In Vitro Study on the Interactions between Native Herring Sperm DNA and Melamine in the Presence of Ca2+ by Spectroscopic and Voltammetric Techniques

In vitro studies on the interactions between native Herring Sperm DNA (HS-DNA) and melamine (MM) in the presence of Ca2+, have been investigated by spectrophotometric, spectrofluorometric, melting temperature (T-m), viscosimetric and cyclic voltammetric techniques. Comparative studies were carried out with those of the denaturalized DNA and absence of Ca2+. Spectrophotometric and spectrofluorometric results showed a slight bathochromic shift (similar to 2 nm) of the absorption band at the 258 nm, with a significant hypochromic effect (the absorbency at 258 nm decreased similar to 0.12, similar to 17 %). A small increase in melting temperature (2 degrees C) and an increase in the fluorescence of methylene blue (MB)-DNA solutions were observed. The cyclic voltammetric study results indicated that some electrochemical-active complexes (MM-Ca2+ and DNA-MM-Ca2+) might be formed with an adsorption controlled quasireversible electrochemical process. For the MM-DNA system in the presence of Ca2+ (1.0 g L-1, pH = 7.0), the charge transfer coefficients (alpha) were 0.27 and 0.25, with the velocity constant (k(s)) at 0.32 and 0.36 s(-1) before and after DNA added, respectively. The interaction constants of the MM-DNA-Ca2+ systems were found to be similar to 105 L mol(-1). The thermodynamic studies suggested that the interaction processes of those in the presence of Ca2+ were exothermic favored (Delta H< 0) and entropy favored (Delta S> 0), which indicated that the MM might interact with HS-DNA by a mixture mode of non-covalent groove binding via hydrogen bonds and electrostatic interaction with the negatively charged nucleic acid sugar-phosphate structure.