X-ray diffraction from faulted cellulose I constructed with mixed Iα–Iβ stacking

Cellulose from higher plants is usually thought to be a composite of the Iα and Iβ allomorphs, with predominance of the latter. Instead of the pure allomorphs, this article proposes that Iα and Iβ stacking patterns coexist within each crystallite, forming a type of crystallographic defect known as stacking fault. Models of faulted crystallites are constructed with mixed Iα–Iβ stacking and their X-ray diffraction intensities are calculated using the Diffracted Intensities From Faulted Xtals (DIFFaX) computer program. Simulated powder diffractograms from faulted crystallites compare favorably with experimental data, modifying diffractogram regions that have been misfit by models based on the Iβ crystal structure. Calculations also reveal that stacking faults generate a signature in the (hkl) dependence of diffraction line broadening, guiding further experimental verification and eventual quantification of stacking faults. Our findings bring an alternative view of native cellulose polymorphism and suggest that the proposed stacking faults are ubiquitous crystallographic defects in cellulose from higher plants.     

进样阀(I)

高效液相色谱进样阀（或进样器）的作用是将一定量的样品送入色谱仪。样品在流动相的带动下进入色谱柱系统完成分离过程。现代高效液相色谱仪对于进样阀的要求如下：（１）耐高压,因为高效液相色谱通常要在３５．０ＭＰａ或更高的压力下工作;（２）进样量精确;（３）进样重复性好;（４）方便、适用,且可根据需要选择不同的进样量;（５）价格低廉;（６）保证在色谱柱中心进样,操作时不产生流量或压力波动。到目前为止,液相色谱进样阀共有３种形式：１．手动注射进样器;２．手动进样阀;３．自动进样器。从原理上讲,自动进样器是在…     

The Unique Ambiphilicity of Tellurium in the [MesitylTe(I)(I2)(I3)]− Anion

A first example of an aryltellurium(II) compound with three different bonding modes to iodine featuring covalent and non-covalent bonds such as two orthogonal, ambiphilic σ-hole interactions is introduced: [MesTe(I)(I₂)(I₃)]⁻. It is a member of a series of mesityltellurenyl anions, which are formed during reactions of (MesTe)₂ with ZnI₂, phenanthroline (phen) and iodine. [Zn(phen)₃][MesTe(I)₂] ( 1 ), [Zn(phen)₃][{MesTe(I)-(I)…Te(I)Mes}{MesTeI₂}] ( 2 ) and [Zn(phen)₃][MesTe(I)(I₂)(I₃)][MesTeI₂] ( 3 ) are isolated depending on the amount of iodine used. The products contain tellurium atoms bonded to a variety of iodine species (I⁻, μ₂-I⁻, I₂ and I₃⁻) and are, thus, perfectly suitable to explore the amphiphilic behavior of tellurium(II) and its relevance for the formation of non-covalent bonds, where tellurium acts as both donor and acceptor simultaneously. The character of chalcogen and halogen bonds are evaluated by the combination of crystallographic data and computational methods.     

超音速射流中I2的弛豫过程 I. 转动弛豫

用激光诱导荧光法测量I_2在He, Ar, N_2等载气射流中转动温度沿射流轴线的分布。分析了速度滑移效应对转动弛豫的影响, 结果表明, 在超音速射流条件下转动弛豫的效率极高。     

Liesegang rings — Part I

Summary The conditions for the formation of revert type ofLiesegang rings have been studied here. Various systems of rhythmic precipitations of silver chromate are produced in a mixtures of agar and gelatin gels under different environmental conditions. Ring systems of silver, copper and other ferricyanides have also been studied in gelatin gel. The observations show that the cause of the revert systems ofLiesegang rings is the high peptizability of the precipitating matter in the media containing gel and the unreacted ions.

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Zusammenfassung Die Bedingungen der Bildung des „umgekehrten“ Types vonLiesegang-Ringen wurden untersucht. Verschiedene Systeme rhythmischer F?llung von Silberchromat wurden in einer Mischung von Agar und Gelatinegelen unter verschiedenen Umgebungsbedingungen erzeugt. Ringsysteme von Kupfer, Silber und anderen Ferricyaniden in Gelatine wurden untersucht. Die Beobachtungen zeigen, da? die Ursache für die „umgekehrten“Liesegang-Ringe in der hohen Peptisierbarkeit der Füllsubstanz im gelhaltigen Medium und den noch nicht reagierten Ionen liegt.

     

Taxayuntin I from Thous Yunnanensis

Sinceexcellentantitumoractivityanduniquemechanismofactionofpaclitaxel(taxol@)werediscovered,chemicalstudiesonTaxusspecieshavebeenextensivelycarriedoutl'2.About300taxoidshavebeenisolatedfromGeneraTaxusandAustrotaxusplants'.Insearchforbioactivetaxoidsa...     

金属材料分析（I）

臧慕文 北京有色金属研究总院分析测试技术研究所教授级高级工程师,长期从事有色金属分析测试研究和管理工作。合编《有色金属合金分析》、《分析化学》、《标准物质及其应用技术》、《金属材料理化测试全书》《有色金属进展第八卷分析检测》等。     

Small Gold(I) and Gold(I)–Silver(I) Clusters by C−Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho-metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au₆L₄](X)₂ are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag₂O leads to gold–silver clusters [Au₄Ag₂L₄](X)₂. Oxo-trigold(I) species [Au₃O]⁺ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au₅], [Au₄Ag], and [Au₁₂Ag₄] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.     

Untersuchungen über Rauwolfia-Alkaloid-Modelle I

Zusammenfassung Es wurden 15 einfache Gramin- und Tryptaminderivate als Modelle des Reserpins hergestellt und pharmakologisch untersucht. Das N-(3--Indolyläthyl)-piperidin (XIII) und das N,N-Diäthyltryptamin (XI) zeigten ein Dreißigstel bzw. ein Vierzigstel der Reserpinwirkung.Herrn Prof. Dr.F. Wessely zum 60. Geburtstag in Dankbarkeit und tiefer Verehrung gewidmet.     

n-C_3H_7I和i-C_3H_7I的激光裂解

Wilson等人曾研究过碘代烷在266nm的激光光解RI→R+I＊(~2P_(1/2))(1)RI→R+I(~2P_(3/2))(2)由于他们所用的光解产物谱仪不能改变产物的检测方向,因而对C_2H_5I,n-C_3H_7I和i-C_3H_7I的光解通道(1)和(2)在飞行时间(TOF)谱上的分离没有成功。我们用束源可转动的分子束激光裂解产物谱仪(飞行距离531mm)研究了CH_3I和C_2H_5I在248nm的激光裂解后,又分别对n-C_3H_7I和i-C_3H_7I进行研究,并实现了I＊(~2P_(1/2))和I(~2P_(3/2))光解通道在TOF谱上的分离,测得光解通道比见表1。     

n-C3H7I和i-C3H7I的激光裂解

Studies on the photofragmentation of n-C_3H_7I and i-C_3H_7I have been carried out by a photofragment spectrometer with rotatable pulsed molecular beam crossed with KrF excimer laser beam. TOF spectra of the iodine atom fragments (Fig.1, 2) which show the separation of the primary photodissociation channels n-C_3H_7I→n-C_3H_7+I~*(~2P_(1/2)) n-C_3H_7+I(~2p_(3/2)) i-C_3H_7I→i-C_3H_7+I~*(~2P_(1/2)) i-C_3H_7+I(~2P_(3/2)) are obtatned at 12 different angles. The distribution of total translational energy E_(CM) of recoiling photofragments are then determined. The ratios I~*/I of the photodissociation channels of n-C_3H_7I and i-C_3H_7I are measured to be 1.61 and 0.96 respectively (Table 1). The ratios I~*/I obtained by photofragment translational energy measurement in this Lab~[3]. are good in agreement with most of results abtained by IR emission~[5] and LIF~[4] measurement except the data of i-C_3H_7I, which is much different from I~*/I=0.35 reported by Bershon~[4] using LIF method.The extent of internal alkyl fragment excitation E_(int)~R is also determined (Table 2) by energy balance. The fraction of the available energy (E_(av1)=E_(CM)+E_(int)~R) which goes into internal exciatation of the alkyl fragment increases from 12.5% for I~* channe of CH_3I to 64% for both channels of i-C_3H_7I. The results are consistent with direct impulsive dynamic model of unimolecular decomposition based on “soft” alkyl radicals.The facts that the ratio I~*/I decreases with increasing carbon atoms and that the difference of the internal excitation of alkyl radicals between the I~* (~2P_(1/2)) and I (~2P_(3/2)) channelsincreases with increasing carbon atoms should be related and important for better understanding the origin of the I(~2P_(3/2)) channel caused by the potential energy surface crossing~[3]. The results of the internal excitation of the alkyl radicals in the photodissociation are also valuable for prediction of secondary products during the UV photolysis of those alkyl iodides in the gas cell.     

Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

The relative reactivity of the I and I phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS ¹³C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I phase was substantially higher than that of the corresponding I component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the I phase of cellulose is indeed more reactive toward acetylation than the I phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of I phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.     

Interactions of the complete cellobiohydrolase I from Trichodera reesei with microcrystalline cellulose Iβ

We describe the construction of a model complex of the cellobiohydrolase I (CBH I) cellulase from Trichoderma reesei bound to a cellulose microfibril in an aqueous environment for use in molecular dynamics (MD) simulations. Preliminary characterization from the initial phases of an MD simulation of this complex is also described. The linker sequence between the two globular domains was found to be quite flexible, and the oligosaccharides bound to this linker were found to prefer to be splayed like the spokes in a wheel due to their hydration requirements. The overall conformations of the two globular domains remained stable in the simulations, although both underwent changes in their orientations.     

见血飞化学成分的研究 I

从见血飞根茎的乙醇提取物中的脂溶性部分, 分得6个化合物, 它们经鉴定为pimpincollin(1), toddaloactone(2), 5-hydroxy-4,8-dimethoxy-furoquinoline(3),skimmianino(4), isopimpinellin(5)和11-acetonyl-dihydronitidine(6), 其中3,6为新生物碱。     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

129I and 129I/127 I ratio determination in environmental biological samples by RNAA, AMS and direct γ -X spectrometry measurements

Different techniques are available for the measurement of ¹²⁹I or ¹²⁹I/¹²⁷ I ratio. Due to the lack of internationalcertified reference material for ¹²⁹I, intercomparison exerciseson the measurement of ¹²⁹I are very rare. This study presents twointercomparison exercises between three techniques: direct -X spectrometry,radiochemical neutron activation analysis and accelarator mass spectrometry.A reference material was constituted with a Fucus serratus collected on thefrench channel coast. A significative correlation between the results givenby the three techniques was proven on this material and on a set of otherFucus serratus samples presenting different activity levels.     

The ILAC Arrangement – Part I

As of August 2001, 38 laboratory accreditation bodies of the International Laboratory Accreditation Cooperation (ILAC) have signed the multi-lateral, mutual recognition arrangement (the ”ILAC Arrangement”) to promote the acceptance of accredited test and calibration data. This Arrangement provides significant technical underpinning to international trade. Until now, there has been no international mutual recognition agreement in laboratory accreditation, which has been a hindrance for some types of international trade. The key to the Arrangement is the developing global network of accredited testing and calibration laboratories that are assessed and recognised as being competent by ILAC Arrangement signatory accreditation bodies. The signatories have, in turn, been peer-reviewed and shown to meet ILAC’s criteria for competence. Now that the ILAC Arrangement is in place, governments can take advantage of it to further develop or enhance trade agreements. The ultimate aim is increased use and acceptance by industry, as well as government, of the results from accredited laboratories, including results from laboratories in other countries. In this way, the free-trade goal of ”a product tested once and accepted everywhere” can be realised.     

Über die Fermentpolymerisation. I

Zusammenfassung Die experimentellen Ergebnisse fremder und eigener Versuche über die Bildung von Dextran werden zusammengestellt und durch ein Reaktionsschema, das widerspruchsfreier ist als die bisher vorgeschlagenen, gedeutet. Fritz Wessely zum 60. Geburtstag in Freundschaft und Verbundenheit zugeeignet.