Development of Novel Molecular Probes of Endogenous Nitric Oxide Detection and Imaging

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Firstly, various types of dithiocarbamate-iron(II) were synthesized and those sensitivities of NO detection were examined. These experiments proposed the structure-sensitivity relationship of dithiocarbamate-iron(II) type complexes in NO detection. Then, a novel concept of NO-detection, radical-exchange, was found using the dithiocarbamate-iron(II) complex and TEMPOL, which is a stable organic radical. In this system, NO bound to the centered iron in the complex to release the TEMPOL, which is a stable organic radical. In this system, NO bound to the centered iron in the complex to release the TEMPOL radical, which can be detected with high-sensitivity. This molecular system could detect NO with 25 times higher sensitivity than that in ordinary dithiocarbamate-iron(II)-type NO-spin traps. As a next stage, we applied this new strategy to make a fluorescent probe of NO. Thus, a dithiocarbamate-iron(II) complex and acridine-labeled TEMPO were used to construct new type of NO-fluorescent probe. This probe could monitor the NO production from a spontaneous NO-releasing agent using the fluorescence decrease of acridine due to the release of the acridine-TEMPO by NO. Finaly, we designed and synthesized a dual fluorescent-labeled probe system using iron (II) complex of a coumaline-labeled cyclam and a fluorescamine-labeled TEMPO. This probe gave the fluorescence based on the fluorescamine when the coumaline was excited due to the fluorescence energy transfer. In this system, NO bound to the iron(II) to release the fluorescamine-TEMPO. The fluorescence in the released fluorescamine-TEMPO was quenched by the newly produced TEMPO radical. This cancelled the fluorescence energy transfer to increase the fluorescence intensity of the coumaline. Thus the probe can monitor the NO production independent on the background fluorescence in biological samples using ratiometry. After all, we have established the basic concept to design a highly sensitive NO probe successfully.