Binding studies of dopamine HCl drug with the mixed {sodium bis(2-ethylhexyl) sulfosuccinate + sodium dodecylsulfate} micelles: Physicochemical, spectroscopic, calorimetric and computational approach

Abstract

Taking into consideration the importance of dopamine HCl as neurotransmitter in controlling central nervous system activities, the studies of binding interactions of dopamine HCl drug with micellar system (imitator of biomembranes) have been conducted by utilizing experimental as well as computational techniques. The systematic knowledge of physicochemical, spectroscopic and calorimetric properties is helpful to understand the physiological actions of biologically active additives in the living organisms. Therefore, mixed aggregation behavior of sodium bis(2-ethylhexyl) sulfosuccinate, AOT and sodium dodecylsulfate, SDS has been explored at diverse mole fractions of AOT, αAOT = 0.25, 0.39 and 0.50 in (1, 2 and 3) × 10−3 mol kg−1 dopamine HCl(aq) solutions by employing different techniques. From conductivity studies, the thermodynamic parameters (∆G°m, ∆H°m and ∆S°m), the molecular interaction parameter (βint) and the excess Gibbs free energy of micellization (∆Gmex) were ascertained at T = (298.15, 308.15, and 318.15) K. Isentropic compressibility (κs), partial specific volume (φv) and partial specific isentropic compressibility (φκ) parameters were computed from the density and sound velocity studies. Binding constant (Kb) and standard Gibbs free energy of binding (∆Gbο) have been evaluated from UV–visible absorption studies for dopamine HCl(aq) solutions at all the studied mole fractions of surfactant mixtures. Through dynamic light scattering (DLS) measurements, the hydrodynamic diameters (Dh) of mixed micellar aggregates have been acquired. Isothermal titration calorimetric (ITC) studies were executed to obtain the values of partitioning constant / binding constant (K), standard molar enthalpy of binding (ΔrHᴼ), standard molar entropy of binding (ΔrSᴼ), and stoichiometry of partitioning / binding (n) of drug with micellar system. Through density functional theory (DFT) calculations, the band gap between HOMO and LUMO for the dopamine-HCl bound mixed micelle system, and interactive features have been obtained. Aforementioned studies favor the supremacy of hydrophilic-hydrophilic / ionic and electrostatic interactions causing the binding among the hydrophilic / ionic groups of dopamine HCl (−OH, H+, Cl−), AOT (–SO3−, –OCO, Na+), and SDS (–OSO3−, Na+).