Molecular-recognition properties of a water-soluble cucurbit[6]uril analogue

[Graphics] The molecular-recognition properties of the cucurbit[6]uril analogue (1) in aqueous buffer (sodium acetate, 50 mM, pH 4.74, 25 degrees C) toward a variety of guests including alkanediamines (6-12), aromatics (1432), amino acids (33-36), and nucleobases (37-42) were studied by fluorescence spectroscopy. For the alkanediamines studied (H2N(CH)(n)NH2, n = 6, 7, 8, 9. 10, 11, 12), the association constants increase as the length of the alkane (n) is increased. Host I is capable of forming strong complexes with guests containing aromatic rings with association constants (K-a) ranging from 10(2) to 10(6) M-1 as a result of the favorable pi-pi 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 K-a values ranging from 10(3) to 10(6) M-1. Consequently, cucurbit[6]uril analogue I 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.