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Wednesday, March 4, 2015

Chemistry Literature Feature, Vol. VIII

Have you seen a good paper lately? Written one? Send it in and have it featured here! treetownchem@gmail.com

In this episode of the Chemistry Literature Feature, we'll take a look at sticky slides that trap bacteria for disease identification, cheap iron catalysts that make expensive chiral molecules, and an experiment with way too many lasers. But first, how precise is your day-to-day performance?

Overheard at Michigan
"I feel like I don't suck at science today. Yesterday, I definitely did, but today I actually know what I'm doing."
Analytical - Supramolecular Scaffolds on Glass Slides as Sugar Based Rewritable Sensor for Bacteria [sic]

Methods for detecting diseases are expensive. On top of the materials cost, a trained technician must be paid to perform the analyses, so both the cost of the device and the cost of the labor needed to run it factor in to the price tag of a diagnostic procedure. As part of an effort to address that concern, the authors of this paper ($, advance article) in Chemical Communications (RSC) have developed a simple procedure for detecting troublesome microbes. The authors coated glass slides with a specially-designed binding agent and a type of ring-shaped sugar called cyclodextrin.The researchers took advantage of the fact that bacteria naturally bind to certain sugars to show selective adhesion of certain cells to the slides based on which types of sugar they prefer. This simple device has the potential to quickly detect and identify infectious microorganisms in a very simple fashion.

Chemical Biology - Polymerase synthesis of DNA labelled with benzylidene cyanoacetamide-based fluorescent molecular rotors: fluorescent light-up probes for DNA-binding proteins
Scientists often use fluorescence-based methods to detect when important biological molecules are interacting with one another. This molecule goes to this molecule and then boom - they light up. However, for DNA-protein interactions, these methods are only well-developed for proteins that change the DNA. The authors of this paper (open access), published in Chemical Communications (RSC), investigated a new type of fluorescence probe capable of reporting on non-enzymatic DNA-protein interactions. These probes are sensitive to the viscosity of their environment. Water near big biomolecules ($) like proteins and DNA tends to be more viscous. The authors showed that their probes lit up much more brightly in viscous environments. Probes of this nature could allow researchers to learn more about hugely important cell processes such as DNA transcription and coiling/uncoiling.

Inorganic - Silica-Supported Tungsten Carbynes (SiO)xW(CH)Mey (x=1, y=2; x=2, y=1): New Efficient Catalysts for Alkyne Cyclotrimerization
Traditionally, catalysts for chemical reactions have been soluble molecules that react with soluble starting materials to produce the desired product. But separating products out of solutions after the reaction is over can be a pain, which translates to higher processing costs at industrial scale. Binding catalysts to solid surfaces to create a heterogeneous catalyst, which can be simply filtered from the reaction, is a growing trend in many areas of chemistry. In a recently-published paper ($) in Organometallics (ACS), researchers bound tungsten-based catalysts to a silica surface and demonstrated that their hybrid catalyst had high activity for cyclotrimerization reactions with alkynes. Additionally, by making the safe assumption that tungsten catalysts were far away from one another (molecularly speaking), the authors were able to shed some more light on the mechanism by which the tungsten catalyst achieves cyclotrimerization.

Inorganic students who love extended solids might also love the Physical paper.

Materials - Controlling the Size of Hot Injection Made Nanocrystals by Manipulating the Diffusion Coefficient of the Solute
Nanocrystalline materials are extremely useful. In addition to showing great promise in a number of different technical applications, their extremely small sizes allow chemists and physicists to investigate fundamental questions related to light-matter interaction. Making nanocrystals uniformly and in specific sizes, then, is very important. The authors of this paper ($) in the Journal of the American Chemical Society delve into the very popular hot injection method for the synthesis of cadmium selenide nanocrystals. They conduct a detailed investigation of what makes this reaction work. Their data shows that cadmium and selenium ions bind to carboxylate additives in solution, and that those carboxylates in turn determine how fast the ions can travel throughout the solution. Using a rigorous model based on classic theories of crystal nucleation, the authors show that control of the diffusion coefficient, or how fast the ions float around solution, is what establishes control over nanocrystal size.

Organic - Relay Iron/Chiral BrΓΈnsted Acid Catalysis: Enantioselective Hydrogenation of Benzoxazinones
Like your right and left hands, chiral molecules are mirror images of one another and cannot be superimposed. Unlike your right and left hands, separating a mixture of chiral molecules into batches of a specific handedness, or chirality, is extremely difficult. In fact, chemists have usually avoided this problem entirely by developing stereoselective synthesis methods that produce exclusively molecules of a given chirality (stereoisomers). Methods that selectively produce one stereoisomer over another are always in high demand. The authors of this paper ($), published in the Journal of the American Chemical Society, have developed a method by which an iron carbonyl catalyst can be used along with a chiral acid to stereoselectively hydrogenate molecules called benzoxazinones. This method improves on other known syntheses by using an extremely cheap iron catalyst as opposed to expensive metals like palladium or ruthenium.

Physical - Channeling Vibrational Energy To Probe the Electronic Density of States in Metal Clusters
Electronic structure describes the energy levels available for compounds to move electrons to and from when making and breaking bonds. Seems important for chemists, right? When it comes to electronic structure, molecules behave one way, bulk solids behave another way, and we know a great deal about both of those regimes. However, when it comes to metal clusters - molecules containing only tens of metal atoms - things get very blurry. The authors of this recent study ($) in the Journal of Physical Chemistry Letters (ACS) used a highly sophisticated laser apparatus to vaporize cobalt metal into small clusters of about ten cobalt atoms. These clusters were then heated by an infrared laser, then hit with an ultraviolet laser. By studying how the clusters' interactions with the ultraviolet laser changed with temperature, the authors were able to experimentally map out the clusters' electronic structure. Information of this nature typically comes from computer simulations, so an experimental verification of those simulations is extremely important.

Author's note: If you're keeping track at home, yes, that was three lasers. This paper has quite possibly the coolest methods section I have ever read.

Remember, if you come across an article that you think should be featured here, send it in! treetownchem@gmail.com

ACS - American Chemical Society
RSC - Royal Society of Chemistry

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