Global Kinetic Constants Research Articles

Kinetic and Thermodynamic Behavior of Extraction of Oleoresin Containing Curcuminoids from Turmeric (Curcuma longa L.) in Acetone and Their Bioavailability

Background: Why this miraculous and amphiphilic compound, the curcumin, which has a very extraordinary therapeutic potential (because can react with many targets in the organism), has a weak bioavailability in the organism and is metabolized in compounds having very weak activity or inactive compounds?. How to improve substantially its bioavailability and therefore its absorption in the organism in order to allow its incorporation in making of pharmaceuticals regardless of its nanoparticles of which obtention is furthermore hardworking?
 Aim: It seems indicated to search the response in the kinetic and thermodynamic behavior of this compound or in its co-administration with the other compounds in vitro in order to understand how to increase its absorption in vivo because bioavailability entails hydrosolubility (hydrophile) of curcuminoids of which the molecules are naturally hydrophobes.
 Objective: So our objective is to make better our understanding of the absorption of natural curcuminoids in the organism without resorting to chemical transformation in nanoparticles that is additionally hardworking.
 Methodology: In this paper, kinetic and thermodynamic study of extraction of oleoresin containing curcuminoids from Turmeric (Curcuma Longa L.), using KUNYIMA’s first law, has been performed in acetone that can be reduced in propan-2-ol which is water-like solvent by catalytic hydrogenating (H2,Ni ) or by chemical reduction (LiAlH4).
 Results: The weak global kinetic constant of extraction of oleoresin containing curcuminoids has been determined at 250 rpm (round per minute) and found the same at 500 rpm (k= 0.1520 ± 0.0005) min-1 for temperature of 27,5°C and constant pressure in acetone in closed system.
 Conclusion: Kunyima’s first law has made possible the kinetic and thermodynamic study of extraction of oleoresin containing curcuminoids from Turmeric. Kinetic constant is a measure of solubility of oleoresin containing curcuminoids and therefore a measure of solubility of curcuminoids in a given solvent, ethanol and acetone being concerned in this paper as solvents. Results show that kinetic constant is inversely proportional to solubility of solvent and it can be a parameter abling the determination of the endothermic or exothermic behavior of extraction of curcuminoids. The endothermic behavior of curcuminoids hereby determined in ethanol and acetone in vitro, increased by magnetic stirring, suggests their weak bioavailability and therefore the weak bioavailability of curcumin. The challenge of this actual research is to improve our understanding of kinetics and thermodynamics of extraction of oleoresin containing curcuminoids from Turmeric in vitro in order to presage their bioavailability still weak for an efficient validated action. The increase of bioavailability will be done whether through improved formulations of curcumin or through new pathways of administration. The conception of curcumin analogous is also a way to promote its effects. More the phenomenon is exothermic in water-like solvents, more the involved chemical compound is bioavailable.
 The study revealed the predominance of keto form of curcumin in acetone and the lack of bioavailability of curcumin (curcuminoids) through the endothermic behavior of extraction of oleoresin containing curcuminoids and through the weak global kinetic constant.
 The variation of entropy in acetone has shown without surprise the disturbance of the system after extraction.
 The values of kinetic constants in acetone and ethanol as water-like solvents have been compared and showed the great solubility of curcuminoids in acetone evidenced by the weak kinetic constant compared to that in ethanol.
 Curcumin predicts anyway hopeful future.

Kinetic and Thermodynamic Study of Extraction of Oleoresin Containing Curcuminoids from Turmeric (Curcuma Longa L.)

Numerous studies are nowadays undertaken across the world laboratories on turmeric and show its excellent virtues in various fields such as medicine, pharmacology, cosmetics, and so forth. In this paper, to enlarge the domain of scientific knowledge, a kinetic and thermodynamic behavior of curcuminoid extraction from Curcuma longa L has been investigated in the dilute medium using ethanol as solvent under a magnetic stirrer. Through the KUNYIMA method, by means of the KUNYIMA first law, the global kinetic constant has been calculated at 250 rounds per minute (rpm) and the data have shown its Constance at 500 rounds per minute at the same temperature (27.5 °C). The kinetic constant can serve to build a commercial tank of production of curcuminoids using the sizing factor to endow the Democratic Republic of the Congo with its home technology of curcuminoids extraction as is hereby discussed. Extraction enthalpy and entropy have been calculated in a closed system using the Arrhenius relation. The results of enthalpy indicate that the extraction of curcuminoids is an endothermic phenomenon. This endothermic behavior of the extraction of curcuminoids in ethanol under a magnetic stirrer probably suggests the predominance of the enol form of curcumin in presence of its tautomeric ketone form. Also, the extraction of curcuminoids in ethanol is an endothermic phenomenon and this last phenomenon probably suggests its non-bioavailability. The energy promoting solubilization of curcuminoids arises from the solvent, under a magnetic stirrer, that can meet its alike with the hydroxyl group (like dissolves like). The value of the variation of entropy has evidently suggested the disturbance of the natural order after extraction. Note that KUNYIMA's second law has been hereby announced.

The enzymatic action of Vipoxin on insoluble long-chain phospholipid Langmuir monolayers

In recent years some toxins such as Vipoxin that is isolated from the venom of Vipera ammodytes meridionalis have provoked scientific interest due to their intriguing structure, enzymatic activities, and potential for medical applications. This paper considers the kinetics of the enzymatic action of Vipoxin on long-chain phospholipids’ monolayers of Palmitoyl-oleoyl-phosphatidyl-choline (POPC), Palmitoyl-oleoyl-phosphatidyl-glycerol (POPG), and Palmitoyl-oleoyl-phosphatidyl-ethanolamine (POPE) spread at air-water interfaces. To analyze theoretically the enzyme activity that is altered by the presence of insoluble lipolytic products we adapted the classical Michaelis-Menten kinetic model and an experimental approach that utilizes the β- cyclodextrin ( β-CD ) as a solubilizing agent. This allowed us to obtain the global kinetic constants of the enzymatic reaction catalyzed by the Vipoxin. Using AFM, we also analyzed the influence of the monolayer structure on the kinetics of the enzyme reaction by measuring the observed structures and microheterogeneities of the LB films transferred from monolayers that either contained β-CD or without β-CD . • Kinetics of the enzymatic action of Vipoxin on long-chain phospholipid monolayers is studied. • An adapted Michaelis-Menten kinetic model for fitting the data is applied. • The global kinetic constants of Vipoxin action are obtained. • The interfacial behavior of studied systems is visualized by AFM.

Democratic Republic of Congo Moringa Seeds Oil Extraction: Kunyima Method Application

Background: The poisoning, one of the nowadays most serious problem of public health in Democratic Republic of Congo since two decades, has made many victims because of the lack of information and because of the population impoverishment unable to accede to health care. The Democratic Republic of Congo has a very rich and diversified vegetable patrimony with known therapeutic properties needing only appropriate technology to deal with the extraction process of oils or active principles.
 Aim and Objective: The overall purpose pursued is to endue the country with appropriate (home) technology to solve somewhat the public health problem in DRC. The kinetic study of oil transfer from liquid- solid extraction has been undertaken in view of the phenomenon uptake in order to make possible home technology of reactors sizing, nowadays absent in underdeveloped countries. This is a technical work related to the extraction, modeling and quantification of moringa seeds oil.
 Methodology: KUNYIMA method has been successfully extended to the moringa seeds oil extraction in petroleum ether using Soxhlet device to assess its validity. The figures have been plotted by means of Origin 8 program.
 Results: When log⁡〖1/(m_(o_e )-m_e )〗 is plotted as a function of time, linear behavior has been obtained at constant temperature (56°C) in dilute medium. The global kinetic constant of this time dependent phenomenon has been calculated [(k=1.2607±0.0591) h^(-1)] to make possible the reactor building for the oil production. The comparison of some parameters of extraction ( me , k ,....)between gourd seeds oil and moringa seeds oil measured and calculated in the same experimental conditions shows in petroleum ether a greater kinetic activity of solvent for gourd seeds oil than for moringa seeds oil followed by significant extraction of gourd seeds oil as fast as the time advanced (kGSO > kMSO).
 This observation suggests the existing difference of structures between the two species as it is hereby discussed. Moreover it has been pointed out previously that if the difference in absolute value is not of the same errors magnitude order it would interpret the solvent effect. It should be noted however it has been observed the ratio [m_s/m_e >1] where the kinetic constant is high (gourd seeds oil) and m_s/m_e <1 where the kinetic constant is low (moringa seeds oil) and this ratio might likewise better give information on solvent effect. Prediction is done of getting possibility of sigmoid curve in the case of the presence of different solvation equilibria. Also the sigmoid obtaining depends likely on both the structure of extractant solvent and the structure of extracted material. In that case the kinetic constant will be calculated in the upright region of sigmoid curve.
 Conclusion: Kunyima method has been successfully used in the case of moringa seeds oil extraction. Kunyima method consists in best uptake of the phenomenon, in expressing it in suitable mathematical model in order to determine its velocity through its kinetic constant before sizing the experimentation reactor. The reactor volume depends on both the sizing factor and the desired volumic debit.

Action of Vipoxin and its separated components on monomolecular film of Dilauroylphosphatidylcholine at the air/water interface

The growing research interest about neurotoxin Vipoxin is inspired by its intriguing heterodimeric structure and the resulting interactions between Vipoxin’s basic catalytic subunit and the acidic regulatory subunit.In this paper we studied the enzymatic action of Vipoxin and its individual components on Dilauroylphosphatidylcholine (DLPC) monolayers at air-water interfaces. We applied the classical surface barostatic method and interpreted our experimental data with an adapted Michaelis-Menten kinetic model. This approach allowed us to obtain the global kinetic constants together with the interfacial specific activity of Vipoxin and its subunits. Using reconstituted Vipoxin complexes formed by incubating the enzymatic VBC-sPLA2 and non-catalytic VAC subunits in different ratios, we showed that the activity of the reconstituted mixture VAC:VBC-sPLA2 (1:1), which should correspond to the composition of Vipoxin, is higher than that of the natural Vipoxin complex. Finally, Vipoxin heterodimers in the DLPC monolayer were imaged by Atomic force microscope (AFM) and statistically analyzed.

Oxidation Stability of Diesel/Biodiesel Fuels Measured by a PetroOxy Device and Characterization of Oxidation Products

In the present work, the oxidation stability of diesel, rapeseed (RME), and soybean (SME) fatty acid methyl esters (FAME) and a blend of diesel with 10% (v/v) RME (B10–RME) was studied. Fuel samples were aged in the PetroOxy test device from 383 to 423 K at 7 bar. Experiments were conducted in oxygen excess, and the global kinetic constants were determined. The global kinetic constants for diesel, B10–RME, and RME at 383 K were 7.92 × 10–6, 2.78 × 10–5, and 8.87 × 10–5 s–1, respectively. The oxidation products formed at different stages of the oxidation were monitored by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis–differential thermal analysis (TGA–DTA), and gas chromatography/mass spectrometry (GC/MS). The impact of the FAME nature and level of blending on the kinetic rate constant and the oxidation products was investigated. Results show that RME oxidation forms C19 epoxy as the main oxidation product, in addition to a methyl ester FAME derivative and short-chain oxidation...

Design of a novel CPC collector for the photodegradation of carbaryl pesticides as a function of the solar concentration ratio

Photodegradation studies of carbaryl pesticides were performed as a function of solar concentration using newly designed CPC collectors with different geometric solar concentration ratios. Design of a Multiple Compound Parabolic Concentrator, or MCPC, was performed by taking into account both that photocatalytic degradation efficiency is a function of the square root of photon flow intensity that excites the photocatalyst and that TiO2 is able to absorb more sunlight (photons) than the provided in utilising a 1-sun geometric concentration ratio (CR). The Multiple Compound Parabolic Concentrator was initially designed to carry out photocatalytic degradation studies as a function of geometric solar concentration ratio between 1 sun and 2 suns and subsequently to explore the possibility of using CPC collectors in photocatalysis studies with a solar concentration ratio greater than 1 sun. TiO2 photocatalysts, immobilised over 1.40-meter-long Duran glass tubes, were specially fabricated for this experiment. Finally, to evaluate the photoreactor performance, the photocatalytic degradation of the carbaryl pesticide was used carried out. When the photocatalytic reactor equipped with the CPC solar concentrator of 1 sun was used to carry out degradation processes under UV+TiO2 and UV+TiO2+H2O2 conditions, degradation levels of 41% and 79% were reached, respectively. Alternatively, when the photocatalytic reactor equipped with the CPC solar concentrator of 2 suns was used to degrade the same pollutant under the same conditions, degradation levels of 54% and 92% were achieved, respectively. To complete the characterisation of the above mentioned degradation processes, the experimental values of parameters such as global kinetic constants, TOC and COD, were determined.

Savinase proteolysis of insulin Langmuir monolayers studied by surface pressure and surface potential measurements accompanied by atomic force microscopy (AFM) imaging

The mechanism of the enzymatic action of Savinase on an insulin substrate organized in a monolayer at the air–water interface was studied. We followed two steps experimental approach classical surface pressure and surface potential measurements in combination with atomic force microscopy imaging. Utilizing the barostat surface balance, the hydrolysis kinetic was followed by measuring simultaneously the decrease in the surface area and the change of the surface potential versus time. The decrease in the surface area is a result of the random scission of the peptide bonds of polypeptide chain, progressively appearance of amino acid residues, and their solubilization in the aqueous subphase. The interpretation of the surface potential data was based on the contribution of the dipole moments of the intact and broken peptide groups which remain at the interface during the proteolysis. An appropriate kinetic model for the Savinase action was applied, and the global kinetic constant was obtained. The application of the AFM revealed the state of the insulin monolayers before and after the Savinase action. The comparison of the topography of the films and the roughness analysis showed that insulin Langmuir–Blodgett (LB) films transferred before the enzyme action were flat, while at the end of hydrolysis, roughness of films has increased and the appearance of 3D structures was observed.

Hydrolysis of mixed monomolecular films of tricaprylin/dilauroylphosphatidylcholine by lipase and phospholipase A2

The purpose of this article was to describe the kinetics of the enzymatic action of one or more enzymes on mixture of substrates organized in 2D structures in order to mimic some situations existing in biological or industrial systems. Hydrolysis of the mixed monomolecular films of tricaprylin/dilauroylphosphatidylcholine (TC8/DiC12PC) by Thermomyces lanuginosus lipase (TLL) and phospholipase A₂ (PLA₂) was studied by measuring the decrease of the surface area and change of the surface potential at barostatic conditions. The decrease of the surface area detects the transition of the substrate into reaction products and their solubilization while the change of the surface potential detects the contribution of dipole moment of the molecules remaining at the interface during the hydrolysis. The kinetic models, describing the interfacial hydrolysis allowed us to estimate the values of the global kinetic constants for TC8 and DiC12PC hydrolysis, respectively. The role of interaction between all participants of the catalytic act in that complex catalytic system is shown. The catalytic activity of TLL and PLA₂ is affected by the molecular environment in TC8/DiC12PC mixed monolayers.

Enzymatic proteolysis of alpha gliadin monolayer spread at the air–water interface

The mechanism of the enzymatic hydrolysis under the proteolytic enzyme action of a plant protein alpha gliadin organized as a model monolayer system at the air/water interface was studied. The advantage of the monolayer technique is the ability to control and modify easily the interfacial organization of the molecules and the possibility to optimize the conditions for the hydrolysis. Enzymatic hydrolysis was studied by using a traditional barostat surface balance. The hydrolysis kinetic was followed by measuring simultaneously the decrease of the surface area and change of the surface potential with time. The decrease with time in film area is result of the random scission of the peptide bonds of polypeptide chain and their solubilization in the aqueous subphase. The interpretation of the surface potential data is based on the contribution of the dipole moments of the intact and broken peptide groups. An appropriate kinetic model describing the proteolytic action of a peptidase was applied and the global kinetic constant was obtained. The random scission of the protein chains gave kinetic constants comparable with those measured during the hydrolytic scission of polyester macromolecules but quite different to the values obtained with short-chain lipids.

Comparative study of lipolysis by PLA 2 of DOPC substrates organized as monolayers, bilayer vesicles and nanocapsules

The water-soluble lipolytic enzymes act at the interface of insoluble lipid substrates, where the catalytical step is coupled with various interfacial phenomena as enzyme penetration, solubilization of reaction products, loss of mechanical stability of organized assemblies of phospholipids molecule, etc. One biologically relevant example is the enzymatic hydrolysis of DOPC by PLA 2, which results in cleavage of phospholipids molecules into water insoluble lipolytic products, namely oleic acid and lysophospholipid. In general, the enzymatic activity depends on the substrate organization and molecular environment of the catalytic reaction. The lipolysis by phospholipase A 2 of dioleoylphosphatidylcholine substrates organized as monolayer, bilayers vesicles and lipid nanocapsules was studied by measuring the decrease of the surface area at constant surface pressure or increase of the surface pressure at constant area at air–water interface. A kinetic model describing the coupling of the catalytic act with corresponding interfacial phenomena was developed. By using the kinetic model the values for the global hydrolytic kinetic constants were obtained. The obtained value for the monolayer is five orders of magnitude higher than this obtained with small unilamellar vesicles and six orders of magnitude higher then those obtained with lipid nanocapsules. The comparison shows that the enzymatic catalytic act occurring in the lipid environment of the monolayer is more efficacious than at the vesicle and nanocapsules interfaces.

Folding kinetics and thermodynamics of Pseudomonas syringae effector protein AvrPto provide insight into translocation via the type III secretion system

In order to infect their hosts, many Gram-negative bacteria translocate agents of infection, called effector proteins, through the type III secretion system (TTSS) into the host cytoplasm. This process is thought to require at least partial unfolding of these agents, raising the question of how an effector protein might unfold to enable its translocation and then refold once it reaches the host cytoplasm. AvrPto is a well-studied effector protein of Pseudomonas syringae pv tomato. The presence of a readily observed unfolded population of AvrPto in aqueous solution and the lack of a known secretion chaperone make it ideal for studying the kinetic and thermodynamic characteristics that facilitate translocation. Application of Nzz exchange spectroscopy revealed a global, two-state folding equilibrium with 16% unfolded population, a folding rate of 1.8 s(-1), and an unfolding rate of 0.33 s(-1) at pH 6.1. TrAvrPto stability increases with increasing pH, with only 2% unfolded population observed at pH 7.0. The R(1) relaxation of TrAvrPto, which is sensitive to both the global anisotropy of folded TrAvrPto and slow exchange between folded and unfolded conformations, provided independent verification of the global kinetic rate constants. Given the acidic apoplast in which the pathogen resides and the more basic host cytoplasm, these results offer an intriguing mechanism by which the pH dependence of stability and slow folding kinetics of AvrPto would allow efficient translocation of the unfolded form through the TTSS and refolding into its functional folded form once inside the host.

Action of Humicola lanuginosa lipase on mixed monomolecular films of tricaprylin and polyethylene glycol stearate

The hydrolysis catalyzed by Humicola lanuginosa lipase (HLL) of pure tricaprylin (TC) or stearate of polyethylene glycol 1500 (PEG-St) as well as their mixtures spread as monomolecular films were studied. The catalytic transformation of the two substrates TC or PEG-St into their respective reaction products was detected by measuring simultaneously the decrease in the film area and the surface potential using the “zero order” trough at constant surface pressure. A kinetic model describing the enzymatic hydrolysis was developed. The surface concentrations of the two substrates and their respective reaction products as well as the values of the global kinetic constants of hydrolysis were determined. The experimentally obtained global kinetic constants of the catalytic action of HLL against TC and PEG-St present in mixed monolayers of TC/PEG-St are approximately the same as in the case of pure monolayers. These obtained results give some indications that the activity of enzyme is not significantly affected by the different molecular environments in the mixed monolayers.

Reorganization of lipid nanocapsules at air–water interface: 3. Action of hydrolytic enzymes HLL and pancreatic PLA 2

The action of the hydrolytic enzymes humicola lanuginosa lipase (HLL) and pancreatic phospholipase A 2 (PLA 2) on monolayers formed from lipid nanocapsules (LNC) and model monolayers containing their components, Labrafac ®, Solutol ® and Lipoid ®, is studied by simultaneous measuring the changes in the film area and the surface potential in the “zero order” trough at constant surface pressure ( π). The kinetic models describing the hydrolysis by HLL of the Labrafac, Solutol and their mixtures have been proposed. By using the developed theoretical approach together with the experimental results the surface concentrations of the substrates, hydrolysis products and values of the global kinetic constants were obtained. The comparison between the global kinetic constants in the case of HLL hydrolysis of pure Labrafac, Solutol monolayers and those of the model mixed Labrafac/Solutol monolayers, shows that the rates of hydrolysis are of the same order of magnitude, i.e. an additively of the HLL enzyme action is observed. The composition of the mixed Labrafac/Solutol monolayer, formed after the interfacial LNC destabilization, was estimated.

Action of Humicola lanuginosa lipase on long-chain lipid substrates : 2. Hydrolysis of diolein monolayers

The hydrolysis of 1,2-diolein (DO) monomolecular films by Humicola lanuginosa lipase (HLL) was studied by simultaneous measuring the decrease in the film area and the changes in the surface potential in the “zero-order trough” at constant surface pressure and in the presence of β-cyclodextrin (β-CD). The decrease with time in the film area reflects both the reduction in the area per molecule due to the transformation of substrate DO molecules into the products molecules of monoolein (MO) and oleic acid (OA) and the desorption of the soluble inclusion complexes β-CD–MO and β-CD–OA. The surface potential data were interpreted as an accumulation at the interface of negatively charged products of OA and insoluble β-CD–DO complexes. In the proposed kinetic model, the product solubilization rates in the presence of β-CD and the flux supplied progressively by the moving barrier from the reservoir to the reaction compartment in order to keep the constant surface pressure were taken into account. The surface concentrations of MO and OA transiently present at the interface were determined. The values of the global kinetic constant Q m ′ of hydrolysis of DO to MO were obtained. Comparison with the values of the global kinetic constant of hydrolysis of monoglyceride MO to OA shows that the rates of hydrolysis of diglyceride and monoglyceride by HLL are of the same order of magnitude.

Enzymatic hydrolysis by cutinase of PEG-co PLA copolymers spread monolayers

The mechanism of the hydrolysis by cutinase and the progressive fragmentation of lactic chains in diblock copolymers of PLA with various sizes attached to PEG were studied in a 2D monolayers model system. The hydrolysis kinetics was followed by measuring simultaneously the decrease of the surface area and evolution of the surface potential with time at barostatic conditions. The decrease of the surface area is due to the solubilization of the copolymers as well as of their hydrolytic products: detached PEG blocks and small soluble PLA fragments. The evolution of the surface potential detects the transient interfacial accumulation of charged insoluble PLA fragments. A kinetic model describing the enzymatic hydrolysis was developed and the values for the global hydrolytic kinetic constant were obtained without any fitting parameter. It was found that the global kinetic constant no practically depend on the length of the lactic and the presence of polyethylene–glycol chains.

Differential effects induced by α- and β-endosulfan in lipid bilayer organization are reflected in proton permeability

The effects of two insecticides isomers, α- and β-endosulfan, on the passive proton permeability of large unilamellar vesicles (LUV) reconstituted with dipalmitoylphosphatidylcholine (DPPC) or mitochondrial lipids were reported. In DPPC (LUV) gel phase, at 30 °C, the global kinetic constant ( K) of proton permeability (proportional to the proton permeability) initially increased slightly with the increase of α-endosulfan/lipid molar ratio up to 0.143. In the range from 0.143 to 0.286, a discontinuity in the increment occurred and, above this range, the proton permeability increased substantially. In DPPC fluid phase, at 48 °C, the proton permeability showed a behavior identical to that observed in gel DPPC, with a sharp increase for α-endosulfan/lipid molar ratios ranging from 0.143 to 0.286. At these and higher concentrations, α-endosulfan induced phase separation in the plane of DPPC membranes, as revealed by differential scanning calorimetry (DSC). Conversely to α-endosulfan, β-endosulfan induced only a slight increase in the proton permeability, either in the fluid or the gel phase of DPPC, for all β-endosulfan/lipid molar ratios tested. Additionally, the effects of the endosulfan isomers on the proton permeability of mitochondrial fluid lipid dispersions, at 37 °C, are similar to those described for DPPC. The β-isomer induced a very small effect, and α-endosulfan, at low concentrations, increased slightly the proton permeability, but for insecticide/lipid molar ratios above 0.143 the permeability increased substantially. Consequently, the membrane physical state of synthetic and native lipid dispersions, as affected by the structural features of α- and β-endosulfan, influenced the proton permeability. The effects here observed in vitro suggest that the formation of lateral membrane domains may underlay the biological activity of α-endosulfan in vivo, contributing to its higher degree of toxicity as compared with β-endosulfan.

A hot-atom reaction kinetic model for H abstraction from solid surfaces

Measurements of the abstraction reaction kinetics in the interaction of gaseous H atoms with D adsorbed on metal and semiconductor surfaces, H(g)+D(ad)/S→ products, have shown that the kinetics of the HD products are at variance with the expectations drawn from the operation of Eley–Rideal mechanisms. Furthermore, in addition to HD product molecules, D 2 products were observed which are not expected in an Eley–Rideal scenario. Products and kinetics of abstraction reactions on Ni(100), Pt(111), and Cu(111) surfaces were recently explained by a random-walk model based solely on the operation of hot-atom mechanistic steps. Based on the same reaction scenario, the present work provides numerical solutions of the appropriate kinetic equations in the limit of the steady-state approximation for hot-atom species. It is shown that the HD and D 2 product kinetics derived from global kinetic rate constants are the same as those obtained from local probabilities in the random walk model. The rate constants of the hot-atom kinetics provide a background for the interpretation of measured data, which was missing up to now. Assuming that reconstruction affects the competition between hot-atom sticking and hot-atom reaction, the application of the present model at D abstraction from Cu(100) surfaces reproduces the essential characteristics of the experimentally determined kinetics.

Hydraulic performance of a deep wastewater stabilization pond

The hydraulic performance of a deep wastewater stabilization pond located in the Espinardo Campus of the University of Murcia was studied. The pond has a maximum capacity of 15,000 m 3, with a maximum depth of 8 m. Sulforhodamine B dye is used as a tracer in the experimental study, which was carried out in two different climatic periods, winter and summer, so that the influence of temperature on the internal hydrodynamic of the lagoon could be ascertained. Two types of sample were obtained. One was taken from the mass of water within the pond and the other at the outlet. The mean real residence time ( t ̄ ) was calculated and it was below the spatial time (τ) both in summer and winter. Sampling carried out in the outlet flow along the time allowed the application of population balance models and to analyze the existence of short circuits and dead spaces. The pond active volume was calculated, being 70 and 22% of total volume in winter and summer, respectively. In both seasons, the active zone showed a hydrodynamic behaviour similar to the completely mixed continuous tank reactor (observed in the curves C and in the fitting of the experimental data at outlet and the use of the combined model of Cholette and Cloutier). From the experimental data of the remaining BOD 5 it was possible to calculate the global kinetic constants for organic matter degradation and, from this, the constants at 20°C obtained at the most unfavourable (higher) water temperature observed. Both in winter and summer constants values ( k 20 = 0.46 and 0.32 d −1) seemed to point to the active zone of the system, showing a fundamentally aerobic behaviour.

Laser pyrolysis of hydroxyl-terminated polybutadiene

A method was developed for measuring the dynamic regression rate and plume transmission loss during laser pyrolysis of polymeric binder materials. This method was applied to an investigation of the thermal decomposition of hydroxyl-terminated polybutadiene. Measurements of steady regression rate and surface temperature during constant flux laser pyrolysis were correlated using a zeroth-order, single-step model to obtain global decomposition kinetic constants and the heat of decomposition. At these heating rates (102-104 K/s) the activation energy was Ec = 11 kcal/mole (E, = 5.5 kcal/mole). This is substantially lower than the values that have been obtained by lower heating rate (0.1-1 K/s) methods such as thermogravimetric analysis, differential thermal analysis, and differential scanning calorimeter, indicating that the rate-controlling decomposition step is a strong function of heating rate. It was also found that the addition of carbon black as an opacifier lowers the regression rate significantly, probably due to carbon accumulation on the surface. Pulsed laser pyrolysis tests gave a two-peaked, nonlinear response with one peak near 1 Hz corresponding to condensed phase processes and another peak near 300 Hz corresponding to gas phase processes.