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During the electron transfer chain in cellular respiration, the NADH turns into NAD+ while donating an electron. Those electrons pass through many enzymes and chemical reactions. One such chemical reaction is when it passes through iron II or iron III. Is it possible for NADH to react with iron II or III without any other reactions with enzymes and chemicals? I am asking this because I am interested to know if the reaction between NADH and iron can give oxidize NADH and reduce iron.

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    $\begingroup$ Please clarify. 1. When you refer to iron II and iron III, please indicate whether you are talking about free iron or iron in cytochromes etc. 2. Are you talking about what actually happens in the electron transport chain (ETC) in cells or what would happen if iron were mixed with NADH in a test tube? 3. Or are you asking why the many redox pairs are need in the ETC? Your language ("turns into", "chemicals and enzymes") suggests you might benefit from reading about the ETC and redox couples in a biochemical text (best) or on line. Are you aware that oxygen is the ultimate electron acceptor? $\endgroup$
    – David
    Jan 15, 2023 at 16:57
  • $\begingroup$ Thank you for your response and for clarification: 1. I am referring to free iron atoms and 2. I am asking what would happen if iron were mixed with NADH in test tubes. I realize oxygen is the ultimate acceptor but my main question is: if iron(II) or iron(II) and NADH were mixed, could NADH transfer electrons to iron? and lastly, could NADH donate electrons to regular iron? $\endgroup$ Jan 15, 2023 at 22:29

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Preamble

Although the question relates to a non-biological test-tube reaction, I feel it worth posting an answer because the principle involved is relevant to biological redox reactions.

Qualified Answer

For a chemical reaction to proceed requires two things:

  1. That ΔG, the overall change in Gibbs Free Energy, is negative.
  2. That the activation energy for the reaction can be overcome.

As regards 1: For reactions consisting of two redox half reactions, one needs to first calculate the reduction potential and then, from this, ΔG. (A positive ΔE gives a negative ΔG.) A table of standard reduction potentials taken from this on-line source is shown below.

Table of redox potentials

Without actually doing the calculation (I’ll add it later as an appendix, if requested) it can be seen that ferric iron is almost as good an oxidizing agent as molecular oxygen, and thus has the potential to oxidize NADH.

As regards 2: I know nothing about the activation energy for the reaction of ferric iron with NADH in a test tube, so cannot say whether it would occur spontaneously.

Fe(II) as oxidant

Whether or not a reaction is energetically feasible in which ferrous iron (Fe(II)) oxidizes NADH depends on the redox potential of the half reaction for the reduction of ferrous iron. I cannot find anything for Fe(II)/Fe(I), so perhaps only Fe(II)/Fe(0) is possible, values for which can be found on this Wikipedia page. I leave it as an exercise for the reader to do the calculation.

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  • $\begingroup$ Thank you for your answer, this was very helpful! $\endgroup$ Jan 16, 2023 at 14:16

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