Interaction of DNA and mononucleotides with theophylline investigated using electrochemical biosensors and biosensing

The understanding of DNA-drug interaction mechanism is among the important aspects of biological studies for drug design, discovery and pharmaceutical development processes. Published rather detailed FTIR and UV-visible spectroscopic studies on the interactions of theophylline, theobromine and caffeine with calf thymus DNA have shown effective binding of these methylxanthine derivatives to DNA and RNA involving H-bonds. However, to our knowledge, there is no such investigation using electrochemical approach. As a novelty of the study, in this paper the bioelectrochemical approach has been chosen for the investigation of an interaction of low molecular salmon sperm dsDNA, ssDNA and mononucleotides with theophylline (TP) in aqueous phosphate buffered medium using DNA-based electrochemical biosensors and biosensing in solution phase. Exploitation of the electrochemical approach via changes in square wave voltammetric responses of deoxyguanosine (dGuo) and deoxyadenosine (dAdo) provided a new indication on preferential association of TP with dGuo in the case of double helical dsDNA structure which was not reported previously. Moreover, an attachment of TP molecules outside DNA was found in the presence of high concentration of 3.3 × 10^-4 M TP in solution which diminishes the electron transfer and leads to the difficulties in quantitative evaluation of the TP and dGuo voltammetric responses. The changes in UV-vis and FTIR spectra obtained in the same medium confirmed the association interaction of TP with both nucleobases. Utilizing the model and the published energies of hydrogen bonding stabilization, the formation of a DNA-TP complex was predicted through the intermolecular H-bonds between TP and the NH-CO moiety of guanine and the N-NH₂ moiety of adenine.