I've learnt in chemistry that gaining electrons means reduction, while losing electrons means oxidation. But why is it in Biology textbooks I sometimes come across the term gaining hydrogen??
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$\begingroup$ An example would be nice. It's all about context. And they are confusing terms. An oxidizing agent gets reduced when oxidizing something else etc. $\endgroup$– AliceD ♦Mar 19, 2015 at 7:58
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2$\begingroup$ Additionally I think this topic is better suited at chemistry.stackexchange. $\endgroup$– Chris ♦Mar 19, 2015 at 9:04
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2$\begingroup$ No only biology, this notion is there in organic chemistry as well. Remember reduction of alkenes? One of the most common 'reducing agents' used in organic chemistry is LiAlH₄ $\endgroup$– WYSIWYGMar 19, 2015 at 11:44
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$\begingroup$ So in a system of two compounds participating in a redox reaction: an oxidizing agent accepts electrons, and thus the oxidizing agent becomes reduced, and the other compound which loses electrons becomes oxidized. A reducing agent donates electrons, itself becomes oxidized, and reduces the other compound. In lots of biological reactions, you can stylize the gain or loss of hydrogen as the gain or loss of an electron, because hydrogen generally donates its sole electron to any given bond. $\endgroup$– CKMMar 19, 2015 at 22:06
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$\begingroup$ The definition of electron acceptance and donation came later. Previously oxidation was just addition of oxygen and reduction meant removal of oxygen/addition of hydrogen. $\endgroup$– WYSIWYGMar 20, 2015 at 11:43
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1 Answer
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Hydrogen can accept electrons or donate them, so it can get a bit confusing. For instance, hydrogen donates electrons from a reducing agent. For example, in biology, consider cellular respiration. A co-factor will carry electrons often by reducing an atom with a nitrogen.
The nitrogen atom on the Pyridine group has an oxidation state of +1. When it picks up a hydrogen, to become NADPH, the oxidation state will go to 0 by gaining electrons brought by the hydrogen. Although the hydrogen doesn't bond to the nitrogen directly, it breaks the double bond on the para carbon (The carbon on which the new hydrogen is attached) at the top of the ring, and thus distributes the electrons to the nitrogen.
EDIT - Hydrogen comes from some reducing agent, not a free hydride I'm sure.
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2$\begingroup$ Are you able to annotate the drawing of NADP so that I can follow your explanation better? Thanks :) $\endgroup$– TeigeMar 19, 2015 at 10:33
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$\begingroup$ I agree with @Teige - a reaction instead of a single molecule would help. $\endgroup$– AliceD ♦Mar 19, 2015 at 12:40
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$\begingroup$ There is no Hydride-Anion present in any living cell. $\endgroup$– Chris ♦Mar 19, 2015 at 16:38
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$\begingroup$ Oxidation state and charge are not the same thing. The pyridine in NAD+ is positively charged, but that does not mean that it is +1 oxidation state. $\endgroup$ Mar 19, 2015 at 19:57