Existence Of Cooperative Effects Research Articles

Methanol Steam Reforming over ZnO/ZnZrOx: Performance Enhanced with a Cooperative Effect

AbstractThe steam reforming of methanol (SRM) provides an efficient approach for the H2 production, but current SRM catalysts suffer from low activity, selectivity and stability. Herein, we report that ZnO nanoparticles (NPs) supported on ZnZrOx solid solution have excellent catalytic properties for SRM. The systematic studies suggest that ZnO/ZnZrOx catalysts with smaller ZnO domain (1–2 nm) are more selective and active than those with larger ZnO NPs. The existence of cooperative effect between the ZnO NPs (for methanol activation) and ZnZrOx solid solution (for water activation) was verified by the control experiment with ZnO/Al2O3 and ZnZrOx as catalysts. In situ DRIFTS of SRM and TPSR/MS studies suggest that the reaction undergoes through formates pathway over ZnO/ZnZrOx, where ZnO NPs and ZnZrOx work in a cooperative mode to favor the SRM reaction and suppress the side reactions. The optimized ZnO/ZnZrOx catalyst affords 99.7 % methanol conversion with CO selectivity as low as 2.4 % for single‐pass in a fixed bed reactor.

Effects of touristic development on Mediterranean island wildlife

Islands harbor unique and sensitive wildlife. Little is currently known, however, on how touristic development affects island species. We analyzed how tourism-associated infrastructure impacts wildlife and habitat availability across a representative Mediterranean island landscape (Naxos, Aegean Sea, Greece). First, we aimed to quantify how human-built structures (buildings and roads) affect island bird and reptile populations. Additionally, we investigated whether specific factors associated with this development such as cats, water, and food shape these impacts. Second, we mapped and quantified how touristic-dominated development over 33 years has changed landscape habitat availability for wildlife. We used wildlife field surveys and analyses to elucidate the spatial responses of wildlife to development, and combined this with a compilation of image-derived spatial data of the recent infrastructure expansion. Native birds declined strongly close to buildings and roads, and were replaced there by non-native invasive species. Reptiles also largely disappeared close to human development; appearing to be influenced by predation by pet cats. Over the study period, 1982–2015, human-built structures nearly doubled. Combining the increase in infrastructure numbers with each structure’s estimated ecological footprint, 100 m, revealed that only 20.5% of the potential wildlife habitat remains unaffected by development in the study region. This study demonstrates the landscape-level effects of diffuse tourism-dominated development on island wildlife and suggests the existence of cooperative effects between touristic expansion and exotic species. Given the pervasive presence of tourism in island habitats, it raises concerns about its effects on resident biodiversity.

Cooperative efects on the formation of 4-methyloxycarbonyl-2-azetidinone clusters

In this paper we study the manifestations of cooperative effects in the formation of clusters4-methyloxycarbonyl-2-azetidinone. Structural properties of the clusters were obtained at the DFT/B3LYP/6-311Gd level of calculation, while the energetic ones were calculated at the B3LYP/6-311Gd, B3LYP/6-31++Gd,p and HCTH407/6-31++Gd,p DFT levels. The calculated structural parameters were compared with those corresponding to crystal structures reported for similar compounds in the Cambridge Structural Database. It is obtained that the theoretically optimized clusters form hydrogen bond patterns resembling those patterns reported for the crystal structure of azetidinone derivatives. We find that, due to the formation of consecutives hydrogen bonds of the type N-H…O between the 2-azetodinone rings, the addition of monomers gradually increases the stabilization energy per monomer of the system. It is also observed that after the hexamer formation, the value of this stabilization energy tends to reach an asymptotic limit, behavior typical of the existence of cooperative effects. Additionally, manifestations of these effects were observed in the variations with the size of the clusters of the calculated charges and of the structural parameters.

Non-crystalline surface-modified hollow nanospheres of silica (HNS): Synthesis, characterization and catalytic application

Non-crystalline surface-modified hollow nanospheres of silica (HNS) with different amine groups were synthesized by the co-condensation under neutral conditions. The obtained materials were characterized by N2 adsorption–desorption isotherms, Fourier-transform infrared spectroscopy (FTIR), transmission electron micrographs (TEM), scanning electron micrographs (SEM), back titration, elemental analysis and thermogravimetric analysis (TGA). The effect of organoamine type, amine density, and the presence of silanol groups on the catalytic activity was investigated. The capping of silanols with trimethylsilyl groups resulted in a reduction in catalytic activity, indicating the existence of cooperative effect between amine and silanol in the condensation reaction.

The peptidyltransferase center of Escherichia coli ribosomes : Binding sites for the cytidine 3′-phosphate residues of the aminoacyl-tRNA 3′-terminus and the interrelationships between the acceptor and donor sites

The substrate specificity of the acceptor site of peptidyltransferase of Escherichia coli 70 S ribosomes was investigated in Ac-Phe-tRNA·poly(U)·70 S ribosome (system A) and tRNA Phe·poly(U)·C-A-C-C-A-Phe·70 S ribosome (system B) systems by using C-C-A-Gly, C-C-A-Phe, C-A-Gly and C-A-Phe as analogs of the 3′-terminus of aminoacyl-tRNA. It was found that an addition of C p residue to C-A-Gly and C-A-Phe resulted in an increase of the acceptor activity in system A; the increase is more remarkable for C-A-Gly than for C-A-Phe, while the acceptor activities of C-C-A-Gly and C-C-A-Phe are roughly similar. On the other hand, dramatically increased binding affinities of C-C-A-Phe and C-C-A-Gly relative to C-A-Phe and C-A-Gly for the A site of peptidyltransferase were observed in system B using an inhibition assay; C-C-A-Phe binds much more strongly than C-C-A-Gly. The results indicate the important role of the third C p residue and the aminoacyl moiety of the 3′-terminus of aminoacyl-tRNA in the interaction with the acceptor site of peptidyltransferase, as well as the existence of cooperative effects between A and P sites of peptidyltransferase. These effects, depending on an occupancy of P site, may significantly influence the specificity of the peptidyltransferase A site.

An investigation of phonon scattering by chromous ions in MgO by thermal conductivity measurements

The effects of X -irradiation, thermoluminescence and heat treatment on the thermal conductivity principally between 1 and 4 °K of nominally pure and Cr-doped MgO have been examined. It is concluded that the Cr2+ion produced by X -irradiation is responsible for the very strong excess phonon scattering. An analysis of the data shows that the scattering has both resonant and non-resonant components and that if the non-resonant component is proportional to concentration, the resonant component is proportional to the square root of the concentration indicating the existence of cooperative effects. The resonant scattering occurs atca. 4 cm-1in reasonable agreement with the calculated energy separation 5.6 cm-1of theEandA2levels of Cr2+(Fletcher & Stevens 1968). The work also indicates that the thermal conductivity at 4.2 °K provides a useful method of determining the Cr2+concentration in MgO.

Threonine Deaminase of Clostridium tetanomorphum: I. PURIFICATION AND PROPERTIES

Abstract Threonine deaminase (l- threonine hydrolyase (deaminating), EC 4.2.1.16) has been purified approximately 700-fold from extracts of Clostridium tetanomorphum. Both threonine and serine can serve as substrates, but threonine is deaminated 5 to 10 times more rapidly than serine. Pyridoxal phosphate, a reducing agent, and alkaline pH are required for the deamination of either amino acid. A plot of the rate of reaction at increasing substrate concentration gives a sigmoidal curve. Addition of adenosine diphosphate stimulates the reaction markedly at low substrate concentrations and yields a curve approaching a rectangular hyperbola. Kinetic analysis using the empirical Hill equation indicates the existence of cooperative effects between substrate sites in the absence of ADP and little interaction, if any, in the presence of ADP. ADP may be replaced by guanosine and inosine diphosphates and less effectively by uridine and cytosine diphosphates; dATP and thymidine diphosphates have little stimulatory activity. Experiments with 14C-ADP show that the enzyme binds ADP. The enzyme is inhibited by pyridoxal phosphate binding agents, by sulfhydryl reagents, urea, detergents, and substrate analogues. ADP protects the enzyme against low concentrations of sulfhydryl inhibitors and hydrogen bond-breaking agents but not against other inhibitors. ADP (and the other nucleotides mentioned above), phosphate buffer at pH 7.0, divalent cations, and, to a lesser extent, monovalent cations, protect the enzyme against inactivation by heat and against loss of activity on dilution. Dialysis of enzyme preparation at an alkaline pH decreases the ability of the enzyme to bind 14C-ADP and reduces the catalytic response to ADP. Conversely, addition of agents that combine with pyridoxal phosphate inhibits catalysis but does not inhibit the binding of 14C-ADP. These differential effects suggest that the substrate and allosteric effector are bound to separate sites on the enzyme.