共查询到20条相似文献,搜索用时 78 毫秒
1.
Jia Wei Mao Hong Zhou Yun Feng Chen Gong Zhen Cheng Zhi Quan Pan 《Transition Metal Chemistry》2012,37(4):385-391
An asymmetrical bis-pyridine pendant-armed macrocyclic heterobinuclear complex, [ZnNiL](ClO4)2·CH3CN (H2L was derived from the condensation between 3,3′-((ethane-1,2-diylbis((pyridin-2-ylmethyl)azanediyl))bis(methylene))bis(2-hydroxy-5-methylbenzaldehyde)
and 1.3-diaminopropane), has been synthesized and characterized by physico-chemical and spectroscopic methods. The asymmetric
unit contains two complete macrocyclic complexes that are nevertheless quite similar to one another. The Zn–Ni separations,
bridged by the two phenoxides, are 3.107 and 3.141 Ǻ, respectively. The phosphate hydrolysis catalyzed by the complex was
investigated using bis(4-nitrophenyl)phosphate (BNPP) as the substrate. The catalytic rate constant (k
cat) is 1.64 × 10−3 s−1 at pH 7.4 and 25 °C, which is 108-fold higher than that of the corresponding uncatalyzed reaction. The interaction between the complex and calf thymus (CT)
DNA was investigated by UV–vis absorption, viscosity experiments, and cyclic voltammetry. The complex shows good binding propensity
to calf thymus DNA via intercalation with a binding constant of 5 × 104 M−1. The agarose gel electrophoresis studies show that the complex has a concentration-dependent DNA cleavage activity. 相似文献
2.
Jian-Zhang Li Fa-Mei Feng Bin Xu Wei-Dong Jiang Sheng-Ying Qin 《Transition Metal Chemistry》2008,33(5):655-660
Abstract Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL1
2 Cl, CoL1
2) or morpholino pendants (MnL2
2Cl, CoL2
2) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of
complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have been also examined. The rate increases
with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with
the crown-free analogues MnL2
2Cl and CoL2
2, the crowned Schiff base complexes (MnL1
2Cl, CoL1
2) exhibit higher catalytic activity. The pseudo-first-order-rate (
k
obs
) for the PNPP hydrolysis catalyzed by the complex MnL1
2Cl containing benzo-10-aza-crown ether is 1.06 × 103 times that of spontaneous hydrolysis of PNPP at pH = 7.00, 25 °C, [S] = 2.0 × 10−4 mol dm−3.
Graphical Abstract
Studies on
p-nitrophenyl
picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants
Jian-zhang Li*, Fa-mei Feng, Bin Xu,Wei-dong Jiang
Key Laboratory of Green and Technology, Department of Chemistry, Sichuan University of Science & Engineering, Zigong, Sichuan,
643000, P.R. China
Sheng-ying Qin
Department of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, P.R. China
Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL1
2Cl, CoL1
2) or morpholino pendants (MnL2
2Cl, CoL2
2) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with PNPP. A kinetic
model of PNPP cleavage catalyzed by these complexes is proposed. Compared with the crown-free analogy MnL2
2Cl and CoL2
2, the crowned Schiff base complexes (MnL1
2Cl, CoL1
2) exhibit higher catalytic activity.
相似文献
3.
Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives
of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10−4 l mol−1 s−1. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of
sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate
constant of 0.005 s−1. 相似文献
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.
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
6.
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
7.
Javed MR Rashid MH Nadeem H Riaz M Perveen R 《Applied biochemistry and biotechnology》2009,157(3):483-497
Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg−1 protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein
liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol−1 at optimum temperature (55 °C), and its temperature quotient (Q
10) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V
max for CMC hydrolysis was 854 U mg−1 protein and K
m was 20 mg CMC ml−1. The turnover (k
cat) was 356 s−1. The pK
a1 and pK
a2 of ionisable groups of active site controlling V
max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol−1, ΔG* = 64.57 kJ mol−1 and ΔS* = −195.05 J mol−1 K−1, respectively. Activation energy for irreversible inactivation ‘E
a(d)’ of the endoglucanase was 378 kJ mol−1, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol−1, 111.36 kJ mol−1 and 833.06 J mol−1 K−1, respectively. 相似文献
8.
Two multidentate ligands: N,N′-di-(propionic acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L1) and N,N′-di-(3′-methylbutyric acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L2) were synthesized. The hydrolytic kinetics of
p-nitrophenyl phosphate (NPP) catalyzed by complexes of L1 and L2 with La(III), Gd(III) have been studied. Both LnL and LnLH−1 have been examined as catalysis for the hydrolysis of NPP in aqueous solution at 298 K, I = 0.10 mol dm−3 KNO3 at the pH range 7.4–9.1, respectively. Kinetic studies show that both LnL and LnLH−1 have catalytic activity, but LnLH−1 is more active than LnL in the hydrolysis of NPP. The second-order rate constants for the hydrolysis of NPP are kGdL1H−1 = 0.01399 mol−1 dm3 s−1, kGdL1 = 0.0000110 mol−1 dm3 s−1 for complexes GdL1H−1 and GdL1, respectively. A new mechanism was proposed for the hydrolysis of NPP catalyzed by LnL and LnLH−1. 相似文献
9.
A. I. Lytkin N. V. Chernyavskaya V. E. Litvinenko 《Russian Journal of Coordination Chemistry》2011,37(12):893-896
The enthalpies of complexation between N,N-bis(carboxymethyl)aspartic acid (H4Y) and the Pb2+ ion at 298.15 K were determined from calorimetric data for a wide range of the ionic strengths (KNO3). The thermodynamic characteristics ΔH, ΔG, and ΔS, of formation of the complexes PbHY− and PbY2− were calculated for zero and fixed ionic strengths. The results obtained were interpreted. 相似文献
10.
M. A. Grin R. A. Titeev O. M. Bakieva D. I. Brittal I. A. Lobanova I. B. Sivaev V. I. Bregadze A. F. Mironov 《Russian Chemical Bulletin》2008,57(10):2230-2232
A conjugate of the bacteriochlorophyll a derivative with the cobalt bis(dicarbollide) anion [3,3′-Co(1,2-C2B9H11)2]− was synthesized. 相似文献
11.
Mohammad M. Fares Adeeb S. El-faqeeh Hasan Ghanem Mohammad E. Osman Elfatih A. Hassan 《Journal of Thermal Analysis and Calorimetry》2010,99(2):659-666
The synthesis, characterization, and hydrogel properties of starch-g-(tert-butylacrylate) and starch-g-(n-butylacrylate) copolymers were studied. The optimum conditions for the grafting process of tert-butylacrylate into 1.0 g of starch were as follows: [tert-butylacrylate] = 0.04 mol/L, [CAN] = 9.0 × 10−4 mol/L, temperature = 20 °C in 100 mL solution, whereas the results using n-butylacrylate monomer were as follows: [n-butylacrylate] = 0.04 mol/L, [CAN] = 4.0 × 10−3 mol/L, temperature = 30 °C in 100 mL solution. The grafting evidences of monomers into starch were done through TG and its
derivative DTG for thermal changes and mass losses, scanning electron microscope (SEM) for morphological changes, powder X-ray
for crystallinity measurements and FTIR for functional group changes. Acid hydrolysis method was used efficiently to allow
the calculations of the viscosity average molecular weight (M
v) of the grafted chains on starch and consequently the real percent of grafting efficiency (i.e. %GY). The capability of starch-g-(n-BAC) hydrogel to absorb water were found 10 times more than starch-g-(tert-BAC) hydrogel, which were clarified through the X-ray and SEM results. 相似文献
12.
M. S. Klenov A. M. Churakov O. V. Anikin Yu. A. Strelenko V. A. Tartakovsky 《Russian Chemical Bulletin》2009,58(10):2047-2057
Salts of N-nitro-O-(4-nitrophenyl)hydroxylamine were synthesized by a new method of oxidative nitration, involving the reaction of O-(4-nitrophenyl)hydroxylamine with KNO2 or NaNO2 in the presence of PhI(OAc)2 or PhIO as oxidants. When using Na15NO2, the samples containing the nitro group labeled with the 15N isotope were obtained. Acidification of the appropriate salt gave N-nitro-O-(4-nitrophenyl)hydroxylamine. It is the first N-nitrohydroxylamine isolated in the H-form. Its thermal stability was investigated and the probable mechanism of decomposition
was suggested. From a comparison of the 14N and 15N NMR spectra of N-nitro-O-(4-nitrophenyl)hydroxylamine with those of its O- and N-methylated derivatives, its equilibrium with the aci-form (N=NOOH) was inferred. 相似文献
13.
Summary. The regioselective reaction of N1-benzyl-N2-(4-nitrophenyl)ethanediamide with dialkyl acetylenedicarboxylates or alkyl propiolates in the presence of triphenylphosphine
leads to dialkyl 4-benzylamino-1-(4-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylates or alkyl 4-benzylamino-1-(4-nitrophenyl)-2-oxo-5-pyrrolidinecarboxylates in good yields. 相似文献
14.
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
15.
16.
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
17.
Sasithorn Uttatree Pakorn Winayanuwattikun Jittima Charoenpanich 《Applied biochemistry and biotechnology》2010,162(5):1362-1376
The benzene tolerant Acinetobacter baylyi isolated from marine sludge in Angsila, Thailand could constitutively secrete lipolytic enzymes. The enzyme was successfully
purified 21.89-fold to homogeneity by ammonium sulfate precipitation and gel-permeable column chromatography with a relative
molecular mass as 30 kDa. The enzyme expressed maximum activity at 60°C and pH 8.0 with p-nitrophenyl palmitate as a substrate and found to be stable in pH and temperature ranging from 6.0-9.0 to 60-80°C, respectively.
A study on solvent stability revealed that the enzyme was highly resisted to many organic solvents especially benzene and
isoamyl alcohol, but 40% inhibited by decane, hexane, acetonitrile, and short-chain alcohols. Lipase activity was completely
inhibited in the presence of Fe2+, Mn2+, EDTA, SDS, and Triton X-100 while it was suffered detrimentally by Tween 80. The activity was enhanced by phenylmethylsulfonyl
fluoride (PMSF), Na+, and Mg2+ and no significant effect was found in the presence of Ca2+ and Li+. Half of an activity was retained by Ba2+, Ag+, Hg+, Ni2+, Zn2+, and DTT. The enzyme could hydrolyze a wide range of p-nitrophenyl esters, but preferentially medium length acyl chains (C8-C12). Among natural oils and fats, the enzyme 11-folds favorably catalyzed the hydrolysis of rice bran oil, corn oil, sesame
oil, and coconut oil in comparison to palm oil. Moreover, the transesterification activity of palm oil to fatty acid methyl
esters (FAMEs) revealed 31.64 ± 1.58% after 48 h. The characteristics of novel A. baylyi lipase, as high temperature stability, organic solvent tolerance, and transesterification capacity from palm oil to FAMEs,
indicate that it could be a vigorous biocatalyzer in the prospective fields as bioenergy industry or even in organic synthesis
and pharmaceutical industry. 相似文献
18.
19.
Jungang Gao X. Zhang L. Huo H. Zhao 《Journal of Thermal Analysis and Calorimetry》2010,100(1):225-232
The curing kinetics of a bi-component system about o-cresol-formaldehyde epoxy resin (o-CFER) modified by liquid crystalline p-phenylene di[4-(2,3-epoxypropyl) benzoate] (p-PEPB), with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent, were studied by non-isothermal differential
scanning calorimetry (DSC) method. The relationship between apparent activation energy E
a and the conversion α was obtained by the isoconversional method of Ozawa. The reaction molecular mechanism was proposed. The results show that
the values of E
a in the initial stage are higher than other time, and E
a tend to decrease slightly with the reaction processing. There is a phase separation in the cure process with LC phase formation.
These curing reactions can be described by the Šesták–Berggren (S–B) equation, the kinetic equation of cure reaction as follows:
\frac\textda\textdt = Aexp( - \fracE\texta RT )am ( 1 - a )n {\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = A\exp \left( { - {\frac{{E_{\text{a}} }}{RT}}} \right)\alpha^{m} \left( {1 - a} \right)^{n} . 相似文献
20.
Two long-chain multidentate ligands: 2,9-di-(n-2′,5′,8′-triazanonyl)-1,10-phenanthroline (L1) and 2,9-di-(n-4′,7′,10′-triazaundecyl)-1,10-phenanthroline (L2) were synthesized. The hydrolytic kinetics of p-nitrophenyl phosphate (NPP) catalyzed by complexes of L1 and L2 with La(III) and Gd(III) have been studied in aqueous solution at 298 K, I = 0.10 mol · dm−3 KNO3 at pH 7.5–9.1, respectively. The study shows that the catalytic effect of GdL1 was the best in the four complexes for hydrolysis
of NPP. Its kLnLH−1, k
LnL and pK
a are 0.0127 mol−1 dm3 s−1, 0.000022 mol−1 dm3 s−1 and 8.90, respectively. This paper expounds the result from the structure of the ligands and the properties of the metal
ions, and deduces the catalysis mechanism. 相似文献