Spotlights Cite This: J. Phys. Chem. Lett. 2018, 9, 3098−3098
Spotlights: Volume 9, Issue 11
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MOLECULAR INSIGHT INTO THE SLIPPERINESS OF ICE
SIMILARITY BETWEEN AMORPHOUS AND CRYSTALLINE PHASES: THE CASE OF TiO2 For nearly a century, the nature of the amorphous state and the structure of glasses has been an unresolved problem; in particular, the relation between the structure of amorphous solids and the corresponding crystals remains uncertain. To compare structures of crystalline polymorphs with each other, and with the amorphous phase of the same compound, it is most natural to present a similarity map like the one shown in the Letter by Mavračić et al. (10.1021/acs.jpclett.8b01067). Although the authors used a sophisticated structural descriptor to obtain this map, they show that it can be partially understood and rationalized in terms of simple structural properties, such as polyhedral connectivity and bonding between atomic constituents. They suggest, however, that a full understanding of structural similarity is made possible only with the use of the advanced mathematical framework that they used. The authors note that it is possible to quantify the extent of structural similarity between amorphous and crystalline phases, thus shedding light on a controversial issue that has been debated for more than 50 years. According to Mavračić et al., individual systems can show a degree of similarity toward certain crystalline polymorphs (as they show for the case of TiO2), and the similarity is not necessarily confined to shortrange order. For some amorphous systems, the network building units might be very similar to those of a crystalline polymorph, whereas other systems might show distorted network building units but more intermediate-range order. Consequently, it is difficult to settle the matter solely within a pictorial model. The authors report that the problem can be tackled quantitatively, within a rigorous mathematical framework, by using structural descriptors. As more sophisticated and targeted structural descriptors become available, similar structural maps are likely to be used in many areas of atomistic−structural research and not only in the world of solid state and materials. With the rise of the fundamental understanding of structure−property relationships, such maps could become a valuable tool for compound property prediction.
In this world of dubious claims and “fake news,” there remains at least one thing we can all agree on: Ice is slippery. This may sound like a simple fact, but the slipperiness of ice has fascinated scientists for more than a century, with no real consensus about its origin. Many scientists point to the presence of a thin lubricating film of liquid water to account for the low friction on ice, but direct evidence of the presence of such a layer under sliding conditions has been elusive. In their Letter, Weber et al. (10.1021/acs.jpclett.8b01188) combine macroscopic friction measurements with surface specific spectroscopy and molecular dynamics simulations to show that ice is slippery without the presence of a liquid water layer. Their measurements show that friction on ice is inversely proportional to the mobility of a single layer of weakly bonded water molecules that diffuse over the ice surface in a rolling motion, thereby facilitating the sliding.
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DIRECT STRUCTURAL ANNOTATION OF MEMBRANE PROTEIN AGGREGATION LOCI USING PEPTIDE-BASED REVERSE MAPPING
In 1985 Ronald Reagan was the leader of the United States, and Michael J. Fox ruled at the box office in “Back to the Future.” Within the next 10 years, both powerful figures would be diagnosed with devastating neurodegenerative diseases, bringing greater attention to the challenges of Alzheimer’s and Parkinson’s diseases and the need for research that could lead to treatments and cures. Progress has been made, and a greater understanding of neurodegenerative diseases has been achieved, but much work remains. For example, it is known that membrane protein aggregation is associated with neurodegenerative diseases, and efforts to map protein aggregation have had some success, but the molecular elements that drive the structural transition from functional to amyloidogenic βsheet polymers remain elusive. In their Letter, Lella and Mahalakshmi (10.1021/acs.jpclett.8b00953) tackle the need for a simple and accurate method for mapping aggregation sites with confidence. They describe and validate a simple, costeffective method that they call “reverse-mapping,” which accurately maps aggregation hotspots in membrane proteins to the amino acid level. The method provides a clean readout of aggregation sequences and can demarcate single-site changes of similar hydrophobicity. They report that the method can be successfully applied even to a β-rich membrane protein and can demarcate subtle differences in the primary sequence. Using this method, they have mapped the aggregation-prone regions of three human nanopore ion channels that are known to be biologically important in neurodegenerative diseases. The authors propose that their bottom-up approach using peptides will be a useful tool to investigate the structural and biophysical properties of all membrane proteins. © 2018 American Chemical Society
pubs.acs.org/JPCL
Published: June 7, 2018 3098
DOI: 10.1021/acs.jpclett.8b01605 J. Phys. Chem. Lett. 2018, 9, 3098−3098
