title: Stereodefined phosphorothioate analogues of DNA: relative thermodynamic stability of the model PS-DNA/DNA and PS-DNA/RNA complexes.
abstract: Thermodynamic data regarding the influence of P-chirality on stability of duplexes formed between phosphorothioate DNA oligonucleotides (of either stereo-defined all-R(P) or all-S(P) or random configuration at the P atoms) and complementary DNA or RNA strands are presented. Measured melting temperatures and calculated DeltaG(37)(o) values showed that duplexes formed by PS-DNA oligomers with DNA strands are less stable than their unmodified counterparts. However, relative stability of the duplexes ([all-R(P)]-PS-DNA/DNA vs [all-S(P)]-PS-DNA/DNA) depends on their sequential composition rather than on the absolute configuration of PS-oligos, contrary to the results of theoretical considerations and molecular modeling reported in the literature. On the other hand, for all six analyzed pairs of diastereomers, the [all-R(P)]-PS isomers form more stable duplexes with RNA templates, but the origin of stereodifferentiation depends on the sequence with more favorable entropy and enthalpy factors which correlated with dT-rich and dA/dG-rich PS-oligomers, respectively.
mesh_terms: D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D019277:Entropy; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D012313:RNA / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013816:Thermodynamics; D013873:Thionucleotides / Q000737:chemistry*
chemical_list: D009692:Nucleic Acid Heteroduplexes; D009838:Oligodeoxyribonucleotides; D013873:Thionucleotides; D012313:RNA; D004247:DNA