Interaction of fluorescently labeled triethyleneglycol and peptide derivatives with β-cyclodextrin.

A triethyleneglycol (TEG) chain, a linear peptide, and a cyclic peptide labeled with 7-methoxycoumarin-3-carboxylic acid (MC) and 7-diethylaminocoumarin-3-carboxylic acid (DAC) were used to thoroughly study Förster resonance energy transfer (FRET) in inclusion complexes. (1) H NMR evidence was given for the formation of a 1:1 inclusion complex between β-cyclodextrin (β-CD) and the fluorophore moieties of model compounds. The binding constant was 20 times higher for DAC than for MC derivatives. Molecular modeling provided additional information. The UV/Vis absorption and fluorescence properties were studied and the energy transfer process was quantified. Fluorescence quenching was particularly strong for the peptide derivatives. The presence of β-CDs reduced the FRET efficiency slightly. Dye-labeled peptide derivatives can thus be used to form inclusion complexes with β-CDs and retain most of their FRET properties. This paves the way for their subsequent use in analytical devices that are designed to measure the activity of matrix metalloproteinases.