Spectroscopic study on binding behaviors of different structural nonionic surfactants to cyclodextrins

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry

Background:

• Polyethylene glycol (10) n-octylphenyl ether (OPE) and polyethylene glycol (10) tert-octylphenyl ether (Triton X-100, TX) are non-ionic surfactants.
• Beta-cyclodextrin (beta-CD) and its methylated derivative (DM-beta-CD) are cyclic oligosaccharides known for forming inclusion complexes.

Purpose of the Study:

• To investigate the inclusion complex formation between OPE and TX with beta-CD and DM-beta-CD.
• To elucidate the binding stoichiometry and the influence of cyclodextrin structure on guest encapsulation.

Main Methods:

• Surface tension measurements.
• Steady-state fluorescence spectroscopy of OPE and TX.
• Phosphorescence spectroscopy using 1-bromonaphthalene (BN) as a probe.
• Dynamic and static fluorescence quenching studies.

Main Results:

• Beta-CD forms 1:1 inclusion complexes with both OPE and TX, entrapping their hydrophobic moieties.
• The tert-octyl group of TX is not encapsulated into DM-beta-CD due to steric hindrance from methyl groups.
• Inclusion of the phenyl groups was confirmed by iodide quenching and energy transfer studies.
• Molecular analyses suggest conformational adjustments of the octyl groups within the beta-CD cavity.

Conclusions:

• Beta-CD effectively forms inclusion complexes with OPE and TX, with specific binding modes influenced by guest structure.
• DM-beta-CD's modified rim restricts the inclusion of bulkier guests like TX.
• Further guest addition can induce significant deformation of the octyl chains within the complex.