Slashdot Mirror
New Molecule With Switchable Chirality
Nanotechnology writes: "Available here, The molecule was developed by adding copper ions to a derivative of the amino acid methionine. The investigators were then able to switch the molecule's chirality by the addition or removal of an electron. Furthermore, they found that the molecule's chirality could be switched repeatedly, and that the two forms of the molecules polarized light in opposite directions." Especially interesting is this line from The Canary Lab's home page ("Research"): "We are also scrutinizing other aspects of signal detection technology. We prepared a new polymer very similar in structure to polyaniline ... The new polymer was designed to serve as a molecular wire for attaching electrochemical sensor molecules to electrodes."
I think what people often mean by chiral is not only the above definition but the important additional point that you do not have a 50-50 mix of the two mirror image forms (called enantiomers). Most molecules that are manufactured artificially are chiral but you get a 50-50 mix of both forms so it isn't very useful. By contrast, almost all biological molecules are chiral and appear in only one form (all DNA everywhere, in every living thing, winds the same way).
Since it is unusual and difficult, it is considered a big deal when scientists preferentially create one mirror image, thereby introducing some asymmetry where previously there had been none.
Definition:
A term used to describe a molecule which, in
a given configuration, cannot be superimposed
on its mirror image. This is in contrast to
achiral molecules which can be superimposed
on their mirror images. The two mirror image versions of
the molecule are known as "levo" (left-handed),
abbreviated "L," or "dextro" (right handed),
abbreviated "D," depending on which way they
rotate polarized light.
chiral compound
Definition:
A molecule that has an asymmetric center and can
be found in two non-superimposable mirror-image
forms (enantiomers).
Science and Biotechnology Dictionary
Simplistically a chiral compound is one which would appear different if viewed in a mirror. For example, your left hand cannot be imposed on top of your right hand as they are mirrors of each other. Your hands are chiral.
Biological molecules are (almost) always chiral and normally organisms can only cope with one version of a molecule and not its mirror.
Chiral molecules rotate plane polarised light. A molecule's mirror will rotate the light in the other direction. This is why they may have a use in "liquid crystal displays and non-linear optics".
A chiral compound is one that is 'non-superimposable with its mirror image'. In other words, it can exist in 'right-handed' and 'left-handed' forms.
There are a variety of reasons for worrying about chirality. As mentioned, chiral molecules rotate the plane of polarised light. This can be used for display tech - imagine two polaroid filters paralell to each other, each polarising at a different angle. Light comes in, gets polarised by the first filter, and can't get through because its polarised at the wrong angle. Now stick a layer of your switchable-chiral molecule inbetweem the filters. If its in one form, then it rotates the polarisation of the polarised light to match the other filter, and light goes through. In the other form, it does it in the opposite direction, and the polarised light is at a different 'wrong' angle, and doesn't get through. Use lots of little bits of switchable compound, and you have a nice LCD-like display. You can do something similar with one filter and a mirror, too.
Or how about nanotech? Put electrons into/take electrons out of these molecules, and they change shape. Have these molecules in contact with other molecules, and you can cause shape-changes in those, too (possibly causing them to gain/lose electrons). Could be used for molecular machinery, or for 'molecular computers', which use such molecules instead of conventional semicondutor tech.
1. a step toward optical switching, is this? :P
/. is only inhabited by trolls this weekend? Is it sunny spring in U.S. as well, or what?
2. a step toward optical computing?
3. a practical nano-level machine part.
4. nano-sized lighting effects
If there's anyone who knows more about those, I'd be happy to hear whether they're relevant.
Is it just me or is this in its digital simplicity a much clearer advancement than the Canadian light-trap earlier this week? At least I find this exact data much more trustworthy.
Obviously, it'll take a while before this will be a part of any nanofactories' product line outcomes. In fact, those nanofactories have not yet been invented either. Who cares, if it's going to take another 20-50 years or so. The future is on its way!-)
OT: how come
I think, therefore thoughts exist. Ego is just an impression.
Chirality refers to the stereochemistry of an atom, usually carbon. Carbon forms 4 bonds with things, each bond at a 109.5 degree angle (not 90!). At this angle, each atom bonded forms the corner of a tetrahedron with the carbon smack in the center, to maximize distance between each bonded substance.
If the 4 objects bonded to the carbon is different, then the carbon is said to be chiral. This means that there is a NONIMPOSIBLE MIRROR IMAGE of this compound. A good example would be your hands. Your left hand is a mirror image of your right hand, but you cannot (palm down) overlay them. So, for molecule CClBrI, 2 of the bonded halogens (Cl, Br, I) cannot overlap in the mirror image.
Chirality affects everything around us. For one thing, chiral molecules are optically active, meaning that it rotates plane polarized light, much like crystals in an LCD display. Cool thing is, say a molecule rotates plane polarized light 30 degrees clockwise. It's mirror image molecule (remember, these things come in pairs) will rotate it 30 degs counterclockwise.
Biological activity is also governed by chirality. Sugar, for instance, is chiral (take karo syrup and 2 polarizing filters and play with it if you don't believe me). alpha-D-Glucose (one of the two sugars that form common table sugar, the other is alpha-d-FRUCTOSE) rotates light clockwise (I believe), and upon polymerization it forms starch, which we humans have an enzyme (also chiral) that can break it down. There is another form of glucose that rotates light counterclockwise called beta-D-glucose, and when that forms *CELLULOSE* upon polymerization. Because our enzymes are chiral, it will cleave starge (alpha polymer) into glucose, and we can digest it, but it won't cleave the beta polymer (cellulose). Termites and cows have a bacteria in their stomach that will synthesise the mirror image enzyme that will cleave the beta polymer, hence, they can eat cellulose, we can't.
There are very cool implications to this. First of all, virtually all drugs are chiral, and in synthesis we have to perform isolation. Isolation of chiral substances often involves chromatography, and the chromatography column packing material to resolve chiral compounds are often (you guessed it) chiral. Improvement made in separation techniques will give better catalysts and better synthesis options, which in turn opens up new bio and non-bio synthetic techniques towards new material. Optical activity is used for LCDs, so potentially this could be used in LCD display (though the impact here is not that great, there are existing material that can fit this bill). Other potential applications include the possibility of using this in a electro-optical computer system.
IANA chemist, but IIRC biological molecules sometimes appear in left-handed and right-handed versions, but the two versions do different things. For example, one of the molecules that gives oranges an orangey flavour - its mirror image is found in lemons, giving them a different flavour. Also with some drugs, the right-handed version might be beneficial and all the side effects come from the left-handed version. But it's difficult to manufacture one without getting an equal amount of the other. See the article Happily, it's an asymmetrical world for more.
(As for polarizing light in two different directions, I don't see why that's such a big deal. Liquid crystals do this already depending on what voltage you apply to them.)
-- Ed Avis ed@membled.com
No, it might not have been accidental. Somewhere down the line something might have started out one way (by choice) but then evolution would have dictated that the sucessful species generate enzymes and whatnots that are a specific chiraltiy.
Look at the post I made in the other thread explaining the importance of chirality and the difference between cellulose and starch, and the difference in the enzyme requires to cleave it.
Let's say that you're some protozoa somewhere, and you need to break down a food source that has a certain chirality. In order to be sucessful, your enzymes must fit this chirality requirement (much like threads on pipes) for this reaction to occur). From here on, your proteins, RNAs, DNAs, must all evolve to be of a certain chirality for everything to work...
Um...it's the wrong fsckin' answer?
Anyone with OChem 101 can tell you that. And I'm a chemistry major.
-=- SiliconKnight
The two enantiomers of a chiral (asymmetrical) molecule are identical in every respect, except that they are mirror-images of each other. Call the two enantiomers of this particular molecule L and R. If you add an electron to L you get L-plus-an-electron (call it L+e) which by definition cannot be any less stable than R+e - in other words, the flip from one to the other simply can't be caused by the addition of the electron by itself.
I'm sure that these research findings are genuine but they've been edited into meaninglessness in order to make a press release - rather like the recent "space is flat" story, which, by the time it was "explained" for the general public, made no sense at all. The rules of editing press releases are:
One thing that might have been omitted:
Anything like that does give the possibility of an electron causing a symmetry-flip, because you're not flipping a whole system, just one part of it, and there's nothing to stop a system where one part only is flipped being significantly different from one where it isn't. The system consisting of two left gloves is about as valuable as the system consisting of two right gloves (system flipped as a whole) but a lot less valuable than the system consisting of one left and one right glove!But I wish someone would get hold of the real information and fill in the gaps...
This is a classical example of a collision of two different worlds with two very different sets of interest: slashdot vs. science. Let me elaborate.
One of the less original ideas, though, is the announcement of a new type of memory. Anything can be sold to the public as a new memory. I have seen so many proposals for new types of memories come and go that I'll believe them when I see them.
These new chiral molecules do have special applications, I cite their website:
That's all right, but is it really a story for slashdot?
Liquid crystal displays utilise a feature of liquid crystals in that they line up differently when a voltage is applied, and this twisted alignment causes polarised light passing through them to be rotated. There is a polarising filter on both sides (or on one side with reflective layer at the back so light goes through the same filter twice).
When a voltage is applied, the area appears to go black, because the light polarised by the first filter has been rotated so that it doesn't go through the second filter. Where no voltage has been applied, the light goes through as normal.
Scale this up a bit, make the areas to which you can selectively apply a voltage smaller, add a back light, print a matrix of magenta, cyan, and yellow blobs on the screen, and you have an LCD screen. The screen will be black when off because the two polarising layers are at right angles to each other, and no light gets through unless something (the liquid crystal layer) rotates the light between the two polarising filters.
You can play with this if you have an old LCD calculator, and take it apart. If you find a removable polarising filter, you may be able to reverse it and find that your calculator now does white digits on a black background.
Alternatively, you can remove it altogether, and have a calculator that only you can read (because you are wearing polarising shades).
Back to the subject at hand; Will this process make LCD panel displays easier to build or cheaper? With CRT monitor prices dropping like, errm.. CRT monitors, nothing seems to be happening to LCD monitor prices; they are still ridiculously expensive (although I'm still drooling over the prospect of getting a nice 17" LG Electronics display (Saw one at Linux Expo, London last year, and it made me wonder what it was I've been looking at all this time...))
On the other hand this does seem to be quite relevant to nanotechnology. There is an analogy in the visual system, where a pigment in the retina absorbs a photon and changes conformation (not chirality) -- this shape change ultimately triggers the neural impulse etc. The researchers do specifically mention sensors in their information, so perhaps this sort of chirality change would be useful as a detector of some sort. Or if you could bind one end of the molecule to a larger molecule like a protein, you'd have a teensy tiny lever arm. Neato.
I am quite civilized, and I should be brought a beer immediately. -- Bruce Sterling
Always was L and R for me, but then I took O-chem, ummm, 17 years ago now so maybe it's obsolete terminology. US vs. the world thing, perhaps? (I was in the US) Where did you take O-chem? Non US chemists out there, can you comment? Any IUPAC board members read /.? (cackle)
I am quite civilized, and I should be brought a beer immediately. -- Bruce Sterling
I am former member of the Canary lab (back when I was doing my PhD), and here is one of the first papers we published on dynamically chiral compounds: http://www.ch.ic.ac.uk/ectoc/echet96/papers/003/in dex.htm This web paper was written back in 1996, and has some animations, as well as some more background on chiral compounds (tripodal metal complexes in particular). Some of the structures need to use a plugin from www.mdli.com (ChemChime). Simple explanation: In these systems, there is equal probability of finding either conformation (left-handed or right-handed), in the systems we were working, a single point derivatization of the organic part leads to a bias towards one of the conformation w/ respect to the other, hence dynamic chiral control.
-- jmcastagnetto "Life is, don't ask", Me.