Anionic polymer-coated magnetic nanocomposites for immobilization with palladium nanoparticles as catalysts for the reduction of 4-nitrophenol

This study focuses on the synthesis of magnetite nanoparticles (MNP) coated with poly(poly(ethylene glycol) methacrylate) (PPEGMA) and/or poly(acrylic acid) (PAA) to anchor palladium nanoparticles (Pd) for their application as recyclable catalysts in the reduction of 4-nitrophenol (4NP). It was hypothesized that the abundance of oxygen atoms in PPEGMA enabled coordination with the Pd and provided good water dispersibility of the nanocomposites, while anionic PAA stabilized Pd and reduced the catalyst aggregation through electrostatic repulsion. Three different polymer coatings on MNP (PAA, PPEGMA, and PAA-co-PPEGMA polymers) were investigated to assess their influence on both the catalytic activity and reusability of the catalysts. Transmission electron microscopy (TEM) analysis indicated the distribution of spherical Pd nanoparticles (3-5 nm in diameter) and MNP (9-12 nm in diameter). Photocorrelation spectroscopy (PCS) revealed an average hydrodynamic size of the catalysts ranging from 540 to 875 nm in diameter, with a negative charge on their surface. The Pd content of the catalysts ranged from 4.30 to 6.33% w/w. The nanocomposites coated with PAA-co-PPEGMA polymers exhibited more favorable catalytic activity in the 4NP reduction than those coated with PAA or PPEGMA homopolymers. Interestingly, those containing PAA (e.g., PAA and PAA-co-PPEGMA polymers) exhibited good reusability for the 4NP reduction with a slight decrease in their catalytic performance after 26 cycles. This indicates the important role of carboxyl groups in PAA in maintaining high tolerance after multiple uses.

Magnetite Nanoparticles Functionalized with Thermoresponsive Polymers as a Palladium Support for Olefin and Nitroarene Hydrogenation

A thermoresponsive and recyclable nanomaterial was synthesized by surface modification of magnetite nanoparticles (MNPs) with poly(N-isopropylacrylamide-co-diethylaminoethyl methacrylate) (P(NIPAAm-co-DEAEMA)), having PNIPAAm as a thermoresponsive moiety and PDEAEMA for catalyst binding. Palladium (Pd) nanoparticles were incorporated into this material, and the resulting nanocatalyst was efficient in the hydrogenation of olefins and nitro compounds with turnover frequencies (TOFs) up to 750 h^-1. Consistent catalytic activity in 10 consecutive runs was observed when performing the hydrogenation at 45 °C, i.e., above the lower critical solution temperature (LCST) of the copolymer (37 °C), followed by cooling to 15 °C, i.e., below the LCST of the copolymer.

Alginate-based magnetic nanosorbent immobilized with aptamer for selective and high adsorption of Hg2+ in water samples

Alginate-coated magnetic nanocluster (MNC) immobilized with Hg²⁺-specific aptamer was synthesized to obtain the nanosorbent with high adsorption capacity and high selectivity for trace analysis of inorganic mercury (Hg²⁺) in water samples. Magnetite nanoparticle was first synthesized by a co-precipitation of iron precursors in the presence of alginate to obtain alginate-coated MNC, followed by immobilization with avidin. Hg²⁺-Specific DNA aptamer labeled with biotin was then conjugated on the MNC surface via specific avidin-biotin interaction to form aptamer-immobilized MNC. Coating the MNC with alginate can improve its water dispersibility and also increase its adsorption capacity toward Hg²⁺ (350 mg/g). It exhibited high selectivity through thymine-Hg²⁺-thymine (T-Hg²⁺-T) interaction with high tolerance to other foreign ions. This nanosorbent showed linearity over the Hg²⁺ concentration range of 0.2-10 μg/L with a correlation coefficient of 0.9977, limit of detection of 0.46 μg/L, and enrichment factor of 13. Moreover, it also showed a potential for detection of Hg²⁺ in drinking and tap water samples with satisfactory recoveries.

Poly(acrylic acid)-grafted magnetite nanoparticle conjugated with pyrrolidinyl peptide nucleic acid for specific adsorption with real DNA

Magnetite nanoparticle conjugated with pyrrolidinyl peptide nucleic acid (MNP@PNA) was synthesized for use as both a magnetic nano-support and a probe for specific adsorption with complementary deoxyribonucleic acid (DNA). MNP@PNA with the size ranging between 120 and 170 nm in diameter was prepared via a free radical polymerization of acrylic acid in the presence of acrylamide-grafted MNP to obtain negatively charged magnetic nanoclusters, followed by ionic adsorption with PNA. According to fluorescence spectrophotometry and gel electrophoresis, this MNP@PNA can differentiate between fully matched, single-base mismatched and fully mismatched synthetic DNAs tagged with different fluorophores. UV-vis spectrophotometry and gel electrophoresis indicated that MNP@PNA can be used for specific adsorption with real DNA (zein gene of maize) having complementary sequence with the PNA probe. This novel anionic MNP conjugated with the PNA probe might be potentially applicable for use as a magnetic support for DNA base discrimination and might be a promising tool for testing genetic modification.

Magnetite nanoparticle with positively charged surface for immobilization of peptide nucleic acid and deoxyribonucleic acid

We herein report the surface modification of magnetite nanoparticle (MNP) with the (co)polymer of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and/or diethylamino ethyl methacrylate (DEAEMA) via atom transfer radical polymerization (ATRP) for use as anion exchanger solid support for detection of DNA sequence using peptide nucleic acid (PNA) probe. Molar ratio of the PEGMA:DEAEMA (co)polymer was systematically varied to tune the positive charges on the particle surface. Kinetic studies of the (co)polymerizations were investigated via 1HNMR to disclose the relative reactivity of the (co)polymers in the reaction. Zeta potential of the (co)polymer-grafted MNP was analyzed by photo correlation spectroscopy (PCS). Transmission electron microscopy (TEM) and PCS indicated an improvement in the particle dispersibility in water upon quaternization of the DEAEMA entities grafted on the particle surface. From the preliminary results, these (co)polymer-grafted MNPs can be used as a nanosolid support to differentiate between full match and single-base mismatch DNA sequences using an acpcPNA probe. These novel cationic MNPs might be efficiently applicable for use as a magnetically guidable tool for detection of DNA sequences.