A novel composite of multiwalled carbon nanotubes (MWNTs) and molecularly imprinted polymers (MIPs) was prepared by using dopamine (DA) as a template molecule. Selective copolymerization of methacrylic acid and trimethylolpropane trimethacrylate (copoly(MAA-co-TRIM)) in the presence of DA was achieved at the vinyl group functionalized MWNT surface. Vinyl groups modified on MWNTs surface are a key factor for the formation the composite of MWNTs-MIPs. Attenuated total reflection Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and thermogravimetric analysis were used to characterize the composite structure and determine the grafted MIPs quantities in the composite. The properties such as adsorption dynamics, special binding, and selective recognition capacity were evaluated. The results demonstrated that MWNTs-MIPs not only possessed a rapid dynamic adsorption but also exhibited a high selectivity toward DA, compared to epinephrine. The electrochemical sensor fabricated by modifying MWNTs-MIPs on the glassy carbon electrode could recognize DA from ascorbic acids (AA), indicating DA could be detected in the presence of AA. And the modified electrode was used to detect the concentration of DA with a linear range of 5.0 × 10 -7 to 2.0 × 10 -4 mol/L.
Light-driven CO 2 reduction into high value-added product is a potential route to convert and store solar energy. Here, using the hydroxyls on an oxyhydroxide photocatalyst, CoGeO 2 (OH) 2 , as solid-state proton source to reduce the CO 2 into CH 4 is proposed. It is found that under irradiation, the lattice hydroxyls on surface of CoGeO 2 (OH) 2 are oxidized by photogenerated holes, resulting in the generation of oxygen vacancies (O Vs ) and protons. The photoinduced O Vs (Lewis acid) and its proximal surface hydroxyls (Lewis base) are more likely to form the frustrated Lewis acid-base pairs, which can capture, activate, and reduce CO 2 with the assistance of protons into CH 4 . The surface lattice hydroxyls are able to regenerate when the catalyst is exposed to the water molecule-containing atmosphere, thus achieving a sustainable CO 2 conversion. The proposed CO 2 reduction by self-breathing surface hydroxyls may open a new avenue to use photocatalysis for energy conversion.
A simple method for the preparation of core-shell micro/nanostructured magnetic molecularly imprinted polymers (MIPs) for protein recognition is described. Magnetic MIPs were synthesized by copolymering gamma-aminopropyltrimethoxysilane and tetraethyl orthosilicate at the surface of Fe(3)O(4) nanospheres, which were directly covalently bound with template molecule, bovine hemoglobin (BHb), through imine bond. Transmission electron microscopy and scanning electron microscopy images showed that the Fe(3)O(4) nanospheres with diameter about 50-150 nm were coated with the MIPs layer with average thickness about 10 nm, which enabled the magnetic MIPs to have a sensitive and fast magnetic response. The proximity between the thickness of MIPs layer and the spatial size of BHb indicated that the imprinted sites almost situated at the surface of magnetic MIPs, leading a rapid adsorption saturation within 1 h. And the adsorption amounts of magnetic MIPs toward BHb were estimated to be 10.52 mg/g at pH 6.5, which was 4.6 times higher than that of magnetic nonmolecularly imprinted polymers. Meanwhile, the result of selective test showed that the magnetic MIPs had an excellent recognition capacity to BHb compared to the other nontemplate proteins. Except for the spatial size complementary between BHb and the binding sites in magnetic MIPs, the electrostatic interaction also was proven to be an important factor for recognizing the imprinting molecule.
The effects of Se(IV) on the structure and function of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT) purified from the cytoplasm of Escherichia coli were studied. The coding region of human AS3MT complementary DNA was amplified from total RNA extracted from HepG2 cell by reverse transcription PCR. Soluble and active human AS3MT was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 degrees C. Spectra (UV-vis, circular dichroism, and fluorescence) were first used to probe the interaction of Se(IV) and recombinant human AS3MT and the structure-function relationship of the enzyme. The recombinant human AS3MT had a secondary structure of 29.0% alpha-helix, 23.9% beta-pleated sheet, 17.9% beta-turn, and 29.2% random coil. When Se(IV) was added, the content of the alpha-helix did not change, but that of the beta-pleated sheet increased remarkably in the conformation of recombinant human AS3MT. Se(IV) inhibited the enzymatic methylation of inorganic As(III) in a concentration-dependent manner. The IC(50) value for Se(IV) was 2.38 muM. Double-reciprocal (1/V vs. 1/[inorganic As(III)]) plots showed Se(IV) to be a noncompetitive inhibitor of the methylation of inorganic As(III) by recombinant human AS3MT with a K (i) value of 2.61 muM. We hypothesized that Se(IV) interacts with the sulfhydryl group of cysteine(s) in the structural residues rather than the cysteines of the active site (Cys156 and Cys206). When Se(IV) was combined with cysteine(s) in the structural residues, the conformation of recombinant human AS3MT changed and the enzymatic activity decreased. Considering the quenching of tryptophan fluorescence, Cys72 and/or Cys226 are deduced to be primary targets for Se(IV).
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