Hydrogen adsorption on functionalized nanoporous activated carbons

There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions.

Stochastic and deterministic processes interact in the assembly of desert microbial communities on a global scale

Extreme arid regions in the worlds' major deserts are typified by quartz pavement terrain. Cryptic hypolithic communities colonize the ventral surface of quartz rocks and this habitat is characterized by a relative lack of environmental and trophic complexity. Combined with readily identifiable major environmental stressors this provides a tractable model system for determining the relative role of stochastic and deterministic drivers in community assembly. Through analyzing an original, worldwide data set of 16S rRNA-gene defined bacterial communities from the most extreme deserts on the Earth, we show that functional assemblages within the communities were subject to different assembly influences. Null models applied to the photosynthetic assemblage revealed that stochastic processes exerted most effect on the assemblage, although the level of community dissimilarity varied between continents in a manner not always consistent with neutral models. The heterotrophic assemblages displayed signatures of niche processes across four continents, whereas in other cases they conformed to neutral predictions. Importantly, for continents where neutrality was either rejected or accepted, assembly drivers differed between the two functional groups. This study demonstrates that multi-trophic microbial systems may not be fully described by a single set of niche or neutral assembly rules and that stochasticity is likely a major determinant of such systems, with significant variation in the influence of these determinants on a global scale.

Adsorption of metal cations by hydrous aluminium(III) or iron(III) hydroxide precipitates: enhancement by EDTA and related chelate molecules

Stoichiometrically equivalent concentrations of ethylenediaminetetraacetate, EDTA, and of related chelating anions increase the adsorption of ca. millimolar concentrations heavy metal aqua-ions on amorphous precipitates of aluminium(III) or iron(III) hydroxide and, although higher concentrations decrease the adsorption, poly-EDTA, a polyelectrolyte containing EDTA functional groups, shows no such decrease.

Inhibitory Effect of Phosphonium-Based Ionic Liquids on Coal Oxidation

To develop a chemical inhibitor that can efficiently suppress coal oxidation, nine tetraalkylphosphonium-based ionic liquids (ILs) and one imidazolium-based IL [1-allyl-3-methylimidazolium chloride ([AMIm]Cl)] were examined as additives. These ILs were used to treat and investigate the inhibitory effect on the oxidation activity and the structure of lignite coal. Characterization using thermogravimetric analysis showed that phosphonium-based ILs are able to inhibit coal oxidation up to 400 degrees C with the tributylethylphosphonium diethylphosphate ([P-4,P-4,P-4,P-2][DEP]) found to be the most effective. In contrast to the tetraalkylphosphonium-based ILs, inhibition using [AMIm]Cl was only found to be effective at temperatures below 250 degrees C, indicating that the tetraallcylphosphonium-based ILs may be more suitable for the future application of suppressing coal spontaneous combustion over a wide range of temperatures. Fourier transform infrared spectroscopic data showed that the various functional groups change in the coal following IL treatment, which are a decrease in the minerals and hydrogen bonds in all treated coals, while decreased aliphatic hydrocarbon and increased carbonyl bonds only appeared in some samples. During the oxidation of coal, the decomposition of aliphatic hydrocarbon groups is inhibited and the formation of carbonyl groups is delayed, so that the evolved gas concentration decreased, as shown by the temperature-programmed oxidation-mass spectrometry results. The deployment of the [P-4,P-4,P-4,P-2][ DEP] and tributylmethylphosphonium methylsulfate Its as additives also show good inhibitory effect on coal oxidation over the temperature range studied, and a relatively stronger interaction between [P-4,P-4,P-4,P-2] [DEP] and coal is demonstrated by the additive model.

Evolution of Antimicrobial Peptides to Self-Assembled Peptides for Biomaterial Applications

Biomaterial-related infections are a persistent burden on patient health, recovery, mortality and healthcare budgets. Self-assembled antimicrobial peptides have evolved from the area of antimicrobial peptides. Peptides serve as important weapons in nature, and increasingly medicine, for combating microbial infection and biofilms. Self-assembled peptides harness a “bottom-up” approach, whereby the primary peptide sequence may be modified with natural and unnatural amino acids to produce an inherently antimicrobial hydrogel. Gelation may be tailored to occur in the presence of physiological and infective indicators (e.g. pH, enzymes) and therefore allow local, targeted antimicrobial therapy at the site of infection. Peptides demonstrate inherent biocompatibility, antimicrobial activity, biodegradability and numerous functional groups. They are therefore prime candidates for the production of polymeric molecules that have the potential to be conjugated to biomaterials with precision. Non-native chemistries and functional groups are easily incorporated into the peptide backbone allowing peptide hydrogels to be tailored to specific functional requirements. This article reviews an area of increasing interest, namely self-assembled peptides and their potential therapeutic applications as innovative hydrogels and biomaterials in the prevention of biofilm-related infection.

Does wave exposure determine the interactive effects of losing key grazers and ecosystem engineers?

The consequences of biodiversity loss in the face of environmental change remain difficult to predict, given the complexity of interactions among species and the context-dependency of their functional roles within ecosystems. Predictions may be enhanced by studies testing how the interactive effects of species loss from different functional groups vary with important environmental drivers. On rocky shores, limpets and barnacles are recognised as key grazers and ecosystem engineers, respectively. Despite the large body of research examining the combined effects of limpet and barnacle removal, it is unclear how their relative importance varies according to wave exposure, which is a dominant force structuring intertidal communities. We tested the responses of algal communities to the removal of limpets and barnacles on three sheltered and three wave-exposed rocky shores on the north coast of Ireland. Limpet removal resulted in a relative increase in microalgal biomass on a single sheltered shore only, but led to the enhanced accumulation of ephemeral macroalgae on two sheltered shores and one exposed shore. On average, independently of wave exposure or shore, ephemeral macroalgae increased in response to limpet removal, but only when barnacles were removed. On two sheltered shores and one exposed shore, however, barnacles facilitated the establishment of fucoid macroalgae following limpet removal. Therefore, at the scale of this study, variability among individual shores was more important than wave exposure per se in determining the effect of limpet removal and its interaction with that of barnacles. Overall, these findings demonstrate that the interactive effects of losing key species from different functional groups may not vary predictably according to dominant environmental factors.

Silicon-Directed Rhenium-Catalyzed Allylic Substitutions with N‑Hydroxycarbamates, N‑Hydroxysulfonamides, and Hydroxamic Acids

A rhenium-catalyzed N-selective allylic amination reaction of N-hydroxycarbamates has been developed. This reaction occurs with excellent N/O selectivity and with complete carbon selectivity on the allylic system. The reaction is tolerant of many functional groups and also proceeds with N-hydroxysulfonamides and hydroxamic acids.

An alkyne hydrosilylation–Hiyama coupling approach to highly functionalised 1,3-dienes

A high yielding and robust protocol for the stereodefined synthesis of 1,3-dienes has been established through a hydrosilylation–Hiyama coupling strategy. In all cases the products were formed as single E,E isomers and conditions are tolerant of a wide range of functional groups not compatible with other methods.

Coastal upwelling drives intertidal assemblage structure and trophic ecology

ecosystems. Coastal oceanic upwelling, for example, has been associated with elevatedbiomass and abundance patterns of certain functional groups, e.g., corticated macroalgae.In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthiccomposition, structure and trophic ecology across eighteen shores varying in theirproximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scalesof >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmedby the stable isotope values (δ13C and δ15N) of consumers, including a dominantsuspension feeder, grazers, and their putative resources of POM, epilithic biofilm, andmacroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel,Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previousstudies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation,ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Ourresults showed macroalgal assemblage composition, and benthic consumer assemblagestructure, varied significantly with the intertidal influence of coastal upwelling, especiallycontrasting bays and coastal headlands. Coastal topography also separated differences inconsumer resource use. This suggested that coastal upwelling, itself driven by coastlinetopography, influences intertidal communities by advecting nearshore phytoplankton populationsoffshore and cooling coastal water temperatures. We recommend the isotopic valuesof benthic organisms, specifically long-lived suspension feeders, as in situ alternativesto offshore measurements of upwelling influence

The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.

Liquids with permanent porosity

Porous solids such as zeolites and metal-organic frameworks are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption-desorption cycles, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity. To achieve this, we designed cage molecules that provide a well-defined pore space and that are highly soluble in solvents whose molecules are too large to enter the pores. The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas. Our results provide the basis for development of a new class of functional porous materials for chemical processes, and we present a one-step, multigram scale-up route for highly soluble 'scrambled' porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.

Using Vibrational Infrared Biomolecular Spectroscopy to Detect Heat-Induced Changes of Molecular Structure in Relation to Nutrient Availability of Prairie Whole Oat Grains on a Molecular Basis

Background To our knowledge, there is little study on the interaction between nutrient availability and molecular structure changes induced by different processing methods in dairy cattle. The objective of this study was to investigate the effect of heat processing methods on interaction between nutrient availability and molecular structure in terms of functional groups that are related to protein and starch inherent structure of oat grains with two continued years and three replication of each year. Method The oat grains were kept as raw (control) or heated in an air-draft oven (dry roasting: DO) at 120 °C for 60 min and under microwave irradiation (MIO) for 6 min. The molecular structure features were revealed by vibrational infrared molecular spectroscopy. Results The results showed that rumen degradability of dry matter, protein and starch was significantly lower (P <0.05) for MIO compared to control and DO treatments. A higher protein α-helix to β-sheet and a lower amide I to starch area ratio were observed for MIO compared to DO and/or raw treatment. A negative correlation (−0.99, P < 0.01) was observed between α-helix or amide I to starch area ratio and dry matter. A positive correlation (0.99, P < 0.01) was found between protein β-sheet and crude protein. Conclusion The results reveal that oat grains are more sensitive to microwave irradiation than dry heating in terms of protein and starch molecular profile and nutrient availability in ruminants.

CoO nanoparticles embedded in three-dimensional nitrogen/sulfur co-doped carbon nanofiber networks as a bifunctional catalyst for oxygen reduction/evolution reactions

High-performance and low-cost bifunctional electrocatalysts play crucial roles in oxygen reduction and evolution reactions. Herein, a novel three-dimensional (3D) bifunctional electrocatalyst was prepared by embedding CoO nanoparticles into nitrogen and sulfur co-doped carbon nanofiber networks (denoted as CoO@N/S-CNF) through a facile approach. The carbon nanofiber networks were derived from a nanostructured biological material which provided abundant functional groups to nucleate and anchor nanoparticles while retaining its interconnected 3D porous structure. The composite possesses a high specific surface area and graphitization degree, which favors both mass transport and charge transfer for electrochemical reaction. The CoO@N/S-CNF not only exhibits highly efficient catalytic activity towards oxygen reduction reaction (ORR) in alkaline media with an onset potential of about 0.84 V, but also shows better stability and stronger resistance to methanol than Pt/C. Furthermore, it only needs an overpotential of 1.55 V to achieve a current density of 10 mA cm^-2, suggesting that it is an efficient electrocatalyst for oxygen evolution reaction (OER). The ΔE value (oxygen electrode activity parameter) of CoO@N/S-CNF is calculated to be 0.828 V, which demonstrates that the composite could be a promising bifunctional electrocatalyst for both ORR and OER.

Reactions of polycarbonate with cyclohexene oxide and phosphites: A density functional study

Epoxides and phosphites are often used as additives to stabilize the properties of polymers, including bisphenol A polycarbonate (BPA-PC). We describe density functional (DF) calculations of the reactions of cyclohexene oxide (CHO, cyclohexane epoxide) and phosphites with chain segments of BPA-PC, with the aim of identifying possible reaction paths and energy barriers. The reactions of CHO with the OH-terminated PC chains and with the carbonate group are exothermic, although there is an energy barrier in each case of more than 10 kcal/mol. A comparison of results for different CHO isomers demonstrates the importance of steric effects. The reactions between the same groups of the PC chain and the phosphites 2-[2,4-bis(tert-butyl)phenoxy]-5,5-dimethyl-1,3,2-dioxaphosphorinane] (BPDD) and trimethyl phosphite (TMP), and their phosphonate isomers are characterized by large energy barriers.

Density functional study of reactions of phenoxides with polycarbonate

Density functional calculations with simulated annealing have been used to study the reactions of chains of bisphenol A polycarbonate (BPA-PC) with sodium phenoxide (NaOPh), diphenyl carbonate (DPC), and tetraphenylphosphonium phenoxide (PPh4OPh). These calculations extend our work on the reactions of LiOPh, NaOPh, and phenol with the cyclic tetramer of BPA-PC. We study, in particular, chain growth catalyzed by NaOPh and PPh4OH. The energy barriers for reactions with PPh4OPh are somewhat larger than those involving LiOPh and NaOPh, but they are significantly lower than those involving phenol (HOPh), due in part to the collective rearrangement of phenyl groups in the reacting molecules. We discuss in the Appendix the bonds between alkali metal atoms (Na in the present calculations) and other atoms (here oxygen) that are analogous to the more familiar "hydrogen bonds".