Improvement of Fluorescence Characteristics of Coumarins: Syntheses and Fluorescence Properties of 6-Methoxycoumarin and Benzocoumarin Derivatives as Novel Fluorophores Emitting in the Longer Wavelength Region and Their Application to Analytical Reagents

To improve the fluorescence characteristics, especially emission wavelength, of coumarins, various 3-substituted-6-methoxycoumarin derivatives were synthesized, and then benzocoumarin derivatives were also synthesized in expectation of the shift to the longer wavelength region by the extension of the conjugated system. Their fluorescence properties were investigated spectrophotometrically in acetonitrile and evaluated from the viewpoint of the intramolecular charge transfer (ICT) between push- and pull-substituents in the ground and the excited states. Among them, benzocoumarin derivatives especially fluoresced in the longer wavelength around 540 nm with remarkably large Stokes shifts beyond 10,000 cm(-1). Using such fluorophores, some novel fluorescence derivatization reagents for carboxylic acids, alcohols, phenols, and amines were preliminarily prepared as an example, and their derivatized products were also found to fluoresce in the longer wavelength region with large Stokes shifts.

Recent progress in derivatization methods for LC and CE analysis

The derivatization procedure with a suitable fluorescence or chemiluminescence reagent is performed for the purpose of increasing the detection sensitivity and selectivity, in high-performance liquid chromatography (HPLC) and/or capillary electrophoresis (CE). In this article, recent derivatization methods and their applications to biosamples are described. In HPLC, femto mol order of mass detection limits are obtained by derivatization. Regarding the fluorescence reagents, the use of water-soluble reagents has been effective to avoid an undesired adsorption in the process of determination of peptides. In CE, the advantages of having extremely low mass detection limits (ranging from atto to yocto mol level) and requiring only a very short analysis time (less than a few minutes) are made possible by using laser-induced fluorescence or near infra-red detections.