多类型模型的Hydrodynamic极限

本文研究一类具有平移不变有限程的变相速率和不同的扩散速率的多类型模型的Hydrodynamic行为。在合适的条件下,证明了该模型的Hydrodynamic极限是一个非线性反应扩散方程的解     

Determination of analogs of sildenafil and vardenafil in foods by column liquid chromatography with a photodiode array detector, mass spectrometry, and nuclear magnetic resonance spectrometry

Two analogs of sildenafil and vardenafil in food were detected by column liquid chromatography (LC) with a photodiode array detector. They were isolated by preparative LC; their structures were established by mass spectrometry and nuclear magnetic resonance spectrometry. One analog was found to be methisosildenafil (compound A), 5-(5-(3,5-dimethylpiperazin-1-ylsulfonyl)-2-ethoxy-phenyl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]-pyrimidin-7(6H)-one. It is a sildenafil analog with a dimethylpiperazine ring substituted for the methylpiperazine group. The second analog, hydroxyvardenafil (compound B) is reported for the first time in this study. Hydroxyvardenafil's International Union of Pure and Applied Chemistry name is 2-(2-ethoxy-5-(4-(2-hydroxyethyl)-piperazin-1-ylsulfonyl)phenyl)-5-methyl-7-propyl-imidazo[1,5-f][1,2,4]triazin-4(3H)-one. The novel vardenafil analog has a hydroxyl group added to the ethylpiperazine group.     

Spectroscopic characterization and molecular structure of 3,14‐dimethyl‐2,6,13,17‐tetraazapentacyclo[16.4.0.12,17.16,13.07,12]tetracosane

Constrained cyclam derivatives have been found to exhibit anti‐HIV effects. The strength of binding to the CXCR4 receptor correlates with anti‐HIV activity. The conformation of the macrocyclic compound is very important for co‐receptor recognition. Therefore, knowledge of the conformation and crystal packing of macrocycles has become important in developing new highly effective anti‐HIV drugs. Structural modifications of N‐functionalized polyaza macrocyclic compounds have been achieved using various methods. A new synthesis affording single crystals of the title tetraazapentacyclo[16.4.0.1^2,17.1^6,13.0^7,12]tetracosane macrocycle, C₂₂H₄₀N₄, is reported. Formaldehyde reacts readily at room temperature with the tetraazatricyclo[16.4.0.0^2,17]docosane precursor to yield a macropolycycle containing two five‐membered rings. Characterization by elemental, spectroscopic and single‐crystal X‐ray diffraction analyses shows that the asymmetric unit contains half of a centrosymmetric molecule. The molecular structure shows a trans conformation for the two methylene bridges owing to molecular symmetry. The crystal structure is stabilized by intramolecular C—H…N hydrogen bonds. NMR and IR spectroscopic properties support the methylene‐bridged macrocyclic structure.     

The investigation of electrospun polymer nanofibers as a solid-phase extraction sorbent for the determination of trazodone in human plasma

A novel micro-extraction procedure was developed through the use of an electrospun polymer nanofiber as a solid-phase extraction (SPE) sorbent to directly extract trazodone from human plasma. The target compound was then monitored by a high performance liquid chromatography with ultraviolet detector (HPLC-UV) system. Parameters of influencing the extraction efficiency, such as fiber diameter, fiber packing amount, eluted solvent, pH and ionic strength were investigated. Under the optimized conditions, a linear response for trazodone over the range of 20-2000 ng mL⁻¹ was achieved with a γ² value of 0.9996. The precision of the method was examined with relative standard deviations of 5.7, 2.7, 2.2% corresponding to 50, 200, and 500 ng mL⁻¹, respectively, of trazodone spiked into 0.1 mL of plasma samples. The extraction recoveries of 58.3-75.2% and the relative recoveries of 94.6-105.5% were obtained. The limit of detection (LOD) was determined to be 8 ng mL⁻¹. A 15 min of HPLC gradient was successfully applied to determine trazodone from human plasma. Due to its simplicity, selectivity and sensitivity, the method may be applied to pharmacokinetic and pharmacodynamic studies of drugs.     

Investigation of tyrosine nitration and nitrosylation of angiotensin II and bovine serum albumin with electrospray ionization mass spectrometry

Protein tyrosine nitration is one of the important regulatory mechanisms in various cellular phenomena such as cell adhesion, endo/exo-cytosis of cellular materials, and signal transduction. In the present study, electrospray ionization tandem mass spectrometry (ESI-MS/MS) with a linear ion-trap mass spectrometer was applied for identification of nitrated proteins and localization of the modified tyrosine residues. When angiotensin II(DRVYIHPF) was nitrated in vitro with tetranitromethane (TNM), the mass spectrum showed a shift of +45 Da which corresponded to tyrosine nitration. An additional +29 Da mass shift was also detected by ESI-MS. This differed from nitrated peptide analysis with matrix-associated laser desorption/ionization mass spectrometry (MALDI-MS), which showed oxygen neutral loss from the nitrated tyrosine residues upon laser irradiation. Hence the +29 Da mass shift of the nitrated peptide observed by ESI-MS suggested the introduction of an NO group for nitrosylation of tyrosine residues. To confirm this in vitro nitrosylation on the protein level, bovine serum albumin was in vitro nitrated with TNM and analyzed by ESI-MS/MS. As expected, +29 as well as +45 Da mass shifts were detected, and the +29 Da mass shift was found to correspond to the modification on tyrosine residues by NO. Although the chemical mechanism by which this occurs in ESI-MS is not clear, the +29 Da mass shift could be a new potential marker of nitrosylated peptides.     

Size prediction of recombinant human growth hormone nanoparticles produced by supercritical fluid precipitation

Solution-enhanced dispersion by supercritical fluids (SEDS) was applied to produce nano-sized recombinant human growth hormone (hGH) particles. Ethanol was used to help the supercritical carbon dioxide to extract water from the aqueous protein solution. Various sizes of hGH nanoparticles were successfully prepared with a narrow particle size distribution from aqueous ethanol solution without using any additive. The theoretical particle sizes were deduced from the calculated droplet sizes based on a modified Jasuja’s equation. The calculated mean particle sizes and the experimentally obtained ones were compared and the results showed an excellent correlation coefficient (R ²) of 0.995. Figure Distribution of hGH Nano-particles     

Quick quantification of proteins by MALDI

Previously, we reported that the matrix‐assisted laser desorption ionization spectrum of a peptide became reproducible when an effective temperature was held constant. Using a calibration curve drawn by plotting the peptide‐to‐matrix ion abundance ratio versus the peptide concentration in a solid sample, a peptide could be quantified without the use of any internal standard. In this work, we quantified proteins by quantifying their tryptic peptides with the aforementioned method. We modified the digestion process; e.g. disulfide bonds were not cleaved, so that hardly any reagent other than trypsin remained after the digestion process. This allowed the preparation of a sample by the direct mixing of a digestion mixture with a matrix solution. We also observed that the efficiency of the matrix‐to‐peptide proton transfer, as measured by its reaction quotient, was similar for peptides with arginine at the C‐terminus. With the reaction quotient averaged over many such peptides, we could rapidly quantify proteins. Most importantly, no peptide standard, not to mention its isotopically labeled analog, was needed in this method. Copyright © 2015 John Wiley & Sons, Ltd.     

In-Depth TEM Investigation on Structural Inhomogeneity within a Primary LixNi0.835Co0.15Al0.015O2 Particle: Origin of Capacity Decay during High-Rate Discharge

The structural stability of cathode materials during electrochemical reactions, in particular, under high-rate discharge, is pertinent to the design and development of new electrode materials. This study investigates the structural inhomogeneity that develops within a single LiNi_0.835Co_0.15Al_0.015O₂ (NCA83) particle during a fast discharging process under different cutoff voltages. Some of the NCA83 particles discharged from a high cutoff voltage (4.8 V) developed surface areas in which the layered structure was recovered, although the interiors retained the degraded spinel structure. These micro- and nano-scale structural inversions from high cutoff voltage seem highly correlated with structural evolutions in the initial charged state, and may ultimately degrade the cycling stability. This study advances understanding of the structural inhomogeneity within primary particles during various electrochemical processes and may facilitate the development of new Ni-rich cathode materials.