Host–Guest Interaction Studies of Isoproterenol Hydrochloride with Β-Cyclodextrin in an Aqueous Medium Probed by Volumetric, Acoustic, and Spectroscopic Approach

Abstract

In this work, we attempted to analyze thermochemical properties along with a spectroscopy approach to better understand the molecular interactions between β-cyclodextrin (β-CD) and the pharmaceutical compound isoproterenol hydrochloride (IPH) in an aqueous solution at a range of temperatures starting from 293.15 to 313.15 K at an atmospheric pressure P = 0.1 MPa. The volumetric and rheological properties of IPH, such as apparent molar volume and apparent molar isentropic compressibility, with their corresponding limiting parameters in the variable compositions of β-cyclodextrin (0.001, 0.005, and 0.010 mol·kg–1), were enumerated at different temperatures using the measured density and speed of sound measurements. Transfer parameters reveal dominant hydrophilic–hydrophilic interactions in a ternary system. In addition to this, the sign of points toward the structure-breaking characteristics of IPH in the binary and ternary solutions. A proton NMR titration experiment illustrated that IPH was incorporated into a hydrophobic pocket of β-CD with a 1:1 stoichiometry which was confirmed by Scott’s plot, and a binding energy of 22.5 M–1 was found for the IPH−β-CD complex.