Kinetic models of stem cell growth

A kinetic equation of the growth of stem cell populations has been suggested based on the quasichemical model of biological growth proposed earlier. A cycle of sequential stages of the development of stem cells is represented by quasichemical equations. The kinetic equations that describe the cell cycle allow us to quantitatively predict the development of stem cell inoculates of different types depending on the conditions. A kinetic model was developed in which the kinetic parameters were the experimental characteristics of population growth, unlike the parameters of extrapolation imitation models. The kinetic model is in good agreement with experiment within the error of the measurement procedure.     

Kinetic approach for the purification of nucleotides with magnetic separation

The isolation of β‐nicotinamide adenine dinucleotide is of great importance since it is widely used in different scientific and technologic fields such as biofuel cells, sensor technology, and hydrogen production. In order to isolate β‐nicotinamide adenine dinucleotide, first 3‐aminophenyboronic acid functionalized magnetic nanoparticles were prepared to serve as a magnetic solid support and subsequently they were used for reversible adsorption/desorption of β‐nicotinamide adenine dinucleotide in a batch fashion. The loading capacity of the 3‐aminophenyboronic acid functionalized nanoparticles for β‐nicotinamide adenine dinucleotide adsorption was 13.0 μmol/g. Adsorption kinetic and isotherm studies showed that the adsorption process followed a pseudo‐second‐order kinetic model and the experimental data can be represented using Langmuir isotherm model. The 3‐aminophenyboronic acid functionalized magnetic nanoparticles were proposed as an alternative support for the β‐nicotinamide adenine dinucleotide purification. The results elucidated the significance of magnetic separation as a fast, relatively simple, and low‐cost technique. Furthermore, the magnetic supports can be reused at least five times for purification processes.     

Physical separation of straw stem components to reduce silica

In this paper, we describe ongoing efforts to solve challenges to using straw for bioenergy and bioproducts. Among these, silica in straw forms a low-melting eutectic with potassium, causing slag deposits, and chlorides cause corrosion beneath the deposits. Straw consists principally of stems, leaves, sheaths, nodes, awns, and chaff. Leaves and sheaths are higher in silica, while chaff, leaves, and nodes are the primary sources of fines. Our approach to reducing silica is to selectively harvest the straw stems using an in-field physical separation, leaving the remaining components in the field to build soil organic matter and contribute soil nutrients.     

Kinetic determination of carminic acid by its inhibition of lanthanide-sensitized luminescence

 The stopped-flow mixing technique was used to develop a simple and fast kinetic method for the determination of carminic acid based on its inhibitory effect on the fluorescence intensity of the europium(III)- diphacinone-ammonia system in the presence of Triton X-100. Analytical data can be obtained within 10 s after the reactants are mixed, which minimizes manipulation and enables the ready application of the proposed method to routine analyses for carminic acid in orange soft drinks. The dynamic range of the calibration graph was 0.5–15 μg ml^-1 and the relative standard deviation less than 4%. The analytical recoveries obtained by applying the method directly to the analysis of samples ranged from 90.0 to 111.8%. Received : 11 November 1995/Revised: 2 February 1996/Accepted: 6 February 1996     

Kinetic separation of carbon dioxide and methane on a copper metal-organic framework

Separation of carbon dioxide and methane is an important issue in upgrading low-quality natural gas. Adsorption equilibria and kinetics of CO(2) and CH(4) on a copper metal-organic framework (MOF), Cu(hfipbb)(H(2)hfipbb)(0.5) [H(2)hfipbb=4,4'-(hexafluoroisopropylidene) bis(benzoic acid)], were investigated to evaluate the feasibility of removing CO(2) from CH(4) in a pressure swing adsorption process using this new MOF adsorbent. The heat of adsorption of CO(2) on the Cu-MOF at zero-coverage (29.7 kJ/mol) is much lower than those on a carbon molecular sieve and a zeolite 5A adsorbent; and the heat of adsorption of CH(4) on the Cu-MOF (21.4 kJ/mol) is similar to that on the zeolite 5A adsorbent and smaller than that on a carbon molecular sieve. The Cu-MOF being investigated has apertures of (~3.5 × 3.5 ?), which favors the kinetically controlled separation of CO(2) and CH(4). The kinetic selectivity is found to be 26 at 298 K, and the overall selectivity (combining the equilibrium and kinetic effects) is about 25 for an adsorption separation process. These results suggest that the Cu-MOF adsorbent is an attractive alternative adsorbent for the CO(2)/CH(4) separation.     

Kinetic study on reactive extraction for chiral separation of phenylsuccinic acid enantiomers

The kinetics of the extraction of phenylsuccinic acid (PSA) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) in a modified Lewis cell was studied, in which HP-β-CD dissolved in 0.1 mol L^?1 NaH₂PO₄/H₃PO₄ buffer solution (pH = 2.5) was selected as the chiral extractant. PSA enantiomers were extracted from organic phase to aqueous phase in the extraction module. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of this extraction module. The different parameters affecting the extraction rate such as agitation speed, interfacial area, initial concentration of PSA enantiomers in organic phase as well as HP-β-CD concentration in aqueous phase were separately studied. The experimental results demonstrate that the extraction reactions are fast. The reactions were found to be first order with respect to PSA and second order with respect to HP-β-CD with forward rate constants of 3.4 × 10^?2 m⁶ mol^?2 s^?1 for R-PSA and 9.96 × 10^?3 m⁶ mol^?2 s^?1 for S-PSA. These data will be useful in the design of extraction processes.     

反应萃取手性分离苯基琥珀酸对映体动力学研究

通过恒界面池研究了羟丙基-β-环糊精(HP-β-CD)萃取苯基琥珀酸对映体(PSA)动力学.采用伴随化学反应的萃取理论获得萃取动力学.实验分别考察了搅拌速率、界面面积、对映体浓度和萃取剂浓度等条件对PSA对映体萃取动力学的影响.实验结果表明:HP-β-CD萃取PSA对映体的反应为快反应;对对映体反应是一级反应,对萃取剂反应是二级反应;R-PSA,S-PSA反应速率常数分别为3.4×10-2m6mol-2s-1,9.96×103m6mol-2s-1.这些数据对萃取过程的设计是很重要的.     

Kinetic determination of hexacyanoferrates by their inhibition of an oscillating chemical reaction

A method for the kinetic determination of traces of hexacyanoferrate based on an oscillating chemical reaction is presented. In a Belousov-Zhabotinskii reaction system, by using a bromide ion-selective electrode, the amplitude decrease of the potentiometric oscillation is linearly proportional to the concentration of Fe(CN)^3?₆ [or Fe(CN)^4?₆] in the range 7 × 10^?8?5 × 10^?6 M. The relative standard deviation for 1 × 10^?6 M Fe(CN)^3?₆ is 2.7% (n = 6). Cyclic voltammetry was applied to study the mechanism of the proposed system. The procedure was utilized to determine hexacyanoferrates in silver plating and photographic solutions.     

Kinetic separation of hexane isomers by fixed-bed adsorption with a microporous metal-organic framework

A three-dimensional microporous metal-organic framework Zn(BDC)(Dabco)0.5 (BDC = 1,4-benzenedicarboxylate, Dabco = 1,4-diazabicyclo [2,2,2]octane), having two types of intersecting pores to encapsulate linear hexane and to block branched hexanes, and thus exhibiting highly selective sorption with respect to n-hexane, has been successfully applied to the kinetic separation of hexane isomers by fixed-bed adsorption.     

Subliminal light control of dark adaptation kinetics in Phycomyces phototropism

The dark adaptation kinetics of Phycomyces phototropism depend critically on the experimental protocol. When sporangiophores that had been light-adapted to a fluence rate of 1 W m-2 at 447 nm were exposed to dim unilateral light, the adaptation kinetics showed exponential decay (6 min time constant). However, when light-adapted sporangiophores were kept for variable intervals in darkness (i.e. in presence of traditional red safelight) and then exposed to dim unilateral test light, the decay kinetics of adaptation were biexponential with a rapid decay during the first minute (1 min time constant), followed by a slow recovery (11 min time constant). Thus, the dim subliminal light given after the sporangiophores had been adapted to 1 W m-2, was actually perceived, and exerted control over the dark-adaptation process. The observed acceleration of dark-adaptation kinetics constitutes a novel light effect of the sporangiophore. At wavelength 383 nm this effect was not observed. Because a beta-carotene lacking mutant, L91 (genotype carB), was unmodified in dark-adaptation kinetics measured in the presence or absence of subliminal light, it appears that beta-carotene is not involved in the photocontrol of adaptation.     

Kinetic theory of gas separation in a nanopore and comparison to molecular dynamics simulation

Kinetic mesoscopic theory derived from an atomistic model is applied to study permeation and separation of gases in a single rectangular pore. The goal is to judge the analytical method against the results of molecular dynamics simulation and to demonstrate the ease and relevance of analytical theories to calculate density profiles, flux, permeance, and separation factors. The permeance is linked to the amount of gas adsorbed in the pore and the effect of the effective gas-wall interaction on adsorption is explored. The effects of pore size, temperature, and the parameters of the pore wall interaction are investigated and reproduce the trends found in the numerical simulation of permeation of a mixture of methane and carbon dioxide in a carbon nanopore.     

Kinetic parameters from thermogravimetric curves

A novel procedure is presented for the evaluation of kinetic parameters, activation energy (E) and reaction order (n), from thermogravimetric (TG) traces. From given values of conversion (α) and corresponding temperatures (T) are calculated values of E corresponding to various arbitrary values of n. Then, the resulting arbitrary E-values may be plotted against respective n-values and the region bounded by intersecting curves used to simultaneously estimate E and n. This procedure was tested against theoretical data, teflon, sodium bicarbonate, and magnesium hydroxide, and was found to be satisfactory. Some advantages of this method are: it is relatively simple to use; it allows the user to readily discern whether the data are homogeneous and, if not, at what conversions the data deviate. A less sensitive ancillary procedure is also described which can dispense with plotting in the estimation of E and n.     

Kinetic data from DTA measurements

The theory of Borchardt and Daniels for the determination from the DTA curve of the fraction decomposed (α) is used. The probable mechanism, activation energy (E) and frequency factor (Z) can be found by the trial and error method from the plot ofα vs.T for a decomposition reaction which can be expressed by the equation $$\log g(\alpha ) = \log p(E/RT) + \frac{{ZE}}{{Rq}}$$ The use of tables of log g(α) for different mechanisms, and plots of the function logp(E/RT _α) vs. temperature for different activation energies is described. The influence is shown of the mechanism of the process, activation energy, frequency factor and heating rate (q) on the shape of the DTA curve. The kinetic data for the decomposition of several solids obtained by the described method are in good agreement with those obtained from literature sources.     

Determination of Kinetic Parameters from GPC-Data

Abstract

The molecular weight distribution and its first moments of selected polymers were experimentally determined through GPC-investigations with additional molecular weight detection. In on-line operation discontinuously functioning Ubbelohde-viscometer was used for the determination of degree of polymerization in dependence on elution volume.

The relation between the experimentally determined values and relative kinetic parameters were derived for some polymers prepared by radical mechanism. The relative constants which determines the branching structure in polymer can be now calculated.

From the investigated polymers the effect of chemical nature of monomer units for the branching formation was determined.     

Preparative HPLC separation of bambuterol enantiomers and stereoselective inhibition of human cholinesterases

We separated and characterized the enantiomers of bambuterol (5-[-(tert-butylamino)-1-hydroxyethyl]-m-phenylene-bis(dimethylcarbamate) hydrochloride), which is used in racemic form as a prodrug of terbutaline, a β₂-adrenoceptor agonist. The enantioseparation was attempted on several chiral HPLC columns, and the most effective separation was achieved on the amylose-based Chiralpak AD column. Since in vivo conversion of bambuterol into terbutaline involves hydrolysis by butyrylcholinesterase (EC 3.1.1.8), we studied the reaction of enantiomers with eight human BChE variants. Both enantiomers inhibited all studied BChE variants; however, the rate of inhibition with the (R)-enantiomer was about five times faster than with the (S)-enantiomer. (R)-bambuterol inhibition rate constants for homozygous usual (UU), fluoride-resistant (FF) or atypical (AA) variant ranged from 6.4 to 0.11 min^-1μM^-1. The inhibition rates for heterozygotes were between the respective constants for the corresponding homozygotes. An erratum to this article can be found at     

Absorption and emission spectroscopic characterization of blue-light receptor Slr1694 from Synechocystis sp. PCC6803

The BLUF protein Slr1694 from the cyanobacterium Synechocystis sp. PCC6803 is characterized by absorption and emission spectroscopy. Slr1694 expressed from E. coli which non-covalently binds FAD, FMN, and riboflavin (called Slr1694(I)), and reconstituted Slr1694 which dominantly contains FAD (called Slr1694(II)) are investigated. The receptor conformation of Slr1694 (dark adapted form Slr1694(r)) is transformed to the putative signalling state (light adapted form Slr1694(s)) with red-shifted absorption and decreased fluorescence efficiency by blue-light excitation. In the dark at 22 degrees C, the signalling state recovers back to the initial receptor state with a time constants of about 14.2s for Slr1694(I) and 17s for Slr1694(II). Quantum yields of signalling state formation of approximately 0.63+/-0.07 for both Slr1694(I) and Slr1694(II) were determined by transient transmission measurements and intensity dependent steady-state transmission measurements. Extended blue-light excitation causes some bound flavin conversion to the hydroquinone form and some photo-degradation, both with low quantum efficiency. The flavin-hydroquinone re-oxidizes slowly back (time constant 5-9 min) to the initial flavoquinone form in the dark. A photo-cycle dynamics scheme is presented.