Quantification of the distribution of cetylpyridinium chloride on the external and internal surfaces of montmorillonite: Relevance in antifungal activity assessment

YARZA, FLORENCIA; MORANTES, CESAR FERNÁNDEZ; MONTES, MARÍA L.; BELLOTTI, NATALIA; SALDUONDO, JOAQUIN; YAPAR, SAADET; CRAVERO, FERNANDA; TORRES SÁNCHEZ, ROSA M.

MATERIALS CHEMISTRY AND PHYSICS

ELSEVIER SCIENCE SA

Año: 2020

0254-0584

Two raw bentonites, from Argentina (Mt-A) and Turkey (Mt-T), rich inmontmorillonite, were loaded with different concentrations of cetylpyridinium chloride(CP), ranging from 50 % to 150 % of their respective cation exchange capacity (CEC).Their antifungal activity was tested against Alternaria alternata and Chaetomiumglobosum. Thermal analysis was used to identify the different surface adsorption sites ofthe CP on the montmorillonite (Mt) samples as well as to quantify the surfactant amountrelated to each process, which could play a key role in the antifungal capacity of thesynthesized materials. Three different CP interaction processes with the Mt surface siteswere observed. Two occurring at the outer Mt surface (electrostatic interaction betweenCP and the negative surface sites of Mt (B), and Van der Waals (VdW) interactionsbetween long tails of CP molecules (A) and one at the inner (or interlayer) Mt surfacedue to the cation exchange between CP and the inorganic interlayer cations (C). Thesimultaneous occurrence of these processes was confirmed by the increase of theinterlayer thickness due to the entrance of CP by C process and the decrease of theinitial negative zeta potential values by A and C processes, respectively.The antifungal activity of clays against strains of A. alternata and C. globosum, wasevaluated by agar diffusion assay. Then, the inhibition diameter was related to the actualCP load and its distribution according to A, B, and C processes. Samples with thehighest inhibition zone, Mt-A-CP150, and Mt-T-CP150, presented the greatest actualCP loaded (103 and 110 % CEC, respectively). For both samples, the CP amount relatedto the A process was the lowest, with values around 10 % CEC, while the majorcontribution occurs for the CP related to the B process (49.9 and 57.7 % CEC,respectively). The Pearson correlation coefficients ρ determined between inhibitionzone diameters and CP amount related to each adsorption process indicated that the Aand B processes play a key role in the controlled release of the CP from theorganoclays.For A. alternata the ρ values for A and B processes resulted in 0.84 and 0.87, whilefor C. globosum 0.84 and 0.91, respectively, being non-significant for C process in bothcases.These results allow proposing these materials for possible antifungal applications,preventing CP degradation, and enhancing the durability of the materials.