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The better reducing agent ineach of the given pairs:
NADH/H2O
UQH2/FADH2
Cyt c (reduced)/Cyt b (reduced)
FADH2/ NADH
NADH/ FMNH2
Introduction:
Reduction is a process of the gain of H+ (hydrogen ions) or the loss of O (oxygen), whileoxidation is a process of the gain of oxygen or the loss of hydrogen. Oxidizing agents add an oxygen to another substance or remove a hydrogen from a substance. Reducing agent, sn the other hand, either add a hydrogen or remove an oxygen from a compound.
Explanation of Solution
Better reducing agents out of the mentioned substances in the given pairs of compounds are discussed below:
NADH/H2O: NADH (reduced Nicotinamide adenine dinucleotide)is a better reducing agent because water molecule is considered weak as both, oxidizing as well as reducing agent, as it can reduce only a limited number of substances, whereas NADH can reduce a variety of substances. Moreover, the redox potential of NADH is lower as compared to the water molecules.
UQH2/FADH2: UQH2(Ubiquinol-10-reduced) is a better reducing agent because it can easily propagate electrons from complex I. Moreover, its redox potential is significantly lower than the FADH2 moiety.
Cyt c (reduced)/Cyt b (reduced): Cyt b (Cytochrome b), in its reduced form, is a better reducing agent because it can easily liberate electrons to reduce cytochrome a and has a much lower reduction potential than Cyt c.
FADH2/NADH: NADH (Nicotinamide adenine dinucleotide) is a better reducing agent than FADH2 (Flavin adenine dinucleotide) because of its lower reduction potential value and the ability to easily liberate electrons.
NADH/FMNH2: FMNH2 (flavin mononucleotide) is a better reducing agent than NADH ((Nicotinamide adenine dinucleotide) because of the fact that it can easily donate electrons and has a considerably lower reduction potential.
Therefore, it can be concluded that the ability to act as a reducing agent depends on the intricate reduction potential of a chemical species. In case a chemical species has a high reduction potential, it has a strong affinity for electrons, while a low reduction potential facilitates easy liberation of electrons. The liberated electrons can be used to reduce other molecules and therefore, a low reduction potential value confers higher reducing capabilities.
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