What's the differences of "hopping", "tunneling" and "superexchange"?

Basically, summarizing and missing a lot of physicochemical concepts, Hopping mechanisms is the transmission of the proton/hole/electron, etc, charge thereafter, over the orbitals of the different species involved into the process, i.e, all the molecules that are between the donor and the acceptor. In the Superexchange the orbitals of all these species are needed to configure the suitable environment, but the charge is only localized in the donor and in the acceptor, not in the intermediate species.

Take a look to this book,

and to this review

Thanks Farid , detailed interpretation, and Sanchez-Martinez, and all your valuable clues! The concepts are new to me. I'd look into the books and article before asking for furthur details.

I found a paragraph in "Peptide-Mediated Intramolecular Electron Transfer: Long-Range Distance Dependence" (Chem. Rev. 1992, 92, 381-394 , Page 382), might be related to superexchange in "biological " context:

"

Intramolecular electron transfer may or may not use the intervening bridge molecular orbitals to accomplish effective electronic coupling between the donor and acceptor. When the electron transfer proceeds directly from the edge of the donor to the edge of the acceptor by mechanisms not involving the orbitals of the bridging peptide it is referred to as a through-space (or noncovalently linked) pathway. Since all our studies are in aqueous solution, the phrase "through space" does not imply 'through vacuum" since the pathway may involve solvent, ion pairing, and/or other noncovalent interactions. If on the other hand the orbitals of the bridging group assist in carrying the charge transfer between the donor and acceptor, the pathway is referred to as a through-bond pathway and the coupling between the donor and acceptor is therefore achieved through the orbitals of the bridging groups, in addition to other medium effects. In these cases the mechanisms of electron transfer have been discussed by a number of authors and is referred to as a superexchange mechanism. 27-30

"

There must be a correspondence between the descriptions here and that in quantum mechanics.

Any suggestions?

Dear Farid, I noticed the figure. What I can see is that bridging groups is analogous to an anion. Then I cannot go further.

In fact, the problem is I have difficulty in understanding a sentence:

In the article mentioned in the main question, it says "Thus, we can rule out the possibility of direct two-step electron hopping.......Thus, we conclude that the electron tunneling from the isoalloxazine ring to substrates must be mediated by adenine through a super-exchange mechanism."(Page 8108)

Thanks Farid , very detailed interpretation and clues! New things for me to study.

The paper, sure, I have sent it to you via message.

 

 

Oh. Finally I found the exact answer in this great TUTORIAL REVIEW

Electron transfer in peptides and proteins

by

Meike Cordes and Bernd Giese 

@

The keypoints are

"that an overlap between donor and acceptor orbitals allows electron tunneling or super-exchange between the redox partners"

"the separating matrix is regarded as a bridge between the two redox partners, with bridge orbitals involved in electronic communication between donor and acceptor,

thereby lowering the potential barrier and facilitating electron tunneling"

"Since ET rates drop exponentially with increasing distance, a practical upper limit for reasonably fast ET through proteins exists"

"Distances that exceed the upper limit for fast electron tunneling reactions can be overcome in a multistep hopping process"

"the main characteristics of sequential ET (hopping) are the occurrence of chemical intermediates"

"superexchange ET shows a strong exponential distance dependence, whereas electron hopping exhibits only weak distance dependence"