Michael Cuddy edited The_consecutive_two_step_reversible__.tex  almost 8 years ago

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Note that, for the purposes of this analysis, the inter-conversion of the major isomers is ignored. This is a valid assumption if the rate of inter-conversion of $B \longleftrightarrow C$ is small. We estimate from cursory analysis of the data that the rate constants for this process are at least two orders of magnitude smaller than the pathway that proceeds through the minor isomer.   However, a steady-state approximation for the system of rate equations is not valid for the minor isomer because its concentration changes appreciably and is not significantly different from those concentrations of either major isomer. Thus, the differential equations in (2)-(4) are solved explicitly. The exact solutions to these equations are:  \begin{equation}  B(t) = B_0[\frac{k_{-1}k_{-2}}{mn}+\frac{k_1(m-k_2-k_{-2})}{m(m-n)}\mathrm{e}^{-mt}+\frac{k_1(k_2+k_{-2}-n)}{n(m-n)}\mathrm{e}^{-nt}] \\  \end{equation}   \begin{equation}  A(t) = B_0[\frac{k_{1}k_{-2}}{mn}-\frac{k_1(k_{-2}-m)}{m(m-n)}\mathrm{e}^{-mt}-\frac{k_1(k_{-2}-n)}{n(m-n)}\mathrm{e}^{-nt}] \\  \end{equation}   \begin{equation}  B(t) = B_0[\frac{k_{-1}k_{-2}}{mn}+\frac{k_1(m-k_2-k_{-2})}{m(m-n)}\mathrm{e}^{-mt}+\frac{k_1(k_2+k_{-2}-n)}{n(m-n)}\mathrm{e}^{-nt}] \\  \end{equation}   \begin{equation}  C(t) = B_0[\frac{k_{1}k_{2}}{mn}-\frac{k_1k_{2}}{m(m-n)}\mathrm{e}^{-mt}+\frac{k_1k_{2}}{n(m-n)}\mathrm{e}^{-nt}]  

\begin{equation}  q = (p^2-4(k_1k_2+k_{-1}k_{-2}+k_1k_{-2}))^\frac{1}{2}  \end{equation}  The values of \textit{m} and \textit{n} generally differ by less than an order of magnitude within the range of rate constant values expected for Reaction (1). Thus, fits to time-dependent data in the form of $y(t) = y_0+\Lambda\mathrm{e}^{-\lambda{}t}+K\mathrm{e}^{-\kappa{}t}$ tend to converge to the form $y(t) = y_0+\alpha{}\mathrm{e}^{-\beta{}t}$. We take advantage of this to approximate $\textit{k}_1$ by fitting data for major isomer \textit{B} with a single exponential such that equation (5) (6)  may be rearranged as: \begin{equation}  B(t) = B_0[\frac{k_{-1}k_{-2}}{k_1k_2+k_{-1}k_{-2}+k_1k_{-2}}+[\frac{k_1k_2+k_1k_{-2}}{k_1k_2+k_{-1}k_{-2}+k_1k_{-2}}]\mathrm{e}^{-x_1t}]  \end{equation}