DNA Transitions by an Adsorption Impedance Study.

We present a detailed adsorption study of the interface platinum-calf thymus DNA (13 kbp) as a function of concentration, temperature and a constant pH of 7.3. The application of EIS technique and its analysis by complex capacitance spectra is used to determine the structural behavior of the system. The study was carried out at open circuit potential and three different temperatures, 20, 30 and 40°C, making possible to detect changes in the double-layer structure at the electrode interface. An eqtfivalent circuit approach similar to the one proposed by Frumkin-Metik-Gaikazyan-Randles is used to analyze the results and to determine a characteristic time-constant of the adsorption process. The equivalent circuit parameters, i.e double layer capacitance (C_dl), adsorption capacitance (C_ad), adsorption resistance (R_ad) and charge transfer resistance (R_ct) are inspected as a function of DNA concentrations and temperatures. From this analysis as well as the study of the characteristic time-constant it was possible to identify two transitions of the double-layer structure at DNA concentrations ca. 0.36 ± 0.07 and 1.50 mg/mL. EIS results transformed into complex capacitance spectra are successfully compared with those obtained by rheological methods which allow us to identify molecule interactions at the overlap and entanglement concentrations, C* and C_e, respectively. [ABSTRACT FROM AUTHOR]