Using techniques pioneered by IBM Research Zurich, this is the first ever AFM image of a single molecule. The most detailed single image of a pentacene molecule you'll ever see, in fact.

Seriously, I'm amazed. I had no idea atomic force microscopy could be this powerful. The researchers have apparently achieved this stunning resolution by coating the tip of their microscope probe with carbon monoxide. I'm a little hazy on the details, to be honest, as I haven't had a chance to read much about it just yet.

The most amazing part if that you can actually see the chemical bonds in the molecule, as regions of electron density. You can even see the bonds to the peripheral hydrogen atoms. Interestingly, there seems to be a lot more electron density on the two end rings of the molecule. This seems to fit quite well with what we know about pentacene. As aromatic molecules go, it isn't really very aromatic at all. Its electrons aren't as delocalised as many others. As a result, chemical reactants tend to attack the centre of the molecule, where the bonds are weakest.


Source: BBC Science and Environment

Chlorhexidine. Also known as N,N'-hexane-1,6-diylbis[N-(4-chlorophenyl)(imidodicarbonimidic diamide)]. Chemical antiseptic. Bactericidal to both gram-positive and gram-negative bacteria, as well as having bacteriostatic action. It also tastes bloody awful.

Unfortunately, I have a dental cavity and couldn't get a dentist's appointment until tomorrow morning. This means that mouthwash is necessary to keep this tooth clean until I can get it looked at. Mouthwash, brushing and eating very carefully.

Still, maybe next time I'll buy a slightly less vile tasting mouthwash. Amusingly, a lot of mouthwashes are actually sweetened with sucralose...

I was flicking through the rather marvellous webcomic, Abstruse Goose, recently, when I happened upon this particular comic (click the panel for the full version). Wait, what? Chlorinated sugar? This piqued my curiosity somewhat, so cat-like as ever*, I decided to investigate further. It turns out that, as they say, many a true word is spoken in jest.

Make no mistake. The artificial sweetener sucralose, more popularly known as Splenda®, is precisely that. Chlorinated sugar. It's also known as 1',4,6'-Trichlorosucrose, E955 or (deep breath!) 1,6-dichloro-1, 6-dideoxy-β-D-fructofuranosyl-4-chloro-4-deoxy-α-D-galactopyranoside. Containing chlorine atoms covalently bonded to carbon atoms, it's an organochloride compound (also known as a chlorocarbon). This makes me raise a slightly skeptical eyebrow. Now, I have nothing against chlorine, but the releasing of chlorocarbons into the environment on a large scale? That makes me a bit uneasy.

I'll make no secret of the fact that I detest artificial sweeteners. As opposed to the good old fashioned sugar that our digestive systems have spent hundreds of millions of years evolving to digest efficiently, many people seem to favour fabricated chemicals which apparently taste "sweeter". As far as I'm concerned, they spoil the taste of things. Since when did "no added sugar" come to mean "icky artificial sweeteners added instead of sugar"? Couldn't they just - you know - not add any sugar? But enough of my ranting. I have a little more than just personal opinion to go on here.

The two molecules to the left are sucrose and sucralose. A disaccharide, sucrose is made from one molecule of fructose and one of glucose. It's the dominant type of sugar in sugar cane and sugar beet. Just plain ordinary table sugar. The same kind found across the world.

Sucralose, as the Splenda® people rightly claim, is "made from sugar". Just chop off a couple of hydroxy groups and swap them with chlorine (which is, admittedly, easier said than chemically reacted). In fairness, it is perhaps the least awful tasting of the artificial sweeteners still available**. In fact it seems to be steadily replacing aspartame, which is arguably a good thing.

So what's the big deal? What's my problem with chlorinated sugar? The trouble with organochlorides is that, while not necessarily toxic, they're notoriously stable. A good example would be a certain famous chlorocarbon.

Now let me make it quite clear -- I'm not comparing sucralose to DDT. They're very different chemicals, with different uses, reactivities, stabilities and so forth. The point to this paragraph is more to highlight precisely how stable large chlorocarbons can be, with DDT being a prominent example. DDT was used widely as a pesticide during 1940s and 1950s, due to it being extremely toxic to invertebrates, but "safe" to vertebrates like people. Except that it isn't as safe as was once thought. Actually, it's been linked to diabetes, asthma, neurological problems and birth abnormalities, as well as being a suspected carcinogen. The trouble was that DDT was stupidly stable. It just didn't break down. As a result, it accumulated in the world's ecosystems, ravaging coastal invertebrate wildlife and steadily building up in the tissues of predatory animals. Disturbingly, DDT was still found in human blood samples as recently as 2005 and is regularly found in food samples tested by the FDA.

Sucralose is similarly stable (albeit less so), and when it does break down, it doesn't break into anything harmful. No other sweetener holds the accolade of being considered "safe" by the Center for Science in the Public Interest. The trouble is that it's low calorie because it isn't really absorbed by the human body. Most will pass straight through you, with only around 4 - 12% actually being metabolised. Indeed, the Swedish Environmental Protection Agency has cautioned about potential rising levels of the stuff in wastewater. Water treatment plants were shown to have little effect on sucralose, with it being present at moderate levels in effluent water.

Of course, as I said above, not all organochlorides are toxic as such. I'm certainly not saying that Splenda® is evil. Quite the contrary, it's been found by repeated tests to be perfectly safe at the kind of levels involved in daily food consuption***. Though, knowing how chlorocarbons have caused environmental issues in the past, I can't help but hope that the scientists involved in manufacturing the stuff know exactly what they're unleashing on the world.

Personally, I'll be sticking to natural sugars. If nothing else, in my humble opinion, they taste nicer.



*On that note, I don't take too well to being herded either.

**I say 'still available'. Several have been taken off the market after being found to break down into toxic fragments. Which is still better than in ancient times -- the less said about sugar of lead the better!

***It's worth noting though, that not much data exists regarding higher levels of sucralose, and those data that do exist don't look good. But then, almost anything is toxic at a sufficiently high dosage.

Mangoes really have quite a rich flavour. Rich and complex, with plenty of subtleties. Despite this, they're actually fairly easy to use in cooking. As it happens, the complex mango flavour is contributed to by a whole host of different volatile flavour compounds. These are the main ones. Some of these are a bit obscure, but I've given some possible food pairing options for what I could find...

• 3-carene
  A rather unusual looking, fruity smelling turpene. 3-carene is found in the flavours of several herbs and spices, including angelica, anise, basil, bergamot, cinnamon, rosemary, sage and thyme. It's also found in citrus fruits, such as lime and orange (particularly blood orange).
  
  
• ethyl dodecanoate
  A long chain ester also known as ethyl laurate. Interestingly, it's found in several alcoholic spirits, including cognac, malt whiskey and dark rum. It's actually created by yeast, as the alcohol's still being fermented.
  
  
• hexyl hexanoate
  Found in apple peel and peaches.
  
  
• methyl hexanoate
  A beautifully fruity ester, found in the flavours of passionfruit, papaya, kiwi fruit, soursop, oysters, pineapple, blue cheese, white wine, cider, cranberry, melon, olive, raspberry and strawberry!
  
  
• geranyl acetate
  A floral smelling ester. Found in apple, apricot, bergamot, butterscotch, citrus fruits, corriander, pineapple, tomato, raspberry and rose. It's also found in some rums.
  
  
• χ-octalactone
  
  
• χ-nonalactone
  
  
• citronellol
  The main aroma compound in citronella, this chemical is also found in a few different types of fruit, including apple, apricot, peach, cherry, pineapple, raspberry and various citrus fruit. It's also found in black tea and rose oil.
  
  
• carvone
  A spicy smelling compound, carvone gives the bite to caraway seeds and dill, as well as being found in spearmint and (to a much lesser extent) peppermint. It's also found in mandarin orange peel.
  
  
• α-ionone
  Ionones are amongst a group of compounds known as rose ketones. Ionone contributes to the flavour of roses, raspberries, carrots, violets and certain red wines.
  
  
• limonene
  As it's name implies, limonene is a major aroma compound in lemons, as well as oranges.
  
  
• myrcene
  Found in bay leaves and verbena.
  
  
• β-phellandrene
  A peppery, slightly cistrussy smelling turpene, found in eucalyptus and water fennel.
  
  
• α-terpineol / β-terpineol
  An alcohol, closely related to limonene.
  
  
• toluene
  Wait... what? Toluene!?
  
  
• benzaldehyde
  One of the main contributors to the aroma of almonds. It's also found in apricots and cherries. What's more, it's closely related to toluene, which seems to make the previous chemical make more sense.
  
  
• (Z)-3-hexen-1-ol
  Found in broccoli, sweet peppers and pumpkins.
  

Mango Image: Fir0002/Flagstaffotos

Published data: Narain & Galvão (2002)
Wow... There was an international Mango symposium? Cool.

Yep. That's right. An anion made up of uranium and oxygen is called a uranate. UO₂^2-, UO₃^2- and UO₄^2- are all types of uranate. Wait. It gets funnier. If you were to react one of these things in the lab, say, to attach it to a benzene molecule? Technically, that reaction would be called uranation.

I know, I know. It's puerile humour. But puerile humour is just so easy to do when talking about uranates! In fact, uranates tend to be yellow in colour. Conentrated uranium oxide (an intermediate stage in uranium ore processing) is called yellowcake. Despite its unfortunate sounding name, yellowcake is used to prepare fuel for the nuclear reactors in power stations. It's produced by all countries that mine uranium.

As for the uranium ore itself, the most common is known as uranite (mostly uranium dioxide, UO₂). Interestingly, due to uranium decaying by emitting alpha particles, the immensely rare element technetium can be found in uranite ores. Uranites were also the first place helium was discovered on Earth (seeing as an α particle is just the nucleus of a helium atom). See? I can be puerile and interesting at the same time!

Actually, perhaps the most common uranate is a complex ion called diuranate, U₂O₇^2-. The smaller uranate ions tend to lump together into these larger ions. And yes, they're all yellow too. I wonder, if Martin Heinrich Klaproth realised the unfortunate humour in all of this in 1789 when he discovered the element, he might not have named it after the planet William Herschel had discovered 8 years earlier. A planet which, alas, provides similar humour for astronomers. Us scientists can be a childish bunch sometimes.

Perhaps the coolest use of diuranate though, is as an additive to glassware. Uranium glass (sometimes known as vaseline glass) has a striking lime green hue to it. Ultraviolet will also make uranium glass fluoresce. While the uranium is still emitting α particles, the mere 1-2% of uranium found in most modern uranium glass makes it essentially harmless -- barely above everyday background radiation. A sensitive geiger counter will pick it up. A more meagre one probably wouldn't register the difference. Any stray α particles which do actually escape from the glass aren't even capable of penetrating human skin. Uranium used to be used in glassware quite widely before the advent of nuclear technology. These days, it's rather fallen out of favour, though you can still find it in antiques and certain novelty items. And marbles.

Incidentally, those marbles are available for sale on a site called United Nuclear. If not for the fact that there's almost certainly some restriction on importing uranium, I'd be quite tempted...

I'll admit. I've been slack recently. Very slack, in fact. Because it's rare that I'd miss an opportunity to have a quick rant about something as cool as this!

This little beast, is an ethyl formate molecule. Any organic chemist will tell you without hesitation that it's an ester, and esters are the lovely fruity smelling compounds that make undergrads feel slightly floaty when they're leaving labs (or maybe that was just me...). Anyway, ethyl formate contributes specifically to two things: the smell of rum and the flavour of raspberries. Admittedly, it's not the main contributor to raspberry flavour (that would be raspberry ketone) but it's a significant one all the same.

For any passing molecular gastronomers, this means that rum and raspberries can and will taste good together! Something for me to experiment with at the weekend, perhaps...

But anyone with an eye on the news lately will know one other interesting thing about ethyl formate -- it's recently been discovered in interstellar space! Specifically, in our old friend, the Sagittarius B2 molecular cloud -- the galactic core's chemical cornucopia. Astrochemists found ethyl formate, together with propyl cyanide via radio astronomy (using the IRAM 30m telescope). These are argued as the most complex molecules ever detected in interstellar space (though a lot of us could argue the case for PAH molecules). Interestingly, as well, they lend a little more strength to the ongoing searches for those elusive amino acids. Seemingly, it's an exciting time to be an astrochemist right now!

So there you have it. Rum and raspberries. A flavour pairing straight from the heart of the Milky Way!


Paper -- arXiv:0902.4694v1

So as everyone knows, chopping onions makes you cry. I've seen people chop onions wearing swimming goggles to try and prevent tears and, interestingly, this can actually work. But not necessarily for the reason you think. Allow me to explain...

Onions, like most plants in the family Alliaceae produce a compound called allicin. It's the compound responsible for the characteristic pungent smell of raw onions. This chemical is also the plant's primary defense mechanism. It's antibacterial, antifungal and repels pests. The thing is though, allicin is only formed in large quantities when onions are damaged -- by a chef's knife, for instance.



When you cut an onion, enzymes rapidly generate allicin. After creating allicin, more enzymes break it down into sulfenic acids. These sulfenic acids are extremely volatile, so they get carried away as vapour. They're also quite unstable, and will rapidly convert to sulfuric acid on contact with water.

Onions make you cry because while chopping them, you inhale this onion vapour. When sulfenic acids come into contact with your tear ducts, they react and turn into sulfuric acid. It's this weak sulfuric acid solution in your tear ducts that causes the tears and stinging sensation while chopping onions.

So just covering your eyes isn't actually enough. Wearing goggles can work, because they can also pinch your nose and close off your tear ducts. A much easier solution though, is to simply take a step back while chopping onions, breathe through your mouth and never ever lean over the chopping board while you're chopping.

Doesn't time fly? A month is nearly up, and it'll soon be time for me to put up the submissions for this month's TGRWT. If anyone's planning on sharing some gastronomical delights, there's still plenty of time to e-mail me with recipes and pictures. Believe me, what I've received so far looks just delicious!


In the meantime though...

So as with a lot of foods, these isn't any one single flavour compound that gives roses their beautiful flavour and aroma. Actually there are a selection of them. Collectively, these volatile molecules are known as rose ketones. The main components are ionones, damascones and damascenones. The specific combination of these is one of the reasons why different roses are prized for subtly different aromas.

Back when I was actually studying aromatherapy, rose oil was probably the most expensive essential oil in the world. It probably still is, even though techniques for making it have improved (they extract it with supercritical carbon dioxide these days). Good thing then, that rose ketones don't need to be present in very high concentrations to be noticeable. Even in the roses themselves, the aroma compounds are found in relatively low quantities.

Actually, these compounds and other similar ones are found in a wide range of different foods (particularly raspberries and certain red wines), albeit usually only in small quantities. In cooked foods, they're actually found in several root vegetables, because rose ketones are produced when beta carotene starts to break down. Similar partially oxidised fragments of carotene can contribute to the flavour of cooked carrots, parsnips and sweet potatoes.

Interesting little molecule, sydnone. It's a mesoionic heterocyclic aromatic. In other words, it's an aromatic ring which is charged both negatively and positively, and both charges are delocalised.

Mesoionic compounds, while effectively neutral overall, cannot be assigned an uncharged structure. In fact, they can't actually be fully described by any one structure at all. Due to the delocalisation, at least one of the charges tends to fall on two or more different atoms (though the positive charge stays associated with the ring, regardless of the other).



Sydnone's actually the only one of these compounds I know about, and it's more of a curiosity than a useful compound. Replace that keto (=O) group with an imine (=NH) though, and you'll find it in a couple of stimulant drugs (dopamine reuptake inhibitors). Ok, so technically I suppose that means I know about two mesoionic compounds...

Sydnone is also a substituted hydrazine. A nitrogen analog of ethane, hydrazine is commonly used as rocket fuel, and was the US military's excuse for shooting down a defunkt satellite last year.

Silabenzene is one of those chemical curiosities. With little use except to theoretical organic chemists, it's a benzene molecule with one carbon atom replaced by a silicon "pendant" atom. A heterocyclic aromatic.

For a long time it was believed to be unstable and impossible to isolate, having only been observed in matrix isolation. In fact, chemists tried for years to succesfully synthesise the stuff, only finally succeeding in 2000. They couldn't even make silabenzene itself (as in my litle diagram here), because of its high reactivity. Instead they needed to use a steric protective group -- in other words, they attached a bulky molecule to the silicon to stop anything getting close enough to react with it! The first silicon heterocycle created was 2-silanaphthalene, synthesised three years earlier in 1997.

Now benzene, as you may know, is a very stable molecule, thanks to its big delocalised cloud of π-bonded electrons. That means that in chemical reactions, it's a lot easier to attach something to a benzene ring than to break it open. Carbon-carbon bonds are tough.

Silicon, on the other hand, is rubbish at forming π-bonds. It's especially rubbish at forming π-bonds with carbon atoms. Even though silabenzene is actually aromatic, the carbon tends to suck all the electrons away from the silicon, making a highly polar bond which is quite easy to split apart. As a result, Si-C double bonds are highly reactive.

I have to wonder though, if it were possible to create one, how stable a polycyclic molecule like pyrene might be with a silicon atom trapped in the centre of it...