On the Coloring Reaction of Dibromomethyl Carboxyazo with Iron

The reagents of unsymmetrical carboxyazo group as coloring agents are often used in the spectrophotometric determination of calcium, barium and aluminum, but rarely used in that of iron. Dibromomethyl carboxyazo is a new coloring agent, and can be used in the determination of barium. It is not found that the agent is used in that of other elements.     

Metabolism of cheese whey lactose by kluyveromyces fragilis for energy and growth under batch condition

The fermentation of lactose byKluyveromyces fragilis is an exothermic reaction in which heat is released, resulting in a rise in reactor temperature. A heat balance was performed on a 5-L batch reactor used for single cell protein (SCP) production to determine the portions of cheese whey lactose used for energy and growth. On the average, about 88% of lactose was used for growth, and 12% was used for energy. The lactose consumed during the lag and stationary phases was used mostly for cell endogenous growth and respiration, whereas that consumed during the exponential growth phase was used for cell multiplication and energy. The heat released varied from 6.5 to 8.9 kJ/g cell. Because of the proper design of the fermenter, the temperature of the medium did not rise above 33°C; thus, no cooling system was needed.     

Construction of Multi‐Substituted Benzenes via NHC‐Catalyzed Reactions of Carboxylic Esters

A carbene‐catalyzed ester activation reaction for the synthesis of multi‐substituted benzenes is developed. Tetra‐substituted benzene compounds are efficiently synthesized through this methodology. Compared with aldehyde substrates used in previous reports, the ester substrates used here are much more readily available and inexpensive. In addition, the TEMPO oxidant used here is more inexpensive than the quinones commonly used in related carbene‐catalyzed reactions.     

Evaluating changes of writhe in computer simulations of supercoiled DNA

We compute changes in the writhe of a polygonal space curve when one of the vertices is displaced. The resulting expressions can be used in simulations of supercoiled DNA. For Brownian dynamics simulations, the expressions can be used to eliminate the explicit twisting degree of freedom. For Monte Carlo simulations, they can be used in fast local moves. Preliminary Monte Carlo simulations using only such fast local moves show that these can be used to efficiently simulate small DNA supercoils.     

药物发现中常用化合物库特征描述与对比分析

随着计算技术的发展和分子模拟软件的日趋成熟, 虚拟筛选已经在药物发现过程中发挥着越来越重要的作用. 在虚拟筛选过程中, 所使用化合物库的质量对先导化合物发现的成功率起着至关重要的作用. 本文通过对已知药物库、天然产物库、中药原植物化学成分库、筛选常用商业化合物库以及研究者所在实验室建立的化合物库的分析比较, 从化合物库的分子多样性、化学空间和分子骨架等多个方面提取并对比每一种化合物库的特征, 发现了已知药物库与中药原植物化学成分库的特征相似性, 揭示了中药原植物化学成分库作为筛选库的类药性优势, 并且深化了对几种筛选用化合物库特征的认识和理解.     

固相微萃取-气相色谱法测定食品包装材料中残留有机溶剂

提出了一种以固相微萃取与气相色谱-氢火焰联用技术为基础的测定食品包装材料中15种常用有机溶剂(苯类、醇类、酮类、酯类等)的方法。选择聚二甲亚砜作为固相微萃取的萃取相,采用DB-624毛细管色谱柱进行分离。在优化的试验条件下,15种有机残留溶剂在20min内能很好地分离,15种溶剂的测定下限(10S/N)为0.08～0.69μg.dm-2。加标回收率为60.0%～115.0%,相对标准偏差(n=5)为2.17%～8.34%。     

气相色谱法分离和测定溶剂型木器涂料中正丁醇与苯系物

在气相色谱法测定溶剂型木器涂料中正丁醇及苯系物(包括苯、甲苯及二甲苯)时采用了VF-200MS型号的毛细管色谱柱。由于此型号的毛细管柱具有较强极性,不仅能达到正丁醇与苯系物之间的有效而满意的分离,而且还能使苯系物(包括苯、甲苯、乙苯、二甲苯)之间和二甲苯的同分异构体之间的有效分离。测定中采用正戊烷作内标和用火焰离子检测器检测。此方法的检出限(2S/N)在1.7~3.5 ng之间。用一含有正丁醇的硝基漆样品按所提出的方法进行多次重复测定,并在此样品的基础上加入各被测化合物的标准后进行测定,从而对方法的回收率和精密度作了测试,测得其回收率在87.8%~100.0%之间,测定值的相对标准偏差(n=6)均小于2.5%。     

Electrochemical determination of hesperidin using mesoporous SiO2 modified electrode

A simple micro-capillary electrophoresis system to be used as disposable device was developed. A short commercial capillary was used as the separation channel, hydrostatic pressure generated by the sample employed for injection, and a voltage of 200 V used for separation in a 6 cm long capillary assisted by hydrostatic pressure of the carrier. The device was used for the separation of dopamine and catechol. Good reproducibility and efficiency was obtained. Because the instrumentation and operation conditions were simplified, and a replaceable modular separation channel was used, the proposed micro-capillary electrophoresis system is potentially useful in disposable devices.     

Exact solutions of lattice polymer models

We consider directed path models of a selection of polymer and vesicle problems. Each model is used to illustrate an important method of solving lattice path enumeration problems. In particular, the Temperley method is used for the polymer collapse problem. The ZL method is used to solve the semi-continuous vesicle model. The Constant Term method is used to solve a set of partial difference equations for the polymer adsorption problem. The Kernel method is used to solve the functional equation that arises in the polymer force problem. Finally, the Transfer Matrix method is used to solve a problem in colloid dispersions. All these methods are combinatorially similar as they all construct equations by considering the action of adding an additional column to the set of objects.     

Grid‐based algorithm to search critical points,in the electron density,accelerated by graphics processing units

Using a grid‐based method to search the critical points in electron density, we show how to accelerate such a method with graphics processing units (GPUs). When the GPU implementation is contrasted with that used on central processing units (CPUs), we found a large difference between the time elapsed by both implementations: the smallest time is observed when GPUs are used. We tested two GPUs, one related with video games and other used for high‐performance computing (HPC). By the side of the CPUs, two processors were tested, one used in common personal computers and other used for HPC, both of last generation. Although our parallel algorithm scales quite well on CPUs, the same implementation on GPUs runs around 10× faster than 16 CPUs, with any of the tested GPUs and CPUs. We have found what one GPU dedicated for video games can be used without any problem for our application, delivering a remarkable performance, in fact; this GPU competes against one HPC GPU, in particular when single‐precision is used. © 2014 Wiley Periodicals, Inc.     

A new titrant for perchlorate: Cetyltrimethylammonium bromide

Cetyltrimethylammonium bromide is used in the precipitation titration of perchlorate, with potentiometric end-point detection. A perchlorate, fluoroborate or nitrate ion-selective electrode may be used. The method is more sensitive than the commonly used titration with tetraphenylarsonium chloride. It can be used over the pH range from 1.20 to at least 12.8. The titrant is much cheaper than tetraphenylarsonium chloride.     

Computational models for the helix tilt angle

The concept of hydrophobic imbalance and that of hydrophobic and hydrophilic centers are used along with side chain models in the computation of helix orientation and tilt angle in or near a membrane. Rotamer statistics are used to infer typical side chain positions and chain length for each amino acid, and the results are used in fast computation of helix orientation. Sliding windows are used to compute local tilt angles on long alpha-helices that defy idealized modeling and generate tilt angle profiles. Seven different procedures based on different formulas and hydrophobicity scales are used for comparison. These procedures generated very similar tilt angle profiles. These profiles provide insights into helix deformation, membrane destabilization, and similarity and differences between membrane proteins.     

Electrospray doxorubicin-loaded polycaprolactone-polyethylene glycol nanospheres/poloxamer-chitosan thermogel: A promising candidate for clinical applications

In recent years, polymer nanospheres have been considered as one of the most common materials in the drug delivery domain. In this research, polycaprolactone-polyethylene glycol (PCL-PEG) blend nanospheres were produced using the electrospray method to load doxorubicin. Also, these nanospheres can be used for injection in the treatment site by poloxamer-chitosan thermogel. In this research, PCL and PEG were used as raw materials to produce nanospheres. Then, doxorubicin was used for loading in nanospheres. The electrospray method was chosen as the method of nanosphere production. In the next step, poloxamer-chitosan thermogel was used for injection at the treatment site. In this method, Fourier transform infrared spectroscopy, scanning electron microscopy, and rheometer techniques were used to identify the compounds and properties of the obtained specimens. Also, the MTT test was used to investigate toxicity. The results showed that PCL-PEG polymer nanospheres were produced by loading doxorubicin using the electrospraying method with a diameter of 185 ± 23 nm. Also, these nanospheres were used for injection in the treatment site using poloxamer-chitosan thermogel. The amount of drug release in the PLX-CS (DOX-PCL-PEG)NSs was 63% in 144 h at medium pH 5.5. In the drug release system, the in-vitro method was utilized to study the release of PLX-CS (DOX-PCL-PEG) NSs. PCL-PEG nanospheres combined in poloxamer-chitosan thermogel polymer showed the controlled release of doxorubicin, therefore, the evaluated drug release system is considered a valuable perspective as an efficient and safe route for drug delivery in the target tissue and treating various types of cancer. This research can be used as a new method in drug delivery systems.     

Photosensitized degradation of organic pollutants in water: processes and analytical applications

Photosensitized degradation has been used to remove a broad range of organic pollutants, generally with mineralization to CO₂ and other inorganic products such as Cl⁻ and . TiO₂ and Fe³⁺ are the photosensitizers mainly used to accelerate the degradation of persistent organic chemicals. Various analytical techniques were used to identify the degradation products and to monitor the degradation kinetics. Chromatographic techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC) and ion-exchange were used. Other analytical techniques, such as total organic carbon analysis, UV–visible spectrophotometry, spectrofluorimetry, and potentiometry, were also used. When the photodegradation is carried out in water, extraction methods such liquid–liquid extraction or solid-phase extraction need to be used, followed by GC or HPLC analysis. We review the analytical methods used for the identification of the products formed in photodegradation studies. Kinetic studies of the degradation are also reported.     

Independently controlling protein dot size and spacing in particle lithography

Particle lithography is a relatively simple, inexpensive technique used to pattern inorganics, metals, polymers, and biological molecules on the micro- and nanometer scales. Previously, we used particle lithography to create hexagonal patterns of protein dots in a protein resistant background of methoxy-poly(ethylene glycol)-silane (mPEG-sil). In this work, we describe a simple heating procedure to overcome a potential limitation of particle lithography: the simultaneous change in feature size and center-to-center spacing as the diameter of the spheres used in the lithographic mask is changed. Uniform heating was used to make single-diameter protein patterns with dot sizes of approximately 2-4 or 2-8 μm, depending on the diameter of the spheres used in the lithographic mask, while differential heating was used to make a continuous gradient of dot sizes of approximately 1-9 μm on a single surface. We demonstrate the applicability of these substrates by observing the differences in neutrophil spreading on patterned and unpatterned protein coated surfaces.     

Computer monitoring of sugars,acids and volatile compounds in fermentations

Head-space gas chromatography coupled to computer-assisted mass spectrometry is used to follow the formation kinetics of ethanol in fermentations. High-performance liquid chromatography, coupled to a computerized integrator, is used to follow the kinetics of disappearance of sugars and the formation of acids during the fermentation process. Flow injection analysis is used to monitor feed streams of low sugar content during downstream processing and recovery of the lactic acid. The kinetics pattern of volatile and nonvolatile products can be used in order to control fermentation parameters.     

Thickness Measurements of Thin Perfluoropolyether Polymer Films on Silicon and Amorphous-Hydrogenated Carbon with X-Ray Reflectivity, ESCA and Optical Ellipsometry

Experimental techniques used to measure structural parameters of thin films such as thickness, density, and coverage provide important insights into the physical properties of these films. Structural parameters are also often used to predict the eventual performance of thin films. In this study, we use three different measurement techniques-X-ray reflectivity (XRR), electron spectroscopy for chemical analysis (ESCA), and optical ellipsometry-to measure the thickness of molecularly thin perfluoropolyether (PFPE) polymer films on silicon substrates and carbon overcoats. PFPE films are commonly used to lubricate surfaces in magnetic recording devices. Here, we use XRR to measure the absolute thickness of the films, which, in turn, is used to test the validity of ESCA and ellipsometry thickness measurements. Excellent agreement is found among the three methods, provided that a 25-? electron mean-free path (MFP) is used for the PFPE film and the substrate in ESCA (single MFP model), that the bulk PFPE refractive index is used in ellipsometry, and that adventitiously adsorbed hydrocarbons are properly taken into account. Copyright 2000 Academic Press.     

Capillary Electrophoresis Separation Techniques and Mechanisms in Dilute Polymer Matrices

Capillary electrophoresis in ultradilute derivatized solutions is used to separate nucleic acid fragment mixtures. Pulsed field techniques are used to improve resolution. Protocols in which pulse parameters are varied during the course of the separation are used to increase the range of fragment sizes separated. Fluorescence microscopy is used to study the separation mechanism in ultradilute solution.     

液相色谱中的一个新的表征参数Z——Ⅰ.反相液相色谱中非极性小分子溶质分离体系

文中首次提出了液相色谱中溶质计量置换保留模型中的计量参数Z可作为液相色谱的一个新的表征参数。Z值除了可作为溶质构象表征参数外,在限定条件下,亦可分别作为溶质种类、大小和空间效应、流动相中置换剂和所用固定相特性及有关溶质分离选择性大小的表征参数。本法以非极性小分子苯的取代物为例对此进行了说明。