Diaza-18-crown-6 hydroxyquinoline derivatives as flexible tools for the assessment and imaging of total intracellular magnesium

Although magnesium is essential for a number of biological processes crucial for cell life, its distribution and intracellular compartmentalization have not been thoroughly elucidated yet, mainly because of the inadequacy of the available techniques to map intracellular magnesium distribution. For this reason, particular interest has been recently raised by a family of fluorescent molecules, diaza- 18-crown-6 8-hydroxyquinolines (DCHQ1 and its derivatives), that show a remarkable affinity and specificity for magnesium, higher than all the commercially available probes, thus permitting the detection of the total intracellular magnesium. A recently optimized synthetic approach to DCHQ using microwave heating allowed us to easily generate a variety of substituted DCHQ derivatives with improved fluorescence, uptake and selective localization with respect to the original reference material (DCHQ1). The introduction of aromatic side groups enhanced the fluorescence response in cells and also improved intracellular uptake and retention of the probes even after washing. Enhanced uptake has also been achieved with an acetoxymethyl ester derivative that is recognized by the intracellular esterases. Finally, the insertion of two long hydrophobic side chains allowed a better staining of the membranes due to the high affinity to the lipophilic environment. These results show the potential of these new fluorescent probes as effective tools for shedding light on total intracellular magnesium distribution and homeostasis.