Magnetic ferroferric oxide and polydopamine molecularly imprinted polymer nanocomposites based electrochemical impedance sensor for the selective separation and sensitive determination of dichlorodiphenyltrichloroethane (DDT).

Dichlorodiphenyltrichloroethane (DDT) is a kind of broad-spectrum insecticides, which is potentially toxic and persistently threatens the safety of environment and food, due to their stability in nature and difficulty to degrade. For the first time, a novel impedance chemical sensor based on magnetic Fe3O4 and polydopamine molecularly imprinted polymer magnetic nanoparticles (PDA@Fe3O4 MIP MNPs) was designed. Bisphenol A (BPA) and dopamine were used as virtual template molecules and functional monomer for MIP synthesis, respectively. Recognition cavities formed in PDA layers could specifically recognize and effectively adsorb DDT molecules, with the help of virtual templates that had similar molecular structure to DDTs. The as-prepared PDA@Fe3O4-MIP MNPs could be used for specific adsorption and efficient extraction of target molecules 4,4'-DDT from food samples. The electrochemical impedance of the PDA@Fe3O4-MIP MNPs increased sensitively with the adsorption of 4,4'-DDT, the correlationship between of the electrochemical impedance response and the concentration of 4,4'-DDT were applied in the construction of electrochemical impedance sensors for the determination of 4,4'-DDT. The sensor showed a good linear relationship between the charge transfer resistance (Rct) and the 4,4'-DDT concentration over a range from 1 × 10-11 to 1 × 10-3 mol L-1 with a detection limit of 6 × 10-12 mol L-1. The sensor also exhibited excellent sensitivity and selectivity as well as high stability for the detection of pesticide residues and other environmentally harmful chemicals in various food samples.

Titanium dioxide and polypyrrole molecularly imprinted polymer nanocomposites based electrochemical sensor for highly selective detection of p-nonylphenol.

We developed a new electrochemical sensor based on TiO2 and polypyrrole (PPy) molecularly imprinted polymer (MIP) nanocomposites for the high selective detection of p-nonylphenol in food samples, which is considered as a kind of endocrine disrupting chemical and harmful to human health. With p-nonylphenol as template molecules, the molecularly imprinted polymer was synthesized by the chemical oxidative polymerization of pyrrole and deposited on the surface of TiO2 nanoparticles to form partially encapsulated PPy@TiO2 nanocomposites, denoted as NP-PPy@TiO2 MIP. p-Nonylphenol was bound in the PPy matrix through hydrogen bond and π-π interaction between p-nonylphenol and PPy skeleton. NP-PPy@TiO2 MIP nanocomposites were modified onto glassy carbon electrode (GCE) and p-nonylphenol molecules were excluded from PPy layers by potentiostatic sweeping at the potential of 1.3 V. The as-prepared electrochemical sensor obtained a large amount of micro cavities in PPy layer which could specially recognize and combine target molecules p-nonylphenol. After special adsorption of p-nonylphenol from samples, p-nonylphenol embedded in the PPy layer exhibited a strong differential pulse voltammetry (DPV) response at 0.56 V, which can be used for the detection of p-nonylphenol with a linearly proportional concentration range of 1.0 × 10-8 to 8 × 10-5 mol/L and a detection limit of 3.91 × 10-9 mol/L. The good stability, reproducibility and specificity of the resulting MIP electrochemical sensor are demonstrated. It might open a new window for investigation of selectively electrochemical sensing of small organic molecules from their analogues with the molecular imprinting technique.

Catalytic arylsulfonyl radical-triggered 1,5-enyne-bicyclizations and hydrosulfonylation of α,ß-conjugates.

A catalytic bicyclization reaction of 1,5-enynes anchored by α,ß-conjugates with arylsulfonyl radicals generated in situ from sulfonyl hydrazides has been established using TBAI (20 mol%) and Cu(OAc)2 (5 mol%) as co-catalysts under convenient conditions. In addition, the use of benzoyl peroxide (BPO) as the oxidant and pivalic acid (PivOH) as an additive was proven to be necessary for this reaction. The reactions occurred through 5-exo-dig/6-endo-trig bicyclizations and homolytic aromatic substitution (HAS) cascade mechanisms to give benzo[b]fluorens regioselectively. A similar catalytic process was developed for the synthesis of γ-ketosulfones. These reactions feature readily accessible starting materials and simple one-pot operation.