Talk:Iron–sulfur protein

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Merge proposal

I propose to merge Iron-sulfur cluster into this one. We also have an article on ferredoxin, which I propose to leave alone. Comments are welcome, but soon because I plan to act otherwise in the next day or so.--Smokefoot (talk) 22:44, 30 December 2007 (UTC)[reply]

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Wiki Education assignment: CHEM 4610 F22

This article was the subject of a Wiki Education Foundation-supported course assignment, between 6 September 2022 and 22 December 2022. Further details are available on the course page. Student editor(s): 8959j (article contribs).

— Assignment last updated by 8959j (talk) 03:15, 25 September 2022 (UTC)[reply]

Hello everyone!

I propose introducing some subtopics, as well as some figures and contributing the following to the Iron-Sulphur Proteins article,

Subtopic: Structure-Function Principles

To serve their various biological roles, iron-sulfur proteins effect rapid electron transfers and span the whole range of physiological redox potentials from -600 mV to +460 mV.
Iron-sulfur proteins are involved in various biological electron transport processes, such as photosynthesis and cellular respiration, which require rapid electron transfer to sustain the energy or biochemical needs of the organism.

Subtopic: High Covalency

Fe3+-SR bonds have unusually high covalency which is expected. When comparing the covalency of Fe3+ with the covalency of Fe2+, Fe3+ has almost double the covalency of Fe2+ (20% to 38.4%) ([4]). Fe3+ is also much more stabilized than Fe2+. Hard ions like Fe3+ normally have low covalency because of the energy mismatch of the metal Lowest Unoccupied Molecular Orbital with the ligand Highest Occupied Molecular Orbital.
The covalency of iron-sulfur proteins increasing means that the H2O’s are decreasing the covalency because HOH-S Hydrogen-bonding pulls the sulfur electrons. Therefore, lower covalency can donate the sulfur lone pair to Fe3+/2+. Subsequently, covalency stabilizes Fe3+ more than Fe2+, Fe3+ is more destabilized by the HOH-S hydrogen-bonding.
The Fe3+ 3d orbital energies follow the “inverted” bonding scheme which fortuitously has the Fe3+ d-orbitals closely matched in energy with the sulfur 3p orbitals which gives high covalency in the resulting bonding molecular orbital[5]. This high covalency lowers the inner sphere reorganization energy[5] and ultimately contributes to a rapid electron transfer.

Any suggestions or edits are welcome and would be really appreciated! — Preceding unsigned comment added by 8959j (talk • contribs) 20:27, 19 November 2022 (UTC)[reply]

Response

"To serve their various biological roles, iron-sulfur proteins effect rapid electron transfers and span the whole range of physiological redox potentials from -600 mV to +460 mV."

describe structural factors that regulate the redox potentials. Many reviews discuss this effect.

"Iron-sulfur proteins are involved in various biological electron transport processes, such as photosynthesis and cellular respiration, which require rapid electron transfer to sustain the energy or biochemical needs of the organism."

But what can be said other than ET is very fast. You could cite reviews that discuss why the rates are high.

"Subtopic: High Covalency Fe3+-SR bonds have unusually high covalency which is expected."

Says who?

"When comparing the covalency of Fe3+ with the covalency of Fe2+, Fe3+ has almost double the covalency of Fe2+ (20% to 38.4%) ([4]). Fe3+ is also much more stabilized than Fe2+. Hard ions like Fe3+ normally have low covalency because of the energy mismatch of the metal Lowest Unoccupied Molecular Orbital with the ligand Highest Occupied Molecular Orbital."

metal ions do not have covalency.

"The covalency of iron-sulfur proteins increasing means that the H2O’s are decreasing the covalency because HOH-S Hydrogen-bonding pulls the sulfur electrons. Therefore, lower covalency can donate the sulfur lone pair to Fe3+/2+. Subsequently, covalency stabilizes Fe3+ more than Fe2+, Fe3+ is more destabilized by the HOH-S hydrogen-bonding."

Maybe a safer topic is H-bonding to Fe-SR.

"The Fe3+ 3d orbital energies follow the “inverted” bonding scheme which fortuitously has the Fe3+ d-orbitals closely matched in energy with the sulfur 3p orbitals which gives high covalency in the resulting bonding molecular orbital[5]. This high covalency lowers the inner sphere reorganization energy[5] and ultimately contributes to a rapid electron transfer."

Covalency and bonding in these species are very demanding mushy topics. Maybe safer topic for a student would be bonding or MO scheme for Fe4S4(SR)4 clusters.

"Any suggestions or edits are welcome and would be really appreciate"

My advice: keep your contributions brief, rely on books and reviews for references.--Smokefoot (talk) 23:28, 19 November 2022 (UTC)[reply]

Thank you for your comments and advice. I've changed the covalency of iron-sulfur protein section to discuss H-bonding to Fe-SR as you suggested:

There is HO-H—S-Cys H-bonding from external H₂O’s positioned by the protein close to the active site and this H-bonding decreases the lone pair electron donation from the Cys-S donor to the Fe^3+/2+. Using lyophilization to remove these external H₂O’s results in increased Fe-S covalency, which means that the H₂O’s are decreasing the covalency because HOH-S Hydrogen-bonding pulls the sulfur electrons.

Again, comments on this section are welcome!

I also forgot to mention my references before!

References

1. Solvation effects on S K-edge XAS spectra of Fe-S proteins: normal and inverse effects on WT and mutant Rubredoxin

Sun, N.; Dey, A.; Xiao, Z.; Wedd, A.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.

J. Amer. Chem. Soc. 2010, 132(36), 12639.

2. Electronic Structure Contributions to Electron-Transfer Reactivity in Iron-Sulfur Active Sites:

Pierre Kennepohl and Edward I. Solomon

a. “Kinetics of Electron Transfer” Inorg. Chem. 2003, 42(3), 696-708 8959j (talk) 05:16, 4 December 2022 (UTC)[reply]

WP:SECONDARY--Smokefoot (talk) 13:53, 4 December 2022 (UTC)[reply]