Discuss how the following factors determine the rate of electron transfer in biological systems:
(a) the distance between electron donor and acceptor, and
(b) the reorganization energy of redox active species and the surrounding medium.

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Explanation:

(a). HOW THE DISTANCE BETWEEN ELECTRON DONOR AND ACCEPTOR AFFECTS THE RATE OF ELECTRON TRANSFER IN BIOLOGICAL SYSTEM:

Distance between the acceptor and the donor can affect in two ways; short distance and long distance effect.

Short distance causes

electronic orbitals of donor and acceptor directly overlap whereas in LONG DISTANCE reactions this coupling is indirect because of

sequential overlaps of atomic orbitals of the donor, the intervening medium, and the orbitals of the acceptor.

(b). HOW REORGANIZATION ENERGY OF REDOX ACTIVE SPECIE SURROUNDING MEDIUM AFFECTS:

the reorganized energy does not depend on the pre-existing intra molecule electric field. The charge transferred inside the molecule interacts with its aqueous surroundings.

Reorganized energy can be calculated using Poisson-Boltzmann equation.