College of Science

Content on demand for fourth year advanced materials and manufacturing students

2013-05-24T08:44:29Z

Content on demand for fourth year advanced materials and manufacturing students Brabazon, Dermot; Donovan, Lynda; Egan, Andrew; O'Mahony, Michael P.; Melia, Mark; Smyth, Barry There is growing recognition of the key role that social and informal learning play in Higher Education. There is also increasing interest in technologies that enable, capture and channel this type of learning to students at their point of need and personalised to their ability. The objective of this project was to leverage research technologies from the areas of adaptive hypermedia, social and semantic search to create an application to deliver learning resources to students tailored to their specific learning needs. In this project, some 130 digital learning resources, specific to a final year advanced materials and manufacturing module, were made available to the students via a Help Block plugin in the Moodle Virtual Learning Environment. The students were required to use the Help Block as a just-in-time learning resource to help them complete a continuous assessment assignment. The assignment required the students to select an advanced manufacturing process and associated material describing the manufacturing process steps, control and specifications and presenting the technological benefits of the process and material used relative to competing processes and materials. Post-trial, students were asked to complete a questionnaire to describe their experience with the Help Block in terms of whether it assisted them in completing the assignment, for example, and its ease of use. The system, evaluation findings, and some suggestions for future system enhancements are presented in the paper. ISEE 2012, 4th International Symposium of Engineering Education, The University of Sheffield, UK, 18th -20th July 2012

Quaternarized pdppz: synthesis, DNA-binding and biological studies of a novel dppz derivative that causes cellular death upon light irradiation.

2013-05-16T10:54:10Z

Quaternarized pdppz: synthesis, DNA-binding and biological studies of a novel dppz derivative that causes cellular death upon light irradiation. Elmes, Robert B.P.; Erby, Marialuisa; Cloonan, Suzanne M.; Quinn, Susan J.; Williams, D. Clive; Gunnlaugsson, Thorfinnur The quaternarized pdppz derivative 1 was shown to bind strongly to DNA with concomitant changes in its ground and excited state photophysical properties. Furthermore, the compound also showed rapid cellular uptake, and induced apoptosis upon light irradiation in various cancer cell lines after 24 hours of incubation.

Synthesis and photophysical evaluations of fluorescent quaternary bipyridyl-1,8-naphthalimide conjugates as nucleic acid targeting agents

2013-05-16T10:51:21Z

Synthesis and photophysical evaluations of fluorescent quaternary bipyridyl-1,8-naphthalimide conjugates as nucleic acid targeting agents Ryan, Gary J.; Elmes, Robert B.P.; Quinn, Susan J.; Gunnlaugsson, Thorfinnur A family of organic molecules containing the DNA intercalating chromophores, 4-nitro- and 4-amino 1,8-naphthalimide, conjugated to a diquat derivative by an ‘orthogonal’ phenyl spacer have been prepared and characterised. Their binding interactions with double-stranded DNA were studied by a variety of spectroscopic techniques. These charged organic compounds are found to exhibit excellent binding affinities to DNA with binding constants comparable to those exhibited by metal complexes.

A comparative picosecond transient infrared study of 1-methylcytosine and 5'-dCMP that sheds further light on the excited states of cytosine derivatives

2013-05-16T09:22:07Z

A comparative picosecond transient infrared study of 1-methylcytosine and 5'-dCMP that sheds further light on the excited states of cytosine derivatives Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Watson, Graeme W.; Clark, Ian P.; Greetham, Gregory M.; Parker, Anthony W.; Towrie, Michael; Kelly, John M.; Quinn, Susan J. The role of N1-substitution in controlling the deactivation processes in photoexcited cytosine derivatives has been explored using picosecond time-resolved IR spectroscopy. The simplest N1-substituted derivative, 1-methylcytosine, exhibits relaxation dynamics similar to the cytosine nucleobase and distinct from the biologically relevant nucleotide and nucleoside analogues, which have longer-lived excited-state intermediates. It is suggested that this is the case because the sugar group either facilitates access to the long-lived (1)n(O)Ï * state or retards its crossover to the ground state.

Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state

2013-05-16T09:17:19Z

Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Kelly, John M.; Clark, Ian P.; Parker, Anthony W.; Greetham, Gregory M.; Towrie, Michael; Magno, Luís M.; Quinn, Susan J. The decay pathways of UV-excited cytosine polymers are investigated using picosecond time-resolved infrared spectroscopy. Similar yields of a non-emissive (1)nÏ * state are found in the single-stranded dC(30) polymer as in the dCMP monomer, but with a longer lifetime in the polymer (80 ps vs. 39 ps). A longer lifetime is also found in the d(CpC) dinucleotide. No evidence of excimer states is observed, suggesting that localised (1)nÏ * excited states are the most significant intermediates present on the picosecond timescale.

Excited state behaviour of substituted dipyridophenazine Cr(III) complexes in the presence of nucleic acids

2013-05-16T09:12:35Z

Excited state behaviour of substituted dipyridophenazine Cr(III) complexes in the presence of nucleic acids Wojdyla, Michal; Smith, Jayden A.; Vasudevan, Suni; Quinn, Susan J.; Kelly, John M. The photophysics and photochemistry of [Cr(phen)2(dppz)]3+ and its 11,12-substituted derivatives [Cr(phen)2(X2dppz)]3+ {X = Me or F} have been studied in the presence of purine nucleotides or DNA using steady state and time-resolved absorption and luminescence spectroscopy. 5'-Adenosine monophosphate (5'-AMP) shows only a weak interaction with the excited states of each complex. By contrast they are efficiently quenched by 5'-guanosine monophosphate (5'-GMP), consistent with photo-induced electron transfer. Laser flash photolysis spectroscopy in the presence of 5'--GMP suggests that both forward and back electron-transfers are rapid. All complexes also display a strong affinity for DNA and evidence for both static and dynamic quenching mechanisms is provided.

Incandescent Porous Carbon Microspheres to Light up Cells: Solution Phenomena and Cellular Uptake

2013-05-16T09:09:06Z

Incandescent Porous Carbon Microspheres to Light up Cells: Solution Phenomena and Cellular Uptake Duffy, Paul; Magno, Luís M.; Yadavc, Rahul B.; Roberts, Selene K.; Ward, Andrew D.; Botchway, Stanley W.; Colavita, Paula E.; Quinn, Susan J. Carbon based materials are attractive for biological applications because of their excellent biocompatibility profile. Porous carbons with high specific surface area are particularly interesting because it is possible in principle to leverage their properties to deliver high drug payloads. In this work, porous carbon microspheres with high specific surface area were prepared and studied in solution and in cells. Raman optical tweezer trapping of microspheres, excited by 532 nm, results in graphitization and incandescence in solvents that display poor heat conduction. Fluorescence confocal microscopy imaging was used to demonstrate the uptake of fluorescently labelled microspheres by cells and the ability to leverage their optical absorptivity in order to cause carbon graphitization and cell death.

Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin

2013-05-16T08:30:41Z

Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin Keane, Páraic M.; Gallagher, Shane A.; Magno, Luís M.; Leising, Miriam J.; Clark, Ian P.; Greetham, Gregory M.; Towrie, Michael; Gun'ko, Yurii; Kelly, John M.; Quinn, Susan J. The photophysical properties of 2.3 nm thioglycolic acid (TGA) coated CdTe quantum dots (QDs) prepared by a reflux method have been studied in the presence of cationic meso-tetrakis(4-N-methylpyridyl) zinc porphyrin (ZnTMPyP4). Addition of the CdTe QDs to the porphyrin in H2O results in a marked red-shift and hypochromism in the porphyrin absorption spectrum, indicative of a non-covalent binding interaction with the QD surface. Only low equivalents of the quantum dot were required for complete quenching of the porphyrin fluorescence revealing that one quantum dot may quench more than one porphyrin. Similarly addition of porphyrin to the quantum dot provided evidence for very efficient quenching of the CdTe photoluminescence, suggesting the formation of CdTe'porphyrin aggregates. Definitive evidence for such aggregates was gathered using small angle X-ray spectroscopy (SAXS). Ultrafast transient absorption data are consistent with very rapid photoinduced electron transfer (1.3 ps) and the resultant formation of a long-lived porphyrin species.

The Microbial Cell Factory

2013-05-07T11:59:53Z

The Microbial Cell Factory Murphy, Cormac D. Microorganisms have been used for decades as sources of antibiotics, vitamins and enzymes and for the production of fermented foods and chemicals. In the 21st century microorganisms will play a vital role in addressing some of the problems faced by mankind. In this article three of the current applications in which microbes have a significant role to play are highlighted: the discovery of new antibiotics, manufacture of biofuels and bioplastics, and production of fine chemicals via biotransformation.

Production of human metabolites of the anti-cancer drug flutamide via biotransformation in Cunninghamella species

2013-05-01T10:40:59Z

Production of human metabolites of the anti-cancer drug flutamide via biotransformation in Cunninghamella species Amadio, Jessica; Murphy, Cormac D. Fungi belonging to the genus Cunninghamella have enzymes similar to those employed by mammals for the detoxification of xenobiotics, thus they are useful as models of mammalian drug metabolism, and as a source for drug metabolites. We report the transformation of the anti-cancer drug flutamide in Cunninghamella sp. The most predominant phase I metabolites present in the plasma of humans, 2-hydroxyflutamide and 4-nitro-3-(trifluoromethyl)aniline, were also produced in Cunninghamella cultures. Other phase I and phase II metabolites were also detected using a combination of HPLC, GC–MS and 19F-NMR.

Production of the Novel Lipopeptide Antibiotic Trifluorosurfactin via Precursor-Directed Biosynthesis.

2013-05-01T10:24:36Z

Production of the Novel Lipopeptide Antibiotic Trifluorosurfactin via Precursor-Directed Biosynthesis. O'Connor, Neil K.; Rai, Dilip K.; Clark, Benjamin R.; Murphy, Cormac D. Incorporation of fluorine into antibiotics can moderate their biological activity, lipophilicity and metabolic stability. The introduction of fluorine into an antimicrobial lipopeptide produced by Bacillus sp. CS93 via precursor-directed biosynthesis is described. The lipopeptide surfactin is synthesised non-ribosomally by various Bacillus species and is known for its biological activity. Administering 4,4,4-trifluoro-dl-valine to cultures of Bacillus sp. CS93 results in the formation of trifluorosurfactin in quantities sufficient for detection by LC–MS/MS. 19F NMR analysis of the culture supernatant revealed that the bulk of the fluorinated amino acid was transformed and thus was unavailable for incorporation into surfactin. Detection of ammonia, and MS analysis indicated that the transformation proceeds with deamination and reduction of the keto acid, yielding 4,4,4-trifluoro-2-hydroxy-3-methylbutanoic acid.

Synthesis and spectroscopic studies of chiral CdSe quantum dots

2013-04-30T11:16:22Z

Synthesis and spectroscopic studies of chiral CdSe quantum dots Gallagher, Shane A.; Moloney, Mícheál P.; Wojdyla, Michal; Quinn, Susan J.; Kelly, John M.; Gun'ko, Yurii K. Using microwave irradiation, water soluble, optically active, penicillamine (Pen) capped CdSe nanocrystals with broad spectral distribution (430-780 nm) of photoluminescence have been produced and studied by a range of instrumental techniques including absorption, circular dichroism and both steady state and time resolved photoluminescence spectroscopy. The photoluminescence of these nanocrystals is attributed to emission from surface defect states. The decay of the excited state in the nanosecond region, which can be analysed as a triple exponential, depends strongly on the emission wavelength selected, but only weakly on the excitation wavelength.

Anisotropic spatial clustering of TB in cattle - the implications for control policy

2013-04-25T14:10:17Z

Anisotropic spatial clustering of TB in cattle - the implications for control policy Kelly, Gabrielle E. Bovine TB is a disease that affects cattle and the wildlife badger, species Meles meles, in Ireland and the UK, and badgers have been implicated in the spread of the disease in cattle. Efforts to eradicate the disease that have included localized badger culling, have not been successful. In a study to understand how the disease spreads, Kelly and More [1] determined that the disease spatially clusters in cattle herds and estimated the practical spatial ranges at which this occurs. We extend this work by examining possible anisotropy in clustering and the consequences for TB control policy. 1st Conference on Spatial Statistics 2011 – Mapping Global Change, Enschede, The Netherlands, March, 2011

Clustering Ordinal Data via Latent Variable Models

2013-04-25T13:59:27Z

Clustering Ordinal Data via Latent Variable Models McParland, Damien; Gormley, Claire Item response modelling is a well established method for analysing ordinal response data. Ordinal data are typically collected as responses to a number of questions or items. The observed data can be viewed as discrete versions of an underlying latent Gaussian variable. Item response models assume that this latent variable (and therefore the observed ordinal response) is a function of both respondent specific and item specific parameters. However, item response models assume a homogeneous population in that the item specific parameters are assumed to be the same for all respondents. Often a population is heterogeneous and clusters of respondents exist; members of different clusters may view the items differently. A mixture of item response models is developed to provide clustering capabilities in the context of ordinal response data. The model is estimated within the Bayesian paradigm and is illustrated through an application to an ordinal response data set resulting from a clinical trial involving self-assessment of arthritis. IFCS 2013 Conference of the International Federation of Classification Societies, Tilburg University, The Netherlands, from July 14-17, 2013

A long term observational study of the impact of badger removal on herd restrictions due to bovine TB in the Irish midlands during 1989-2004

2013-04-24T15:42:29Z

A long term observational study of the impact of badger removal on herd restrictions due to bovine TB in the Irish midlands during 1989-2004 Kelly, Gabrielle E.; Condon, J.; More, Simon John; Dolan, L.; Higgins, I.; Eves, J. An observational study was carried out, using data collected from four areas in the Irish midlands, between 1989 and 2004, to critically evaluate the long-term effects of proactive badger culling and to provide insights into reactive badger culling tuberculosis (TB) prevalence in cattle. Confirmed cattle herd TB incidence is the outcome measure used throughout. Relative to reactive culling, proactive badger culling was associated with a decrease in incidence in each of the 16 years of observation, which encompassed periods of both intensive and less-intensive badger removal. By 2004, we observed a decrease of 22% [95% confidence interval (CI) 15-29, P<0.001] in the entire proactive and 37% (95% CI 25–47, P<0.001), in the inner proactive removal areas. The size of the decrease increased with time (P=0.055). There was a decrease (constant over time) of at least 14% (95% CI 76–97, P=0.013) in incidence in the inner compared to the outer control area (herds ≤2 km, >2 km, from proactive removal area boundaries, respectively). Incidence in the outer proactive removal area (herds <1.6 km from the proactive removal boundary) was similar to the inner control area (P=0.890). Incidence in the outer control area and total control area, compared to a neighbouring area some distance away, increased over the course of the study. Differences with the total control area were not statistically significant but the outer control area was 11% higher than the neighbouring area by 2004 (borderline significance P=0.057).

Body mass index and height over three generations: evidence from the Lifeways cross-generational cohort study

2013-04-24T15:38:54Z

Body mass index and height over three generations: evidence from the Lifeways cross-generational cohort study Murrin, Celine; Kelly, Gabrielle E.; Tremblay, Richard E.; Kelleher, Cecily Background: Obesity and its measure of body mass index are strongly determined by parental body size. Debate continues as to whether both parents contribute equally to offspring body mass which is key to understanding the aetiology of the disease. The aim of this study was to use cohort data from three generations of one family to examine the relative maternal and paternal associations with offspring body mass index and how these associations compare with family height to demonstrate evidence of genetic or environmental cross-generational transmission. Methods: 669 of 1082 families were followed up in 2007/8 as part of the Lifeways study, a prospective observational cross-generation linkage cohort. Height and weight were measured in 529 Irish children aged 5 to 7 years and were self-reported by parents and grandparents. All adults provided information on self-rated health, education status, and indicators of income, diet and physical activity. Associations between the weight, height, and body mass index of family members were examined with mixed models and heritability estimates computed using linear regression analysis. Results: Self-rated health was associated with lower BMI for all family members, as was age for children. When these effects were accounted for evidence of familial associations of BMI from one generation to the next was more apparent in the maternal line. Heritability estimates were higher (h2 = 0.40) for mother-offspring pairs compared to father-offspring pairs (h2 = 0.22). In the previous generation, estimates were higher between mothersparents (h2 = 0.54-0.60) but not between fathers-parents (h2 = -0.04-0.17). Correlations between mother and offspring across two generations remained significant when modelled with fixed variables of socioeconomic status, health, and lifestyle. A similar analysis of height showed strong familial associations from maternal and paternal lines across each generation. Conclusions: This is the first family cohort study to report an enduring association between mother and offspring BMI over three generations. The evidence of BMI transmission over three generations through the maternal line in an observational study corroborates the findings of animal studies. A more detailed analysis of geno and phenotypic data over three generations is warranted to understand the nature of this maternal-offspring relationship.

Spatial clustering of TB-infected cattle herds prior to and following proactive badger removal

2013-04-24T15:33:46Z

Spatial clustering of TB-infected cattle herds prior to and following proactive badger removal Kelly, Gabrielle E.; More, Simon John Bovine tuberculosis (TB) is primarily a disease of cattle. In both Ireland and the UK, badgers (Meles meles) are an important wildlife reservoir of infection. This paper examined the hypothesis that TB is spatially correlated in cattle herds, established the range of correlation and the effect, if any, of proactive badger removal on this. We also re-analysed data from the Four Area Project in Ireland, a large-scale intervention study aimed at assessing the effect of proactive badger culling on bovine TB incidence in cattle herds, taking possible spatial correlation into account. We established that infected herds are spatially correlated (the scale of spatial correlation is presented), but at a scale that varies with time and in different areas. Spatial correlation persists following proactive badger removal.

Estimating the extent of spatial association of Mycobacterium bovis infection in badgers in Ireland

2013-04-24T15:26:29Z

Estimating the extent of spatial association of Mycobacterium bovis infection in badgers in Ireland Kelly, Gabrielle E.; McGrath, Guy; More, Simon John Mycobacterium bovis infects the wildlife species badgers Meles meles who are linked with the spread of the associated disease tuberculosis (TB) in cattle. Control of livestock infections depends in part on the spatial and social structure of the wildlife host. Here we describe spatial association of M. bovis infection in a badger population using data from the first year of the Four Area Project in Ireland. Using second-order intensity functions, we show there is strong evidence of clustering of TB cases in each the four areas, i.e. a global tendency for infected cases to occur near other infected cases. Using estimated intensity functions, we identify locations where particular strains of TB cluster. Generalized linear geostatistical models are used to assess the practical range at which spatial correlation occurs and is found to exceed 6 in all areas. The study is of relevance concerning the scale of localized badger culling in the control of the disease in cattle.

Spatio-Temporal Modelling of TB in Cattle Herds

2013-04-24T14:22:45Z

Spatio-Temporal Modelling of TB in Cattle Herds Kelly, Gabrielle E. We examine spatial association of bovine TB in cattle herds using data from Ireland. Badgers (Meles meles), a protected species under the Wildlife Act 1976 (OAG 2012), have been implicated in the spread of the disease in cattle. Current disease control policies include reactive culling (in response to TB outbreaks) of badgers in the index and neighbouring farms. Kelly and More (2011) using generalized linear geostatistical models, established that TB clusters in cattle herds and estimated the practical spatial ranges at which this occurs. Here this work is extended by taking into account possible anisotropy. Changes in spatial association over two time periods are also examined. The results have direct implications for establishing scale and direction in reactive culling. They are also of import regarding the evaluation of vaccines for badgers and cattle.

Towards selective catalytic oxidations using in-situ generated H2O2

2013-04-18T17:04:12Z

Towards selective catalytic oxidations using in-situ generated H2O2 Sullivan, James A.; O'Callaghan, Niamh A series of Ti-modified mesoporous SiO2 materials (SBA-15 and MCF) are prepared, characterised and used as catalysts in the selective epoxidation of a probe alkene (cyclohexene) using H2O2 as an oxidising agent. Similarly, a series of mesoporous SiO2-supported monometallic and bimetallic DMAP-stabilized Au and Pd nanoparticles were prepared, characterised and used as catalysts in the production of H2O2 from dilute H2(g) + O2(g) mixtures.The metallic nanoparticles were then supported on the Ti-modified mesoporous SiO2 and these hybrid materials were characterised and their activities in the selective epoxidation of alkenes in the presence of H2 (g) + O2 (g) mixtures (where H2O2 would be formed in situ) were studied. The bimetallic Au / Pd nanoparticles (which were most active in the production of H2O2 from H2 and O2) were not the most active or selective in the combined reaction. This was ascribed to the Pd component of the nanoparticles promoting hydrogenation of the probe alkene more rapidly than the formation of H2O2. The selectivity of Au nanoparticles in the presence of H2(g) + O2(g) was higher than that of the same catalysts in the presence of H2O2(aq).

Rare earth (La, Nd, Pr) doped ceria zirconia solid solutions for soot combustion

2013-04-18T11:10:19Z

Rare earth (La, Nd, Pr) doped ceria zirconia solid solutions for soot combustion Dulgheru, Petrica; Sullivan, James A. A series of rare earth (RE) (La, Nd, Pr) ceria zirconia materials were analysed for their soot combustion activity in air and in NO/O2. The materials were characterised using DRIFT spectroscopy. In general the presence of the RE dopant increases the activity of undoped CexZr1-xO2. The La and Pr doped catalysts showed increased low temperature activity in the presence of NO/O2 while the effect was less pronounced in case of Nd - doped samples. FTIR data has shown that the catalysts interact differently to NO/O2 mixtures in that they do not form significant quantities of adsorbed nitrite-type species. We postulate that this species is a precursor to NO2 formation which in turn increases soot combustion.

Influence of Surface Groups on Poly(propylene imine) Dendrimers Antiprion Activity

2013-04-15T13:36:32Z

Influence of Surface Groups on Poly(propylene imine) Dendrimers Antiprion Activity McCarthy, James M.; Moreno, Beatriz Rasines; Filippini, Damien; Komber, Hartmut; Maly, Marek; Cernescu, Michaela; Brutschy, Bernhard; Appelhans, Dietmar; Rogers, Mark S. Prion diseases are characterized by the accumulation of PrP(Sc), an aberrantly folded isoform of the host protein PrP(C). Specific forms of synthetic molecules known as dendrimers are able to eliminate protease-resistant PrP(Sc) in both an intracellular and in vitro setting. The properties of a dendrimer which govern this ability are unknown. We addressed the issue by comparing the in vitro antiprion ability of numerous modified poly(propylene-imine) dendrimers, which varied in size, structure, charge, and surface group composition. Several of the modified dendrimers, including an anionic glycodendrimer, reduced the level of protease resistant PrP(Sc) in a prion strain-dependent manner. This led to the formulation of a new working model for dendrimer/prion interactions which proposes dendrimers eliminate PrP(Sc) by destabilizing the protein and rendering it susceptible to proteolysis. This ability is not dependent on any particular charge of dendrimer, but does require a high density of reactive surface groups.

Influence of surface functionality of poly(propylene imine) dendrimers on protease resistance and propagation of the scrapie prion protein

2013-04-15T12:10:27Z

Influence of surface functionality of poly(propylene imine) dendrimers on protease resistance and propagation of the scrapie prion protein Fischer, Marlies; Appelhans, Dietmar; Schwarz, Simona; Klajnert, Barbara; Bryszewska, Maria; Voit, Brigitte; Rogers, Mark S. Accumulation of PrP(Sc), an insoluble and protease-resistant pathogenic isoform of the cellular prion protein (PrP(C)), is a hallmark in prion diseases. Branched polyamines, including PPI (poly(propylene imine)) dendrimers, are able to remove protease resistant PrP(Sc) and abolish infectivity, offering possible applications for therapy. These dendrimer types are thought to act through their positively charged amino surface groups. In the present study, the molecular basis of the antiprion activity of dendrimers was further investigated, employing modified PPI dendrimers in which the positively charged amino surface groups were substituted with neutral carbohydrate units of maltose (mPPI) or maltotriose (m3PPI). Modification of surface groups greatly reduced the toxicity associated with unmodified PPI but did not abolish its antiprion activity, suggesting that the presence of cationic surface groups is not essential for dendrimer action. PPI and mPPI dendrimers of generation 5 were equally effective in reducing levels of protease-resistant PrP(Sc) (PrP(res)) in a dose- and time-dependent manner in ScN2a cells and in pre-existing aggregates in homogenates from infected brain. Solubility assays revealed that total levels of PrP(Sc) in scrapie-infected mouse neuroblastoma (ScN2a) cells were reduced by mPPI. Coupled with the known ability of polyamino dendrimers to render protease-resistant PrP(Sc) in pre-existing aggregates of PrP(Sc) susceptible to proteolysis, these findings strongly suggest that within infected cells dendrimers reduce total amounts of PrP(Sc) by mediating its denaturation and subsequent elimination.

Differentiating prion strains using dendrimers

2013-04-15T12:01:25Z

Differentiating prion strains using dendrimers McCarthy, James M.; Rasines, Beatriz; Appelhans, Dietmar; Rogers, Mark S. A panel of repetitively branched synthetic molecules known as dendrimers is used to identify and differentiate between different strains of the prion infectious agent, the protein-based pathogen responsible for prion disorders—a group of invariably fatal neurodegenerative diseases

The nature of surface deposits following valeric acid interactions with Al2O3-supported Alkaline Earth Oxide catalysts: Towards cellulosic biofuels

2013-04-15T11:39:32Z

The nature of surface deposits following valeric acid interactions with Al2O3-supported Alkaline Earth Oxide catalysts: Towards cellulosic biofuels Sullivan, James A.; Sherry, Linda Two Al2O3-supported alkaline earth metal oxide catalysts (MgO and BaO) were contacted with valeric acid at 250 °C. Each formed amounts of 5-nonanone (BaO more than MgO). A significant deposition of hydrocarbonaceous material onto the catalyst surface is noted. This adsorbed material is characterised using TGA and FTIR and relates to a carboxylate species.

The Preparation of Group II Oxide Catalysts Through Acetate Calcination: The Influence of a Support on the Nature of the Final Catalyst.

2013-04-15T11:37:04Z

The Preparation of Group II Oxide Catalysts Through Acetate Calcination: The Influence of a Support on the Nature of the Final Catalyst. Sullivan, James A.; Sherry, Linda The preparation of supported and unsupported group II oxide catalysts through oxidation of analogous group II acetates (Mg, Ca and Ba) in the presence and absence of a mesoporous silica material (SBA-15) was analysed using TGA. In the absence of the mesoporous support the acetates oxidised at different temperatures with a stability trend whereby Mg

Anti-prion drug mPPIg5 inhibits PrPC conversion to PrPSc

2013-04-15T11:54:11Z

Anti-prion drug mPPIg5 inhibits PrPC conversion to PrPSc McCarthy, James M.; Franke, Markus; Resenberger, Ulrike K.; Waldron, Sibeal; Simpson, Jeremy C.; Tatzelt, Jörg; Appelhans, Dietmar; Rogers, Mark S. Prion diseases, also known as transmissible spongiform encephalopathies, are a group of fatal neurodegenerative diseases that include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in humans. The 'protein only hypothesis' advocates that PrPSc, an abnormal isoform of the cellular protein PrPC, is the main and possibly sole component of prion infectious agents. Currently, no effective therapy exists for these diseases at the symptomatic phase for either humans or animals, though a number of compounds have demonstrated the ability to eliminate PrPSc in cell culture models. Of particular interest are synthetic polymers known as dendrimers which possess the unique ability to eliminate PrPSc in both an intracellular and in vitro setting. The efficacy and mode of action of the novel anti-prion dendrimer mPPIg5 was investigated through the creation of a number of innovative bio-assays based upon the scrapie cell assay. These assays were used to demonstrate that mPPIg5 is a highly effective anti-prion drug which acts, at least in part, through the inhibition of PrPC to PrPSc conversion. Understanding how a drug works is a vital component in maximising its performance. By establishing the efficacy and method of action of mPPIg5, this study will help determine which drugs are most likely to enhance this effect and also aid the design of dendrimers with anti-prion capabilities for the future.

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates

2013-04-08T15:44:51Z

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates Balobaid, Laila; Craig Carville, N.; Manzo, Michele; Gallo, Katia; Rodriguez, Brian J. Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 µm in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer, can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth, and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

Photoreduction of SERS-active metallic nanostructures on chemically-patterned ferroelectric crystals

2013-04-08T15:41:56Z

Photoreduction of SERS-active metallic nanostructures on chemically-patterned ferroelectric crystals Craig Carville, N.; Manzo, Michele; Damm, Signe; Castiella, Marion; Collins, Liam; Denning, Denise; Weber, Stefan A. L.; Gallo, Katia; Rice, James H.; Rodriguez, Brian J. Photodeposition of metallic nanostructures onto ferroelectric surfaces is typically based on patterning local surface reactivity via electric field poling. Here, we demonstrate metal deposition onto substrates which have been chemically patterned via proton exchange (i.e., without polarization reversal). The chemical patterning provides the ability to tailor the electrostatic fields near the surface of lithium niobate crystals and these engineered fields are used to fabricate metallic nanostructures. The effect of the proton exchange process on the piezoelectric and electrostatic properties of the surface is characterized using voltage modulated atomic force microscopy techniques, which combined with modeling of the electric fields at the surface of the crystal, reveal that the deposition occurs preferentially along the boundary between ferroelectric and proton exchanged regions. The metallic nanostructures have been further functionalized with a target probe molecule, 4-aminothiophenol, from which surface enhanced Raman scattering (SERS) signal is detected, demonstrating the suitability of chemically patterned ferroelectrics as SERS-active templates.

Production of anticancer polyenes through precursor-directed biosynthesis

2013-05-16T08:26:39Z

Production of anticancer polyenes through precursor-directed biosynthesis Clark, Benjamin R.; O'Connor, Stephen; Fox, Deirdre; Leroy, Jacques; Murphy, Cormac D. The biosynthesis of the pyrrolyl moiety of the fungal metabolite rumbrin originates from pyrrole-2-carboxylic acid. In an effort to produce novel derivatives with enhanced biological activity a series of substituted pyrrole-2-carboxylates were synthesised and incubated with the producing organism, Auxarthron umbrinum. Several 4-halo-pyrrole-2-carboxylic acids were incorporated into the metabolite yielding three new derivatives: 3-fluoro-, 3-chloro- and 3-bromo-isorumbrin, which were generated in milligram quantities enabling cytotoxicity assays to be conducted. The 3-chloro- and 3-bromo-isorumbrins had improved activity against HeLa cells compared with rumbrin; 3-bromoisorumbrin also showed dramatically improved activity towards a lung cancer cell line (A549).

Bacterial production of hydroxylated and amidated metabolites of flurbiprofen

2013-04-08T15:13:01Z

Bacterial production of hydroxylated and amidated metabolites of flurbiprofen Bright, Tara V.; Clark, Benjamin R.; O'Brien, Eimear; Murphy, Cormac D. Several Streptomyces and Bacillus strains were examined for their ability to transform the anti-inflammatory drug flurbiprofen 1 to the hydroxylated metabolites that are found in humans after ingestion of this compound. Of the seven Streptomyces spp. examined, all but one transformed flurbiprofen to the main mammalian metabolite 4′-hydroxyflurbiprofen 2, and the majority also produced 3′,4′-dihydroxyflurbiprofen 3. Three strains, Streptomyces griseus DSM40236 and ATCC13273, and Streptomyces subrutilis DSM40445, also elaborated 3′-methoxy, 4′-hydroxy-flurbiprofen 4. None of the Bacillus spp. examined yielded these metabolites. Examination of the extracted supernatants of Streptomyces lavenduligriseus and Streptomyces rimosus by fluorine-19 nuclear magnetic resonance (19F NMR), indicated new resonances and these new fluorometabolites were purified by HPLC and revealed to be flurbiprofenamide 5 and 7-hydroxyflurbiprofenamide 6 after MS and NMR analyses. Subsequent re-examination of the culture supernatants from Bacillus subtilis IM7, Bacillus megaterium NCIMB8291 and B. megaterium ATTC14581 showed that these strains also produced 5 and 6. Resting cell investigations suggested that the amidation reaction employed nitrogen from an as yet unidentified amino acid.

The impact of a catastrophic storm event on benthic macroinvertebrate communities in upland headwater streams and potential implications for ecological diversity and assessment of ecological status

2013-04-03T11:35:14Z

The impact of a catastrophic storm event on benthic macroinvertebrate communities in upland headwater streams and potential implications for ecological diversity and assessment of ecological status Feeley, Hugh B.; Davis, Stephen; Bruen, Michael; Blacklocke, Sean; Kelly-Quinn, Mary Upland headwater streams are dynamic systems, responding rapidly to changes in climatic conditions. This study examined the effects of a catastrophic rainfall event, that occured on 24 October 2011 on the east coast of Ireland, on the macroinvertebrate community composition and structure of four headwater streams in the river Liffey catchment located in the Wicklow Mountains. The ecological status before and after the storm were also evaluated. The water level and pH of each stream were recorded using continuous monitoring equipment, while rainfall data for the study period were sourced from a local weather station. Benthic macroinvertebrates were investigated before and after the storm event using Surber sampling. Results showed rapid and large increases in water level and significant declines in stream pH in response to intensive rainfall during the storm. The high water levels also caused major physical damage and abrasion in all four streams, that significantly altered instream habitats. The storm event induced significant losses to the richness and/or density of most taxonomic groups, with the exception of the Plecoptera. Furthermore, the overall community composition and structure changed significantly, most likely as a result of physical disturbance, given the relative persistence of acid-sensitive taxa and the relatively short period of harsh acidic conditions (<5 pH). Interestingly however, the ecological status of each of the four study sites, tested using Stream Risk Score (SSRS), Biological Monitoring Working Party (BMWP) and the Average Score Per Taxon (ASPT) indices, was unaltered by the loss in richness and densities. This was likely a result of the maintenance of plecopteran richness and the absence of organic pollution, thus highlighting the need to develop appropriate indices to assess the ecological status of streams and rivers affected by physical disturbance caused by large storm events. Ultimately, catastrophic storm events in upland headwater streams have potentially major implications for the maintenance of regional macroinvertebrate diversity within affected regions.

Boundary behaviour of functions which possess universal Taylor series

2013-04-03T10:44:55Z

Boundary behaviour of functions which possess universal Taylor series Gardiner, Stephen J. It is known that, for any simply connected proper subdomain Ω of the complex plane and any point ζ in Ω, there are holomorphic functions on Ω that possess ‘universal’ Taylor series expansions about ζ; that is, partial sums of the Taylor series approximate arbitrary polynomials on arbitrary compacta in ℂ\ Ω that have connected complement. This paper establishes a strong unboundedness property for such functions near every boundary point. The result is new even in the case of the disc, where it strengthens work of several authors.

Opioid mediated activity and expression of mu and delta opioid receptors in isolated human term non-laboring myometrium

2013-03-28T15:09:10Z

Opioid mediated activity and expression of mu and delta opioid receptors in isolated human term non-laboring myometrium Fanning, Rebecca A.; McMorrow, Jason P.; Campion, Deirdre P.; Carey, Michael F.; O'Connor, J. J. The existence of opioid receptors in mammalian myometrial tissue is now widely accepted. Previously enkephalin degrading enzymes have been shown to be elevated in pregnant rat uterus and a met-enkephalin analogue has been shown to alter spontaneous contractility of rat myometrium. Here we have undertaken studies to determine the effects of met-enkephalin on in vitro human myometrial contractility and investigate the expression of opioid receptors in pregnant myometrium. Myometrial biopsies were taken from women undergoing elective caesarean delivery at term. Organ bath experiments were used to investigate the effect of the met-enkephalin analogue [d-Ala 2, d-met 5] enkephalin (DAMEA) on spontaneous contractility. A confocal immunofluorescent technique and real time PCR were used to determine the expression of protein and mRNA, respectively for two opioid receptor subtypes, mu and delta. DAMEA had a concentration dependent inhibitory effect on contractile activity (1×10−7 M–1×10−4 M; 54% reduction in contractile activity, P<0.001 at 1×10−4 M concentration). Mu and delta opioid receptor protein sub-types and their respective mRNA were identified in all tissues sampled. This is the first report of opioid receptor expression and of an opioid mediated uterorelaxant action in term human non-labouring myometrium in vitro

Synthesis of a conformationally constrained delta-amino acid building block

2013-03-20T12:15:19Z

Synthesis of a conformationally constrained delta-amino acid building block O'Reilly, Elaine; Pes, Lara; Ortin, Yannick; Mueller-Bunz, Helge; Paradisi, Francesca Conformationally restricted amino acids are important components in peptidomimetics and drug design. Herein, we describe the synthesis of a novel, non-proteinogenic constrained delta amino acid containing a cyclobutane ring, cis-3(aminomethyl)cyclobutane carboxylic acid (ACCA). The synthesis of the target amino acid was achieved in seven steps, with the key reaction being a base induced intramolecular nucleophilic substitution. A small library of dipeptides was prepared through the coupling of ACCA with proteinogenic amino acids.

Note : Network random walk model of two-state protein folding : Test of the theory

2013-03-14T15:02:20Z

Note : Network random walk model of two-state protein folding : Test of the theory Berezhkovskii, Alexander M.; Murphy, Ronan D.; Buchete, Nicolae-Viorel We study two-state protein folding in the framework of a toy model of protein dynamics. This model has an important advantage: it allows for an analytical solution for the sum of folding and unfolding rate constants [A. M. Berezhkovskii, F. Tofoleanu, and N.-V. Buchete, J. Chem. Theory Comput. 7, 2370 (2011)10.1021/ct200281d] and hence for the reactive flux at equilibrium. We use the model to test the Kramers-type formula for the reactive flux, which was derived assuming that the protein dynamics is described by a Markov random walk on a network of complex connectivity [A. Berezhkovskii, G. Hummer, and A. Szabo, J. Chem. Phys. 130, 205102 (2009)10.1063/1.3139063]. It is shown that the Kramers-type formula leads to the same result for the reactive flux as the sum of the rate constants.

Effect of organic solvents on the activity and stability of halophilic alcohol dehydrogenase (ADH2) from Haloferax volcanii

2013-03-01T10:01:10Z

Effect of organic solvents on the activity and stability of halophilic alcohol dehydrogenase (ADH2) from Haloferax volcanii Alsafadi, Diya; Paradisi, Francesca The effect of various organic solvents on the catalytic activity, stability and substrate specificity of alchohol dehydrogenase from Haloferax volcanii (HvADH2) was evaluated. The HvADH2 showed remarkable stability and catalysed the reaction in aqueous–organic medium containing dimethyl sulfoxide (DMSO) and methanol (MeOH). Tetrahydrofuran and acetonitrile were also investigated and adversely affected the stability of the enzyme. High concentration of salt, essential to maintain the enzymatic activity and structural integrity of the halophilic enzyme under standard conditions may be partially replaced by DMSO and MeOH. The presence of organic solvents did not induce gross changes in substrate specificity. DMSO offered a protective effect for the stability of the enzyme at nonoptimal pHs such as 6 and 10. Salt and solvent effects on the HvADH2 conformation and folding were examined through fluorescence spectroscopy. The fluorescence findings were consistent with the activity and stability results and corroborated the denaturing properties of some solvents. The intrinsic tolerance of this enzyme to organic solvent makes it highly attractive to industry.

A comparison of two novel alcohol dehydrogenase enzymes (ADH1 and ADH2) from the extreme halophile Haloferax volcanii

2013-02-28T11:10:16Z

A comparison of two novel alcohol dehydrogenase enzymes (ADH1 and ADH2) from the extreme halophile Haloferax volcanii Timpson, Leanne M.; Liliensiek, Ann-Kathrin; Alsafadi, Diya; Cassidy, Jennifer; Sharkey, Michael A.; Liddell, Susan; Allers, Thorsten; Paradisi, Francesca Haloarchaeal alcohol dehydrogenases are exciting biocatalysts with potential industrial applications. In this study, two alcohol dehydrogenase enzymes from the extremely halophilic archaeon Haloferax volcanii (HvADH1 and HvADH2) were homologously expressed and subsequently purified by immobilized metal-affinity chromatography. The proteins appeared to copurify with endogenous alcohol dehydrogenases, and a double Δadh2 Δadh1 gene deletion strain was constructed to prevent this occurrence. Purified HvADH1 and HvADH2 were compared in terms of stability and enzymatic activity over a range of pH values, salt concentrations, and temperatures. Both enzymes were haloalkaliphilic and thermoactive for the oxidative reaction and catalyzed the reductive reaction at a slightly acidic pH. While the NAD+-dependent HvADH1 showed a preference for short-chain alcohols and was inherently unstable, HvADH2 exhibited dual cofactor specificity, accepted a broad range of substrates, and, with respect to HvADH1, was remarkably stable. Furthermore, HvADH2 exhibited tolerance to organic solvents. HvADH2 therefore displays much greater potential as an industrially useful biocatalyst than HvADH1.

Targeting tumour necrosis factor-α in hypoxia and synaptic signalling

2013-02-22T10:08:59Z

Targeting tumour necrosis factor-α in hypoxia and synaptic signalling O'Connor, J. J. Tumour necrosis factor (TNF)-α is a pro-inflammatory cytokine, which is synthesised and released in the brain by astrocytes, microglia and neurons in response to numerous internal and external stimuli. It is involved in many physiological and pathophysiological processes such as gene transcription, cell proliferation, apoptosis, synaptic signalling and neuroprotection. The complex actions of TNF-α in the brain are under intense investigation. TNF-α has the ability to induce selective necrosis of some cells whilst sparing others and this has led researchers to discover multiple activated signalling cascades. In many human diseases including acute stroke and inflammation and those involving hypoxia, levels of TNF-α are increased throughout different brain regions. TNF-α signalling may also have several positive and negative effects on neuronal function including glutamatergic synaptic transmission and plasticity. Exogenous TNF-α may also exacerbate the neuronal response to hypoxia. This review will summarise the actions of TNF-α in the central nervous system on synaptic signalling and its effects during hypoxia.

Determination of a universal series

2013-01-14T17:12:15Z

Determination of a universal series Mouze, Augustin; Nestoridis, Vassili; Papadoperakis, Ioannis; Tsirivas, Nikolaos The known proofs for universal Taylor series do not determine a specific universal Taylor series. In the present paper, we isolate a specific universal Taylor series by modifying the proof in [30]. Thus we determine all Taylor coefficients of a specific universal Taylor series on the disc or on a polygonal domain. Furthermore in non simply connected domains, when universal Taylor series exist, we can construct a sequence of specific rational functions converging to a universal function, provided the boundary is good enough. The solution uses an infinite denumerable procedure and a finite number of steps is not sufficient. However we solve a Runge's type problem in a finite number of steps.

Ostrowski-type theorems for harmonic functions

2013-01-14T17:07:58Z

Ostrowski-type theorems for harmonic functions Manolaki, Myrto Ostrowski showed that there are intimate connections between the gap structure of a Taylor series and the behaviour of its partial sums outside the disk of convergence. This paper investigates the corresponding problem for the homogeneous polynomial expansion of a harmonic function. The results for harmonic functions display new features in the case of higher dimensions.

Two-phase quadrature domains

2013-01-14T16:24:52Z

Two-phase quadrature domains Gardiner, Stephen J.; Sjödin, Tomas Recent work on two-phase free boundary problems has led to the investigation of a new type of quadrature domain for harmonic functions. This paper develops a method of constructing such quadrature domains based on the technique of partial balayage, which has proved to be a useful tool in the study of one-phase quadrature domains and Hele-Shaw flows.

The influence of SO2-/4 on the catalytic combustion of soot using O-2 and NO/O-2 mixtures over Na-promoted Al2O3 catalysts

2013-01-11T14:54:04Z

The influence of SO2-/4 on the catalytic combustion of soot using O-2 and NO/O-2 mixtures over Na-promoted Al2O3 catalysts Sullivan, James A.; Keane, Orla; Maguire, Linda Na/Al2O3 catalysts are tested in the soot oxidation reaction using O-2 and NO/O-2 as oxidising agents. The activity of the catalysts . varies with oxidising agent and the presence of surface SO42-.. NO(g) increases conversion of soot to COx-. Surface SO42- has no effect on activity for the C-(s) + O-2 reaction but decreases activity in the Carbon + NO/O-2 oxidation. This is interpreted in terms of SO42- blocking NO adsorption sites, thus poisoning the 4 NO + O-2 --> NO2 reaction, which is essential for the NOx promoted oxidation.

Selective H-D exchange catalysed by aqueous phase and immobilised Pd nanoparticles

2013-01-09T17:33:12Z

Selective H-D exchange catalysed by aqueous phase and immobilised Pd nanoparticles Sullivan, James A.; Flanagan, Keith A.; Hain, Holger Pd nanoparticles (with a mean diameter of 3.4 ± 0.5 nm) prepared through BH4− reduction of Na2PdCl4 can catalyse selective H–D exchange (through reaction with D2O) at the carbon α to the N atom of a pyridine ring. Oxidised Pd(II) complex species also present as dissolved species in the nanoparticle dispersion play no part in the exchange. We have studied the effects of several different variables on the rate of the selective H–D exchange activity for a model pyridine, i.e. 4-dimethylaminopyridine (DMAP). These variables include temperature, nanoparticle aging, nanoparticle re-reduction with H2 and nanoparticle immobilisation onto multi-walled carbon nanotubes (MWCNTs). We have also extended the study to related pyridine containing molecules.

Attempts at an in-situ Raman study of Ceria / Zirconia catalysts in PM combustion

2013-01-09T17:26:14Z

Attempts at an in-situ Raman study of Ceria / Zirconia catalysts in PM combustion Sullivan, James A.; Dulgheru, Petrica; Atribak, Idriss; Bueno-López, Agustín; García-García, Avelina CexZr1−xO2 catalysts with various Ce/Zr contents were studied using Raman spectroscopy under different gaseous atmospheres, at different temperatures and in the presence of a model soot. Catalysts with high concentrations of Zr fluoresced at elevated temperatures making analysis of their spectra impossible. This effect became even more pronounced at higher temperatures. CeO2 and solid solutions with relatively low concentrations of Zr showed a red shift and a decrease in intensity of the characteristic F2g peak at high temperatures under different atmospheres. The magnitude of the latter effect was higher under reducing atmospheres. These changes are reversible upon cooling, showing that they relate to a lattice expansion effect rather than any major chemical change to the material. In the presence of the model soot the Raman spectra of all materials was much decreased due to the absorption of the incident and scattered radiation by the soot particles. The presence of soot does not change the relative intensities or positions of the peaks in the spectra of the solid solutions. Evidence is shown for the production of a Ce3+–CO species following interaction between the soot and the surface at high temperature in an inert atmosphere.

Beneficial and problematic interactions between NOx trapping materials and carbonaceous particulate matter

2013-01-09T17:02:06Z

Beneficial and problematic interactions between NOx trapping materials and carbonaceous particulate matter Sullivan, James A.; Keane, Orla; Cassidy, Andrew The presence of a NOx trapping BaO component with a Pt active phase does not per-se promote carbon combustion. However when coupled with trap regeneration, promotion of soot combustion is seen. Operating NOx trapping materials promote combustion due to the periodic localised increases in [NO2](g) generated during the regeneration rather than due to a co-generated exotherm. However, it has been noted that the presence of soot prevents NOx traps from employing their full trapping capacity.

Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles

2013-01-09T16:40:18Z

Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles Flanagan, Keith A.; Sullivan, James A.; Mueller-Bunz, Helge 4-Dimethylaminopyridine (DMAP)-stabilized palladium nanoparticles with a mean diameter of 3.4 +/- 0.5 mn are prepared from the aqueous phase reduction of Na2PdCl4 using NaBH4 in the presence of DMAP. TEM and UV-vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation. H-1 NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP)(4)(OH)(2) by X-ray crystallography. Following extensive analysis, it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms alpha to the endocyclic nitrogen atom on the DMAP-stabilizing ligands through reaction with D2O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.

Suzuki coupling activity of an aqueous phase Pd nanoparticle dispersion and a carbon nanotube/Pd nanoparticle composite

2013-01-09T16:40:53Z

Suzuki coupling activity of an aqueous phase Pd nanoparticle dispersion and a carbon nanotube/Pd nanoparticle composite Sullivan, James A.; Flanagan, Keith A.; Hain, Holger An aqueous phase dispersion of Pd nanoparticles stabilised by 4-dimethylaminopyridine (DMAP) promotes model Suzuki coupling reactions. The dispersion contains Pd nanoparticles of 3.4 ± 0.5 nm and a Pd(II) species (Pd(DMAP)4(OH)2) which forms following aerobic oxidation of the nanoparticles. The activity of the nanoparticle dispersion in promoting the Suzuki reactions is directly proportional to the size of the halogen on the substrate (as is usual for these coupling reactions) and also to the age of the nanoparticle dispersion. The Pd(DMAP)4(OH)2 complex can be isolated from the dispersion and is found to be very active in promoting the reactions. Its formation following aerobic oxidation of the nanoparticles is proposed as the reason for the improved activity of the dispersion with age. The nanoparticles present in the dispersion can, through displacement of the stabilising ligand, be immobilised onto functionalised multi-walled carbon nanotubes (MWCNTs) and the composite formed is an active and recyclable catalyst. The MWCNT/Pd-DMAP NP composite acts as a reservoir of dissolved Pd species, which function as homogeneous catalysts under reaction conditions.

The combustion of carbon particulates using NO/O2 mixtures : The influence of SO42− and NOx trapping materials

2013-01-07T17:30:30Z

The combustion of carbon particulates using NO/O2 mixtures : The influence of SO42− and NOx trapping materials Sullivan, James A.; Keane, Orla The activity of several catalysts are studied in the soot combustion reaction using air and NO/air as oxidising agents. Over Al2O3-supported catalysts NO(g) is a promoter for the combustion reaction with the extent of promotion depending on the Na loading. Over these catalysts SO42− poisons this promotion by preventing NO oxidation through a site blocking mechanism. SiO2 is unable to adsorb NO or catalyse its oxidation and over SiO2-supported Na catalysts NO(g) inhibits the combustion reaction. This is ascribed to a competition between NO and O2. Over Fe-ZSM-5 catalysts the presence of a NOx trapping component does not increase the combustion of soot in the presence of NO(g) and it is proposed that this previously reported effect is only seen under continuous NOx trap operation as NO2 is periodically released during regeneration and thus available for soot combustion. Experiments during which the [NO](g) is varied show that CO, rather than an adsorbed carbonyl-like intermediate, is formed upon reaction between NO2 (the proposed oxygen carrier) and soot.

NH3 and urea in the selective catalytic reduction of NOx over oxide-supported copper catalysts

2013-01-07T17:24:05Z

NH3 and urea in the selective catalytic reduction of NOx over oxide-supported copper catalysts Sullivan, James A.; Doherty, Julie A. The temperature-programmed activity of a series of oxide-supported (TiO2, Al2O3 and SiO2) Cu catalysts formed from two different Cu precursors (Cu(NO3)(2) and CuSO4) for the selective catalytic reduction of NOx using solutions of urea as a reductant have been determined. These activities are compared to those found using NH3 as a reducing agent over the same catalysts in the presence of H2O and it is found that catalysts that are active for the selective reduction of NOx with NH3 are inactive for its reduction using solutions of urea. Poisoning of the surface by H2Oads is not responsible for all of this decrease in activity and it is postulated that the urea is not hydrolysing to form NH3 over the catalysts but rather is oxidising to form N-2 or forming passivated layers of polymeric melamine complexes on the surface. The catalysts were characterised by temperature-programmed reduction while temperature-programmed desorption and oxidation of NH3 and temperature programmed decomposition of urea are used to characterise the interaction of both reductants with the various catalysts.