Complex Kinetic Behavior Research Articles

Hepatic removal of two fractions of indocyanine green after bolus injection in anesthetized pigs

In the anesthetized pig, we studied the kinetics after intravenous bolus injection of two fractions of indocyanine green (ICG): the genuine ICGg (95-99% of total) and a degradation product, ICGdp (1-5%). Plasma concentrations were followed in the carotid artery and a hepatic vein. ICGg disappearance curves (n = 7) were biexponential with rate constants alpha = 0.189 +/- 0.021 min-1 and beta = 0.0356 +/- 0.0061 min-1. The hepatic extraction fraction was constant with time. A detailed mathematical analysis showed this to be in disagreement with the conventional assumption that the biexponential plasma disappearance curve is a result of backflux from the liver storage to plasma. In contrast, our observations were predicted by an alternative model assuming temporary extrahepatic, extravasal redistribution during first-order, one-way hepatic uptake. Nevertheless, when a large bolus of sulfobromophthalein (BSP) was injected 20 min after ICG, a net backflux of ICG could be demonstrated, presumably due to countertransport. Thus a sufficient description of ICGg kinetics must include the complex kinetic behavior of the hepatic membrane carrier involved. Mass spectrometry suggested that ICGdp is formed by two ICGg molecules. Plasma elimination of ICGdp was slower (alpha = 0.0094 +/- 0.0007 min-1). Analysis of the bile after bolus injection (n = 2) of ICGdp revealed two possible metabolites of ICGdp that were not found in urine. Since BSP injection did not alter the ICGdp disappearance curve, ICGdp is probably not taken up by the same hepatic membrane carrier as ICGg.

The Reaction of EDTA With Metallothionein and its SeparateClusters: Complex Kinetic Behavior With Novel ProteinConcentration Dependence

The Reaction of EDTA With Metallothionein and its SeparateClusters: Complex Kinetic Behavior With Novel ProteinConcentration Dependence

Study on the kinetics of the reaction of thymol blue with acidic bromate catalysed by Ru(III) or V(V)

The kinetics of the reaction between thymol blue and acidic bromate catalysed by Ru(III) or V(V) have been studied by monitoring the absorbance at 544 nm. The reaction showed a complex kinetic behaviour. The possible application to the catalytic determination of Ru(III) and V(V) is discussed.

Free radical synthesis of α,ω‐primary amino functionalized polyisoprene through the functional thermal inferter [bis(N‐(2‐phthalimidoethyl)piperazine)]thiuram disulfide

AbstractThe primary amino functional iniferter [bis(N(2‐phthalimidoethyl)piperazine)]thiuram disulfide (PEPTD) was synthesied and characterized. Thermal polymerization of isoprene in the presence of the initiator afforded α,ω‐functionalized polyisoprene with primary amino end‐groups after cleavage of the phthalimido group with butylamine. The kinetics of polymerization of isoprene using this iniferter was studied at 80, 85, 90 and 100°C. Interestingly, isoprene showed a complex kinetic behavior. The different parameters, related to initiation, chain transfer and primary radical termination reactions, as well as the constants for thermal decomposition of the initiator, were determined. From the Arrhenius plot, the activation energy of the overall decomposition constant of PEPTD (2 f kd) was calculated to be 110 kJ/mol. The functionality of the telechelics was examined by GPC.

Calculation of subsite affinities of human small intestinal glucoamylase-maltase.

Several years ago, Hiromi et al. (1973) Biochim. Biophys. Acta 302, 362-375 proposed a theory for the action patterns of glucoamylases, based on data from steady-state kinetics. The Michaelis-Menten constants (Km) and the turnover number for maltooligosaccharides were used to evaluate the subsite affinities. We have now used this method for evaluating the subsite affinities for glucoamylases(EC 3.2.1.3)-maltase (EC 3.2.1.20) from human intestinal mucosa. For calculation of the subsite affinities, A1 and A2, and the intrinsic rate constant kint, we use a modified algorithm and a computer program for nonlinear least square fitting. Considerable substrate inhibition was shown by maltotriose, minor inhibition by maltotetraose, and no inhibition by maltose and the other maltooligosaccharides. This indicates a more complex kinetic behaviour of the enzyme with respect to maltotriose. Evaluation of the subsites reveals that A2 is the main binding site (18.1 kJ/mol), whereas the other affinities, with the exception of A1, are lower than 2.5 kJ/mol.

Determination of chemical kinetics by DSC measurements: Part 2. Experimental results

In part 1 (Thermochim. Acta, 225 (1993) 143) a method to evaluate DSC measurements was developed and tested with simulated data. Part 2 contains experimental results for three different chemical reactions for which the kinetic data are determined. Provided correct baseline and time lag corrections are applied, reliable kinetic data can be obtained using this evaluation method. In contrast to other methods of evaluating DSC traces to obtain kinetic data, the method described here makes no assumptions about the order of reaction. Thus complex kinetic behaviour such as autocatalysis is readily apparent.

Reversible ATP-dependent transition between two forms of human cytosolic thymidine kinase with different enzymatic properties

Human cytosolic thymidine kinase, subunit molecular mass about 24 kDa, is a tetramer in the presence of ATP but a dimer in the presence of thymidine or without substrates. The pure, substrate-free enzyme showed complex, non-hyperbolic thymidine substrate kinetics with an apparent Km of 15 microM. Incubation with ATP at 4 degrees C induced a time-dependent transition to an enzyme form with hyperbolic kinetics and a 20-fold lower Km value for thymidine (0.7 microM) but the same maximal velocity as for cytosolic thymidine kinase (TK1) without ATP. Removal of the ATP by carboxymethyl chromatography reestablished the non-hyperbolic kinetics with the low affinity for thymidine (Km(app) = 12 microM), and this enzyme form could be reversed once more by ATP incubation to the high affinity enzyme form. Similar shifts could not be induced by thymidine. The activating effect of ATP depended on the concentration of enzyme protein in a linear manner. These results indicate that ATP is a positive effector of cytosolic thymidine kinase, controlling a kinetically slow transition between two molecular forms of the enzyme. A hypothetical reaction mechanism is presented to explain the complex kinetic behavior.

The role of intermediate oxidation states of technetium in catalysis of the oxidation of hydrazine by oxo-anions. Part 2. Perchlorate ions

The oxidation of hydrazine by an aqueous acid perchlorate medium is catalysed very efficiently by TcO4– ions in a manner recalling the nitrate ion system. The reaction shows an induction period followed by a fast stage of evolution of N2, and a high turnover number (>60) but no residue of unreacted hydrazine is left in contrast to the nitrate system, especially under strongly acid conditions. The concentration of TcIV in the system goes through two maxima as reaction proceeds, the first being extremely sharp, the second much broader. This complex kinetic behaviour has been computer-modelled reasonably successfully. The colour changes depend on the acidity of the system, but some coloured products have been characterised by UV/VIS and/or ESR spectroscopy.

Kinetics of Inhibition of Horse Liver Alcohol Dehydrogenase byp-Methylbenzyl Hydroperoxide

The complex kinetic behaviour of p-methylbenzyl hydroperoxide in its inhibitory action on horse liver alcohol dehydrogenase was examined. The kinetic patterns are markedly different at very low (<10−8 M) and high (> 10−7 M) hydroperoxide concentrations. In both cases very low inhibition constants (4nM and 14nM, respectively) were found. A possihle mechanistic model based on these results is discussed.

Steady-state kinetic analysis of aldehyde dehydrogenase from human erythrocytes.

The steady-state kinetics of purified cytoplasmic aldehyde dehydrogenase (EC 1.2.1.3) from human erythrocytes have been studied at 37 degrees C. Previous studies of the enzyme from several mammalian sources, which used a lower assay temperature, have been difficult to interpret because of the substrate activation by acetaldehyde which led to complex kinetic behaviour. At 37 degrees C the initial-rate data do not depart significantly from Michaelis-Menten kinetics. Studies of the variation of initial rates as a function of the concentrations of both substrates and studies of the inhibition by NADH were consistent with a sequential mechanism being followed. High-substrate inhibition by acetaldehyde was competitive with respect to NAD+. The enzyme was not inhibited by the product acetate and thus the results of these studies, although consistent with an ordered mechanism in which NAD+ was the first substrate to bind, were inconclusive. That such a mechanism was followed was confirmed by determination of the initial-rate behaviour in the presence of acetaldehyde and glycolaldehyde as alternative substrates. When the reciprocal of the initial rate of NADH formation was plotted against the acetaldehyde concentration at a series of fixed ratios between that substrate and glycolaldehyde, a linear 'mixed inhibition' pattern was obtained, confirming the mechanism to be ordered with NAD+ being the leading substrate and with kinetically significant ternary complex-formation.

INDUCTION OF A TRANSIENT ENHANCEMENT OF LOW LEVEL CHEMILUMINESCENCE IN INTACT LEAVES BY ANAEROBIC TREATMENT

— Intrinsic low level chemiluminescence of dark adapted intact leaves exhibits a transient enhancement of light emission when ambient air is replaced with an anaerobic atmosphere. Re establishing aerobic conditions gives rise to a complex kinetic behavior of the light emission in the post-anoxic phase. Metabolic changes within the leaf are suggested to be responsible for this phenom enon, where intactness of the leaf is found to be of crucial importance. Leaf homogenate showed nearly oxygen independent chemiluminescence. In contrast, low level chemiluminescence of UV-light damaged leaves and of chloroplast preparations was inhibited by oxygen depletion. Spectral analyses of the ultraweak light emission from the intact leaf indicates that in both aerobic and anaerobic cases, the source of the ultraweak light is the same. The similarity to the spectrum of delayed fluorescence also obtained from the leaf suggests that chlorophyll is the light emitting species.

Large conducting potassium channel reconstituted from airway smooth muscle.

Microsomal fractions were prepared from canine and bovine airway smooth muscle (ASM) by differential and gradient centrifugations. Surface membrane vesicles were characterized by binding assays and incorporated into planar lipid bilayers. Single-channel activities were recorded in symmetric or asymmetric K+ buffer systems and studied under voltage and Ca2+ clamp conditions. A large-conductance K(+)-selective channel (greater than 220 pS in 150 mM K+) displaying a high Ca2+, low Ba2+, and charybdotoxin (CTX) sensitivity was identified. Time analysis of single-channel recordings revealed a complex kinetic behavior compatible with the previous schemes proposed for Ca(2+)-activated K+ channels in a variety of biological surface membranes. We now report that the open probability of the channel at low Ca2+ concentration is enhanced on in vitro phosphorylation, which is mediated via an adenosine 3',5'-cyclic monophosphate-dependent protein kinase. In addition to this characterization at the molecular level, a second series of pharmacological experiments were designed to assess the putative role of this channel in ASM strips. Our results show that 50 nM CTX, a specific inhibitor of the large conducting Ca(2+)-dependent K+ channel, prevents norepinephrine transient relaxation on carbamylcholine-precontracted ASM strips. It was also shown that CTX reversed the steady-state relaxation induced by vasoactive intestinal peptide and partially antagonized further relaxation induced by cumulative doses of this potent bronchodilatator. Thus it is proposed that the Ca(2+)-activated K+ channels have a physiological role because they are indirectly activated on stimulation of various membrane receptors via intracellular mechanisms.

Improved methods for the analysis of dispersed kinetics in heterogeneous systems

Heterogeneous systems often show complex kinetic behaviour attributed to the presence of a distribution of rate constants which reflects the distribution of particle sizes in the system. The characterisation of this distribution from the experimental data is not straightforward. Existing techniques for the analysis of dynamic light scattering data, where a similar problem arises, can be used to analyse the data from dispersed kinetics. This unified approach is applied to the analysis of both kinetic and dynamic light scattering data for polydisperse colloidal systems. Together with two techniques, cumulant analysis and CONTIN, an improved log normal particle size model is introduced. The power of the model is assessed by comparison with a model-free approach studying the kinetics of interfacial electron transfer from TiO2 colloids to methyl viologen in solution.

Evaluation and Elimination of the Interference Effects of Three Cephalosporins on the Kinetic-Spectrophotometric Determination of Creatinine in Serum Using the Jaffe Reaction

Abstract The cephalosporins studied, cefotaxime, cefazolin and cefoxitin react with alkaline picrate showing a complex kinetic behaviour which include a decomposition step in the case of cefotaxime and cefazolin. Cefoxitin does not conform strictly to pseudo-first order kinetics which seems to indicate that one or more intermediate reaction products might be formed before the final complex, or this might be unstable. The presence of the cephalosporins leads to results affected by systematic errors in the determination of creatinine in serum. This effect can be minimized for cefotaxime and cefazolin by choosing a specific time interval to process the analytical signal, δA. These intervals are 180–45 and 60–10s, respectively. The presence of cefoxitin requires the application of the generalized standard-addition method, which involves the simultaneus determination of creatinine and cefoxitin by measuring the δA for two different time intervals.

Emulsion polymerization of butadiene, 3. Kinetic effects of stirring conditions and monomer/water ratio

The stirring speed n influences the emulsion polymerization of butadiene, (1) by reducing the effective emulsifier concentration [E]eff available for particle nucleation and stabilization at high n, and (2) by limiting diffusion of monomer to the latex particles at low n. The large density difference between butadiene and water promotes the breaking up of droplets at high n, while the same condition constitutes a large driving force for (partial) phase separation at low n. Increasing the monomer/water ratio at constant [E] decreases [E]eff, and thus the final particle number. At monomer volume fractions >0,6 mixed emulsions are likely to be formed initially, reducing [E]eff even further. In the presence of mixed emulsions, polymerization in the monomer phase may no longer be neglected, giving rise to a complex kinetic behaviour.

The effects of assay temperature on the complex kinetics of acetaldehyde oxidation by aldehyde dehydrogenase from human erythrocytes

Several studies have shown preparations of the cytosolic aldehyde dehydrogenase (EC 1.2.1.3) from sheep and human liver and from human erythrocytes to exhibit complex kinetic behaviour in which the dependence of the initial velocity on the concentration of acetaldehyde gives rise to downwardly curving double-reciprocal plots. This behaviour has often been analysed in terms of a sharp discontinuity in the double-reciprocal plots and its possible implications for the oxidation of acetaldehyde and other pharmacologically important aldehydes has been a subject of speculation. In the present work, it is shown that the purified, apparently homogeneous, enzyme from human erythrocytes exhibits such complex kinetic behaviour when initial rates are determined at 25°, although the double-reciprocal plots describe a smooth curve with no sharp discontinuity. However, when the assays were performed at 37° there was no significant deviation from Michaelis-Menten kinetics over a wide range of acetaldehyde concentrations (0.2–30 mM). At higher concentrations of acetaldehyde inhibition occurred which was competitive with respect to NAD +. These results, which indicate that the complex kinetic behaviour of aldehyde dehydrogenase is not important at physiological temperature, are interpreted in terms of the mechanisms that have been advanced to explain the phenomena.

Kinetics of water formation on Pt(111)

Measurements using modulated molecular beam relaxation spectroscopy identify ODa consumption as the rate‐limiting step for D2O formation on Pt(111). In the limit of low surface coverage, D2O is produced via two parallel pathways, Da+ODa→D2Oa with activation energy Ea≊16 kcal/mol, and 2ODa→D2Oa+Oa with Ea≊18 kcal/mol. From these results the reactions Da+Oa →ODa, Da+ODa→D2Oa, and D2Oa+Oa→2ODa are found to be exothermic with enthalpy changes ΔH≊−16, −9, and −8 kcal/mol, respectively, and ΔHOHa≊−61 kcal/mol is obtained for the heat of adsorption of hydroxyl on platinum. The general features of the reaction mechanism cause complex kinetic behavior, manifest as changes in the apparent order of the rate function and the effective activation energy as surface temperature and reactant pressures are varied. The implications for transient and steady‐state rate measurements are discussed.

The effects of interface attachment kinetics on solidification interface morphologies

The presence of an interface kinetic effect significantly influences microstructures that form during the solidification of alloys. In order to quantitatively evaluate the effect of interface kinetics on microstructure formation, critical directional solidification studies have been designed in the pivalic acid-ethanol (PVA-Eth) system, in which significant anisotropies in interface properties are present. The interface kinetic effect is studied in high-purity PVA by measuring the interface temperature of a planar interface which is growing under steady-state conditions. In a binary system of PV A-Eth, the interface kinetic effect is characterized by examining the variations in dendritic microstructural scales with velocity and composition and by examining the planar interface instability condition. The variations in the dendrite tip radius,R, the primary spacing, and the secondary arm spacing near the dendrite tip with velocity,V, as well as with composition, have been characterized. Experimental results at a given composition showedVR2. to be constant, and those at constant velocity showed δTsR2 to be constant, where δTs is the product of the liquidus slope and the concentration difference at the dendrite tip. In order to characterize the system properly, additional experiments were carried out to measure the liquidus temperatures of the system. These experimental results are then compared with the theoretical models of planar interface instability and of dendritic growth to evaluate the role of interface kinetics on microstructure formation. Based on the theoretical models for planar and dendritic growth in an anisotropic system, the results on the interface kinetic effects are analyzed to give an insight into the possible phenomena which contribute to the complex kinetic behavior that is observed experimentally in the PVA system.

Thick Film ZnO Resistive Gas Sensors: Analysis of Their Kinetic Behavior

Thick film polycrystalline gas sensors for hydrogen partial pressure determination in hydrogen‐air mixtures present a very complex kinetic behavior that demands to be thoroughly clarified in order for them to be used in practical applications. For this reason a systematic investigation has been carried out on the time and temperature dependence of the electrical conductivity of films deposited via spray pyrolysis on ceramic substrates in the temperature range 498‐573 K in the presence of dispersed Pt as the catalyst. Results of this investigation show that the hydrogen‐assisted reaction of desorption of surface chemisorbed oxygen occurs in parallel with a reaction of direct reduction in the whole range of temperatures investigated. When accounting for this parasitic reaction, a good fit of the partial pressure and time dependence of the electrical conductivity with the theoretical predictions has been observed by assuming a conductivity dominated by Schottky barriers at grain boundaries.

A computational model of the structure and extinction of strained, opposed flow, premixed methane-air flames

The application of laminar flamelet concepts to turbulent flame propagation requires a detailed understanding of strained laminar flames. Here we use numerical methods, including are-length continuation, to simulate the complex chemical kinetic behavior in premixed methane-air flames that are stabilized between two opposed-flow burners. We predict both the detailed structure and the extinction limits for these flames over a range of fuel-air mixtures. In addition to discussing the flame structure, a sensitivity analysis provides further insight on the chemical behavior near extinction. Finally, we discuss the comparison of the predictions with Law's experimental extinction data. An especially important aspect of this comparison is the recognition that fluid mechanical aspects of the traditional strained-flame analysis are deficient in representing experiments such as Law's. We develop and solve a new system of equations that is able to describe the experiments much more accurately.