Experimental and theoretical vibrational study of the fungicide pyraclostrobin

ALFREDO NICOLÁS DOMINGUEZ; GERMÁN EZEQUIEL EMMERT; DIEGO MAURICIO GIL; ALVAREZ, ROSA M. S.

SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY.

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2021

1386-1425

The vibrational study of the pyraclostrobin (methyl N-(2-{[1-(4-chlorophenyl)-1H-pyrazol-3-yl]oxymethyl}phenyl) N-methoxycarbamate) molecule, a synthetic fungicide for agricultural uses, was performed.Pyraclostrobin belongs to the strobilurin family and acts by inhibiting the fungus respiratory chain at thelevel of Complex III, becoming an excellent agent for preventive, curative and eradicative activitiesagainst a wide range of fungal plant pathogens. However, its presence needs to be monitored to avoidthe excessive and/or improper use that may compromise human or environmental health. The FTIRand Raman spectra of pyraclostrobin in pure solid state were recorded and compared with those obtainedfrom both the substance in CH2Cl2 solution and in an agricultural commercial product (Comet BASF).The spectral analysis was complemented with quantum-chemical calculations at the DFT level(B3LYP/6-311G*) for the predictions of the molecular geometry and its vibrational behavior. The highflexibility of the molecule was explored by performing potential energy scans on several dihedral anglesand the results suggested that the main conformer of pyraclostrobin is that possessing the ortho-substituted benzene ring in perpendicular orientation regarding the plane that contains the ether group and thepyrazole ring, although the presence of a second preferred conformation in the experimental vibrationalspectra was not ruled out. Among the many vibrational bands of pyraclostrobin that were well identifiedin the spectrum of the composite product for agricultural use, the one located at 936 cm1 stood out. Thissignal was assigned to a vibration of the pyrazole ring and promised to be a good candidate as marker ofthe presence of the fungicide in complex matrixes.