Sequence dependence, charge transfer rate

Sequence Dependence of Charge Transfer Rate Through DNA. 131... 

Figure 3. Examples of DNA sequences containing a stilbenedicarboxamide electron acceptor Sa. The rates of charge transfer between the primary G (green) and the distal GG doublet (red) strongly depend on the Intervening base sequence as explained in the text. For all sequences, hole transitions between G and GG are shown by arrows. Numbers next to the arrows are the values of rate constants for the hole transfer between G and GG. Corresponding average times for this process are given in parentheses.

In more complex organic reactions involving several charge transfer or chemical steps in the reaction sequence, it is often possible for one step to have a smaller rate constant than another. If this situation applies to the second or subsequent steps in a sequence, then the steps prior to the ratecontrolling step can usually be regarded as almost at equilibrium, and the surface concentrations of intermediates, 6, can then be expressed as a function of potential, so that there are two parts of the rate equation where potential-dependent terms are involved. 

Figure 4.6 shows the electrochemical activity of deposited poly(MG) onto RVC, and in each case, a nonlinear dependence that resembles Michaelis-Menten-type kinetics is observed. This observation agrees with the model proposed in 1985 by Gorton et al. [51] for mediator-modified electrodes for NADH oxidation, and it agrees with similar studies in 1990 and 2001 [53,105]. This model postulates the formation of a charge transfer (CT) complex in the reaction sequence between NADH and the mediator, because the observed reaction rate starts to decrease with the increase in NADH concentration, analogous to the Michaelis-Menten kinetics of enzymatic reactions. Catalytic activity of poly(MG) is inversely proportional to the thickness of the polymer, and the number of deposition cycles is consistent with observations in the literature for other NADH mediators [26,44,47,49]. This is attributed to the low partition coefficient of NADH and the diffusion coefficient of NADH within the... 

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