Characterization of Three-Dimensionally Extended Hydrophobic Cavities. Difference in Molecular Recognition Ability Between Steroid and Octopus Cyclophanes

Abstract

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. ©

Synthesis, Aggregation, and Binding Behavior of Synthetic Amphiphilic Receptors

“…These values are very high when compared to those in chloroform ( K a < 5000 M -1 ). They are of the same order of magnitude as those found for amphiphilic cyclophanes with nonionic guests . The titration curves of 6 and 9 with Magneson above the CAC of the amphiphile could only be fitted if it was assumed that only half of the host molecules are involved in the binding process.…”

“…Several calixarenes bearing long aliphatic chains have been shown to form vesicles or micelles that can bind aromatic guest molecules . Murakami and co-workers have reported on amphiphilic octopus-type cyclophane receptors that form multiwalled vesicles in water . The cavities of these receptors are able to bind negatively charged aromatic guest molecules with high binding constants by an induced fit mechanism.…”

Synthesis, Aggregation, and Binding Behavior of Synthetic Amphiphilic Receptors

“…These values are very high when compared to those in chloroform ( K a < 5000 M -1 ). They are of the same order of magnitude as those found for amphiphilic cyclophanes with nonionic guests . The titration curves of 6 and 9 with Magneson above the CAC of the amphiphile could only be fitted if it was assumed that only half of the host molecules are involved in the binding process.…”

“…Several calixarenes bearing long aliphatic chains have been shown to form vesicles or micelles that can bind aromatic guest molecules . Murakami and co-workers have reported on amphiphilic octopus-type cyclophane receptors that form multiwalled vesicles in water . The cavities of these receptors are able to bind negatively charged aromatic guest molecules with high binding constants by an induced fit mechanism.…”

Synthesis, Aggregation, and Binding Behavior of Synthetic Amphiphilic Receptors

“…These values are very high when compared to those in chloroform ( K a < 5000 M -1 ). They are of the same order of magnitude as those found for amphiphilic cyclophanes with nonionic guests . The titration curves of 6 and 9 with Magneson above the CAC of the amphiphile could only be fitted if it was assumed that only half of the host molecules are involved in the binding process.…”

“…Several calixarenes bearing long aliphatic chains have been shown to form vesicles or micelles that can bind aromatic guest molecules . Murakami and co-workers have reported on amphiphilic octopus-type cyclophane receptors that form multiwalled vesicles in water . The cavities of these receptors are able to bind negatively charged aromatic guest molecules with high binding constants by an induced fit mechanism.…”

Synthesis, Aggregation, and Binding Behavior of Synthetic Amphiphilic Receptors

“…These values are very high when compared to those in chloroform ( K a < 5000 M -1 ). They are of the same order of magnitude as those found for amphiphilic cyclophanes with nonionic guests . The titration curves of 6 and 9 with Magneson above the CAC of the amphiphile could only be fitted if it was assumed that only half of the host molecules are involved in the binding process.…”

“…Several calixarenes bearing long aliphatic chains have been shown to form vesicles or micelles that can bind aromatic guest molecules . Murakami and co-workers have reported on amphiphilic octopus-type cyclophane receptors that form multiwalled vesicles in water . The cavities of these receptors are able to bind negatively charged aromatic guest molecules with high binding constants by an induced fit mechanism.…”