Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation

Carbon stable isotope ((13)C) fractionation in chlorofluorocarbon (CFC) compounds arising from abiotic (chemical) degradation using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 °C) for CFC-113 and CFC-11 using ZVI show quantitative degradation of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (t(1/2)) of 20.5 h, and a ZVI surface-area normalized rate constant (k(SA)) of -(9.8 ± 0.5) × 10(-5) L m(-2) h(-1). CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to t(1/2) = 17.3 h and k(SA) = -(1.2 ± 0.5) × 10(-4) L m(-2) h(-1). Significant kinetic isotope effects of e(‰) = -5.0 ± 0.3 (CFC-113) and -17.8 ± 4.8 (CFC-11) were observed. Compound-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degradation and isotopic fractionation in LFG production, and local atmospheric impact of landfill emissions through the cover. Isotopic fractionations of ?(13)C ~ -13‰ (HCFC-22), ?(13)C ~ -35‰ (CFC-12) and ?(13)C ~ -15‰ (CFC-11) were observed for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope effect for (abiotic) ZVI degradation.

THE ROLE OF H+ AND H-3+ IONS IN THE DEGRADATION OF INTERSTELLAR-MOLECULES

The results of recent laboratory studies of the reactions of H+ and H-3+ with a number of molecular gases are interpreted from the viewpoint of interstellar chemistry. Many of the reactions of these ions result in the ionization and fragmentation of neutral reactant gases. Pseudo-time-dependent calculations of the chemistry in dense molecular clouds indicate that molecular abundances are reduced by the inclusion of such reactions, but generally by less than a factor of 5.

Bacterial dioxygenase- and monooxygenase-catalysed sulfoxidation of benzo[b]thiophenes

Asymmetric heteroatom oxidation of benzo[b]thiophenes to yield the corresponding sulfoxides was catalysed by toluene dioxygenase (TDO), naphthalene dioxygenase (NDO) and styrene monooxygenase (SMO) enzymes present in P. putida mutant and E. coli recombinant whole cells. TDO-catalysed oxidation yielded the relatively unstable benzo[b] thiophene sulfoxide; its dimerization, followed by dehydrogenation, resulted in the isolation of stable tetracyclic sulfoxides as minor products with cis-dihydrodiols being the dominant metabolites. SMO mainly catalysed the formation of enantioenriched benzo[b] thiophene sulfoxide and 2-methyl benzo[b] thiophene sulfoxides which racemized at ambient temperature. The barriers to pyramidal sulfur inversion of 2- and 3-methyl benzo[b] thiophene sulfoxide metabolites, obtained using TDO and NDO as biocatalysts, were found to be ca.: 25-27 kcal mol(-1). The absolute configurations of the benzo[b] thiophene sulfoxides were determined by ECD spectroscopy, X-ray crystallography and stereochemical correlation. A site-directed mutant E. coli strain containing an engineered form of NDO, was found to change the regioselectivity toward preferential oxidation of the thiophene ring rather than the benzene ring.

ENANTIOSELECTIVE BACTERIAL BIOTRANSFORMATION ROUTES TO CIS-DIOL METABOLITES OF MONOSUBSTITUTED BENZENES, NAPHTHALENE AND BENZOCYCLOALKENES OF EITHER ABSOLUTE-CONFIGURATION

Enzyme-catalysed kinetic resolution and asymmetric dihydroxylation routes to enantiopure cis-diol metabolites of arenes and benzocycloalkenes of either absolute configuration have been developed using appropriate strains of the bacterium Pseudomonas putida.

SULFOXIDES OF HIGH ENANTIOPURITY FROM BACTERIAL DIOXYGENASE-CATALYZED OXIDATION

Selected strains of the bacterium Pseudomonas putida (previously shown to effect dioxygenase-catalysed asymmetric cis-dihydroxylation of alkenes) have been found to yield chiral sulfoxides from the corresponding sulfides with a strong preference for the (R)- or (S)-configurations but without evidence of sulfone formation; similar results obtained using an Escherichia coli clone (pKST11, containing the Tod C1 C2 B and A genes encoding toluene dioxygenase from P. putida NCIMB 11767) are again consistent with a stereoselective dioxygenase-catalysed sulfoxidation.

PHOTOCATALYTIC DEGRADATION OF 4-CHLOROPHENOL MEDIATED BY TIO2 - A COMPARATIVE-STUDY OF THE ACTIVITY OF LABORATORY MADE AND COMMERCIAL TIO2 SAMPLES

The photocatalytic efficiencies of laboratory made and commercial TiO2 samples were compared using a standard test reaction: the photomineralization of 4-chlorophenol (4-CP) to CO2, H2O and HCl mediated by Degussa P25 TiO2 in a batch reactor. The results show that the rate of photodegradation of 4-CP, sensitized by a sample of TiO2, shows no clear simple dependence on physical characteristics such as the degree of crystallinity, the surface area and the percentage of H2O.

Electrical methods of controlling bacterial adhesion and biofilm on device surfaces.

This review will summarize the significant body of research within the field of electrical methods of controlling the growth of microorganisms. We examine the progress from early work using current to kill bacteria in static fluids to more realistic treatment scenarios such as flow-through systems designed to imitate the human urinary tract. Additionally, the electrical enhancement of biocide and antibiotic efficacy will be examined alongside recent innovations including the biological applications of acoustic energy systems to prevent bacterial surface adherence. Particular attention will be paid to the electrical engineering aspects of previous work, such as electrode composition, quantitative electrical parameters and the conductive medium used. Scrutiny of published systems from an electrical engineering perspective will help to facilitate improved understanding of the methods, devices and mechanisms that have been effective in controlling bacteria, as well as providing insights and strategies to improve the performance of such systems and develop the next generation of antimicrobial bioelectric materials.

Haloalkane degradation and assimilation by Rhodococcus rhodochrous NCIMB -13064

The bacterium Rhodococcus rhodochrous NCIMB 13064, isolated from an industrial site, could use a wide range of 1-haloalkanes as sole carbon source but apparently utilized several different mechanisms simultaneously for assimilation of substrate. Catabolism of 1-chlorobutane occurred mainly by attack at the C-1 atom by a hydrolytic dehalogenase with the formation of butanol which was metabolized via butyric acid. The detection of small amounts of gamma-butyrolactone in the medium suggested that some oxygenase attack at C-4 also occurred, leading to the formation of 4-chlorobutyric acid which subsequently lactonized chemically to gamma-butyrolactone. Although 1-chlorobutane-grown cells exhibited little dehalogenase activity on 1-chloroalkanes with chain lengths above C-10, the organism utilized such compounds as growth substrates with the release of chloride. Concomitantly, gamma-butyrolactone accumulated to 1 mM in the culture medium with 1-chlorohexadecane as substrate. Traces of 4-hydroxybutyric acid were also detected. It is suggested that attack on the long-chain chloroalkane is initiated by an oxygenase at the non-halogenated end of the molecule leading to the formation of an omega-chlorofatty acid. This is degraded by beta-oxidation to 4-chlorobutyric acid which is chemically lactonized to gamma-butyrolactone which is only slowly further catabolized via 4-hydroxybutyric acid and succinic acid. However, release of chloride into the medium during growth on long-chain chloroalkanes was insufficient to account for all the halogen present in the substrate. Analysis of the fatty acid composition of 1-chlorohexadecane-grown cells indicated that chlorofatty acids comprised 75% of the total fatty acid content with C-14:0, C-16:0, C-16:1, and C-18:1 acids predominating. Thus the incorporation of 16-chlorohexadecanoic acid, the product of oxygenase attack directly into cellular lipid represents a third route of chloroalkane assimilation. This pathway accounts at least in part for the incomplete mineralization of long-chain chloroalkane substrates. This is the first report of the coexistence of a dehalogenase and the ability to incorporate long-chain haloalkanes into the lipid fraction within a single organism and raises important questions regarding the biological treatment of haloalkane containing effluents.