Spectral fingerprints of picarbutrazox and its major hydrolysis products: A combined UV-vis, FTIR, Raman and DFT...

The hydrolysis behavior of the fungicide picarbutrazox (PBZ) was investigated with an emphasis on the spectroscopic differentiation of its major transformation products. PBZ and three major hydrolysis products (HP1-HP3) were characterized experimentally using UV-vis, Fourier-transform infrared (FTIR), and surface-enhanced Raman scattering (SERS)/Raman spectroscopy, and the observed spectral features were interpreted with the aid of density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. PBZ exhibits two distinct UV-vis absorption bands at 223 and 273 nm, whereas hydrolysis leads to pronounced spectral changes. HP1 shows a single dominant absorption band at approximately 224 nm, HP2 retains two absorption bands with a blue-shifted long-wavelength feature at around 262 nm, and HP3 displays absorption mainly in the deep-UV region (210-220 nm). FTIR spectra reveal systematic shifts in characteristic vibrational bands associated with carbonyl, CN, and ring skeletal vibrations, reflecting the structural reorganization induced by hydrolysis. In the SERS/Raman spectra, each compound presents a distinct fingerprint pattern, with HP1 exhibiting a prominent diagnostic Raman band at 1007 cm^-1 that is absent in PBZ. The calculated UV-vis, infrared, and conventional Raman spectra supported the assignment of major absorption and vibrational bands, whereas the Raman calculations were not intended to directly simulate SERS intensities. Theoretical analyses further indicate that hydrolysis induces redistribution of charge density and excitation localization, providing a molecular-level explanation for the observed spectral divergence. These results demonstrate that combined multi-spectroscopic measurements and quantum-chemical calculations enable reliable identification and differentiation of PBZ and its hydrolysis products, and provide practical spectral fingerprints for analytical identification of pesticide hydrolysis products. This work provides a PBZ-specific framework linking hydrolysis-product identification, multi-spectroscopic fingerprints, and molecular-level interpretation of hydrolysis-induced spectral changes.