Quenching studies of pyrenoyl glutamic acid derivatives

The preparation and fun characterization of fluorescent labeled N-pyrenoyl- L-glutamic acid diethyl ester (2) and 4-(N-Boc-L-glutamide(O-benzyl ester)) -N,N'-dimethylaniline (3) by the DCC-HOBT protocol is described. The benzyl group in 3 was removed by hydrogenation giving the free acid 4-(N-Boc-L-gl utamide(OH))-N,N-dimethylaniline (4). The steady-state and time-resolved fl uorescence quenching studies were performed in order to distinguish ground state quenching taking place in a hydrogen-bonded complex and dynamic quenc hing. Weak molecular interactions between the fluorophore 2 and the quenche r 4 leading to a 1:1 complex were detected by H-1-NMR titration experiments . The association constants were determined by fluorescence methods to be i n the order of 3.8-4.0 x 10(3) M-1 for all systems investigated. The bimole cular quenching constants k(d) are in the order of 1.0-1.28 x 10(10) M-1 s( -1) indicating a diffusion controlled electron transfer process.