title: 31P-NMR analysis of the B to Z transition in double-stranded (dC-dG)3 and (dC-dG)4 in high salt solution.
abstract: In 4M NaCl solutions (dC-dG)n (n = 3,4; approximately 9 mM) exist as a mixture o +/- B and Z forms. The low and high field components of two 31P NMR resonances originating from internal phosphodiester groups are assigned to the GpC and CpG linkages, respectively. Low temperatures stabilize the Z-forms, which completely disappear above 50 degrees C (n = 3) and 65 degrees C (n = 4). delta H = -44 and -17 kJ/mol for B to Z transition in the hexamer and octamer duplexes, respectively. Temperature dependent changes (0-50 degrees C range) in the spin-lattice relaxation times at 145.7 MHz are distinctly different for the 31P nuclei o +/- GpC and CpG groups. The relaxation data can be explained by assuming that the GpC phosphodiester groups undergo more local internal motion than do the CpG groups.
mesh_terms: D002151:Calorimetry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D009841:Oligonucleotides; D009994:Osmolar Concentration; D013329:Structure-Activity Relationship
chemical_list: D009838:Oligodeoxyribonucleotides; D009841:Oligonucleotides; C041751:tri(deoxycytidylic acid-deoxyguanylic acid); C041754:tetra(deoxycytidylic acid-deoxyguanylic acid)