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21.
Elías Molins Amílcar Labarta Javier Tejada Amparo Caubet Santiago Alvarez 《Transition Metal Chemistry》1983,8(6):377-380
Summary Magnetic moments and57Fe Mössbauer spectra at room temperature and at liquid nitrogen temperature of polynuclear ligand-bridged iron phthalocyanines, FePcL (L = pyrazine and 4,4-bipyridyl), are reported. The experimental data are in agreement with a pseudo-octahedral environment around the iron(II) cation. Partially oxidized derivatives, FePc(pz)I0.26 and FePc(bipy)I1.06 have been synthesized and their57Fe Mössbauer spectra and magnetic moments within the same temperature range obtained. Oxidation is shown to be metal centred and the iodine is found to be in I– form for FePc(pz)0.26 and as both I– and I
3
–
species for FePc(bipy)I1.06. While the magnetic moment of FePc(pz) increases upon oxidation, the opposite occurs for FePc(bipy). 相似文献
22.
Hong J Kim YH Gil JH Cho K Jung JH Han SY 《Rapid communications in mass spectrometry : RCM》2002,16(22):2089-2093
The structural determination of sn-1 and sn-2 hexadecanoic lysophosphatidylcholine (LPC) regioisomers was carried out using fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecules produced diverse product ions due mainly to charge remote fragmentations. Based on the information obtained from the CID spectra of protonated and sodiated molecules, sn-1 and sn-2 hexadecanoic LPC isomers could be discriminated. Especially, the abundance ratio of the diagnostic ion pair [m/z 224/226] in the CID spectra of [M + H](+) ions was shown to be greatly different. Moreover, the CID-MS/MS spectra of sodium-adducted molecules for hexadecanoic LPC isomers showed characteristic product ions such as [M + Na - 103](+), [M + Na - 85](+), and [M + Na - 59](+), by which their regio-specificity can be differentiated. 相似文献
23.
We describe the preparation of 1,4′-bipyrazolyls and 4-pyrazolylpyrimidines by the reaction of 2-pyrazolyl-3-dimethylamino acrylate and acrylonitrile with double nucleophilic reagents such as hydrazines, urea and guanidine. Reactions were performed under microwave irradiation in 5-60 min. This is a useful procedure for the preparation of valuable compounds with applications in medicinal and coordination chemistry. 相似文献
24.
A nonadiabatic quantum dynamic model has been developed to study the process of electron emission from a low-work-function metal surface. The process is initiated by scattering a highly vibrationally excited NO molecule from a surface composed of a Cs layer covering a Ru crystal. The model addresses the increasing quantum yield of the electron emission as a function of the molecular vibrational excitation and incident kinetic energy. The reaction mechanism is identified as a long-range harpooning electron transfer to a molecular ion which is then accelerated toward the surface. Upon impact, the molecular ion emits its excess electron. 相似文献
25.
Single bacterial cells, each expressing a different library variant, were compartmentalized in aqueous droplets of water-in-oil (w/o) emulsions, thus maintaining a linkage between a plasmid-borne gene, the encoded enzyme variant, and the fluorescent product this enzyme may generate. Conversion into a double, water-in-oil-in-water (w/o/w) emulsion enabled the sorting of these compartments by FACS, as well as the isolation of living bacteria cells and their enzyme-coding genes. We demonstrate the directed evolution of new enzyme variants by screening >10(7) serum paraoxonase (PON1) mutants, to yield 100-fold improvements in thiolactonase activity. In vitro compartmentalization (IVC) of single cells, each carrying >10(4) enzyme molecules, in a volume of <10 femtoliter (fl), enabled detection and selection despite the fast, spontaneous hydrolysis of the substrate, the very low initial thiolactonase activity of PON1, and the use of difusable fluorescent products. 相似文献
26.
A. Gil 《Adsorption》1998,4(3-4):197-206
The micropore structure of four microporous materials (two zeolites, ZSM-5 and Y-82; an activated carbon and an alumina pillared clay) and their binary physical mixtures (50-50 wt%) have been examined by nitrogen adsorption at 77 K. Various micropore sizes have been considered from the stages on the micropore filling mechanism in the microporous materials. The application of the Dubinin-Astakhov (DA) equation to characterize and obtain the adsorption potential distributions of the microporous materials is presented. 相似文献
27.
Solid-phase methodology for the preparation of pyrrolo[3,2-d]pyrimidine-6-carboxylates with diversity at the N3 pyrmidine nitrogen has now been elaborated to allow for the generation of pyrrolopyrimidine libraries with members possessing diversity at the N3, N5, and C6 positions. The diversification of the N5 position was achieved by treating the parent resin-bound pyrrolo[3,2-d]pyrimidines 3 with an alkyl halide in the presence of Cs2CO3 in DMF. Modification of the C6 carboxylate of resin-bound pyrrolopyrimidines 3-5 was first achieved by hydrolysis of the benzyl ester using LiOH in a mixture of THF/H2O/MeOH. Further alteration of the C6 position of resin-bound pyrrolo[3,2-d]pyrimidine-6-carboxylic acids 6-8 was then performed by activation with triphosgene and treatment with an amine to furnish resin-bound pyrrolo[3,2-d]pyrimidine-6-amides. Twenty-two pyrrolo[3,2-d]pyrimidines 1a-v with different substituents at the N3, N5, and C6 positions were obtained in yields of 21-83% and purities of 61-98% after cleavage from the solid support. 相似文献
28.
We have been studying the problem of heterogeneity of OH groups in zeolites HY for a long time. The heterogeneity was suggested by the shift of the IR band of OH groups restoring upon ammonia desorption and also by the fact that the band of OH groups forming hydrogen bonds was relatively broad (broader than for homogeneous acidic OH). In the present study we present another important argument for heterogeneity: the splitting of the IR band of free OH and OD groups in a zeolite of Si/Al=8.3 dealuminated by (NH4)2SiF6 treatment. Such a splitting is the best seen in low temperature spectra of OD groups. We found less acidic 3640 cm−1 (AlO)(SiO)2SiO1HAl(OSi)3 and more acidic 3625 cm−1 (SiO)3SiO1HAl(OSi)3 groups. The presence of these two kinds of hydroxyls corresponds to the presence of Si(2Al) and Si(1Al), respectively, detected in 29Si MAS NMR spectra. We also found a small amount of strongly acidic 3599 cm−1 hydroxyls interacting with extraframework Al species. 相似文献
29.
Gil Markovich Stuart Pollack Rina Giniger Ori Cheshnovsky 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):98-100
We have measured the photoelectron-spectra of I? (H2O)n clusters in the size range n=1–60. We have found that the first six water molecules form a solvation layer with an average 0.35 eV electrostatic stabilization of the anion. At larger cluster sizes the electrostatic stabilization of water does not fit a continuous dielectric solvent. The most stable structures of the clusters consist of internally solvated anions. In the size range n=34–40 we have found evidence for existence of cluster structures with surface solvated anions. 相似文献
30.
High-temperature hydrolysis of Zn(II) and Mn(II) alkoxides in a high boiling point solvent in the presence of surfactants was used to prepare surfactant-coated Zn(1-x)Mn(x)O nanocrystals with average size of 5.5 nm and x = 0.04 +/- 0.03. The magnetic properties of the nanocrystals were measured both for isolated particles diluted in a hydrocarbon matrix and for a nanocrystal powder. Nanocrystals of manganese oxide and ZnO coated with manganese oxide were prepared for comparison to the Zn(1-x)Mn(x)O nanocrystals. We find that the manganese ions primarily substitute zinc ions in the hexagonal ZnO lattice, and part of them are ferromagnetically coupled up to room temperature even in isolated noninteracting nanocrystals. The rest of the ions are magnetically disordered or uncoupled. Surprisingly, these small Zn(1-x)Mn(x)O nanocrystals poses relatively large low-temperature magnetic coercivity and relatively high blocking temperature in the isolated form, which indicate large magnetic anisotropy. In the nanocrystal powder the coercive field decreased significantly. This study highlights the advantages of working with noninteracting single domain particles of these intriguing materials. 相似文献