Synthesis and crystal structures of fluorescent receptors for 9-butyladenine

Two pyrene containing fluorescent receptors, 2-(1-pyrenyl)benzoic acid (FR-1) and 8-(1-pyrenyl)-1-naphthoic acid (FR-2), have been designed and synthesized to mimic a pyrene dinucleotide for molecular recognition of 9-butyladenine (9-BuA). The X-ray crystal structures of the receptors FR-1 and FR-2 along with the binding substrate 9-BuA have been determined. FR-1 has the carboxyl group in the same plane as the phenyl group whereas the pyrenyl group is perpendicular to the phenyl group. However, both carboxyl and pyrenyl groups in FR-2 are parallel to each other but perpendicular to the naphthyl group. The binding constant for FR-2 to 9-BuA was found to be 7896±2187 M−1, which is 8.3-fold greater than that for FR-1 (953±129 M−1). The results indicate that the complex of 9-BuA with FR-2 is more stable than that with FR-1 by 1.2 kcal/mol. In addition, the molecular recognition of 9-BuA with the receptors can also be observed using fluorescence spectroscopy.