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Octahydroxypyridine[4]arene Self‐Assembles Spontaneously To Form Hexameric Capsules and Dimeric Aggregates
Author(s) -
EvanSalem Tamar,
Cohen Yoram
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700461
Subject(s) - chemistry , dimer , chloroform , random hexamer , pyrogallol , nuclear magnetic resonance spectroscopy , trifluoroacetic acid , solvophobic , crystallography , two dimensional nuclear magnetic resonance spectroscopy , calixarene , proton nmr , monomer , diffusion , stereochemistry , molecule , organic chemistry , polymer , physics , thermodynamics
Abstract In recent years it has been observed that resorcin[4]arenes and pyrogallol[4]arenes form hydrogen‐bonded hexameric capsules in nonpolar solvents. In the present study we have used NMR spectroscopy, with an emphasis on diffusion NMR, to investigate the self‐assembly and the aggregation mode of solutions of octahydroxypyridine[4]arene ( 1 b ) in chloroform. In spectroscopic studies, the hexameric capsule of C ‐undecylresorcin[4]arene ( 2 b ) was used as a reference compound and in some cases also as an internal reference. The current diffusion NMR spectroscopy study shows, in contrast to a previous report, that compound 1 b self‐assembles spontaneously into hexameric and dimeric aggregates in solutions in chloroform. The 1 H NMR and diffusion NMR spectroscopic studies on a solution of 1 b in CHCl 3 show the presence of new upfield‐shifted peaks, which diffuse with the same diffusion coefficient as the hexameric peaks in the spectrum. Therefore, these new upfield‐shifted peaks were attributed to encapsulated CHCl 3 molecules. Interestingly, diffusion NMR measurements showed that the addition of trifluoroacetic acid (6.7 equiv), which had no effect on the hexameric capsules of 2 b , led to the disassembly of the hexamer and the dimer of 1 b into its monomers. Therefore, we conclude that compound 1 b self‐assembles spontaneously into hexameric capsules in nonpolar organic solvents, as do resorcin[4]arenes 2 b and 2 c and pyrogallol[4]arenes 3 a and 3 b .