共查询到20条相似文献,搜索用时 15 毫秒
1.
Rybachenko V. I. Chotii K. Yu. Kovalenko V. V. Schroeder H. 《Russian Journal of General Chemistry》2001,71(5):786-788
The equilibrium constants of acetyl transfer between O-acetylonium salts of a series of pyridine N-oxides and 4-(4-dimethylaminostyryl)pyridine N-oxide in acetonitrile and methylene chloride were determined. The equilibrium constants correlate with the acid-base characteristics of the N-oxides and with the heats of reactions calculated quantum-chemically. 相似文献
2.
Rybachenko V. I. Schroeder G. Chotii K. Yu. Kovalenko V. V. Lenska B. Red'ko A. N. 《Theoretical and Experimental Chemistry》2000,36(6):334-337
22 Acetyl group exchange reactions between N-acetoxypyridinium salts and 4-dimethylaminopyridine, 4-morpholinopyridine, and N-methylimidazole in acetonitrile at 298 K have been studied. The rate constants varied from 105 to 10–4 L/mol·s, and the equilibrium constants ranged from 109 to 10–9. The rates and equilibrium constants of these reactions did not comply with the Brönsted equation. The kinetics of the acetyl exchange reactions are well described by a correlation equation containing squared terms. 相似文献
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Dr. Yvonne Abel Dr. Ivan Vlassiouk Dr. Enno Lork Prof. Dr. Sergei Smirnov Prof. Dr. Marat R. Talipov Prof. Dr. Franz-Peter Montforts 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(71):17120-17127
In donor–acceptor dyads undergoing photoinduced electron transfer (PET), a direction or pathway for electron movement is usually dictated by the redox properties and the separation distance between the donor and acceptor subunits, while the effect of symmetry is less recognized. We have designed and synthesized two isomeric donor–acceptor assemblies in which electronic coupling between donor and acceptor is altered by the orbital symmetry control with the reorganization energy and charge transfer exothermicity being kept unchanged. Analysis of the optical absorption and luminescence spectra, supported by the DFT and TD-DFT calculations, showed that PET in these assemblies corresponds to the Marcus inverted region (MIR) and has larger rate for isomer with weaker electronic coupling. This surprising observation provides the first experimental evidence for theoretically predicted adiabatic suppression of PET in MIR, which unambiguously controlled solely by symmetry. 相似文献
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Popova S. S. Ol'shanskaya L. N. Pominova T. V. 《Russian Journal of Electrochemistry》2002,38(4):362-368
Effect of the anion nature on the cathodic intercalation of lithium into graphite is studied. The duration of a discharge process and the capacity of Li
x
C6 electrodes increase in the row Cl– HSO4
– < ClO4
– < SCN–. The highest negative potential of an Li
x
C6 electrode is reached when lithiating in an LiSCN non-aqueous solution. X-ray diffraction and microstructure analyses confirm the presence in the electrode's upper layers of predominantly layered compounds Li
x
C6A
y
, where A is anion. In deep layers, the principal intercalation product is Li
x
C6. 相似文献
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Ashis Kumar Satpati Manoj Kumbhakar Sukhendu Nath Haridas Pal 《Journal of photochemistry and photobiology. A, Chemistry》2008,200(2-3):270-276
Electron transfer (ET) rates between quinone acceptors and amine donors in micellar media show Marcus inversion behavior on correlating with the free energy changes of the ET reactions. The onset of Marcus inversion in these systems is seen to be tuned by about 0.25 eV by changing the type of the micelle. The results are rationalized on the basis of two-dimensional ET theory where ET occurs along intramolecular coordinate with non-equilibrium configuration along solvation coordinate. Maximum ET rates are seen to vary by about one order of magnitude in different micelles, and are attributed to the micelle-dependent changes in the separations of the interacting quinone–amine pairs. Tunings of Marcus inversion and ET rates by changing micellar microenvironments have been observed and suggested to have useful implications in different applied areas. 相似文献
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Hassan Keypour Mohammad Hasan Zebarjadian Majid Rezaeivala Mojtaba Shamsipur Hamid Reza Bijanzadeh 《Journal of solution chemistry》2014,43(7):1218-1231
Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with two new branched amines, 4,7-bis(2-pyridylmethyl)-4,7-diazadecane-1,10-diamine (L1) and 4,8-bis(2-pyridylmethyl)-4,8-diazaundecane-1,11-diamine (L2), in acetonitrile and nitromethane. A competitive 7Li NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with L1 and L2 in the same solvent systems. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data with an equation that relates the observed chemical shifts to the formation constant. In both solvents, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+ > Zn2+ > Mn2+ > Li+. 相似文献
10.
The kinetics of photooxidation of pyruvate was investigated in presence of zinc oxide catalyst under illumination of visible light. The influence of different parameters such as concentrations of reactants, amount of catalyst and irradiation time was studied on the redox reaction under pseudo‐first order conditions. The results indicated that amount of catalyst, presence of electron accepter in solution and irradiation time was the key factors influencing the efficiency of photo‐oxidation of pyruvate to acetyl. 相似文献
11.
The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties. 相似文献
12.
The linear isopiestic relation has been used together with a well-known thermodynamic equation to establish a new predictive equation for freezing point depression. This equation can provide predictions for multicomponent solutions conforming to the linear isopiestic relation using only information on the corresponding binary subsystems. The predictive capability of the equation has been tested by comparing with the experimental data at 25°C reported in the literature and particularly those of Pathwardhan and Kumar. The systems used are NaCl—MgCl2—H2O, NaCl—BaCl2—H2O, NaCl—CaCl2—H2O, LiCl—NaCl—H2O, LiCl—KCl—H2O, LiCl—CsCl—H2O, NaCl—KCl—H2O, and NaBr—KBr—H2O. The predictions of the two equations agree well with the experimental data although our new equation is, in general, better. 相似文献
13.
Three-component reaction of an enolizable compound, such as acetophenone, methyl acetoacetate, 4-hydroxycoumarin, 2-naphthol, or 3-hydroxy-2-naphthoic acid; an aromatic aldehyde, and acetonitrile induced by phosphorus pentoxide and hexamethyldisiloxane leads to 2-acetylamino ketones, methyl 3-(acetylamino aryl methyl)-3-oxobutanoates, 3-(acetylamino aryl methyl)-4-hydroxycoumarins, 1-(acetylamino aryl methyl)-2-naphthols, or 4-(acetylamino aryl methyl)-3-hydroxy-2-naphthoic acids in excellent yields. 相似文献
14.
Vapour Pressure Investigations in the System Zn? Si? P Equilibrium pressures on the compounds SiP, Zn3P2, and ZnSiP2 were determined with a Bourdon-Manometer. Corresponding to the decomposition of the compounds the free reaction energies were calculated from the Kp data. Considering Cp-T functions it was possible to determine standard data of the heat of formation and the entropy of SiP, Zn3P2, and ZnSiP2. As a result of our investigations considerations of stability were carried out in the system Zn? Si? P. 相似文献
15.
Sampling surface snow on a large test field always leads to a spread of analyte concentration data which partly follows a Gaussian distribution and partly a rectangular one as can be observed from the analysis of literature data. The spread depends on the nonuniformity of the air–snow interface in the field and on the extent of reproducibility of all the procedures used from sampling to analysis. Consequently a sample relevant to a restricted surface might be poorly representative of the surrounding area. Contamination of the sample during the gathering and storing steps is assumed to be the main source of nonrandom results (outliers). Using various statistical tools we were able to evaluate which part of the spread was due to the snow surface nonuniformity in the case of many samples collected in the same test field. In the case of samples gathered in different geographical areas, the possibility of finding correlations among points is greatly enhanced when three or more analytes are considered for each sample. When the same correlation is found for some analytes and a variable tentatively tested, information can be gained about the source of chemical content of snow samples. The use of UV pretreatment of snow samples has been proven to cut down the interference of organics on the electrochemical process in DPASV, allowing one to obtain accurate and reproducible data. 相似文献
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In this work, polypyrrole films with ferrocenecarboxylic acid incorporated (PPy/FCA) were prepared on a glassy carbon (GC)
electrode in chloroform as an aprotic solvent with low dielectric constant, convenient for the preparation of the films by
a precipitation mechanism. The electrochemical behaviour of the PPy/FCA-coated GC electrode was studied by cyclic voltammetry
in aqueous solution with low pH. The results obtained show that the electrochemical response of FCA incorporated in polypyrrole
is consistent with a reversible surface oxidation. An obvious electrocatalytic effect of PPy/FCA on the oxidation of ascorbic
acid is observed in aqueous solution.
Received: 30 July 1998 / Accepted: 3 March 1999 相似文献
18.
A. A. Yakovleva 《Russian Journal of Electrochemistry》2000,36(12):1275-1282
Mechanisms of the formation and doping of polypyrrole films and their behavior in aqueous media are studied by voltammetry, chronoamperometry, and other methods combined with IR spectroscopy and the tracer technique. The last two methods reveal that pyrrole molecules in acid media form complexes with protons and anions, and that a strong interaction occurs in a polypyrrole film between links of polypyrrole chains and anions, leading to a change in their structure. The obtained data are used to propose a mechanism for the synthesis of polypyrrole films, which includes the discharge of a complex of protonated pyrrole with the anion yielding radical cations, which induce the growth and development of polypyrrole chains. It is stressed that the incorporation of anions into a film (doping) occurs in the course of its formation during the discharge and partial destruction of the pyrrole complexes with the anion. 相似文献
19.
Solvent‐Assisted Linker Exchange: An Alternative to the De Novo Synthesis of Unattainable Metal–Organic Frameworks 下载免费PDF全文
Olga Karagiaridi Dr. Wojciech Bury Dr. Joseph E. Mondloch Prof. Dr. Joseph T. Hupp Prof. Dr. Omar K. Farha 《Angewandte Chemie (International ed. in English)》2014,53(18):4530-4540
Metal‐organic frameworks (MOFs) have gained considerable attention as hybrid materials—in part because of a multitude of potential useful applications, ranging from gas separation to catalysis and light harvesting. Unfortunately, de novo synthesis of MOFs with desirable function–property combinations is not always reliable and may suffer from vagaries such as formation of undesirable topologies, low solubility of precursors, and loss of functionality of the sensitive network components. The recently discovered synthetic approach coined solvent‐assisted linker exchange (SALE) constitutes a simple to implement strategy for circumventing these setbacks; its use has already led to the generation of a variety of MOF materials previously unobtainable by direct synthesis methods. This Review provides a perspective of the achievements in MOF research that have been made possible with SALE and examines the studies that have facilitated the understanding and broadened the scope of use of this invaluable synthetic tool. 相似文献
20.
Egor I. Nagaev Ilya V. Baimler Alexey S. Baryshev Maxim E. Astashev Sergey V. Gudkov 《Molecules (Basel, Switzerland)》2022,27(19)
The influence of laser radiation of a typical surgical laser on the physicochemical properties of the Bovine Serum Albumin (BSA) protein was studied. It was established that the physicochemical characteristics of optical breakdown weakly depend on the concentration of protein molecules. At the same time, the patterns observed for an aqueous solution of BSA irradiated with a laser for different time periods were extremely similar to the classical ones. It was established that after exposure to laser radiation, the optical density of protein solutions increases. At the same time, the intensity of BSA fluorescence due to aromatic amino acid residues decreases insignificantly after exposure to laser radiation. In this case, the position of the excitation and emission maximum does not change, and the shape of the fluorescence spot on 3D maps also does not change significantly. On the Raman spectrum after exposure to laser radiation, a significant decrease in 1570 cm−1 was observed, which indicates the degradation of α-helices and, as a result, partial denaturation of BSA molecules. Partial denaturation did not significantly change the total area of protein molecules, since the refractive index of solutions did not change significantly. However, in BSA solutions, after exposure to laser radiation, the viscosity increased, and the pseudoplasticity of aqueous solutions decreased. In this case, there was no massive damage to the polypeptide chain; on the contrary, when exposed to optical breakdown, intense aggregation was observed, while aggregates with a size of 400 nm or more appeared in the solution. Thus, under the action of optical breakdown induced by laser radiation in a BSA solution, the processes of partial denaturation and aggregation prevail, aromatic amino acid residues are damaged to a lesser extent, and fragmentation of protein molecules is not observed. 相似文献