Yuanzong Li

Fluorescence reaction of terbium(III) with nucleic acids in the presence of phenanthroline

Abstract The fluorescence enhancement reaction of terbium(III) with DNA or RNA in the presence and absence of phenanthroline (Phen) was studied. Studies involving natural and denatured calf thymus DNA, fish sperm DNA and yeast RNA revealed that the presence of phen enhanced the net fluorescence 3–12-fold. The results suggest a 1 : 2 molar ratio of terbium(III) and phen for the ternary complex. Maximum fluorescence was produced in the pH range 6.8–7.2. The calibration graphs was linear between 0.4 and 15.0 or 20.0 μg ml −1 for thermally denatured nucleic acids and the detection limits were 0.1–0.2 μg ml −1 . The relative standard deviation (six replicates) was within 3.0% in the linear range. Yeast RNA could be determined in the presence of up to 40% calf thymus DNA and the latter was determined when the content of yeast RNA in synthetic samples was below 10%.

A new competitive enzyme-linked immunosorbent assay (ELISA) for determination of estrogenic bisphenols

Bisphenol A and other hydroxylated diphenylalkanes (generally known as bisphenols) have been identified as potential estrogenic substances. In this paper, a specific polyclonal antibody was produced against these compounds by immunization of rabbits with a conjugate of 4,4-bis (4-hydroxyphenyl) valeric acid and bovine serum albumin (BHPVA-BSA). The polyclonal antibody showed specific recognition of the bisphenol structure, while the cross reactions of other common phenolic compounds such as phenol, hydroquinol and p-hydroxybenzoic acid were all lower than 1%. The linear range of bisphenol A calibration curve was 1-10 000 ng ml(-1). Real water samples and mouse serum samples were spiked with known amount of bisphenol A and measured by the competitive ELISA. Recoveries were between 92 and 105%. The detection limits were found to be 0.1 ng ml(-1) for real water samples and 2 ng ml(-1) for serum samples. The method is very useful for monitoring bisphenol compounds in environmental and biological samples.

Sulfonamide imprinted polymers using co-functional monomers

Abstract Molecular imprinted polymers (MIPs) prepared using combination of acrylamide (ACM) and 4-vinylpyridine (4-Vpy) as co-functional monomers exhibited efficient recognition properties in both organic and aqueous media as HPLC stationary phase. The results indicate that amide and pyridine groups in functional monomers formed strong hydrogen-bonding interaction with the template molecule, and specific recognition sites were created within the polymer matrix during the imprinting process. When sulfamethoxazole (SMO) was used as template, a MIP prepared in a polar organic solvent (acetonitrile) using the combination of ACM and 4-Vpy showed better recognition of template than the polymer prepared in the same solvent using the combination of acidic monomer (methacrylic acid) and basic monomer 4-Vpy. On the contrary, when sulfamethazine (SMZ) was used as template, a MIP prepared using the combination of methacrylic acid (MAA) and 4-Vpy showed better recognition of template than the polymer prepared using the combination of ACM and 4-Vpy. Our results indicate that in organic media the degree of retention of the sample molecules on the imprinted polymers was controlled by the hydrogen-bonding interaction between the sample molecules and the polymer, while in aqueous media it was determined to a considerable extent by hydrophobic interactions. In both media the shape, size and the electronic structure of the template molecule were all-important factors in the recognition process.

Picolinamide–Cu(Ac)2-imprinted polymer with high potential for recognition of picolinamide–copper acetate complex

Abstract In this report, with semi-empirical quantum method, we have studied the conformation and energy of supermolecule composed of picolinamide and its positional isomers with methacrylic acid. We tried to explore the reason why picolinamide was not likely to show imprinting effect when using methacrylic acid as functional monomer in our previous work. In order to produce imprinting effect, which was not achieved based on hydrogen bonding interaction, we have synthesized a molecular-imprinted polymer (MIP) based on copper ion coordination in prepolymerization. The complex in prepolymerization was composed of copper(II), acetate, picolinamide and 4-vinylpyridine (4-Vpy). Suprisingly, the MIP had high selectivity to picolinamide–copper acetate complex, and changes of either copper ion, picolinamide or acetate would result in decrease in the imprinting effect. This is also the first example where the high selective recognition of the MIP to its template was achieved mainly by inhibiting the binding of non-template rather than enhancing the binding of the template. And this report can be also looked upon as a first step towards the solution to the problem of imprinting of template that contains intramolecular hydrogen bond.

Kinetic deoxyribose degradation assay and its application in assessing the antioxidant activities of phenolic compounds in a Fenton-type reaction system

Abstract Pro-oxidant properties of phenolic antioxidants, which are derived from their iron recycling reactivity, render the traditional deoxyribose degradation assay invalid to assess the hydroxyl radical-scavenging activity in Fenton-type reaction systems. In the present paper, we studied in detail the interactions between iron and phenolic compounds, and established a kinetic deoxyribose method by taking advantage of the distinct difference between the completion time of Fenton reaction and that of the iron-reducing process. With the newly established kinetic method, we investigated the effects of phenolics on hydroxyl radical formation in a Fenton-type system and determined successfully the second rate constants of hydroxyl radical-scavenging reactions. The site-specific and non-site-specific hydroxyl radical-scavenging ability suggested that both direct hydroxyl radical-scavenging potency and iron-chelating capacity accounted for their inhibitory effects on deoxyribose oxidation degradation. This method, more simple, time saving, and applicative than the traditional deoxyribose assay, produces as accurate results (RSD

Development and characterization of an immunoaffinity column for the selective extraction of bisphenol A from serum samples.

An immunoaffinity column (IAC) was developed by covalently coupling polyclonal antibodies against estrogenic bisphenols to CNBr-activated Sepharose 4B. The IAC showed high affinity for bisphenol A, while phenol was barely retained. Proteins in the sample matrix showed little nonspecific adsorption on the column. The best binding solvent for bisphenol A was found to be 0.01 mol l(-1) phosphate-buffered saline (PBS) and the optimal operating temperature was 4 degrees C. The bound bisphenol A could be quantitatively recovered by 1 ml of methanol-water (80:20) with an average recovery of 91.8% and a relative standard deviation of 7.1% (n=6). The immunoaffinity column has been successfully used for the isolation and purification of bisphenol A from serum samples.

Electrocatalytic reduction of dioxygen on hemin based carbon paste electrode

A hemin-modified carbon paste electrode was constructed by a simple, rapid and effective method. The electrochemical behaviour of the modified electrode was characterized by cyclic voltammetry. The modified electrode obtained was very stable and exhibited electrocatalytic response for the reduction of oxygen. The possible mechanism for the catalytic reduction of dioxygen is discussed. The dioxygen is reduced via a one-step reduction accompanying four electrons and four protons transfer at pH 7–11.

Time-resolved fluorescence studies of the interaction of the Eu3+ complexes of tetracycline analogues with DNA

The interaction of the Eu3+ complexes of tetracycline analogues with DNA has been examined by using UV-visible absorption and fluorescence spectra. Among the tetracycline series, the europium fluorescence sensitized by tetracycline (TC) and oxytetracycline (OTC) were enhanced by DNA more than those of other antibiotics in the series. Therefore, Eu3+-TC-DNA and Eu3+-OTC-DNA systems were investigated by time-resolved fluorescence. The Eu3+-OTC complex is a more sensitive fluorescence probe for selective determination of DNA than the Eu3+-TC complex. Detection limits (signal/ noise = 2) for DNA are 2.4 and 5.0 ng ml−1 for the OTC and TC systems, respectively.

Synthesis, characterization and biocompatibility of poly(2-ethyl-2-oxazoline)–poly(d,l-lactide)–poly(2-ethyl-2-oxazoline) hydrogels

A novel thermoreversible hydrogel based on poly(2-ethyl-2-oxazoline)-derived amphiphilic triblock copolymer, poly(2-ethyl-2-oxazoline)-poly(D,L-lactide)-poly(2-ethyl-2-oxazoline) (PEOz-PLA-PEOz), was developed. The synthesis of PEOz-PLA-PEOz was carried out by coupling monohydroxylated PEOz-PLA diblocks with adipoyl chloride as coupling agent and dimethylamino pyridine as catalyst. The tube inverting and rheological tests showed that triblock copolymers had sol-gel-sol transition behavior with increasing temperature, and the gelation was found to be thermoreversible. The critical gelation concentration, the sol-gel transition temperature at a given concentration depended on the EOz/LA ratio and the molecular weight of PEOz. Scanning electron microscopy observation revealed that the resultant bulky gel exhibited an interconnected porous three-dimensional (3D) microstructure after freeze-drying. In addition, the hydrogels showed good cytocompatibility in vitro. MTT assays revealed that the human skin fibroblast cells encapsulated within the hydrogels were viable and proliferated inside the 3D scaffold. This newly described thermoreversible hydrogel demonstrated attractive properties to serve as cell matrix for a variety of tissue engineering applications or pharmaceutical delivery vehicles.

Chromatographic characterization of sulfonamide imprinted polymers

Sulfamethazine and sulfamethoxazole are anti-bacterial and anti-infective agents. Molecular imprinted polymers of these agents were prepared by the technique of non-covalent molecular imprinting polymerization. The functional monomers used include methacrylic acid, 4-vinylpyridine, acrylamide or a combination of methacrylic acid and 4-vinylpyridine. The polymers obtained were packed in a high-performance liquid chromatography (HPLC) column, and the molecular recognition mechanism regulating the binding behavior was studied using chromatography. The results showed that methacrylic acid was suitable for synthesizing sulfamethazine-selective polymer, whereas 4-vinylpyridine was suitable for sulfamethoxazole. Although these two compounds have similar structures, the interactions between them and the monomers are different. The selective polymers are expected to be of use for analyzing sulfonamide compounds in the food industry and clinic applications.