Application of Congo red dye as a molecular probe to investigate the kinetics and thermodynamics of the formation processes of arachin and conarachin nanocomplexes

Abstract

The thermodynamics and kinetics of arachin-Congo red (ARA-CR) and conarachin-Congo red (CON-CR) interactions were studied using surface plasmon resonance. KCl led to a reduction of up to 55% in the values of the associated kinetic constants, but it had less influence on the dissociation rates (less than 12%). The change in ionic strength had little effect on the thermodynamic stability of the complexes, but it did reduce their affinities ( Kb(25ºC)[ARA-CR]º from 3.52 to 2.44 × 103 M−1 and ( Kb(25ºC)[CON-CR]º from 15.1 to 12.5 × 103 M−1). The shielding of the electrical double layer favored ARA-CR hydrophilic interactions (ΔHº [ARA-CR]º decreased from −30.60 to −42.98 kJ mol−1). On the other hand, hydrophobic interactions came to dominate during the formation of [CON-CR]º (ΔHº [CON-CR]º( increased from −11.21 to 28.34 kJ mol−1 and TΔSº 25º[CON-CR]º increased from 12.64 to 51.73 kJ.mol−1). The data presented here improve our understanding of plant-based protein nanocarriers of small bioactive molecules.