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1.
Desmond A. Young Daneel Ferreira David G. Roux 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):835-849
The structure and stereochemistry of four synthetic “angular” tetraflavanoid-condensed tannin derivatives are examined by high-resolution variable temperature 1H NMR. spectroscopy, and hence correlated with their dynamic behavior. Three “angular” oligomers exist as stable rotational isomers at ambient temperatures, thus contrasting with the mobility about their interflavanoid bonds of most natural profisetinidin “trimeric” and “tetrameric” homologs. A “linear” tetraflavanoid analog results from one of these regioselectively controlled condensations. 相似文献
2.
The fluorescence decay of the tertiary aliphatic animes trimethylamine (TMA), triethylamine (TEA) and tri-n-propylamine (TPA) in the vapour phase excited between 260 and 215 nm has been shown to consist of a single, wavelength-dependent, component when the first excited state is uniquely excited, but two components when the first and second excited states are simultaneously excited. This dual exponentiality persists at pressures as low as 10 mTorr, and it is argued that the two-component decay does not arise from collisional vibrational relaxation. 相似文献
3.
Aliyu D. Mohammed Desmond A. Young Hermanus C. M. Vosloo 《Research on Chemical Intermediates》2017,43(4):2187-2200
Glycerol acrylate (GA) is synthesised by an acryloylation reaction with acryloyl chloride. An ester was used as a cross-linking agent at varying proportions in the synthesis of poly acrylic acid (PAA). The amount of cross-linking density in the product (GA-PAA) and degree of neutralisation determine the absorbency of the polymer samples. A sample of GA-PAA containing 0.8 % GA was discovered to absorb 395 and 66 g/g of water and saline solution, respectively. Different solvent uptakes were tested with the sample showing varying capacity for different solvents. The temperature of the reaction was maintained at 60 °C and a reaction time of 2½ h. FTIR, TGA, SEM and XRD analyses were used to characterise the products. 相似文献
4.
For the work on the synthesis of 2-acyl-5-methoxynaphthoquinones as tricyclic analogues of daunomycinone1, we wanted to develop an efficient regioselective synthesis of 5-methoxy-2-acyl-1-naphthols without using Lewis acids. This requirement precluded the use of the thermal Fries but not the photo-Fries rearrangement. Although the mechanistic aspects of the photo reaction have received much study2, the reaction has been little used preparatively3 because it usually gives poor yields of hydroxy ketones even when only one product is possible. 相似文献
5.
An efficient procedure for the oxidation of acetophenone to phenylglyoxal and its subsequent in situ conversion to the title compound is described herein. 相似文献
6.
Muchena J. Kailemia Melvin Park Desmond A. Kaplan Andre Venot Geert-Jan Boons Lingyun Li Robert J. Linhardt I. Jonathan Amster 《Journal of the American Society for Mass Spectrometry》2014,25(2):258-268
High-field asymmetric waveform ion mobility spectrometry (FAIMS) is shown to be capable of resolving isomeric and isobaric glycosaminoglycan negative ions and to have great utility for the analysis of this class of molecules when combined with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and tandem mass spectrometry. Electron detachment dissociation (EDD) and other ion activation methods for tandem mass spectrometry can be used to determine the sites of labile sulfate modifications and for assigning the stereochemistry of hexuronic acid residues of glycosaminoglycans (GAGs). However, mixtures with overlapping mass-to-charge values present a challenge, as their precursor species cannot be resolved by a mass analyzer prior to ion activation. FAIMS is shown to resolve two types of mass-to-charge overlaps. A mixture of chondroitin sulfate A (CSA) oligomers with 4–10 saccharides units produces ions of a single mass-to-charge by electrospray ionization, as the charge state increases in direct proportion to the degree of polymerization for these sulfated carbohydrates. FAIMS is shown to resolve the overlapping charge. A more challenging type of mass-to-charge overlap occurs for mixtures of diastereomers. FAIMS is shown to separate two sets of epimeric GAG tetramers. For the epimer pairs, the complexity of the separation is reduced when the reducing end is alkylated, suggesting that anomers are also resolved by FAIMS. The resolved components were activated by EDD and the fragment ions were analyzed by FTICR-MS. The resulting tandem mass spectra were able to distinguish the two epimers from each other. Figure
? 相似文献
7.
Glycoproteins are produced by the post‐translational modification process of proteins and they play an important role in mediating various biological processes. Our understanding towards biochemical functions of individual glycoproteins has been seriously hampered due to the heterogeneous expression of carbohydrate parts in glycoproteins. Despite the advancement in recombinant expression and chromatographic techniques, the isolation of pure glycoforms remains nearly impossible. To obtain homogenous glycoproteins, tremendous efforts hves been spent in developing various ligation and glycosylation techniques. This minireview discusses selected methods for the preparation and ligation of glycopeptides. The importance of the development of new chemical synthesis method for glycoproteins has also been discussed, which would be one of the next directions in this field. 相似文献
8.
9.
Chunmei Ouyang Honghai Wang Ping Shum Songnian Fu Jia Haur Wong Kan Wu Desmond Rodney Chin Siong Lim Vincent Kwok Huei Wong Kenneth Eng Kian Lee 《Optics Communications》2011,284(2):619-624
We experimentally demonstrate a passively mode-locked fiber laser employing a fiber-based semiconductor saturable absorber (SSA) operating in transmission. Polarization rotation locked vector solitons are observed in the laser. Due to the intrinsic dynamic feature of the laser, period-doubling of these vector solitons has also been observed. Furthermore, extra spectral sidebands are formed on the optical spectrum, caused by the energy exchange between the two orthogonal polarization components of the vector solitons. By careful reduction of the pump power together with fine adjustment to the cavity birefringence, period-one state can further be obtained. Additionally, the phase noise properties of the vector soliton fiber laser have also been characterized experimentally and analytically. 相似文献
10.
Betweenness measures provide quantitative tools to pick out fine details from the massive amount of interaction data that is available from large complex networks. They allow us to study the extent to which a node takes part when information is passed around the network. Nodes with high betweenness may be regarded as key players that have a highly active role. At one extreme, betweenness has been defined by considering information passing only through the shortest paths between pairs of nodes. At the other extreme, an alternative type of betweenness has been defined by considering all possible walks of any length. In this work, we propose a betweenness measure that lies between these two opposing viewpoints. We allow information to pass through all possible routes, but introduce a scaling so that longer walks carry less importance. This new definition shares a similar philosophy to that of communicability for pairs of nodes in a network, which was introduced by Estrada and Hatano [E. Estrada, N. Hatano, Phys. Rev. E 77 (2008) 036111]. Having defined this new communicability betweenness measure, we show that it can be characterized neatly in terms of the exponential of the adjacency matrix. We also show that this measure is closely related to a Fréchet derivative of the matrix exponential. This allows us to conclude that it also describes network sensitivity when the edges of a given node are subject to infinitesimally small perturbations. Using illustrative synthetic and real life networks, we show that the new betweenness measure behaves differently to existing versions, and in particular we show that it recovers meaningful biological information from a protein-protein interaction network. 相似文献