‘Honeycomb’ nanotube assembly based on thiacalix[4]arene derivatives by weak interactions

Crystallisation of six thiacalix[4]arene derivatives from hexane–chloroform leads to ‘honeycomb’ nanotube architectures and each tubular stack is surrounded by six close tubular neighbours via weak interactions, such as S⋯π interactions, C–H⋯π interactions, and so on.

Synthesis and conformational analysis of cyclic homooligomers from pyranoid ε-sugar amino acids

New pyranoid ε-sugar amino acids were designed as building blocks, in which the carboxylic acid and the amine groups were placed in positions C2 and C3 with respect to the tetrahydropyran oxygen atom. By using standard solution-phase coupling procedures, cyclic homooligomers containing pyranoid ε-sugar amino acids were synthesized. Conformation analysis was performed by using NMR spectroscopic experiments, FTIR spectroscopic studies, X-ray analysis, and a theoretical conformation search. These studies reveal that the presence of a methoxy group in the position C4 of the pyran ring produces an important structural change in the cyclodipeptides. When the methoxy groups are present, the structure collapses through interresidue hydrogen bonds between the oxygen atoms of the pyran ring and the amide protons. However, when the cyclodipeptide lacks the methoxy groups, a U-shape structure is adopted, in which there is a hydrophilic concave face with four oxygen atoms and two amide protons directed toward the center of the cavity. Additionally, we found important evidence of the key role played by weak electrostatic interactions, such as the five-membered hydrogen-bonded pseudocycles (C5) between the amide protons and the ether oxygen atoms, in the conformation equilibrium of the macrocycles and in the cyclization step of the cyclic tetrapeptides.

Helical self-assembly of 2-(1,4,7,10-tetraazacyclododecan-1-yl)cyclohexan-1-ol (cycyclen)

The title macrocyclic amino alcohol compound, C(14)H(30)N(4)O, is investigated as a solid-state synthon for the design of a self-assembled tubular structure. It crystallizes in a helical column constructed by stereospecific O-H···N and N-H···N interactions. The hydrogen-bonding interactions, dependent upon macrocyclic ring helicity and molecular conformation, link R,R and S,S enantiomers in a head-to-tail fashion, forming a continuous hydrophilic inner core.

Highly Sheared Anti-Parallel Dipolar Carbonyl···Carbonyl Interaction in the Crystal Packing of Strapped Crown-3-Pyromellitimide

Non-covalent dipolar interactions between pairs of carbonyls have been demonstrated to play a significant role in the crystal packing and formation of supramolecular structural architecture of small organic molecules. Under high dilution, the strapped crown-3-pyromellitimide 4 and macrocyclic crown-6-bispyromellitimide 5 were synthesised in concert and demonstrated selective molecular recognition towards Na+ and K+, respectively. The molecular structure of strapped crown-3-pyromellitimide 4 was solved using X-ray crystallography and an unusual highly sheared anti-parallel dipolar carbonyl···carbonyl interaction was observed in the crystal packing. The intermolecular interaction has a torsion angle of 44.1°, and deviates from the three idealised motifs reported in literature. This finding further highlights the importance and versatility of dipolar carbonyl···carbonyl interaction in the crystal packing of organic molecules.