Experimental investigation of catalytic and non-catalytic surface reactions on SiO2 thin films with shock heated oxygen gas

The present study is to investigate the interaction of strong shock heated oxygen on the surface of SiO2 thin film. The thermally excited oxygen undergoes a three-body recombination reaction on the surface of silicon dioxide film. The different oxidation states of silicon species on the surface of the shock-exposed SiO2 film are discussed based on X-ray Photoelectron Spectroscopy (XPS) results. The surface morphology of the shock wave induced damage at the cross section of SiO2 film and structure modification of these materials are analyzed using scanning electron microscopy and ion microscopy. Whether the surface reaction of oxygen on SiO2 film is catalytic or non-catalytic is discussed in this paper.

Re-use of chicken litter across broiler cycles – managing the food-borne pathogen risk

Thus the objectives of this study can be broadly categorised as follows:-  Evaluate current practices adopted (e.g. litter pile-up) prior to re-use of litter for subsequent chicken cycles  To establish pathogen die-off that occurs during currently adopted methods of in-shed treatment of litter  To establish simple physical parameters to monitor this pathogen reduction and create an understanding of such reduction strategies to aid in-shed management of re-use litter  To carry out studies to assess the potential of the re-used litter (once spread) to support pathogens during a typical chicken production cycle.  To provide background data for the development of a simple code of practice for an in-shed litter pile-up process

On-farm Campylobacter and Escherichia coli in commercial broiler chickens: Re-used bedding does not influence Campylobacter emergence and levels across sequential farming cycles

Limitations in quality bedding material have resulted in the growing need to re-use litter during broiler farming in some countries, which can be of concern from a food-safety perspective. The aim of this study was to compare the Campylobacter levels in ceca and litter across three litter treatments under commercial farming conditions. The litter treatments were (a) the use of new litter after each farming cycle; (b) an Australian partial litter re-use practice; and (c) a full litter re-use practice. The study was carried out on two farms over two years (Farm 1, from 2009–2010 and Farm 2, from 2010–2011), across three sheds (35,000 to 40,000 chickens/shed) on each farm, adopting three different litter treatments across six commercial cycles. A random sampling design was adopted to test litter and ceca for Campylobacter and Escherichia coli, prior to commercial first thin-out and final pick-up. Campylobacter levels varied little across litter practices and farming cycles on each farm and were in the range of log 8.0–9.0 CFU/g in ceca and log 4.0–6.0 MPN/g for litter. Similarly the E. coli in ceca were ∼log 7.0 CFU/g. At first thin-out and final pick-up, the statistical analysis for both litter and ceca showed that the three-way interaction (treatments by farms by times) was highly significant (P < 0.01), indicating that the patterns of Campylobacter emergence/presence across time vary between the farms, cycles and pickups. The emergence and levels of both organisms were not influenced by litter treatments across the six farming cycles on both farms. Either C. jejuni or C. coli could be the dominant species across litter and ceca, and this phenomenon could not be attributed to specific litter treatments. Irrespective of the litter treatments in place, cycle 2 on Farm 2 remained campylobacter-free. These outcomes suggest that litter treatments did not directly influence the time of emergence and levels of Campylobacter and E. coli during commercial farming.

Microeconometric Studies on Unemployment and Business Cycles

Väitöskirja koostuu neljästä esseestä, joissa tutkitaan empiirisen työntaloustieteen kysymyksiä. Ensimmäinen essee tarkastelee työttömyysturvan tason vaikutusta työllistymiseen Suomessa. Vuonna 2003 ansiosidonnaista työttömyysturvaa korotettiin työntekijöille, joilla on pitkä työhistoria. Korotus oli keskimäärin 15 % ja se koski ensimmäistä 150 työttömyyspäivää. Tutkimuksessa arvioidaan korotuksen vaikutus vertailemalla työllistymisen todennäköisyyksiä korotuksen saaneen ryhmän ja vertailuryhmän välillä ennen uudistusta ja sen jälkeen. Tuloksien perusteella työttömyysturvan korotus laski työllistymisen todennäköisyyttä merkittävästi, keskimäärin noin 16 %. Korotuksen vaikutus on suurin työttömyyden alussa ja se katoaa kun oikeus korotettuun ansiosidonnaiseen päättyy. Toinen essee tutkii työttömyyden pitkän aikavälin kustannuksia Suomessa keskittyen vuosien 1991 – 1993 syvään lamaan. Laman aikana toimipaikkojen sulkeminen lisääntyi paljon ja työttömyysaste nousi yli 13 prosenttiyksikköä. Tutkimuksessa verrataan laman aikana toimipaikan sulkemisen vuoksi työttömäksi jääneitä parhaassa työiässä olevia miehiä työllisinä pysyneisiin. Työttömyyden vaikutusta tarkastellaan kuuden vuoden seurantajaksolla. Vuonna 1999 työttömyyttä laman aikana kokeneen ryhmän vuosiansiot olivat keskimäärin 25 % alemmat kuin vertailuryhmässä. Tulojen menetys johtui sekä alhaisemmasta työllisyydestä että palkkatasosta. Kolmannessa esseessä tarkastellaan Suomen 1990-luvun alun laman aiheuttamaa työttömyysongelmaa tutkimalla työttömyyden kestoon vaikuttavia tekijöitä yksilötasolla. Kiinnostuksen kohteena on työttömyyden rakenteen ja työn kysynnän muutoksien vaikutus keskimääräiseen kestoon. Usein oletetaan, että laman seurauksena työttömäksi jää keskimääräistä huonommin työllistyviä henkilöitä, jolloin se itsessään pidentäisi keskimääräistä työttömyyden kestoa. Tuloksien perusteella makrotason kysyntävaikutus oli keskeinen työttömyyden keston kannalta ja rakenteen muutoksilla oli vain pieni kestoa lisäävä vaikutus laman aikana. Viimeisessä esseessä tutkitaan suhdannevaihtelun vaikutusta työpaikkaonnettomuuksien esiintymiseen. Tutkimuksessa käytetään ruotsalaista yksilötason sairaalahoitoaineistoa, joka on yhdistetty populaatiotietokantaan. Aineiston avulla voidaan tutkia vaihtoehtoisia selityksiä onnettomuuksien lisääntymiselle noususuhdanteessa, minkä on esitetty johtuvan esim. stressin tai kiireen vaikutuksesta. Tuloksien perusteella työpaikkaonnettomuudet ovat syklisiä, mutta vain tiettyjen ryhmien kohdalla. Työvoiman rakenteen vaihtelu saattaa selittää osan naisten onnettomuuksien syklisyydestä. Miesten kohdalla vain vähemmän vakavat onnettomuudet ovat syklisiä, mikä saattaa johtua strategisesta käyttäytymisestä.

The Human UDP-Glucuronosyltransferases: Studies on Substrate Binding and Catalytic Mechanism

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Catalytic vapor-phase oxidation of p-xylene over tin vanadate

Rates of oxidation of p-xylene were measured in the temperature range 320 to 420 °C using tin vanadate as catalyst in an isothermal differential flow reactor. The amounts of p-xylene converted were determined by analyzing the main products (p-tolualdehyde, maleic anhydride, p-toluic acid and traces of terephthalic acid). Negligible amounts of products of complete combustion were formed. The reaction rates obtained for p-xylene followed the relation, Image based on the redox model. The mechanism of the reaction was determined by conducting different sets of experiments and it was found that the reaction followed the parallel-consecutive mechanism, in which p-tolualdehyde and maleic anhydride were formed from the parallel route whereas p-toluic acid was formed from the consecutive route.

Computational analyses of the catalytic and heparin-binding sites and their interactions with glycosaminoglycans in glycoside hydrolase family 79 endo-d-glucuronidase (heparanase)

Mammalian heparanase is an endo-β-glucuronidase associated with cell invasion in cancer metastasis, angiogenesis and inflammation. Heparanase cleaves heparan sulfate proteoglycans in the extracellular matrix and basement membrane, releasing heparin/heparan sulfate oligosaccharides of appreciable size. This in turn causes the release of growth factors, which accelerate tumor growth and metastasis. Heparanase has two glycosaminoglycan-binding domains; however, no three-dimensional structure information is available for human heparanase that can provide insights into how the two domains interact to degrade heparin fragments. We have constructed a new homology model of heparanase that takes into account the most recent structural and bioinformatics data available. Heparin analogs and glycosaminoglycan mimetics were computationally docked into the active site with energetically stable ring conformations and their interaction energies were compared. The resulting docked structures were used to propose a model for substrates and conformer selectivity based on the dimensions of the active site. The docking of substrates and inhibitors indicates the existence of a large binding site extending at least two saccharide units beyond the cleavage site (toward the nonreducing end) and at least three saccharides toward the reducing end (toward heparin-binding site 2). The docking of substrates suggests that heparanase recognizes the N-sulfated and O-sulfated glucosamines at subsite +1 and glucuronic acid at the cleavage site, whereas in the absence of 6-O-sulfation in glucosamine, glucuronic acid is docked at subsite +2. These findings will help us to focus on the rational design of heparanase-inhibiting molecules for anticancer drug development by targeting the two heparin/heparan sulfate recognition domains.

Deciphering the Distinct Role for the Metal Coordination Motif in the Catalytic Activity of Mycobacterium smegmatis Topoisomerase I

Mycobacterium smegmatis topoisomerase I (Mstopol) is distinct from typical type IA topoisomerases. The enzyme binds to both single- and double-stranded DNA with high affinity, making specific contacts. The enzyme comprises conserved regions similar to type IA topoisomerases from Escherichia coli and other eubacteria but lacks the typically found zinc fingers in the carboxy-terminal domain. The enzyme can perform DNA cleavage m the absence of Mg2+ but religation needs exogenously added Mg2+. One molecule of Mg2+ tightly bound to the enzyme has no role in DNA cleavage but is needed only for the religation reaction. The toprim. (topoisomerase-primase) domain in MstopoI comprising the Mg2+ binding pocket, conserved in both type IA and type II topoisomerases, was subjected to mutagenesis to understand the role of Mg2+, in different steps of the reaction. The residues D108, D110, and E112 of the enzyme, which form the acidic triad in the DXDXE motif, were changed to alanines. D108A mutation resulted in an enzyme that is Mg2+ dependent for DNA cleavage unlike Mstopol and exhibited enhanced DNA cleavage property and reduced religation activity. The mutant was toxic for cell growth, most likely due to the imbalance in cleavage-religation equilibrium. In contrast, the E112A mutant behaved like wild-type enzyme, cleaving DNA in a Mg2+-independent fashion, albeit to a reduced extent. Intra- and intermolecular religation assays indicated specific roles for D108 and E112 residues during the reaction. Together, these results indicate that the D108 residue has a major role during cleavage and religation, while E112 is important for enhancing the efficiency of cleavage. Thus, although architecturally and mechanistically similar to topoisomerase I from E. coli, the metal coordination pattern of the mycobacterial enzyme is distinct, opening up avenues to exploit the enzyme to develop inhibitors.

Increased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic Catalysts

In the studies reported so far on dendrimer-mediated catalysis, the efficacies of the catalytic units were studied and compared primarily across the generations. In order to identify the efficacy of an individual catalytic unit with respect to the number of such units present within a given generation, a series of catalysts were prepared within a generation. Dendrimers incorporated with phosphinemetal complexes were chosen for the study and as many as 11 catalysts within three generations were synthesized. The C-C bond-forming reactions, namely, the Heck and the Suzuki coupling reactions, were then selected to study the catalytic efficiencies of the series of partially and fully phosphine-metal complex functionalized dendrimers. The efficacies of the formation of cinnamate and biphenyl. catalyzed by the dendritic catalysts, were compared. The comparative analyses show that an individual catalytic site is far more effective in its catalytic activity when presented in multiple numbers, i.e., in a multivalent dendritic system, than as a single unit within the same generation, i.e., in a monovalent dendritic system. The study identifies the beneficial effects of the multivalent presentation of the catalytic moieties, both within and across the dendrimer generations.

Substrate specificity plays an important role in uncoupling the catalytic and scaffolding activities of rat testis DNA topoisomerase IIalpha

Topoisomerase II (topo II) is a dyadic enzyme found in all eukaryotic cells. Topo II is involved in a number of cellular processes related to DNA metabolism, including DNA replication, recombination and the maintenance of genomic stability. We discovered a correlation between the development of postnatal testis and increased binding of topo IIalpha to the chromatin fraction. We used this observation to characterize DNA-binding specificity and catalytic properties of purified testis topo IIalpha. The results indicate that topo IIalpha binds a substrate containing the preferred site with greater affinity and, consequently, catalyzes the conversion of form I to form IV DNA more efficiently in contrast to substrates lacking such a site. Interestingly, topo IIalpha displayed high-affinity and cooperativity in binding to the scaffold associated region. In contrast to the preferred site, however, high-affinity binding of topo IIalpha to the scaffold-associated region failed to result in enhanced catalytic activity. Intriguingly, competition assays involving scaffold-associated region revealed an additional DNA-binding site within the dyadic topo IIalpha. These results implicate a dual role for topo IIalpha in vivo consistent with the notion that its sequestration to the chromatin might play a role in chromosome condensation and decondensation during spermatogenesis.

Electronic coupling and catalytic effect on H2 evolution of MoS2/graphene nanocatalyst

Inorganic nano-graphene hybrid materials that are strongly coupled via chemical bonding usually present superior electrochemical performance. However, how the chemical bond forms and the synergistic catalytic mechanism remain fundamental questions. In this study, the chemical bonding of the MoS2 nanolayer supported on vacancy mediated graphene and the hydrogen evolution reaction of this nanocatalyst system were investigated. An obvious reduction of the metallic state of the MoS2 nanolayer is noticed as electrons are transferred to form a strong contact with the reduced graphene support. The missing metallic state associated with the unsaturated atoms at the peripheral sites in turn modifies the hydrogen evolution activity. The easiest evolution path is from the Mo edge sites, with the presence of the graphene resulting in a decrease in the energy barrier from 0.17 to 0.11 eV. Evolution of H2 from the S edge becomes more difficult due to an increase in the energy barrier from 0.43 to 0.84 eV. The clarification of the chemical bonding and catalytic mechanisms for hydrogen evolution using this strongly coupled MoS2/graphene nanocatalyst provide a valuable source of reference and motivation for further investigation for improved hydrogen evolution using chemically active nanocoupled systems.

An Insight to the Dynamics of Conserved Water Molecular Triad in IMPDH II (Human): Recognition of Cofactor and Substrate to Catalytic Arg 322

Inosine 5' monophosphate dehydrogenase (IMPDH II) is a key enzyme involved in the de novo biosynthesis pathway of purine nucleotides and is also considered to be an excellent target for cancer inhibitor design. The conserve R 322 residue (in human) is thought to play some role in the recognition of inhibitor and cofactor through the catalytic D 364 and N 303. The 15 ns simulation and the water dynamics of the three different PDB structures (1B3O, 1NF7, and 1NFB) of human IMPDH by CHARMM force field have clearly indicated the involvement of three conserved water molecules (W-L, W-M, and W-C) in the recognition of catalytic residues (R 322, D 364, and N 303) to inhibitor and cofactor. Both the guanidine nitrogen atoms (NH1 and NH 2) of the R 322 have anchored the di- and mono-nucleotide (cofactor and inhibitor) binding domains via the conserved W-C and W-L water molecules. Another conserved water molecule W-M seems to bridge the two domains including the R 322 and also the W-C and W-L through seven centers H-bonding coordination. The conserved water molecular triad (W-C - W-M - W-L) in the protein complex may thought to play some important role in the recognition of inhibitor and cofactor to the protein through R 322 residue.

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh2)(2)N(R) (R = Pr-i, H, Ph and -CH2-C6H4-CH=CH2) complexes at 40 degrees C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = Pr-i > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile "copper-olefin" complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper-phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism. (C) 2008 Elsevier B. V. All rights reserved.