Dynamic chiral cyclohexanohemicucurbit[12]uril.

NMR spectroscopy and DFT modeling studies of chiral cyclohexanohemicucurbit[12]uril indicate that the macrocycle adopts a concave octagonal shape with two distinct conformational flexibilities in solution. Methylene bridge flipping occurs at temperatures above 265 K, while urea monomers rotate at temperatures above 308 K, resulting in the loss of confined space within the macrocycle.

Formation and trapping of the thermodynamically unfavoured inverted-hemicucurbit[6]uril.

Formation of inverted-cis-cyclohexanohemicucurbit[6]uril (i-cis-cycHC[6]), with up to 33% isolated yield, can be induced at the expense of thermodynamically favoured cis-cycHC[6]. Reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous precipitation of the formed macrocycles. Different binding affinities of three diastereomeric cycHC[6]s with trifluoroacetic acid is demonstrated.

Size-Control by Anion Templating in Mechanochemical Synthesis of Hemicucurbiturils in the Solid State.

Self-organization is one of the most intriguing phenomena of chemical matter. While the self-assembly of macrocycles and cages in dilute solutions has been extensively studied, it remains poorly understood in solvent-free environments. Provided here is the first example of using anionic templates to achieve selective assembly of differently-sized macrocycles in a solvent-free system. Using acid-catalyzed synthesis of cyclohexanohemicucurbiturils as a model, size-controlled, quantitative synthesis of 6- or 8-membered macrocycles by spontaneous anion-directed reorganization of mechanochemically-made oligomers in the solid state is demonstrated.

Fingerprinting postblast explosive residues by portable capillary electrophoresis with contactless conductivity detection.

A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of postblast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual-opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from postblast residues using an optimized separation electrolyte composed of 20 mM MES, 20 mM l-histidine, 30 µM CTAB and 2 mM 18-crown-6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive.