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排序方式: 共有118条查询结果,搜索用时 11 毫秒
1.
Juray De Wilde Denis Constales Geraldine J. Heynderickx Guy B. Marin 《International Journal of Multiphase Flow》2007
The propagation speeds of linear waves in gas–solid suspensions depend strongly on the solids volume fraction and the wave frequency. The latter is due to gas–solid momentum transfer and allows a simple test on filtered gas–solid momentum transfer models. Such models may predict linear wave propagation speeds different from those obtained with the non-filtered model at wave frequencies higher than the filter frequency, but not at wave frequencies lower than the filter frequency. 相似文献
2.
Geraldine S.P. Ritchie Alan M. Posner Ian M. Ritchie 《Journal of Electroanalytical Chemistry》1981,123(2):397-407
Variation of the lifetime of a mercury drop with potential was used to determine the pzc of mercury in the presence of soil humic acids and their aluminium complexes. In all cases there was an overall net shift in the pzc in the cathodic direction. Variation in the extent of the shift with pH and concentration indicated greater adsorption of negatively charged species. The shift was smaller in the presence of aluminium humates, probably due to a decrease in the negative charge of the humic acid molecules after complexing. The use of electroanalytical techniques for metal speciation studies in soils and natural water, if humic materials are known to be present, might therefore be limited. 相似文献
3.
McGowan G Parsons S Sadler PJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(15):4396-4404
cis-[PtCl2(NH3)(2-picoline)] (AMD473) is a sterically-hindered anticancer complex with a profile of chemical and biological activity that differs significantly from that of cisplatin. Adducts of AMD473 with neutral 9-ethylguanine (9-EtGH) and anionic (N1-deprotonated) 9-ethylguanine (9-EtG) as perchlorate and nitrate salts, and also a nitrate salt of the trans isomer (AMD443), were prepared and their structures determined by X-ray crystallography: cis-[Pt(NH3)(2-pic)(9-EtGH)2](ClO4)2 (1).2H(2)OMe(2)CO, cis-[Pt(NH3)(2-pic)(9-EtGH)2](NO3)2 (2).2H2O, cis-[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (3),3.5 H2O, trans-[Pt(NH3)(2-pic)(9-EtGH)(9-EtG)]NO3 (4).8H2O. In all cases, platinum coordination is through N7 of neutral (1, 2) and anionic (3, 4) guanine. In each complex, the guanine bases are arranged in the head-to-tail conformation. In complex 1, there is an infinite array of six-molecule cycles, based on both hydrogen bonding and pi-pi stacking of the 2-picoline and guanine rings. Platinum(II) coordinated at N7 acidifies the N1 proton of neutral 9-ethylguanine (pKa = 9.57) to give pKa1 = 8.40 and pKa2 = 8.75 for complex 2, and pKa1 = 7.77 and pKa2 = 9.00 for complex 4. In complexes 3 and 4, three intermolecular hydrogen bonds are formed between neutral and deprotonated guanine ligands involving O6, N1 and N2 sites. Unusually, both of the platinated guanine bases of complexes 3 and 4 participate in this triple G triple bond G hydrogen bonding. This is the first report of X-ray crystal structures of nucleobase adducts of the promising anticancer drug AMD473. 相似文献
4.
We report in situ spectroscopic measurements monitoring the adsorption of a series of carboxylate surfactants onto the surface of the semisoluble, ionic solid fluorite (CaF2). We employ the surface-specific technique, vibrational sum-frequency spectroscopy (VSFS), to examine the effect that surfactant adsorption has on the bonding interactions and orientation of interfacial water molecules through the alteration of the electric properties in the interfacial region. In addition, we report on the chain length and headgroup dependence of the formation of hydrophobic self-assembled monolayers on the surface of the solid phase. Differences in chain length and headgroup functionality lead to large changes in the adsorption behavior and structuring of the monolayers formed and the interactions of interfacial water molecules with these monolayers. Fundamental studies such as these are essential for understanding the mechanisms involved in the surfactant adsorption process, information that is important for industrially relevant processes such as mineral ore flotation, waste processing, and petroleum recovery. 相似文献
5.
A weakly bonded SO2:H2O surface complex is found at the vapor/water interface prior to the reaction and dissolution of SO2 into the aqueous phase. The results have important implications for understanding the formation of atmospheric aerosols and understanding the atmospheric sulfur cycle. 相似文献
6.
Monique?SabatyEmail author Sandrine?Grosse Geraldine?Adryanczyk Séverine?Boiry Frédéric?Biaso Pascal?Arnoux David?Pignol 《BMC biochemistry》2013,14(1):28
Background
YedY, a molybdoenzyme belonging to the sulfite oxidase family, is found in most Gram-negative bacteria. It contains a twin-arginine signal sequence that is cleaved after its translocation into the periplasm. Despite a weak reductase activity with substrates such as dimethyl sulfoxide or trimethylamine N-oxide, its natural substrate and its role in the cell remain unknown. Although sequence conservation of the YedY family displays a strictly conserved hydrophobic C-terminal residue, all known studies on Escherichia coli YedY have been performed with an enzyme containing a 6 histidine-tag at the C-terminus which could hamper enzyme activity.Results
In this study, we demonstrate that the tag fused to the C-terminus of Rhodobacter sphaeroides YedY is detrimental to the enzyme’s reductase activity and results in an eight-fold decrease in catalytic efficiency. Nonetheless this C-terminal tag does not influence the properties of the molybdenum active site, as assayed by EPR spectroscopy. When a cleavable His-tag was fused to the N-terminus of the mature enzyme in the absence of the signal sequence, YedY was expressed and folded with its cofactor. However, when the signal sequence was added upstream of the N-ter tag, the amount of enzyme produced was approximately ten-fold higher.Conclusion
Our study thus underscores the risk of using a C-terminus tagged enzyme while studying YedY, and presents an alternative strategy to express signal sequence-containing enzymes with an N-terminal tag. It brings new insights into molybdoenzyme maturation in R. sphaeroides showing that for some enzymes, maturation can occur in the absence of the signal sequence but that its presence is required for high expression of active enzyme.7.
Panambur G Zhang Y Yesayan A Galstian T Bazuin CG Ritcey AM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(9):3606-3615
Polyion complexes formed by monolayers of quaternary ammonium amphiphiles containing the 4-nitro-4'-alkoxy azobenzene chromophore spread at the surface of aqueous solutions of a number of anionic polyelectrolytes were investigated. In general, pi-A isotherms were found to depend on the nature of the polyion present in the subphase, with monolayers of complexes involving polycarboxylates tending to exhibit larger limiting areas than those formed with polysulfonates or polysulfates. Monolayers of the polyion complexes can be transferred to hydrophilic solid substrates to yield Z-type LB films, although some peeling off for more than 10 layers is an impediment. X-ray reflectivity measurements indicate that relatively smooth and uniform films are obtained up to about 10 layers. Average layer thicknesses are, however, significantly smaller than extended molecular lengths, implying that the amphiphiles are strongly inclined from the surface normal. Polarized FT-IR measurements also indicate poor molecular orientation perpendicular to the surface. Preliminary SHG measurements for LB films of two systems, 12Q/CMC-Na and 12Q/PAA, confirm the presence of noncentrosymmetric out-of-plane chromophore ordering. Stable signals are observed for elevated temperatures up to 130 degrees C and for a period of 4 months at room temperature. To the best of our knowledge, this represents the first report of stable SHG in LB films of polyion complexes. 相似文献
8.
Simon J. Holder Geraldine G. Durand Chert‐Tsun Yeoh Elodie Illi Nicholas J. Hardy Tim H. Richardson 《Journal of polymer science. Part A, Polymer chemistry》2008,46(23):7739-7756
A series of ABA amphiphilic triblock copolymers possessing polystyrene (PS) central hydrophobic blocks, one group with “short” PS blocks (DP = 54–86) and one with “long” PS blocks (DP = 183–204) were synthesized by atom transfer radical polymerization. The outer hydrophilic blocks were various lengths of poly(oligoethylene glycol methyl ether) methacrylate, a comb‐like polymer. The critical aggregation concentrations were recorded for certain block copolymer samples and were found to be in the range circa 10−9 mol L−1 for short PS blocks and circa 10−12 mol L−1 for long PS blocks. Dilute aqueous solutions were analyzed by transmission electron microscopy (TEM) and demonstrated that the short PS block copolymers formed spherical micelles and the long PS block copolymers formed predominantly spherical micelles with smaller proportions of cylindrical and Y‐branched cylindrical micelles. Dynamic light scattering analysis results agreed with the TEM observations demonstrating variations in micelle size with PS and POEGMA chain length: the hydrodynamic diameters (DH) of the shorter PS block copolymer micelles increased with increasing POEGMA block lengths while maintaining similar PS micellar core diameters (DC); in contrast the values of DH and DC for the longer PS block copolymer micelles decreased. Surface‐pressure isotherms were recorded for two of the samples and these indicated close packing of a short PS block copolymer at the air–water interface. The aggregate solutions were demonstrated to be stable over a 38‐day period with no change in aggregate size or noticeable precipitation. The cloud point temperatures of certain block copolymer aggregate solutions were measured and found to be in the range 76–93 °C; significantly these were ∼11 °C higher in temperature than those of POEGMA homopolymer samples with similar chain lengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7739–7756, 2008 相似文献
9.
Nadiah Zafar Geraldine Agusti Hatem Fessi 《Journal of Dispersion Science and Technology》2017,38(4):577-583
Researchers work on different optimization methods to come up with preparation methods, which show the desired or targeted outcomes. Moreover, nowadays, research is more focused on developing formulations which contain biodegradable polymers. The objective of the present systematic study was to achieve the abovementioned goals by using a cationic ammonio methacrylate copolymer (Eudragit® RS100). A Double-emulsion solvent evaporation technique was used. This methodology was chosen because the particles formed by this method allow encapsulation of both hydrophilic and hydrophobic active molecules. It also has applications in diverse fields such as drug delivery, food, cosmetics, and pharmaceutical industries.The aim of this research work was to investigate the influence of various process control parameters, such as stabilizer chemical nature and amount, ultra Turrax® stirring speed and time, the morphology, size, and size distribution of the final dispersions. Then, the prepared particles were characterized using a Scanning Electron Microscope (SEM) and a Laser Diffraction Particle Size Analyzer. This study helped us to know which parameters have a drastic effect on the colloidal properties of the particles. 相似文献
10.
Dr. Geraldine Echue Prof. Guy C. Lloyd‐Jones Dr. Charl F. J. Faul 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(13):5118-5128
A chiral perylene diimide building block has been prepared based on an amine derivative of the amino acid L ‐phenylalanine. Detailed studies were carried out into the self‐assembly behaviour of the material in solution and the solid state using UV/Vis, circular dichroism (CD) and fluorescence spectroscopy. For the charged building block BTPPP, the molecular chirality of the side chains is translated into the chiral supramolecular structure in the form of right‐handed helical aggregates in aqueous solution. Temperature‐dependent UV/Vis studies of BTPPP in aqueous solution showed that the self‐assembly behaviour of this dye can be well described by an isodesmic model in which aggregation occurs to generate short stacks in a reversible manner. Wide‐angle X‐ray diffraction studies (WXRD) revealed that this material self‐organises into aggregates with π–π stacking distances typical for π‐conjugated materials. TEM investigations revealed the formation of self‐assembled structures of low order and with no expression of chirality evident. Differential scanning calorimetry (DSC) and polarised optical microscopy (POM) were used to investigate the mesophase properties. Optical textures representative of columnar liquid–crystalline phases were observed for solvent‐annealed samples of BTPPP. The high solubility, tunable self‐assembly and chiral ordering of these materials demonstrate their potential as new molecular building blocks for use in the construction of chiro‐optical structures and devices. 相似文献