Synthesis of coumarin-appended cyclophanes and evaluation of their complexation with myoglobin

Abstract

Coumarin-appended cyclophanes bearing positively or negatively charged side chains were synthesized as a water-soluble host (1a or 1b, respectively). Host 1a and 1b showed fluorescence bands with fluorescence maxima at 404 nm originated from coumarin moiety. As a host for guest molecules by using macrocyclic cavity, cationic host 1a binds anionic guests such as 6-p-toluidinonaphthalene-2-sulfonate (TNS), 6-anilinonaphthalene-2-sulfonate (2,6-ANS), and 8-anilinonaphthalene-1-sulfonate (1,8-ANS) more strongly than anionic host 1b, reflecting intermolecular electrostatic interactions. In addition, both host 1a and 1b showed protein surface recognition and fluorescence response toward myoglobin, a small and globular protein. The fluorescence intensity originating from the hosts decreased upon the addition of myoglobin, reflecting the formation of 1a- and 1b-myoglobin complexes. On the other hand, such fluorescence response of 1a and 1b was almost negligible for other proteins such as egg white albumin, bovine serum albumin, human albumin, concanavaline A, fibrinogen, γ-globlin, peanut agglutinin, trypsin, and lysozyme.