Proposed Kinetic Model Research Articles

Label-free imaging of hemoglobin degradation and hemosiderin formation in brain tissues with femtosecond pump-probe microscopy.

The degradation of hemoglobin in brain tissues results in the deposition of hemosiderin, which is a major form of iron-storage protein and closely related to neurological disorders such as epilepsy. Optical detection of hemosiderin is vitally important yet challenging for the understanding of disease mechanisms, as well as improving surgical resection of brain lesions. Here, we provide the first label-free microscopy study of sensitive hemosiderin detection in both an animal model and human brain tissues.Methods: We applied spectrally and temporally resolved femtosecond pump-probe microscopy, including transient absorption (TA) and stimulated Raman scattering (SRS) techniques, to differentiate hemoglobin and hemosiderin in brain tissues. The label-free imaging results were compared with Perls' staining to evaluate our method for hemosiderin detection.Results: Significant differences between hemoglobin and hemosiderin transient spectra were discovered. While a strong ground-state bleaching feature of hemoglobin appears in the near-infrared region, hemosiderin demonstrates pure excited-state absorption dynamics, which could be explained by our proposed kinetic model. Furthermore, simultaneous imaging of hemoglobin and hemosiderin can be rapidly achieved in both an intracerebral hemorrhage (ICH) rat model and human brain surgical specimens, with perfect correlation with Perls' staining.Conclusion: Our results suggest that rapid, label-free detection of hemosiderin in brain tissues could be realized by femtosecond pump-probe microscopy. Our method holds great potential in providing a new tool for intraoperative detection of hemosiderin during brain surgeries.

COMPARATIVE ANALYSIS OF SOME EXISTING KINETIC MODELS WITH PROPOSED MODELS IN THE BIOSORPTION OF THREE HEAVY METALS IN A FLOW-BATCH REACTOR USING FIVE SELECTED MICRO-ORGANISMS

The biosorption of three heavy metal ions namely; Zn 2+ , Cu 2+ and Mn 2+ using five microorganisms namely; Bacillus circulans, Pseudomonas aeruginosa, Staphylococcus xylosus, Streptomyces rimosus and Yeast (Saccharomyces sp.) were studied. In this paper, the effectiveness of six existing and two proposed kinetic models were compared using two statistical parameters namely; linear regression coefficient of correlation (R 2 ) and average relative error (ARE%) which were employed to study the performance of each model on the biosorption of the three heavy metals by the individual biosorbents. In terms of highest values of R 2 , first proposed model accounted for 46.7%, Pseudo second-order kinetics model 40% while Elovich, Webber-Morris and second proposed kinetic models accounted for 6.7% respectively of the total results for biosorption of the three heavy metals by five selected microorganisms. But based on values of ARE%, first proposed kinetic model accounted for 93.3% while pseudo second-order kinetic model accounted for 6.7% of the results for biosorption of the three heavy metals by the five microbes. http://dx.doi.org/10.4314/njt.v35i3.29

Kinetic modeling of low density lipoprotein oxidation in arterial wall and its application in atherosclerotic lesions prediction

Oxidation of low-density lipoprotein (LDL) is one of the major factors in atherogenic process. Trapped oxidized LDL (Ox-LDL) in the subendothelial matrix is taken up by macrophage and leads to foam cell generation creating the first step in atherosclerosis development. Many researchers have studied LDL oxidation using in vitro cell-induced LDL oxidation model. The present study provides a kinetic model for LDL oxidation in intima layer that can be used in modeling of atherosclerotic lesions development. This is accomplished by considering lipid peroxidation kinetic in LDL through a system of elementary reactions. In comparison, characteristics of our proposed kinetic model are consistent with the results of previous experimental models from other researches. Furthermore, our proposed LDL oxidation model is added to the mass transfer equation in order to predict the LDL concentration distribution in intima layer which is usually difficult to measure experimentally. According to the results, LDL oxidation kinetic constant is an important parameter that affects LDL concentration in intima layer so that existence of antioxidants that is responsible for the reduction of initiating rates and prevention of radical formations, have increased the concentration of LDL in intima by reducing the LDL oxidation rate.

Simplified kinetic model for steam reforming of ethanol on a Ni/Al2O3 catalyst

AbstractEthanol steam reforming is a promising method for hydrogen production. Kinetic studies are carried out over a nickel‐based catalyst from 200 to 600°C. A simplified Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic model was proposed with nine parameters, where the surface decomposition of methane is assumed as the rate determining step (RDS), and while all other reaction steps are set as reversible. It is postulated that the velocity of the backward reaction step of the dissociative methane adsorption is similar to all other equilibrium reactions proposed, while the forward reaction step is set as the RDS. In addition, the formation of adsorbed carbon species is excluded due to the fact that SRE experiments were performed with excess water, suggesting that OH species, excluding O species formation, stick better on active Ni surface than methane. In addition, a power law kinetic model was used for analysis; the activation energy was 31.8 kJ/mol, and the reaction order of ethanol pressure was 1.52. Experimental results were successfully demonstrated by both kinetic models. The purpose of this work was to develop a simplified mechanistic model to replace empirical models (power rate model) and other proposed kinetic models that are too complex for an applied kinetic process. It was found that the simplified LHHW kinetic model has a better fit than that of the power law model. The proposed kinetic model works well over a wide temperature range (200–600°C).

Synthesis of palm oil-based trimethylolpropane ester as potential biolubricant: Chemical kinetics modeling

The environmental impact of large amounts of lubricants from mineral oils has become an increasingly important issue. The use of rapidly biodegradable lubricants, vegetable products as well as modified vegetable oil esters, could significantly reduce the environmental pollution compared to mineral oils. A kinetic/mathematical model describing chemical transesterification of palm oil-based methyl esters (POMEs) with trimethylolpropane (TMP) to polyol esters has been developed. The kinetics of the transesterification reaction was modeled as three distinct elementary reversible series–parallel reaction mechanisms. The model considers the transesterification reaction to take place in both forward and reverse directions. The resulting kinetics equations were solved using ode45 solver function in MATLAB, where the rate constants of the proposed kinetic model were determined by minimization of errors based on the optimum criteria of statistical analysis and by comparing the component concentrations at maximum and at equilibrium. The forward and reverse rate constants of all three steps involved in the transesterification reaction were reported. The validity of the model was tested by comparing the observed experimental values with the theoretical calculated data. A good correlation between simulated results and experimental data was observed, confirming that the model was able to predict the rate constants with plausible accuracy. The new proposed kinetic model would facilitate the design of a pilot-scale chemical reactor for the transesterification of POME with TMP to obtain palm oil-based polyol esters as a potential biolubricant.

Fructose production by chicory inulin enzymatic hydrolysis: A kinetic study and reaction mechanism

In this paper, a reaction scheme for fructose production by inulin enzymatic hydrolysis is proposed, taking into account the possibility of dealing with a mixture of enzymes acting on a mixture of polymers as substrate. The scheme is subsequently simplified to obtain a stoichiometric relationship between the fructose product and the reacted substrate. The former may be measured by HPLC, while the latter is the subject of kinetic investigations. Our proposed kinetic model is defined within temperature and substrate concentration ranges of industrial interest (40–60 °C and 3–60 g/L, respectively). Some assumptions were made in order to simplify the model, which is based on a minimum number of parameters. These hypotheses were always specified and assumed only on the basis of convenience and rational consideration. Eventually, the kinetic model was successfully validated by comparison with a vast set of experimental results.

Kinetic Analysis of the Entire RNA Amplification Process by Qβ Replicase

The kinetics of the RNA replication reaction by Qbeta replicase were investigated. Qbeta replicase is an RNA-dependent RNA polymerase responsible for replicating the RNA genome of coliphage Qbeta and plays a key role in the life cycle of the Qbeta phage. Although the RNA replication reaction using this enzyme has long been studied, a kinetic model that can describe the entire RNA amplification process has yet to be determined. In this study, we propose a kinetic model that is able to account for the entire RNA amplification process. The key to our proposed kinetic model is the consideration of nonproductive binding (i.e. binding of an enzyme to the RNA where the enzyme cannot initiate the reaction). By considering nonproductive binding and the notable enzyme inactivation we observed, the previous observations that remained unresolved could also be explained. Moreover, based on the kinetic model and the experimental results, we determined rate and equilibrium constants using template RNAs of various lengths. The proposed model and the obtained constants provide important information both for understanding the basis of Qbeta phage amplification and the applications using Qbeta replicase.

BUBBLE EFFECTIVENESS IN CYCLOHEXANE NON-CATALYTIC OXIDATION PROCESS

The bubble effectiveness in liquid phase cylohexane non-catalytic oxidation process is discussed in this paper. Then the bubble effectiveness and a new proposed kinetic model are used in the mathematical model of the industrial reactor for the cyclohexane non-catalytic oxidation process. Furthermore, simulation and optimization based on this reactor model are carried out. The results of simulation show that the reactor model using the concept of bubble effectiveness agrees better with the plant data, and the results of optimization are much better than the present industrial production level, which will help to improve the operation of the reactor section and design of new installations.

Kinetics Study on Heterogeneous Catalytic Wet Air Oxidation of Phenol using Copper/Activated Carbon Catalyst

Heterogeneous kinetics of catalytic wet air oxidation (CWAO) of phenol was studied using copper supported on activated carbon as the catalyst and oxygen as the oxidant. Both mass transfer effect and deactivation of catalyst can affect the kinetics measurement. To eliminate the mass transfer barriers, the study was conducted in a stirred tank batch reactor using catalysts of very small particle size. In order to prevent the catalyst deactivation caused by copper leaching from the support, saturated pH buffer solution was added into the reaction system and the initial phenol and catalyst concentrations were reduced. A mathematic model was proposed following the Langmuir-Hinshelwood mechanism to simulate the reaction kinetics. It is believed through simulation that the dissolved oxygen is adsorbed by the catalyst in molecular form which subsequently starts to degrade phenol on the catalyst surface. Both reaction rate constant and activation energy were determined for a temperature range of 140 - 160 oC and an oxygen partial pressure range of 0.4 - 1.6 MPa. The proposed mechanism and kinetic model were found to be in good agreement with experimental results.

A kinetic model for enzyme interfacial activity and stability: pa-hydroxynitrile lyase at the diisopropyl ether/water interface.

A kinetic framework is developed to describe enzyme activity and stability in two-phase liquid-liquid systems. In particular, the model is applied to the enzymatic production of benzaldehyde from mandelonitrile by Prunus amygdalus hydroxynitrile lyase (pa-Hnl) adsorbed at the diisopropyl ether (DIPE)/aqueous buffer interface (pH = 5.5). We quantitatively describe our previously obtained experimental kinetic results (Hickel et al., 1999; 2001), and we successfully account for the aqueous-phase enzyme concentration dependence of product formation rates and the observed reaction rates at early times. Multilayer growth explains the early time reversibility of enzyme adsorption at the DIPE/buffer interface observed by both enzyme-activity and dynamic-interfacial-tension washout experiments that replace the aqueous enzyme solution with a buffer solution. The postulated explanation for the unusual stability of pa-Hnl adsorbed at the DIPE/buffer interface is attributed to a two-layer adsorption mechanism. In the first layer, slow conformational change from the native state leads to irreversible attachment and partial loss of catalytic activity. In the second layer, pa-Hnl is reversibly adsorbed without loss in catalytic activity. The measured catalytic activity is the combined effect of the deactivation kinetics of the first layer and of the adsorption kinetics of each layer. For the specific case of pa-Hnl adsorbed at the DIPE/buffer interface, this combined effect is nearly constant for several hours resulting in no apparent loss of catalytic activity. Our proposed kinetic model can be extended to other interfacially active enzymes and other organic solvents. Finally, we indicate how interfacial-tension lag times provide a powerful tool for rational solvent selection and enzyme engineering.

Kinetics and thermal characterization of thermoset cure

AbstractThe differential scanning calorimeter (Perkin‐Elmer DSC‐1) is used to characterize the cure of a general‐purpose polyester during isothermal and scanning experiments. The technique is based on a new proposed model for the kinetics of isothermal cure. The model yields results which are in good agreement with experimental isothermal rate of reaction and integral heat of reaction data. It also gives some information about the residual reactivity of the sample after an isothermal cure experiment. With the aid of the proposed kinetic model, it is possible to obtain integral heats of reaction and rates of heat generation at different temperatures during a scanning experiment. The difference between the rate of heat input to the sample and the heat of reaction at any instant during scanning may be used to calculate the specific heat of the sample at the same instant. Specific heat data show two maxima during each scanning experiment. These maxima may be associated with transitions occurring during cure in the melt and rubbery states.