New fluorescent chemosensors for magnesium ions in living cells

Although magnesium ions play a key role in many fundamental biological processes, information about its intracellular regulation is still scarce, due to the lack of appropriate detection methods. Here, we report the spectroscopic characterization of two diaza-18-crown-6 hydroxyquinoline derivatives (DCHQ) and we propose their application for the determination of total Mg ²⁺ concentration and in confocal imaging as effective Mg ²⁺ indicators. DCHQ derivatives 1 and 2 bind Mg ²⁺ with much higher affinity than other available probes (K _d = 44 and 73 mM, respectively) with a concomitant strong fluorescence increase. On the other hand, the fluorescence intensity is not significantly affected by other divalent cations, most importantly Ca ²⁺, or by pH changes within the physiological range. Evidence is provided on the use of fluorometric data to derive totalcellular Mg ²⁺ content, which is in agreement with atomic absorption data. Furthermore, we show that DCHQ compounds can be effectively employed to map intracellular ion distribution and movements in live cells by confocal microscopy. These findings suggest that DCHQ derivatives may serve as new probes for the study of Mg ²⁺ regulation, allowing sensitive and straightforward detection of both static and dynamic signals.