Enlightening binding behaviour of sulfonatocalix[4]arene receptor with 2-acetoxybenzoic acid through the lens of experiments and theory

Abstract

The inclusion behaviour of 2-acetoxy benzoic acid (ASA, aspirin) within the para-sulfonatocalix[4]arene (SCX4) host has been characterized employing UV–visible, 1H NMR, vibrational spectroscopy, electrospray ionization mass spectrometry (ESI–MS) and chromatography experiments in conjunction with the density functional theory. It has been shown that the ASA ⊂ SCX4 complex possesses 1:1 stoichiometry and is more stable toward oxidative conditions than in acidic and basic media compared to the free ASA guest. The complexation of SCX4 with the ASA emerges with signature in the ‘frequency up-shift’ of its Ar-OH (~14 cm−1) and SO3− (~36 cm−1) stretching vibrations whereas the carbonyl stretching vibration from the ester group engenders shift in the opposite direction (red shift) in the measured infrared spectra. These inferences are corroborated through the density functional theory.