Electrochemical and Spectroscopic Study of Samarium Ion Interaction with DNA in Different pHs

In this work, for the first time the electrochemical behavior of the Sm3+ and Sm3+ ion interaction with short single strand DNA (ssDNA) sequence in two pHs was studied. Then the UV-Vis spectroscopic method was used for supporting these evidences. The interaction between Sm3+ and ssDNA have different binding mode in different pHs. The ratio between [Sm3+] and [ssDNA] is dependence to pH and pKa of bases. In pH 2.7 Sm3+ binds to ssDNA mainly by electrostatic attraction. Binding number, n, of 2 of Sm3+ per ssDNA and binding constant, k´, of 1.75 × 10-3 M-1 were obtained with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. In this pH, the bases of ssDNA are totally protonated and Sm3+ interacts electrostatically with phosphate groups. The UV-Vis study showed similar results. The results in pH 5.5 show that Sm3+ can bind to ssDNA with electrostatic and covalent bond. In this pH, beside phosphate groups, the bases can be interacted to Sm3+, too. The binding number 4 of Sm3+ per ssDNA was obtained.