosphoric acid