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Tuesday, April 21, 2015

Chemistry Literature Feature, Vol. IX

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

Overheard at Michigan: Snapchat Edition
These results not sponsored by Dell, but I can't
really understand why.
Once again, it's time to look at six cool papers from five cool fields and also organic chemistry! In this ninth episode of the Chemistry Literature Feature, we'll take a look at a paper that pulls the old bait-and-switch on drug-resistant cancers, a one-step experimental verification of some really old kinetics thinking, and a new look at how frustrated Lewis pairs catalyze hydrogen activation. But first, at your left, a simulation gone horribly wrong!

Analytical - Microimaging of Transient Concentration Profiles of Reactant and Product Molecules during Catalytic Conversion in Nanoporous Materials
Studying chemical kinetics - the individual steps that compose a chemical reaction and their respective rates - is hard. Kinetic information is even more elusive during reactions on solid surfaces where the diffusion of substrates to small, stationary active sites plays an intimate role. The authors of this study ($) in Angewandte Chemie (GDCh) present a cutting-edge technique that uses infrared spectroscopy to track the progress of benzene molecules through a network of porous glass decorated with nickel catalyst particles during gas-phase benzene hydrogenation. The infrared technique provides information not only on the rates of benzene consumption and cyclohexane production, but also on where within the catalyst material these processes occur. The data is the among the first in-situ verifications of kinetics principles that were proposed in the early part of the 20th century.

Chemical Biology - Nucleotides with Altered Hydrogen Bonding Capacities Impede Human DNA Polymerase η by Reducing Synthesis in the Presence of the Major Cisplatin DNA Adduct
Cisplatin, a surprisingly simple inorganic complex, is a widely-used drug in cancer therapy. It functions by binding to DNA and fouling up the action of enzymes called polymerases that make new copies of DNA during cell replication. However, some cancers become resistant to platinum treatments by using specialized polymerases capable of working around cisplatin. The authors of this paper ($) in the Journal of the American Chemical Society have studied the effects of a synthetic nucleotide - a DNA building block - administered along with cisplatin. The idea is that the synthetic nucleotide inhibits a specific kind of DNA polymerase capable of working around the cisplatin. The authors found that polymerase grabs their synthetic nucleotide, which is too large for it to handle, and incorporates it into the DNA strand, but then the polymerase is prevented from completing DNA replication. While far from an in vivo cell study, this paper furthers an interesting new addition to cancer therapies.

Inorganic - Anionic Metal-Organic Framework for Adsorption and Separation of Light Hydrocarbons
If you've been following this blog for a while now, you'll have realized that I can't resist sharing a good paper about metal-organic frameworks (MOFs). MOFs are solid-state "coordination polymers" with huge internal surface areas that have promise for applications in a number of important chemical processes. In this recent communication ($), published in Inorganic Chemistry (ACS), the authors report a new nickel-based MOF with an interesting "interpenetrated" structure. The MOF is capable of adsorbing very high quantities of light hydrocarbons like acetylene and methane due to a crystal structure which is more than half void space. This compound shows initial promise as a separation agent for light hydrocarbons - a process which is accomplished currently by time- and energy-intensive fractional distillation.

Materials -  Ab initio study of doping effects on LiMnO2 and Li2MnO3 cathode materials for Li-ion batteries
So-called "over-lithiated oxides" have been investigated recently as electrode materials for lithium-ion batteries; the idea here is that with more lithium ions jammed into the structure, the compound stores more charge, which translates to a longer lifetime for your cell phone battery. However, over-lithiated oxides such as Li2MnO3 are rarely used in pure form, and studies to understand the effects of doping these materials - intentionally adding impurities to produce a desired effect - are underway. This computational work ($), published in the Journal of Materials Chemistry A (RSC) investigates the effects of 12 total dopants on key performance metrics for lithium-ion cathode materials: electronic conductivity, ionic conductivity, thermodynamic stability, and electrochemical potential. The paper is brimming with information. Highlighting only one conclusion would be a disservice, but this work could serve as a great reference for synthetic chemists in the battery field.

Organic - Biomimetic Total Synthesis of Santalin Y
Total synthesis is a phrase used by chemists to refer to the painstaking process of synthesizing large and complex molecules, usually of a biological origin. These molecules usually contain many stereocenters or reactive functional groups, making their artificial synthesis a huge challenge. The authors of this short paper ($) in Angewandte Chemie (GDCh) have developed a total synthesis for santalin Y, a bright yellow pigment found in certain kinds of sandalwood. The highlight of the paper is the installation of five (!) stereocenters in a single chemical step - usually one is hard enough. This step earned the study the "Very Important Paper" designation by Angewandte's editors. While santalin Y might not be the most exciting molecule ever, these total synthesis investigations force chemists to develop creative ways of building molecular motifs which expands the set of tools available for creating other molecules.

Physical - Are intramolecular frustrated Lewis pairs also intramolecular catalysts? A theoretical study on H2 activation
A frustrated Lewis pair arises when two groups on the same molecule, one Lewis acid and one Lewis base, are prevented from forming an adduct by some steric factor, such as a carbon skeleton that keeps them apart. Frustrated Lewis pairs (FLPs) are a little like two angry hockey players held apart by the referee - when they want to go at it, the space between them is a very dangerous place to be. This high-energy non-interaction has been investigated for its role in catalysis, specifically small-molecule activation. The prevailing hypothesis is that the FLP binds a small molecule and then, in order to stabilize the high energy cost of not forming an adduct, rips the molecule apart. A recent paper ($) published in Physical Chemistry and Chemical Physics (RSC) presents the results of some calculations that suggest that some types of FLPs may not catalyze reactions by that mechanism at all, but by a dimeric pathway in which two FLP molecules cooperate to catalyze the reaction two times at once. The authors propose that their pathway is favored due to steric considerations, paving the way for an experimental kinetic investigation.

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

ACS - American Chemical Society
GDCh - Gesellschaft Deutscher Chemiker (German Chemical Society)
RSC - Royal Society of Chemistry

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