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Driving force reaction

However, even the best experimental technique typically does not provide a detailed mechanistic picture of a chemical reaction. Computational quantum chemical methods such as the ab initio molecular orbital and density functional theory (DFT) " methods allow chemists to obtain a detailed picture of reaction potential energy surfaces and to elucidate important reaction-driving forces. Moreover, these methods can provide valuable kinetic and thermodynamic information (i.e., heats of formation, enthalpies, and free energies) for reactions and species for which reactivity and conditions make experiments difficult, thereby providing a powerful means to complement experimental data. [Pg.266]

The B state responds much less to changes in donor and acceptor properties than the TICT state, and Eq. (5.1) can often be easily fulfilled by increasing donor and/or acceptor strength. In addition to these two factors which deliver the decisive part of the reaction driving force, polar solvent stabilization SOiv and the mutual Coulombic attraction C of the linked donor and acceptor radical anion/cation also help to preferentially stabilize the TICT state with respect to the precursor B state. [Pg.114]

In all protein-protein complexes studied to date in which cytochrome c has been a partner, it has been shown that the ET rates depend strongly on the reaction driving force. It follows that variations in the reorganization energy could control ET rates in these cases [12]. In redox enzymes with two or more active centers, ET between two centers could be turned on by lowering X at roughly constant — AG [1]. Indeed, a proposal has been advanced that this type of mechanism would be an efficient way to gate the electron flow in a redox-linked proton pump such as cytochrome oxidase [75]. [Pg.127]

The relationships between rate of cleavage, bond strength and radical-anion redox potential can be combined in one concept. In this, cleavage rate is dependent on a reaction driving force, defined as the difference between the redox potential of the substrate radical-anion and the redox potential of the product anion in equ-librium with the coiresponding radical (E° for bromine ion, bromine radical as an example). [Pg.94]

Figure 13 Activation enthalpy for back ET from colloidal Sn02 films to a series of covalently attached dyes as a function of reaction driving force. See caption to Fig. 11 for identification of the dyes. Figure 13 Activation enthalpy for back ET from colloidal Sn02 films to a series of covalently attached dyes as a function of reaction driving force. See caption to Fig. 11 for identification of the dyes.
Figure 16 Modified Pourbaix diagram for Sn02 illustrating the origin of the pH dependence of (see Ref. 73) and showing how the overall back-reaction driving force (Ech - Ef) changes with pH. Insufficient data are available to estimate the driving force for the ET step in isolation (cf. Fig. 15). Figure 16 Modified Pourbaix diagram for Sn02 illustrating the origin of the pH dependence of (see Ref. 73) and showing how the overall back-reaction driving force (Ech - Ef) changes with pH. Insufficient data are available to estimate the driving force for the ET step in isolation (cf. Fig. 15).
This reaction is exothermic by 53 kcal., and a number of authors have felt that this large exothermicity can provide the reactions driving force. However, if one begins to examine the details of such a reaction, then one must consider that it must occur either thru a precursor alkylperoxy radical in competition with Reaction 1, or else that it occurs as a four-center reaction. This is illustrated below. [Pg.150]

KIEs in excess of 1.010 for the rate-determining formation of an t]1-superoxide species. A significant decrease from the 180 EIEs determined for such structures (i.e., 1.005-1.015 in Table 9.1) is actually expected due to variations in the transition state structure, which arise from changes in the reaction driving force.47 The possibility that an rj -superoxide intermediate is formed reversibly, as a... [Pg.441]

Fig. 3 (A) Free energy reaction profdes, constructed from intersecting parabolas, for addition of water to a simple carbocation that show the change in reaction barrier with changing reaction driving force. (B) Free energy profile for thermoneutral addition of water to a carbocation for which the observed activation barrier is equal to the intrinsic barrier A. Fig. 3 (A) Free energy reaction profdes, constructed from intersecting parabolas, for addition of water to a simple carbocation that show the change in reaction barrier with changing reaction driving force. (B) Free energy profile for thermoneutral addition of water to a carbocation for which the observed activation barrier is equal to the intrinsic barrier A.
Application of Marcus rate theory to proton transfer in enzyme-catalyzed reactions was discussed by Kresge and Silverman, 1999. Relationships of log KIE and kinetics of the enzyme catalysis (kcat) and parameters of the reaction driving force were found to be in agreement with the Marcus model. [Pg.56]

The general patterns of the energy contributions to (FC) are more easily discussed than the entropy contributions, and the energy contributions will be emphasized here. Equations (15-18) and (29) predict a complex dependence of ket on the reaction driving force. In the diabatic limit this corresponds to variations in the intersections of the reactants and products PE surfaces with the differences in their PE minima this is illustrated in Figure 2 for the diabatic (a) and weak-coupling (b) limits. [Pg.1183]


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See also in sourсe #XX -- [ Pg.344 , Pg.345 , Pg.346 ]




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