How do nutrients and pharmaceuticals decompose?

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How do nutrients and pharmaceuticals decompose?

Postby Jorpho » Thu Feb 25, 2016 5:40 am UTC

I've been idly pondering those famous examples of fast-food meals that look much the same as they did to begin with after sitting around for a couple of years. Many will quickly tell you that once they dry out, they aren't a particularly hospitable environment for bacteria and thus there is no particular reason for anything else to happen.

So I was thinking: what exactly happens to those big ol' organic molecules over time, as long as they're not exposed to much else other than the atmosphere? There's lots of talk of pharmaceuticals and herbal preparations losing their "potency" over time, but are there common decomposition pathways?

I guess "oxidative decomposition" is the obvious answer. For some reason the first thing to come to mind was ascorbic acid, which wikipedia helpfully points out decomposes into a bunch of miscellaneous (and apparently harmless?) smaller acids. Is that fairly standard?

The bigger question is if you could end up with anything dangerous. I guess you can't expect to spontaneously generate strychnine or atropine or whatnot, but it seems to me cyanide or formaldehyde could be feasible. But then, I would think that those would already be reactive enough to react with some other decomposition product rather than accumulate on their own – and that anything likely to break down into something dangerous over time would be just as likely to do so during ordinary human metabolism anyway, and thus wouldn't be safe to begin with.

We never really covered anything like this in chemistry class back in the day.

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Re: How do nutrients and pharmaceuticals decompose?

Postby p1t1o » Thu Feb 25, 2016 9:03 am UTC

Looks like you’ve got most of it covered to be honest.

Another mechanism of decomposition is UV light, if the substance is exposed to sunlight, which can break certain bonds quite readily. This is why you often see medicines and such coming in dark brown bottles.

Larger, more complex molecules are generally, but not always, quite fragile and just by virtue of being at room temperature, random fluctuations can break bonds too, contributing to the slow loss of potency of some substances.

Some substance, which may or may not be in solid form, also depend on the presence of water for their structure, if they were to dry out, this can "denature" some larger molecules as well.
Last edited by p1t1o on Thu Feb 25, 2016 11:19 am UTC, edited 1 time in total.

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Re: How do nutrients and pharmaceuticals decompose?

Postby Neil_Boekend » Thu Feb 25, 2016 9:58 am UTC

Some medicine is packaged in aluminium sealed strips: no bacteria, no oxygen and no UV light. Still it decomposes. AFAIK many large and complex molecules tend to fall apart after a while.
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Re: How do nutrients and pharmaceuticals decompose?

Postby thoughtfully » Fri Feb 26, 2016 1:07 am UTC

There's also volatile compounds that simply evaporate, say with fresh herbs and the like.
Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.
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