Core-shell metal-organic framework/silica hybrid with tunable shell structure as stationary phase for high performance liquid chromatography.

Metal-organic framework/silica composite (SSU) were prepared by growing UiO-66 on the amino-functionalized SiO2 core-shell spheres (SiO2@dSiO2) via a simple one-pot synthesis approach. By controlling the concentration of Zr4+, the obtained SSU have two different morphologies: spheres-on-sphere and layer-on-sphere. The spheres-on-sphere structure is formed by the aggregation of UiO-66 nanocrystals on the surface of SiO2@dSiO2 spheres. SSU-5 and SSU-20, which contain spheres-on-sphere composites have mesopores with a pore size of about 45 nm in addition to the characteristic micropores of UiO-66 with a pore size of 1 nm. In addition, UiO-66 nanocrystals were grown both inside and outside the pores of SiO2@dSiO2, resulting in a 27% loading of UiO-66 in the SSU. The layer-on-sphere is the surface of SiO2@dSiO2 covered with a layer of UiO-66 nanocrystals. SSU with this structure has only a characteristic pore size of about 1 nm belonging to UiO-66 and is therefore not suitable as a packed stationary phase for high performance liquid chromatography. The SSU spheres were packed into columns and tested for the separation of xylene isomers, aromatics, biomolecules, acidic and basic analytes. With both micropores and mesopores, SSU with spheres-on-sphere structure achieved baseline separation of both small and large molecules. Efficiencies up to 48,150, 50,452 and 41,318 plates m - 1 were achieved for m-xylene, p-xylene and o-xylene, respectively. The relative standard deviations of the retention times of anilines for run-to-run, day-to-day and column-to-column were all less than 6.1%. The results show that the SSU with spheres-on-sphere structure has great potential for high performance chromatographic separation.

[State of the art of mixed-mode stationary phase].

With the development of science and technology, more and more complex samples like peptides and proteins need to be separated. It is difficult to separate them by single mode chromatography. Due to the unique separation character of mixed-mode chromatography, the same separation performance can be obtained in mixed-mode chromatography in one separation as multidimensional chromatography. And some disadvantages of multidimensional chromatography can be avoided in mixed-mode chromatography, such as the complexity of the system, the poor compatibility of mobile phases and the long analytical time. More and more attention is devoted to the mixed-mode chromatography in recent years. The focus on the mixed-mode chromatography is to design new structures of mixed-mode stationary phase. At present, mixed-mode stationary phases included reversed-phase/ion-exchange, reversed-phase/hydrophilic, hydrophilic/ion-exchange, zwitterionic and trimode mixed-mode stationary phases. The kinds of mixed-mode stationary phases are summarized and their features and applications in different fields are discussed in this review.

[Determination of N-nitrosodimethylamine in beer by frozen zone melting liquid-liquid extraction/gas chromatography].

A simple and effective sample enrichment method of frozen zone melting liquid-liquid extraction was optimized and validated for the analysis of trace N-nitrosodimethylamine (NDMA) in beer samples. The method was based on high pressure liquid-liquid extraction with a low temperature frozen step. The 90 mL beer was placed in a container with 10 mL dichloromethane. After agitation, the sample was kept in a freezer for 16 h at -19 degrees C. The organic extract was analyzed by gas chromatography with a flame ionization detector (GC-FID). The accuracy, precision, detection and quantification limits and linearity of the method were evaluated. The results showed that the calibration curve of NDMA was linear in the range of 5-200 mg/L with a good correlation coefficient (r2) of 0.999 6. The recoveries at the spiked levels of 5, 10 and 20 mg/L were 84.94%, 83.24%, 85.14% with the relative standard deviations (n = 7) of 3.06%, 3.19%, 2.63%, respectively. The ordinary extraction method of N-nitrosodimethylamine in beer includes the four steps of low-temperature distillation, liquid-liquid extraction, rotary evaporation and nitrogen blowing concentration. With the extremely low volume of solvent used, the proposed extraction method proved to be easy and simple, and adequate for high-throughput analysis at low cost.

[Preparation of a new stationary phase with s-triazine and amide embedded and its application in separation of basic compounds].

A new kind of silica-bonded reserved stationary phase with s-triazine and amide polar groups embedded for HPLC was obtained by step-wise reactions of silica gel with s-triazine, gamma-aminopropyltriethoxysilane, ethanediamine and dodecanoyl chloride. The new stationary phase was characterized by elemental analysis. After that, a column packed with the new stationary phase was used to separate basic compounds. A commercial C18 column was also tested under the same chromatographic conditions for comparison. The results indicated that the ligand was successfully bonded to the surface of the silica and the maximum relative deviations of element contents were within 5% for carbon, nitrogen and hydrogen by three times. Furthermore, in the separation of five basic anilines and four basic pyridines, the excellent selectivity and symmetrical peak shapes provided a reference for advancing the commercialization of the new stationary phase.

[Analysis of amines in water samples by high performance liquid chromatography-laser induced fluorescence detection].

A sensitive high performance liquid chromatography (HPLC)-laser induced fluorescence detection (LIFD) method was developed for the determination of amines. The derivatization and separation conditions were investigated. Under the optimized conditions, spermidine, putrescine and histamine were analyzed. The limits of detection (LODs) of the three biogenic amines (S/N = 3) were as low as 10(-10) mol/L. This method showed excellent stability. The RSDs of retention times and peak areas of the three biogenic amines were lower than 0.3% and 3%, respectively. This method was applied in biogenic amine analysis in water samples, and the average recoveries were in the range of 94.99%-104.7%. Furthermore, the amines in seven tea samples were analyzed by this method, and satisfactory results were achieved. The developed assay is of excellent sensitivity and good reproducibility, which can be used in the analysis of the amines in water samples.

[Determination of sulfur amino acids in feedstuffs by high performance liquid chromatography coupled with pre-column derivatization].

A method of quantitative analysis of sulfur amino acids in feedstuffs by high performance liquid chromatography coupled with pre-column derivatization was developed. Before the feedstuffs were hydrolyzed under acidic condition, the cystine and methionine in the feedstuffs were oxidized to cysteic acid and methionine sulfone respectively by performic acid, and then derivatized by 2,4-dinitrofluorobenzene. The separation was performed on an Elite AAK C18 column (250 mm x 4.6 mm, 5 microm) by the gradient elution of 0.05 mol/L sodium acetate and acetonitrile-water (50: 50, v/v) as the mobile phase with a flow rate of 1.2 mL/min at 31 degrees C. The detection wavelength was set at 360 nm. The linearities of cystine and methionine were good in the ranges of 0.4 - 16.0 mg/L and 0.7 - 29.6 mg/L with the correlation coefficients of 0.999 9 and 0.999 8, respectively. The quantification limits (S/N = 10) were 2.6 microg/kg, 3.1 microg/kg, and the recoveries were 100.28% - 102.00% and 105.72% - 107.89%, respectively. The method can be adapted to the accurate quantification of the sulfur amino acids in feedstuffs.

[The effects of microcystin-LR on the mRNA expression levels of base excision repair genes and genes related to apoptosis].

OBJECTIVE: To explore the effects of microcystin-LR (MCLR) on the expression of base excision repair genes and genes related to apoptosis. METHODS: The BRL-3A cells were exposed to different concentrations of MCLR for various periods of time and the cell viability was measured by MTT. The mRNA expression was determined with the quantitative real-time polymerase chain reaction (QRT-PCR). RESULTS: The viability of BRL-3A cells significantly reduced in a concentration- and time-dependent manner. In 30 µg/ml group, the mRNA expression level (1.327 ± 0.028) of p53 increased significantly at 24 h after exposure, as compared with the other groups (1.005 ± 0.117, 0.862 ± 0.154, 1.028 ± 0.056 and 1.015 ± 0.091) (P < 0.05). The mRNA expression levels (5.080 ± 0.729, 5.820 ± 0.373, 6.018 ± 0.359 and 6.183 ± 0.515) of Bax in all exposure groups were significantly higher than that (1.024 ± 0.277) in control group at 24 h after exposure. However, the Bax mRNA expression level (0.604 ± 0.146) in the 30 µg/ml group at 72 h after exposure was significantly lower than those (1.004 ± 0.107, 0.811 ± 0.142, 0.855 ± 0.101 and 0.814 ± 0.056) in other groups (P < 0.05). When compared with control group (1.006 ± 0.132) and 1 µg/ml group (1.034 ± 0.241), the mRNA expression level (0.488 ± 0.147) of PARP1 in 30 µg/ml group at 48 h after exposure decreased significantly (P < 0.05). Furthermore, the mRNA expression levels (0.594 ± 0.180, 0.491 ± 0.015 and 0.305 ± 0.091) of JWA, XRCC1 and PARP1 in 30 µg/ml group at 72 h after exposure decreased significantly, as compared with the other groups (P < 0.05). CONCLUSION: The induction of gene expression is a transient phenomenon that occurred at different times of exposure for different genes. Inhibition of MCLR on the base excision repair gene expression may play important role in the course of MCLR promoting liver tumor.

[Analysis of six acidic components in hops extracts by high performance liquid chromatography].

A method of high performance liquid chromatography (HPLC) was developed for the separation and determination of six acidic components (cohumulone, humulone, adhumulone, colupulone, lupulone and adlupulone) in hops extracts. The effects of several important factors, such as the addition of acid, the organic solvent of elution solution and the column temperature, were investigated to acquire the optimum conditions. The separation was carried out on a Hypersil ODS2 column (250 mm x 4. 6 mm, 5 microm). A mixture of acetonitrile-0. 1% (v/v) phosphoric acid solution (pH 2. 2) (65: 35, v/v) was used as the mobile phase at a flow rate of 1. 0 mL/min in isocratic elution mode. The column temperature was kept at room temperature, and the detection wavelength was set at 315 nm. The six acidic components reached baseline separation, and were identified by ultraviolet spectroscopy, infrared spectroscopy and mass spectrometry. The results show that this method is suitable for the analysis of acidic components in hops extracts owing to the stable and simple performance.

[Development and evaluation of a novel three-dimensional adjustable confocal laser-induced fluorescence detector].

Laser-induced fluorescence detector (LIFD) is one of the most sensitive detectors in analytical chemical files. Confocal optical configuration is widely used in LIFDs. Two effective approaches used to achieve the best signal to noise ratio (S/N) are increasing the confocal precision and minimizing the background noise. A novel three-dimensional adjustable confocal LIFD was developed, using a new three-dimensional adjustable supporter of reflector and modularized optical system. A detection limit (S/N = 3) of 1 x 10(-12) mol/L and a linear dynamic range of 3 orders of magnitude were obtained using fluorescein isothiocyanate (FITC) standard as the test sample. The noise level and drift levels were 8.0 x 10(-3) mV and 1.4 x 10(-3) mV/h, respectively, which were almost 10 times lower than before. And the stability of the LIFD was evaluated by five replicate injections of 5 x 10(-9) mol/L FITC, and the relative standard deviations (RSDs) of peak height and peak area were 0.38% and 0.41%, respectively. Further more, three biogenic amines, which were derivatized by FITC, were separated by high performance liquid chromatography (HPLC) and then detected by the novel LIFD. And the detection limits (S/N = 3) ranged 0.01 to 0.02 nmol/L, which were better than other methods. Therefore, the LIFD is highly sensitive, as well as shows a real low noise level and good reproducibility.

Hydrolysis of plasmid DNA and RNA by amino alkyl naphthalimide as metal-free artificial nuclease.

A strategy of dimethylamino alkyldiimide conjugated with an intercalator of naphthalimide for hydrolysis of DNA was suggested and evaluated. 4 can hydrolyze 4 kb plasmid DNA into 2 kb fragments with GC and GG selectivity, which represents a novel example of sequence- or site-selective metal-free DNA artificial nuclease. Results also show it could hydrolyze RNA efficiently.

Thio-heterocylic naphthalimides with aminoalkyl side chains: novel alternative tools for photodegradation of genomic DNA without impairment on bioactivities of proteins.

Thio-heterocylic naphthalimides (R1-R5) were designed, synthesized and evaluated as nonmetallic and long-wavelength photocleavers. Some of them showed highly efficient abilities in the degradation of plasmid and genomic DNA under the mild conditions without obvious impairment on the proteins' bioactivities, when compared with frequently applied nucleic acids removal reagents or precipitants. Their differences in photodegradation selectivity to DNA rather than proteins were dependent on their photodamage mechanisms and binding modes with bio-macromolecules. When maize genomic DNA was used as substrate, 2.38 x 10(-4) M of R5 exhibited the nuclease activity of 8 Unit DNase I, R5 has some characteristic as a typical catalyst as no consumption after two cycles of the photodegradation for DNA. The experiments of enzymatic activity assay and immunology activity analysis showed that R5 was safe to proteins, suggesting its potential in the removal of transgenic material during the preparation of bioactive proteins or enzyme preparations.