In this study, we investigated the thermal decomposition mechanisms of perfluoroalkyl ether carboxylic acids (PFECAs) and short-chain perfluoroalkyl carboxylic acids (PFCAs) that have been manufactured as replacements for phased-out per- and polyfluoroalkyl substances (PFAS). C–C, C–F, C–O, O–H, and CC bond dissociation energies were calculated at the M06-2X/Def2-TZVP level of theory. The α-C and carboxyl-C bond dissociation energy of PFECAs declines with increasing chain length and the attachment of an electron-withdrawing trifluoromethyl (−CF3) group to the α-C. Experimental and computational results show that the thermal transformation of hexafluoropropylene oxide dimer acid to trifluoroacetic acid (TFA) occurs due to the preferential cleavage of the C–O ether bond close to the carboxyl group. This pathway produces precursors of perfluoropropionic acid (PFPeA) and TFA and is supplemented by a minor pathway (CF3CF2CF2OCFCF3COOH → CF3CF2CF2· + ·OCFCF3COOH) through which perfluorobutanoic acid (PFBA) is formed. The weakest C–C bond in PFPeA and PFBA is the one connecting the α-C and the β-C. The results support (1) the C–C scission in the perfluorinated backbone as an effective PFCA thermal decomposition mechanism and (2) the thermal recombination of radicals through which intermediates are formed. Additionally, we detected a few novel thermal decomposition products of studied PFAS.
This study investigates the potential of Pythium oligandrum (strains M1 and 00X48) as a biocontrol agent in suppressing the growth of Fusarium culmorum and the production of mycotoxins during the malting of naturally contaminated barley (Hordeum vulgare). The effects of the biocontrol agent on F. culmorum-infected barley malt (BM) were evaluated through real-time PCR and its impact on mycotoxin production was determined by quantitative analysis of deoxynivalenol (DON) and deoxynivalenol-3-glucoside (D3G). The effect of treatment on BM and beer quality were also determined through European Brewery Convention (EBC) standard methods. Optimal treatment with P. oligandrum strains M1 and 00X48 yielded a 59% and 48% reduction in F. culmorum contamination, by 37% and 17% lower DON, and 27% and 32% lower D3G, respectively. BM treated with both P. oligandrum strains exhibited quality enhancement; beer produced from the BM treated with P. oligandrum strain M1 resulted in no quality deterioration and with 26% and 18% less DON and D3G, respectively, transferred to the final product.
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