Spectroscopic Analysis of the Binding of Paraquat and Diquat Herbicides to Biosubstrates

• Main Authors: Francesca Macii, Rebecca Detti, Francesca Rita Bloise, Stefania Giannarelli, Tarita Biver
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: intercalation; external binding; transport; inner filter effect; micelles; liposomes
• Online Access: https://www.mdpi.com/1660-4601/18/5/2412

The study of the interaction of persistent organic pollutants with biosubstrates helps to unravel the pathways for toxicity, however, few mechanistic data are present in the literature for these systems. We analyzed the binding of paraquat (PQ) and diquat (DQ) herbicides to natural calf thymus DNA and a DNA G-quadruplex by spectrophotometric titrations, ethidium bromide exchange tests, viscometry, and melting experiments. The interaction with bovine serum albumin (BSA) protein was studied spectrofluorimetrically at different temperatures. The retention of the targets on positive, negative, and neutral micellar aggregates and liposomes was analyzed by ultrafiltration experiments. Despite some favorable features, PQ and DQ only externally bind natural DNA and do not interact with DNA oligonucleotides. Both herbicides bind bovine serum albumin (BSA). PQ binds BSA mainly according to an electrostatics-driven process. However, ultrafiltration data also show that some hydrophobic contribution participates in the features of these systems. The practical problems related to unfavorable spectroscopic signals and inner filter effects are also discussed. Overall, both herbicides show a low affinity for nucleic acids and weak penetration into liposomes; in addition, the equilibrium constants values found for BSA system suggest optimal conditions for transport in the body.