title: Influence of tetraalkyl ammonium ions on the structure of poly (rG-dC).poly (rG-dC): unexpected transitions among the Z, A and B conformations.
abstract: The conformation of the double-stranded, mixed ribodeoxyribo polynucleotide, poly (rG-dC).poly (rG-dC), has been examined in the presence of tetraalkyl ammonium ions. Tetramethyl ammonium ion stabilizes the "low salt" Z conformation (1) of the polymer from submillimolar to molar concentrations of the counterion. In the presence of tetraethyl and tetrapropyl ammonium ions the polymer exists in the low salt Z form up to 2 mM concentration of the counterions and then flips to the right hand helical A form. With tetrabutyl ammonium counterions the polymer is in an A conformation at low ion concentrations and converts to a B form at concentrations greater than thirty millimolar. These results are interpreted in terms of electrostatic and solvent interactions of the polynucleotide.
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D004247:DNA / Q000187:drug effects; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D009838:Oligodeoxyribonucleotides; D009843:Oligoribonucleotides; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*
chemical_list: D009838:Oligodeoxyribonucleotides; D009843:Oligoribonucleotides; D000644:Quaternary Ammonium Compounds; D013757:Tetraethylammonium Compounds; C052377:tetrapropylammonium; D019789:Tetraethylammonium; D004247:DNA; C009405:tetrabutylammonium; C027917:tetramethylammonium