ANALYSIS OF CONCENTRATION FORCING IN HETEROGENEOUS CATALYSIS

The steady-state kinetics of parallel reaction networks

We infused 11 mmol/kg of intravenous ethanol into dogs with either intact renal function (n = 5) or ureteral ligation (n = 7), and studied by frequent blood sampling and by urine collection the time and mode of ethanol equilibration, the elimination parameters, and the comparison of observed equilibrated plasma ethanol levels to levels predicted either by linear or by nonlinear kinetics. Equilibration time was 25 min or less, renal fraction of elimination was less than 5% of total elimination, and both linear (elimination rate) and nonlinear (Vmax and Km) elimination parameters were not different between dogs with intact renal function and dogs with anuria. Serum sodium concentration did not change throughout the experiments, eliminating the hypothesis that acute ethanol load creates clinically significant temporary osmotic water transfer from the intracellular into the extracellular compartment. Distribution volumes of ethanol from linear kinetics were slightly, but not statistically, greater than volumes from nonlinear kinetics. Equilibrated plasma ethanol levels predicted by linear kinetics agreed closely with observed levels greater than 4 mmol/liter, but underestimated observed levels less than 4 mmol/liter. Equilibrated plasma ethanol levels predicted by nonlinear kinetics agreed with observed levels throughout the range of observed concentrations. The use of linear kinetics to predict blood ethanol levels should be limited to the pseudolinear portion of the blood alcohol curve.

The linearity of the (AMT) kinetics of amitriptyline has been tested in 135 depressed dosed twice daily by measuring plasma. Their (AMT) and nortriptyline (NT) levels under steady-state conditions. The AMT concentration/dose ratios at low and high dosages were not significantly different and there was a linear relationship between the dose ratios and the concentration ratios. No change in the metabolic ratio (AMT/NT) was observed between the two dosages. Although the results are consistent with linear AMT kinetics, there may have been nonlinear kinetics in some patients as the ratio between the concentration/dose ratios in them at low and high dosages was greater than one. Those patients were characterized by a low concentration/dose ratio at low dosage. No clinical adverse effect appeared in the study.

Rapid adsorption of arsenate from water on a novel hybrid of zirconia oxide anchored rGO functionalised carbon foam

In this paper, an efficient numerical procedure for calculating the solution of the non–linear neutron point kinetics equations in the field of nuclear reactor dynamics is presented. The explicit finite difference method is applied to solve the non–linear neutron point kinetics equations with temperature feedback reactivity. The numerical solution obtained by explicit finite difference scheme is an approximate solution based on neutron density, the precursor's concentration of multi–group delayed neutrons, and the reactivity function. The method is investigated over data of nuclear reactor–type compositions, with appropriate initial conditions applying in three types of reactivity: step, ramp and temperature feedback. The computational results show that this numerical approximation method is straightforward and effective for solving the non–linear point kinetics equations. Numerical results addressing the time behaviour of neutron density and results of this method with different types of reactivity are presented graphically. The comparisons of results with other referred methods are also discussed.

Novelties of low energy microwave irradiation in tri-phase vis-à-vis bi-liquid phase-transfer catalysis in selective etherification of aromatic phenols

Forced thermal cycling of catalytic reactions: Experiments and modelling

Social-like bacteria, fungi, and protozoa communicate chemical and behavioral signals to coordinate their specializations into an ordered group of individuals capable of fitter ecological performance. Examples of microbial “social” behaviors include sporulation and dispersion, kin recognition, and nonclonal or paired reproduction. Paired reproduction by ciliates is believed to involve intra- and intermate selection through pheromone-stimulated “courting” rituals. Such social maneuvering minimizes survival-reproduction tradeoffs while sorting superior mates from inferior ones, lowering the vertical spread of deleterious genes in geographically constricted populations and possibly promoting advantageous genetic innovations. In a previous article, I reported findings that the heterotrich Spirostomum ambiguum can out-complete mating rivals in simulated social trials by learning behavioral heuristics which it then employs to store and select sets of altruistic and deceptive signaling strategies. Frequencies of strategy use typically follow Maxwell-Boltzmann (MB), Fermi-Dirac (FD), or Bose-Einstein (BE) statistical distributions. For ciliates most adept at social decision making, a brief classical MB computational phase drives signaling behavior into a later quantum BE computational phase that condenses or favors the selection of a single fittest strategy. Appearance of the network analogue of BE condensation coincides with Hebbian-like trial-and-error learning and is consistent with the idea that cells behave as heat engines, where loss of energy associated with specific cellular machinery critical for mating decisions effectively reduces the temperature of intracellular enzymes cohering into weak Fröhlich superposition. I extend these findings by showing the rates at which ciliates switch serial behavioral strategies agree with principles of chemical reactions exhibiting linear and nonlinear Arrhenius kinetics during respective classical and quantum computational phases. Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from quantum tunneling in social information processing.

This work contributes to the generalization of the Non-faradaic Electrochemical Modification of Catalytic Activity effect, known under the acronym NEMCA. This effect is observed for the first time over an oxide catalyst, namely IrO2 supported on yttria-stabilized-zirconia. The activity of the IrO2 catalyst for the complete ethylene oxidation is remarkably and reversibly increased by polarizing the catalyst-solid electrolyte interface. The reaction rate in excess oxygen is enhanced by at least an order of magnitude, when the catalyst is polarized positively with respect to a reference electrode. The rate enhancement may be up to 1·104 times higher than the rate of O2- supply to the catalyst. The application of low negative potentials generally causes the rate to decrease. However, under a limited range of experimental conditions, namely temperatures above 370 °C and high overpotentials, the cathodic polarization induces a rate enhancement. The ethylene oxidation kinetics over an IrO2 catalyst exhibits a Langmuir-Hinshelwood behaviour with competitive adsorption of reactants. The rate dependence on the oxygen partial pressure indicates that the reaction may proceed via an intermediate. The electrochemical promotion of the catalyst is most effective in oxygen-rich gas phase compositions, where the rate is essentially limited by the ethylene adsorption. In-situ cyclic voltammetry is used to maintain the reaction rate at a higher value than under open-circuit conditions. This simple method of investigation has just entered in the world of catalysis and provides valuable information on the state of the catalyst surface. The redox processes involving very small amounts of electroactive species can only be studied in low oxygen pressures. The main finding of this work is the experimental evidence that the electrochemical promotion of the ethylene oxidation rate is linearly related to the electrical charge stored at the electrode-electrolyte interface, measured by cyclic voltammetry. The voltammetric analysis of the IrO2 catalyst in air shows that, upon positive polarization, the catalyst surface is oxidized to a higher oxide IrO2+δ which is responsible for the rate enhancement observed.

Photodegradation of organic and inorganic pollutants by L-tyrosine@AC/Fe3O4 nanocomposites under visible light: Evaluation of linear and nonlinear kinetics, isotherm models, scavengers effect, and antibacterial activity

DNA as an enzyme: The effect of imidazole derivatives as cofactors and metal ions as activators or inhibitors

Nucleophilic Catalysis of Oxime Ligation

The nucleophilic aromatic substitution (SNAr) between GSH and 2,4-dinitrochlorobenzene was studied in reverse micellar systems composed of limited amounts of water, a surfactant with a polar head and a nonpolar tail, and the organic solvent 2,2,4-trimethylpentane. When the surfactant was positively charged and contained an aromatic ring in the polar head, the second-order rate constant was increased by approximately two orders of magnitude as compared to that in aqueous solution. The rate enhancement could be attributed to the stabilization of the negatively charged Meisenheimer σ-complex by the positively charged polar head and the weak aromatic ring’s electric quadrupole interactions of the surfactant. The reaction rate in reverse micelles composed of neutral polar head groups (Triton X-100) was increased by 3-fold, which may be explained by the interactions of the hydroxy groups of Triton molecules with the π-system of the Meisenheimer complex. An inverse relationship between the molar concentration [H2O]/[surfactant] ratio, which reflects the inclusive volume of the reverse micellar particle, and the rate enhancement was observed for positively charged or hydroxy-containing reverse micelles, but opposite results were obtained with negatively charged reverse micelles. These reverse micellar systems thus mimic the active site of a detoxification enzyme, glutathione transferase, in which stabilization of the Meisenheimer complex by a positively charged arginine residue, on-edge quadrupole interactions of aromatic amino acids, and the hydroxy group of tyrosine or threonine have been proposed in the enzyme-catalysed SNAr conjugation.

Under appropriate conditions, significant microwave-specific enhancement of the reaction rate of an organic chemical reaction can be observed. Specifically, the unimolecular Claisen rearrangement of allyl p-nitrophenyl ether (ApNE) dissolved in naphthalene was studied under microwave heating and conventional convective (thermal) heating. Under constant microwave power, reaching a temperature of 185 °C, a 4-fold rate enhancement was observed in the microwave over that using convective heating; this means that the microwave reaction was proceeding at an effective temperature of 202 °C. Conversely, under constant temperature microwave conditions (200 °C), a negligible (∼1.5-fold) microwave-specific rate enhancement was observed. The largest microwave-specific rate enhancement was observed when a series of 300 W pulses, programmed for 145-175 °C and 85-155 °C cycles, where 2- and 9-fold rate enhancements, over what would be predicted by conventional thermal heating, was observed, respectively. The postulated origins of the microwave-specific effect are purely thermal and arise from selective heating of ApNE, a microwave-absorbing reactant in a nonabsorbing solvent. Under these conditions, excess heat is accumulated in the domains around the ApNE solute so that it experiences a higher effective temperature than the measured temperature of the bulk medium, resulting in an accelerated unimolecular rearrangement.

Plasmonic metal nanoparticles (e.g., Ag, Au, and Cu) constitute a class of materials that interact with light via the excitation of localized surface plasmon resonance (LSPR). Numerous studies have reported substantial enhancements in the rates of chemical reactions on illuminated plasmonic nanoparticle catalysts compared to corresponding systems in the absence of illumination. There are two mechanisms that have been proposed to explain the LSPR-induced chemical reactivity. One mechanism assumes a local plasmon-induced hot charge-carrier-mediated activation of the reactants, while the other assumes an LSPR-induced equilibrium heating of the catalyst, which leads to energy transfer to and chemical reaction of the adsorbed reactants. In this contribution, we developed a setup amenable to accurate in situ catalyst temperature and kinetic reaction rate measurements. We employed this setup to study the LSPR-induced rate enhancement in a case study of the CO oxidation reaction on plasmonic, monometallic Ag nanoparticle catalysts supported on α-Al2O3. We explored various Ag loadings and clustering levels. Our data show that the equilibrium heating of the catalyst cannot fully explain the illumination-induced plasmonic rate enhancements. This is the case even for high loading and clustering of Ag nanoparticles, where the equilibrium heating significantly increases. Based on the analysis, we propose that local effects, related to the plasmon-induced activation of adsorbates (reactants) via electronic excitation of the reactant or photothermal heating of the reactants that is highly localized to the individual nanoparticles, play a critical role in driving LSPR-induced chemical reactions.