This study investigates critical structure–reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While C n F2n+1–COO– with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric C n F2n+1–CH2CH2–COO– and C n F2n+1–SO3 – showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO–, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C–F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C–F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C–F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.

dCorrinoids are cobalt-containing molecules that function as enzyme cofactors in a wide variety of organisms but are produced solely by a subset of prokaryotes. Specific corrinoids are identified by the structure of their axial ligands. The lower axial ligand of a corrinoid can be a benzimidazole, purine, or phenolic compound. Though it is known that many organisms obtain corrinoids from the environment, the variety of corrinoids that can serve as cofactors for any one organism is largely unstudied. Here, we examine the range of corrinoids that function as cofactors for corrinoid-dependent metabolism in Dehalococcoides mccartyi strain 195. Dehalococcoides bacteria play an important role in the bioremediation of chlorinated solvents in the environment because of their unique ability to convert the common groundwater contaminants perchloroethene and trichloroethene to the innocuous end product ethene. All isolated D. mccartyi strains require exogenous corrinoids such as vitamin B 12 for growth. However, like many other corrinoid-dependent bacteria, none of the well-characterized D. mccartyi strains has been shown to be capable of synthesizing corrinoids de novo. In this study, we investigate the ability of D. mccartyi strain 195 to use specific corrinoids, as well as its ability to modify imported corrinoids to a functional form. We show that strain 195 can use only specific corrinoids containing benzimidazole lower ligands but is capable of remodeling other corrinoids by lower ligand replacement when provided a functional benzimidazole base. This study of corrinoid utilization and modification by D. mccartyi provides insight into the array of strategies that microorganisms employ in acquiring essential nutrients from the environment.

This study explores structure–reactivity relationships for the degradation of emerging perfluoroalkyl ether carboxylic acid (PFECA) pollutants with ultraviolet-generated hydrated electrons (eaq –). The rate and extent of PFECA degradation depend on both the branching extent and the chain length of oxygen-segregated fluoroalkyl moieties. Kinetic measurements, theoretical calculations, and transformation product analyses provide a comprehensive understanding of the PFECA degradation mechanisms and pathways. In comparison to traditional full-carbon-chain perfluorocarboxylic acids, the distinct degradation behavior of PFECAs is attributed to their ether structures. The ether oxygen atoms increase the bond dissociation energy of the C–F bonds on the adjacent −CF2– moieties. This impact reduces the formation of H/F-exchanged polyfluorinated products that are recalcitrant to reductive defluorination. Instead, the cleavage of ether C–O bonds generates unstable perfluoroalcohols and thus promotes deep defluorination of short fluoroalkyl moieties. In comparison to linear PFECAs, branched PFECAs have a higher tendency of H/F exchange on the tertiary carbon and thus lower percentages of defluorination. These findings provide mechanistic insights for an improved design and efficient degradation of fluorochemicals.

Dehalococcoides ethenogenes strain 195 (DE195) was grown in a sustainable syntrophic association with Desulfovibrio vulgaris Hildenborough (DVH) as a co-culture, as well as with DVH and the hydrogenotrophic methanogen Methanobacterium congolense (MC) as a tri-culture using lactate as the sole energy and carbon source. In the co-and tri-cultures, maximum dechlorination rates of DE195 were enhanced by approximately three times (11.0±0.01 lmol per day for the co-culture and 10.1 ± 0.3 lmol per day for the tri-culture) compared with DE195 grown alone (3.8 ± 0.1 lmol per day). Cell yield of DE195 was enhanced in the co-culture (9.0 ± 0.5 Â 10 7 cells per lmol Cl À released, compared with 6.8 ± 0.9 Â 10 7 cells per lmol Cl À released for the pure culture), whereas no further enhancement was observed in the tri-culture (7.3±1.8 Â 10 7 cells per lmol Cl À released). The transcriptome of DE195 grown in the co-culture was analyzed using a wholegenome microarray targeting DE195, which detected 102 significantly up-or down-regulated genes compared with DE195 grown in isolation, whereas no significant transcriptomic difference was observed between co-and tri-cultures. Proteomic analysis showed that 120 proteins were differentially expressed in the co-culture compared with DE195 grown in isolation. Physiological, transcriptomic and proteomic results indicate that the robust growth of DE195 in co-and tri-cultures is because of the advantages associated with the capabilities of DVH to ferment lactate to provide H 2 and acetate for growth, along with potential benefits from proton translocation, cobalamin-salvaging and amino acid biosynthesis, whereas MC in the tri-culture provided no significant additional benefits beyond those of DVH.