4-(8-Eth­oxy-2,3-dihydro-1H-cyclo­penta­[c]quinolin-4-yl)butane-1-peroxol

In the title mol­ecule, C18H23NO3, the hydro­per­oxy­butyl substituent is nearly fully extended, with the four torsion angles in the range 170.23 (10)–178.71 (9)°. The O—O distance in the hydro­peroxide group is 1.4690 (13) Å. This group acts as an inter­molecular hydrogen-bond donor to a quinoline N atom. This results in dimeric units about the respective inversion centers, with graph-set notation R 2 2(18)

Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase from Escherichia coli O9a

WbdD is a bifunctional kinase/methyltransferase that is responsible for regulation of lipopolysaccharide O antigen polysaccharide chain length in Escherichia coli serotype O9a. Solving the crystal structure of this protein proved to be a challenge because the available crystals belonging to space group I23 only diffracted to low resolution (>95% of the crystals diffracted to resolution lower than 4 angstrom and most only to 8 angstrom) and were non-isomorphous, with changes in unit-cell dimensions of greater than 10%. Data from a serendipitously found single native crystal that diffracted to 3.0 angstrom resolution were non-isomorphous with a lower (3.5 angstrom) resolution selenomethionine data set. Here, a strategy for improving poor (3.5 angstrom resolution) initial phases by density modification and cross-crystal averaging with an additional 4.2 angstrom resolution data set to build a crude model of WbdD is desribed. Using this crude model as a mask to cut out the 3.5 angstrom resolution electron density yielded a successful molecular-replacement solution of the 3.0 angstrom resolution data set. The resulting map was used to build a complete model of WbdD. The hydration status of individual crystals appears to underpin the variable diffraction quality of WbdD crystals. After the initial structure had been solved, methods to control the hydration status of WbdD were developed and it was thus possible to routinely obtain high-resolution diffraction (to better than 2.5 angstrom resolution). This novel and facile crystal-dehydration protocol may be useful for similar challenging situations.Publisher PDFPeer reviewe

Facile Synthesis of Tuneable Azophosphonium Salts

Azophosphonium salts have a facile synthesis and can be readily tuned at the para position of the aryl group and at the phosphorus position with the use of bulky phosphines, leading to a range of coloured compounds. A relation between the Hammett sigma(+)(para) constant and the colour and P-31 NMR chemical shift was explored. The compounds were characterised by NMR spectroscopy, UV/Vis spectroscopy and single-crystal X-ray structure crystallography.Peer reviewe

Thin Films of Molybdenum Disulfide Doped with Chromium by Aerosol-Assisted Chemical Vapor Deposition (AACVD)

A combined single-source precursor approach has been developed for the deposition of thin films of Cr-doped molybdenum disulfide (MoS₂) by aerosol-assisted chemical vapor deposition (AACVD). Tris­(diethyldithiocarbamato)­chromium­(III) can also be used for the deposition of chromium sulfide (CrS). Films have been analyzed by a range of techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and powder X-ray diffraction (pXRD) to elucidate film morphology, composition, and crystallinity. The presence of Cr in the MoS₂ films produces a number of striking morphological, crystallographic, and nanomechanical changes to the deposited films. The chromium dopant appears to be uniform throughout the MoS₂ from the scanning transmission electron microscopy (STEM) EDX spectrum imaging of nanosheets produced by liquid-phase exfoliation of the thin films in <i>N</i>-methyl-2-pyrollidone

Wzi Is an Outer Membrane Lectin that Underpins Group 1 Capsule Assembly in Escherichia coli

Many pathogenic bacteria encase themselves in a polysaccharide capsule that provides a barrier to the physical and immunological challenges of the host. The mechanism by which the capsule assembles around the bacterial cell is unknown. Wzi, an integral outer-membrane protein from Escherichia coli, has been implicated in the formation of group 1 capsules. The 2.6 angstrom resolution structure of Wzi reveals an 18-stranded beta-barrel fold with a novel arrangement of long extracellular loops that blocks the extracellular entrance and a helical bundle that plugs the periplasmic end. Mutagenesis shows that specific extracellular loops are required for in vivo capsule assembly. The data show that Wzi binds the K30 carbohydrate polymer and, crucially, that mutants functionally deficient in vivo show no binding to K30 polymer in vitro. We conclude that Wzi is a novel outer-membrane lectin that assists in the formation of the bacterial capsule via direct interaction with capsular polysaccharides.Publisher PDFPeer reviewe