Partially hydrolyzed poly(2-oxazoline)s as a new class of biocompatible modifiers of montmorillonites for the adsorption and decontamination of the organophosphate paraoxon

Cationic (co)polymers play an important role in many (bio)applications, such as drug and gene delivery, antimicrobial agents, integral parts of hydrogels, and others. Here, we present cationic copolymers prepared by partial hydrolysis of poly(2-ethyl-2-oxazoline) as a new type of polymeric modifier of clay minerals with improved biocompatibility toward potential utilization in biomedical and environmental applications. Statistical poly(2-ethyl-2-oxazoline-co-ethylene imine)s (PEtOx-co-PEI) of different compositions (degree of hydrolysis 9, 12, 22, 28, 55 and 56 %, respectively) are prepared by a two-step synthetic protocol consisting of a living cationic ring-opening polymerization of 2-ethyl-2-oxazoline and the subsequent acidic hydrolysis of poly(2-ethyl-2oxazoline). We demonstrate that above 22 mol% of ethylene imine (EI) units, prepared copolymers are positively charged as seen from the zeta potential measurements. The XRD patterns of the powder samples of PEtOxco-PEI modified organoclays are analyzed in order to evaluate the impact of the initial concentration of copolymers, used for sample preparation, on the changes in basal spacing value (d001), reflecting the expansion of the interlayer space. We observe the expansion of the interlayer space in montmorillonite (MMT), a clay mineral from the smectite group, dependently on the composition of copolymers and the content of the copolymer in MMT. The presence of copolymers in the interlayer space of MMT decreases in vitro cytotoxicity of virgin MMT as determined in 3T3 mice fibroblasts. MMT modified with PEtOx-co-PEI can have strong potential as a drug delivery vehicle, for tissue engineering applications, or as a sorption material. However, a key application explored in this study is the removal and degradation of the organophosphate paraoxon, a highly toxic insecticide and potent chemical warfare agent. Here, we show adsorption and, importantly, also hydrolytic decomposition of the model substrate paraoxon as a representative of organophosphates at physiological neutral pH (Tris buffer pH 7.4). Hydrolysis of paraoxon is easy to follow due to chromogenicity, where the spectral change is given by the release of 4-nitrophenolate with a different UV-VIS spectrum than paraoxon. MMT modified with the soluble partially hydrolyzed poly(2-ethyl-2-oxazoline) with 59 mol% EI units significantly increases the hydrolysis rate of paraoxon compared to non-modified pristine MMT. These findings highlight the potential of PEtOx-co-PEImodified MMT for biomedical applications and environmental remediation, particularly in detoxifying hazardous organophosphates.