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WOS:000448348600049 Organogelators have a wide range of use in everyday life including drug delivery and controlled release, surface coating and paper industry. In this study, a series of model bisamides have been analyzed as potential organogelators. These molecules are connected by odd and even numbered methylene units (n) in length ranging from 2 to 9. By constructing layers of those molecules along the growth direction we provide an insight into the self-assembly process. A complete systematic analysis of the computational results with B3LYP/6-311+G** suggests that the self-assembly of these potential organogelators is influenced by the odd-even effect, the relative direction of amide carbonyl groups, the bridging spacer chain length and the presence of a chiral alpha carbon. The aforementioned factors alter the strength of the intermolecular hydrogen bonds as well as the van der Waals interactions, which in turn may affect the self-assembly process of gelation and result in the formation of aggregates with different shapes. It is found that molecules with short central chains have an energetic preference for antiparallel arrangement over their parallel analogues as a result of stronger hydrogen bonding interactions. As the central chain elongates, the free energy difference between antiparallel and parallel structures decreases suggesting a compromise between hydrogen bonding and van der Waals interactions. The complete structural analysis suggests ribbon-like structures for achiral even-antiparallel and woven-like structures for odd-parallel systems, respectively. Upon creation of asymmetry on the alpha carbon, a twisted ribbon-like and a coiled coil-like structure are observed for even and odd systems, respectively. Our computational results are in accordance with the experimental results and provide an insight into the self-assembly of layers of bisamides.

Poly(silafluorene-phenylenedivinylene)s and poly((tetraphenyl)-silole- phenylenedivinylene)s are promising materials to be used as chemical sensors for explosives detection. The optoelectronic properties of these polymers as well as their constituent units have been investigated by modeling the properties of their excited states. Natural Transition Orbital analysis and topological φS descriptor assessment have been used to qualitatively and quantitatively characterize the physical nature of the transitions constituting the absorption spectra. The main transitions observed in all oligomers are associated to be a π-π∗ transition of the bridging moiety. Lower energy transitions of charge transfer character are further considered to understand the fluorescence quenching mechanism upon the complexation of these polymers with the analytes. Indeed the charge-transfer character of the first excited state leads to the emergence of thermal deactivation channels and hence to luminescence quenching.

Above its critical aggregation concentration the tfa salt of the peptide A6K self-assembles into micron long, hollow nanotubes with uniform diameters of 52 nm and crystalline order. Here we combine the use of SAXS with cryoTEM and cryo-electron tomography (cryoET, 3D cryoTEM) to study the formation process of the 2D crystalline A6K nanotubes. This study reveals that the formation of these tubes in fact is a crystal growth process, involving different mechanisms depending on the conditions used. Inorganic crystals have been demonstrated to form not only through ion-by-ion addition but also through non-classical mechanisms including oriented attachment. Here we show an organic crystalline material that can form through molecule-by-molecule growth as well as through oriented attachment. We discuss the mechanisms in relation to the supersaturation levels of the peptide solutions and the molecular interactions between the peptide molecules in the tubular assemblies. The proposed mechanisms are supported by semi-empirical molecular orbital calculations and time resolved dissolution experiments. This article was originally published with incorrect page numbers (p. 3463-3470)

The alcoholysis of cyclic meso-anhydrides catalyzed by β-amino alcohols has been investigated with DFT quantum mechanics to determine the mechanism of this reaction. Both nucleophilic catalysis and general base catalysis pathways are explored for methanol-induced ring opening of an anhydride catalyzed by a chiral amino alcohol. The nucleophilic pathway involves a late transition state with a high energy barrier. In this mechanism, methanolysis is expected to take place following the amine-induced ring opening of the anhydride. In the base-catalyzed mechanism, methanol attack on one carbonyl group of the meso-anhydride is assisted by the β-amino alcohol; the amine functionality abstracts the methanol proton. The chiral amino alcohol also catalyzes the reaction by stabilizing the oxyanion that forms upon ring opening of the anhydride by hydrogen bonding with its alcoholic moiety. Both stepwise and concerted pathways have been studied for the general base catalysis route. Transition structures for both are found to be lower in energy than in the nucleophilic mechanism. Overall this study has shed light on the mechanism of the β-amino alcohol-catalyzed alcoholysis of cyclic meso-anhydrides, showing that the nucleophilic pathway is approximately 100 kJ mol(-1) higher in energy than the general base pathway.