Spotlights Cite This: J. Phys. Chem. Lett. 2018, 9, 3798−3798
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Spotlights: Volume 9, Issue 13
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ABSORPTION SPECTRA OF FAD EMBEDDED IN CRYPTOCHROMES The godwit, the whimbrel, and the indigo bunting may have unfamiliar names, but all three are birds that possess an ability that has long captured people’s interest around the world: seasonal migration by air. Dubbed “avian magnetoreception,” the intriguing ability of migrating birds to perceive the Earth’s magnetic field and use it for navigation is well documented, but its underlying biophysical mechanism is not yet fully understood. Experiments have shown that the wavelength of the ambient light is crucial for the magnetic compass sense: The migratory birds could utilize the magnetic compass when exposed to blue or green light but not when only red light was available. Evidence suggests that the photoreceptor protein cryptochrome may be the key to avian magnetoreception because it can host the so-called radical pair intermediates that are sensitive to external magnetic perturbations. A key component of cryptochrome is a flavin adenine dinucleotide (FAD) cofactor known to absorb light in the visible region of the electromagnetic spectrum. The required light-activation of the avian magnetic compass could naturally be explained if this FAD cofactor shows absorption at the specific light wavelengths under which the magnetic compass sense is operational. Nielsen et al. (10.1021/acs.jpclett.8b01528) tested this hypothesis by calculating the absorption spectra of FAD embedded in six different cryptochromes, including a homology model of Erithacus rubecula cryptochrome 4, which is thought to be responsible for magnetic sensing in the European robin. The authors found that the calculated spectra do not extend into the green region of the visible part of the electromagnetic spectrum, leading to the conclusion that the electronic properties of the embedded FAD cannot deliver a complete explanation to the observed phenomenon. The authors propose that a secondary, as-yet-unknown photoreceptor or cofactor exists that would drastically change the absorption spectrum of the magnetic sensor, extending it into the green region of the electromagnetic spectrum.
condensation kinetics of water on single aerosol particles of varying viscosities ranging from very dry to very humid conditions and over a wide temperature range. They found that the time scale for particle equilibration is fast, even for glassy amorphous particles, and depends only weakly on viscosity.
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HYDROGEN BOND LENGTH AS A KEY TO UNDERSTANDING SWEETNESS Roses are red, violets are blue, sugar is sweetbut that’s not always true. In fact, different sugars have different levels of sweetness despite their many chemical similarities. In their Letter, Bruni et al. (10.1021/acs.jpclett.8b01280) address the different sweetness levels of three monosaccharides: fructose, which is the sweetest of the group; glucose, which is a factor of 2 less sweet than fructose; and mannose, which is tasteless, with a bitter aftertaste. The authors determined the structure of the hydration shell of these molecules in solution via neutron diffraction experiments in combination with computer simulations. They found that, in order to elicit a sweet taste, a sugar must exhibit at least two atomic sites available for hydrogen bonds with water (or with the receptor) and a hydrophobic site within the so-called sweetness triangle model. The authors show a correlation between the sweetness of these molecules and the strength of their hydrogen bonds with water. The findings may prove useful in the synthesis of new, better-tasting artificial sweeteners.
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CONDENSATION KINETICS OF WATER ON AMORPHOUS AEROSOL PARTICLES The term “aerosol” carries negative connotations for many people of a certain age, prompting mental images of Aqua Net clouds in the ladies room and dire warnings about holes in the ozone layer on the local news. Of course, an aerosol is simply a suspension of particles in the air, and some aerosols will protect you from others, as in the case of an asthma patient’s rescue inhaler providing drug delivery directly to the lungs to counteract airborne pollutants. Much is known about the behavior of particles in an aerosol, but much remains to be learned as well. In their Letter, Rothfuss et al. (10.1021/ acs.jpclett.8b01365) note that quantifying the kinetics of the condensation of water and dissolution of viscous amorphous particles is important for understanding the hygroscopic response of aerosol particles in the atmosphere and for inhalation aerosol therapies. The authors explored the © 2018 American Chemical Society
Published: July 5, 2018 3798
DOI: 10.1021/acs.jpclett.8b02008 J. Phys. Chem. Lett. 2018, 9, 3798−3798
