Pectin gelation with chlorhexidine: Physico-chemical studies in dilute solutions

Low methoxyl pectin is known to gel with divalent cations (e.g. Ca2+, Zn2+). In this study, a new way of pectin gelation in the presence of an active pharmaceutical ingredient, chlorhexidine (CX), was highlighted. Thus chlorhexidine interactions with pectin were investigated and compared with the well-known pectin/Ca2+ binding model. Gelation mechanisms were studied by several physico-chemical methods such as zeta potential, viscosity, size measurements and binding isotherm was determined by Proton Nuclear Magnetic Resonance Spectroscopy (H-1 NMR). The binding process exhibited similar first two steps for both divalent ions: a stoichiometric monocomplexation of the polymer followed by a dimerization step. However, stronger interactions were observed between pectin and chlorhexidine. Moreover, the dimerization step occurred under stoichiometric conditions with chlorhexidine whereas non-stoichiometric conditions were involved with calcium ions. In the case of chlorhexidine, an additional intermolecular binding occurred in a third step. (C0 2016 Elsevier Ltd. All rights reserved.