学术期刊列表

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The development of protocols for direct catalytic acceptorless dehydrogenation of N-heterocycles with metal-free catalysts holds the key to difficulties in green and sustainable chemistry. Herein, an N-oxyl radical (TEMPO) acting as an oxidant in combination with electrochemistry is used as a synthesis system under neutral conditions to produce N-heterocycles such as benzimidazole and quinazolinone. The key feature of this protocol is the utilization of the TEMPO system as an inexpensive and easy to handle radical surrogate that can effectively promote the dehydrogenation reaction. Mechanistic studies also suggest that oxidative TEMPOs redox catalytic cycle participates in the dehydrogenation of 2,3-dihydro heteroarenes.

The first page of this article is displayed as the abstract.

Automated software was developed to analyze the molecular formula of organic molecules and peptides based on high-resolution MS/MS spectroscopic data. The software was validated with 96 compounds including a few small peptides in the mass range of 138–1569 Da containing the elements carbon, hydrogen, nitrogen and oxygen. A Micromass Waters Q-TOF Ultima Global mass spectrometer was used to measure the molecular masses of precursor and fragment ions. Our software assigned correct molecular formulas for 91 compounds, incorrect molecular formulas for 3 compounds, and no molecular formula for 2 compounds. The obtained 95% success rate indicates high reliability of the software. The mass accuracy of the precursor ion and the fragment ions, which is critical for the success of the analysis, was high, i.e. the accuracy and the precision of 850 data were 0.0012 Da and 0.0016 Da, respectively. For the precursor and fragment ions below 500 Da, 60% and 90% of the data showed accuracy within ≤0.001 Da and ≤0.002 Da, respectively. The precursor and fragment ions above 500 Da showed slightly lower accuracy, i.e. 40% and 70% of them showed accuracy within ≤0.001 Da and ≤0.002 Da, respectively. The molecular formulas of the precursor and the fragments were further used to analyze possible mass spectrometric fragmentation pathways, which would be a powerful tool in structural analysis and identification of small molecules. The method is valuable in the rapid screening and identification of small molecules such as the dereplication of natural products, characterization of drug metabolites, and identification of small peptide fragments in proteomics. The analysis was also extended to compounds that contain a chlorine or bromine atom.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

NMR-based metabonomics has been widely employed to understand the stressor-induced perturbations to mammalian metabolism. However, inter-sample chemical shift variations for metabolites remain an outstanding problem for effective data mining. In this work, we systematically investigated the effects of pH and ionic strength on the chemical shifts for a mixture of 9 urinary metabolites. We found that the chemical shifts were decreased with the rise of pH but increased with the increase of ionic strength, which probably resulted from the pH- and ionic strength-induced alteration to the ionization equilibrium for the function groups. We also found that the chemical shift variations for most metabolites were reduced to less than 0.004 ppm when the pH was 7.1–7.7 and the salt concentration was less than 0.15 M. Based on subsequent optimization to minimize chemical shift variation, sample dilution and maximize the signal-to-noise ratio, we proposed a new buffer system consisting of K2HPO4 and NaH2PO4 (pH 7.4, 1.5 M) with buffer–urine volume ratio of 1 : 10 for human urinary metabonomic studies; we suggest that the chemical shifts for the proton signals of citrate and aromatic signals of histidine be corrected prior to multivariate data analysis especially when high resolution data were employed. Based on these, an optimized sample preparation method has been developed for NMR-based urinary metabonomic studies.

Simple and sensitive chemiluminescence (CL) and CL imaging methods have been developed for the magnetic bead-based DNA hybridization assay. The assay relies on the high sensitivity and long stable light signal of the CL system in which horseradish peroxidase (HRP) catalyzes the luminol–H2O2 reaction with para-iodophenol (PIP) as the enhancer. In this protocol, a sandwich DNA hybridization is performed by mixing the target DNA with the magnetic bead-captured DNA and the biotinylated reporter DNA, followed through the biotin–streptavidin reaction with conjugated HRP, and then the conjugated HRP is determined by the CL system. The proposed CL protocol is suitable for for the detection of sequence-specific DNA related to the avian influenza A H1N1 virus at levels as low as 10 amol, and the CL imaging detection has a similar sensitivity. The sensitivities of the proposed methods with the HRP label are better than most of the metal nanoparticle-based methods, and are comparable with that of utilizing amplified techniques for DNA hybridization detection. In addition, the perfectly complementary DNA sequences and the single-base mismatched DNA sequences can be better distinguished by a thermally-stringent hybridization and washing steps. So, the proposed CL method can offer great promise for single-nucleotide polymorphism (SNP) analysis. Moreover, the proposed method may have significant potential for the simultaneous detection of various DNA sequences when different capture DNA sequences and reporter DNA sequences are used in a microarray.