Host-Guest Sensing Interactions of Calixarene-Entrapped Para-Aminobenzoic Acid Using the Langmuir Technique

TL;DR: The Langmuir technique has been used to study the interactions between calixarenes and para-aminobenzoic acid (PABA). The results show that the interaction between calixarenes and PABA happens at the lower rim of calixarenes.

Abstract: Calixarenes are frequently studied as the host supramolecule in drug carrier applications. The ability to encapsulate and control drug delivery is due to their unique structures with a hydrophobic upper rim and a hydrophilic lower rim. Para-aminobenzoic acid (PABA) is a drug used as the main ingredient in sunscreen products with photoallergic contact dermatitis effects. This study has been motivated by the necessity of developing a PABA sensor even at a deficient concentration. In this work, the uses of two calixarenes, calix[4]arene (C4) and calix[6]arene (C6), in entrapping the PABA drug have been studied using the Langmuir technique. In the Langmuir-Blodgett trough, calixarenes in solution form were prepared and spread on the subphase to form the Langmuir monolayer. The formation of Langmuir films by C4 and C6 has been investigated based on the surface pressure-area ( - ) isotherm and surface potential-area ( - ) isotherm recorded using Langmuir apparatus KSV 2000 System 2. The differences and changes of the isotherms with the presence of para-aminobenzoic acid (PABA) in the subphase during the formation of Langmuir films have been observed and studied. The interactions between calixarenes and PABA have been shown by the effective dipole moment ( ) of the calixarene-PABA complexes calculated based on the results using the Helmholtz equation. Host-guest interaction shown by the sensing of PABA by calixarenes happens most probably at the lower rim of calixarenes due to the amphiphilic property of calixarenes. The findings of this study can be applied to the potential application of drug sensors using C4 and C6.