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I'm writing a research paper on psilocybin. I need to know the correct chemical structure. When I look online it it shows different ones. There is one with two OH molecules attached to the phosphorous and there is one with one OH and one O- attached to the phosphorous. There is also one that I found with a O+ attached to the phosphorous. Are they all they same or are they interchangeable? Are there different ones? I can't find a clear answer. Any help is greatly appreciated.

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Clearly, it cannot be an $\ce{O+}$, as that would require a triple bond to the oxygen, making the phosphorus in the middle quite unhappy.

Of the other two alternatives, both are correct -- however, it matters what environment you're considering the molecule. In neutral or slightly basic conditions, it will be an $\ce{O-},$ while in slightly acidic conditions, it will be an $\ce{OH}.$

Let me know if you need any clarification on why this is the case -- I have no idea what your level of knowledge is.

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  • $\begingroup$ Thank you for the prompt answer. My knowledge is fairly low. Can you tell me which it would be in it's natural form? Why would they differ due to ph? $\endgroup$ – Alex Jun 29 '16 at 4:19
  • $\begingroup$ Since this is a natural product (found in mushrooms), most likely it is found primarily inside of cells, which have a close to neutral pH. Thus, it is likely found in its deprotonated form (the one with the $\ce{O-}$). The reason that pH matters is because the difference between $\ce{OH}$ and $\ce{O-}$ is a measly little $\ce{H+}$ (notice that regular hydrogen has one proton and one electron, so $\ce{H+}$ has lost its electron, and is simply a proton - hence the word de- proton -ated). pH is just a fancy way of measuring the amount of $\ce{H+}$ found in a solution, so that's why pH matters. $\endgroup$ – kosyumote Jun 29 '16 at 5:17
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    $\begingroup$ This answer completely neglects, that it is a zwitterion, and that both structures will be present at all times. The degree of protonation/deprotonation is of course pH dependent. Resonance of the phosphate group is also important. $\endgroup$ – Martin - マーチン Jun 29 '16 at 7:11
  • $\begingroup$ I know this... but I suspect that the original question was asked with no intention of understanding the actual chemistry regarding the phosphate group, but rather to find the correct structure to put into a report of some sort. While the degree of protonation on both the phosphate and the amino varies, the "most natural" form is indeed the zwitterion. Of course, there will be 4 different structures in equilibrium with each other (ignoring the second deprotonation of the phosphate), but the one most prevalent at physiological pH is the zwitterion. $\endgroup$ – kosyumote Jun 29 '16 at 14:52
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    $\begingroup$ pH and pKa are the measure of the amount of dissociation, or H+ ions. At pH7, there are 0.0000001 H+ ions for each molecule of H2O. The pKa of water is 14; at pH 14 half of the water will be deprotonated. The pKa of psilicybin is around 6.5; at pH 6.5 half of the psilocybin will be dissociated (O-). In neutral conditions (pH7) the amount of dissociated (O-) psilocybin will be higher than the "associated" (OH) psilocybin. Cytosolic pH of fungal cells is about 6.95. At pH 8, roughly 90% of psilocybin will be in the O- form. At ph 10.4 ~50% of the dimethylamine nitrogen will be deprotonated. $\endgroup$ – Ben Welborn Jun 29 '16 at 21:25

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