[Study of helix-coil transition of an oligodeoxyribonucleotide with self-complementary sequence d-ApCpApTpGpT by 1H-NMR].

The helix-coil transition of dACATGT was investigated by 1H-NMR spectroscopy at 276 and 400 MHz. The results suggest that the fraying process only consists of two stages: The AT extreme base pairs open at first then the GC internal and AT central base pairs open simultaneously at higher temperatures. The midpoint temperature of each base pair, the helix-coil dissociation constants and the corresponding enthalpy were determined from the delta = f (t degree) curves of non exchangeable protons. The unusual line width of the H1, proton resonance of the cytidine residue, observed at t less than 42 degree C was attributed to the fact that this proton is located in the proximity of the (cytoxine) C = O ... H2N (guanine) hydrogen bond.