Supramolecular green chemistry; An eco-friendly spectrophotometric approach for determination of non-chromophoric methacholine via host-guest interactions with 4-sulfocalix[4]arene

Abstract

Supramolecular chemistry has gained an increasing attention in different disciplines of pharmaceutical community. Methacholine chloride (MCh) is a parasympathomimetic bronchoconstrictor which is a gold standard diagnostic tool for asthma through methacholine challenge test. The determination of MCh is a substantial analytical problem due to the lack of chromophore in its structure, therefore direct spectrophotometry becomes not possible for MCh quantification. In this work, we have exploited the high spectral absorptivity of 4-sulfocalix[4]arene (SCX4) and its exceptional complexation towards choline-mimetic guests to develop a method to quantify MCh. The host guest interaction between MCh and SCX4 produces an inclusion complex that can be investigated using different UV-spectrophotometric methods [dual wavelength method (DWM), ratio difference method (RDM) and ratio derivative method (1DD)]. The proposed methods are based on measurement of the manipulated absorbance of the formed complex peak after resolving the overlap from the host SCX4 spectrum followed by quantitation of MCh. Validation of the methods was performed in compliance with ICH guidelines, regression analysis showed good linearity over the concentration ranges of 10.0–150.0 μM for DWM and 10.0–170.0 μM for RDM and 1DD. The limit of quantification and detection were estimated to be 7.5 μM, 2.5 μM for DWM, 5.2 μM, 1.6 μM for RDM and 5.0 μM, 1.7 μM for 1DD, respectively. The complexation binding ratio and stability constant were calculated to be 1:1 and 7.20 × 104 ± 1.60 M−1, respectively, using continuous variation Job's method. Also, these methods have been used to determine MCh in Povocholine® formulation and in spiked human plasma. Moreover, the greenness of the proposed analytical procedures was evaluated by National Environmental Methods Index and Analytical Eco-Scale and the promising junction between the supramolecular chemistry and the eco-friendly spectrophotometric approaches was highlighted.