Kinetics conformational

Oscarson et al. (1983a) found that the kinetics of As(III) depletion (oxidation plus sorption) by uncoated Mn02 or Mn coated with Al or Fe oxides or CaC03 involved two rates one before and one after 30 min. The kinetics conformed to first-order kinetics. Arsenite depletion kinetics decreased significantly as the degree of coatings increased (Table 8.1). This... 

The factor a is a measure of the accessibility of the bonds (13), and k is the specific rate constant for the rate of breaking of normal IC-O-4 C bonds in the anhydroglucose chain (k in Equations 1-3 equals ak). The expression 100[1 /(DPn)t — 1/(DP )0] gives the percentage of the initial number of bonds that have been broken. Equation 4 is also the equation that would apply if an equal number of bonds were broken in equal periods of time, that is, at a constant rate of chain scissioning (zero-order kinetics). Conformance to Equation 4, therefore, cannot be taken as proof of first-order kinetic behavior (12). 

Luisi addressed this problem and recognized that the phenomenon can be dissected into two concepts.In the first case, flexibility describes an equilibrium in which the molecule exists in a small number of conformations relative to all those conceivably based on the molecular structure. This thermodynamic conformational flexibility describes a situation in which many rapidly interconverting conformations exist. The second concept relates to the rate of interconversion among different conformations hence, this is a kinetic conformational flexibility related to the energy barriers between conformations. The potential energy barriers govern the shape of macromolecules. 

A r-jump and stopped-flow study of the rapid anation of a five-co-ordinate copper(ii) aqua-complex by azide and thiocyanate has its main interest as a model system for the active site of a metalloenzyme. The kinetics conform to the Eigen-Wilkins mechanism (rate-determining water release, /d). ... 

Current applications of NMR in monitoring equilibrium and kinetic conformational states of the protein-folding have been reviewed. A recurring... 

Complexes whose aquation kinetics conform to this pattern include [Cr(NH3)5(N3)] +, [Cr(NHs)6(03CCCl3)] +, and [CrCOH ) -... 

Fernandez A 1990 Glassy kinetic barriers between conformational substates in RNA Phys. Reine Lett. 64 2328-233... 

Van Tassel P R, Guemourl L, Ramsden J J, Tar]us G, VIot P and Talbot J 1998 A model for the Influence of conformational change on protein adsorption kinetics J. Colloid Interfaoe Sc/. 207 317-23... 

Abstract. A model of the conformational transitions of the nucleic acid molecule during the water adsorption-desorption cycle is proposed. The nucleic acid-water system is considered as an open system. The model describes the transitions between three main conformations of wet nucleic acid samples A-, B- and unordered forms. The analysis of kinetic equations shows the non-trivial bifurcation behaviour of the system which leads to the multistability. This fact allows one to explain the hysteresis phenomena observed experimentally in the nucleic acid-water system. The problem of self-organization in the nucleic acid-water system is of great importance for revealing physical mechanisms of the functioning of nucleic acids and for many specific practical fields. 

Curiously enough, bulky substituents on nitrogen increase this reactivity towards methyl iodide (119). This has been related to a steric decompression of the thiocarbonyl group in the transition state. Furthermore, knowledge of the ratio of conformers in the starting 4-alkyl-3-i-Pr-A-4-thiazoline-2-thiones and in the resulting 4-alkyl-3-i-Pr-2-methylthiothi-azolium iodides combined with a Winstein-Holness treatment of the kinetic data indicates that in the transition state, the thiocarbonyl bond is approximately 65% along the reaction coordinate from the initial state... 

With these kinetic data and a knowledge of the reactor configuration, the development of a computer simulation model of the esterification reaction is iavaluable for optimising esterification reaction operation (25—28). However, all esterification reactions do not necessarily permit straightforward mathematical treatment. In a study of the esterification of 2,3-butanediol and acetic acid usiag sulfuric acid catalyst, it was found that the reaction occurs through two pairs of consecutive reversible reactions of approximately equal speeds. These reactions do not conform to any simple first-, second-, or third-order equation, even ia the early stages (29). 

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