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Invited for this month's cover is the Quantum Chemistry group (ALGC) of the Free University of Brussels (VUB) in collaboration with the Molecular Design and Synthesis (MolDesignS) group of the KU Leuven. The image shows how a variety of computational techniques, such as density functional theory, molecular dynamics, and the noncovalent interaction index, can be used to virtually zoom in on the noncovalent interactions that are key for the supramolecular hydrogelation of bis-urea-based gelators. Read the full text of the article at 10.1002/cplu.201900551., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The current approach to designing low-molecular-weight gelators relies on a laborious trial-and-error process, mainly because of the lack of an accurate description of the noncovalent interactions crucial for supramolecular gelation. In this work, we report a multiscale bottom-up approach composed of several computational techniques to unravel the key interactions in a library of synthesized bis-urea-based gelators and rationalize their experimentally observed hydrogelation performance. In addition to density functional theory calculations and molecular dynamics, the noncovalent interaction index is applied as a tool to visualise and identify the different types of noncovalent interactions. Interestingly, as well as hydrogen bonds between urea moieties, hydrogen bonds between a urea moiety and a pyridine ring were shown to play a detrimental role in the early aggregation phase. These findings enabled us to explain the hydrogelation performance observed in a library of twelve bis-urea derivatives, which were synthesized with 58-95 % yields. From this library, three compounds were discovered to effectively gel water, with the most efficient hydrogelator only requiring a concentration of 0.2 w/v%., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Synthetic hydrogels address a need for affordable, industrially scalable scaffolds for tissue engineering. Herein, a novel low molecular weight gelator is reported that forms self-healing supramolecular hydrogels. Its robust synthesis can be performed in a solvent-free manner using ball milling. Strikingly, encapsulated cells spread and proliferate without specific cell adhesion ligands in the nanofibrous material.

In this article, an analytical methodology to investigate the proteinaceous content in atmospheric size-resolved aerosols collected at the Zeppelin observatory (79 °N, 12 °E) at Ny Ålesund, Svalbard, from September to December 2015, is proposed. Quantitative determination was performed after acidic hydrolysis using ultrahigh-performance liquid chromatography in reversed-phase mode coupled to electrospray ionization tandem mass spectrometry. Chromatographic separation, as well as specificity in the identification, was achieved by derivatization of the amino acids with N-butyl nicotinic acid N-hydroxysuccinimide ester prior to the analysis. The chromatographic run was performed within 11 min and instrumental levels of detection (LODs) were between 0.2 and 8.1 pg injected on the column, except for arginine which exhibited an LOD of 37 pg. Corresponding method LODs were between 0.01 and 1.9 fmol/m 3 , based on the average air sampling volume of 57 m 3 . The sum of free amino acids and hydrolyzed polyamino acids was shown to vary within 6-2914 and 0.02-1417 pmol/m 3 for particles in sizes < 2 and 2-10 μm in equivalent aerodynamic diameter, respectively. Leucine, alanine, and valine were the most abundant among the amino acids in both aerosol size fractions. In an attempt to elucidate source areas of the collected aerosols, 5- to 10-day 3D backward trajectories reaching the sampling station were calculated. Overall, the method described here provides a first time estimate of the proteinaceous content, that is, the sum of free and polyamino acids, in size-resolved aerosols collected in the Arctic. Graphical Abstract ᅟ.