Synthesis of the ABCD trioxadispiroketal subunit of azaspiracid-1: an iodoetherification-dehydroiodination strategy for complex spiroketals

An unusual spiroketalization strategy in which a hydroxyalkene serves as a precursor to a cyclic enol ether was applied to the synthesis of the ABCD trioxadispiroketal subunit of azaspiracid-1. The trioxadispiroketal product, which represents a double anomeric effect, was obtained as a single trioxadispiroketal diastereomer. A key ploy in the synthesis of the CD segment was the use of a cyclopropane as a synthon for the C-14 methyl group.     

Detection of volatile organic compounds by temperature-programmed desorption combined with mass spectrometry and Fourier transform infrared spectroscopy

A temperature-programmed desorption (TPD) device connected to a mass spectrometer was used to detect volatile organic compounds from air samples. The main aim was to develop an analytical method, by which both non-polar and polar organic components can be detected in the same run. In TPD, the adsorbed compounds are desorbed from the resin more slowly than in the conventional trapping techniques, such as purge-and-trap technique, in which the resin is flash-heated and the compounds are desorbed at the same time to a cryogenic trap or an analytical column. In TPD, the adsorbent resin acts also as an analytical column. In this way it is possible to obtain more rapid analysis, and also a more simple instrumentation, which can be used on-line and on-site. In this work, a new version of TPD device, which uses a resistor for heating and a Peltier element for rapid cooling, was designed and constructed. Various adsorbent resins were tested for their adsorption and desorption properties of both polar and non-polar compounds. When using a mixture of adsorbent resins, Tenax TA and HayeSep D, it was possible to analyze both polar, low-molecular weight compounds, such as methanol and ethanol, and non-polar volatile organic compounds, such as benzene and toluene, in the same run within 15 min including sampling. The same TPD principle was also tested using a Fourier transform infrared spectrometer as an analytical instrument, and the results showed that it was possible to obtain a separation of similar compounds, such as hexane and heptane, and still retaining the same sensitivity as the original on-line FTIR instrument.     

5-(5-Aryl-1,3,4-oxadiazole-2-carbonyl)furan-3-carboxylate and new cyclic C-glycoside analogues from carbohydrate precursors with MAO-B, antimicrobial and antifungal activities

Cyclization of acyclic C-glycoside derivatives 1a,b to 2a,b as the major isomers, and 4a,b as the minor isomers were carried out. The isopropylidene derivatives 3a,b were prepared, as well as the hydrazide derivative 6, which was condensed with a variety of aldehydes to give hydrazones 7a-e which were also prepared from the compounds 12a-e. Acetylation of 7a,d gave the corresponding acetyl derivatives 8a,d, respectively. In addition, the dicarbonyl compound 9 was prepared in the hydrate form, which reacted with a number of aroylhydrazines to give the corresponding bisaroylhydrazones 10a-d, which were cyclized into 1,3,4-oxadiazoles 11a-d. Furthermore, two of the prepared compounds were examined to show the ability to activate MAO-B. In addition a number of prepared compounds showed antibacterial and antiviral activities.     

Initiation Mechanism of Polymerization of Acryl－amide by Ceric Ion／2－Benzoyl Acetanilide System

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基于拉曼高光谱成像的乳粉真伪非定向筛查新方法研究

乳粉真伪问题是我国食品安全的突出问题之一,其非定向筛查是分析科学领域的前沿热点。该研究提出一种稳健建模驱动的拉曼高光谱成像方法(RMD-RHIM),借助其图谱合一的数据特征,将乳粉中未知掺杂物识别问题转化为奇异样本识别问题,有效解决了乳粉中掺杂物的不确定性问题。在RMD-RHIM中,首先采用自适应迭代重加权惩罚最小二乘算法(airPLS)扣除拉曼光谱的背景信息,再通过改进迭代自权重偏最小二乘法(mIRPLS)准确识别乳粉拉曼高光谱成像信号中的畸变像素点,并转化为可视化的二值图像,实现了乳粉真伪的非定向筛查。结果表明,RMD-RHIM方法对阳性和阴性样品的识别率分别达到了98.3%和93.3%,可满足乳粉工业快速筛查的需求,并为其它食品样本的非定向筛查提供了一种新手段。     

Chemometric interpretation of pesticide occurence in soil samples from an intensive horticulture area in north Portugal

An extensive monitoring programme of pesticides was carried out in soil samples from an intensive horticulture area in north of Portugal, putting into practice the needs for increased control of soil quality as far as organic pollution is concerned. The area under investigation was additionally defined as vulnerable to nitrates due to local soil and aquifer characteristics, which might be extended to pesticides contamination. Five sampling sites were selected and soils analysed at three depths in eight sampling campaigns, for the period of 2 years. A stepwise multivariate statistical approach was selected to uncover most relevant patterns inside a complex environmental data matrix. Cluster analysis was applied both to group pesticides and samples, giving a primary and unsupervised overlook of privileged relationships. Clusters of persistent pesticides and selected herbicides were identified, whereas sample classes were also formed and disposed geographically. Thirty eight percent of analysed soils samples fell into one class characterized by low contamination (class 1 in cluster analysis), which is entirely representative of the sampling site no. 1. Afterwards, linear discriminant analysis was applied to identify those pesticides, which had a higher impact in the definition of classes. Finally, factor analysis using a five component model was implemented in order to bring to light the constitution and data variance explained by each of the five main principal components, as well as, their relation to pest management practices. A factor was identified (PC1 – 22% variance) composed of chlorinated pesticides, which was representative of one of the investigated sites indicating its high contamination status. Qualitative main findings and class average concentration values were obtained through this multivariate statistical approach.     

Cell surface-anchored fluorescent aptamer sensor enables imaging of chemical transmitter dynamics

A fluorescent aptamer sensor was applied to the analysis of extracellular chemical transmitter dynamics. We utilized a tocopherol-labeled aptamer, which allowed the direct anchoring of the fluorescent aptamer on the cell surface while retaining its performance as a fluorescent sensor. The fast-responsive fluorescent DNA aptamer sensor, which targets adenine compounds, was anchored on the surface of brain astrocytes. Fluorescence imaging of the aptamer-anchored astrocytes enabled the real-time monitoring of release of adenine compounds as a gliotransmitter, which was synchronized with calcium wave propagation in neighboring cells.     

Carbon nanotube-enhanced separation of DNA fragments by a portable capillary electrophoresis system with contactless conductivity detection

It was demonstrated that separation of DNA fragments by a CE-contactless conductivity detection system (CE-CCD) could be enhanced with multiple-wall carbon nanotubes (MWCNs) as buffer additive. For HaeIII digest of PhiX174 DNA, optimized MWCN concentration was obtained when the MWCN was above its threshold concentration, at which MWCN could form a network in the buffer as pseudostationary phase to provide additional interaction sites. In the case of larger DNA, MWCN near or below its threshold concentration was enough to provide great improvement of the resolution, which was shown by the separation of the 2-Log DNA ladder. Furthermore, the buffer containing MWCN could provide a more stable baseline in the CE-CCD system, owing to less fluctuation of its conductivity. Compared with CE-UV, CE-CCD with MWCN could provide lower LODs as well as better resolution.     

Substituent effects on the electrophilic activity of nitroarenes in reactions with carbanions

The effect on electrophilic activity of substituents located para, ortho, and meta to the nitro group of nitrobenzenes was determined by using vicarious nucleophilic substitution of hydrogen (VNS) with the carbanion of chloromethyl phenyl sulfone (1) as the model process. Values for the relative activities of substituted nitroarenes are given relative to nitrobenzene, which was taken as the standard. This process was chosen as a model reaction because it meets key criteria, such as the wide range of substituents that can be present on the nitrobenzene ring, a low sensitivity to steric hindrance, and in particular the possibility of ensuring conditions in which the overall relative rates of reaction in competitive experiments are equal to the relative rates of nucleophilic addition. The values of relative rates of addition, which were taken to be a measure of electrophilic activity, were determined by competitive experiments in which pairs of nitroarenes competed for the VNS reaction with carbanion of 1. A comprehensive set of data for effects of substituents on the electrophilic activity of nitroarenes is presented for the first time.     

Cellulose production based on hemicellulose hydrolysate from steam-pretreated willow

The production cost of cellulolytic enzymes is a major contributor to the high cost of ethanol production from lignocellulosics using enzymatic hydrolysis. The aim of the present study was to investigate the cellulolytic enzyme production ofTrichoderma reesei Rut C 30, which is known as a good cellulase secreting micro-organism, using willow as the carbon source. The willow, which is a fast-growing energy crop in Sweden, was impregnated with 1–4% SO₂ and steam-pretreated for 5 min at 206°C. The pretreated willow was washed and the wash water, which contains several soluble sugars from the hemicellulose, was supplemented with fibrous pretreated willow and used for enzyme production. In addition to sugars, the liquid contains degradation products such as acetic acid, furfural, and 5-hydroxy-methylfurfural, which are inhibitory for microorganisms. The results showed that 50% of the cellulose can be replaced with sugars from the wash water. The highest enzyme activity, 1.79 FPU/mL and yield, 133 FPU/g carbohydrate, was obtained at pH 6.0 using 20 g/L carbon source concentration. At lower pHs, a total lack of growth and enzyme production was observed, which probably could be explained by furfural inhibition.     

Search for Non-Protein Protease Inhibitors Constituted with an Indole and Acetylene Core

A possible inhibitor of proteases, which contains an indole core and an aromatic polar acetylene, was designed and synthesized. This indole derivative has a molecular architecture kindred to biologically relevant species and was obtained through five synthetic steps with an overall yield of 37% from the 2,2′-(phenylazanediyl)di(ethan-1-ol). The indole derivative was evaluated through docking assays using the main protease (SARS-CoV-2-M^pro) as a molecular target, which plays a key role in the replication process of this virus. Additionally, the indole derivative was evaluated as an inhibitor of the enzyme kallikrein 5 (KLK5), which is a serine protease that can be considered as an anticancer drug target.     

Development and optimization of porphyrin gas sensing LB films

A series of meso-substituted metal-free porphyrins has been developed which show high sensitivity to NO2 gas in the sub-5 ppm concentration range. By selecting different substituents, it has been possible to improve in a systematic manner the response time and sensitivity of the porphyrin LB film to NO2. Initially, a sulphonamino substituent yielded a fairly long response time of around 450 s but this was shortened considerably when this substituent was changed for a stearamido group. Further modifications resulted in achieving a porphyrin LB film which exhibited a t50 response time of only 11 s. By using an optically inert calixarene host material in which the porphyrin guest was incorporated, it was possible to obtain t50 values as low as 5 s.     

谷朊蛋白的改性及应用

近20年来,利用动植物等可再生资源代替当前广泛使用的石化材料成为热门研究方向,是消除污染、保护环境、实现绿色化学、推进人类社会与环境和谐发展的唯一途径.谷朊蛋白是谷类淀粉加工的副产物,是植物代谢产生的天然植物蛋白,一种生物可降解、可再生的天然高分子.由于其独特的粘弹性、延伸性、薄膜成型性和热凝固性等,越来越受到人们的重视,不仅拓宽了在食品工业中的应用领域,还可作为价格适宜、性能优良的高分子材料应用于其它领域.本文介绍了有关谷朊蛋白的组成、近年来国内外改性原理和方法,及其潜在的应用.     

调节剂存在下双金属氰化络合催化剂催化环氧丙烷聚合的动力学

研究了双金属氰化络合催化剂DMC催化环氧丙烷调节聚合的动力学 .通过测定反应过程体系压力的变化来决定聚合的起始速率 ,发现聚合反应速率与分子量调节剂浓度Tr的线性函数的 - 1次方成正比 .考察了DMC催化剂在反应不同阶段的远红外吸收变化 ,提出了聚合反应可能的反应历程 ,并推导出调节聚合的动力学方程 .研究结果表明调节聚合的动力学特点在于链引发是发生在催化剂与单体之间 ,而不是催化剂与调节剂之间     

Control of Excited‐State Conformations in B,N‐Acenes

We present a new concept to control the conformations of molecules in the excited state through harvesting negative hyperconjugation. The strategy was realized with the 2,3,1,4‐benzodiazadiborinane scaffold, which was prepared by a new synthetic procedure. Photochemical studies identified dual light emission, which was assigned to well‐defined conformers. The emission at longer wavelength can be switched off by restricting the rotational degrees of freedom in the solid state as well as by controlling the energy levels of the excited states through adjusting the solvent polarity.     

Effect of ionomers on mechanical properties, morphology, and rheology of polyoxymethylene and its blends with methyl methacrylate-styrene-butadiene copolymer

Two ionomers, ethylene-methacrylic acid copolymer ionized with sodium cation (EMA-Na) and zinc cation (EMA-Zn), were employed as impact modifiers to prepare blends with polyoxymethylene (POM) via a melt extrusion. A copolymer of methyl methacrylate-styrene-butadiene (MBS) used as a co-impact modifier was also incorporated into the blends. The mechanical properties, thermal properties, morphology, and rheology were studied. A moderate toughening was observed for POM/ionomer binary blends, which was attributable to the rubbery natural and good adhesion of the ionomers. EMA-Zn exhibited a much better toughening effect than EMA-Na because of its higher elasticity and stronger interaction with POM. The incorporation of the ionomers into POM/MBS blends resulted in an improvement of mechanical properties, which was attributable to the compatibilizing effect of ionomer on POM/MBS blending system. The observation of scanning electron microscopy demonstrated that the finer phase domains were caused by incorporation of ionomers, which, acting as a compatibilizer as well as an impact modifier, reduced the interfacial tension and improved the interfacial adhesion between the phases. Differential scanning calorimetry investigation indicated that the presence of ionomer in the blends disturbed the crystallization of POM and resulted in a decrease in the crystallinity of POM. The evaluation of melt flow index revealed an increase in viscosity of the blends by incorporation of the ionomers, which was caused the ionic interaction between POM and the ionomers.     

Preparation of bimodal HDPEs with metallocene on Cr‐montmorillonite support

Previously described Cr‐montmorillonite (Cr‐MMT) was found to retain reactivity in the ethylene polymerization reaction regardless of which alkyl‐metal was used for workup in the preparation process, as long as alkylaluminium was used as a cocatalyst in the actual polymerization reaction. Introduction of hydrogen pressure was found to regulate the polymerization to give the product polymer with a narrower weight distribution, albeit with a somewhat smaller average molecular weight. Supporting metallocene onto Cr‐MMT produced a binuclear catalyst system which gave rise to bimodal polyethylene (PE). Polymer composition of the produced high density polyethylenes (HDPEs) could be controlled by changing factors such as the polymerization conditions and the identity of the metallocene compounds. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3722–3728, 2010     

The Zimmermann reaction and a correction for irrelevant absorption

Two similar modifications of a previously described aqueous Zimmermann reaction for 17-ketosteroids were studied to see whether the Allen correction for irrelevant background absorption could be accurate when pure steroids were compared against a single steroid as a calibrator. Dehydroisoandrosterone was selected as the standard because most procedures use it for that purpose. In one procedure in which varied spectral shapes, wide-ranging peak maximum values, and molar absorptivities were evident, accuracy of recovery was poor. In a second procedure, in which the primary variation was in band width rather than in either fine structures or molar absorptivities, the results were more accurate though still inaccurate as compared to peak measurement calculations. It would seem that this correction could only be valid for those procedures in which calibrator and analyte yield spectra which show better uniformity than the two procedures described here.     

Vinyl and alkynyl pyrimidines as michael acceptors: an approach to a cylindrospermopsin substructure

Vinyl pyrimidine 9 and alkynyl pyrimidine 24 undergo base-mediated intramolecular conjugate addition reactions in which a carbamate and a urea, respectively, behave as nitrogen nucleophiles. The cyclic carbamate derived from 9 was converted to 11 via a metalation-oxidation reaction in which 2-phenylsulfonyl-3-phenyloxaziridine behaves as a hydroxylation reagent. The cyclic urea derived from 24 was converted to cylindrospermopsin substructure 30 using dimethyldioxirane to introduce the C(7) hydroxyl group.     

Anionic oligomerization of dimethyl itaconate

Methanolic solutions of alkali metal and magnesium methoxides were used as initiators for the oligomerization of dimethyl itaconate in methanol, DMF and DMSO. The yield of oligomers was higher in the aprotic solvents. The oligomeric mixtures contained a preponderance of trimer, the structure of which was elucidated by mass spectrometry as a cyclohexane derivative. The oligomers contained no methoxyl end-groups, and initiation is postulated to be an acid-base reaction, in which the allylic hydrogen α- to the carbonyl is abstracted. This belief was supported by the fact that the use of sodium naphthalene and triethylamine as initiators gave the same oligomers. The trimer was tested as a plasticizer.