Abstract
Equilibrium melting curves were obtained for triplexes, formed by single stranded DNA containing an A10 target with bis-PNA consisting of two T10 decamers. Thermodynamic parameters of melting were determined for Na+ concentrations 50, 200 and 600mM by two methods. The melting enthalpy ΔS° was evaluated from the width of the differential melting curves and from the concentration dependence of the melting temperature. The latter method allowed also evaluating the melting entropy ΔS°. The following results were obtained: ΔH° =—137 kcal/M, ΔS° =—368 cal/M-K, ΔG°298=—27 kcal/M. No dependence of ΔH°, ΔS° and ΔG°29g was observed upon ionic strength within the accuracy of the experiment (± 10%). The absolute values of ΔH°, ΔS° and ΔG°298 are 2 to 3 times higher than the published values of corresponding melting parameters for decameric PNA/DNA duplexes of various nucleic base sequences. The origin of the extremely high stability of the triplexes is discussed.
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