Global Compartmental Analysis of the Excited-State Reaction between Fluorescein and (±)-N-Acetyl Aspartic Acid

Abstract

Fluorescein is a complex fluorophore which at the physiological pH can exist as mono- and dianion forms. In a previous article (J. Phys. Chem. A 2001, 105, 6320−6332), we showed that fluorescein displays an excited-state proton transfer reaction which interconverts the mono- and dianion forms in the presence of a suitable proton donor−acceptor. Because fluorescein is a frequently used fluorescent label in biological systems, it is of interest to know if amino acids with acidic side chains are able to induce fluorescein excited-state proton transfer reactions. We have selected (±)-N-acetyl aspartic acid, N-AcAsp, as a model donor−acceptor which mimics the interaction of the aspartic acid residues with the fluorescent label in native proteins. We present absorption and emission properties which show that N-AcAsp at 1 M concentration induces the excited-state proton transfer reaction between the mono- and dianion of fluorescein. The kinetics of this excited-state process was characterized from time-resolved ...