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排序方式: 共有226条查询结果,搜索用时 15 毫秒
71.
72.
Maria PC Gal JF Massi L Burk P Tammiku-Taul J Tamp S 《Rapid communications in mass spectrometry : RCM》2005,19(4):568-573
A concerted theoretical (density-functional theory) and experimental electrospray mass spectrometry study was conducted on the formation of cesium cation adducts with small molecules taken as models of specific interactions sites in humic substances. Electrospray experiments with phenol, benzoic acid, salicylic acid, and phthalic acid, in methanolic solution containing cesium nitrate, were performed using a quadrupole ion trap. The formation of positively charged mixed clusters, [Cs(CsNO3)(n)(CsA1)(m)(Cs2A2)(p)]+ (A1 = benzoate, salicylate, and hydrogenophthalate, A2 = phthalate), was observed. Calculations of structures and bonding energetics of Cs+ in simple adducts formed with NO3-, CsNO3, A-, AH, and CsA are reported. The observation of variable cluster stoichiometry (n, m and p values) was interpreted in terms of more or less favorable interaction energies between Cs+ and the neutral species constituting the clusters. Phenol did not form clusters in significant abundances, despite a strong calculated interaction between Cs+ and cesium phenolate. This was attributed to its weak acid dissociation in the electrospray solution. 相似文献
73.
Laine O Osterholm H Järvinen H Wickström K Vainiotalo P 《Rapid communications in mass spectrometry : RCM》2000,14(6):482-495
Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for qualitative and quantitative end-group analysis of a small molecular weight polyester, poly(2-butyl-2-ethyl-1,3-propylene phthalate). The presence of carboxyl-terminated linear and cyclic polyester oligomers was confirmed with the help of simple sample preparation methods. The presence of carboxyl end-groups in the polyester chains was verified through their formation of carboxylate salts with alkali metal cations. Cyclic oligomers were identified through deuterium exchange of the exchangeable protons of the polyester. Various inorganic salts were tested for salt formation of the carboxyl end-groups, but only the alkali metal salts proved effective. The influence of the alkali metal salts on the results of the quantitative end-group analysis was also studied. The relative amounts of differently terminated and cyclic oligomers were calculated when the alkali metal salts were used with different matrices. The results showed that both the salts and the matrices used in sample preparation can have a marked effect on the quantitative results of the end-group analysis. The measurements were carried out using 2,5-dihydroxybenzoic acid (DHB), 1,8, 9-trihydroxyanthracene (dithranol), and 2-(4-hydroxyphenylazo)benzoic acid (HABA) as matrix compounds. Dithranol and HABA repeatably exhibited similar results, and these results differed from those obtained with DHB probably because of the different ionization mechanisms in the MALDI process. Copyright-Copyright 2000 John Wiley & Sons, Ltd. 相似文献
74.
Anne M. Sauer Frank R. Fronczek Betty C. R. Zhu William E. Crowe Gregg Henderson Roger A. Laine 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(5):o254-o256
Nootkatone, or (4R,4aS,6R)‐4,4a,5,6,7,8‐hexahydro‐4,4a‐dimethyl‐6‐(1‐methylethenyl)naphthalen‐2(3H)‐one, C15H22O, a sesquiterpene with strong repellent properties against Formosan subterranean termites and other insects, has the valencene skeleton. The dibromo derivative (1S,3R,4S,4aS,6R,8aR)‐1,3‐dibromo‐6‐isopropyl‐4,4a‐dimethyl‐1,2,3,4,5,6,7,8‐octahydronaphthalen‐2‐one, C15H24Br2O, has two independent molecules in the asymmetric unit, which differ in the rotation of the isopropyl group with respect to the main skeleton. The C—Br distances are in the range 1.950 (4)–1.960 (4) Å. Both independent molecules form zigzag chains, with very short intermolecular carbonyl–carbonyl interactions, having the perpendicular motif and O⋯C distances of 2.886 (6) and 2.898 (6) Å. These chains are flanked by intermolecular Br⋯Br interactions of distances in the range 4.067 (1)–4.218 (1) Å. The absolute configuration of the dibromo derivative was determined, from which that of nootkatone was inferred. 相似文献
75.
76.
Sellinger A Tamaki R Laine RM Ueno K Tanabe H Williams E Jabbour GE 《Chemical communications (Cambridge, England)》2005,(29):3700-3702
A new solution processable nanocomposite material has been prepared via the Heck coupling of octavinylsilsesquioxane with a selected bromoaromatic hole transport compound. Resultant electroluminescent devices show an 18% improvement in external quantum efficiencies over their small molecule analogues. 相似文献
77.
Whispering-gallery modes in silica microspheres can be accessed very efficiently with the recently introduced stripline pedestal antiresonant reflecting optical waveguide (SPARROW) structure. This integrated-optics coupling technique creates novel application opportunities for the high-Q spherical cavities. We report the demonstration of a narrow-band wavelength-drop configuration utilizing SPARROW waveguides and a silica microsphere. 相似文献
78.
Kenneth Laine Ketner 《Historia Mathematica》1982,9(3):326-332
Carolyn Eisele's unique, ongoing career as a scholar is sketched, and the importance of her contributions to Peirce Studies and other fields is emphasized. The essay concludes with a series of suggestions about how to interpret Peirce's works based on themes related to the pioneering efforts of Dr. Eisele. 相似文献
79.
80.
Dr. Mikko Linnolahti Dr. Anniina Laine Prof. Tapani A. Pakkanen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(22):7133-7142
Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)n(AlMe3)m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe3 molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co‐catalytic activity in olefin‐polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex. 相似文献