What's that Crud in My NMR Sample?

Scene:

The reaction finished in 20 minutes by TLC. You grabbed a quick aliquot for LCMS; one peak! Quickly, you quenched, extracted, perhaps pushed through a silica plug for good measure. After concentration, a gorgeous white powder formed, so you pulled high vac for 20 minutes and rushed down to "get your proton on." But, darn it! Still wet with traces of, well, something...

Friends, has this ever happened to you? Trace impurities in otherwise perfect spectra lead to much head-scratching and SI docs labeled "final product_spectrum 5." 

The three papers linked to this post should help.

• Nudelman, Gottlieb, Kotlyar - 1997. The one that started it all.

• Fulmer, Miller, Sherdan, Gottlieb, Nudelman, Stoltz, Bercaw, Goldberg. Updated for 2010, with an organometallics bent. Now includes gases!

• Babij, McCusker, Whiteker, Canturk, Choi, Creemer, DeAmicis, Hewlett, Johnson, Knobelsdorf, Li, Lorsbach, Nugent, Ryan, Smith, Yang, 2016. The new kids on the block: greener solvents for process chemistry and scale-up. *Update (23 Feb) - A kind commenter points out that #3 is free to download under the ACS AuthorChoice program. Sweet!

The new chart offers recommendations (colored arrows) based on Chem21 assessments of environmental impact, safety, and toxicity. Shown above are chemical shift tables (1H) in deuterated chloroform, acetone, and dimethyl sulfoxide.

If I were joining a synthetic lab this year, or starting an internship / work-study, I'd download 'em all and thumbtack liberally to the back of my bench. Guaranteed utility.

Did Someone Say Pink Slime?

Face it: School lunches have always looked a bit dodgy. Thick, overcooked casseroles. Spongy grey sandwich patties. Slabs of greasy pizza. Thus, when industrial beef producers suggested one more (cheap) processed ingredient, cash-strapped school districts gladly agreed.

Source: theblaze.com

So began the "Pink Slime" fiasco (picked up by the msnbc* Vitals blog, NPR's The Salt, and, of course, our friends at change.org). What is it? If you come from the ranch side of the equation, you refer to pink slime as lean, finely-textured beef (LFTB). Connective tissue and scraps from industrial butcher plants are mixed with ammonia gas or ammonium hydroxide, which degrades the protein matrix of collagen and elastin into component amino acids, and sterilizes the resulting goopy mass against microbes like E. coli. The final product can be blended into hamburger and other "finished" meat products.


So, what are the arguments against this bio-sludge (besides appearance)? First, consider nutrition: there's less in pink slime than in other meat products. There's a higher fraction of insoluble protein, which may be hard to digest, but on the plus side, there's less fat in LFTB than in standard ground chuck. Despite its off-putting look, the final material may actually have a composition closer to soy protein than beef.

pH meter
Source: General Tools

Second, how much ammonia is required? Levels high enough to raise the goop's pH to ~9 seem to kill all pathogens, but batches tested by the NYT back in 2009 showed pH levels as low as 7.75. So what? Well, since pH tracks logarithmically, that corresponds to 18x less total base, which might reduce any ammonia odors but correlates to increased bacterial contamination. 


Finally, it's all about the labeling. A generation of parents accustomed to fighting high-fructose corn syrup (oops, "corn sugar"), artificial dyes, and allergens in processed foods would prefer including ammonia in the final ingredient list. However, manufacturers - and the USDA - consider this a production step, not a discrete additive like ammonium phosphate (leavening agent) or ammonium chloride (licorice, baked goods). 

Mmm...beef.
Source: picturedepot.com

Time will tell if the public uprising surrounding pink slime will lead to cancellation of school lunch contracts. But processed meat products aren't going away anytime soon: consider chicken nuggets, hot dogs, sausages, or scrapple (if you're into that). Or the ubiquitous gelatin, made from bones and cartilage, which gives the gummy to bears and puts the gel in Jell-O. 


*Chemophobia update - Ye Gods, msnbc. Way to scare everyone. How about a scientific fact check? Ammonia is not a "pink chemical" - it's colorless, and you don't use it to leaven cakes (see ammonium phosphate, above). Backtracking to the original report, we see mention of flammability and building bombs . . .really? Ammonia is much more commonly used to clean floors and windows.