Reactivity of crotonaldehyde and propene over Au/Pd(111) surfaces

The surface chemistry of crotonaldehyde and propene, primary and secondary reaction products in the aerobic selective oxidation of crotyl alcohol, has been studied by temperature-programmed reaction over Au/Pd(111) surface alloys. Gold strongly promotes desorption versus reaction at mole fractions ≥0.3 (crotonaldehyde) and ≥0.8 (CH); only ∼5% of the chemisorbed aldehyde or alkene react over Au-rich alloys. Surprisingly, co-adsorbed oxygen strongly suppresses crotonaldehyde decomposition over both clean Pd(111) and alloy surfaces, while CH combustion, an important undesired side-reaction over unpromoted Pd(111), is also moderated by Au. © the Owner Societies.

In situ studies of structure-reactivity relations in biodiesel synthesis over nanocrystalline MgO

High temperature processing of solvothermally synthesised MgO nanoparticles promotes striking changes in their morphology, and surface chemical and electronic structure. As-prepared NanoMgO comprised ∼4 nm cubic periclase nanocrystals, interspersed within an amorphous Mg(OH)(OCH3) matrix. These crystallites appear predominantly (1 0 0) terminated, and the overall material exhibits carbonate and hydroxyl surface functionalities of predominantly weak/moderate base character. Heating promotes gradual crystallisation and growth of the MgO nanoparticles, and concomitant loss of Mg(OH)(OCH3). In situ DRIFTS confirms the residual precursor and surface carbonate begin to decompose above 300 °C, while in situ XPS shows these morphological changes are accompanied by the disappearance of surface hydroxyl/methoxide species and genesis of O- centres which enhance both the surface density and basicity of the resulting stepped and defective MgO nanocrystals. The catalytic performance in tributyrin transesterification with methanol is directly proportional to the density of strong surface base sites. © 2010 Elsevier B.V. All rights reserved.

Structure-reactivity correlations in MgAl hydrotalcite catalysts for biodiesel synthesis

A series of [Mg(1−x)Alx(OH)2]x+(CO3)x/n2− hydrotalcite materials with compositions over the range x = 0.25–0.55 have been synthesised using an alkali-free coprecipitation route. All materials exhibit XRD patterns characteristic of the hydrotalcite phase with a steady lattice expansion observed with increasing Mg content. XPS measurements reveal a decrease in both the Al and Mg photoelectron binding energies with Mg incorporation which correlates with the increased intra-layer electron density. All materials are effective catalysts for the liquid phase transesterification of glyceryl tributyrate with methanol for biodiesel production. The rate increases steadily with Mg content, with the Mg rich Mg2.93Al catalyst an order of magnitude more active than MgO, with pure Al2O3 being completely inert. The rate of reaction also correlates with intralayer electron density which can be associated with increased basicity.© 2005 Elsevier B.V. All rights reserved.

Structure-reactivity correlations in the selective aerobic oxidation of cinnamyl alcohol:in situ XAFS

The structural evolution of a Pd/C catalyst during the liquid phase selective aerobic oxidation of cinnamyl alcohol has been followed by in situ XAFS and XPS. The fresh catalyst comprised highly dispersed, heavily oxidised Pd particles. Cinnamyl alcohol oxidation resulted in the rapid reduction of surface palladium oxide and a small degree of concomitant particle growth. These structural changes coincided with a large drop in catalytic activity. Prereduced Pd/C exhibited a significantly lower initial oxidation rate demonstrating the importance of surface metal oxide in effecting catalytic oxidation. Use of a Pd black model system confirmed that the oxide→metal transformation was the cause, and not result, of catalyst deactivation.

Structure-reactivity correlations in sulphated-zirconia catalysts for the isomerisation of α-pinene

A range of mesoporous sulphated zirconias with tuneable structural and catalytic properties have been prepared by direct impregnation. The surface sulphate coverage can be readily varied, achieving a maximum value of ∼0.2 monolayers. High-temperature calcination induces the crystallisation of tetragonal zirconia while suppressing the monoclinic phase and enhances surface acidity. Superacid sites only appear above a critical threshold SO4 coverage of 0.08 mL (corresponding to 0.44 wt% total S). Sulphated zirconias show good activity towards α-pinene isomerisation of under mild conditions. Conversion correlates with the number Brønsted acid sites, while the selectivity towards mono- versus polycyclic products depends on the corresponding acid site strength; superacidity promotes limonene formation over camphene.

Effects of recombinant human DNase and hypertonic saline on airway inflammation in children with cystic fibrosis

Recombinant human DNase (rhDNase) is an established treatment in cystic fibrosis (CF), but it may liberate cationic mediators bound to DNA in the airways. An alternative mucolytic therapy is hypertonic saline (HS); however, HS may potentiate neutrophilic inflammation. We compared the effect of rhDNase and HS on cationic proinflammatory mediators in CF sputum. In a randomized, crossover trial, 48 children with CF were allocated consecutively to 12 weeks of once-daily 2.5 mg rhDNase, alternate-day 2.5 mg rhDNase, and twice-daily 7% HS. Sputum levels of total interleukin-8 (IL-8), free IL-8, myeloperoxidase, eosinophil cationic protein, and neutrophil elastase (NE) activity were measured before and after each treatment. The change in mediator levels from baseline with daily rhDNase and HS was not significant; however, with alternate-day rhDNase, there was an increase in free IL-8. When changes in mediator levels with daily rhDNase were compared with alternate-day rhDNase and HS, no significant differences were detected. Only changes in NE activity were associated with changes in lung function. In summary, we were unable to show that rhDNase or HS promote airway inflammation in CF.

Structure and reactivity of sol-gel sulphonic acid silicas

A range of mesoporous solid sulphonic acid catalysts have been prepared from a mercaptopropyl-trimethoxysilane (MPTS) precursor by sol-gel synthesis. The creation of surface sulphonic acid functionality via thiol oxidation has been followed by XPS and Raman spectroscopy. It is possible to continuously vary the sulphonic acid loading from 1 to 12wt.% while maintaining pore volume and mesostructure. The resulting materials exhibit high thermal stability and acid strength across the composition range and show good activity and selectivity in esterification and condensation reactions. © 2002 Elsevier Science B.V. All rights reserved.

Nucleoside diphosphate kinase--a component of the [Na+1]- and [Cl-]-sensitive phosphorylation cascade in human and murine airway epithelium

We have shown that proteins within apically enriched fractions of human nasal respiratory epithelium vary their phosphohistidine content with ambient [Cl-] and other anion concentrations. This membrane-delimited phosphorylation cascade includes a multifunctional protein histidine kinase - nucleoside diphosphate kinase (NDPK). NDPK is itself a cascade component in both human and ovine airway, the self-phosphorylation of which is inhibited selectively by [Na+] in the presence of ATP (but not GTP). These findings led us to propose the existence of a dual anion-/cation-controlled phosphorylation-based "sensor" bound to the apical membrane. The present study showed that this cascade uses ATP to phosphorylate a group of proteins above 45 kDa (p45-group, identities unknown). Additionally, the Cl- dependence of ATP (but not GTP) phosphorylation is conditional on phosphatase activity and that interactions exist between the ATP- and GTP-phosphorylated components of the cascade under Cl--free conditions. As a prelude to studies in cystic fibrosis (CF) mice, we showed in the present study that NDPK is present and functionally active in normal murine airway. Since NDPK is essential for UTP synthesis and regulates fetal gut development, G proteins, K+channels, neutrophil-mediated inflammation and pancreatic secretion, the presence of ion-regulated NDPK protein in mouse airway epithelium might aid understanding of the pathogenesis of CF.

Low gravity rotational culture and the integration of immunomodulatory stem cells reduce human islet allo-reactivity

Modification of human islets prior to transplantation may improve long-term clinical outcome in terms of diabetes management, by supporting graft function and reducing the potential for allo-rejection. Intragraft incorporation of stem cells secreting beta (β)-cell trophic and immunomodulatory factors represents a credible approach, but requires suitable culture methods to facilitate islet alteration without compromising integrity. This study employed a three-dimensional rotational cell culture system (RCCS) to achieve modification, preserve function, and ultimately influence immune cell responsiveness to human islets. Islets underwent intentional dispersal and rotational culture-assisted aggregation with amniotic epithelial cells (AEC) exhibiting intrinsic immunomodulatory potential. Reassembled islet constructs were assessed for functional integrity, and their ability to induce an allo-response in discrete T-cell subsets determined using mixed islet:lymphocyte reaction assays. RCCS supported the formation of islet:AEC aggregates with improved insulin secretory capacity compared to unmodified islets. Further, the allo-response of peripheral blood mononuclear cell (PBMC) and purified CD4+ and CD8+ T-cell subsets to AEC-bearing grafts was significantly (p < 0.05) attenuated. Rotational culture enables pre-transplant islet modification involving their integration with immunomodulatory stem cells capable of subduing the allo-reactivity of T cells relevant to islet rejection. The approach may play a role in achieving acute and long-term graft survival in islet transplantation.

Using an in vitro human airway model to study the toxic effects of components of e-cigarettes

Cigarette smoke is a complex mixture of more than 4000 hazardous chemicals including the carcinogenic benzopyrenes. Nicotine, the most potent component of tobacco, is responsible for the addictive nature of cigarettes and is a major component of e-cigarette cartridges. Our study aims to investigate the toxicity of nicotine with special emphasis on the replacement of animals. Furthermore, we intend to study the effect of nicotine, cigarette smoke and e-cigarette vapours on human airways. In our current work, the BEAS 2B human bronchial epithelial cell line was used to analyse the effect of nicotine in isolation, on cell viability. Concentrations of nicotine from 1.1µM to 75µM were added to 5x105 cells per well in a 96 well plate and incubated for 24 hours. Cell titre blue results showed that all the nicotine treated cells were more metabolically active than the control wells (cells alone). These data indicate that, under these conditions, nicotine does not affect cell viability and in fact, suggests that there is a stimulatory effect of nicotine on metabolism. We are now furthering this finding by investigating the pro-inflammatory response of these cells to nicotine by measuring cytokine secretion via ELISA. Further work includes analysing nicotine exposure at different time points and on other epithelial cells lines like Calu-3.

Using apparent activation energy as a reactivity criterion for biomass pyrolysis

The reactivity of chemically isolated lignocellulosic blocks, namely, α-cellulose, holocellulose, and lignin, has been rationalized on the basis of the dependence of the effective activation energy (Eα) upon conversion (α) determined via the popular isoconversional kinetic analysis, Friedman’s method. First of all, a detailed procedure for the thermogravimetric data preparation, kinetic calculation, and uncertainty estimation was implemented. Resulting Eα dependencies obtained for the slow pyrolysis of the extractive-free Eucalyptus grandis isolated α-cellulose and holocellulose remained constant for 0.05 < α < 0.80 and equal to 173 ± 10, 208 ± 11, and 197 ± 118 kJ/mol, thus confirming the single-step nature of pyrolysis. On the other hand, large and significant variations in Eα with α from 174 ± 10 to 322 ± 11 kJ/mol in the region of 0.05 and 0.79 were obtained for the Klason lignin and reported for the first time. The non-monotonic nature of weight loss at low and high conversions had a direct consequence on the confidence levels of Eα. The new experimental and calculation guidelines applied led to more accurate estimates of Eα values than those reported earlier. The increasing Eα dependency trend confirms that lignin is converted into a thermally more stable carbonaceous material.

Reactions of singlet oxygen and singlet oxygen mimics with dicyclopropylethylenes: Comparison of reactivity and mechanisms

An extensive study of the reaction pathways of 1,1-dicyclopropyl ethylene, cis- and trans- 1,2-dicyclopropylethylenes has been undertaken with different electrophiles 4-methyl-1,2,4-triazoline-3,5-dione (MTAD), tetracyanoethylene (TCNE), and singlet oxygen $\rm(\sp1O\sb2).$ Comparison of reactivity and reaction mechanisms among the electrophiles is investigated. Singlet oxygen exhibits significantly lower reactivity compared to the other electrophiles. MTAD and TCNE react with dicyclopropylethylenes to produce predominantly $\sp{\prime\prime}2+2\sp{\prime\prime}$ adducts and a small amount of the "ene" adducts. The $\sp{\prime\prime}2+2\sp{\prime\prime}$ is the major product presumably because of the high activation energy leading to the highly strained "ene" products. Solvent trapping studies provide strong evidence of a "stepwise" mechanism, involving a zwitterionic or aziridinium imide as an intermediate from the study of the reactions products of dicyclopropylethylenes and MTAD. ^

Local biomass control on the composition and reactivity of particulate organic matter in aquatic environments

Freshwater ecosystems have been recognized as important components of the global carbon cycle, and the flux of organic matter (OM) from freshwater to marine environments can significantly affect estuarine and coastal productivity. The focus of this study was the assessment of carbon dynamics in two aquatic environments, namely the Florida Everglades and small prairie streams in Kansas, with the aim of characterizing the biogeochemistry of OM. In the Everglades, particulate OM (POM) is mostly found as a layer of flocculent material (floc). While floc is believed to be the main energy source driving trophic dynamics in this oligotrophic wetland, not much is known about its biogeochemistry. The objective of this study was to determine the origin/sources of OM in floc using biomarkers and pigment-based chemotaxonomy to assess specific biomass contributions to this material, on a spatial (freshwater marshes vs. mangrove fringe) and seasonal (wet vs. dry) scales. It was found that floc OM is derived from the local vegetation (mainly algal components and macrophyte litter) and its composition is controlled by seasonal drivers of hydrology and local biomass productivity. Photo-reactivity experiments showed that light exposure on floc resulted in photo-dissolution of POC with the generation of significant amounts of both dissolved OM (DOM) and nutrients (N & P), potentially influencing nutrient dynamics in this ecosystem. The bio-reactivity experiments determined as the amount and rate of CO2 evolution during incubation were found to vary on seasonal and spatial scales and were highly influenced by phosphorus limitation. Not much is known on OM dynamics in small headwater streams. The objective of this study was to determine carbon dynamics in sediments from intermittent prairie streams, characterized by different vegetation cover for their watershed (C4 grasses) vs. riparian zone (C3 plants). In this study sedimentary OM was characterized using a biomarker and compound specific carbon stable isotope approach. It was found that the biomarker composition of these sediments is dominated by higher plant inputs from the riparian zone, although inputs from adjacent prairie grasses were also apparent. Conflicting to some extent with the River Continuum Concept, sediments of the upper reaches contained more degraded OM, while the lower reaches were enriched in fresh material deriving from higher plants and plankton sources as a result of hydrological regimes and particle sorting.

Photo-Reactivity of Natural Dissolved Organic Matter from Fresh to Marine Waters in the Florida Everglades, USA

Natural dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of carbon cycling in aquatic systems. The combined effect of light absorbance properties and related photo-production of reactive species are essential in determining the reactivity of DOM. Optical properties and in particular excitation–emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) have been used increasingly to track sources and fate of DOM. Here we describe studies conducted in water from two estuarine systems in the Florida Everglades, with a salinity gradient of 2 to 37 and dissolved organic carbon concentrations from 19.3 to 5.74 mg C L−1, aimed at assessing how the quantity and quality of DOM is coupled to the formation rates and steady-state concentrations of reactive species including singlet oxygen, hydroxyl radical, and the triplet excited state of DOM. These species were related to optical properties and PARAFAC components of the DOM. The formation rate and steady-state concentration of the carbonate radical was calculated in all samples. The data suggests that formation rates, particularly for singlet oxygen and hydroxyl radicals, are strongly coupled to the abundance of terrestrial humic-like substances. A decrease in singlet oxygen, hydroxyl radical, and carbonate radical formation rates and steady-state concentration along the estuarine salinity gradient was observed as the relative concentration of terrestrial humic-like DOM decreased due to mixing with microbial humic-like and protein-like DOM components, while the formation rate of triplet excited-state DOM did not change. Fluorescent DOM was also found to be more tightly coupled to reactive species generation than chromophoric DOM.