This is a bizzare molecule. As I was discussing yesterday, structure-odor relationships are tricky. One very reliable predictor, though, is that the compounds of the later chalcogens (that is, compounds containing a sulfur, selenium, or tellurium atom) stink. Sulfur being the second most common member of this group after oxygen, this usually means thiols.

Thiols have a prodigous appetite for metal, especially mercury. This led to a second name for them: mercaptans (describing their ability to capture mercury).

All this leads up to a truly unusual thiol: grapefruit mercaptan. You’ll notice it looks like another terpene, like carvone and damascone. Grapefruit mercaptan is such a singular compound because it is a nice-smelling thiol. It’s another one I haven’t smelled, but I’m told it’s very complex and grapefruity. It’s also unique because not many things synthesize thiols on purpose (thiols being reactive and stinky - skunks are a notable exception here).

The Wikipedia article notes that this is a bit of a thorn in the flavor industry’s side - almost ALL thiols stink, and this is a notable exception. Thiols have a nasty habit of oxidizing to form dimers in the presence of oxygen (R-SH -> R-S-S-R), and even if grapefruit mercaptan doesn’t stink, its decomposition products probably do. All these leads to a not-so-hot flavoring agent.

Here’s the structure:

See you Monday.

I will admit to more than a casual fascination with smell. I am forever wafting vials of compounds for a whiff - which I get more and more flak for, as people get more and more cautious. I figure a few femtograms of small molecules here and there are the last thing that will do me in.

Perfumers (and biologists) still are looking for structure-odor rules, which prove to be continuously elusive. As I’ve mentioned before, one problem here is language; describing odor is hard! Read the rest of this entry »

I’ll admit it - sometimes, when I have no idea what molecule to write up, I’ll look at the American Chemical Society’s Molecule of the Week Page. And sometimes I pick the one with a name that makes me smirk. Enter zingerone:

The name is easily dissected. Zingerone is a natural product from ginger. “Zinger” is ostensibly from the ineffable zest associated with ginger. “-one” is the suffix associated with the functional group known as a ketone.

As the ACS page notes, zingerone shares some common structural characteristics with capsaicin and vanillin:

Thinking like enters into it when a chemist looks at the structure and metabolic pathways leading to chemicals that plants make. The really weird stuff always seems to come from plants. There is a whole subfield of chemistry known as natural products chemistry devoted to studying this stuff. Plants, you see, are distinctly lacking in legs, fangs, claws, and guns, and they have had to make do with some (often strikingly toxic) chemical defenses. You see it in sea life, too, as in the case of fugu’s tetrodotoxin.

Vanillin (and I’d guess the other “vanillinoids”, but I’m not sure), are synthesized from two closely related amino acids, phenylalanine and tyrosine. As naturally occuring amino acids, they are ubiquitous, and find their way into all sorts of structures (since they’re relatively “cheap” to use).

Have a good weekend.

Esters are a continuing source of fascination for me. Chemically, they’re unremarkable. If you heat an alcohol and carboxylic acid together under conditions that allow it to eliminate water (say, by doing the reaction in the alcohol or acid under concern, if one’s liquid), they will form a compound called an ester. Usually you add a trace of additional acid as a catalyst - a drop of hydrochloric acid solution is common.

What’s remarkable, though, is the smell. Pentanol (amyl alcohol, in old-school chemspeak, rarely used, but I learned this ester as “amyl butyrate”) is unremarkable, and it smells like most low-molecular weight alcohols - a bit like ethanol, a bit like lighter fluid. Butyric acid, however, is Satan’s own carboxylic acid - it is a sort of B.O./vomit/Sex Panther odor. Read the rest of this entry »

This one is obvious. It smells like, well, vanilla. Exactly like vanilla. Some people claim that it is a simplistic, cloying version of vanilla and you should always buy real vanilla extract instead of synthetic (which is mostly vanillin); I say these people are exaggerating. While you can definitely smell a difference, vanillin gets you 95% of the way there, and it isn’t a one-note wonder. If the smell weren’t so ubiquitous we’d find it much more amazing. Earthy and rich, yet spicy and vibrant, it really is a singular aroma. Read the rest of this entry »

So, if you read a bit during the week, you might have guessed that I was alluding to the purple line on our chromatograph being an optical brightener. If not, here’s the idea:

You know the stereotype of the “blue-haired little old lady”? This comes from the fact that they used to use certain dyes, such as Prussian blue, to color their hair. This is because grey hair is often not grey but a little bit yellow. For whatever reason, some decided that a whitish tinge was aesthetically a bit better. Color mixing isn’t quite as simple as it seems. Adding a hint of blue to something yellow can actually make it look whiter. This was the idea with bluing hair - too much, though, and it was obvious. As anyone who’s owned a white undershirt for longer than a week can attest, these get a bit dingy too. Bluing to the rescue. Such dyes were commonly added to the laundry.
At least until quite recently. While I have no idea what the state of the art is in hair-dying, I know that laundry scientists have largely switched to a class of compounds called optical brighteners. These are compounds that absorb light in the UV and near-UV (a little bit of which is available even inside), and re-emit it at lower energy, in the blue end of the spectrum. This ends up making things look even whiter. I had a hard time picking an example; there are many dyes that do this. One subclass of optical whiteners is the coumarins, though, and I love coumarin:

Read the rest of this entry »

The other day we talked chirality. Here’s the example they give in every organic chemistry class when they’re teaching chirality. Carvone!

Read the rest of this entry »

Here is a topical one, Tamiflu. A lot of people are interested in it because it’s likely to be helpful against the “bird flu” strain of the H5N1 influenza subtype. Specifically, the concern is that bird flu might mutate into a form that is transmissible between humans. Today, some humans have gotten it - however, we don’t know of anyone who got it from a human - it’s occurred only in humans who work closely with birds.

I’m covering the drug in two parts. Today, we’re talking about the synthesis and precursors. Tomorrow, we’ll talk about how it works biochemically as an antiviral drug. Let’s get straight to the structure:

Posted in Drugs, Biology, Medicine, Perfumey, Origin of Life | 2 Comments »