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Better tools for combating insect borne diseases by understanding influences on the fate of common pesticides in paint formulations

Periodic Reporting for period 1 - ChiPyrNMR (Better tools for combating insect borne diseases by understanding influences on the fate of common pesticides in paint formulations)

Periodo di rendicontazione: 2017-09-01 al 2019-08-31

Malaria is a life-threatening disease caused by parasites transmitted to people through the bites of infected mosquitoes. Approximately half of the world’s population is at risk of malaria: in 2017, 87 countries and territories suffered from ongoing malaria transmission.i The World Health Organisation (WHO) only declared Europe malaria free as recently as 2016,ii nevertheless it is important to prevent its return. Zika virus, dengue fever and yellow fever are other examples of diseases transmitted by mosquitoes belonging to the genus Aedes; for all these diseases, a vaccine is not yet available or is under clinical trials; therefore, WHO affirms that prevention control is the main way to reduce their spreading, and the use of insecticides constitutes one of the key measures.iii
Insecticidal paints were shown to have comparable performances with respect to other forms of effective vector control, with advantages from several points of view, such as economic, practical and environmental.iv The active ingredients of all WHO-recommended vector controls come from only four classes of insecticides: pyrethroids, organochlorines, organophosphates and carbamates.v We selected pyrethroids as our test insecticide because these compounds are the safest for public health use from both a human and an environmental point of,vii
The topic of the ChiPyrNMR project has been the analysis of chiral pyrethroids aiming at understanding, controlling and improving their stability in complex matrices like paint. NMR spectroscopy was selected as main analytical technique because it allows to investigate in-situ interaction and degradation phenomena at a molecular levelviii and it is already largely employed in paint characterization.ix
The scientific activity can be divided in two main parts. In the first part of the project the focus was on the analysis of pyrethroids stability in dependence of experimental conditions such as pH and temperature. Different degradation paths were identified, namely isomerization of the chiral centres, chemical degradation (hydrolysis) and nucleophilic addition; each of these paths determined the formation of different by-products which were fully identified and characterized by combining different analytical techniques (chromatography, mass spectrometry) to NMR spectroscopy. Furthermore, macrocycles were tested as stability enhancers for chiral pyrethroids, giving interesting results which can be the starting point for future investigations.
The second part of the project was instead dedicated to method development. Among the NMR pulse sequences available and used for analysis of small molecules in complex matrices, the CPMG (Carr-Purcell-Meiboom-Gill) one was chosen as a tool for “filtering” the NMR spectra of complex mixtures by exploiting the differences in relaxation between small molecules and polymers. A multivariate approach (design of experiment) was adopted in order to find a correlation between the acquisition parameters, the experimental ones and the efficiency of the filter, with particular effort in preserving the possibility to perform quantitative analysis.
A tailored analytical method for handling and analysing paint samples containing pyrethroids was then developed, guaranteeing the identification and quantification of the insecticide and the related by-products present in the matrix.
The results of these investigations were presented at different scientific conferences (MCAA 2018, EUROMAR 2018 and SMASH 2018) and two scientific papers are going to be submitted to peer review journals for publication.
The results of the ChiPyrNMR project allowed to better understand the degradation paths of pyrethroids given particular experimental conditions, and the method developed for the analysis of small molecules (in this case chiral pyrethroids) in paint guarantees advantages from several points of view. By using NMR spectroscopy for this investigation, the experimental time for the measurement is considerably reduced (economical advantage); a relatively small amount of organic solvent is required for the analysis in comparison with the actual analytical method which relies on chromatographic measurements where far more solvent is used (environmental impact) and, most importantly, even the slightest variation in the eluent composition determines important differences in the analysis. The NMR method developed is very robust therefore can guarantee more reliable results.

iv K. L. Schiøler, M. Alifrangis, U. Kitron et al., PLoS Negl. Trop. Dis. 2016, 10, e0004518 (and references therein).
vi United States President’s Malaria Initiative. PMI guidelines for entomological monitoring and insecticide resistance management. Washington DC, 2010.
vii M. M. Sibanda, W. W. Focke, F. J. W. J. Labuschagne et al., Malar. J. 2011, 10, 307.
viii A. Martinez-Yusta, E. Goicoechea, M. D. Guillen, Nuclear Magnetic Resonance (NMR) 2014, D. K. Rao, ed.; Nova Science Publishers, Inc. Hauppauge, N. Y., 221.
ix A. Szczygiel, Nucl. Magn. Reson. 2016, 45, 142.
ActiveinsectideImpurities MethoddevelopmentforNMR analysisofpyrethroidsin complexmatrices