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Inclusion Behavior of β‐Cyclodextrin with Bipyridine Molecules: Factors Governing Host‐Guest Inclusion Geometries
Author(s) -
Zhao YanLi,
Benítez Diego,
Yoon Il,
Stoddart J. Fraser
Publication year - 2009
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200800373
Subject(s) - triclinic crystal system , crystallography , chemistry , supramolecular chemistry , monoclinic crystal system , aqueous solution , molecule , bipyridine , orthorhombic crystal system , cyclodextrin , pyridine , crystal structure , stereochemistry , organic chemistry
Abstract Guest Effect : The differences of nitrogen atom positions and the bridge bonds linked to two pyridine rings of some bipyridine guests can significantly affect the binding abilities and inclusion geometries of β‐cyclodextrin with the guests in both the solution and solid states.The 1:1 complexation of β‐cyclodextrin (β‐CD) with structurally similar bipyridine guests which lead to the formation of six inclusion complexes ( 1 – 6 ) of β‐CD with 4,4′‐vinylenedipyridine, 2,2′‐vinylenedipyridine, 1‐(2‐pyridyl)‐2‐(4‐pyridyl)ethylene, 4,4′‐ethylene‐dipyridine, 4,4′‐dithiodipyridine, and 2,2′‐dithiodipyridine has been investigated comprehensively by X‐ray crystallography in the solid state and by 1 H NMR spectroscopy and microcalorimetric titration in aqueous solution. The complex formation constants ( K S ) for the stoichiometric 1:1 host–guest inclusion complexation of β‐CD with the bipyridine derivatives were determined in aqueous solution by microcalorimetry and the host–guest inclusion geometries of the complexes were deduced from 1 H ROESY NMR spectroscopy. It transpires that the guest bipyridine molecules are included in the β‐CD cavity with a range of different inclusion geometries. In the solid state, the crystal superstructures for the β‐CD complexes 1 , 4 , and 5 are characterized by the triclinic crystal system (space group P 1) commensurate with AAAA type supramolecular aggregation. By contrast, the β‐CD complexes 2 , 3 , and 6 display either monoclinic (space group P 2 1 ) or orthorhombic (space group C 222 1 ) crystal systems, characteristic of ABAB type supramolecular aggregation. The results demonstrate that the relative locations of the nitrogen atom positions and the bridge‐bond links between the two pyridine rings in these bipyridine guests, not only lead to distinct crystal systems and space groups, but also to different binding geometries and thermodynamical parameters on complexation of the bipyridines with β‐CD. The knowledge obtained from this research improves our understanding of the molecular recognition and self‐assembly processes exhibited by β‐CD, both in the solid state and in aqueous solution.