Degradation of 4-fluorophenol by Arthrobacter sp. strain IF1

A Gram-positive bacterial strain capable of aerobic biodegradation of 4-fluorophenol (4-FP) as the sole source of carbon and energy was isolated by selective enrichment from soil samples collected near an industrial site. The organism, designated strain IF1, was identified as a member of the genus Arthrobacter on the basis of 16S ribosomal RNA gene sequence analysis. Arthrobacter strain IF1 was able to mineralize 4-FP up to concentrations of 5 mM in batch culture. Stoichiometric release of fluoride ions was observed, suggesting that there is no formation of halogenated dead-end products during 4-FP metabolism. The degradative pathway of 4-FP was investigated using enzyme assays and identification of intermediates by gas chromatography (GC), GC–mass spectrometry (MS), high-performance liquid chromatography, and liquid chromatography–MS. Cell-free extracts of 4-FP-grown cells contained no activity for catechol 1,2-dioxygenase or catechol 2,3-dioxygenase, which indicates that the pathway does not proceed through a catechol intermediate. Cells grown on 4-FP oxidized 4-FP, hydroquinone, and hydroxyquinol but not 4-fluorocatechol. During 4-FP metabolism, hydroquinone accumulated as a product. Hydroquinone could be converted to hydroxyquinol, which was further transformed into maleylacetic acid and β-ketoadipic acid. These results indicate that the biodegradation of 4-FP starts with a 4-FP monooxygenase reaction that yields benzoquinone, which is reduced to hydroquinone and further metabolized via the β-ketoadipic acid pathway

Solid-phase molecular recognition of cytosine based on proton-transfer reaction. Part II. supramolecular architecture in the cocrystals of cytosine and its 5-Fluoroderivative with 5-Nitrouracil

<p>Abstract</p> <p>Background</p> <p>Cytosine is a biologically important compound owing to its natural occurrence as a component of nucleic acids. Cytosine plays a crucial role in DNA/RNA base pairing, through several hydrogen-bonding patterns, and controls the essential features of life as it is involved in genetic codon of 17 amino acids. The molecular recognition among cytosines, and the molecular heterosynthons of molecular salts fabricated through proton-transfer reactions, might be used to investigate the theoretical sites of cytosine-specific DNA-binding proteins and the design for molecular imprint.</p> <p>Results</p> <p>Reaction of cytosine (Cyt) and 5-fluorocytosine (5Fcyt) with 5-nitrouracil (Nit) in aqueous solution yielded two new products, which have been characterized by single-crystal X-ray diffraction. The products include a dihydrated molecular salt (CytNit) having both ionic and neutral hydrogen-bonded species, and a dihydrated cocrystal of neutral species (5FcytNit). In CytNit a protonated and an unprotonated cytosine form a triply hydrogen-bonded aggregate in a self-recognition ion-pair complex, and this dimer is then hydrogen bonded to one neutral and one anionic 5-nitrouracil molecule. In 5FcytNit the two neutral nucleobase derivatives are hydrogen bonded in pairs. In both structures conventional N-H^...O, O-H^...O, N-H^+...N and N-H^...N^-intermolecular interactions are most significant in the structural assembly.</p> <p>Conclusion</p> <p>The supramolecular structure of the molecular adducts formed by cytosine and 5-fluorocytosine with 5-nitrouracil, CytNit and 5FcytNit, respectively, have been investigated in detail. CytNit and 5FcytNit exhibit widely differing hydrogen-bonding patterns, though both possess layered structures. The crystal structures of CytNit (D<it>p</it>k_a= -0.7, molecular salt) and 5FcytNit (D<it>p</it>k_a= -2.0, cocrystal) confirm that, at the present level of knowledge about the nature of proton-transfer process, there is not a strict correlation between the D<it>p</it>k_avalues and the proton transfer, in that the acid/base <it>p</it>k_astrength is not a definite guide to predict the location of H atoms in the solid state. Eventually, the absence in 5FcytNit of hydrogen bonds involving fluorine is in agreement with findings that covalently bound fluorine hardly ever acts as acceptor for available Brønsted acidic sites in the presence of competing heteroatom acceptors.</p

Characterisation of weak intramolecular interactions in the topology of the experimental charge density of 2,2 '-ethynylenedibenzoic acid

The computational complexity of optimum decoding for an orthogonal space-time block code {cal G}_N satisfying {cal G}_N^H{cal G}_N=c(∑_{k=1}^Kos_ko^2)I_N where c is a positive integer is quantified. Four equivalent techniques of optimum decoding which have the same computational complexity are specified. Modifications to the basic formulation in special cases are calculated and illustrated by means of examples. This paper corrects and extends and unifies them with the results from the literature. In addition, a number of results from the literature are extended to the case c&gt;1.Funding agencies|Center for Pervasive Communications and Computing at the University of California, Irvine||Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||Knut and Alice Wallenberg Foundation|