Spotlights pubs.acs.org/JPCL
Spotlights: Volume 8, Issue 17
■
VIBRONIC ORIGIN OF THE QY ABSORPTION TAIL OF BACTERIOCHLOROPHYLL A VERIFIED BY FLUORESCENCE EXCITATION SPECTROSCOPY AND QUANTUM CHEMICAL SIMULATIONS Most children would be able to explain photosynthesis as it occurs in plants, proudly sharing their knowledge of the words “chlorophyll” and “oxygen”, but they are probably unaware that some bacteria are capable of photosynthesis as well. Some photosynthetic bacteria produce oxygen, but those that contain bacteriochlorophylls (BChl) are anoxygenic. The outstanding position of BChl molecules in this important process relies on their unique optical and redox properties, which have yet to be fully understood. In isolated molecules, the couplings between electrons and nuclei determine the shape and structure of their optical spectra, whereas, in the solvent phase, the added guest− host interactions and basic origin of the inhomogeneous or disorder broadening further modify the spectra. Leiger et al. (10.1021/acs.jpclett.7b01704) used fluorescence excitation spectroscopy to follow the red-tail absorbance of individual solvated BChl a molecules, and they found a very long, quasiexponentially falling absorbance tail up until 940 nm, far past the commonly considered end of the BChl a absorption spectrum. Parallel quantum chemical calculations, along with confirming the experimental results, suggest that this spectrum may extend still further to the red. Theoretical analysis of the data showed that overtones of the fundamental vibrational modes create a virtual continuum of vibrational states in the ground electronic state and thus are responsible for the specific shape of the Qy electronic absorption spectrum of BChl a.
porcine brain, and bovine heart, but none that contain branched-chain fatty acids, such as those found in Bacillus subtilis and many pathogenic bacteria. B. subtilis is commonly used as a model system for Gram-positive bacteria and as a model organism in the study of biofilms, morphogenesis, and more. Nickels et al. (10.1021/acs.jpclett.7b01877) also note that B. subtilis is straightforward to cultivate and process, so they chose to study it as a candidate for a commercially available extract. The authors describe an experimental procedure for producing the physical lipid extract from B. subtilis cultures, and they provide a detailed experimental characterization of the physical extract, including the composition, melting temperature, average transverse structure, and mechanical properties. They also provide their validated computational model for use in future experimental and computational investigations.
■
REACTIONS OF CRIEGEE INTERMEDIATES WITH NON-WATER GREENHOUSE GASES: IMPLICATIONS FOR METAL FREE CHEMICAL FIXATION OF CARBON DIOXIDE With atmospheric concentrations of greenhouse gases at levels unprecedented in at least 800,000 years, there is a growing urgency to better understand the chemistries involved and to find efficient solutions to minimize the impact on the global climate. Kumar and Francisco (10.1021/acs.jpclett.7b01762) report the results of their theoretical study of the possible reactions between Criegee intermediate and greenhouse gases. Their findings suggest that the Criegee intermediate preferably interacts with carbon dioxide (compared with two other greenhouse gases, nitrous oxide and methane) and leads to the exothermic formation of the cyclic carbonate with a moderate barrier, contradicting previous assumptions that suggested the barrierless formation of the cyclic adduct. The authors’ findings of a possible role of Criegee chemistry in removing harmful CO2 from the atmosphere may aid in the future design of more efficient carbon-capture technologies.
■
SULFUR AS AN ACCEPTOR TO BROMINE IN BIOMOLECULAR HALOGEN BONDS Interest in the halogen bond (X-bond) as a tool in the biological sciences has grown since its rediscovery as a stabilizing interaction that both conveys specificity in inhibitor recognition and controls the structure and stability of nucleic acids and proteins. Sulfur has recently gained attention as a potential X-bond target in drug design, but there is currently very little understanding of its X-bonding potential in a biological system. Ford et al. (10.1021/acs.jpclett.7b01725) found that sulfur is comparable to oxygen as a halogen bond acceptor in a biological system, even in geometries that are not as ideal for this type of interaction. The authors found that the geometric constraints are not as stringent for sulfur as for oxygen, making sulfur a viable target in the design of halogenated inhibitors against clinically important enzymes.
■
BACILLUS SUBTILIS LIPID EXTRACT, A BRANCHED-CHAIN FATTY ACID MODEL MEMBRANE Lipid extracts are often used as a model biomembrane by researchers, drug designers, and bioindustrial producers, who study membrane proteins and investigate the physical chemistry of the cell membrane itself. There are many commercially available extracts, including those from Escherichia coli, yeast, © 2017 American Chemical Society
Published: September 7, 2017 4325
DOI: 10.1021/acs.jpclett.7b02280 J. Phys. Chem. Lett. 2017, 8, 4325−4325
