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- Title
Stability of a Short DNA Duplex as a Function of Temperature: the Effect of ΔC<sub>p</sub> and Added Salt Concentration.
- Authors
Drobnak, Igor; Seručnik, Mojca; Lah, Jurij; Vesnaver, Gorazd
- Abstract
Recently, it has been shown that ΔCp effects accompanying the helix-to-coil transitions of DNA duplexes are not negligible. To find out if this is the case also with a short model (5'-CGAATTCG-3')2 duplex we studied its thermal unfolding by high sensitivity differential scanning calorimetry (DSC) at 0, 0.1, 0.3 and 1 M added NaCl. We succesfully described the measured DSC thermograms by the model function that is based on the two-state approximation of the unfolding process and contains three adjustable parameters: T½ -- the melting temperature, ΔH(T½) -- enthalpy of unfolding at T½ and ΔCp -- the change of heat capacity upon DNA unfolding. These ΔH(T½) values are in good agreement with those obtained by the straightforward integration of the DSC thermograms. From the available experimental data a ΔH(T½) versus T½ plot was constructed and ΔCp was obtained as a slope of the observed linear relationship. We believe that excellent agreement between this ΔCp and the one obtained as adjustable parameter from fitting the experimental DSC thermograms strongly supports our suggestion that ΔCp accompanying unfolding of DNA is independent of temperature an added salt concentration and may be accurately determined from the described fitting procedure. Analysis of our results shows that even for short DNA duplexes the errors in the nearest-neighbor estimates of ΔG(25 °C), ΔH(25 °C) and ΔS(25 °C) of unfolding based on the ΔCp = 0 assumption may be significant. It also shows that the experimental T½ versus ln[Na+] slope depends on the salt concentration and agrees reasonably well with the one predicted by the electrostatic polyelectrolyte theory.
- Subjects
DNA; TEMPERATURE; SALT; THERMODYNAMICS; CALORIMETRY; STABILITY (Mechanics)
- Publication
Acta Chimica Slovenica, 2007, Vol 54, Issue 3, p445
- ISSN
1318-0207
- Publication type
Article