Colorimetric sensing ensemble for citrate in water

A copper(II)-assisted guanidiniocarbonyl pyrrole receptor 1-Cu2+ was synthesized, and its binding properties toward some organic acids were determined in aqueous solution. This receptor exhibited high selectivity and affinity for citrate over other similar analytes, the association constant reached 105 M−1 in protic media at neutral pH. By using indicator displacement assay with pyrocatechol violet (PV) as indicator, distinct color changes were observed upon addition of citrate to the aqueous solution of the chemosensing ensemble (PV-1-Cu2+), which showed great potential for the quantitative and qualitative analyses of citrate.