Abstract
The double helical structure of DNA offers various binding sites for the interaction of ligands or proteins. Interactions using minor groove, major groove, and through intercalation are the major types of binding mechanisms of DNA-ligand interactions. The lowering in the absorption intensity along with bathochromic shift is the indication of intercalation binding mode of the dye into the base pairs of the DNA. In this study, the interaction of phenothiazine dyes with calf-thymus DNA (ctDNA) in physiological buffer (pH 7.4) was studied using UV-visible, fluorescence, circular dichroism (CD), and UV-thermal denaturation spectroscopy. The binding constants were calculated at different temperatures with the help of fluorescence spectroscopy. CD signals signify that B-form of DNA might become more compact, upon binding of the dyes. Also, induced circular dichroism is observed which confirms the dye-DNA complex formation. Stabilization of DNA double helix upon binding with dyes was confirmed by the increase in Tm of ctDNA. Based on thermal melting profiles, it was found that thionine acetate is most promising in stabilizing the DNA double helix, in comparison to other two dyes. Also, binding constants calculated by fluorescence is in accordance with the thermal melting analysis. These results are indicative of the intercalation binding mode between dyes and the DNA. The binding affinity of the dyes to DNA is found to be in order as thionine acetate > azure A > azure B. Such preliminary studies facilitate our understanding about various types of DNAligand interactions and provide clues for designing new and more effective drugs.
Highlights
The interaction studies of small molecule with nucleic acids are much-explored research area due to their binding to the nucleic acid structures and their interface in transcription and replication processes
Azure A, and azure B were purchased from Helix Biosciences
The spectroscopic analysis of the interaction of the three phenothiazinium dyes (Thionine acetate, azure A, Azure B) with calf-thymus DNA (ctDNA) was carried out using biophysical techniques such as UVabsorption, fluorescence, circular dichroism and thermal melting analysis
Summary
The interaction studies of small molecule with nucleic acids are much-explored research area due to their binding to the nucleic acid structures and their interface in transcription and replication processes. The interaction studies of ligands with the DNA are highly important in the area of chemotherapeutic applications. It is very well documented that anticancer drugs show their biological action through their interaction with the DNA molecule. To understand the molecular mechanism of the DNA-drug interaction and their effect on a particular disease, this spectroscopic study of the comparative analysis of various dyes had been planned and performed. Thionine acetate (TA), azure A (AA), and azure B (AB) are phenothiazinium dyes with the identical basic phenothiazinium skeleton, with variations in the groups present at 3 and 7 positions (Figure 1)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
