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81.
Zhengchun Liu Björn Classon Per J. Garegg Bertil Samuelsson 《Journal of carbohydrate chemistry》2013,32(1):65-76
ABSTRACT Ammonium 2,3,6-trideoxy-2,6-epithio-D-manno-2-octenoate (8), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-talo-octanoate (10a), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-galacto-octanoate (10b) and ammonium 2,3,6-trideoxy-2,6-epithio-oxa-D-glycero-D-galacto-octanoate (13) have been synthesised as potential inhibitors of the enzyme CMP-KDO synthetase. The key step in the synthesis of 8 was the elimination of water from methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-thio-D-manno-2-octulosonate (4) using chlorodiphenylphosphine, imidazole and bromine to give the unsaturated methyl 2,3,6-trideoxy-2,6-epithio-4,5:7,8-di-O-isopropylidene-D-manno-2-octenoate (5). For the synthesis of 10a and 10b, zinc reduction of methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-S-(4-methoxybenzyl)-6-thio-2-O-(trichloro-tert-butoxycarbonyl)-D-manno-2-octenoate (2) gave an epimeric mixture of an α-hydroxyester 6 which was ring closed by in situ activation of the hydroxyl group using triphenylphosphine and tri-iodoimidazole followed by cleavage of the p-methoxybenzyl group to give 7a and 7b, which then were deprotected to give 10a and 10b. 相似文献
82.
Johan R. Johansson Yubo Wang Dr. Mattias P. Eng Prof. Nina Kann Prof. Per Lincoln Dr. Johanna Andersson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6246-6256
The slow dissociation of DNA threading intercalators makes them interesting as model compounds in the search for new DNA targeting drugs, as there appears to be a correlation between slow dissociation and biological activity. Thus, it would be of great value to understand the mechanisms controlling threading intercalation, and for this purpose we have investigated how the length of the bridging ligand of binuclear ruthenium threading intercalators affects their DNA binding properties. We have synthesised a new binuclear ruthenium threading intercalator with slower dissociation kinetics from ct‐DNA than has ever been observed for any ruthenium complex with any type of DNA, a property that we attribute to the increased distance between the ruthenium centres of the new complex. By comparison with previously studied ruthenium complexes, we further conclude that elongation of the bridging ligand reduces the sensitivity of the threading interaction to DNA flexibility, resulting in a decreased AT selectivity for the new complex. We also find that the length of the bridging ligand affects the enantioselectivity with increasing preference for the ΔΔ enantiomer as the bridging ligand becomes longer. 相似文献
83.
In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites. 相似文献
84.
Eva Greibe Magnus Leth-Møller Sofie Stampe Per Ovesen Michael Pedersen Elke Hoffmann-Lücke 《Biomedical chromatography : BMC》2022,36(6):e5350
Artificial sweeteners are widely used as substitutes for sugar. The sweeteners are generally considered safe, however their whereabouts during pregnancy and lactation and the effect on child development are poorly explored. There is a need for new tools to measure these substances during pregnancy and lactation. Here, we describe the development and validation of a sensitive liquid chromatography–tandem mass spectrometry method for the simultaneous quantification of acesulfame, cyclamate, saccharin and sucralose in human plasma, umbilical cord blood, amniotic fluid and breast milk. The samples were prepared by protein precipitation and separated on a Luna Omega Polar C18 column (2.1 × 50 mm, 1.6 μm). Electrospray ionization in negative mode and multiple reaction monitoring were used to monitor the ion transitions. The validated concentration ranges were from 1 to 500 ng/ml (10–500 ng/ml for sucralose). Interassay precisions were all ≤15% and the accuracies were within ±15%. Stability, linearity, dilution integrity, carryover and recovery were also examined and satisfied the validation criteria. Finally, this analytical method was successfully applied on spiked samples of plasma, umbilical cord blood, amniotic fluid and breast milk, proving its suitability for use in clinical studies on artificial sweeteners, including during pregnancy and lactation. 相似文献
85.
运用多重态计算方法研究了在正八面体对称性的晶体场中Co2+离子的2p电子X射线L2,3吸收边光谱, 研究了Co2+离子和周围的配位离子之间的正八面体(Oh)晶体场效应和相应的电荷转移效应对于吸收光谱的影响. 系统讨论了在多重态计算中起作用的所有物理参数对CoO和CoCl2的X射线吸收光谱特性的特定影响及其物理机制. 将计算得出的光谱数据和同样具有Oh对称性结构Co2+离子的CoO和CoCl2实验光谱数据进行了对比, 在实验光谱数据中发现的特征被确定为来自不同自旋态, 并且光谱强度的变化与晶体场的强度相关, 揭示了其中包含的电荷转移效应. 本文为低对称性复杂系统的多重态计算提供了一个基础的参考标准, 可以适用于含有钴元素或其它过渡金属的复杂体系的X射线吸收光谱的理论计算. 相似文献
86.
Kokol Vanja Vivod Vera Peršin Zdenka Čolić Miodrag Kolar Matjaž 《Cellulose (London, England)》2021,28(10):6545-6565
Cellulose - Bio-based, renewable and biodegradable products with multifunctional properties are also becoming basic trends in the textile sector. In this frame, cellulose nanofibrils (CNFs) have... 相似文献
87.
Mechanistic Insights into the Pd‐Catalyzed Direct Amination of Allyl Alcohols: Evidence for an Outer‐Sphere Mechanism Involving a Palladium Hydride Intermediate
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Supaporn Sawadjoon Dr. Per J. R. Sjöberg Dr. Andreas Orthaber Prof. Olle Matsson Dr. Joseph S. M. Samec 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1520-1524
The mechanism of direct amination of allyl alcohol by a palladium triphenylphosphite complex has been explored. Labelling studies show that the reaction proceeds through a π‐allylpalladium intermediate. A second‐order dependence of reaction rate on allyl alcohol concentration was observed. Kinetic isotope effect studies and ESI‐MS studies are in agreement with a reaction proceeding through a palladium hydride intermediate in which both O–H bond and C–O bond cleavages are involved in rate‐determining steps. A stereochemical study supports an outer‐sphere nucleophilic attack of the π‐allylpalladium intermediate giving complete chiral transfer from starting material to product. 相似文献
88.
Ana Gisela Cunha Qi Zhou Per Tomas Larsson Lars A. Berglund 《Cellulose (London, England)》2014,21(4):2773-2787
Moisture sorption decreases dimensional stability and mechanical properties of polymer matrix biocomposites based on plant fibers. Cellulose nanofiber reinforcement may offer advantages in this respect. Here, wood-based nanofibrillated cellulose (NFC) and bacterial cellulose (BC) nanopaper structures, with different specific surface area (SSA), ranging from 0.03 to 173.3 m2/g, were topochemically acetylated and characterized by ATR-FTIR, XRD, solid-state CP/MAS 13C-NMR and moisture sorption studies. Polymer matrix nanocomposites based on NFC were also prepared as demonstrators. The surface degree of substitution (surface-DS) of the acetylated cellulose nanofibers is a key parameter, which increased with increasing SSA. Successful topochemical acetylation was confirmed and significantly reduced the moisture sorption in nanopaper structures, especially at RH = 53 %. BC nanopaper sorbed less moisture than the NFC counterpart, and mechanisms are discussed. Topochemical NFC nanopaper acetylation can be used to prepare moisture-stable nanocellulose biocomposites. 相似文献
89.
Manolo C. Per Emily K. Fletcher Ellen T. Swann Deidre M. Cleland 《Journal of computational chemistry》2020,41(27):2378-2382
We assess the performance of variational (VMC) and diffusion (DMC) quantum Monte Carlo methods for calculating the radical stabilization energies of a set of 43 carbon-centered radical species. Even using simple single-determinant trial wavefunctions, both methods perform exceptionally well, with mean absolute deviations from reference values well under the chemical accuracy standard of 1 kcal/mol. In addition, the use of DMC results in a highly concentrated spread of errors, with all 43 results within chemical accuracy at the 95% confidence level. These results indicate that DMC is an extremely reliable method for calculating radical stabilization energies and could be used as a benchmark method for larger systems in future. 相似文献
90.
Steffen M. Brülls Dr. Valentina Cantatore Zhenping Wang Dr. Pui Lam Tam Dr. Per Malmberg Jessica Stubbe Prof. Dr. Biprajit Sarkar Prof. Dr. Itai Panas Prof. Dr. Jerker Mårtensson Prof. Dr. Siegfried Eigler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(29):6694-6702
Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet-chemical non-covalent functionalization of graphene with cationic π-systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF-SIMS. The charged π-systems show a p-doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p-doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping. 相似文献