THERMODYNAMIC PARAMETERS OF COOPERATIVE HELIX-TO-COIL TRANSITIONS FROM SYNTHETIC-A-U-RICH OLIGORIBONUCLEOTIDES UP TO 14 BASEPAIRS

Heat induced helix-to-coil transitions are studied in the form of ultr aviolet-hypochromicity profiles by absorbance spectroscopy, and DELTAC (p)-curves by differential scanning calorimetry of self-complementary ribonucleotides. The results are analyzed and compared. Van 't Hoff tr ansition enthalpies derived by UV-experiments incorporating concentrat ion variations are found to differ from six-parameter and two-paramete r Marquardt-fits on the melting profiles. A measure for the maximum nu mber of nucleotides in intermediate states is obtained from a statisti cal deconvolution. It yields a range from 12.5% for the shortest nucle otide up to 31.5% for r(UA)7. Model independent calorimetric data are reported. A limit for intra-molecular loop-formation preference is rea ched by rG(UA)6C within this sequence.