Quenching studies of pyrenoyl glutamic acid derivatives

Abstract

The preparation and full 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-glutamide(OH))–N,N-dimethylaniline (4). The steady-state and time-resolved fluorescence quenching studies were performed in order to distinguish ground state quenching taking place in a hydrogen-bonded complex and dynamic quenching. Weak molecular interactions between the fluorophore 2 and the quencher 4 leading to a 1∶1 complex were detected by ¹H-NMR titration experiments. The association constants were determined by fluorescence methods to be in the order of 3.8–4.0 × 10³ M^–1 for all systems investigated. The bimolecular quenching constants k_q are in the order of 1.0–1.28 × 10¹⁰ M^–1 s^–1, indicating a diffusion controlled electron transfer process.