Molecular-Recognition Properties of a Water-Soluble Cucurbit[6]uril Analogue

The molecular-recognition properties of the cucurbit[6]uril analogue (1) in aqueous buffer (sodium acetate, 50 mM, pH 4.74, 25 °C) toward a variety of guests including alkanediamines (6−12), aromatics (14−32), amino acids (33−36), and nucleobases (37−42) were studied by fluorescence spectroscopy. For the alkanediamines studied (H2N(CH)nNH2, n = 6, 7, 8, 9, 10, 11, 12), the association constants increase as the length of the alkane (n) is increased. Host 1 is capable of forming strong complexes with guests containing aromatic rings with association constants (Ka) ranging from 102 to 106 M-1 as a result of the favorable π−π interactions that occur between host 1 and the aromatic rings of the guest when bound in the cavity of 1. Biologically relevant guests such as amino acids and nucleobases are also bound in the cavity of 1 with Ka values ranging from 103 to 106 M-1. Consequently, cucurbit[6]uril analogue 1 functions as a versatile fluorescent sensor for the presence of a wide range of chemically and biologically important substances in aqueous solution including nitroaromatics, neurotransmitters, amino acids, and nucleobases.