Development of a cell permeable ratiometric chemosensor and biomarker for hydrogen sulphate ions in aqueous solution†
Abstract
A newly designed organic moiety, 5H-5,7a,12-triaza-dibenzo[a,e]azulen-6-one (L) containing a seven membered ring behaves as a hydrogen sulphate ion selective ratiometric chemosensor. The formulation and detailed structural characterisation of L have been established using physico-chemical, spectroscopic tools and single crystal X-ray diffraction study. On additions of hydrogen sulphate ions to the solution of L in HEPES buffer (1 mM; water : ethanol (v/v), 98 : 2) at 25 °C at biological pH, a new fluorescence peak generated at 483 nm was increased with concomitant decrease of the weak fluorescence of L at 430 nm through an isoemissive point at 449 nm due to the selective binding of HSO4− ions with L in a 1 : 1 ratio with a binding constant (K) of 4.13 × 106 M−1, and detects HSO4− ions as low as 5.5 × 10−7 M. The ratiometric enhancement of the fluorescence is based on intermolecular hydrogen bonding assisted chelation enhanced fluorescence (CHEF) process which has been evidenced by 1HNMR titration and supported by theoretical (DFT) calculations. The probe (L) having no cytotoxic effect is also useful for the detection of intracellular HSO4− ion concentrations under a fluorescence microscope.