Spectroscopic and Chemometrics Analysis of the Hydrolytic Process of Folpet and Its Interaction with DNA

Hydrolysis of the pesticide folpet [N-(trichloromethylthio) phthalimide] in aqueous solution in the absence or presence of calf thymus DNA (ctDNA) was investigated using UV–Vis absorption spectroscopy, and the interactions of folpet and its hydrolyzates with ctDNA were determined by fluorescence and circular dichroism spectroscopy, coupled with viscosity and melting temperature measurements. The absorption spectra data was further analyzed by alternate least squares, a chemometrics method, and the concentration profiles of the reacting species (folpet, unstable intermediate, phthalimide and phthalic acid) and their pure component spectra were simultaneously extracted to monitor the hydrolytic process. It was found that the hydrolytic process consists of at least two steps, generation of an unstable intermediate and production of its end hydrolyzates, phthalimide and phthalic acid. Addition of ctDNA significantly affects the hydrolysis of folpet. The results from the competitive binding with intercalator ethidium bromide, ctDNA melting and viscosity measurements, and circular dichroism studies indicate that folpet and the intermediate can intercalate into the double-helix of DNA, phthalic acid is bound to DNA by a partial intercalation, while phthalimide does not show binding to ctDNA. Moreover, the binding of folpet (or the intermediate) and phthalic acid to ctDNA induced structural changes of the DNA.