Sanyog Sharma

New tripodal and dipodal colorimetric sensors for anions based on tris/bis-urea/thiourea moieties

Seven neutral tripodal and dipodal receptors having mesitylene/triethylbenzene as core moiety, urea/thiourea as binding groups and p-nitrobenzene as signalling unit have been reported. The receptors act as selective colorimetric, naked eye sensors for small and spherical F− ion with some interference from tetrahedral ions. Thiourea derivatives form stable 1:1 H-bonded complexes with F− anion and to some extent with anions, whereas for urea derivatives, the recognition is simply based on acid–base reaction between ureidic protons and basic F− ions and is a completely reversible phenomenon. The pre-organisation of thiourea derivatives coupled with their high-intrinsic acidity is supposed to help them in the formation of strong H-bonded complexes with F− anion. The urea-based receptors do not respond at lower concentrations of the anion, but at higher concentrations, they undergo completely reversible deprotonation concomitant with a colorimetric change, with the production of stable [HF2]− anion.

Nanomolar fluorogenic detection of Al(III) by a series of Schiff bases in an aqueous system and their application in cell imaging

Three positional isomers of a Schiff base containing -OH as end groups have been synthesized and evaluated for selective Al(III) detection due to inhibition of ESIPT, PET and activation of CHEF in 70% aqueous medium. Devoid of any conventional fluorophore, these sensors have nanomolar detection limits with high quantum yields and naked eye sensing of Al(III). Moreover, these probes have been demonstrated to enable the Al(III) detection in live human HeLa cells and rat C6 glioma cells using a confocal microscope.