Spotlights pubs.acs.org/JPCL
Spotlights: Volume 7, Issue 23
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DYNAMICS OF THE HYDRATION WATER OF ANTIFREEZE GLYCOPROTEINS Polar seawater is cold enough to freeze the average mackerel solid, so how do Arctic and Antarctic fish survive and thrive? The simple answer: Antifreeze! From the Antarctic toothfish to the Arctic cod, polar fish create their own antifreeze proteins and glycoproteins (AFPs and AFGPs). These molecules permanently attach to ice crystals in the blood and impede their growth, thus maintaining the fluidity of the blood. Despite decades of research on AFGPs, the exact molecular mechanism of antifreeze protection remains unclear. In their Letter, Groot et al. (10.1021/acs.jpclett.6b02483) used polarization-resolved femtosecond infrared spectroscopy to study the dynamics of water in solutions of AFGPs. They found that a fraction of the water molecules was strongly slowed down by the interaction with the AFGP surface. The fraction of slow water molecules scales with the size and concentration of AFGP, and the effect of AFGPs on the dynamics of water is comparable to the effect of nonantifreeze proteins, both at room temperature and at 1 °C. The addition of borate inhibited the antifreeze activity but did not affect the dynamics of water hydrating the AFGP. The borate induced gel formation by forming cross-links between the AFGP sugar groups, a finding that supports a mechanism in which the sugar unit of AFGP forms the active ice-binding site.
hydrogen. The most common methods produce hydrogen that contains a small fraction of carbon monoxide, which must be removedoften using methane. Zhao et al. tackle this problem in their Letter using computational techniques (10.1021/ acs.jpclett.6b02443). They propose a cleaner way to separate CO from H2 when the mixed gas is dissolved in water; their method uses ice nanotubes to trap CO when formed inside of carbon nanotubes. Using molecular dynamics simulations, the authors found that quasi-one-dimensional polygonal CO and H2 hydrates can be formed spontaneously at ambient pressure in single-walled carbon nanotubes. They also report that preferential adsorption of CO over H2 molecules is found in octagonal and nonagonal ice nanotubes at ambient pressure due to the much lower value of the potential of mean force difference for CO than H2 to enter the nanochannel. The method has potential applications in hydrogen purification and beyond.
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MECHANISTIC INSIGHTS INTO THE CHALLENGES OF CYCLING A NONAQUEOUS NA−O2 BATTERY There may be no such thing as the perfect battery. Each type has its own benefits and drawbacks, and superoxide-based nonaqueous metal−oxygen batteries are no exception. They can store a great deal of energy, and they exhibit high roundtrip efficiencies, but their cycling performance has been disappointing. The life expectancy of a battery is a key selling point; therefore, research is ongoing to extend the life of the nonaqueous metal−oxygen battery. In their Letter, Liu et al. (10.1021/acs.jpclett.6b02267) provide mechanistic insights into the cycling characteristics of a superoxide-based nonaqueous Na−O2 battery. The authors used microscopy and spectroscopy techniques to study the reversible and irreversible processes in Na−O2 batteries, and their findings suggest that the primary reason for cell failure is the side reaction products covering the carbon electrode surface and hindering electron transfer across the electrode−electrolyte interface. These side reactions seem to stem from the chemical aggressiveness of Na−O2 in both the solid-phase and the dissolved species in the electrolyte.
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CO SEPARATION FROM H2 VIA HYDRATE FORMATION IN SINGLE-WALLED CARBON NANOTUBES Hydrogen−oxygen fuel cells are a promising competitor to traditional energy sources, and their advantages are many. Hydrogen fuel cells are highly efficient and, unlike combustion engines, do not produce greenhouse gases. Unfortunately, the same cannot be said for industrial production of the required © 2016 American Chemical Society
Published: December 1, 2016 4956
DOI: 10.1021/acs.jpclett.6b02705 J. Phys. Chem. Lett. 2016, 7, 4956−4956
