Diacylated 1,10-diaza-18-crown-6 as an Alternative Template for Fluorescent Sensors of Calcium Ions

The performance of many known fluorescent sensors for Ca²⁺ is pH-dependent. We set out to address this by preparing a novel calcium sensor based on diacylated 1,10-diaza-18-crown-6 and containing no basic centres. The sensor is sensitive to sub-millimolar levels of Ca²⁺ and partially tolerant of an aqueous environment. However, it suffers from a lack of selectivity over some other divalent cations, and retained pH sensitivity in the acidic range. The relations between these properties and the sensor's structure are discussed.