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111.
Ionic dynamics in room temperature molten salts (ionic liquids) containing 1-alkyl-3-methylimidazolium cations is investigated by molecular-dynamics simulations. Calculations were performed with united atom models, which were used in a previous detailed study of the equilibrium structure of ionic liquids [S. M. Urahata and M. C. C. Ribeiro, J. Chem. Phys. 120, 1855 (2004)]. The models were used in a systematic study of the dependency of several single particle time correlation functions on anion size (F-, Cl-, Br-, and PF6-) and alkyl chain length (1-methyl-, 1-ethyl-, 1-butyl-, and 1-octyl-). Despite of large mass and size of imidazolium cations, they exhibit larger mean-square displacement than anions. A further detailed picture of ionic motions is obtained by using appropriate projections of displacements along the plane or perpendicular to the plane of the imidazolium ring. A clear anisotropy in ionic displacement is revealed, the motion on the ring plane and almost perpendicular to the 1-alkyl chain being the less hindered one. Similar projections were performed on velocity correlation functions, whose spectra were used to relate short time ionic rattling with the corresponding long time diffusive regime. Time correlation functions of cation reorientation and dihedral angles of the alkyl chains are discussed, the latter decaying much faster than the former. A comparative physical picture of time scales for distinct dynamical processes in ionic liquids is provided. 相似文献
112.
113.
Birge Zimmermann Huisgen 《Inventiones Mathematicae》1992,108(1):369-383
Summary Counterexamples to the first Finitistic Dimension Conjecture are constructed. In fact, for any fieldk and any integerm2, there exist finite dimensionalk-algebras such that the little finitistic dimension of ism, while the big finitistic dimension ism+1. Our examples are monomial relation algebras; within this class of algebras the big and little finitistic dimensions cannot differ by more than 1. The analysis of the examples is based on a sharp picture of arbitrary second syzygies over monomial relation algebras.Oblatum 5-VI-1991 & 28-X-1991This research was partially supported by a grant from the National Science Foundation. It is dedicated to Maurice Auslander on the occasion of his sixtyfifth birthday. 相似文献
114.
Giuseppe Mascolo Mauro Giustini Pier Luigi Luisi Jacques Lang 《Journal of colloid and interface science》1990,140(2)
The coupling reaction between cetylbromide (CB) and trimethylamine (TMA) to yield the surfactant cetyltrimethylammonium bromide (CTAB) is studied in the system chloroform/isooctane (2/1,v/v)/water in which CTAB forms reverse micelles. This system affords an endogenous micelle population growth, i.e., an increase of the concentration of the micelles due to appearance of the surfactant in situ. The reaction is studied in the presence of preexisting CTAB reverse micelles. The rate of CTAB formation is measured by NMR spectroscopy, and the endogenous micelle population growth is directly monitored by time-resolved fluorescence quenching analysis. Under our experimental conditions, a 100% yield of the chemical reaction brings about a fourfold increase in the population of the reverse micelles. Since the water concentration is constant during chemical reaction, the newly formed water pools are formed at the expense of the initial ones, which brings about a decrease of the average water pool radius during micellar growth. The implication of the endogenous micelle population growth as a model for biological systems is briefly discussed. 相似文献
115.
Haddad Paula S. Mauro Antonio E. Nogueira Vânia M. Klein Stanlei I. 《Transition Metal Chemistry》2003,28(8):899-904
[M(CO)4(N—N)] reacts with CuCl to give new heterobimetallic metal carbonyls of the type [M(CO)4(N—N)(CuCl)], M = W, Mo; N—N = 2,2-bipyridine (bipy), 1,10-phenanthroline (phen). Reactions of [M(CO)4(N—N)(CuCl)] with NaSCN produced the series of complexes of general formula [M(CO)4(N—N)(CuSCN)]. The i.r. spectral of all the bimetallic carbonyls exhibited the general four (CO) band patterns of the precursors. The u.v.–vis. spectral data for precursors and products showed bands associated with * (nitrogen ligands), dd (intrametal), as well as MLCT d* (nitrogen ligands) and MLCT d *(CO) transitions. The [M(CO)4(N—N)(CuX)] (X = Cl, SCN) emission spectra showed only one band associated with the MLCT transition. The t.g. curves revealed a stepwise loss of CO groups. The initial decomposition temperatures of the [M(CO)4(N—N)(CuX)] series suggest that the bimetallic compounds are indeed thermally less stable than their precursors, and the X-ray data showed the formation of MO3, CuMO4, Cu2O and CuO as final decomposition products, M = W, Mo. The spectroscopic data suggests that the heterobimetallic compounds are polymeric. 相似文献
116.
Constable EC Figgemeier E Housecroft CE Olsson J Zimmermann YC 《Dalton transactions (Cambridge, England : 2003)》2004,(13):1918-1927
The synthesis and electronic properties of dinuclear ([(bipy)2Ru(I)M(terpy)][PF6]4(bipy = 2,2'-bipyridine, terpy = 2,2':6',2'-terpyridine; M = Ru, Os)) and trinuclear ([[(bipy)2Ru(I)]2M][PF6]6 M = Ru, Os, Fe, Co) complexes bridged by 4'-(2,2'-bipyridin-4-yl)-2,2':6',2'-terpyridine (I) have been investigated and are compared with those of mononuclear model complexes. The electrochemical analysis using cyclic voltammetry and differential pulse voltammetry reveals that there are no interactions in the ground state between adjacent metal centres. However, there is strong electronic communication between the 2,2'-bipyridine and 2,2':6',2'-terpyridine components of the bridging ligand. This conclusion is supported by a step-by-step reduction of the dinuclear and trinuclear complexes and the assignment of each electrochemical process to localised ligand sites within the didentate and terdentate domains. The investigation of the electronic absorption and emission spectra reveals an energy transfer in the excited state from the terminating bipy-bound metal centres to the central terpy-bound metal centre. This indicates that the bridge is able to facilitate energy transfer in the excited state between the metal centres despite the lack of interactions in the ground state. 相似文献
117.
Pineschi M Bertolini F Haak RM Crotti P Macchia F 《Chemical communications (Cambridge, England)》2005,(11):1426-1428
A conceptually new, simple and practical method for the syn-nucleophilic displacement of aryl and vinyl epoxides and aryl aziridines with (substituted) phenols, using aryl borates as activating nucleophiles under neutral conditions, is reported. 相似文献
118.
Alvarez P Lastra E Gimeno J Bassetti M Falvello LR 《Journal of the American Chemical Society》2003,125(9):2386-2387
Intramolecular [2 + 2] cycloaddition of two C=C bonds in vinylidene complexes [Ru(eta5-C9H7){=C=C(R)H}(PPh3){kappa1-(P)-PPh2(C3H5)][BF4] affords cyclobutylidene complexes [Ru(eta5-C9H7){kappa2-(P,C)-(=CC(R)HCH2CHCH2PPh2)}(PPh3)][BF4], which can be also obtained by reaction of terminal alkynes with [Ru(eta5-C9H7)(PPh3){kappa3-(P,C,C)-PPh2(C3H5)}][PF6]. The reaction proceeds under mild conditions via vinylidene complexes, and the activation parameters were determined by kinetic studies. 相似文献
119.
Maurizio Botta Francesco De Angelis Ingeborg Grgurina Mauro Marzi Rosario Nicoletti 《Journal of heterocyclic chemistry》1985,22(4):1001-1007
The reactivity of Δ3- and Δ2-3-bromomethylcephems toward carboxylate nucleophiles has been studied. The Δ3-bromomethylcephem 1 , less reactive than the Δ2-analogue 4 , is converted in high yields into 3-acyl-oxymethyl-3-cephems 2a-d , generally with no isomerization of the double bond, only within a narrow range of conditions. In particular, the Δ3-7-aminocephalosporanic acid (7-ACA) derivative 2a has been obtained as the only product in 91% yield by treatment of 1 with triethylammonium acetate in acetic acid. The Δ2-bromomethyl-cephem 4 is easily converted into the Δ2-acyloxymethyl-cepheras 5a-d without double bond isomerization, in very high yields. 相似文献
120.
Peter A. Beaven Mauro Marmotti Reinhard Kampmann Joachim Knoth Heinrich Schwenke 《Spectrochimica Acta Part B: Atomic Spectroscopy》2003,58(12):2049-2057
A multi-wire, gas-filled position-sensitive detector has been developed for the simultaneous recording of wavelength-dispersed X-ray signals that enables X-ray fluorescence spectrometry with a limited multi-element capability in the low Z element range. Details of the modular construction of the detector are given. The detector performance was characterized using Al–K radiation and a variable slit system. The detector has been applied in a laboratory spectrometer equipped with an electron source and a double multilayer mirror device as the wavelength-dispersing element. Spectra from Al and Si obtained in the simultaneous acquisition mode show good agreement with calculations performed using a ray-tracing model. 相似文献