why is arsenic toxic to living organisms

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Offline freecw

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why is arsenic toxic to living organisms
« on: 07/12/2010 19:02:49 »
hey I was just wondering why is arsenic toxic to all living  organisms? I wonder because I just read an article about a newly discovered bacteria that uses arsenic instead of phosphate and my biochem ta thought this was cool but I don't see why. arsenic has the same number of valence electrons as phosphorus so it should behave in similar ways I thought? it is a little bit bigger but that shouldn't make a difference between killing you and being one of the most used element in the body. (sorry about any spelling errors, writing this on my itouch in anatomy class)

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Offline Bored chemist

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why is arsenic toxic to living organisms
« Reply #1 on: 07/12/2010 21:00:13 »
While phosphate does act quite a lot like As there are differences.
Notably, it's all very well having a phosphate replaced by arsenate but what happens when the the oxygen levels fall and the As(V) gets converted to As(III)?
Also As(III) compounds tend to react with sulphur compounds and some of those are very important to the body.
It's the latter effect that is responsible for most of the toxicity of As compounds.
Werdly, the toxicity of As can be offset to a degree by Selenium compounds, which are normally rather toxic.
The As and Se bind together very strongly and the resulting compound is too inert to be toxic.
Don't try that at home.
It's a lot safer to use sulphur compounds to try to offset As toxicity.
http://en.wikipedia.org/wiki/Chelation_therapy
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Offline Chemistatwork

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why is arsenic toxic to living organisms
« Reply #2 on: 10/12/2010 16:49:50 »
While phosphate does act quite a lot like As there are differences.
Notably, it's all very well having a phosphate replaced by arsenate but what happens when the the oxygen levels fall and the As(V) gets converted to As(III)?
Also As(III) compounds tend to react with sulphur compounds and some of those are very important to the body.
It's the latter effect that is responsible for most of the toxicity of As compounds.
Werdly, the toxicity of As can be offset to a degree by Selenium compounds, which are normally rather toxic.
The As and Se bind together very strongly and the resulting compound is too inert to be toxic.
Don't try that at home.
It's a lot safer to use sulphur compounds to try to offset As toxicity.
http://en.wikipedia.org/wiki/Chelation_therapy

Yes he is correct. It's always a case of stable>unstable ions when used biologically. For the second part of his post it's a case of fighting fire with fire. Or in this case poison with poison. Different compounds have different affinities to certain types of poisons and is being used effectively to form inert compounds in the body that are harmless.