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Tuesday, August 19, 2014

Chemistry Lit Feature Vol. V

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

Tree Town Chemistry is back! After a mostly unintended summer hiatus, I am gearing up to blog throughout the semester once again. What better way to start back than with a literature feature?

Before we jump into that, I would like to announce that I will also be blogging for the Rackham Graduate School this semester as part of the Student Voices series. The posts there will be for a more general audience and the content will be more on the life side of the work-life spectrum, but I will be sure to cross-post when relevant.

In this episode of the Chemistry Literature Feature, we will look at large-scale characterization of graphene sheets, mechanisms of catalysis by gold complexes, new breakthroughs on the mysteries of energy transfer in photosynthesis, and more. But first:

Overheard at Michigan:
"So I have this black stuff on my platinum and I don't know how to clean it off."
(Labmate takes a quick look.) "Oh yeah, I always just light that on fire. Comes right off."

Analytical: Nondestructive Characterization of the Structural Quality and Thickness of Large-Area Graphene on Various Substrates
Materials chemists spend a lot of time worrying about surfaces - how clean they are, how flat they are, how well-coated they are, etc., and how all of those factors can be controlled. One significant challenge in this process is understanding how microscopic inhomogeneities (nanometer-micrometer size scale) are distributed throughout a macroscopic object. In this study ($), published in Analytical Chemistry (ACS), the authors apply a technique called spectroscopic ellipsometry to quickly build a topological map of graphene films synthesized by chemical vapor deposition on a variety of surfaces. By measuring how the films absorb polarized light, the authors are able to learn about the films' thickness and structural features over macroscopic (millimeter) size scales.

Chemical Biology: The Au clusters induce tumor cell apoptosis via specifically targeting thioredoxin reductase 1 (TrxR1) and suppressing its activity
As chemists, when we think of drugs, we tend to think of organic molecules - some large, some small. However, metals are sometimes used as pharmaceuticals as well, with a well-known example being the platinum-containing chemotherapeutic molecule cisplatin. A recent study ($) published in Chemical Communications (RSC) examines the cancer-fighting properties of well-defined clusters of 25 gold atoms. These clusters, stabilized and disguised from the cell by a peptide wrapper, were shown to enter cancerous cells and trigger their self-destruction by blocking the TrxR1 protein, which keeps the levels of reactive oxygen species inside the cell in check.

Inorganic: An Ultrastable Anode for Long-Life Room-Temperature Sodium-Ion Batteries
Odds are good that you use at least one lithium-ion battery every day of your life, and those odds are only going to get better. The catch? Lithium is rare, which makes it expensive. Chemists, such as the authors of this study ($) from Angewandte Chemie International Edition (GDCh), are investigating replacing the expensive lithium-containing parts of the battery with components made from more common elements such as sodium. In the paper, the authors describe the synthesis, structure, and long-term test behavior of a new sodium-ion battery negative electrode. The material efficiently exchanges sodium ions during charging and discharging up to 3,000 times while retaining ~85% of its capacity.

Materials: Molecular doping of graphene as metal-free electrocatalyst for oxygen reduction reaction
Fuel cells are a hot topic; particularly, a cheap and efficient hydrogen fuel cell would enable us to use hydrogen as a fuel with only pure water as a combustion product. Oxygen reduction is the kinetically limiting step in hydrogen fuel cells, so the faster oxygen reduction becomes, the more energy the fuel cell can pump out. The authors of this study ($), published in Chemical Communications (RSC), investigated a new graphene catalyst chemically modified by small amounts of nitrobenzene ("nitrobenzene-doped graphene"). The catalyst is tested for oxygen reduction activity using several electrochemical methods. The authors found that, although their catalyst was not as active as traditional platinum catalysts, their method of doping graphene significantly increases its activity compared to clean graphene and is worth taking a look at.

Organic: Role of Gold(I) α-Oxo Carbenes in the Oxidation Reactions of Alkynes Catalyzed by Gold(I) Complexes
A particular family of gold(I) complexes is known to catalyze the oxidation of alkynes to vinyl ketones in the presence of an O-atom donor and a nucleophile. However, side products are observed. The reactivity could accounted for if a particularly reactive gold oxo-carbene intermediate was forming, but no direct experimental evidence for that species has been published. To further understand the reaction pathway as catalyzed by gold(I) carbenes, the authors of this paper ($) in the Journal of the American Chemical Society (ACS) carried out a sophisticated study involving mass spectrometry and quantum chemistry calculations. The authors chase after the gold oxo-carbene intermediate and are able to demonstrate that it does indeed form during alkyne oxidations. Based on the difficulty of directly and conclusively identifying short-lived reaction intermediates, this study represents as significant achievement for the field.

Physical: Vibronic coherence in oxygenic photosynthesis
Photosystem II (PSII) is a very special complex. As the authors of this recent study in Nature Chemistry (NPG) point out, it is "the only known natural enzyme that uses solar energy to split water," which makes it a key player in solar energy fixation. With the advent of ultrafast spectroscopic methods (specifically 2-dimensional electronic spectroscopy, 2DES), groups have begun to paint a detailed picture of how the complex interacts with light in hopes of learning what makes it so effective. The authors of this particular paper observe the formation of a coherent excited state in PSII after the complex absorbs light. The coherence, which is a quantum mechanical superposition of two states, was determined to involve both electronic and vibrational states. This "teamwork" between electronic and vibrational motion could be an important factor in what makes PSII so good at charge separation, an important step in photosynthesis.
-University of Michigan research from the Ogilvie group. To read more about this article, check out the press release. Hat tip to Kimberly Daley for discussing coherences.

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

NPG -  Nature Publishing Group
RSC - Royal Society of Chemistry

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