In many cases it is notoriously difficult to determine the exact structure of a molecule, especially with larger ones. Stereocenters tend to make things worse, and interesting molecules tend to have several of them. Have you ever sat up to the neck in a pile of inconclusive spectra and wished you could just hold it and see the molecule just like in those colored balls-and-sticks-models everyone likes to draw in their papers?
Norman Borlaug is considered to be one of the greatest scientists who ever lived. He was the father of the Green Revolution that multiplied agricultural yields all over the planet, saving millions from famine and starvation.
Here’s his advice for young scientists who want to follow in his footsteps:
I have been on to self-healing materials for some time, usually writing about them in my german blog or for newspapers and magazines. Self-healing is what makes biology superior to technology. Organisms don’t just have astonishing properties – materials have, too – but they retain them by constant regeneration and while doing so even adapt to changing conditions. We want, we need our advanced materials to do the same.
This is especially true for superhydrophobic coatings, which cause the Lotus Effect and hence are very promising not only for self-cleaning items, but also for anti-corrosion or anti-adhesive coatings. Everyone who ever scratched barnacles from the bottom of a ship knows how useful this could be. Since a superhydrophobic coating also reduces drag on surfaces, painting commercial ships with such a formulation would be a billion-dollar business.
The coming scarcity of the noble gas Helium has been the topic of a few media articles recently, for example the one by John Timmer from Ars Technica (who also was of great help during my preparation of the interview below). The basic idea comes from Robert Richardson who got the 1996 Physics Nobel for discovering suprafluidity in, yes, Helium. His lecture at the Lindau Nobel Laureate Meeting attracted a great deal of attention, precisely because no one really had ever heard of that problem.
Helium is, essentially a non-renewable resource that is, while being the second-most abundant element in the universe, comparatively scarce on earth. The main source is alpha decay of certain unstable isotopes in minerals, and as you might imagine, that’s a rather slow process. There are several cryogenic applications like high-end NMR spectrometers that won’t run without Helium, so there is no easy replacement. On the other hand, there are huge amounts of helium wasted every day because the gas is kept artificially cheap.
I met Professor Richardson at the Lindau conference and he was kind enough to answer a few questions about the looming resource crisis, it’s causes and possible solutions.
The photoswitching capability of azobenzenes has recently been used extensively in photoreactive supramolecular materials. One of the most astonishing uses of azonenzene photoswitching is the reversible association of these molecules with certain cyclodextrines. Azobenzenes change their structure reversibly under irradiation. There’s a cis-form and a trans-form, and photoisomerisation happens reliably wavelengths of 350 (trans –> cis) and 455 (cis –> trans) nanometer.
As it happens the trans-azobenzene fits snugly in the cyclodextrine cavity, while the bent cis-form doesn’t. This offers a number of interesting possibilities, ranging from the inevitable switchable hydrogels to rather more amazing structures, such as switchable ion channels and functionalized surfaces. (more…)
Axial-chirality or atropisomerism is a very useful property as demonstrated by various chiral catalysts containing BINOL, BINAP and similar groups, but not only there. Many important natural products like e.g. the antibiotic Vancomycin are also atropisomers, which makes this property a very important aspect of stereoselective chemical synthesis. Which is extremely difficult to achieve synthetically with sufficient enantiomeric excesses. I personally always considered it next to impossible, except in special cases, when, for example, one configuration is enforced over the other by the shape of the rest of the molecule.
However, it seems that I’m wrong and that there is a way. Recently a group around Jeffrey L. Gustafson from Yale made some interesting progress in that direction. They report a tripeptide catalyst that mediates highly enantioselective electrophilic bromination of aromatic rings. The significance for atropisomerism stems from the fact that bromine atoms next to a biaryl single bond effectively prevent rotation around this bond if another functional group is present at the other ring.
With increasing demand for effective separation of small-molecule gases – think of carbon caption and storage – there has been a lot of research recently into strategies and materials suitable for those applications. The traditional way to separate gases like nitrogen, oxygen or carbon dioxide is to freeze them out one by one, which is a very energy-consuming and in the case of oxygen occasionally even dangerous thing to do (famous last words: “Should my solvent turn blue in the cryo trap?”). Also, you can’t realistically sequester carbon dioxide from power plants this way.
Recently I came across a number of attempts to explain the “handedness” of life – the fact that proteins consist only of L-amino acids – by the crystallization behavior of amino acids. The general idea is that something that happens at the transition between solution and crystal that favors one of the enantiomers over the other. I have to admit that it sounds a lot less esoteric than the idea that polarized starlight somehow influenced the formation of interstellar amino acids sufficiently to create such an effect, but frankly, I don’t buy it.
Even if you don’t follow materials research closely you may have come across the amazing properties of spider silk. The stuff is stronger than steel, yet more elastic than most artificial fibres, despite being made of proteins only. It owes its remarkable strength to hydrogen bonds and its microstructure of amorphous and crystalline domains.
But the really amazing thing about spider silk is its assembly. The precursor protein solution is stored as a stable liquid within the spider’s body, but when it exits through the spinning gland it immediately precipitates into a solid protein thread. This shows not only what amazing tricks are possible with those versatile biomolecules, but also that we have only just begun to unravel their secrets. There have been, however, two recent publications in Nature going a long way to explaining the controlled transition from solution to silk. The one I found most inspiring deals with the molecular details of a pH switch at the N-terminus of silk proteins.
Now that we know that the hole drilled by the Deepwater Horizon will, for the foreseeable time, keep on gushing, we better take a look at the chemicals used to keep the oil from forming a film at the surface. Unsurprisingly, those chemicals are rather toxic by themselves, although they are far less persistent in the environment than crude oil. As far as I know, about 500,000 gallons of dispersants have already been deployed in the Deepwater Horizon disaster, either by ship or by plane.
Somehow this never occurred to me before, but nanoparticles don’t have to be made from metals or other inorganics. They can even be biodegradable. It’s something you tend to forget when you keep reading papers about how metal oxide nanoparticles penetrate cells and catalyze the formation of free radicals or whatever.
But of course there is always the option of creating nano-sized chunks of common polymers. The major drawback is that they don’t have as interesting physical properties of inorganic particles, with all those size-depending effects and abundant catalytically active sites. They are, in short, a lot less interesting than their inorganic counterparts and that’s why you rarely hear about them.
When it comes to chemistry, surfaces are the places to be. Where two phases meet, interesting stuff is bound to happen. One of the phase interactions that received increased attention during the last few years is the peculiar meeting of a liquid and a solid. One rather interesting phenomenon encountered here is the lotus effect, where water drops roll off a surface because it is not only hydrophobic, but also nanostructured to reduce affinity further. We call this, for obvious reasons, superhydrophobic. Afterwards, surfaces were constructed that are superoleophobic, and amazingly one that is both at the same time. This tunable property of a liquid-solid interface is called wettability, and it is probably the prototypal liquid-solid interaction.
From a chemists point of view, however, the concept of wettability has a major flaw: It is entirely macroscopic. You define superhydrophobicity by measuring the contact angle between a drop of water and the surface. On the molecular level the concept of wettability is poorly defined. And that’s not the only example for this problem. There is a general lack of information about molecular and atomic details of liquid-solid interactions, especially when compared to the knowledge to be gained. Just recently a paper about supercooled liquid gold, for example, revealed astonishing details about the way the surface influences the freezing point of a liquid.
It’s well-known that many liquid metals can be cooled below their freezing point. This is, scientists assume, due to dense and symmetric, but non-periodic ordering within the liquid. This theory implies that the freezing point of supercooled metal liquids can be controlled, just like crystallization can be induced by a template – all it takes is something that stabilizes the short-range order of the liquid. In the latest issue of Nature researchers from Grenoble published an impressive proof of this concept, not only showing that phase transistion temperatures depend on several variables, but also revealing the structure forced on the liquid.
Ionic liquids are already known as „green“ solvents since they don’t evaporate and neither burn nor explode, which is what every chemist really is looking for in a solvent. Additionally, they are powerful solvents with easily tunable properties and of course electrically conducting. Very useful stuff, ionic liquids. Unfortunately they are generally at least as toxic as normal solvents, and since they look rather promising for everyday applications like batteries and even cosmetics, that is a serious drawback.
There is, however, one huge advantage to ionic liquids: Since they all consist of cations and anions which can be combined at will, every new compound really means that there are dozens of new, unique solvents available. Although many current compounds are based on quaternary ammonium salts, some of which are potent biocides, the structural diversity of known compounds suggest that truly green ionic liquids are well within reach.
Even from Germany it was near impossible not to catch some of the buzz around this year’s ACS Meeting in San Francisco, especially because there wasn’t just the usual stuff going on. Announcing in advance that “Cold fusion moves closer to the mainstream” was bound to get some extra attention, since most people still consider researchers in this field as being of the underwear-as-headgear variety. Even its supporters tend to agree that this line of research attracts a number of such types.
On the other hand the field has been successfully rebranded as LENR – low energy nuclear reactions – and there is a whole bunch of topics investigated now aside from what Pons and Fleischman originally claimed, so it certainly looks a lot less crackpotty than it did in the early years. The current ringing endorsement by ACS helps, of course.
Chemical Science is – or rather is going to be – a new chemistry journal published by the Royal Society. I’m not entirely sure why we need another general chemistry journal that no one can really read thoroughly anyway, but anyway, I registered for the newsletter and just got the news that the very first paper of the new journal just went online.
The reason why I mention this is that the author of this is well-known to readers of this blog: It’s Bert Meijer from the Eindhoven University of Technology, who will be in Nürnberg at EuCheMS 2010. He is this year’s plenary speaker at the supramolecular systems session and we already introduced him to you here.
Hydrogels are the only materials that have the potential to be used as a replacement material for functional tissues like cartilage, sinews or muscles. However, while the biological wet and soft materials have impressive mechanical properties and are generally very tough, conventional hydrogels are rather brittle and tend to disintegrate under duress. With one exception, though: Double Network hydrogels can take a lot more force, even exceeding biological tissues or rubber. I just read a paper in Soft Matter that discusses why this is so. The mechanism is rather intriguing.
There has been a veritable hype around fullerenes and carbon nanotubes in recent years, so this modification of carbon has extensively researched. What’s a little less known, is that there are other, very similar structures, made of inorganic building blocks, usually transition metal chalcogenides. There is, however, a difference: In most of the inorganic fullerens (IF) there is no preferred minimal structure like C60.
The one notable exception appears to be MoS2, which forms regular octahedral of discrete sizes, which are about 4 times larger than C60. Calculations show that these octahedra are onion-like, made up of several layers and contain between 1000 and 80000 atoms. As with normal carbon fullerenes, there are several ways to obtain such structures, but their growth mechanism is largely unknown.
Well, what do you do if you don’t know the mechanism of a reaction? You try to catch the intermediates somehow. That’s what researchers from Mainz did with the formation of the MoS2-octahedra. It turns out that the shrink-wrap model of fullerene formation applies to this material as well: In the CVD chamber, large sheets form first, which later on contract into the well-known stable forms. To catch the intermediates, their formation needs to be accelerated, which was why iodine was used to increase solid-state diffusion. The result was rather interesting, because the iodine didn’t do just that.
The latest edition of Nano Letters has yet another paper about some sort of piezoelectric fabric that generates electricity when deformed. In Theory, you could wear pants made from this stuff and power, say, your watch just by walking around. Admittedly this isn’t exactly novel. We heard about it already in 2003 (pdf), 2007 and in February last year (at least. I stopped searching after two minutes). Nevertheless, this paper is rather interesting because it moves away from basic materials design and tackles a question that’s closer to applications: How can devices like this be built into everyday clothes? (more…)
Recently I came across a very interesting article on the website of the German magazine Der Spiegel, which informed me that the current way of storing highly radioactive waste was unsuitable, and the reason for this is chemical. Says there:
Now a US-German research group, in an Article in Angewandte Chemie, raises doubts about the basic principle of storage.
Except that they don’t. The paper is about certain actinide borates with rather complicated structures and interesting properties – basic research with a lot of crystallography. Creating the borate compounds was inspired by a method of storing nuclear waste – very active materials are melted into glass rods and enclosed in a steel container. Depending on the condition, some actinides form crystals within the glass. Not much is known about these crystals, except that they appear to be actinide borates.
Surfaces are full of surprises, and of course mysteries. Ertl described the intricacies of ammonia formation on flat platin surfaces decades ago and won a Nobel for it, but what happens between real catalysts and the reactions they accelerate remains largely unknown. When it comes to the behavior of steps, kinks and other surface features under real conditions, we have hardly scratched the surface yet.
That is because usually surface interactions are observed by scientists, for practical reasons, in near vacuum and at low temperatures. Lots and lots of interesting things simply don’t happen in near vacuum at low temperatures. Nevertheless it turned out that even under these conditions adsorbates induced significant changes in surface morphology, especially on steps and other nonconformities. One should assume that the changes observed so far pale in comparison to what more extreme conditions will do to surfaces. As we read in this recent Science paper by Feng Tao et al, that is indeed the case.
There is a rather interesting offer out for scientists interested in reaching out towards the general public. Science Magazine is opening its online coverage of the AAAS Annual Meeting 2010 for guest bloggers. So if you go to San Diego next month consider posting your impressions from the conference on the official blog. That is, if you have something substantial to say. Knowing the internet, Science makes it entirely clear what they don’t want:
Rants, cut-and-paste jobs from presentations you’re giving, or stenography. We don’t want a synopsis of the session you just attended or delivered, but rather its surprising, salient points spelled out for a lay audience.
This sounds like they really aren’t sure if they should do this. However, there will be a prize for the best blog entry, so it may be worth it.
Prizes will consist of: 1st place: The 1st Place Winner will receive $250; 2nd place: the Second Place Winner will receive a fully paid one-year subscription to Science Magazine; 3rd place: the Third Place Winner will receive a AAAS t-shirt in the style and color selected by Sponsor.
If I win, I want a black one. Of course I won’t win, because first, I’m not going and second, I’m not american. I find the second requirement somewhat puzzling, but on the whole the idea is a good one. I hope other journals and organisations follow this example.
The duck-billed Platypus is such an odd creature that one could get the idea that its survival depends on potential predators laughing themselves to death, but in fact it can rely on a far more potent defense. It carries a venomous sting on its hind legs. Envenoming by a male Ornithorhynchus anatinus causes not only immediate excruciating pain, but also a long-lasting hypersensitivity, probably due to nerve damage.
The venom itself is a complex mixtures of peptides, for example defensin-like peptides similar to those found in venomous reptiles. Curiously those don’t go back to a common ancestor but evolved independently in both lines, as genomic analyses show. Another class of toxins consists of peptides related to C-type natriuretic peptides. CNPs are vasorelaxant peptide hormones that are widely distributed many tissues, notably the central nervous system.
There have been many new developments in quantum computing during the last few years, but last Sunday a paper appeared in Nature Chemistry that shows how far the area really has come. It seems that now things are getting really interesting: American and Australian scientists just built a quantum circuit that calculated the energy Eigenvalues of molecular hydrogen to an accuracy of 1 KJ/mol.
Of course we knew these Eigenvalues before, they can be calculated e.g. with DFT calculations. The amazing thing is the quantum circuit part. Quantum computers existed only in theory. Until now.
Since the year 2000 the German ministry for research and education (BMBF) organizes the science years, with every year dedicated to another subject area. There was already a year of chemistry, in 2003, but 2010 promises to be at least in part about molecular sciences, since the topic this year is the future of energy. And there is a lot of chemistry in energy.