PEG–calf thymus DNA interactions: Conformational, morphological and spectroscopic thermal studies

•PEG binds with ctDNA by weak to moderate binding forces and not via intercalative interactions.•PEG able to stabilize ctDNA structure.•PEG causes condensation of ctDNA. The main aim of this study is to provide understanding for the interaction modes and the binding affinity based on the study of PEG 400 that binds to ctDNA. The effects of the PEG-400-to-ctDNA ratio, pH, incubation time and thermal stability of ctDNA on PEG–ctDNA biocomplex formation were studied. UV–vis–NIR absorption analysis indicated that PEG forms a complex with ctDNA via a mechanism other than intercalation. The results of thermal denaturation studies showed that the PEG–ctDNA biocomplex helix was stabilised, with a resulting increase in the PEG–ctDNA melting temperature. FTIR analysis indicated that the PEG binds to ctDNA through weak to moderately strong hydrophilic and hydrophobic interactions with the base pairs of ctDNA. TEM micrographs showed that the addition of PEG to ctDNA caused ctDNA to condense with PEG molecules into an irregular aggregate structure. These results demonstrate that the PEG–ctDNA biocomplex has potential applications in biomedical sciences.