title: Adsorption of zwitterionic drugs onto oxidized cellulose.
abstract: Adsorption of zwitterionic drugs (beta-lactam antibiotics and amino acids) onto samples of oxidized cellulose (OC) with various carboxyl contents and structural characteristics from aqueous and water/alcohol solutions was investigated. The adsorption process can be described according to the theory of localized stoichiometric adsorption and represented by Langmuir isotherms. It was established that the constants of interfacial distribution mainly increase with increased relative sorbate hydrophobicity. The dependencies of adsorption on pH of equilibrium drug solution have a maximum at pH 3-3.5, which is caused by peculiarities of dissociation of OC and sorbates. The drug uptake is shown to increase with an increase of alcohol mole fraction in the solution and transfer to the binary water/isopropanol from water/ethanol solutions. The dominant contribution to the increase of uptake is the desolvation of ionic groups of zwitterions in the solution, which increases with increased alcohol content. The degree of crystallinity of the sorbent has no considerable effect on drug adsorption from aqueous solutions. In water/alcohol solutions the adsorption of drugs by OC samples with similar exchange capacity increases with reducted uniformity of carboxylic group distribution in the volume of the polymer, which is connected with increased accessibility of carboxylic groups for sorbate molecules.
authors.affiliation: Research Institute for Physical Chemical Problems, Belarusian State University, 14 Leningradskaya street, Minsk 220050, Belarus. zimnitsky@tut.by
authors.forename: Dmitry S
authors.initials: DS
authors.lastname: Zimnitsky
authors.forename: Tatiana L
authors.initials: TL
authors.lastname: Yurkshtovich
authors.forename: Pavel M
authors.initials: PM
authors.lastname: Bychkovsky
mesh_terms: D000327:Adsorption; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D002482:Cellulose / Q000493:pharmacokinetics*; D000431:Ethanol; D010084:Oxidation-Reduction; D012996:Solutions; D047090:beta-Lactams / Q000493:pharmacokinetics*
chemical_list: D000900:Anti-Bacterial Agents; D012996:Solutions; D047090:beta-Lactams; D000431:Ethanol; D002482:Cellulose