TSPA (What about the biochemists?)

As I noted in a recent entry on strychnine, NMR is important. Sometimes reference compounds like yesterday's molecule, TMS, will help you out.

This is all well and good for most organic chemists - TMS will go into just about any organic solvent. It won't work so well in water, however, so there's a second, water-soluble chemical shift reference: enter TSPA:

i-b5fa54ab091a07d832fe3739ef15a4f7-tspa.gif

TSPA has a chemical shift of 0, just like TMS, and it's soluble in water - good for biochemists, who have to work in water (with at least a little of its deuterated buddy).

TSPA is probably even more controversial than TMS - it won't evaporate and you're left to other methods to remove it. At the risk of attracting the ire of the organic jocks out there, biomolecules tend to be much more labor-intensive to purify, so once you've sweat out a few months of your life getting a protein or nucleic acid scrupulously clean, you're disinclined to add ANYTHING that doesn't need to be there.

The "reference problem" is a little trickier in water, too, because biochemists often must use elaborate solvent-suppression schemes that utterly obliterate your (potential reference) solvent peak. See here for a (pdf) list, including my favorite, the whimsically named WATERGATE.

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Isn't the shift 0 *by definition*, just as TMS is also 0 *by definition*, or a mole is the number of particles in 12.0000000000000000000000 (etc) g of 12C ???

Of course, there are also the methylenes, which don't resonate at 0 as well (http://dx.doi.org/10.1021/jo971176v)