Pyrethroids are one of the best insecticides suggested by the WHO for public health use against vector-borne diseases. Pyrethroid molecules have chiral centres and can exist in different forms, known as stereoisomers. Since not all the stereoisomers are active insecticides, it’s important to be able to determine the inactive forms of pyrethroids that could affect their efficacy. Insecticidal paint has been proposed as an innovative method to bring insects into contact with the insecticide. It is a more targeted, environmentally safe and less harmful to humans approach against vector-borne diseases. However, pyrethroids become unstable especially when embedded in a complex matrix like paint. With the support of the Marie Skłodowska-Curie programme, the ChiPyrNMR project proposed to investigate the molecular stability of the pyrethroids in paint. “Our goal was to better understand the fate of insecticides in complex matrices and improve their effectiveness in paint,″ explains research fellow Federica Aiello. Researchers used nuclear magnetic resonance (NMR) spectroscopy, a very powerful analytical technique that enables the detection of structural changes at a molecular level. They explored the chemical degradation of insecticides under different pH and temperature conditions over time. In combination with mass spectrometry and chromatography it was possible to analyse the degradation of pyrethroids, and determine whether the molecules had undergone isomerisation or hydrolysis. Scientists were also able to quantify the by-product species present in each case and explore the use of stability enhancers, laying the foundation for future investigations. Considerable effort went towards methodology development for extracting the insecticide from the complex matrix without affecting its stability. Researchers were also able to filter NMR spectra and improve the identification of the insecticide signals while suppressing interfering matrix background signals. Moreover, they developed a tailored analytical method for handling and analysing paint samples containing pyrethroids.
ChiPyrNMR impact and future directions
The NMR-based methodology developed for the analysis of insecticides in paint has several advantages compared to traditional chromatographic measurements. It is more environmentally friendly as it requires a relatively small amount of organic solvent and also cost effective due to the reduced experimental analysis time. According to project coordinator Tony Davies, “the accurate analysis of active additives in complex matrices presents an ever-growing challenge for the analytical community.″ Whether it’s about chemical additives in foodstuff or active insecticides in a complex paint formulation, analysis often must be performed in situ. However, the separation process employed in standard methods involves potentially invasive extraction steps causing the active component to change form and leading to invalid results. In comparison, the ChiPyrNMR advanced NMR method is very robust: it minimises degradation and protects the active ingredient, guaranteeing more reliable results. Vector-borne diseases account for more than 17 % of infectious diseases, leading to over 700 000 deaths every year worldwide. ChiPyrNMR work will contribute to vector control through more effective and perhaps less expensive insecticidal paints. Knowledge gained during the project has the potential to be exploited more widely in other systems and support research into other chemical compounds.
ChiPyrNMR, insecticidal paint, pyrethroid, NMR, chiral configuration