Biology Reference
In-Depth Information
being on either of the iron ions. That is, in the Franck-Condon state, the two iron
ions are chemically equivalent, within the limits set by the Heisenberg Uncertainty
Principle (Reynolds and Lumry 1966). The Franck-Condon complex (i.e., the
reaction system at the Franck-Condon state) can now relax back to the reactant
state or proceed forward to the product state, depending on the sign of the Gibbs
free energy change, D G, accompanying the redox reaction. If D G given by Eq. 2.24
is negative, the reaction proceeds forward (from left to right), and if it is positive,
the reaction proceeds backward (from right to left).
=
G initial ¼ D G 0
RT log *Fe þ 2
Fe þ 3
D G
¼
G final
(2.24)
where G final and G initial are the Gibbs free energy levels of the final and initial states
of the reaction system, D G 0 is the standard Gibbs free energy (i.e., D G at unit
concentrations of the reactants and products), R is the universal gas constant, T is
the absolute temperature of the reaction medium, [*Fe +2 ] is the concentration of the
radioactively labeled ferrous ion (to be distinguished from the unlabeled ferrous
ion, Fe +2 ), and [Fe +3 ] is the concentration of the ferric ion.
2.2.3 The Generalized Franck-Condon Principle (GFCP)
or the Principle of Slow and Fast Processes (PSFP)
It was postulated (Ji 1974a) that the Franck - Condon principle need not be
restricted to electron transfer processes in molecular spectroscopy or inorganic
electron transfer reaction in aqueous media but could be extended to physicochem-
ical processes that involve coupling between two processes whose rates differ
significantly. The generalized version of the Franck-Condon principle was also
referred to as the Principle of Slow and Fast Processes (PSFP) (Ji 1991, pp. 52-56),
which states that:
Whenever an observable process, P, results from the coupling of two partial processes, one
slow (S) and the other fast (F), with F proceeding faster than S by a factor of 10 2 or more,
then S must precede F. (2.25)
Statement 2.25 as applied to enzymic catalysis can be schematically represented
as follows:
h
i
Þ z ,
Þ z
A þ
A þ
B
B
ð
B
Þ r $
ð
B
ð
A
þ
$
ð
A
þ
Þ p
(2.26)
where A and B are the donor (or source) and the acceptor (or sink) of a particle
denoted by (which can be any material entities, either microscopic or macro-
scopic), and the parentheses indicate the immediate environment (also called
microenvironment) surrounding the reactant system, i.e., (A +B) r , or the product
system, i.e., (A + B ) p , where the subscripts r and p stand for reactant and product,
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