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1.
We report ab initio UMP2 calculations of the reaction of CN with HNCO using 6-311G(d,p) basis sets. The obtained results show that the reaction
has two product channels: HNCO+CN→HCN+NCO (1) and HNCO+CN→HNCN+CO (2). Channel (1) is a hydrogen abstraction reaction, which
is a concerted process. The calculated potential energy barrier is 20.80 kJ/mol at UMP2(full)/6-311G(d,p) level. In the range
of reaction temperature (1000-2100 K), the conventional transition theory rate constant for channel (1) ranges from 0.32×10−11 to 6.9×10−11cm3· mol−1· s−1, which is close to the experimental value. Channel (2) is a stepwise reaction involving an intermediate during the process
of reaction. The UMP2(full)/6-311G(d,p) potential energy barrier is 83.42 kJ/mol for the rate-controlling step, which is much
higher than that of channel (1). 相似文献
2.
M. N. Khimich V. A. Nadtochenko L. D. Popov A. S. Burlov V. L. Ivanov N. N. Denisov F. E. Gostev I. V. Shelaev O. M. Sarkisov B. M. Uzhinov 《High Energy Chemistry》2012,46(4):247-252
Dynamics of excited-state intramolecular proton transfer (ESIPT) in o-tosylaminobenzaldehyde has been studied by femtosecond absorption spectroscopy with a time resolution of 30 fs. The characteristic time of this process is ∼100 fs. Differential absorption rate curves exhibit oscillations that are consistent with theoretically predicted ESIPT-promoting vibrational modes. Efficient nonradiative deactivation with a rate constant of 6.25 × 1010 s−1 occurs in the excited product of proton transfer, with internal rotation followed by intersystem crossing being one of the feasible deactivation pathways. 相似文献
3.
4.
Parnajyoti Karmakar Subhasis Mallick Biplab K. Bera Arup Mandal Subala Mondal Sudip K. Mukhopadhyay Alak K. Ghosh 《Transition Metal Chemistry》2010,35(8):911-916
The kinetics of the interaction of glycine-l-leucine (Glyleu) with cis-[Pt(cis-dach)(OH2)2]2+ (dach = 1,2-diaminocyclohexane) has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH2)2]2+], [Glyleu] and temperature at pH 4.0, where the complex exists predominantly as the diaqua species and Glyleu as a zwitterion.
The substitution reaction shows two consecutive steps: the first is the ligand-assisted anation and the second is the chelation
step. The activation parameters for both the steps were evaluated using Eyring’s equation. The low ∆H1≠ (51.9 ± 2.8 kJmol−1) and large negative value of ∆S1≠ (−152 ± 8 JK−1mol−1) as well as ∆H2≠ (54.4 ± 1.7 kJmol−1) and ∆S2≠ (−162 ± 5 JK−1mol−1) indicate an associative mode of activation for both the aqua ligand substitution processes. 相似文献
5.
p-Phenylenediamine was oxidized with p-benzoquinone in the aqueous solutions of methanesulfonic acid (MSA). The conductivity of the products increased with increasing concentration of MSA from 1.5?×?10?12 S cm?1 in 0.1 M MSA up to 3.4?×?10?4 S cm?1 in 5 M MSA. The low-molecular-weight products are basically composed of one p-benzoquinone and two p-phenylenediamine molecules. Their molecular structure is discussed on the basis of mass, Fourier-transform infrared, Raman, NMR and electron paramagnetic resonance (EPR) spectroscopies. The formation of 2,5-di(p-phenylenediamine)-p-benzoquinone protonated with methanesulfonic acid best complies with the information provided by spectroscopic techniques. Its conversion to hydroquinone tautomer explains the formation of unpaired spins observed by EPR and their potential contribution to the conduction. 相似文献
6.
A. A. Druzhinin N. E. Kaurov S. A. Nemkov V. A. Ishutin 《Journal of Analytical Chemistry》2010,65(12):1242-1244
A chemiluminescence method was developed for determining o-chlorobenzylidenemalonic acid dinitrile (o-CBMA DN) in extracts. The method is based on chemiluminescence developed in a strong alkaline solution upon the interaction between
3-aminophthalic hydrazide (luminol) with the superoxide radical formed in the reaction of atmospheric oxygen activated by
hemin with the products of the alkaline hydrolysis of o-chlorobenzylidenemalonic acid dinitrile and with the products of their condensation with p-nitrobenzaldehyde. The luminescence intensity of luminol was proportional to the concentration of o-CBMA DN in the range 1 × 10−6−1 × 10−1 mg/mL. The determination limit for o-CBMA DN was (1 ± 0.3) × 10−6 mg/mL (p = 95%, n = 5, RSD = 29%) at 293 K. 相似文献
7.
A 66-kDa thermostable family 1 Glycosyl Hydrolase (GH1) enzyme with β-glucosidase and β-galactosidase activities was purified
to homogeneity from the seeds of Putranjiva roxburghii belonging to Euphorbiaceae family. N-terminal and partial internal amino acid sequences showed significant resemblance to plant GH1 enzymes. Kinetic
studies showed that enzyme hydrolyzed p-nitrophenyl β-d-glucopyranoside (pNP-Glc) with higher efficiency (K
cat/K
m = 2.27 × 104 M−1 s−1) as compared to p-nitrophenyl β-d-galactopyranoside (pNP-Gal; K
cat/K
m = 1.15 × 104 M−1 s−1). The optimum pH for β-galactosidase activity was 4.8 and 4.4 in citrate phosphate and acetate buffers respectively, while
for β-glucosidase it was 4.6 in both buffers. The activation energy was found to be 10.6 kcal/mol in the temperature range
30–65 °C. The enzyme showed maximum activity at 65 °C with half life of ~40 min and first-order rate constant of 0.0172 min−1. Far-UV CD spectra of enzyme exhibited α, β pattern at room temperature at pH 8.0. This thermostable enzyme with dual specificity
and higher catalytic efficiency can be utilized for different commercial applications. 相似文献
8.
Ping Zhao Mei Wang ShuPing Zhang SiChang Shao XiaoYu Sun SiDe Yao ShiLong Wang 《中国科学B辑(英文版)》2008,51(9):872-877
Due to the nontoxicity and efficient anti-cancer activity, more and more attention has been paid to N-glycoside compounds. Laser photolysis of N-(α-D-glucopyranoside) salicyloyl hydrazine (NGSH) has been performed for the first time. The research results show that NGSH has
high photosensitivity and is vulnerable to be photo-ionized via a monophotonic process with a quantum yield of 0.02, generating
NGSH+· and hydrated electrons. Under the aerobic condition of cells, the hydrated electrons are very easy to combine with oxygen
to generate 1O2 and O2
−, both of which are powerful oxidants that can kill the cancer cells. In addition, NGSH+· can be changed into neutral radicals by deprotonation with a pK
a value of 4.02 and its decay constant was determined to be 2.55×109dm3·mol−1·s−1. NGSH also can be oxidized by SO4
−· with a rate constant of 1.76×109 dm3·mol−1·s−1, which further confirms the results of photoionization. All of these results suggest that this new N-glycoside compound might be useful for cancer treatment.
The same contribution to the work
Supported by the National Natural Science Foundation of China (Grant Nos. 30570376 and 50673078) and Shanghai Project (Grant
Nos. 06JC14068 and 08ZZ21) 相似文献
9.
Yun Wang Jin-Zhu Song Qian Yang Zhi-Hua Liu Xiao-Mei Huang Yan Chen 《Applied biochemistry and biotechnology》2010,162(3):843-854
A gene encoding chitin deacetylase was cloned by polymerase chain reaction from Aspergillus nidulans. Sequencing result showed 40% homology to the corresponding gene from Colletotrichum lindemuthianum. The complete gene contains an open reading frame of 747 nucleotides encoding a sequence of 249 amino acid residues. The
chitin deacetylase gene was subcloned into a pET28a expression vector and expressed in Escherichia coli BL21 and then purified by metal affinity chromatography using a His-bind column. The purified chitin deacetylase demonstrated
an activity of 0.77 U ml−1 for the glycol chitin substrates, and its specific activity was 4.17 U mg−1 for it. The optimal temperature and pH of the purified enzyme were 50 °C and 8.0, respectively. When glycol chitin was used
as the substrate, K
m was 4.92 mg ml−1, and K
cat showed 6.25 s−1, thus the ratio of K
cat and K
m was 1.27 ml s−1 mg−1. The activity of chitin deacetylase was affected by a range of metal ions and ethylenediaminetetraacetic acid. 相似文献
10.
The kinetics of the oxidation of N-aminopiperidine with chloramine was studied at different temperatures, with variable concentrations
of the two reactants and at a pH ranging between 12 and 13.5. The reaction showed to be involving two steps: the first corresponded
to the formation of a diazene intermediate, the second to the evolution of this intermediate into numerous compounds within
a complex reactional chain. The rate law of the first step was determined by the Ostwald method and found to be first order
with respect to each reactant. The rate constant was determined at pH 12.89 and T = 255°C: k
2 = 1.15 × 105 exp(−39/RT) l mol−1 s−1 (E
2 in kJ/mol). With decreasing pH value, the first exhibited acid catalysis phenomena, and diazene was converted into azopiperidine
particularly faster. This created overlapping UV-absorptions between chloramine and azopiperidine, also observed in HPLC.
GC/MS analyses were used to identify some of the numerous by-products formed. Their proportions are dependent of both pH and
the reactants’ concentrations ratio. A reaction mechanism taking this relationship into account was suggested.
Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 112–119.
The article is published in the original. 相似文献
11.
Shenghui Zhang 《Russian Journal of Electrochemistry》2011,47(11):1257-1261
A mesoporous TiO2 (meso-TiO2) was synthesized, and used to prepare modified carbon paste electrode (CPE). The electrochemical sensing properties were
characterized using K3[Fe(CN)6], showing that meso-TiO2 modified CPE possesses larger surface area and higher electron transfer rate. The electrochemical behavior of p-cresol was investigated. At the meso-TiO2 modified CPE, the oxidation peak current of p-cresol remarkably increases, and the oxidation peak potential shifts negatively, suggesting that meso- TiO2 exhibits highly efficient catalytic activity to the oxidation of p-cresol. Based on this, a sensitive, rapid and convenient electrochemical method was developed for the detection of p-cresol. The linear range is from 1.5 × 10−7 and 2.0 × 10−5 mol l−1, and the limit of detection is as low as 8.0 × 10−8 mol l−1. Finally, the new method was successfully used to determine p-cresol in water samples. 相似文献
12.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2008,93(2):423-428
Heat capacity C
p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these measurements. At 298.15 K the values of heat capacity, C
p; entropy, S
m0(T)-S
m0(0); difference in the enthalpy, H
m0(T)-H
m0(0), are equal, respectively, to 144.6±0.3 J K−1 mol−1, 169.0±0.4 J K−1 mol−1 and 24960±50 J mol−1. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial
increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample. 相似文献
13.
S. X. Xiao J. J. Zhang X. Li L. J. Ye H. W. Gu N. Ren 《Journal of Thermal Analysis and Calorimetry》2010,102(2):813-817
A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)3phen]2·4H2O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H2O(s)], [6m-HNBA(s)], [2DyCl3·6H2O(s)], and [Dy(m-NBA)3phen]2·4H2O(s) in the calorimetric solvent (VDMSO:VMeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be
\Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H2O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol−1,
\Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol−1,
\Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl3·6H2O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol−1, and
\Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)3phen]2·4H2O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol−1, respectively. The enthalpy change of the reaction was determined to be
\Updelta\textr H\textmq = 3 6 9. 4 9 ±0. 5 6 \textkJ·\textmol - 1 . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of
formation of [Dy(m-NBA)3phen]2·4H2O(s) was estimated to be
\Updelta\textf H\textmq \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)3phen]2·4H2O(s), 298.15 K] = −5525 ± 6 kJ·mol−1. 相似文献
14.
Glucose 2-oxidase (pyranose oxidase, pyranose:oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor catalyses the oxidation of d-glucose at carbon 2 in the presence of molecular O2 producing d-glucosone (2-keto-glucose and d-arabino-2-hexosulose) and H2O2. It was used to convert d-glucose into d-glucosone at moderate pressures (i.e. up to 150 bar) with compressed air in a modified commercial batch reactor. Several
parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, [enzyme], [glucose], pH, temperature,
nature of fluid and the presence of catalase. Glucose 2-oxidase was purified by immobilized metal affinity chromatography
on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. The rate of bioconversion of d-glucose increased with the pressure since an increase in the pressure with compressed air resulted in higher rates of conversion.
On the other hand, the presence of catalase increased the rate of reaction which strongly suggests that H2O2 acted as inhibitor for this reaction. The rate of bioconversion of d-glucose by glucose 2-oxidase in the presence of either nitrogen or supercritical CO2 at 110 bar was very low compared with the use of compressed air at the same pressure. The optimum temperature (55°C) and
pH (5.0) of d-glucose bioconversion as well as kinetic parameters for this enzyme were determined under moderate pressure. The activation
energy (E
a) was 32.08 kJ mol−1 and kinetic parameters (V
max, K
m, K
cat and K
cat/K
m) for this bioconversion were 8.8 U mg−1 protein, 2.95 mM, 30.81 s−1 and 10,444.06 s−1 M−1, respectively. The biomass of C. versicolor as well as the cell-free extract containing glucose 2-oxidase activity were also useful for bioconversion of d-glucose at moderate pressures. The enzyme was apparently stable at moderate pressures since such pressures did not affect
significantly the enzyme activity. 相似文献
15.
Kinetics of aqua ligand substitution from cis-[Ru(bpy)2(H2O)2]2+ by three vicinal dioximes, namely dimethylglyoxime (L1H), 1,2-cyclohexane dionedioxime (L2H) and α-furil dioxime (L3H) have been studied spectrophotometrically in the 45–60 °C temperature range. The rate constants increase with increasing
dioxime concentration and approach a limiting condition. We propose the following rate law for the reaction in the 3.5–5.5
pH range: where k
2 is the interchange rate constant from outer sphere to inner sphere complex and K
E is the outer sphere association equilibrium constant. Activation parameters were calculated from the Eyring plots for all
three systems: ΔH
≠ = 59.2 ± 8.8, 63.1 ± 6.8 and 69.7 ± 8.5 kJ mol−1, ΔS
≠ = −122 ± 27, −117 ± 21 and −99 ± 26 J K−1 mol−1 for L1H, L2H and L3H, respectively. An associative interchange mechanism is proposed for the substitution process. Thermodynamic parameters calculated
from the temperature dependence of the outer sphere association equilibrium constants give negative ΔG
0 values for all the systems studied at all the temperatures (ΔH
0 = 30.05 ± 2.5, 18.9 ± 1.1 and 11.8 ± 0.2 kJ mol−1; ΔS
0 = 123 ± 8, 94 ± 3 and 74 ± 1 J K−1 mol−1 for L1H, L2H and L3H, respectively), which also support our proposition. 相似文献
16.
P. P. Levin P. V. Aboltin T. F. Shevchenko G. R. Kalamkarov 《High Energy Chemistry》2010,44(6):520-523
The kinetics of quenching of the all-trans-retinal triplet state by air oxygen in aqueous solutions of bovine serum albumin and in a cardiolipin liposome suspension
was investigated by nanosecond laser photolysis. It was established that the quenching reaction rate constant in the albumin
solution (1.8 × 108 l mol−1 s−1) was an order of magnitude less than in liposomes (3.1 × 109 l mol−1 s−1). These constants were 5.0 × 109 and 1.1 × 109 l mol−1 s−1 in methanol and aqueous solutions containing 10 vol % methanol, respectively. The effect of hindered oxygen access to the
Lall-trans-retinal attached to albumin is discussed in terms of its influence on the photooxidation processes in the retina. 相似文献
17.
In neutral zinc the 4p
2 configuration lies above the 3d
104s ionization limit and its levels become perturbers in the continuum. Lines have been identified in the Zn I spectrum for the
multiplet, whereas no lines have been found for transitions to 4p
2 1
D or 1
S. In this paper, cross sections for photoionization from 4s4p levels are reported that reveal the positions and widths of the 4p
2 resonances. Calculations were performed using the multiconfiguration Hartree-Fock (MCHF) and B-spline R-matrix (BSR) method. Results from Breit–Pauli calculations that ignore the background continua are also presented. Included
in the latter are energies for the levels and transition data (transition energies, line strengths, f-values, and A-rates) for all E1 transitions between these
levels. Transition energies and the agreement in the length and velocity values, particularly for allowed transitions, indicate
the accuracy of the computational model. Line widths are compared with other estimates.
Contribution to the Serafin Fraga Memorial Issue. 相似文献
18.
Wei Zhao Aisheng Xiong Xiaoyan Fu Feng Gao Yongsheng Tian Rihe Peng 《Applied biochemistry and biotechnology》2010,162(8):2157-2165
To obtain a high level expression of phytase with favorable characteristics, a codon-optimized phytase gene from Citrobacter freundii was synthesized and transferred into Pichia pastoris. Small-scale expression experiments and activity assays were used to screen positive colonies. After purified by Ni2+–NTA agarose affinity column, the characterizations of the recombinant phytase were determined. The recombinant phytase (r-phyC)
had two distinct pH optima at 2.5 and 4.5 and an optimal temperature at 50 °C. It retained more than 80% activity after being
incubated under various buffer (pH 1.5–8.0) at 37 °C for 1 h. The specific activity, Km, and Vmax values of r-phyC for sodium phytate were 2,072 ± 18 U mg−1, 0.52 ± 0.04 mM, and 2,380 ± 84 U mg−1 min−1, respectively. The enzyme activity was significantly improved by 1 mM of K+, Ca2+, and Mg2+. These characteristics contribute to its potential application in feed industry. 相似文献
19.
V. D. Kiselev E. A. Kashaeva L. N. Potapova A. I. Konovalov 《Russian Chemical Bulletin》2007,56(3):494-498
The effect of hydrostatic pressure below 1000 kg cm−2 on the rate of reactions of o-and p-nitrophenylsulfenyl chlorides with styrene and cyclohexene was studied. The activation and reaction volumes (cm3 mol−1) for the reactions of o-nitrophenylsulfenyl chloride with styrene in acetonitrile (−23.1 and −23.6), 1,2-dichloroethane (−29.2 and −24.7), chlorobenzene
(no, −20.2), and anisole (−25.1 and −21.2) and for the reaction of p-nitrophenylsulfenyl chloride with styrene in carbon tetrachloride (−39.5±1.5 and −22.0) were determined. In carbon tetrachloride
the activation volumes for the reactions of cyclohexene with o-and p-nitrophenylsulfenyl chlorides (−37.7±2.0 and −40.9±1.2 cm3 mol−1, respectively) are almost the same and coincide with the data for the reactions with styrene. The considerable decrease in
the volume of the transition state in the nonpolar solvent is considered as a consequence of the enhanced electrostriction
of carbon tetrachloride in the solvate sphere of the transition state of the reaction, which excludes the nonpolar transition
state of the sulfuran type.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 477–480, March, 2007. 相似文献
20.
The influence of ethanol on fermentation by Pachysolen tannophilus was studied. When xylose utilization rate was 80%, ethanol concentration began to decline. Fermentation of P. tannophilus was affected by ethanol addition in the beginning of fermentation; average xylose consumption rate was 0.065 g·l−1·h−1, and maximum specific growth rate was 0.07 h−1 at 28 g·l−1 ethanol, comparing with the average xylose consumption rate of 0.38 g·l−1·h−1 and maximum specific growth rate of 0.14 h−1 in fermentation with no ethanol addition; P. tannophilus stopped growth at 40 g·l−1 ethanol. When the initial ethanol concentration was 30 g·l−1, the addition of glucose in xylose media made the growth of P. tannophilus better, and the most favorable glucose concentration was 15 g·l−1 with the highest biomass of 1.51 g·l−1 as compared with that of 0.95 g·l−1 in pure xylose media. 相似文献