Sorption of chlorhexidine on cellulose: mechanism of binding and molecular recognition

Chlorhexidine (CH) is an effective antimicrobial agent. There has been very little work published concerning the interactions of CH with, and its adsorption mechanism on, cellulose. In this paper, such physical chemistry parameters are examined and related to computational chemistry studies. Adsorption isotherms were constructed following application of CH to cellulose. These were typical of a Langmuir adsorption isotherm, but at higher concentrations displayed good correlation also with a Freundlich isotherm. Sorption was attributed to a combination of electrostatic (major contribution) and hydrogen bonding forces, which endorsed computational chemistry proposals: electrostatic interactions between CH and carboxylic acid groups in the cellulose dominate with a contribution to binding through hydrogen bonding of the biguanide residues and the p-chlorophenol moieties (Yoshida H-bonding) with the cellulose hydroxyl groups. At high CH concentrations, there is evidence of monolayer and bilayer aggregation. Differences in sorption between CH and another antimicrobial agent previously studied, poly(hexamethylenebiguanide) (PHMB), are attributed to higher molecular weight of PHMB and higher charge density of biguanide residues in CH (due to the relative electron withdrawing effect of the p-chlorophenol moiety).