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CHARACTERIZATION OF THREE‐DIMENSIONALLY EXTENDED HYDROPHOBIC CAVITIES. DIFFERENCE IN MOLECULAR RECOGNITION ABILITY BETWEEN STEROID AND OCTOPUS CYCLOPHANES
Author(s) -
Kikuchi JunIchi,
Inada Masahiko,
Murakami Yukito,
Egami Kazuko,
Suehiro Kuzaki
Publication year - 1997
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199705)10:5<351::aid-poc876>3.0.co;2-6
Subject(s) - cyclophane , chemistry , steroid , molecular recognition , stereochemistry , crystallography , host–guest chemistry , molecule , crystal structure , supramolecular chemistry , organic chemistry , biochemistry , hormone
The guest‐binding behavior of two different cyclophane hosts, each being capable of providing a three‐dimensionally extended hydrophobic cavity toward aromatic guests, was examined in aqueous media: a steroid cyclophane bearing four rigid cholate moieties and an octopus cyclophane having four flexible double‐chain segments. Even though the binding constant for 2,7‐dihydroxynaphthalene with the steroid cyclophane was comparable to that with the octopus cyclophane, the guest binding modes were very different from each other, as confirmed by 1 H NMR spectroscopy. That is, the steroid cyclophane incorporates the guest into its rigid macrocyclic cavity with axial geometry whereas the octopus cyclophane provides a three‐dimensional space created by the macrocyclic skeleton and the flexible hydrocarbon chains so that the long axis of the guest becomes more or less perpendicular to the molecular axis of the host upon complexation. Temperature‐dependent molecular recognition by these hosts toward 8‐anilinonaphthalene‐1‐sulfonate was examined by means of fluorescence spectroscopy. Characteristic differences in the guest‐binding mode between these hosts were sensitively reflected in the thermodynamic entropy change on host–guest complexation and the temperature‐dependent microscopic viscosity experienced by the guest at the binding site. © 1997 John Wiley & Sons, Ltd.