共查询到20条相似文献,搜索用时 15 毫秒
1.
A model assuming that the formation of dimers determines the acoustic properties of liquid mixtures, in the inert solvent cyclohexane, was applied to describe the observed dependences of sound speed on composition. The dimerization constants were estimated. The results allow one to propose that the solutes tend to form associates larger than dimers in concentrated solutions, while in dilute systems solute–solvent interactions play an important role. 相似文献
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Abstract— The evaluation of the equilibrium constants for charge-transfer complex formation has been of interest for five decades. During this time, absorption spectroscopy using Benesi-Hildebrand, or related methods, has been used to obtain the equilibrium constants. These methods require relatively high concentrations of donor or acceptor to be present in solution when weakly bound complexes are studied, conditions that lead to the formation of higher order complexes and inconsistent determinations of these constants. A new method is presented that allows weakly bound charge-transfer complexes to be studied under low concentration conditions and the equilibrium constants to be determined accurately for the first time. Using this method, the equilibrium constant for the formation of 1, 2, 4, 5-tetracyanobenzene/pentamethylbenzene charge-transfer complex was found to be K CT = 6.8 ± 0.3 M −1 with an extinction coefficient at 400 nm of εCT = 150 ± 30cm−1 M−1 . 相似文献
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Two equations of linear type (Eqs. 10 and 17 in the text) have been derived to analyze the IR data to determine the dimerization constant consistently. Equation 10 is to be used to fit the integrated absorbances of the monomer band to obtain the molar monomer absorptivity, ?m, and dimerization constant, K; Eq. 17 is to be used to fit the integrated absorbances of the dimer bands to obtain the molar dimer absorptivity, ?d, and dimerization constant, K. Thus the same dimerization constant can be independently determined either from the monomer band or from the dimer band. The discrepancy between the two determined values provides an assessment of the consistency of determination. The monomer‐dimer self‐association of 2,2‐dimethyl‐3‐ethyl‐3‐pentanol in the solvent of carbon tetrachloride was chosen to demonstrate the utility of these two equations. 相似文献
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采用自动电位酸碱滴定技术研究了水化介孔氧化硅的表面脱质子反应.基于悬浮液的酸碱滴定数据,用Gran图法计算得到了介孔氧化硅表面氢离子键位点浓度.利用FITEQL4.0软件,采用双电层恒电容模型计算得到了相应的表面酸碱平衡常数.结果表明,与无定形氧化硅不同,介孔氧化硅表面存在对应于双齿表面硅羟基≡Si2OH和单齿表面硅羟基≡SiOH的两个脱质子常数,分别为pKa1=6.78±0.15,pKa2=10.25±0.22.根据测定得出的介孔氧化硅表面脱质子常数,构建了不同pH条件下,介孔氧化硅表面优势组分分布图,并讨论了表面电容预赋值对氧化硅表面组分分布的影响. 相似文献
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M. Lopez-Lopez P. Lopez-Cornejo A. García F. Sanchez 《Journal of solution chemistry》2008,37(4):519-526
An equation, which relates the variations of the standard formal potentials of a redox couple in the presence of variable concentrations of a substrate, S, to the Gibbs energies of binding (to the substrate) of the two forms of the couple, has been obtained. The results have been checked using the data corresponding to the [Fe(CN)54-CNpy]2−/3− couple in CTACl micellar solutions. It is observed that K red<K ox, in spite of the higher charge of the reduced form. This fact has been explained through consideration of the dielectric saturation at the micelle/water interface. 相似文献
6.
Self‐Assembly of Three‐Dimensional Supramolecular Polymers through Cooperative Tetrathiafulvalene Radical Cation Dimerization
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Jia Tian Yu‐Di Ding Tian‐You Zhou Dr. Kang‐Da Zhang Prof. Xin Zhao Dr. Hui Wang Prof. Dan‐Wei Zhang Prof. Yi Liu Prof. Zhan‐Ting Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(2):575-584
The self‐assembly of a new type of three‐dimensional (3D) supramolecular polymers from tetrahedral monomers in both organic and aqueous media is described. We have designed and synthesized two tetraphenylmethane derivatives T1 and T2 , both of which bear four tetrathiafulvalene (TTF) units. When the TTF units were oxidized to the radical cation TTF.+, their pre‐organized tetrahedral arrangement remarkably enhanced their intermolecular dimerization, leading to the formation of new 3D spherical supramolecular polymers. The structure of the supramolecular polymers has been inferred on the basis of UV/Vis absorption, electron paramagnetic resonance, cyclic voltammetry, and dynamic light scattering (DLS) analysis, as well as by comparing these properties with those of the self‐assembled structures of mono‐, di‐, and tritopic control compounds. DLS experiments revealed that the spherical supramolecular polymers had hydrodynamic diameters of 68 nm for T1 (75 μM ) in acetonitrile and 105 nm for T2 (75 μM ) in water/acetonitrile (1:1). The 3D spherical structures of the supramolecular polymers formed in different solvents were also supported by SEM and AFM experiments. 相似文献
7.
《Chemphyschem》2003,4(8):809-816
No‐barrier theory is a new approach to the calculation of rate constants for reactions in solution, from the corresponding equilibrium constants. It requires relatively small molecular orbital theory calculations, and has been very successful. It is in the spirit of Marcus theory, but does not require an “intrinsic barrier”. The approach is explained, with an examination of the way in which the ideas on which it is based were “in the air”. 相似文献
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Rate and Equilibrium Constants for the Addition of N‐Heterocyclic Carbenes into Benzaldehydes: A Remarkable 2‐Substituent Effect
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Dr. Christopher J. Collett Dr. Richard S. Massey Dr. James E. Taylor Oliver R. Maguire Dr. AnnMarie C. O'Donoghue Prof. Andrew D. Smith 《Angewandte Chemie (International ed. in English)》2015,54(23):6887-6892
Rate and equilibrium constants for the reaction between N‐aryl triazolium N‐heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3‐(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2‐substituent in these reactions and provide insight into the chemoselectivity of cross‐benzoin reactions. 相似文献
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《Analytical letters》2012,45(10):1967-1980
Abstract The analysis of random errors is discussed for the equilibrium constants of very stable metal complexes, determined through competitive potentiometric methods. Prior to this analysis the calculation of standard deviations both for overall and stepwise equilibrium constants is considered. Clues are given as to how a system can be properly characterized. To illustrate the error analysis, the following systems were selected: Cu(II) and L-2,6-diaminohexanoic acid (L-lysine); Cu(II) and ethylene diaminotetraacetic acid (EDTA); and Cu(II), EDTA and 1,2-dihydroxybenzene (catechol). 相似文献
11.
我们最近对维生素C及其脂溶性衍生物在胶束中的抗氧化活性的研究发现,尽管它们在均相溶液中的活性基本相同,但在胶束中却相差很大,强烈地依赖于氧化剂氮氧自由基及抗氧化剂在胶束中的络合程度.因此,测定它们在胶束中的分配系数及络合平衡常数,对讨论生物抗氧化剂在胶束中的反应活性有重要意义. 相似文献
12.
Shuzo Kutsuna 《国际化学动力学杂志》2013,45(7):440-451
Henry's law constants of six kinds of hydrochlorofluorocarbons (HCFCs) were determined at 313–353 K by means of a phase‐ratio variation headspace method: and (KH353 in M atm?1, ΔHsol in kJ mol?1) = (0.0070 ± 0.0006, –23 ± 2), (0.0038 ± 0.0011, –22 ± 10), (0.0065 ± 0.0007, –21 ± 3), (0.0026 ± 0.0007, –23 ± 8), (0.0016 ± 0.0003, –30 ± 4), and (0.0022 ± 0.0003, –25 ± 4), respectively, for HCFC‐141b (CH3CCl2F), HCFC‐142b (CH3CClF2), HCFC‐123 (CF3CHCl2), HCFC‐124 (CF3CHClF), HCFC‐225ca (CF3CF2CHCl2), and HCFC‐225cb (CClF2CF2CHClF). Errors represent two standard deviations only for the fitting. The decay of headspace partial pressures of these HCFCs via hydrolysis was discerned only for CF3CHCl2 and CF3CF2CHCl2 under the experimental conditions examined. Rate constants (kOH– in M?1 s?1) for aqueous reactions of CF3CF2CHCl2 and CF3CHCl2 with OH? at 313–353 K were determined to be and , respectively, from monitoring changes in headspace partial pressure over prescribed concentrations of aqueous NaOH as a function of the headspace time duration and concentration of aqueous NaOH. The calculations performed included consideration of gas–water equilibrium and hydrolysis at both headspace and room temperatures. The calculation for CF3CHCl2 also included consideration of salting‐out effects: The salting coefficient of NaCl on a natural log basis was determined to be 0.36 ± 0.06 M?1, and this value was used for consideration of the salting‐out effect of NaOH. Whereas the activation energy for CF3CF2CHCl2 was greater than that for CF3CHCl2, the kOH– value at 353 K of CF3CF2CHCl2 was 103 times larger than that of CF3CHCl2, indicating that reaction mechanisms for these two HCFCs differed from each other. The aqueous reaction of CF3CF2CHCl2 with OH? was found to proceed through dehydrofluorination on the basis of detection of CF3CF?CCl2 as a primary degradation product of the reaction and proportionality of the rate constants to both concentrations of CF3CF2CHCl2 and OH?. 相似文献
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Allyloxyporphyrin‐Functionalized Multiwalled Carbon Nanotubes: Synthesis by Radical Polymerization and Enhanced Optical‐Limiting Properties
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Dr. Aijian Wang Yu Fang Wang Yu Dr. Lingliang Long Prof. Dr. Yinglin Song Wei Zhao Dr. Marie P. Cifuentes Prof. Dr. Mark G. Humphrey Prof. Dr. Chi Zhang 《化学:亚洲杂志》2014,9(2):639-648
Allyloxyporphyrin‐functionalized multiwalled carbon nanotubes (MWCNT‐TPP) were synthesized by radical polymerization and characterized by FTIR, UV/Vis absorption, and X‐ray photoelectron spectroscopy; elemental analysis; TEM; and thermogravimetric analysis. Z‐scan studies revealed that this nanohybrid exhibits enhanced nonlinear optical (NLO) properties compared to a control sample consisting of a covalently unattached physical blend of MWCNTs and porphyrin, as well as to the separate MWCNTs and porphyrin. At the wavelengths used, the mechanism of enhanced optical limiting likely involves reverse saturable absorption, nonlinear scattering, and photoinduced electron/energy transfer between the MWCNTs and the porphyrin. The role of electron/energy transfer in the NLO performance of MWCNT‐TPP was investigated by Raman and fluorescence spectroscopy. 相似文献
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Prof. Dr. Holger Braunschweig Dr. Ching‐Wen Chiu Johannes Wahler Dr. Krzysztof Radacki Dr. Thomas Kupfer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(40):12229-12233
As neutral isoelectronic analogues of the elusive cyclopentadienyl cation, boroles have been of interest for their prospective applications as strong Lewis acids, chromophores, and electron acceptors. Recently our group discovered a π‐nucleophilic boryl anion based on the borole system. In an effort to extend borole chemistry, we now report the molecular structure of 1‐chloro‐2,3,4,5‐tetraphenylborole ( 1 ) and its corresponding borole dianion resulting from the two‐electron reduction of 1 with KC8. The thermally induced dimerization of 1 yields an unprecedented boracyclohexadiene/borolene spiro‐bicyclic compound and the resulting dimer was fully characterized including a single‐crystal X‐ray analysis. 相似文献
17.
Optical‐Resolution Photoacoustic Microscopy for Volumetric and Spectral Analysis of Histological and Immunochemical Samples
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Dr. Yu Shrike Zhang Dr. Junjie Yao Chi Zhang Lei Li Prof. Lihong V. Wang Prof. Younan Xia 《Angewandte Chemie (International ed. in English)》2014,53(31):8099-8103
Optical‐resolution photoacoustic microscopy (OR‐PAM) is an imaging modality with superb penetration depth and excellent absorption contrast. Here we demonstrate, for the first time, that this technique can advance quantitative analysis of conventional chromogenic histochemistry. Because OR‐PAM can quantify the absorption contrast at different wavelengths, it is feasible to spectrally resolve the specific biomolecules involved in a staining color. Furthermore, the tomographic capability of OR‐PAM allows for noninvasive volumetric imaging of a thick sample without microtoming it. By immunostaining the sample with different chromogenic agents, we further demonstrated the ability of OR‐PAM to resolve different types of cells in a coculture sample with imaging depths up to 1 mm. Taken together, the integration of OR‐PAM with (immuno)histochemistry offers a simple and versatile technique with broad applications in cell biology, pathology, tissue engineering, and related biomedical studies. 相似文献
18.
Kazuki Sakashita Dr. Yu Shibata Prof. Dr. Ken Tanaka 《Angewandte Chemie (International ed. in English)》2016,55(23):6753-6757
It has been established that a cationic rhodium(I)/binap complex catalyzes the cross‐cyclotrimerization of two molecules of a monosubstituted allene with one molecule of a functionalized alkyne to give 3,6‐dialkylidenecyclohex‐1‐enes. In contrast, the reactions involving di‐ or trisubstituted allenes and/or unfunctionalized alkynes afforded cross‐dimerization products, substituted dendralenes, through β‐hydrogen elimination from the corresponding rhodacycles. 相似文献
19.
To pursue optimum condition in liquid‐liquid‐liquid microextraction (LLLME), extraction parameters dominating extraction efficiency were investigated by theoretical considerations. The theoretical considerations discussed equilibrium model for equilibrium LLLME and non‐equilibrium model for dynamic LLLME. A method described here is a dynamic LLLME technique combined with high‐performance liquid‐chromatography ultraviolet absorbance detection (HPLC/UV) to determine traces of nitrophenols in water. Analytical parameters such as organic phase, acceptor phase volume, sample agitation, extraction time, acceptor phase NaOH concentration, donor phase HCl concentration, salt addition, and absorption wavelength were identified as variable settings. Relative standard deviation (RSD, 1.8‐4.4%), coefficient of estimation (R2, 0.9994‐0.9999), and detection limit (0.032‐0.065 ng mL?1) were achieved under the variable settings. The proposed method was successfully applied to the analysis of a lake water sample, and the relative recoveries of nitrophenols from spiked water sample were up to 92.5%. The variable settings of LLLME close to optimization was responsible for an acceptable extraction efficiency. 相似文献