Mechanism and Structural Insights Into a Novel Esterase, E53, Isolated From Erythrobacter longus

Esterases are a class of enzymes that split esters into an acid and an alcohol in a chemical reaction with water, having high potential in pharmaceutical, food and biofuel industrial applications. To advance the understanding of esterases, we have identified and characterized E53, an alkalophilic esterase from a marine bacterium Erythrobacter longus. The crystal structures of wild type E53 and three variants were solved successfully using the X-ray diffraction method. Phylogenetic analysis classified E53 as a member of the family IV esterase. The enzyme showed highest activity against p-nitrophenyl butyrate substrate at pH 8.5–9.5 and 40°C. Based on the structural feature, the catalytic pocket was defined as R1 (catalytic center), R2 (pocket entrance), and R3 (end area of pocket) regions. Nine variants were generated spanning R1–R3 and thorough functional studies were performed. Detailed structural analysis and the results obtained from the mutagenesis study revealed that mutations in the R1 region could regulate the catalytic reaction in both positive and negative directions; expanding the bottleneck in R2 region has improved the enzymatic activity; and R3 region was associated with the determination of the pH pattern of E53. N166A in R3 region showed reduced activity only under alkaline conditions, and structural analysis indicated the role of N166 in stabilizing the loop by forming a hydrogen bond with L193 and G233. In summary, the systematic studies on E53 performed in this work provide structural and functional insights into alkaliphilic esterases and further our knowledge of these enzymes.

Structural, Electronic and Magnetic Properties of GaMnN, MnN and Rare-Earth Nitride Thin Films

<p>Materials that combine the useful properties of magnetic and semiconducting behaviours are sought for new and developing applications in electronics. In this thesis experimental studies of the properties of disordered thin films of several potentially magnetic semiconducting materials are presented. Previous research on the diluted magnetic semiconductor GaMnN is reviewed as an introduction to a study of GaMnN thin films grown with an ion-assisted deposition technique. Several complementary compositional and structural analysis techniques are used to determine that films can be grown with as much as 18 at. % Mn content and that contain no impurity phases, as are often detected in single crystalline GaMnN preparations with high Mn concentrations. The effects of varying Mn contents on the resistive, optical and magnetic properties of the thin films are investigated. The structural, electronic and magnetic properties of thin films of the potential impurity phase MnN have also been investigated and compared with band structure calculations. Recent predictions that the rare earth nitrides may have extremely useful electronic properties have been almost untested in the literature. A procedure for growing rare earth nitride thin films and capping them to protect from reaction with water vapour allows their resistivity, structural and magnetic properties to be established. The results on GdN, SmN, ErN and DyN support the recent predictions, and a more thorough study on GdN reveals that this material is a ferromagnetic semiconductor below 69 K.</p>

Structural, Electronic and Magnetic Properties of GaMnN, MnN and Rare-Earth Nitride Thin Films

<p>Materials that combine the useful properties of magnetic and semiconducting behaviours are sought for new and developing applications in electronics. In this thesis experimental studies of the properties of disordered thin films of several potentially magnetic semiconducting materials are presented. Previous research on the diluted magnetic semiconductor GaMnN is reviewed as an introduction to a study of GaMnN thin films grown with an ion-assisted deposition technique. Several complementary compositional and structural analysis techniques are used to determine that films can be grown with as much as 18 at. % Mn content and that contain no impurity phases, as are often detected in single crystalline GaMnN preparations with high Mn concentrations. The effects of varying Mn contents on the resistive, optical and magnetic properties of the thin films are investigated. The structural, electronic and magnetic properties of thin films of the potential impurity phase MnN have also been investigated and compared with band structure calculations. Recent predictions that the rare earth nitrides may have extremely useful electronic properties have been almost untested in the literature. A procedure for growing rare earth nitride thin films and capping them to protect from reaction with water vapour allows their resistivity, structural and magnetic properties to be established. The results on GdN, SmN, ErN and DyN support the recent predictions, and a more thorough study on GdN reveals that this material is a ferromagnetic semiconductor below 69 K.</p>

Nanoscale Schottky diodes for studying the activity of aluminum nanoparticles in reaction with water

Hydrogen is a promising fuel for energy storage, transportation, production and consumption. At the same time, hydrogen in its pure form is not found on Earth in large quantities and therefore it is necessary to develop a technology for its production. One of the promising technologies for hydrogen production is the reaction of aluminum nanoparticles with water. At the same time, experimental studies of the elementary mechanisms of this reaction are difficult due to the aggressive properties of a concentrated alkaline solution, which is used to activate the aluminum surface. Here we show that the kinetics of the aluminum-water reaction can be monitored in real time using a Schottky nanodiode sensor, provided that the characteristic size of the nanodiode electrodes does not exceed 10 nm. The investigated nanoparticles are applied to the sensor surface by means of nanofabrication. The charge generated in the aluminum nanoparticles as a result of the reaction creates an electrical signal that is proportional to the rate of the chemical process. This makes it possible to use this technology to study the activity even of small groups of nanoparticles, when the volume of released hydrogen is insufficient to measure the reaction rate.

The Effect of Ozone Treatment on the Physicochemical Properties and Biocompatibility of Electrospun Poly(ε)caprolactone Scaffolds

Ozonation has been proved as a viable surface modification technique providing certain properties to the scaffolds that are essential in tissue engineering. However, the ozone (O3) treatment of PCL scaffolds in aqueous environments has not yet been presented. O3 treatment performed in aqueous environments is more effective compared with traditional, executed in ambient air treatment due to more abundant production of hydroxyl radicals (•OH) within the O3 reaction with water molecules. During interaction with •OH, the scaffold acquires functional groups which improve wettability properties and encapsulate growth factors. In this study, a poly(ε)caprolactone (PCL) scaffold was fabricated using solution electrospinning and was subsequently ozonated in a water reactor. The O3 treatment resulted in the expected occurrence of oxygen-containing functional groups, which improved scaffold wettability by almost 27% and enhanced cell proliferation for up to 14 days. The PCL scaffold was able to withhold 120 min of O3 treatment, maintaining fibrous morphology and mechanical properties.

Catalytic Hydrogen Combustion for Domestic and Safety Applications: A Critical Review of Catalyst Materials and Technologies

Spatial heating and cooking account for a significant fraction of global domestic energy consumption. It is therefore likely that hydrogen combustion will form part of a hydrogen-based energy economy. Catalytic hydrogen combustion (CHC) is considered a promising technology for this purpose. CHC is an exothermic reaction, with water as the only by-product. Compared to direct flame-based hydrogen combustion, CHC is relatively safe as it foregoes COx, CH4, and under certain conditions NOx formation. More so, the risk of blow-off (flame extinguished due to the high fuel flow speed required for H2 combustion) is adverted. CHC is, however, perplexed by the occurrence of hotspots, which are defined as areas where the localized surface temperature is higher than the average surface temperature over the catalyst surface. Hotspots may result in hydrogen’s autoignition and accelerated catalyst degradation. In this review, catalyst materials along with the hydrogen technologies investigated for CHC applications were discussed. We showed that although significant research has been dedicated to CHC, relatively limited commercial applications have been identified up to date. We further showed the effect of catalyst support selection on the performance and durability of CHC catalysts, as well as a holistic summary of existing catalysts used for various CHC applications and catalytic burners. Lastly, the relevance of CHC applications for safety purposes was demonstrated.

Production of ceramic construction materials as an environmental management solution for sulfidic mine tailings

Mine tailings (MT) waste valorization in construction materials can be one possible solution because they may allow an alternative for some applications as an important contribution for a more circular economy. The aim of this work was to study the feasibility of using a sulfidic mine tailing in the production of building materials such as ceramic roof tiles. The introduction of 5, 10 and 20% MT in ceramic roof tiles promoted an improvement on the final properties of these materials. The use of 20%MT has decreased the firing temperature from 1150º to 1050 ºC, hence promoting energy savings and lower costs. Properties as density and water absorption were improved. Firing shrinkage, many times responsible for cracking, also decrease with the use of MT and, in this way, improve the production rate. The 20% MT ceramic formulation achieved the highest value of strength with lowest firing temperature. For the effects of sulphates' emission (SO2 and SO3 gases) upon firing, a solution was proposed involving their reaction with water and, through condensation, providing afterwards sulphuric acid as a process by-product. The use of high sulphide MT in ceramic roof tiles processing could be viewed as a potential safe waste management solution for these particular mine tailings.

Engineering Dirhodium Artificial Metalloenzymes for Diazo Coupling Cascade Reactions

<p>Artificial metalloenzymes (ArMs) are now commonly used to control the stereoselectivity of catalytic reactions, but controlling ArM chemoselectivity remains challenging. In this study, we engineer a dirhodium ArM to catalyze diazo cross-coupling to form an alkene that, in a one-pot cascade reaction, is reduced to an alkane with high enantioselectivity (typically >99% e.e.) by an alkene reductase. The numerous protein and small molecule components required for the cascade reaction had minimal effect on ArM catalysis, while the dirhodium cofactor itself provided only O-H insertion products from reaction with water and glucose under the same conditions. Directed evolution of the ArM led to improved yields and E/Z selectivities for a variety of substrates, which translated well to cascade reaction yields. MD simulations of ArM variants were used to understand the structural role of the cofactor on large-scale scaffold structural dynamics. These results highlight the ability of ArMs to control both catalyst stereoselectivity and chemoselectivity to enable reactions in complex media that would otherwise lead to undesired side reactions.</p>

Engineering Dirhodium Artificial Metalloenzymes for Diazo Coupling Cascade Reactions

<p>Artificial metalloenzymes (ArMs) are now commonly used to control the stereoselectivity of catalytic reactions, but controlling ArM chemoselectivity remains challenging. In this study, we engineer a dirhodium ArM to catalyze diazo cross-coupling to form an alkene that, in a one-pot cascade reaction, is reduced to an alkane with high enantioselectivity (typically >99% e.e.) by an alkene reductase. The numerous protein and small molecule components required for the cascade reaction had minimal effect on ArM catalysis, while the dirhodium cofactor itself provided only O-H insertion products from reaction with water and glucose under the same conditions. Directed evolution of the ArM led to improved yields and E/Z selectivities for a variety of substrates, which translated well to cascade reaction yields. MD simulations of ArM variants were used to understand the structural role of the cofactor on large-scale scaffold structural dynamics. These results highlight the ability of ArMs to control both catalyst stereoselectivity and chemoselectivity to enable reactions in complex media that would otherwise lead to undesired side reactions.</p>