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61.
Complex formation equilibria in binary mixtures of chloroform with dipropyl ether (PE), diisopropyl ether (IPE), methyl tert-butyl ether (MBE), tetrahydrofuran (THF). 1,4-dioxane (DOX), acetone (AC), and methyl acetate (MA) have been analyzed in detail using several association models. Vapor-liquid equilibria, excess enthalpy and excess heat capacity data for these mixtures have been correlated using a multiproperty global fitting procedure. The thermodynamic properties for chloroform +PE, +IPE, +MBE, +AC, and +MA are best correlated using the ideal association model while for chloroform +THF and +DOX the best model is an athermal solvation model where the Flory-Huggins expression for the species activity coefficients is considered. The model parameters, i.e., the equilibrium constant, enthalpies and heat capacities of complexation, were found to be reliable, well representing the chloroform-oxygenated solvent H-bonded complexes. A detailed discussion is given on the test proposed by McGlashan and Rastogi to decide whether the solution contains only 11 complexes or 21 complexes as well. The complex formation equilibria in chloroform mixtures is compared to those previously examined for halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) mixed with the same oxygenated solvents. It was found that the H-bonds formed by halothane are stronger than those formed by chloroform. 相似文献
62.
Stream vectors in three dimensional aerodynamics 总被引:3,自引:0,他引:3
Summary This work deals with the decomposition of a vector fieldu intou=×+. Non homogeneous boundary conditions on or are investigated; applications to the computation of inviscid flows are given; finally a conforming finite element implementation is studied and tested. 相似文献
63.
Electrochemical copolymerization of furan and 3-chlorothiophene was performed at constant electrode potential in a binary
solvent system consisting of boron trifluoride diethyl etherate + ethyl ether (BFEE + EE; ratio 1:2) and trifluoroacetic acid
(10% by volume). The homopolymers and copolymers obtained were studied with cyclic voltammetry, in situ ultraviolet–visible
spectroscopy, in situ resonance Raman spectroscopy, and in situ conductivity measurements. The spectroelectrochemical properties
of the copolymers show intermediate features between polyfuran and poly(3-chlorothiophene). The conductivity changes of homo-
and copolymer films are almost completely reversible when the potential shift direction is reversed.
相似文献
Rudolf HolzeEmail: |
64.
Copper‐Mediated Aromatic Radiofluorination Revisited: Efficient Production of PET Tracers on a Preparative Scale
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Philipp Krapf Fadi Zarrad Elizaveta A. Urusova Dr. Elena Kordys Priv.‐Doz. Dr. Heike Endepols Prof. Dr. Bernd Neumaier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5972-5979
Two novel methods for copper‐mediated aromatic nucleophilic radiofluorination were recently reported. Evaluation of these methods reveals that, although both are efficient in small‐scale experiments, they are inoperative for the production of positron emission tomography (PET) tracers. Since high base content turned out to be responsible for low radiochemical conversions, a “low base” protocol has been developed which affords 18F‐labeled arenes from diaryliodonium salts and aryl pinacol boronates in reasonable yields. Furthermore, implementation of our “minimalist” approach to the copper‐mediated [18F]‐fluorination of (mesityl)(aryl)iodonium salts allows the preparation of 18F‐labeled arenes in excellent RCCs. The novel radiofluorination method circumvents time‐consuming azeotropic drying and avoids the utilization of base and other additives, such as cryptands. Furthermore, this procedure enables the production of clinically relevant PET tracers; [18F]FDA, 4‐[18F]FPhe, and [18F]DAA1106 are obtained in good isolated radiochemical yields. Additionally, [18F]DAA1106 has been evaluated in a rat stroke model and demonstrates excellent potential for visualization of translocator protein 18 kDa overexpression associated with neuroinflammation after ischemic stroke. 相似文献
65.
Transmetalation of Sn[N(SiMe3)2]2 with calcium granules in tetrahydropyran (thp) yields colorless [(thp)2Ca{N(SiMe3)2}2] ( 1 ) which is soluble in common organic solvents. The calcium center is in a distorted tetrahedral environment with Ca–N and Ca–O bond lengths of 231.08(11) and 240.23(9) pm, respectively. The molecular structure is dominated by steric factors leading to a NCaN bond angle of 119.43(6)°. 相似文献
66.
The synthesis of a novel bis-crown quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine discotic and its binding properties to a series of alkali and alkaline-earth metals is reported. A schematic representation of the binding equilibrium of the sensor to the metal is proposed. The binding constant of the sensor to barium(II) was estimated to be 1.4 × 104 M−1 based on 1H NMR studies. 相似文献
67.
Prof. Dr. Achim Müller Dr. Alice Merca Dr. Ahmed Jasim M. Al‐Karawi Somenath Garai Dr. Hartmut Bögge Dr. Guangfeng Hou Prof. Dr. Lixin Wu Dr. Erhard T. K. Haupt Prof. Dr. Dieter Rehder Fadi Haso Prof. Dr. Tianbo Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16310-16318
Unique properties of the two giant wheel‐shaped molybdenum‐oxides of the type {Mo154}≡[{Mo2}{Mo8}{Mo1}]14 ( 1 ) and {Mo176}≡[{Mo2}{Mo8}{Mo1}]16 ( 2 ) that have the same building blocks either 14 or 16 times, respectively, are considered and show a “chemical adaptability” as a new phenomenon regarding the integration of a large number of appropriate cations and anions, for example, in form of the large “salt‐like” {M(SO4)}16 rings (M=K+, NH4+), while the two resulting {Mo146 (K(SO4))16} ( 3 ) and {Mo146 (NH4(SO4))16} ( 4 ) type hybrid compounds have the same shape as the parent ring structures. The chemical adaptability, which also allows the integration of anions and cations even at the same positions in the {Mo4O6}‐type units of 1 and 2 , is caused by easy changes in constitution by reorganisation and simultaneous release of (some) building blocks (one example: two opposite orientations of the same functional groups, that is, of H2O{Mo?O} ( I ) and O?{Mo(H2O)} ( II ) are possible). Whereas Cu2+ in [(H4CuII5)MoV28MoVI114O432(H2O)58]26? ( 5 a ) is simply coordinated to two parent O2? ions of {Mo4O6} and to two fragments of type II , the SO42? integration in 3 and 4 occurs through the substitution of two oxo ligands of {Mo4O6} as well as two H2O ligands of fragment I . Complexes 3 and now 4 were characterised by different physical methods, for example, solutions of 4 in DMSO with sophisticated NMR spectroscopy (EXSY, DOSY and HSQC). The NH4+ ions integrated in the cluster anion of 4 “communicate” with those in solution in the sense that the related H+ ion exchange is in equilibrium. The important message: the reported “chemical adaptability” has its formal counterpart in solutions of “molybdates”, which can form unique dynamic libraries containing constituents/building blocks that may form and break reversibly and can lead to the isolation of a variety of giant clusters with unusual properties. 相似文献
68.
Agnieszka Skórska-Stania Magdalena Śliwa Kamil Musilek Kamil Kuca Josef Jampilek Robert Musiol Barbara J. Oleksyn Jiri Dohnal 《Structural chemistry》2010,21(3):495-501
The investigation of relationships between the molecular structure of the compounds capable to reactivate acetylcholinesterase
(AChE) inhibited by organophosphorus toxins, such as nerve agents and pesticides, is an important step toward synthesis of
more efficient antidota. In the present article, we describe the crystal structures of two new AChE reactivators, which are
bromides of (E)-1,4-bis(4-hydroxyiminomethylpyridinium)-but-2-ene (K075) and of 4,4′-bis(hydroxyiminomethyl)-1,1′-(1,4-phenylenedimethyl)-bispyridinium
(K114). Their molecular geometry and intermolecular interactions in the crystalline state are compared to those in the crystal
structures of the well-known AChE reactivators, obidoxime, and TMB-4. Inspection of hydrogen bonds and other short intermolecular
contacts in the crystalline AChE–obidoxime complex revealed their similarity to those observed in the crystal structures of
K075 and K114. 相似文献
69.
Bassioni G Pillay AE El Kadi M Fegali F Fok SC Stephen S 《European journal of mass spectrometry (Chichester, England)》2010,16(6):679-692
Transition metals can have a significant impact in research related to the dosage optimization of superplasticizers. It is known that the presence of transition metals can influence such doses, and the application of a contemporary instrumental method to obtain the profiles of subsisting transition elements in concrete mixtures would be useful. In this work, inductively-coupled plasma mass spectrometry (ICP-MS) is investigated as a possible tool to track traces of transition metals in concrete mixtures. Depth profiling using ICP-MS on proofed and unproofed concrete shows the presence of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn at trace intensities in the bulk of the samples under investigation. The study demonstrates that the transition metals present in the concrete sample are largely a part of the cement composition and, to a minor degree, a result of exposure to the seawater after curing. The coated concrete samples have a metal distribution pattern similar to the uncoated samples, but slight differences in intensity bear testimony to the very low levels that originate from the exposure to seawater. While X-ray diffraction fails to detect these traces of metals, ICP-MS is successful in detecting ultra-trace intensities to parts per trillion. This method is not only a useful application to track traces of transition metals in concrete, but also provides information to estimate the pore size distribution in a given sample by very simple means. 相似文献
70.
Vlastimil Dohnal Alena Jezkova Lucie Pavlikova Kamil Musilek Daniel Jun Kamil Kuca 《Analytical and bioanalytical chemistry》2010,397(1):109-114
This paper describes determination of the deoxynivalenol and ergosterol in samples from different varieties of barley and,
consequently, malt produced from this barley. In total, 20 samples of barley and 20 samples of barley malt were analyzed.
The alkaline hydrolysis with consequent extraction into hexane was applied to obtain the ergosterol from cereals. Extraction
to acetonitrile/water and subsequent solid-phase extraction (SPE) were used for deoxynivalenol. The determination of the samples
was performed on high-performance liquid chromatography using UV detection (ergosterol) and mass spectrometric detection (deoxynivalenol).
The influence of the malting process on the production of two compounds of interest was assessed from obtained results. Ergosterol
concentration ranged 0.88–15.87 mg/kg in barley and 2.63–34.96 mg/kg in malt, where its content increased to 95% compared
to samples before malting. The malting process was observed as having a significant effect on ergosterol concentration (P = 0.07). The maximum concentration of deoxynivalenol was found to be 641 μg/kg in barley and 499 μg/kg in malt. Its concentration
was lower than the legislative limit for unprocessed cereals (1,250 μg/kg). The statistic effect of the malting process on
deoxynivalenol production was not found. Linear correlation between ergosterol and deoxynivalenol content was found to be
very low (barley R = 0.02, malt R = 0.01). The results revealed that it is not possible to consider the ergosterol content as the indicator of deoxynivalenol
contamination of naturally molded samples. 相似文献