energized electron in photosynthesis?

[SStell]

In the process of photosynthesis, electrons are 'energized' and injected into the electron transfer chain to eventually pump H+ into the lumen. What does 'energized' electron actually mean. Is the electron supposedly spinning faster, vibrating faster, or what? Because it cannot have its velocity changed.

What exactly is an energized electron? And how is it different from a non-energized electron? Thanks

 

[CharonY]

In general an excited electron obtained sufficient energy to leave its original orbital (i.e. leaving ground state) and entering a higher energy band.

[SStell]

That would be for an electron in an orbital energy level of an atom. If it is being transferred from one protein to another in some redox cascade how is this 'energized' energy being transferred. Is it in some alternate quantum state, because its velocity remains pretty slow. So it's not kinetic energy. I 'understand' energy levels in the atom etc. But I don't understand different energy levels of a single electron. Isn't an electron an electron an electron? Or is all about an electron being bumped up to a higher orbital in one molecular orbital which allows it to be transferred to a slightly lower energy orbital in an adjacent molecule and that transfer would be impossible from a lower energy orbital?

[CharonY]

The light absorption moves it into a higher band. From there you are looking at either overlapping bands and tunneling processes.

[SStell]

thanks

[BabcockHall]

One way to describe this is in terms of reduction potentials. The ground state reduction potential of photosystem II is about +1 volts. However, the excited state reduction potential is roughly -1 volt. PS II is the oxygen-evolving photosystem, but a similar idea holds for PS I.

[SStell]

So it seems that the electron is not carrying any 'extra' energy but is being placed into a higher redox potential spot by a molecule that gained its extra energy by just having the extra electron? It's not the electron but the molecule or atom that transfers the electron that has been 'energized'? I guess my query is about different energy levels or 'energized' single electrons. I just didn't think they did that. So it's the molecule or atom that has been 'energized' and not the electron. Or am I as usual completely confused?

[CharonY]

The redox potential is what drives the transfer, which becomes possible once the electron is in a higher energy band (and hence becoming more mobile). Also, during electron transfer a tunneling step is usually needed as the distance between redox centers is too large. And again, the redox potential influences the rate of it happening.

[BabcockHall]

Suppose we have two chemicals A and B, and the reduction potential of B is much more negative than the reduction potential of A. What does that tell you about B versus A?

[SStell]

Babcock, So the electron would likely move from B to A. From low electron affinity to high electron affinity?

 

Charon, So a photon is absorbed by a molecule (chlorophyll) which elevates an electron to a higher energy band, which then allows it to be transferred more easily to a molecule at a more negative redox potential with maybe some quantum tunneling to boot? And so on. So the electron itself is not the carrier of any extra energy but the atom or molecule it came from put that electron in that higher band and that and that alone allows the transfer to atoms of higher electron affinity?

 

My whole confusion comes from the standard everyday diagrams of photosynthesis. They use the term 'energized' electron. I just didn't quite grasp that term. As electrons have no orbitals or energy bands or levels that I was knowledgeable of. I am wrong a lot so this would not be anything new. I usually understood a high energy electron as one with increased velocity as in particle physics etc. Kinetic Energy. So is this an example of higher chemical Potential Energy which allows it to then 'fall' down a cascade of proteins in the electron transfer chain?

[BabcockHall]

SStell, My intention was to think of both A and B as being in their reduced forms. Under those conditions, there would not be any electron transfer. (However if there were a solution that had both B_red and A_ox, then yes, electrons would transfer from B to A.) My point was this: The electrons in B_red are much more easily removed than the electrons in A_red. Putting it another way, B_red is a stronger reducing agent than A_red is.

[SStell]

thanks, I think I am getting it