The C−F bond is one of the strongest single bonds in nature. Although microbial reductive dehalogenation is well known for the other organohalides, no microbial reductive defluorination has been documented for perfluorinated compounds except for a single, nonreproducible study on trifluoroacetate. Here, we report on C−F bond cleavage in two C 6 perand polyfluorinated compounds via reductive defluorination by an organohalide-respiring microbial community. The reductive defluorination was demonstrated by the release of F − and the formation of the corresponding product when lactate was the electron donor, and the fluorinated compound was the sole electron acceptor. The major dechlorinating species in the seed culture, Dehalococcoides, were not responsible for the defluorination as no growth of Dehalococcoides or active expression of Dehalococcoides-reductive dehalogenases was observed. It suggests that minor phylogenetic groups in the community might be responsible for the reductive defluorination. These findings expand our fundamental knowledge of microbial reductive dehalogenation and warrant further studies on the enrichment, identification, and isolation of responsible microorganisms and enzymes. Given the wide use and emerging concerns of fluorinated organics (e.g., perand polyfluoroalkyl substances), particularly the perfluorinated ones, the discovery of microbial defluorination under common anaerobic conditions may provide valuable insights into the environmental fate and potential bioremediation strategies of these notorious contaminants.

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Synthetic supramolecular systems can provide insight into how complex biological systems organize as well as produce self-organized systems with functionality comparable to their biological counterparts. Herein, we study the assembly into superstructures of a system composed of diketopyrrolopyrrole (DPP) donors with chiral and achiral side chains that can form triple hydrogen bonds with perylene diimide (PDI) acceptors into superstructures. The homoaggregation of the individual components as well as the heteroaggregate formation, as a result of π···π stacking and H-bonding, were studied by variable-temperature UV/vis and CD spectroscopies and electronic structure theory calculations. It was found that, upon cooling, the achiral PDIs bind to disordered DPP stacks, which drives the formation of chiral superstructures. A new thermodynamic model was developed for this unprecedented assembly that is able to isolate the thermodynamic binding parameters (ΔH°, ΔS°) for all the different noncovalent contacts that drive the assembly. This novel assembly as well as the quantitative model described in this work may help researchers develop complex self-assembled systems with emergent properties that arise as a direct result of their supramolecular structures.

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Single-crystal-to-single-crystal (SCSC) topochemical polymerizations of diacetylenes can yield nearly defect-free conjugated polymer crystals unattainable by other methods. Aryl-substituted diacetylenes with their potentially greater conjugation have been targeted for years, but until now no one has reported a SCSC polymerization of any aryl-substituted diacetylene. This is presumably due to the rigidity of such diaryl-substituted monomers as well as the lack of control over the supramolecular structure. To address this problem, the polymerization of a terminal phenyldiacetylene was targeted. It was assumed that a terminal diacetylene should demonstrate greater flexibility in the solid state. To establish the necessary (approximately 4.9 A) repeat distance, commensurate with the repeat distance in the polymer, a host-guest system was designed. The chosen diacetylene guest, the amine DABzNH(2), was to be crystallized with the oxalamide dicarboxylic acid host, H(2)og. The plan required a segregation of the hydrogen bonds, amide-amide hydrogen bonds to establish the 4.9 A spacing, and the carboxylate to ammonium ion hydrogen bonds to organize the guest. Prior to carrying out the diacetylene synthesis a series of model salts were studied. Consistent with the hydrophobic effect it was found that amines with large "greasy" substituents assembled according to the design. Once the model studies established that weak interactions could dominate the supramolecular structure of a salt, the actual design was put to the test. The targeted guest, DABzNH(2), was synthesized and crystals of the host-guest salt (DABzNH(3))(2)og were prepared. The resulting crystal structure was in complete accordance with the design. A SCSC polymerization was achieved by a slow annealing treatment lasting about three months. The crystal structure of the resulting polymer not only confirmed the first example of a poly(aryldiacetylene) single crystal, it also revealed an unexpected reaction pathway that shows a major movement involving the rigid aromatic substituent.