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Published on: August 19, 2013
Benzobis(imidazolium)-cucurbit[8]uril complexes for binding and sensing aromatic compounds in aqueous solution
Frank Biedermann1, Urs Rauwald, Monika Cziferszky
1Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK.
Benzobis(imidazolium) salts (BBIs) are stable, fluorescent alternatives to methyl viologen for cucurbit[8]uril assemblies. This tetramethyl benzobis(imidazolium) (MBBI) system enables selective peptide recognition and polymer disassembly, expanding supramolecular chemistry applications.
Area of Science:
- Supramolecular Chemistry
- Materials Science
- Chemical Biology
Background:
- Cucurbit[8]uril (CB[8]) macrocycles selectively bind two guests in water, typically methyl viologen (MV) and an aromatic molecule.
- Expanding the range of guests for CB[8] is crucial for developing new supramolecular applications.
- Benzobis(imidazolium) salts (BBIs) are explored as stable, fluorescent components for supramolecular assemblies.
Purpose of the Study:
- To investigate tetramethyl benzobis(imidazolium) (MBBI) as a potential alternative to MV for CB[8] complexation.
- To characterize the binding interactions between MBBI, CB[8], and various second guests.
- To demonstrate the utility of the MBBI·CB[8] system in sensing and sequence-selective molecular recognition.
Main Methods:
- Isothermal titration calorimetry (ITC) to determine binding affinities and stoichiometry.
- Mass spectrometry and Nuclear Magnetic Resonance (NMR) spectroscopy to confirm complex formation and structural details.
- Fluorescence spectroscopy to assess the optical sensing capabilities of the MBBI·CB[8] complex.
Main Results:
- MBBI forms a 1:1 complex with CB[8] with a high association constant (K(a) = 5.7×10^5 M⁻¹), similar to MV.
- The MBBI·CB[8] complex effectively binds a range of aromatic second guests (K(a) values from 10³ to 10⁵ M⁻¹).
- MBBI exhibits intrinsic fluorescence that is quenched upon binding of the second guest, enabling optical sensing.
- The MBBI·CB[8] system demonstrated sequence-selective peptide recognition and controlled disassembly of polymer aggregates.
Conclusions:
- MBBI is a versatile and advantageous alternative to MV for CB[8]-based supramolecular assemblies, offering fluorescence, stability, and tunability.
- The MBBI·CB[8] system facilitates novel applications in optical sensing, sequence-selective molecular recognition, and controlled material disassembly.
- This work significantly broadens the scope of guests and applications for the cucurbit[n]uril supramolecular chemistry field.
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