The synthesis of a novel long-wavelength fluorescent probe, 3-epoxypropoxy fluorescein, and its properties for labeling of histidine are briefly described in this communication. The probe is highly selective for histidine, and other amino acids with a concentration of 1 000 times higher than that of histidine did not show noticeable interferences. As an application of this probe, fluorescent labeling of histidine in human serum was attempted and the obtained results were in agreement with those given by using histidine-nickel complex adsorptive voltammetry, both of which were within the normal range of the results reported in literatures.
A new and sensitive method for the analysis of amino acids or oligopeptides has been developed by using transamination for fluorescence derivatization. Namely, α-amino group of amino acid or N-terminal amino group of oligopeptide was selectively converted into a highly reactive carbonyl group by transamination, and then coupled with 2,3-diaminonaphthalene to yield a fluorescent compound (a benzoquinoxaline derivative). The product was detected by fluorescence spectoscopy and electrospray mass spectrometry.The product is a polynuclear aromatic compound with a higher fluorescence quantum yield. It has an excitation and emission wavelength of 364nm and 514nm, respectively.The MS analysis confirmed the formation of the expected benzoquinoxaline derivative with a molecular ion peak at m/z268. The whole operation was conducted under mild conditions, and the method may be used to the sensitive detection of amino acids or peptides. It should be noted that some difficulties were encountered in the separation of the reaction products and the control of the reaction conditions, which need to be further improved.
