Buffer effect, mechanism

A second mechanism for reducing deforestation results from the buffering effect of reserves, limiting the extension of cattle... 

This difference in the magnitude of the buffer effect in equilibrium studies versus initial rate studies could be accounted for by at least three possibilities. The first is that under equilibrium and initial rate conditions, BCA exhibits different mechanisms. This is an unattractive hypothesis, and is inconsistent with the well characterized adherence of BCA catalysis to Michaelis-Menten kinetics and to the Haldane relation under initial rate conditions. 

Physicochemical mechanisms which include both dilution and buffering effects. Any acid produced is rapidly diluted by distribution throughout the whole of the extracellular fluid and most of the H ions are removed by the blood buffers. There is inevitably a small decrease in the base/acid ratios of each of the buffer systems present and correspondingly a small reduction in pH. 

The mechanism of the buffer effect can be studied from two points of view a chemical standpoint and a mathematical standpoint. We will examine both viewpoints here. 

The C moles (per solution liter) ofhydroxonium ions added have been completely transformed into C moles of the weak acid HA. Briefly, due to the buffer effect, the addition of C mol/L of the strongest acid that can exist in water (H3O+) has been commuted to the addition of C mol/L of a weak acid that is very poorly dissociated. This is the chemical mechanism of the buffer effect. 

For this type of reaction the value of the solvent deuterium isotope effect is often a conclusive argument for the proposed mechanism 16). Rate measurements of 1 in acetic acid-acetate buffers in light and heavy water resulted in an isotope effect ktiiO lkozo of 2.5, and A oac/ doac of 9. A ratedetermining proton transfer to the /3-carbon atom of the enamine has been proposed and accounts for the experimental results I6-18 Eq. (5). 

Further evidence regarding the mechanism was provided by LynnandBoums643 , who found a pH-dependent carbon-13 isotope effect in the decarboxylation of 2,4-dihydroxybenzoic acid in acetate buffers. The dependence was interpreted in favour of the A-SE2 mechanism, for an increase in acetate concentration would increase kL t and hence partitioning of the intermediate so that k 2 becomes more rate-determining. 

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