It seems our most common everyday O2 molecule happens to be a paramagnetic one (see https://en.wikipedia.org/wiki/Oxygen).

But, does this have a biological relevance as well? In other words, Do any chemical processes occurring within the physical volume of any entity considered "living" depend in any way, shape, or form on oxygen's paramagnetic properties?

(It seems to me the answer would be "no", but I am no expert in this field!)

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    $\begingroup$ This Q is too broad. $\endgroup$ – AliceD Feb 22 at 15:04
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    $\begingroup$ Biology isn't a very narrow field either ; ) Would the following phrasing be any more specific: Do any chemical processes occuring within the physical volume of any entiy considered "living" depend in any way, shape, or form on oxygen's paramagnetic properties? $\endgroup$ – ManRow Feb 22 at 21:03
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    $\begingroup$ The answer is either yes or no; I don't think this is too broad. $\endgroup$ – canadianer Feb 22 at 22:51

The answer to your re-phrased question

"Do any chemical processes occurring within the physical volume of any entiy considered "living" depend in any way, shape, or form on oxygen's paramagnetic properties?

is an emphatic 'yes', and this answer may be substantiated with a single word: haemoglobin.

Pauling and Coryell discovered in 1936 that the oxygen in both oxy-haemoglobin and CO-haemoglobin is diamagnetic, and I quote from the last paragraph of that great paper:

It is shown by magnetic measurements that oxyhemoglobin and carbon-monoxyhemoglobin contain no unpaired electrons; the oxygen molecule, with two unpaired electrons in the free state, accordingly undergoes a profound change in electronic structure on attachment to hemoglobin.

This result has 'stood the test of time' and is a key observation in explaining at a molecular level the allosteric and cooperative properties of haemoglobin. IMO, it is one of Pauling's great observations, and illustrates his phenomenal powers of deduction.

As Pauling points out, Faraday also investigated the magnetic properties of haemoglobin and recorded in his notebook 'Must try recent fluid blood'.

To again quote Pauling and Coryell :

If he had determined the magnetic susceptibilities of arterial and venous blood, he would have found them to differ by a large amount (as much as twenty per cent for completely oxygenated and completely deoxygenated blood); this discovery without doubt would have excited much interest and would have influenced appreciably the course of research on blood and hemoglobin

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    $\begingroup$ Magnetic properties usually do not play a significant role in chemical reaction unless some external magnetic field is applied. The magnetic properties are resultant of the chemical properties and it is the chemical properties that really matter. And how would the biochemistry of oxygen transport be affected because of the magnetic properties of oxygen? The only biological process that I am aware of that is driven by magnetism is magnetotaxis and it involves the ferromagnetic substance magnetite. $\endgroup$ – WYSIWYG Feb 25 at 12:57
  • $\begingroup$ I am not in any way arguing that magnetic properties are directly responsible for the allosteric properties of Hb, merely that the change in magnetic properties of oxygen on binding to Hb shows a major change in the electronic structure of oxygen bound to Hb. And of course, (as Pauling first suggested) binding of oxygen to heme results in an increased affinity of other sites on Hb for oxygen (by subtle changes in salt bridge interactions between subunits?) . When I saw the question, I immediately thought 'Pauling'. $\endgroup$ – user1136 Feb 25 at 14:32
  • $\begingroup$ Ref for Pauling being the first to give a structural explanation for cooperative binding: researchgate.net/profile/Andrea_Mozzarelli/publication/… $\endgroup$ – user1136 Feb 25 at 14:35
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    $\begingroup$ I got your point but I was arguing that the paramagnetism of dioxygen per se does not play any role in any of its biochemical reactions. The chemical properties that cause paramagnetism also affect some of the reactions of dioxygen. So even if those two properties are correlated there is no cause-effect relationship between them. See my answer. $\endgroup$ – WYSIWYG Feb 25 at 14:39

It sounds a bit like chem exam question to be honest... Or at least the answer does... namely that O2 being paramagnetic creates a "spin barrier" that prevents most organic compounds from reacting fast with atmospheric oxygen:

The magnetic properties of O2 are not just a laboratory curiosity; they are absolutely crucial to the existence of life. Because Earth’s atmosphere contains 20% oxygen, all organic compounds, including those that compose our body tissues, should react rapidly with air to form H2O, CO2, and N2 in an exothermic reaction. Fortunately for us, however, this reaction is very, very slow. The reason for the unexpected stability of organic compounds in an oxygen atmosphere is that virtually all organic compounds, as well as H2O, CO2, and N2, have only paired electrons, whereas oxygen has two unpaired electrons. Thus the reaction of O2 with organic compounds to give H2O, CO2, and N2 would require that at least one of the electrons on O2 change its spin during the reaction. This would require a large input of energy, an obstacle that chemists call a spin barrier.

(quote from McQuarrie and Simon's (free) textbook Physical Chemistry: A Molecular Approach).

  • $\begingroup$ And by the way, there also exists a variety of singlet oxygen (1Σ -- second excited state) that is not paramagnetic, but is fairly unstable a room temperature. $\endgroup$ – Fizz Feb 23 at 7:44
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    $\begingroup$ Interesting, so not exactly out of some kind of interaction with magnetic fields of any sort (which is what I usually think of regarding paramagnetism), but rather due to the quantum effects (such as this "spin barrier") that just also happen to give rise to "paramagnetism" as well. It seems the answer would then be "no", although the underlying causes of paramagnetism do give rise to other more "useful" properties (such as inhibitions of chemical reactivity) however. $\endgroup$ – ManRow Feb 23 at 8:30
  • $\begingroup$ I never 'bought' this argument, as oxygen bound to haemoglobin (oxy-Hb) is diamagnetic $\endgroup$ – user1136 Feb 23 at 15:24
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    $\begingroup$ @ManRow you are right. Unless there is an interaction with the applied magnetic field, the magnetic properties per se do not have any effect on the chemical reactions. $\endgroup$ – WYSIWYG Feb 25 at 12:58

According to my reasoning, the answer is no.

Bulk magnetic properties are a resultant of the atomic/molecular (chemical) properties and chemical reactions are usually not dependent on the magnetic properties per se. Magnetic properties can have a role if:

  • There is an externally applied magnetic field (https://chemistry.stackexchange.com/q/24507/5295). Magnetotaxis in some bacteria involves signalling by microcrystals of magnetite and greigite that guide the bacterial locomotion in response to the geo-magnetic field.
  • Some of the reactants or the components of the reaction center exert magnetic field (ferromagnetic materials, for example). Herve et al (1984) showed that incorporation of magnetite particles increased the yield of some intermediates (light absorbing transients) during the photoreduction of benzophenone.

In any case I haven't come across any research that states that the paramagenetism of molecular oxygen is a factor in any biochemical reaction. As pointed out in the other answer, the stable triplet state of dioxygen is slightly less reactive compared to the singlet state. The paramagnetism that results because of the triplet state is not the cause of the lower reactivity. In other words, there is no cause and effect relationship.


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