Poly(ethersulfone) (PES) membranes are widely used in industry for separation and purification purposes. However, the drawback of this type of membranes is fouling by proteins. For that reason, modification of PES membranes has been studied to enhance their protein repellence. This paper presents the first example of enzyme-catalyzed modification of PES membranes. Various phenolic acids (enzyme substrates) were bound to a membrane under very mild conditions (room temperature, water, nearly neutral pH) using only laccase from Trametes versicolor as catalyst. The extent of modification, monitored, for example, by the coloration of the modified membranes, can be tuned by adjusting the reaction conditions. The most significant results were obtained with 4-hydroxybenzoic acid and gallic acid as substrates. The presence of a covalently bound layer of 4-hydroxybenzoic acid on the grafted membranes was confirmed by X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and NMR. In the case of gallic acid, PES membrane modification is mainly caused by adsorption of enzymatically formed homopolymer. The ionization potential of the substrates, and the electronic energies and spin densities of the radicals that are intermediates in the attachment reaction were calculated (B3LYP/6-311G(d,p)) to determine the reactive sites and the order of reactivity of radical substrates to couple with the PES membrane. The calculated order of reactivity of the substrates is in line with the experimental observations. The calculated spin densities in the phenolic radicals are highest at the oxygen atom, which is in line with the formation of ether linkages as observed by IRRAS. The liquid fluxes of the modified membranes are hardly influenced by the grafted layers, in spite of the presence of a substantial and stable new layer, which opens a range of application possibilities for these modified membranes.

Antioxidants may have a positive effect on human health since they can protect the human body against deterioration by reactive oxygen species (ROS). Chitosan has many promising properties as nontoxic, biocompatible, biodegradable, antimicrobial and recently antioxidant properties. Most of the reports on the antioxidant activity of chitosan are based on the ability of amine and hydroxyl group to scavenge free radical to form stable macromolecular radical. In the current study, a new chitosan derivative with extra free amine groups was evaluated using two popular antioxidant evaluation methods (uninhibited/inhibited hyaluronan degradation and decolorization of ABTS method). The result obtained in our study show increase the activity of aminated chitosan for scavenging free radicals than chitosan itself.

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