Zhirong Geng

Preparation and Recognition Properties of Bovine Hemoglobin Magnetic Molecularly Imprinted Polymers

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.

Magnetic molecularly imprinted polymer for aspirin recognition and controlled release

Core-shell structural magnetic molecularly imprinted polymers (magnetic MIPs) with combined properties of molecular recognition and controlled release were prepared and characterized. Magnetic MIPs were synthesized by the co-polymerization of methacrylic acid (MAA) and trimethylolpropane trimethacrylate (TRIM) around aspirin (ASP) at the surface of double-bond-functionalized Fe(3)O(4) nanoparticles in chloroform. The obtained spherical magnetic MIPs with diameters of about 500 nm had obvious superparamagnetism and could be separated quickly by an external magnetic field. Binding experiments were carried out to evaluate the properties of magnetic MIPs and magnetic non-molecularly imprinted polymers (magnetic NIPs). The results demonstrated that the magnetic MIPs had high adsorption capacity and selectivity to ASP. Moreover, release profiles and release rate of ASP from the ASP-loaded magnetic MIPs indicated that the magnetic MIPs also had potential applications in drug controlled release.

A potent antitumor Zn2+ tetraazamacrocycle complex targeting DNA: the fluorescent recognition, interaction and apoptosis studies

A Zn(2+) tetraazamacrocycle complex (2) bearing three naphthalene moieties has been prepared. Complex 2 recognizes, binds and causes damage to DNA, and shows considerable cytotoxicity against human cervical (HeLa), breast (MCF-7) and lung (NCI-H157) cancer cell lines with a different apoptotic pathway from that of cisplatin.

Single-Crystalline EuF3 Hollow Hexagonal Microdisks: Synthesis and Application as a Background-Free Matrix for MALDI-TOF-MS Analysis of Small Molecules and Polyethylene Glycols

Single-crystalline EuF(3) hexagonal microdisks with hollow interior were fabricated to serve as a background-free matrix for analysis of small molecules and polyethylene glycols (PEGs) by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The long-lived excited state of europium ions can transfer energy to high-energy vibrations of organic molecules, which provides the potential technological application in MALDI-TOF-MS analysis of small molecules and PEGs. The efficiency of the hollow microdisks as a novel matrix of low molecular weight compounds was verified by analysis of small peptide, amino acid, organic compounds, and hydroxypropyl beta-cyclodextrin (HP-beta-CD). The advantage of this matrix in comparison with alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) was demonstrated by MALDI-TOF-MS analysis of an amino acid mixture and a peptide mixture. This matrix is successfully used for analysis of PEGs (PEG 2000, PEG 4000, PEG 8000, PEG 15000, and PEG 30000), suggesting a potential for monitoring reactions and for synthetic polymer quality control. The upper limit of detectable mass range was approximately 35,000 Da (PEG 30000). It is believed that this work will not only offer a new technique for high-speed analysis of small molecules and PEGs but also open a new field for applications of rare earth fluorides.

An NBD-armed tetraaza macrocyclic lysosomal-targeted fluorescent probe for imaging copper(II) ions.

An NBD-armed tetraaza macrocyclic lysosomal-targeted fluorescent probe for detecting Cu(2+) was synthesized and used for fluorescence imaging in HeLa cells. The probe was specifically localized in lysosomes and successfully applied to visualize Cu(2+) as well as to monitor Cu(2+) level changes in the lysosomes of living cells.

Indirect Transformation of Coordination‐Polymer Particles into Magnetic Carbon‐Coated Mn3O4 (Mn3O4@C) Nanowires for Supercapacitor Electrodes with Good Cycling Performance

Carbon-coated Mn3O4 nanowires (Mn3O4@C NWs) have been synthesized by the reduction of well-shaped carbon-coated bixbyite networks and characterized by TEM, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon-coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging-discharging measurements were performed. Mn3O4 @C NWs could be charged and discharged faster and had higher capacitance than bare Mn3O4 nanostructures and other commercial materials. The capacitance of the Mn3O4@C NWs was 92% retained after 3000 cycles at a charging rate of 5 Ag(-1). This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn3O4 core and also act as barriers to protect the inner core. These Mn3O4@C NWs could be a promising candidate material for high-capacity, low-cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as-synthesized samples are also reported to investigate the influence of the carbon coating.

Structure-function roles of four cysteine residues in the human arsenic (+3 oxidation state) methyltransferase (hAS3MT) by site-directed mutagenesis.

Cysteine (Cys) residues are often crucial to the function and structure of proteins. Cys157 and Cys207 in recombinant mouse arsenic (+3 oxidation state) methyltransferase (AS3MT) are shown to be related to enzyme activity and considered to be the catalytic sites. The roles of some conserved Cys residues in the N-terminal region of the rat AS3MT also have been examined. However, little is known about the roles of the Cys residues in the middle region. The metabolism of inorganic arsenic in human is different from rat and mouse in some aspects though the AS3MT has a high degree of similarity in these species. In order to determine whether the Cys156 and Cys206 (corresponding to the catalytic sites, Cys157 and Cys207 in the mouse AS3MT) in the hAS3MT act as the catalytic sites and to study the roles of the Cys residues (Cys226 and Cys250) near the catalytic center in the middle region, we designed and prepared four mutants (C156S, C206S, C226S, and C250S) in which one Cys residue replaced by serine by PCR-based site-directed mutagenesis. The native form and cysteine/serine mutants were assayed for enzyme activity, free thiols, and the secondary structures by circular dichroism and Fourier transform infrared. Our data show that, besides C156S and C206S, C250S is another potential important site. C226S seems to have the same action as the wild-type hAS3MT with the consistent K(M) and V(max) values. Meanwhile, selenium can also inhibit the methylation of inorganic arsenic by C226S. All the mutants except C226S are calculated to have dramatic changes in the secondary structures. Cys250 might form an intramolecular disulfide bond with another Cys residue. These findings demonstrate that Cys residues at positions 156, 206, and 250 play important roles in the enzymatic function and structure of the hAS3MT.

New insights into the mechanism of arsenite methylation with the recombinant human arsenic (+3) methyltransferase (hAS3MT)

The catalytic mechanism of the recombinant human arsenic (+3) methyltransferase (hAS3MT) was studied using kinetics, initial velocity and spectroscopy. The production and the distribution of methylated arsenicals changed with various concentrations of arsenite/S-adenosyl-L-methionine (SAM)/thiols, enzyme contents, and incubation times. These results suggest a sequential methylation of arsenite to monomethylated arsenicals (MMA) and dimethylated arsenicals (DMA). In addition, competition exists between the two reactions. hAS3MT showed the greatest activity at pH 8.5 with glutathione (GSH) as the reductant. This might indicate that a balance between the deprotonation and protonation of sulfhydryl groups is required. Initial velocity studies illuminate an ordered sequence for the binding of SAM and arsenite to the hAS3MT; while GSH should probably be placed either as the first reactant or as a reactant combining with the enzyme only after products have been released. The interactions between substrate/cofactors and the hAS3MT were first monitored by UV-visible and circular dichroism spectroscopy. It revealed that arsenite and SAM combined with the hAS3MT before reaction started; whereas, no interactions between GSH and the hAS3MT were detected. Integrating the results from kinetics, initial velocity and spectroscopy studies, an ordered mechanism are originally attained, with the SAM as the first reactant that adds to the hAS3MT and arsenite as the second one. Arsenite is successively methylated reductively, rather than a stepwise oxidative methylation. GSH should combine with the hAS3MT after the methylation to reduce the disulfide bond formed during the catalytic cycle in the hAS3MT to resume the active form of the enzyme.

Functional and structural evaluation of cysteine residues in the human arsenic (+3 oxidation state) methyltransferase (hAS3MT).

Arsenic (+3 oxidation state) methyltransferase (AS3MT) catalyzes the methylation of inorganic arsenic (iAs) and plays important role in the detoxication of this metalloid. There are fourteen cysteine residues in the human AS3MT (hAS3MT), among which twelve are absolutely conserved; Cys334 and Cys360 are unique; Cys368 and Cys369 are identified as a CysCys pair. The roles of several conserved cysteine residues in rat AS3MT and hAS3MT have been reported. Herein, the other conserved cysteine residues (Cys72, Cys271, Cys375) and the unique ones (Cys334, Cys360) were systematically replaced by serine using site-directed mutagenesis to study their functions. The mutants were investigated for enzymatic activity, kinetics, thermal stability and secondary structures. Present results indicate that C72S is completely inactive in methylation of iAs and has distinct changes in the secondary structures; Cys72 might form a critical intramolecular disulfide bond with Cys250; Cys271 and Cys375 do not affect the activity and structure of the hAS3MT. However, the mutations of Cys334 and Cys360 can decrease the enzymatic turnovers and change the conformation of the hAS3MT. The kinetic data show that Cys271, Cys334, Cys360 and Cys375 are not involved in the SAM binding. Additionally, all these cysteine residues except Cys375 affect the thermotropic properties of the hAS3MT.

One-pot template-free synthesis of water-dispersive Fe3O4@C nanoparticles for adsorption of bovine serum albumin

Water-dispersive Fe3O4@C nanoparticles have been successfully synthesized on a large scale via a one-pot template-free solvothermal process. The core–shell structure of the product was confirmed by transmission electron microscopy (TEM) observations. Fourier transform infrared (FT-IR) and X-ray photoelectron spectra (XPS) of the sample indicated that abundant amide carbonyl groups are formed on the surface of the Fe3O4@C nanoparticles. Based on the thermogravimetric analysis (TGA) results, the contents of Fe3O4 and carbon are calculated to be 77.5% and 6.1%, respectively. Magnetic measurements illustrated that the prepared composites are superparamagnetic magnets with a saturation magnetization of 69.2 emu g−1. Because of their hydrophilic core–shell structure, the prepared Fe3O4@C nanoparticles show a high bovine serum albumin (BSA) protein adsorption capacity (82.78 mg g−1) and a fast adsorption rate (60 min) in aqueous solutions. This work demonstrates that the prepared magnetic nanoparticles have promising applications in enzyme and protein immobilization.