moleculeoftheday | April 19, 2007Carbon, with its four valence electrons, is in a unique position; its valence shells are exactly half filled. Compounds of elements with three valence electrons (such as boron) and elements with five valence electrons (such as nitrogen) can act very much like their carbon analogues. Boron nitride, ("BN") for example, can exist in a very hard form, much like diamond. Similarly, many semiconductors are based on combinations of groups III and V. Gallium aluminum arsenide, indium nitride, and aluminum arsenide, for example.
In a few cases, alternating boron-nitrogen compounds can act much like…
moleculeoftheday | April 18, 2007Inulin is polymeric fructose:
Unlike cellulose (another sugar polymer, which comprises such indigestibles as wood), inulin is quite soluble. To you, it's almost entirely undigestible, and so is one of the "soluble fibers" in your diet.
You can find inulin in various plants, such as jicama, onions, and the Jerusalem artichoke. Because of its relative indigestibility, enzymes in your gut often take advantage of its ready availability and digest it. This can increase the population of bacteria in your GI; because of this, inulin is often termed a "probiotic." This is something of a euphemism;…
moleculeoftheday | April 17, 2007Sorry for the short updates this week! Chloranil is an oxidizing agent. Part of its usefulness comes from its solubility in organic solvent, which you don't see with things like permanganate or H2O2.
The idea with chloranil is that it's a stronger p-quinone. It is a pain to use. It's not very soluble, and I've never had very much luck with it.. On the other hand, it has a beautiful yellow color.
moleculeoftheday | April 16, 2007Meta-chloroperbenzoic acid is a common organic oxidant used in synthesis. It is popular in part because it is very easy to handle; another common peracid, peracetic acid, is a liquid.
Like many peroxides, it's somewhat shock sensitive. The mixture sold as MCPBA is actually only about 70-75% MCPBA. The balance is MCBA - meta-chlorobenzoic acid, and water. This serves to desensitize the mixture to shock somewhat.
moleculeoftheday | April 13, 2007Propylene carbonate is a very polar aprotic organic solvent. Usually, this makes synthetic chemists think of DMSO, then DMF, then maybe acetonitrile or HMPA. Not many people will get down far enough on their list to get to name propylene carbonate.
It is the cyclic ester of propylene glycol and carbonic acid. It's surprisingly robust - if propylene carbonate hydrolyzed appreciably, the container would hiss a bit when you opened it (due to CO2 release). I've actually held some propylene carbonate and 6M HCl in a sealed container for a week accidentally; no hiss.
moleculeoftheday | April 12, 2007Benzophenone is a colorless solid, tetrahydrofuran is a colorless liquid, and sodium metal is unremarkable stuff. When pure, it's silvery and bright, but it tarnishes easily in the presence of oxygen or water, leaving it looking like any other metal - kinda greyish silver. If you mix the three together and boil them for a few hours (sometimes you don't even have to do that if everything's very pure and dry), you end up with an impossibly dark royal blue-purple solution. This is benzophenone ketyl radical (and the related benzophenone dianion - reduced one step further by one more atom of Na0…
moleculeoftheday | April 11, 2007Yesterday, I covered the intense odorant found in popcorn. Today's molecule is another intense odorant, cis-hexen-3-al.
This molecule has an odor threshold in the high ppt-low ppb neighborhood. It's responsible for the smell of cut grass. Take a look at the Molecule of the Month entry for more information on hexenal odorants.
moleculeoftheday | April 10, 2007I have a love-hate relationship with microwave popcorn. It can be tasty from time to time. It can be absolutely nauseating, however, at 10am on a Wednesday when someone at work decided to make it for some reason, leaving the office smelling like a movie theater all day. Let's not even talk about the people who let it burn. Part of the reason for popcorn's ability to "carry" is 2-propionyl-1-pyrroline, which can be smelled at incredibly low concentrations.
The compound has a reported odor threshold of 20 picograms per liter, which is 20 parts per quadrillion. Contrast t-butylmercaptan, which…
moleculeoftheday | April 9, 2007Lithium aluminum hydride is one of the most prodigous reducing agents you find in organic synthesis. In organic chemistry, reduction almost always means the addition of hydrogens - the "hydride" part is the business end of LAH. It will reduce just about anything but an olefin or an aromatic ring.
LAH will go absolutely nuts in the presence of water, evolving a great deal of hydrogen and heat. Sodium does the same thing, and you may have seen people blow it up by throwing chunks of it into water. LAH is a powder, and that huge surface area means a very, very, quick reaction. "Quenching" a LAH…
moleculeoftheday | April 5, 2007The pet food recall scare continues unabated; a couple weeks ago, people were pointing at aminopterin, a folic acid analogue, which was covered here. Now, people are pointing fingers at melamine as a potential contaminant.
Melamine is a pretty simple compound, with a number of uses. Here, it's being reported that it's used as a fertilizer, which contaminated some wheat gluten, which ended up in the pet food. Despite the fact that you mostly get carbohydrate from wheat flour; gluten is actually a pretty inexpensive protein source. It's mostly eaten in Asia, but some vegans have picked it up…
moleculeoftheday | April 4, 2007Nitromethane has some odd properties, due to the singular weirdness of the nitro group.
The electron-withdrawing nature of the group makes it a decent acid; in neutral (i.e., pH 7) water, about 1 in 1000 molecules of nitromethane will have a formal negative charge on the carbon and exist as CH2NO2-. There aren't many of these "carbon acids," and their properties make them useful in organic synthesis.
The "nitro" part of nitromethane doesn't disappoint if you associate the prefix/word with nitrous oxide and TNT, either; nitromethane is a very energetic compound and can be explosive (it was…
moleculeoftheday | April 3, 2007Retinal is a pigment in your eyes that is necessary for vision. This is why vitamin A is so essential for vision - retinal is just one oxidation state up from retinol or one down from retinoic acid.
Upon absorbing a packet of light, retinal assumes the trans conformation you see above. Normally, it's found in the cis form (as seen here). This conformational change essentially amounts to a finger pushing a lever; some proteins translate it into a nerve impulse, off it goes to your brain, and hey! look! you've got sight!
The whole system is a little more complicated, especially when you add in…
moleculeoftheday | March 29, 2007Via Fark: a blog last week remarked about McDonald's chicken products, quoting The Omnivore's Dilemma::
But perhaps the most alarming ingredient in a Chicken McNugget is tertiary butylhydroquinone, or TBHQ, an antioxidant derived from petroleum that is either sprayed directly on the nugget or the inside of the box it comes in to "help preserve freshness." According to A Consumer's Dictionary of Food Additives, TBHQ is a form of butane (i.e. lighter fluid) the FDA allows processors to use sparingly in our food: It can comprise no more than 0.02 percent of the oil in a nugget. Which is…
moleculeoftheday | March 28, 2007The American Chemical Society is having its Spring meeting as we speak. One neat thing about a meeting that tries to take on as broad a field as "chemistry" is that there's all kinds of stuff there. Some of it trickles out to the mainstream media - usually picked up by a science reporter (or maybe a university with some PR savvy). This often has a lot to do with the mass appeal or "sellability" of the story the researchers have. Hear me right, this isn't to impugn the science of people who get written up in the press one bit! It's just that most people don't want to pick up the paper and…
moleculeoftheday | March 27, 2007Chloral hydrate was in the news yesterday because it showed up in the autopsy report for Anna Nicole Smith.
Chloral hydrate is what individuals of a certain age (or just aficionados of dated slang) refer to when they mention "slipping someone a Mickey." It is a very simple drug, discovered by von Liebig about 175 years ago.
It has largely been supplanted in popularity by the benzodiazepines, which are much better characterized and less toxic (although they're still addictive). Very small, highly chlorinated molecules like this tend to be hard on your liver, much like carbon tetrachloride and…
moleculeoftheday | March 26, 2007Friday's entry was on juvenile hormone, an epoxide-containing species (as in epoxy, see here and here). Today, I'll show you an example of how we've used it to battle bugs.
Methoprene doesn't contain an epoxide (many of the juvenile hormones don't), but it's a good mimic for JH. In its presence, juvenile insects can grow larger, but they can't achieve sexual maturity. No more adults, no more sex for the bugs, no more bugs for you. Like many insecticides, it has its own set of safety concerns, but this is far from the worst thing out there.
moleculeoftheday | March 24, 2007Special Saturday edition of MoTD: aminopterin.
People have (quite understandably) been a little frantic about the putative taint found in pet food in recent days. Friday, ABC News reported that aminopterin was the contaminant, calling it "rat poison." I can't speak to the accuracy of the claim, but I can tell you that aminopterin isn't the kindest of molecules.
aminopterin, like the previously covered methotrexate, is a folate analogue that has found use in chemotherapy. Both work by impairing nucleic acid synthesis, and are quite toxic (the toxicity, unfortunately, shares the same origin as…
moleculeoftheday | March 23, 2007Epoxides aren't just found in glue and disinfectants (see here and here. They also occur occasionally in nature (not too often, since they're very strained, high-energy structures - this is why they're so reactive and useful). One such example is in JHB3, a "juvenile hormone" found in insects.
Juvenile hormones have several roles, one of which is regulating the development of juvenile insects. A relatively high level of juvenile hormone keeps insects in an immature state, allowing them to grow, but not achieve sexual maturity. Diminished levels of JH allow maturation to adulthood.…
moleculeoftheday | March 22, 2007Yesterday's entry on epichlorohydrin got us halfway to an epoxy resin, with the aid of good old bisphenol A. In that other tube, you'll often find some sort of amine, which, when mixed with a prepolymer like that formed with epichlorohydrin-bisphenol A, heats up and hardens.
This triamino-phenol is one hardener found in epoxy adhesives. It reacts further with the epichlorohydrin, giving a cross-linked, hard (or just firm) epoxy resin. It's also responsible for the smell you probably associate with epoxy.
moleculeoftheday | March 21, 2007Yesterday's entry on epoxides may have brought to mind epoxies. The similarity isn't a coincidence. Chloromethylepoxide, or "epichlorohydrin," is the basis for many epoxy adhexives.
One tube contains some epoxide, such as epichlorohydrin, along with some bisphenol A - the very same stuff you find in polycarbonate. This is actually partially polymerized ("oligomers") - the degree of polymerization and ratio of epichlorohydrin to bisphenol A can determine how hard an epoxy you get - this is often the basis for "soft" epoxies.
It's not over yet, though. Tomorrow I'll cover what's in that other…