Spectrophotometric Study of Inclusion Complexation of Aliphatic Alcohols by β-Cyclodextrins with Azobenzene Tether

Abstract

Two novel β-cyclodextrin (β-CD) derivatives possessing azobenzene functional groups as a spectral probe, i.e., mono{6-O-[4-(phenylazo)phenyl]}-β-cyclodextrin (1) and mono{6-O-[4-((4-nitrophenyl)azo)phenyl]}-β-cyclodextrin (2), were synthesized in high yields, and their complexation behaviors with aliphatic alcohols were evaluated by using UV−vis, circular dichroism, and 1H NMR spectroscopy. The induced circular dichroism (ICD) and 2D NMR spectroscopy investigations revealed that azobenzene groups attached to the β-CD rim can be deeply embedded to the β-CD cavity to form the intramolecular inclusion complexes in 10% DMSO aqueous solution. Increasing the ratio of DMSO in solution results in the gradual exclusion of the azobenzene sidearm from the β-CD cavity. Upon complexation with guest adamantanols, modified β-CD 1 or 2 displays two different binding models, that is, the competitive inclusion model for 2-adamantanol and the co-inclusion model for 1-adamantanol. These two different models reasonably explain the different binding behaviors and molecular selectivities of host β-CDs toward guests. Therefore, besides acting as a spectral probe, azobenzene modified β-CDs can also effectively recognize the size/shape of guest molecules, giving good molecular selectivity up to 91 for 2-adamantanol/(+)-borneol pair by 1 and the moderate enantioselectivity (K - /K + = 2.1) for (−)-/(+)-borneol pair by 2.

A spectrophotometric and NMR study on the formation of an inclusion complex between dopamine and a sulfonated cyclodextrin host

“…Penetration of the guest molecule into the cavity may be complete or, alternatively, only part of the guest molecule may fit within the cavity. Formation of the host-guest complex can be easily monitored using techniques such as UV-visible spectroscopy (UV-vis), nuclear magnetic resonance (NMR), fluorescence spectroscopy, IR spectroscopy, electrochemical approaches and solubility measurements [9][10][11], as the physiochemical properties of the guest molecule caged within the host cavity is very different to that of the free guest.…”

Photophysical Properties and Conformational Effects on the Circular Dichroism of an Azobenzene–Cyclodextrin [1]Rotaxane and Its Molecular Components

“…ICD of azobenzene-modified b-CDX-Orientations driven by the linker: Interestingly, the previously reported [24] azobenzene-modified b-CDX (E)-4 is the closest example to (E)-1 and it shows an ICD spectrum with similar sign relations to that of (E)-1. It is interesting to note that, as the 2D NMR spectroscopy investigations [24] revealed, the azobenzene-modified b-CDX adopts a tilted orientation of the azo group inside the CDX cavity, reasonably due to the steric hindrance arising at the tight methoxy connection between the azo group and the CDX.…”

“…First, a simpler hostguest complex featuring an azobenzene axle, for which the experimental ICD spectrum is available, was considered. [24] For this system we explored available orientations of the linked azobenzene inside the CDX cavity and simulated the ICD spectra. As a second step we analysed the available enantiomers of the full axle of (E)-1 and evaluated the ICD spectra for each pair of enantiomers.…”

“…It is interesting to note that, as the 2D NMR spectroscopy investigations [24] revealed, the azobenzene-modified b-CDX adopts a tilted orientation of the azo group inside the CDX cavity, reasonably due to the steric hindrance arising at the tight methoxy connection between the azo group and the CDX. Therefore, the direction of the p-p* transition moment is not simply parallel to the CDX axis.…”

Theoretical study of α-CD based [3] pseudorotaxanes: the role played by threadlike polymer on the stability of Cyclodextrin dimers

“…1,2 In the context of the supramolecular chemistry, due to its singular architecture, CDs can be used in a large number of molecular devices such as molecular reactors, 3,4 molecular nanotubes, [5][6][7][8] molecular wires [9][10][11] and also in molecular recognition processes. [12][13][14][15][16] Over several decades, the encapsulating phenomena of low molecular weight compounds by CDs have been subject of numerous investigations 17,18 attracting the attention of the scientific community interested in this research area. In the beginning of the 1990s, there were a limited number of works concerning the threading of polymers with CDs.…”