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But I’m just getting home. See you tomorrow.

(hopefully, this week is a bit much)

Dihydroxyacetone is a very, very simple sugar. It is produced by the splitting of hexoses (glucose and fructose) in glycolysis. Most people are interested in it, though, for its role in sunless tanners:

Many sugars, DHA included, can participate in a reaction called the Maillard reaction. In this reaction, sugars react with amino acids and proteins. This can result in brown pigments. DHA (sugar) reacts with skin proteins (amino acids/proteins), providing a rich brown pigment, if you’re lucky, or an orange pigment, if you’re not.

The same reaction responsible for sunless tanning results in meat browning (and flavor). Bizzare.

Night!

Inspired by yesterday’s entry, which wasn’t really a molecule proper, today’s entry is about the diamminesilver (I) complex, better known as Tollens’ Reagent. In practice, this is usually generated by taking a solution of silver (I) nitrate and adding a drop of NaOH solution. This generates some Ag₂O, or silver (I) oxide. Addition of aqueous ammonia will dissolve the silver oxide, generating the diamminesilver (I) complex. Why do we care? Read the rest of this entry »

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.

Back tomorrow!

There sure are a lot of you. Thanks for coming, I am glad people seem to be enjoying the site for the most part!

Monday, I remarked that cyanoacrylate (superglue) adhesives are used by some forensic scientists to expose fingerprints on objects. I actually hadn’t heard of the procedure before and was eager to try it out. As anyone who has known the pleasure of my company for very long can attest, I am not the most patient person in the world. It is with great pleasure that I bring you yet another MOTD experiment, with more camera phone quality pictures!

The general idea here is that cyanoacrylate adhesives are volatile. The most likely cyanoacrylates you’ll encounter are the methyl and ethyl esters, the boiling points of which people seem to disagree on a bit. I decided to just try using a bath of hot water from my faucet, which is about 60C, or 140F, and hoped that would vaporize enough adhesive. Superglue stinks quite a bit, so you know it’s got at least an OK vapor pressure.

I then had to find a) a developing chamber and b) some stuff to get fingerprints on. I’d read that light surfaces were bad for this, since white-on-white was hard to see, so I got whatever I could find that was opaque and in a variety of colors.

The developing chamber ended up being an old pipet tip box (I had intended to use one of those disposable tupperware/gladware containers, but they were occupied by a few, ahem, ongoing experiments with sourdough starters). For fingerprinty objects, I briefly manhandled a Gatorade cap, a Listerine Freshstrips box, and my old Blockbuster Rewards card. My usual clumsiness, compounded by cheap Chinese-manufactured superglue tubes, had resulted in an unfortunate accident which temporarily rendered my right hand incapable of leaving fingerprints, so I had to use old lefty. In the box these went, with about half a mL of superglue squirted into each of two corners. The whole mess went into my science breadpan, filled with an inch or so of hot water. I left it to float for half an hour or so. The image is right before I took it out:

After taking it out, in a rare case of before-the-fact common sense, I put the whole thing in the fridge for about 10 minutes to cool down. This way, I wouldn’t be greeted by a cloud of noxious cyanoacrylate fumes, aching to polymerize on my eyes and sinuses. Below, you can see that it worked, sort of. The fingerprints are actually quite clear in person. Mostly on the Blockbuster card, but you can see a bit on all three. It is probably for the best that I don’t have high-resolution shots of my fingerprints online.

If you haven’t handled much superglue, you might be inclined to think the exposed fingerprints are a powdery, flaky coating based on appearances. It’s not. They are just as hard as any other cured superglue. The exposure is actually a negative cast of my fingerprints, in polycyanoacrylate! This works because your fingerprints contain enough bases (water, certain basic parts of proteins, maybe even certain fats) to initiate superglue polymerization. Let me know if you try it! See you tomorrow.