Bacterial biofilms are cellular communities that produce an adherent matrix. Exopolysaccharides are key structural components of this matrix and are required for the assembly and architecture of biofilms produced by a wide variety of microorganisms. The human bacterial pathogens Escherichia coli and Salmonella enterica produce a biofilm matrix composed primarily of the exopolysaccharide phosphoethanolamine (pEtN) cellulose. Once thought to be composed of only underivatized cellulose, the pEtN modification present in these matrices has been implicated in the overall architecture and integrity of the biofilm. However, an understanding of the mechanism underlying pEtN derivatization of the cellulose exopolysaccharide remains elusive. The bacterial cellulose synthase subunit G (BcsG) is a predicted inner membrane–localized metalloenzyme that has been proposed to catalyze the transfer of the pEtN group from membrane phospholipids to cellulose. Here we present evidence that the C-terminal domain of BcsG from E. coli (EcBcsGΔN) functions as a phosphoethanolamine transferase in vitro with substrate preference for cellulosic materials. Structural characterization of EcBcsGΔN revealed that it belongs to the alkaline phosphatase superfamily, contains a Zn2+ ion at its active center, and is structurally similar to characterized enzymes that confer colistin resistance in Gram-negative bacteria. Informed by our structural studies, we present a functional complementation experiment in E. coli AR3110, indicating that the activity of the BcsG C-terminal domain is essential for integrity of the pellicular biofilm. Furthermore, our results established a similar but distinct active-site architecture and catalytic mechanism shared between BcsG and the colistin resistance enzymes.

A synthetic approach for preparing a variety of heterocyclic tetrahydropentacene derivatives via nucleophilic aromatic substitution reactions of bidentate nucleophiles and tetrafluorotere­phthalonitrile was developed. X-ray crystallography of several products revealed that the compounds containing oxygen and nitrogen heteroatoms are highly planar and engage in π-stacking, while the compounds containing sulfur are bent and do not stack as effectively. The compounds were also highly emissive, and the heteroatom had a significant impact on the emission and electrochemical properties.

The synthesis of the asymmetric ligand 3phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine (L1) and its single-crystal X-ray structure are reported. L1 displays crystallographic symmetry (orthorhombic, Pccn) higher than its molecular symmetry (point group C 1 ) and also displays supercooling, with a difference in the melting and solidification points of over 100 °C. Upon complexation with ZnCl 2 , L1 engages in both primary cation and secondary anion coordination via hydrogen bonding, and the complex exhibits a room-to-low-temperature single crystal-to-crystal phase transition. The ZnCl 2 complex becomes a birefringent fluid mixed with crystalline domains at high temperatures, as detected by polarized optical microscopy. Examination of the photoluminescence properties showed that the emission intensity increased and a pronounced bathochromic shift was observed in the emission maximum upon going from solution to the solid state, for both the ligand and complex, consistent with aggregation-induced emission behavior.

A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives (1 a–c) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c, which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable‐temperature powder X‐ray diffraction, and differential scanning calorimetry. Single‐crystal X‐ray diffraction of methoxy‐substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation‐induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge‐transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.

Biofilms are communities of self-enmeshed bacteria in a matrix of exopolysaccharides. The widely distributed human pathogen and commensal Escherichia coli produces a biofilm matrix composed of phosphoethanolamine (pEtN)-modified cellulose and amyloid protein fibers, termed curli. The addition of pEtN to the cellulose exopolysaccharide is accomplished by the action of the pEtN transferase, BcsG, and is essential for the overall integrity of the biofilm. Here, using the synthetic co-substrates p-nitrophenyl phosphoethanolamine and β-D-cellopentaose, we demonstrate using an in vitro pEtN transferase assay that full activity of the pEtN transferase domain of BcsG from E. coli (EcBcsG ΔN ) requires Zn 2+ binding, a catalytic nucleophile/acid-base arrangement (Ser 278 /Cys 243 /His 396 ), disulfide bond formation, and other newly uncovered essential residues. We further confirm that EcBcsG ΔN catalysis proceeds by a ping-pong bisubstrate−biproduct reaction mechanism and displays inefficient kinetic behavior (k cat /K M = 1.81 × 10 −4 ± 2.81 × 10 −5 M −1 s −1 ), which is typical of exopolysaccharide-modifying enzymes in bacteria. Thus, the results presented, especially with respect to donor binding (as reflected by K M ), have importantly broadened our understanding of the substrate profile and catalytic mechanism of this class of enzymes, which may aid in the development of inhibitors targeting BcsG or other characterized members of the pEtN transferase family, including the intrinsic and mobile colistin resistance factors.

Understanding and control of weak intermolecular interactions, including π-interactions, is an element toward the strategic design of supramolecular materials. In this work, we describe an approach to promoting cofacial π-stacking in the solid state by preparing polycyclic aromatic compounds that bear complementary electron-rich and electron-poor rings. Specifically, we describe the synthesis and single crystal structures of a series of six dissymmetric systems (three dibenzo-p-dioxins and three phenoxazines) comprised of one electron-rich and one electron-deficient ring. In all cases, anti-co-facial π–π interactions were observed, but no significant C–H···π interactions. These observations were compared with similar structures in the Cambridge Structural Database, and it was found that the presence of bulky substituents, lattice solvent, and stronger intermolecular interactions interfere with efficient π-stacking. Both qualitative and quantitative evaluations of the newly reported structures, and database examples, are included.

The synthesis and single crystal structures of 3-phenyl-1-(pyridin-2-yl)-1<i>H</i>-pyrazol-5-amine (<b>L1</b>) and its complex with ZnCl₂are reported. <b>L1</b> exhibits supercooling, with a difference in melting and solidification points of over 100 ^oC. The complex [<b>L1</b>ZnCl₂] has a room-to-low temperature single crystal-to-crystal phase transition in the solid state, while a birefringent fluid phase mixed with crystalline domains is observed at high temperatures. Significant fluorescence enhancement is observed upon formation of the ZnCl₂ complex.

Author(s) of this paper may load this reprint on their own web site or institutional repository provided that this cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.For further information see http://journals.iucr.org/services/authorrights.html Acta Cryst. (2017 Benzothiazole derivatives are a class of privileged molecules due to their biological activity and pharmaceutical applications. One route to these molecules is via intramolecular cyclization of thioureas to form substituted 2-aminobenzothiazoles, but this often requires harsh conditions or employs expensive metal catalysts. Herein, the copper ( ) is required for the cyclization to proceed. As such, this study provides further mechanistic insight into the role of the metal cations in these transformations.