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991.
Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献
992.
993.
994.
J Robert Huber 《Chemphyschem》2004,5(11):1663-1669
This Minireview gives an account of the photochemical decay of nitric acid HNO3 in the gas phase, which has been well investigated under bulk and molecular-beam conditions. Due to the importance of this molecule in atmospheric chemistry, attention was paid to the irradiation regions around 300 and 200 nm, where solar photolysis of HNO3 is expected to be particularly efficient. While the low-energy region is characterized by the products OH and NO2, the high-energy region gives rise to a variety of photochemical decay pathways, dominated by channels which lead to the products HONO + O in different electronic states. 相似文献
995.
996.
A simple and efficient transesterification process for the synthesis of β-ketoester derivatives has been achieved by the reaction of methyl β-ketoester with higher alcohols at 110 °C under solvent-free, catalyst-free conditions and its application in synthesis of 3,4-dihydropyrimidin-2(1H)-ones C-5 ester derivatives via Biginelli reaction has been described. 相似文献
997.
在AM1方法优化构型的基础上,用ZINDO/CI方法计算了系列芳香杂环聚合物的紫外-可见光谱,探索分子结构与其光学性质之间的关系.理论计算结果表明,模型化合物ABPBO,PBO,PBOV和PBODV的紫外-可见光谱最大吸收波长(λmax)依次增加,且相应吸收强度与分子链共轭长度相关.根据线性递变规律推导的理论λmax值与其实验值(薄膜干态紫外吸收)符合得较好.由于质子化效应等环境因素,溶液中测量值较理论值和薄膜紫外吸收偏大. 相似文献
998.
999.
Dietrich-Buchecker C Colasson B Jouvenot D Sauvage JP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(15):4374-4386
The synthesis of two multisite ligands containing four and five 1,10-phenanthroline (phen) chelates in line, respectively, is presented. The connectors are 1,3-phenylene linkers. The two ligands were prepared following multistep procedures, the two key reactions being the Suzuki coupling reaction between aromatic nuclei and the nucleophilic addition of aryllithium derivatives onto a phen fragment. The coordination chemistry of both ligands with Li+ ions was very clean and selective, whereas their reaction with copper(I) led to intractable mixtures of insoluble complexes. The tetraphen and the pentaphen compounds afforded almost quantitatively the four- and five-lithium double-stranded helical complexes, respectively. The helical systems are probably highly wound, as indicated by NMR measurements. The pronounced strain of the 5-Li+ complex is reflected by the easy loss of a lithium cation, as shown by electrospray mass spectrometry. 相似文献
1000.
Liu LX Huang ZL Zhao YD 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):1039-1044
A detailed approach is described for the vibrational spectroscopic encoding of polystyrene-based resin beads by converting the infrared absorption peaks suitable for encoding (encoding peaks) into barcodes. Based on combining the FT-IR measurements and the quantum-chemical computations, the vibrational characteristics of p-tert-butylstyrene monomer, polystyrene and poly(p-tert-butylstyrene) resin beads are analyzed, which are helpful for the selection of encoding peaks. The vibrational spectroscopic encoding of polystyrene-based resin beads could be obtained by converting the wavenumber, intensity and full width at half maximum (FWHM) of the encoding peaks into barcodes automatically through a computer program designed in our laboratory. 相似文献