Characterization of HETEs and related conjugated dienes by UV spectroscopy

Three distinct pairs of HETEs can be distinguished on the basis of their UV spectra. We used hydroxy-linoleates (hydroxy-octadeca-cis-trans-dienoates) as a base for comparisons; both the 9- and 13-hydroxy isomers have identical chromophores with λ_max near 234 nm. The presence of a double bond three carbons removed from the conjugated diene (the chromophore of 9- and 11-HETE) causes a shift in the observed λ_max to near 235 nm. A double bond β to the chromophore (5- and 15-HETE) gives a further shift of 1.5 nm, giving a λ_max between 236–236.5 nm. With double bonds in both these positions (8- and 12-HETE), the λ_max is observed near 237 nm. It is apparent that the exact λ_max of thecis-trans diene chromophore is influenced in a consistent way by the adjacent methylene interruptedcis double bonds. hydroxylinoleate, describes the two primary products of linoleate oxygenation, more properly named 9-hydroxy-octadeca-10trans,12cis-dienoate and 13-hydroxy-octadeca-9cis,11trans-dienoate. Hydroxylinoelaidate refers to the correspondingall-trans dienes. RH-HPLC, reversed-phase high pressure liquid chromatography; SP-HPLC, straight-phase high pressure liquid chromatography.     

Reaction of cellulose xanthate with chromium compounds by UV spectroscopy

Conclusions The type of chemical bond in the chromium compounds obtained which are based on cellulose xanthate has been ascertained.It has been shown that, as a result of an oxidation-reduction reaction between the thiocarbonate groups of the cellulose xanthate and K₂Cr₂O₇ (in acid medium), a chromium xanthate is formed which has a covalent type of bond between the sulfur atoms and chromium.Translated from Khimicheskie Volokna, No. 6, pp. 29–30, November–December, 1987.     

Polymer analysis by higher-order UV/VIS-derivative spectrophotometry

Summary High resolution higher-order UV/VIS derivative spectrophotometry (HODS) has been used for some selected analytical problems of polymers, such as copolymer composition, determination of unconverted monomer in polymer and analysis of polymer additives.Dedicated to Professor Kurt Dialer on his 60th birthday     

The electronic structure of oxide-supported tungsten oxide catalysts as studied by UV spectroscopy

The UV spectra of tungsten oxide catalysts supported on alumina, titania and zirconia, and on titania–alumina and titania–zirconia mixed oxides are reported and discussed. Evidence is provided for the different electronic structure of supports and catalysts, which could affect the behavior of the tungsten oxide centres in the different cases. On alumina, tungsten oxide centres are “isolated” by the insulating support, while on titania-based materials they are likely in electronic contact with each other and with Ti centres through the support conduction band. In the case of WOx2013;ZrO₂, the 5d levels of tungsten ions fall just below of the lower energy limit of the support conduction band. This revised version was published online in July 2006 with corrections to the Cover Date.     

Film formation analysis by diffusive wave spectroscopy

The thin layer analysis is very important for several sectors of industry. Indeed, environmental laws and improvement of performances lead the manufacturers to innovate in the field of coatings and paints. Several classical techniques of characterization (TGA, DMA, etc.) used with this intention do not allow to perform the analysis in situ and are often long and tedious to set up. We propose to solve this problem with a new optical process. Its technology based on multi-speckle diffusive wave spectroscopy (MS-DWS) allows making real-time analysis in a non-destructive way thanks to an optical measurement. The aim of this work is to highlight correlations between this new technology and the classical methods of analysis. Two film forming polymeric materials were studied, a polydimethylsiloxane (PDMS) and a commercial paint based on an aqueous dispersion of acrylic copolymers. The PDMS was chosen for the simplicity of its film forming process and is used as model. The paint having a more complex drying mechanism enables to complete this study.     

紫外光谱测定葡萄糖两相水解液中5-羟甲基糠醛的新方法

采用紫外光谱法快速测定了葡萄糖两相水解液中的5-羟甲基糠醛(5-HMF)的摩尔浓度,实验表明:以5-HMF为标准品,蒸馏水替代葡萄糖的水-二甲基亚砜两相溶液为空白,在284 nm波长处对其中的5-HMF进行了定量分析。测定结果表明,溶液中的5-HMF摩尔浓度在0～0.10 mmol/L范围内与其吸光度值呈现良好的线性关系,并且重现性良好。该方法在抗干扰性实验、精密度实验、回收率实验、稳定性实验和检出限方面均有满意表现,适于快速、准确地测定5-HMF摩尔浓度。     

Copolymer characterization by surface tension

The use of surface tension measurements is proposed as a simple method for the determination of copolymerization ratios. The procedure depends on the parachor of the copolymer in the liquid state (∏), which is defined by ∏ = ∏_s + ∏₀(w_p/w_s)(M_s/M₀) for solutions and ∏ = [DP]∏₀ for liquid or molten polymers, where ∏_s is the parachor of the solvent of molecular weight M_s; w_p and w_s are the weights of the polymer and solvent in solution; while ∏₀ and M₀ are the parachor and molecular weight of the repeating unit of the copolymer, respectively. The validity of this relationship is demonstrated by analysis of the surface tension properties of liquid silicone polymers, polystyrene–Decalin solutions, and molten polymers as well as by the calculation of the composition of some characterized tetrahydrofuran–propylene oxide copolymers. The application of surface tension measurement is also suggested as a means of estimating the degree of chain branching in a polymer.     

Low-density polyethylene depth profile analysis by photoacoustic spectroscopy

Near-infrared photoacoustic spectra of polyethylene (1 mm slab) were taken in the modulation range 10–240 Hz, which corresponds to thermal diffusion layers in the 56?11 μm range. Thick-layer spectra are very similar to polyethylene film transmission spectra, but large differences are observed between the spectra taken at various modulation frequencies. From 10 to 80 Hz, all the spectral band intensities decrease linearly with ω^?a where ω is the light modulation frequency and a varies from 0.48 to 1.00 for different constituent groups. The analysis of spectral intensity as a function of modulation frequency shows that peak intensity ratios of ? CH₃, ?CH₂, and ? OH groups, relative to that of methylene groups, increase as thinner, closer-to-surface polymer layers are sampled. From this we conclude that near-to-surface layers of solid polyethylene are richer in ? CH₃, ?CH₂ and ? OH groups than the polymer bulk.     

我国苯乙烯嵌段共聚物的发展前景分析

苯乙烯类嵌段共聚物（简称SBC）是由苯乙烯与丁二烯（和／或者异戊二烯）以烷基锂为催化剂进行阴离子溶液聚合制得的一种热塑性弹性体．主要包括苯乙烯一丁二烯一苯乙烯嵌段共聚物（简称SBS）、苯乙烯一异戊二烯一苯乙烯嵌段共聚物（简称SIS）以及它们相应的加氢产物——氢化SBS（简称SEBS）和氢化SIS（简称SEPS）4种类型,在制鞋业、塑料改性、沥青改性、防水涂料、液封材料、电线、电缆、汽车部件、医疗器械部件、家用电器、办公自动化和胶粘剂等方面具有广泛的应用     

新型丙烯-乙烯共聚物增韧聚丙烯的研究

丙烯-乙烯共聚物Vistamaxx（VM）是一种丙烯摩尔含量占70％以上的新型弹性体。用VM增韧聚丙烯（PP），考察了PP／VM共混物的力学性能、微观形态结构以及结晶性能，并与乙烯-辛烯共聚物（POE）与PP的共混体系进行了对比。结果表明，常温下VM增韧效果优于POE，PP／VM体系拉伸性能优于PP／POE体系；VM在PP中表现出比POE更好的分散性；VM具有与PP相同的晶型，VM的加入细化了PP的晶粒。     

Monitoring the UV degradation of PVC window frames by microhardness analysis

While well-known methods of bulk analysis of thermal degradation of PVC become standard industrial tools, techniques for the study of surface damage produced by weathering are not generally considered. In this paper we present a new test, based on microhardness measurements, which can be used as a complementary technique for the study of this phenomenon. Comparison of this method with color changes and specific elongation at break measurement has been established for PVC window frames.     

UV/HREELS spectroscopy of benzene on Pt(110)

Some years ago, LEED studies of Ogletree et al. and Wander et al. found that benzene undergoes a structural rearrangement when the benzene adsorbs on platinum. In contrast, Horsley et al. proposed that the benzene adsorbs without undergoing significant distortion. In this paper UV/HREELS spectroscopy is used to examine benzene adsorption on Pt(110). We find that the benzene can adsorb into two different states: a weakly bound form of benzene with UV/HREELS spectrum similar to gas-phase benzene, and a strongly bound form of benzene with UV/HREELS and IR/HREELS spectra which are consistent with formation of a diene (e.g., 1,4-cyclohexadiene). A comparison of our data to the results of Wander et al. and Horsley et al. shows that the weakly bound form of benzene is consistent with Horsley’s assignments, while the strongly bound species looks as expected from the work of Wander et al. The conclusion from our study then is that Wander et al. and Horsley et al. are both correct. They are just studying different forms of benzene on the platinum surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Discriminant analysis of vegetable oils by near-infrared reflectance spectroscopy

Discriminant analysis of four vegetable oil types (cotton-seed, peanut, soybean and canola) was performed by near-infrared reflectance spectroscopy. The objective of this study was to provide an alternate method to differentiate vegetable oil types and to classify unknown oil samples. Second derivative spectra of the vegetable oils were subjected to discriminate analysis with Mahalanobis distances principles. A four-wavelength (1704, 1802, 1816 and 2110 nm) equation was derived, which produced a sum of inverse squared distance of 0.0548. Although all four groups were successfully separated with a chi square of 18.9, the soybean oil group is more dispersed in space than the other three groups. Iodine values of the soybean oil samples suggest that this group may have a wide range of hydrogenation states. Discriminant analysis can be successfully used to differentiate vegetable oil types and possibly could also be used to differentiate degree of hydrogenation and oxidative states of oils.     

紫外光谱技术在超临界流体技术中的应用

在阐述超临界CO2萃取工艺原理的基础上,分别介绍了离线和在线紫外-可见光光谱技术在超临界流体技术中的应用情况,分析了在线紫外光谱技术的应用特点,指出了在线检测应用中所遇到的问题,同时对其前景进行了展望。     

Force measurement enabling precise analysis by dynamic force spectroscopy

Dynamic force spectroscopy (DFS) makes it possible to investigate specific interactions between two molecules such as ligand-receptor pairs at the single-molecule level. In the DFS method based on the Bell-Evans model, the unbinding force applied to a molecular bond is increased at a constant rate, and the force required to rupture the molecular bond is measured. By analyzing the relationship between the modal rupture force and the logarithm of the loading rate, microscopic potential barrier landscapes and the lifetimes of bonds can be obtained. However, the results obtained, for example, in the case of streptavidin/biotin complexes, have differed among previous studies and some results have been inconsistent with theoretical predictions. In this study, using an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS, we investigated the effect of the sampling rate on DFS analysis. The shape of rupture force histograms, for example, was significantly deformed at a sampling rate of 1 kHz in comparison with that of histograms obtained at 100 kHz, indicating the fundamental importance of ensuring suitable experimental conditions for further advances in the DFS method.     

TiO2丙烯酸复合涂料屏蔽性能分析

本文以纳米TiO2为紫外线吸收物．测试其不同浓度下的紫外吸收效果。并以纳米TiO2为添加物制备丙烯酸酯复合涂料．测试其紫外光屏蔽效果。     

Quantitative analysis of protein far UV circular dichroism spectra by neural networks

A new method based on neural network theory is presented toanalyze and quantify the information content of far UV circulardichroism spectra. Using a backpropagation network model witha single hidden layer between input and output, it was possibleto deduce five different secondary structure fractions (helix,parallel and antiparallel ß-sheet, ß-turnand random coil) with satisfactory correlations between calculatedand measured secondary structure data. We demonstrate that foreach wavelength interval a specific network is suitable. Theremaining discrepancy between the secondary structure data fromneural network prediction and crystallography may be attributedto errors in the determination of protein concentration andrandom noise in the CD signal, as indicated by simulations.     

聚砜超滤膜表面辐照改性研究

以聚砜为膜材料,聚乙二醇（PEG）为添加剂,采用浸入沉淀相转化法制备聚砜平板超滤膜,然后对实验制备的聚砜膜进行紫外辐照改性,考察了辐照对聚砜膜结构和性能的影响,研究了膜辐照前后断裂强度的变化,通过表面接触角测定仪、红外分析仪（FTIR）、扫描电镜（SEM）、改性膜的纯水通量和截留性能等方法来表征膜辐照前后的结构和性能变化。研究表明,聚砜膜断裂强度经辐照后强度变小,但是降低幅度不大;在乙醇溶液中紫外辐照后,开始纯水通量提高而截留率降低,但降低幅度不大,时间增加到一定时通量又降低,截留率变化也不大;表面接触角随辐照时间的增长而减小,表明改性后膜表面的亲水性得到明显改善;通过FTIR分析证实在聚砜膜表面产生了新的官能团;SEM实验证实反应只发生在聚砜膜的表面而非膜内部。聚砜超滤膜经紫外辐照改性取得了良好的效果。