Related Experiment Video
Updated: Aug 7, 2026
10:35
Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals
Published on: May 29, 2018
Excited-state tautomerization dynamics of 7-hydroxyquinoline in beta-cyclodextrin
Han Jung Park1, Oh-Hoon Kwon, Chil Seong Ah
1School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Encapsulating 7-hydroxyquinoline in beta-cyclodextrin significantly alters its excited-state tautomerization dynamics compared to water. This encapsulation enhances fluorescence and selectively accelerates reactions by stabilizing intermediates.
Area of Science:
- Photochemistry
- Supramolecular Chemistry
- Chemical Kinetics
Background:
- 7-hydroxyquinoline (7HQ) exhibits excited-state tautomerization, a process sensitive to its environment.
- Beta-cyclodextrin (β-CD) is a host molecule capable of encapsulating guest molecules, altering their properties.
- Understanding excited-state dynamics is crucial for applications in fluorescence and reaction control.
Purpose of the Study:
- To compare the excited-state tautomerization dynamics of 7HQ in beta-cyclodextrin (β-CD) versus pure water.
- To elucidate the influence of the hydrophobic β-CD cavity on reaction intermediates and kinetics.
- To explore the potential of encapsulation for enhancing fluorescence and controlling reaction selectivity.
Main Methods:
- Isotope-dependent fluorescence kinetics measurements.
- Absorption and emission spectral analysis.
- Comparative study in aqueous solution and within β-CD inclusion complexes.
Main Results:
- The tautomerization of 7HQ proceeds stepwise via an anionic intermediate in both water and β-CD.
- Encapsulation in β-CD significantly slows enol-deprotonation (40 ps in water to 170 ps in β-CD).
- Encapsulation in β-CD significantly accelerates imine-protonation (160 ps in water to 85 ps in β-CD), attributed to the instability of charged species in the hydrophobic cage.
Conclusions:
- Beta-cyclodextrin encapsulation dramatically alters the excited-state tautomerization pathway of 7-hydroxyquinoline.
- The hydrophobic nature of the β-CD cavity influences the stability and reactivity of the anionic intermediate.
- Encapsulation offers a viable strategy to enhance fluorescence and selectively accelerate chemical reactions by modulating reaction dynamics.
Related Concept Videos
02:30Stability of Substituted Cyclohexanes
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:10Radical Chain-Growth Polymerization: Overview
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
02:02Chair Conformation of Cyclohexane
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...