Many of you have this in your homes. If you have those slow-dissolving tablets that leave a bleachy smell in your water, there’s a good chance you have N-chloro-N-bromo-dimethylhydantoin in one of those giant tablets in your toilet tank.

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As we’ve discussed, gold is among the so-called “noble metals,” named as such for their lack of reactivity. Gold won’t dissolve in concentrated solutions of nitric acid or hydrochloric acid. Both are strong acids, and nitric acid is a potent oxidizer, which tends to help quite a bit in dissolving metals. It turns out chloride and an oxidizer are the necessary and sufficient conditions to dissolve gold.

Enter aqua regia, which is just a mixture of the two acids (providing both the chloride plus the oxidizer). Typically you use ~25% concentrated nitric acid and ~75% concentrated hydrochloric acid, but other proportions are known (the other one I see some people use is 75/25, which I think is quite a bit nastier.

Like so many colorfully named classics, aqua regia derives its name from alchemy. As you have no doubt figured out, it is from the Latin for “royal water,” from its gold-eating superpowers. It was discovered in 800 AD by the alchemist Abu Musa Jabir ibn Hayyan.

One unique thing about aqua regia is that it decays after being mixed up, so you always have to make it fresh. The nitric acid slowly works on the chloride ion, generating chlorine gas, leading to a pleasant swimming-pool aroma if you just catch a whiff, or choking fumes if you get more than that (Chlorine is really a violent poison in much higher concentrations than you run into at the pool, and it has been used as a war gas).

Also generated is the toxic nitrosyl chloride (NOCl), which is a beautiful reddish-orange. So you mix concentrated nitric acid (colorless, or maybe tinted just barely yellow, but mostly clear), concentrated hydrochloric acid (colorless), and you get a red-orange, bubbling, smelly solution that can dissolve gold. Can you imagine what the alchemists must have thought of this?

My very favorite story about aqua regia is this: during World War II, a Hungarian chemist living in Denmark, George de Hevesy, dissolved two fellow scientists’ Nobel Prizes in aqua regia literally as the Nazis stormed into Copenhagen so they wouldn’t be stolen (he assumed, correctly, that the Nazis would just leave the chemicals alone). After the war, he recovered the gold, and the Nobel committee recoined the prizes. You can read more about it here.

See you tomorrow.

Here is one with which many readers will be acquainted first hand: nicotine. Named after Jean Nicot, tobacco booster extraordinaire, nicotine is an alkaloid that occurs in the whole nightshade family, of which tobacco is a member. Typically people will give the structure on the left, below.

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This is one of those molecules that everyone who does chemistry has heard of, but you rarely hear about it outside chemistry and engineering. HF is a member of the acids of group VII - that is, HF, HCl, HBr, and HI. If you paid attention in general chemistry, you know all Bronsted acids dissociate into their conjugate base and a proton, that is, HX -> H⁺ + X^-. This is the definition of a Bronsted acid - I am only saying Bronsted to be technically correct since there is another type of acid that we won’t get into today that doesn’t have to involve protons at all.

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99 years ago, a Japanese researcher was looking into some puzzling stuff. A broth of kelp, when boiled down, yielded some brown crystals that tasted like, well, essence of savoriness. “Savory” is one of those flavors that is hard to pinpoint - for salty, sweet, sour, bitter, we have archetypes - sugar, sodium chloride, lemon juice, and alkaloids, which you don’t taste on their own very often. As Barry Sharpless noted, he won’t taste a compound with a nitrogen atom in it - these are the bulk of our alkaloids, many of which are psychotropic (not nearly all, though). The best everyday example of a bitter compound I can think of is tonic water, which is bitter due to the alkaloid quinine.

Anyway, savoriness, or “umami,” as he put it, is hard to pinpoint. Those crystals he found came close, which were those of the much-maligned monosodium glutamate, or MSG:

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Lead is one of the most familiar heavy metals to people. Disquieting is the fact that so many people haven’t handled it because of all the concern about its toxicity. Fishing weights are increasingly being replaced with heavy but less-toxic alternatives, like bismuth.

If you’ve never handled lead, please try it. I worry that it will go the way of mercury and you just won’t be able to get it in ten years. I can get all sorts of weird stuff in a chemistry building, but you don’t really have that luxury. It is soft and magic. If you have it in bar form you can bend it like Superman. It will make your week. Just wash your hands afterwards, and don’t store it in the butter dish.
Enter one of my heroes, Theodore Gray, with his Periodic Table Table. His entry on lead does the element more justice than I will. He also notes a few places you can get lead: hardware stores, fishing stores, and Wal-Mart. With lead’s wide use in plumbing, it probably won’t go away as quickly as I claim (the symbol for lead, Pb, comes from the latin plumbum. as you might expect, this is where the word plumbing comes from).

Lead is a lot like mercury - toxic, but not so terrible. You can handle lead pretty freely - for instance, I’d hold lead in my hands, not mercury. You can dent it with your fingernail. It’s surprisngly heavy, but not as heavy as gold or tungsten. Like mercury, the soluble compounds are much worse. One is Lead (II) acetate:

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Here’s a quacky one for you. If you lived through the 70’s, you remember this as Laetrile. Amygdalin is a cyanide compound found in almond, peach pits, and some other stone fruits. Fun fact: “amygdala,” like in your brain, comes from the same Greek root as amygdalin. Here, it describes the source of the compound, in “amygdala,” it describes the shape of the structure. Sort of like naming the pituitary “Mr. Peanut,” then translating it into a dead tongue for some added class.

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Here’s a neat and weekend-appropriate one. I’ve alluded to the fact that your body processes small amounts of endogenous alcohol in the course of metabolism. As such, you have evolved some enzymes to process ethanol. The enzymes are meant for ethanol, since that’s what organisms saw for the most part in the course of evolution. As we’ve seen with drugs and poisons, though, other molecules can fit just fine into the active pocket of an enzyme and it can do its business on them, too. Sometimes this works in your favor, sometimes not. In the case of alcohol, it’s great. If you didn’t have a processing enzyme, it would be much more harmful than it is; it would have to wait around to pass through your urine (it could fit into a few other enzymes, but not very well; I believe this is the major alternative pathway).

What happens is your body takes alcohol and begins to oxidize it. Ethanol turns into acetaldehyde, which turns into acetic acid, which your body knows how to handle fine. The ethanol to acetaldehyde step is catalyzed by the enzyme alcohol dehydrogenase and requires one NAD+ (nicotinamide adenine dinucleotide, an endogenous oxidizing agent involved in glycolysis. The acetaldehyde to acetate step also requires NAD+ and is catalyzed by aldehyde dehydrogenase.
Relative to Anglos, many Asians have a paucity of aldehyde dehydrogenase, causing acetaldehyde to build up when ethanol is consumed. This causes the flushed face seen in many Asians after even moderate alcohol consumption. In all populations, NAD+ is limiting; your body simply does not have that much. It is regenerated, but slowly, so even after moderate alcohol consumption, NADH (the metabolite of NAD+) to NAD+ regeneration is the limiting step in the alcohol to acetate cycle. This is poorly understood — understandably. Not many research dollars get routed to hangover prevention, since it’s essentially a nuisance and considered a “disease of excess.”
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GHB stands for gamma-hydroxybutyrate. It has received buckets of terrible press in recent years that would certainly have resulted in lawsuits in both directions if it was a patented pharmaceutical. Let’s take a look at the structure, then we will take a look at the days of yore when GHB was a blameless little molecule you bought at GNC (or you could get from Aldrich for organic synthesis). Then, we’ll take a look at the subsequent demonization and where we stand today.

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Tetraethyllead is another one of those organometallic compounds that is absolutely bizzare unless you work with them yourselves. It’s got lead in it - in fact, it’s over 60% lead by weight, but it’s a clear, lipophilic liquid. It has the effect of decreasing the tendency for gas to combust prematurely in an engine, or “knock.” That is, when added to gasoline, it increases its octane rating. This is all an octane rating is - a measure of a fuel’s propensity to prevent knock. 87 is more likely to knock in a high-compression engine than 91.

Here is the structure of tetraethyl lead:

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