Study of γ-cyclodextrin host-guest complex and nanotube aggregate by fluorescence correlation spectroscopy

Area of Science:

• Supramolecular chemistry
• Nanotechnology
• Spectroscopy

Background:

• Cyclodextrins (CDs) are known for their ability to form inclusion complexes with various molecules.
• Coumarin dyes are frequently used as fluorescent probes in chemical and biological systems.
• Understanding the self-assembly of host-guest complexes is crucial for designing nanomaterials.

Purpose of the Study:

• To investigate the formation and characteristics of nanotube aggregates using gamma-cyclodextrin (γ-CD) and coumarin 153 (C153).
• To determine the size, binding constants, and dynamics of these supramolecular assemblies.
• To analyze the microenvironment of the coumarin dye within the aggregate using fluorescence lifetime measurements.

Main Methods:

• Fluorescence Correlation Spectroscopy (FCS) was employed to study the dynamics and aggregation behavior.
• Burst Integrated Fluorescence Lifetime (BIFL) histograms were used to probe the local environment of the dye.
• Analysis of fluorescence intensity fluctuations provided binding constants and kinetic information.

Main Results:

• Formation of large γ-CD:C153 nanotube aggregates with an average length of ~770 nm was observed.
• The aggregate length is significantly larger (~480 times) than individual γ-CD:C480 complexes, implying ~950 γ-CD units per aggregate.
• Three distinct fluorescence lifetimes for C153 indicated its presence in bulk water, at the aggregate ends, and within the aggregate core.

Conclusions:

• γ-CD can form extensive nanotube aggregates with C153 through noncovalent interactions.
• FCS and fluorescence lifetime measurements provide valuable insights into the structure and dynamics of these supramolecular systems.
• The study demonstrates the potential of CD-based self-assembly for creating nanoscale structures with distinct microenvironments.