moleculeoftheday | October 24, 2007As I've mentioned several times before, NMR is vital to modern chemistry (and medicine, for that matter).
Nb3Sn, or niobium-tin, is a superconductor that's used in modern high-field NMR (MRI) magnets.
moleculeoftheday | October 23, 2007Mischmetal is a mixture of a some rare earth metals, mostly cerium and lanthanum. The cerium, when finely divided, is pyrophoric - it burns.
When you mix mischmetal with some iron and magnesium oxides, it's a lot more brittle, and you can chip off little flakes, which give sparks. That's your lighter flint.
moleculeoftheday | October 19, 2007Lewisite is nasty stuff - it's a compound of arsenic with two labile chlorines. As I mentioned yesterday, BAL is its antidote.
Lewisite is a chemical weapon from a particularly brutal era in this regard, and you hear about it a lot less these days. However, there's still plenty floating around...
Have a good weekend.
moleculeoftheday | October 18, 2007Lewisite is nasty stuff, which I'll cover tomorrow. Tonight, it's an antidote, which is simply the dithio analogue of glycerine. It enjoys the more colorful name of BAL, or British Anti-Lewisite.
BAL is an antidote to Lewisite. It's one of the few compounds that enjoys the use of a longish common name in the literature because, honestly, it's just such a great name. "British Anti-Lewisite." I much prefer it to 1,2-dithioglycerol or anything like that...
Being a geometrically fortunate dithiol, BAL is an antidote to many other heavy metals. Dunno if anyone pays attention to the chiral center.
moleculeoftheday | October 17, 2007Thiophene is a simple five-membered sulfur-containing heterocycle - it's the sulfur analogue of furan.
It's an interesting heterocycle in its own right but it's probably best known as a contaminant in benzene - almost all the bottles you get a hold of today proclaim they're "thiophene free."
It wasn't always the case, as chemists who were trained more than a decade or two ago will tell you. My advisor in undergrad told me stories about having to remove the thiophene from benzene, which entailed shaking the benzene with concentrated sulfuric acid in a giant separatory funnel. Pressure builds…
moleculeoftheday | October 12, 2007Diazolidinyl urea is a broad-spectrum biocide that is ubiquitous in cosmetics:
It does an admirable job. You'll see it EVERYWHERE once you start reading labels. It tends to be pretty benign, but a contact allergy can result, which makes it hard to find a usable suite of hygeine products for those afflicted.
moleculeoftheday | October 11, 2007DCMU is a simple aromatic molecule, and a pretty specific electron acceptor for the photosystem II protein found in plants. What does this mean?
Electron transfer reactions are important in all of life; plants use it in photosynthesis. Some DCMU will kill your plants nicely, and it's a broad-spectrum insecticide. Similarly, all eukaryotes use proton transfer in their mitochondrion. This is why 2,4-dinitrophenol will help you lose weight like crazy (if it doesn't kill you, which isn't exactly unlikely). Different mechanism, but you're still collapsing a gradient and wreaking havoc on a vital…
moleculeoftheday | October 10, 2007Uracil mustard is a mimic of the RNA component and DNA precursor uracil, and it also has a few reactive ends that can do some damage.
Those chlorines amount to very reactive ends; the idea here is that they're hopefully a little better targeted than generally toxic molecules like the plain old nitrogen mustards. Hopefully, most of your cancer drug ends up in cancer cells, and targeting DNA bases (which they go through like crazy) has been a common strategy.
moleculeoftheday | October 9, 2007Retene is an aromatic molecule that occurs when forest fires happen - burning trees makes it.
The isopropyl is a dead giveaway for a terpene, which are ubiquitous among natural products (and their forest-fire synthesized derivatives).
It makes a picrate, too!
moleculeoftheday | October 8, 2007Picric acid is a simple enough organic acid - its nitro groups withdraw electrons, making it a pretty strong acid for a phenol. However, it's got a slightly darker side: it's to TNT what phenol is to toluene. Those nitroes come with a price.
Picric acid is funny; like raney nickel, it's much more benign under water. For this reason, it's sold that way. Dry picric acid or its metal salts can be quite nasty. From time to time you hear about an old container of the stuff being discovered and the bomb squad coming out.
moleculeoftheday | October 2, 2007Nitinol is an alloy of nickel and titanium. It can do some neat stuff:
Nitinol exhibits "shape memory" - which is an advertising-type name, really. This just means it's not permanently deformable below a critical temperature, above which it will "remember" its shape, upon cooling. For this reason, it's been called a "smart metal" and has been used in dentistry and orthodontia (gotta find something good to hold up to those caramels the kids keep eating...).
Travelling the rest of the week and back next Monday.
moleculeoftheday | October 1, 2007Tin is a nice enough metal, strong and nontoxic enough that for some time we made food-grade cans and foil using it in part. It has a darker side, however: tin pest.
Below a relatively high temperature (ca 13C/55F), "white tin" can convert to a different, more brittle phase, "grey tin." This is called tin pest. Tin, stored cold, will crumble.
Cruelly, such processes are autocatalytic and are difficult to stop once they start (save storing your tin at more friendly temperatures). As the wikipedia article notes, tin pest killed North Pole explorers, Napoleon's men, and destroyed church organs.…
moleculeoftheday | September 28, 2007As 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:
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…
moleculeoftheday | September 27, 2007As I alluded to in a recent entry, NMR has been vital to science in recent decades - it's used in characterizing chemicals, cells, people, textiles - just about anything people have managed to figure out how to get into a strong enough field.
Like many organosilicon compounds, tetramethylsilane has a very low "chemical shift" - this is where its usefulness comes in - TMS has a shift of exactly zero, so you can use it as an internal reference.
A lot of people dislike TMS because it's just another thing you have to get rid of. Fortunately, it's barely a liquid - it boils just above room…
moleculeoftheday | September 24, 2007Pyridine is simply benzene with a nitrogen substituted for one of the CHs:
Such a simple change has myriad effects. The addition of the electronegative nitrogen makes pyridine a good base (it's commonly used in reactions that generate protons to mop up the acid as you go). The same change makes it miscible with water (benzene is only about 0.2% soluble).
Most importantly, however, pyridine stinks. Even at high dilution. It's not a normal piercing chemical scent, either, it has a distinct biological richness that the nitrogenous heterocycles seem to deliver on especially well (witness the…
moleculeoftheday | September 21, 2007Benzophenone is something you probably encounter most often in sunscreen:
It looks like it should be a profoundly fluorescent molecule to the semi-initiated, but for quantum-mechanical reasons, it is instead a phosphorescent molecule and won't emit much at all at room temperature.. If you cool it down to liquid nitrogen temperatures you can see emission from the "triplet state."
You can also make a great solution-phase drying reagent from it - benzophenone ketyl. It's one of the neater things in an organic lab - a boiling purple solution giving you clear, pure, dry solvent.
moleculeoftheday | September 20, 2007The previous entry on cyclohexadiene reminded me of another important piece in some hydrogenations - Raney nickel.
If you have an alloy of nickel and aluminum, and put a chunk of it into a sodium hydroxide solution, you'll end up dissolving the aluminum selectively (generating some hydrogen gas along the way). You'll end up with a little aluminum, mostly nickel, with a high surface area and quite a bit of hydrogen gas adsorbed to the nickel - true to periodic theory, Ni acts much like Pd and Pt with respect to hydrogen.
Raney nickel comes as a slurry in water - if you let it get dry in air,…
moleculeoftheday | September 18, 2007Integral to organic chemistry is hydrogenation - sometimes you need to make a functional group something a little less oxidized. For example, an azide or a nitrile can become an amine.
Often, we just use hydrogen for this! Metals like palladium can work some real magic doing the heavy lifting here. Process chemists hate hydrogen gas, though, and rightly so - everyone knows about its tendency to explode. It's worse, though - most hydrocarbons have a flammable range of about 1-8% in air - any more, and there's just not enough oxygen to support combustion. Any less, and you don't get enough heat…
moleculeoftheday | September 17, 2007While taking organic chemistry, most people end up learning about octane ratings. If gasoline burns too fast, engine knock occurs. A number of factors influence this, the easiest of which to appreciate is branching. By definition, so-called "isooctane" (the structure of which I didn't even realize was the below until today) has an octane rating of 100.
n-heptane has one of 0. 87% isooctane, 13% n-heptane would give you an octane rating the same as regular gas (but wouldn't make very good gasoline, for reasons to be discussed another time...
High octane fuels won't give you better mileage or…
moleculeoftheday | September 13, 2007Strychnine is a well-known poison and detective novel trope with a moderately low LD50 (ca 10mg). You find it more often in NMRs these days.
NMR jocks love strychnine for some reason. It is a pretty good example of a molecule with a hard-to-solve structure that NMR quickly dispatches - see this PDF for some background. I don't get why it always seems to be around in NMR rooms, though - there's the rack of about 40 standards and forgotten samples (who is leaving all these tubes behind?), one of which contains enough strychnine for a decade of Agatha Christie novels - these are those…