Molecular insights into rhodamine dye binding with natural okra mucilage

The interactions of four rhodamine derivatives-Rhodamine B (RB), Rose Bengal (RS), Rhodamine 101 (R101), and Nile Blue (NB)-with okra (Hibiscus esculentus) mucilage were systematically explored to uncover their binding mechanism and structure-affinity relationships. All dyes display strong binding (K ∼10⁵ M^-1), following the order NB > R101 > RB > RS, underscoring the critical role of molecular structure in governing affinity. Thermodynamic parameters reveal a cooperative driving force, with exothermic enthalpy (ΔH = -0.99 to -5.91 kcal·mol^-1) and favorable entropy contributions (ΔS = 5.57-20.88 cal·mol^-1·K^-1), indicating synergistic non-covalent interactions. Molecular docking not only validates the experimental observations but also provides detailed structural insights into the binding modes, highlighting key interaction sites responsible for enhanced affinity.