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1.
Kevin Hing-Nin Poon Yu-Ling Cheng 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):211-222
Quartz crystal microbalance (QCM) was used to study the self-assembly of per-6-thio-β-cyclodextrin (t7-βCD) on gold surfaces, and the subsequent inclusion interactions of immobilized βCD with adamantane-poly(ethylene glycol)
(5,000 MW, AD-PEG), 1-adamantanecarboxylic acid (AD-C) and 1-adamantylamine (AD-A). From a 50 μM solution of t7-βCD in 60:40 DMSO:H2O, a t7-βCD layer was formed on gold with surface density of 71.7 ± 2.7 pmol/cm2, corresponding to 80 ± 3% of close-packed monolayer coverage. Gold sensors with immobilized t7-βCD were then exposed alternately to six different concentrations of AD-PEG, 500 μM AD-C or 500 μM AD-A aqueous solutions
for association, and water for dissociation. Association of AD-PEG conformed to a Langmuir isotherm, with a best fit equilibrium
constant K = 125,000 ± 18,000 M−1. For AD-C and AD-A, association (k
a
) and dissociation (k
d
) rate constants were extracted from kinetic profiles by fitting to the Langmuir model, and equilibrium constants were calculated.
The parameters for AD-C were found to be: k
a
= 100 ± 5 M−1 s−1, k
d
= 110 (±18) × 10−4 s−1, and K = 9,400 ± 1,700 M−1. For AD-A, k
a
= 58 ± 6 M−1 s−1, k
d
= 154 (±7) × 10−4 s−1, and K = 3,800 ± 400 M−1. The results demonstrate the utility of QCM as a tool for studying small molecule surface adsorption and guest–host interactions
on surfaces. More specifically, the kinetic and thermodynamic data of AD-C, AD-A, and AD-PEG inclusion with immobilized t7-βCD form a basis for further surface association studies of AD-X conjugates to advance surface sensory and coupling applications. 相似文献
2.
Maria das Graças Nunes Matos Vivian Gouveia Diniz Cesar Augusto Moraes de Abreu Augusto Knoechelmann Valdinete Lins da Silva 《Adsorption》2009,15(1):75-80
Heavy metals can be removed from effluents and recovered using physico-chemical mechanisms as biosorption processes. In this
work “Arribada” seaweed biomass was employed to assess its biosorptive capacity for the chromium (Cr3+) and lead (Pb2+) cations that usually are present in waste waters of plating industries. Equilibrium and kinetic experiments were conducted
in a mixed reactor on a batch basis. Biosorption equilibrium and fluid-solid mass transfer constants data were analyzed through
the concept of ion exchange sorption isotherm. The respective equilibrium exchange constants (K
eqCr=173.42, K
eqPb=58.86) and volumetric mass transfer coefficients ((k
mCr
a)′=1.13×10−3 s−1, (k
mPb
a)′=0.89×10−3 s−1) were employed for the dynamic analysis of Cr and Pb sorption in a fixed-bed flow-through sorption column. The breakthrough
curves obtained for both metals were compared with the predicted values by the heterogeneous model (K
eqCr=171.29, K
eqPb=60.14; k
mCr
a=7.81×10−2 s−1, k
mPb
a=2.43×10−2 s−1), taking into account the mass transfer process. The results suggest that these algae may be employed in a metal removal/recovery
process at low cost.
An erratum to this article can be found at 相似文献
3.
Hossein Amani Mohammad Reza Mehrnia Mohammad Hossein Sarrafzadeh Manouchehr Haghighi Mohammad Reza Soudi 《Applied biochemistry and biotechnology》2010,162(2):510-523
There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology
of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector
was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y
p/x), biosurfactant on sucrose (Y
p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g−1, 0.18 g g−1, and 0.03 g l−1 h−1, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y
x/s, Y
p/x, Y
p/s, and Y of 0.42 g g−1, 0.595 g g−1, 0.25 g g−1, and 0.057 g l−1 h−1, respectively. The biosurfactant maximum production, 2.5 g l−1, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient
(K
L
a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s−1, respectively. Comparison of K
L
a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with
K
L
a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water
flooding in the sand pack. 相似文献
4.
The surface of multi-purpose cellulosic office paper has been analysed by inverse gas chromatography (IGC). The parameters determined were the dispersive component of the surface free energy, the enthalpy of adsorption and the entropy of adsorption of polar and apolar probes, the Lewis acidity constant, K
a, and the Lewis basicity constant, K
b. It can be concluded that the dispersive component of the surface free energy, s
d decreases with temperature, in the range 50–90°C. The temperature coefficient of s
d, ds
d/dT, is –0.35 mJm –2K–1. The values of K
a and K
b were determined to be 0.11±0.011 and 0.94±0.211, respectively. The predominant surface basicity agrees with expectation, bearing in mind the presence of calcium carbonate, and of a styrene-acrylic copolymer, in the surface sizing formulation. It is thought that during the drying stages following the surface sizing treatment, the starch used as the binder migrates to the interior of the surface sizing layer and then to the paper bulk itself. This migration contributes to a decrease in the hydrophilicity of the surface, and also results in the surface showing only slight Lewis. 相似文献
5.
Inverse gas chromatography is used to study the surface properties of the untreated and chemically treated kaolinite samples.
Changes in the enthalpy of adsorption for a variety of probes and in the surface energy of clays are measured and the effect
of modification of the natural clay after chemical treatment with Na2CO3 is determined. The surface energy of the natural clay increased by the modification due to an increase in the surface area.
It can be concluded that the dispersive component of surface free energy, γ
s
d
, decreases with temperature in the 200–275°C temperature range for both samples. Temperature coefficients of γ
s
d
for untreated and modified kaolinites are −0.1185 and −0.3966 mJ/(m2 °C) with the correlation coefficients (R
2) of 0.8479 and 0.965, respectively. From the retention data for polar probes at infinite dilution, information on the accessibility
of surface sites to the probes and on the acid-base character of the surface is obtained. The specific free energy of adsorption,
the specific enthalpy of adsorption (ΔH
sp), and the specific entropy of adsorption of polar probes on initial and modified kaolinites are determined. The ΔH
sp values correlated with the donor numbers and modified acceptor numbers of the probes to quantify the acidity (K
A) and basicity (K
D) parameters of clay surfaces. The values of K
A and K
D for initial and modified kaolinites are determined to be 0.1202 and 0.2803; 0.0130 and 0.0408 with the correlation coefficients
of −0.9805 and −0.9782, respectively. The unmodified clay sample indicated a more acidic character, while the modified clay
sample conferred a largely basic character. Consequently, the predominant surface basicity of the modified kaolinite agrees
with expectation, bearing in mind the treatment with Na2CO3, taking into consideration that such a modification contributes to a decrease in the hydrophilicity of the surface and also
results in the surface showing only weak Lewis acidity.
The text was submitted by the authors in English. 相似文献
6.
A model was proposed to calculate some thermodynamic parameters for the acid dissolution process of a bentonite containing
a calcium-rich smectite as clay mineral along with quartz, opal and feldspar as impurities. The bentonite sample was treated
with H2SO4 by applying dry method in the temperature range 50–150°C for 24 h. The acid content in the dry bentonite-sulphuric acid mixture
was 45 mass%. The total content (x) of Al2O3, Fe2O3 and MgO remained in the undissolved sample after treatment was taken as an equilibrium parameter. An apparent equilibrium
constant, K
a, was calculated for each temperature by assuming K
a=(x
m−x)/x where x
m is the total oxide content of the natural bentonite. Also, an apparent change in Gibbs free energy, ΔG
ao, was calculated for each temperature by using the K
a value. The graphs of lnK
a
vs. 1/T and ΔG
ao
vs. T were drawn and then the real change in both the enthalpy, ΔH
o and the entropy, ΔS
o, values were calculated from the slopes of the straight lines, respectively. Inversely, real ΔG
o and K values were calculated from the real ΔH
o and ΔS
o values through ΔG
o = −RT ln K = ΔH
o − TΔS
o equation. The best ΔH
o and ΔS
o fittings to this relation were found to be 65687 J mol−1 and 164 J mol−1K−1, respectively. 相似文献
7.
The regression diagnostics algorithm REGDIA in S-Plus is introduced to examine the accuracy of pK
a predicted with four programs: PALLAS, MARVIN, PERRIN and SYBYL. On basis of a statistical analysis of residuals, outlier
diagnostics are proposed. Residual analysis of the ADSTAT program is based on examining goodness-of-fit via graphical diagnostics
of 15 exploratory data analysis plots, such as bar plots, box-and-whisker plots, dot plots, midsum plots, symmetry plots,
kurtosis plots, differential quantile plots, quantile-box plots, frequency polygons, histograms, quantile plots, quantile-quantile
plots, rankit plots, scatter plots, and autocorrelation plots. Outliers in pK
a relate to molecules which are poorly characterized by the considered pK
a program. Of the seven most efficient diagnostic plots (the Williams graph, Graph of predicted residuals, Pregibon graph,
Gray L–R graph, Index graph of Atkinson measure, Index graph of diagonal elements of the hat matrix and Rankit Q–Q graph of
jackknife residuals) the Williams graph was selected to give the most reliable detection of outliers. The six statistical
characteristics, Fexp,R2,RP2,MEP,AIC{F_{\rm exp},R^{2},R_{\rm P}^{2},{\it MEP},{\it AIC}}, and s in pK
a units, successfully examine the specimen of 25 acids and bases of a Perrin’s data set classifying four pK
a prediction algorithms. The highest values Fexp,R2,RP2{F_{\rm exp},R^{2},R_{\rm P}^{2}} and the lowest value of MEP and s and the most negative AIC have been found for PERRIN algorithm of pK
a prediction so this algorithm achieves the best predictive power and the most accurate results. The proposed accuracy test
of the REGDIA program can also be extended to test other predicted values, as log P, log D, aqueous solubility or some physicochemical properties. 相似文献
8.
H. X. Ma B. Yan Z. N. Li J. R. Song R. Z. Hu 《Journal of Thermal Analysis and Calorimetry》2009,95(2):437-444
The title compound 3,3-dinitroazetidinium (DNAZ) 3,5-dinitrosalicylate (3,5-DNSA) was prepared and the crystal structure has
been determined by a four-circle X-ray diffractometer. The thermal behavior of the title compound was studied under a non-isothermal
condition by DSC and TG/DTG techniques. The kinetic parameters were obtained from analysis of the TG curves by Kissinger method,
Ozawa method, the differential method and the integral method. The kinetic model function in differential form and the value
of E
a and A of the decomposition reaction of the title compound are f(α)=4α3/4, 130.83 kJ mol−1 and 1013.80s−1, respectively. The critical temperature of thermal explosion of the title compound is 147.55 °C. The values of ΔS
≠, ΔH
≠ and ΔG
≠ of this reaction are −1.35 J mol−1 K−1, 122.42 and 122.97 kJ mol−1, respectively. The specific heat capacity of the title compound was determined with a continuous C
p mode of mircocalorimeter. Using the relationship between C
p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic
time-to-explosion) was obtained. 相似文献
9.
10.
Thermal Decomposition of Some Chemical Compounds Used As Food Preservatives and Kinetic Parameters of This Process 总被引:1,自引:0,他引:1
Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate,
sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained,
the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated
from TG curves ranged from 28.9% for sodium formate to 77.8% for sodium nitrate(V), while sodium sulphate showed a mass increment
of 5.6%. Kinetic parameters such as activation energy (E
a ), frequency factor (A ) and reaction order (n ) were calculated from TG, DTG and T curves. Sodium formate shows the highest values of E
a and A which amount to 171.7 kJ mol–1 and 5.8⋅1014 s–1 , respectively, while the lowest ones, E
a =28.2 kJ mol–1 and A =3.65⋅102 s–1 belong to sodium nitrate(V).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
pKa prediction for acidic phosphorus‐containing compounds using multiple linear regression with computational descriptors
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Ninety‐six acidic phosphorus‐containing molecules with pKa 1.88 to 6.26 were collected and divided into training and test sets by random sampling. Structural parameters were obtained by density functional theory calculation of the molecules. The relationship between the experimental pKa values and structural parameters was obtained by multiple linear regression fitting for the training set, and tested with the test set; the R2 values were 0.974 and 0.966 for the training and test sets, respectively. This regression equation, which quantitatively describes the influence of structural parameters on pKa, and can be used to predict pKa values of similar structures, is significant for the design of new acidic phosphorus‐containing extractants. © 2016 Wiley Periodicals, Inc. 相似文献
12.
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
13.
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
14.
Pascale Bénézeth Donald A. Palmer David J. Wesolowski 《Journal of solution chemistry》1997,26(1):63-84
The three molal dissociation quotients for citric acid were measured potentiometrically with a hydrogen-electrode concentration
cell from 5 to 150°C in NaCl solutions at ionic strengths of 0.1, 0.3, 0.6, and 1 molal. The molal dissociation quotients
and available literature data at infinite dilution were fitted by empirical equations in the all-anionic form involving an
extended Debye-Hückel term and up to five adjustable parameters involving functions of temperature and ionic strength. This
treatment yielded the following thermodynamic quantitites for the first dissociation equilibrium at 25°C: logK
1a=−3.127±0.002, ΔH
1a
o
=4.1±0.2 kJ-mol−1, ΔS
1a
o
=−46.3±0.7 J-K−1-mol−1, and ΔCp
1a
o
=−162±7 J-K−1-mol−1; for the second acid dissociation equilibrium at 25°C: logK
2a
=−4.759±0.001, ΔH
2a
o
=2.2±0.1, ΔS
2a
o
=−83.8±0.4, and ΔCp
2a
o
=−192±15, and for the third dissociation equilibrium at 25°C: logK
3a=−6.397±0.002, ΔH
3a
o
=−3.6±0.2, ΔS
3a
o
=−134.5±0.7, and ΔCp
3a
o
=−231±7. 相似文献
15.
Kazakova V. M. Pesterev P. A. Minina N. E. 《Russian Journal of General Chemistry》2003,73(7):1114-1118
The spin densities in radical cations of 22 substituted nitro- and m-dinitrobenzenes were calculated by the INDO method. For radical anions of substituted nitrobenzenes, a good linear correlation was obtained between the spin densities sNsN and experimental hyperfine coupling constants with the nitrogen atoms of the NO2 groups (a
N): a
N = K
N
s
N
s
N, where K
N = 428.58 (R
2 = 0.96). For radical anions of substi- tuted m-dinitrobenzenes, no satisfactory agreement between the calculated and experimental a
N constants was attained. 相似文献
16.
Z. Fengqui H. Rongzu S. Jirong G. Hongxu 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(7):1034-1036
The kinetic parameters of the exothermic decomposition of the title compound in a temperatureprogrammed mode have been studied
by means of DSC. The DSC data obtained are fitted to the integral, differential, and exothermic rate equations by the linear
least-squares, iterative, combined dichotomous, and least-squares methods, respectively. After establishing the most probable
general expression of differential and integral mechanism functions by the logical choice method, the corresponding values
of the apparent activation energy (E
a), preexponential factor (A), and reaction order (n) are obtained by the exothermic rate equation. The results show that the empirical kinetic model function in differential
form and the values of E
a and A of this reaction are (1 − α)−4.08, 149.95 kJ mol−1, and 1014.06 s−1, respectively. With the help of the heating rate and kinetic parameters obtained, the kinetic equation of the exothermic
decomposition of the title compound is proposed. The critical temperature of thermal explosion of the compound is 155.71°C.
The above-mentioned kinetic parameters are quite useful for analyzing and evaluating the stability and thermal explosion rule
of the title compound.
The text was submitted by the authors in English. 相似文献
17.
Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by Nuclear Magnetic Resonance
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The dynamic NMR (DNMR) method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14(s=2, 3 and 4).The escape rate constant, k-, was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, Ea-, was obtained based on the Arrhenius equation through temperature variation experiments.Results show that the orders of magnitude of k- for 14-s-14 and 12-s-12 are respectively 10 and 103 s-1, Ea- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/mol.Furthermore, increases and Ea- decreases with the spacer length growing.In combination with the micro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the micelles.The two-step molecular exchange mechanism for Gemini surfactants was therefore supported. 相似文献
18.
S. V. Myakin V. Yu. Nikonova V. G. Korsakov V. V. Samonin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(9):1622-1628
The sorption capacity of activated carbon with respect to Cu2+ cations was found to be enhanced considerably upon its chemical modification with fullerenes and during its electron-beam
processing. It was discovered that introducing fullerenes (20 μg/g) into activated carbon leads to a change in the chemical
composition of its surface, due to changes in the system of conjugated bonds in activated carbon leading to an increase in
the content of Br?nsted acid (pK
a 0–5) and weakly base (pK
a 8–11) sites capable of cation exchange on the material surface. We conclude that electron-beam processing (optimal dose,
25–50 kGy) facilitates the rearrangement of bonds on the surface of activated carbon, thereby increasing the number of Lewis
base and Br?nsted acid sites capable of adsorbing metal ions in accordance with the donor-acceptor and cation-exchange mechanism,
respectively. 相似文献
19.
Asim K. Das 《Transition Metal Chemistry》1992,17(6):484-488
The equilibria and kinetics of the reaction of FeIII with salicylaldehyde ando-hydroxyacetophenone, leading to 1∶1 chelate formation, have been studied at different temperatures (25–35°C) and ionic strength,
I = 1.0 mol dm−3 (NaClO4+HClO4). A dual path mechanism involving both Fe
aq
3+
and Fe(OH)
aq
2+
species and undissociated free ligand (LH) is consistent with the experimental observations where [H+]≫[Fe]T≫[L]T (where [Fe]T and [L]T stand for total concentrations of iron and ligand respectively). The results conform to kobs/B = k1[H+]+k2Kh where B = [Fe]T/(Kh+[H+])+1/Q; Kh = hydrolysis constant of Fe
aq
3+
; k1, k2 are the forward second order rate constants of Fe
aq
3+
and Fe(OH)
aq
2+
, respectively, and Q is the equilibrium constant of the reaction, Fe3++LH⇋FeL2++H+. Thermodynamic parameters for each of the steps have been determined. Fe(OH)
aq
2+
appears to react in a dissociative fashion (Eigen-Tamm mechanism), whilst Fe
aq
3+
appears to react through the associative inter-change (Ia) mechanism. The equilibrium constants (Q) obtained spectrophotometrically are compared with those obtained from kinetic studies.
TMC 2638 相似文献
20.
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