Chemistry Literature Feature, Vol. X

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It's the tenth blog-o-versary of the Chemistry Literature Feature! In celebration, here are ten (minus four) cool chemistry papers, one from each of the chemical disciplines. This time, we'll learn what gives the "sea sapphire" its color, see single molecules of proteins stick to a platinum surface, and see a new technique for learning about the fate of photoexcited electrons in an important photocatalyst material.

Don't know what a sea sapphire is? Neither did I!

Analytical - Observation of Single-Protein and DNA Macromolecule Collisions on Ultramicroelectrodes
Chemistry is typically understood "in the ensemble" - that is, a large number of atoms or molecules are observed simultaneously. Recently, particularly in spectroscopic fields, researchers have gone to great lengths to investigate single-molecule systems where ensemble behavior is impossible. The authors of this communication ($) in the Journal of the American Chemical Society designed an experiment where large molecules - proteins, polystyrene beads, and strands of DNA - were placed in solution with an extremely small platinum electrode (linked photo shows a carbon fiber ultramicroelectrode). These "insulating objects" block the flow of electric current from the electrode. The study examines how the size and shape of the objects contribute to the observed changes in the current and paves the way for further investigation into macromolecule behavior in solution via electrochemical methods - without the use of a complicated laser.

Chemical Biology - Structural Basis for the Brilliant Colors of Sapphirinid Copepods
I never thought I would learn of an animal's existence from the Journal of the American Chemical Society, but the authors of this communication ($) took an interest in figuring out what gives color to the sapphirinid copepod. Sappirinid copepods are millimeter-sized animals similar to plankton that inhabit oceans around the globe. The males have crystalline shells that scatter light, creating brilliant flashes of color when the sun hits them just right - an evolutionary adaptation known as "death wish."* The communication explains why different copepods flash different colors. The authors used scanning electron microscopy to examine the crystal sizes in the copepod shells and also the thickness of the liquid cytoplasm layer between the crystal layers, finding that copepods of different colors show differences in the cytoplasm layer thickness rather than crystal size. The variance in spacing between the crystals in the copepod shells gives rise to the observed colors via photonic effects similar to what gives opals their colors.

*: editorial, sort of

Inorganic - A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1'-Ferrocenediyl Backbone
N-heterocyclic carbenes (NHCs) are some of the most interesting ligands in organometallic chemistry. Sad graduate students have synthesized hundreds of NHCs by varying the size and electronic properties of substituents near the carbene site, and the fruits of these modifications are often made manifest in the catalytic properties of metal-NHC complexes. Traditional NHC ligands are based on a 5-membered imidazole ring. Lately, however, synthetic chemists have explored NHCs with larger rings, showing that straining the bond angles near the carbene increases its reactivity. The authors of this recent paper ($) in Inorganic Chemistry (ACS) perform a thorough investigation of a new series of 6-membered NHCs made chiral by a ferrocene backbone. Their NHC molecule is extremely reactive and is capable reacting with dichloromethane and acetonitrile. The authors go on to characterize the compound electrochemically in preparation for future synthetic work to take advantage of its chirality.

Materials - Fabrication of Self-Cleaning, Reusable Titania Templates for Nanometer and Micrometer Scale Protein Patterning
Biological sensing technologies are becoming smaller and smaller, and nanopatterned arrays created using laser etching methods are emerging to the forefront of miniaturization efforts. Both for research and commercial applications, easily-renewed biosensor arrays are cost-effective and attractive. The authors of this paper ($) in ACS Nano present a method for decorating a titanium dioxide surface with organic groups capable of binding proteins. A separate step makes the rest of the surface inert to proteins, allowing the authors to bind proteins in an array pattern in specific locations on the film. This is supported with fluorescence microscopy, which causes the proteins to light up and determines where they are. The protein-bound film can function as a biosensor. Importantly, though, the authors demonstrate that shining strong ultraviolet light on the film causes the titanium oxide to chew up all the proteins, leaving the film surface free to bind a new set of proteins and create a new biosensor from the recycled surface.

Materials chemistry readers will get an especial kick out of the Chemical Biology article as well.

Organic - Base-Promoted β-C(sp3)-H Functionalization of Enaminones: An Approach to Polysubstituted Pyridines
If you've ever studied or practiced organic chemistry, you know that the reactions can quickly become an excessive soup of starting materials, acids or bases, catalysts, solvents, and additives. In addition to adding up in terms of complexity, all of these reagents contribute to the cost of a reaction, both energetically, monetarily, and environmentally. The group who published this recent paper ($) in the Journal of Organic Chemistry (ACS) has discovered a very simple base-promoted route for joining ynones to ethylamines for the production of pyridine rings. With only two equivalents of base, the two molecules snap together like Legos, then eliminate water to yield the pyridine product. Pyridines are useful throughout organic chemistry, both as structural motifs and also as common binding sites for metals, so a convenient and versatile route (34 pyridines reported!) such as this could be quite useful.

Physical - Chronoabsorptometry To Investigate Conduction-Band-Mediated Electron Transfer in Mesoporoous TiO2 Thin Films
Photochemical processes - like solar cells, for example - depend on the ability of an excited-state electron to move throughout a material to a site where it can do useful work. However, a bunch of things can happen to it along the way, and simple methods to understand these various processes and, critically, how quickly they happen relative to one another, are in short supply. A new paper ($) in the Journal of Physical Chemistry C (ACS) provides a thorough mathematical introduction to a technique called chronoabsorptometry, in which optical spectroscopy is used to keep track of the state of a probe molecule bound to the surface of the TiO2 under study. The electronic properties of the TiO2 film are controlled separately by an electrical potential. The authors vary the potential while watching the probe to learn more about how photoexcited electrons move through the film. By matching their results with previously published conclusions from other, more widely-used techniques, the authors are able to verify the validity of their method.

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