共查询到20条相似文献,搜索用时 31 毫秒
1.
Gibbs energies of activation for viscous flow of binary water (1) + dimethyl sulfoxide (2) mixtures, Δμ
12○, and of lysozyme (3) in corresponding ternary mixtures, Δμ
3○, were determined at 298.15 K. The binary mixtures have a maximum in the value of the excess quantity for Δμ
12○ at a dimethyl sulfoxide mole fraction of x
2≈0.31. The values of Δμ
3○ are larger than Δμ
12○ at all values of x
2, even when normalized by their molar volumes, suggesting that the solvents interact more strongly with lysozyme than with
themselves. The values of Δμ
3○ significantly increased in the range of x
2=0.3 to 0.4 because of an increase in solvent-lysozyme interactions, which resulted from an increase in the accessible surface
area of lysozyme that was exposed by its unfolding. The mean value obtained for Δμ
3○ per amino acid of lysozyme at x
2=0.2 is greater than that for hydrophobic amino acids, indicating that the solvent interacts with hydrophilic amino acids
more strongly than with hydrophobic ones. 相似文献
2.
V. G. Badelin V. I. Smirnov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(7):1163-1168
The integral enthalpies of solution of L-methionine in water-methanol, water-ethanol, water-n-propanol, and water-iso-propanol mixtures were measured calorimetrically at alcohol concentrations x
2 = 0–0.4 mole fractions. The standard enthalpies of solution (Δsol
H
o) and transfer of L-methionine (Δtr
H
o) from water to a binary solvent were calculated. The influence of the structure and properties of L-methionine and the composition
of aqueous-organic mixtures on its enthalpy characteristics was considered. The enthalpic pair interaction coefficients (h
xy
) between L-methionine and alcohol molecules were calculated; they were positive and increased in the series methanol (MeOH),
ethanol (EtOH), n-propanol (n-PrOH), iso-propanol (i-PrOH). The enthalpy characteristics of solution and transfer of L-methionine were compared with those of glycine, L-threonine,
L-alanine, and L-valine in similar binary solvents. 相似文献
3.
Multiwalled carbon nanotubes-polymeric alizarin film modified electrode was made. The electrochemical behavior of levofloxacin
hydrochloride on modified electrode was studied with cyclic voltammetry, linear sweep voltammetry and chronopotentiometry.
The results indicated that the electrical oxidation of levofloxacin hydrochloride on MWNT-PAR electrode, in HAc-NaAc buffer
solution at pH 4.2 was irreversible and was controlled by diffusion. Some important parameters m, n, D, E
D, ΔS
rc and ΔH
rc of the electrochemical process were evaluated. Good linearity relationship between peak current and its concentration in
the range of 5.0 × 10−6–1.0 × 10−4 mol l−1 was found, of which the equation was I
p(A) = −5.456 × 10−6 0.2667c, the correlative coefficient r = −0.9976 and detect limitation was 4.0 × 10−7 mol l−1. The recovery of levofloxacin hydrochloride in levofloxacin hydrochloride injection was between 94.6 and 104.7%. 相似文献
4.
Thermodynamic characteristics of alanine-18-crown-6 ether complexes in binary water-acetone solvents
T. R. Usacheva I. A. Kuz’mina V. A. Sharnin I. V. Chernov E. Matteoli 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(1):36-39
The formation of 18-crown-6 ether (18C6) complexes with D,L-alanine (Ala) in mixed wateracetone solvents with 0.0, 0.08, 0.17,
0.22, and 0.30 mole fractions of acetone (T = 298.15 K) was investigated by means of calorimetry. Thermodynamic characteristics of the reaction of the molecular [Ala18C6]
complex formation (Δr
G°, Δr
H°, and TΔr
S°) were calculated on the basis of calorimetric data. Analysis of solvation contributions of reagents into the enthalpy of
the [Ala18C6] formation reaction showed that the changes in the reaction energy when the solvent composition is varied are
determined by the changes in the solvate state of 18C6. 相似文献
5.
L. A. Kochergina A. V. Volkov E. A. Khokhlova O. N. Krutova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(5):881-889
The heat effects of the reaction of aqueous solution of L-serine with aqueous solutions of HNO3 and KOH were determined by calorimetry at temperatures of 288.15, 298.15, and 308.15 K, and ionic strength values of 0.2,
0.5, and 1.0 (background electrolyte, KNO3). Standard thermodynamic characteristics (Δr
H
o, Δr
G
o, Δr
S
o, ΔC
p
o) of the acid-base reactions in aqueous solutions of L-serine were calculated. The effect of the concentration of background
electrolyte and temperature on the heats of dissociation of amino acid was considered. The combustion energy of L-serine by
bomb calorimetry in the medium of oxygen was determined. The standard combustion and formation enthalpies of crystalline L-serine
were calculated. The heats of dissolution of crystalline L-serine in water and solutions of potassium hydroxide at 298.15
K were measured by direct calorimetry. The standard enthalpies of formation of L-serine and products of its dissociation in
aqueous solution were calculated. 相似文献
6.
E. Matteoli L. Lepori T. R. Usacheva V. A. Sharnin 《Journal of Thermal Analysis and Calorimetry》2009,97(3):811-816
The influence of H2O–EtOH and H2O–Acetone mixed solvents at various compositions on the thermodynamics of complex formation reaction between crown ether 18-crown-6
(18C6) and glycine (Gly) was studied. The standard thermodynamic parameters of the complex [Gly18C6] (log K°, Δr
H°, Δr
S°) were calculated from thermochemical data at 298.15 K obtained by titration calorimetry. The complex stability and its formation
enthalpy increase with increasing the non aqueous component concentration in both mixed solvents. The thermodynamic data were
discussed on the basis of the solvation thermodynamic approach and the solvation contributions of the reagents and of the
complex to the complex stability were analyzed. 相似文献
7.
L. A. Kochergina A. V. Emel’yanov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(10):1742-1747
Heats of reaction of glycylglycine with nitric acid and potassium hydroxide solutions are determined by two calorimetric procedures
at 288.15, 298.15, 308.15 K and an ionic strength of solution of 0.25, 0.50, and 0.75 in the presence of KNO3. Standard thermodynamic characteristics (Δr
H°, Δr
G°, Δr
S°, and Δp
C°) are calculated for the acid-base reactions in aqueous peptide solutions. The effects of the concentration of background
electrolyte and temperature on the heats of dissociation of glycylglycine are considered. 相似文献
8.
L. A. Kochergina S. G. Grosheva O. N. Krutova 《Russian Journal of Inorganic Chemistry》2011,56(9):1481-1486
The heats of reactions between an L-asparagine solution and HNO3 solutions were measured calorimetrically within different pH ranges at 298.15, 308.15, and 318.15 K and an ionic strength
of 0.5, 1.0, and 1.5 (KNO3 and LiNO3). The heats of stepwise dissociation of L-asparagine were determined. The standard thermodynamic characteristics (Δ
r
H
o, Δ
r
G
o, δ
r
S
o, and ΔC
p
⪧) of the acid-base interactions in aqueous solutions of the amino acid were calculated. A relationship between the thermodynamic
characteristics of the dissociation of L-asparagine and its structure was considered. 相似文献
9.
The protonation equilibria for some phenolic acids in nonaqueous solutions have been studied by pH-potentiometry. The dissociation
constants, pK
a, of these phenolic acids and the thermodynamic functions, ΔG
o,ΔH
o and ΔS
o, for the successive and overall protonation processes of these phenolic acids have been derived at different temperatures
in three different mixtures of water and dioxane (mole fractions of dioxane were 0.083, 0.174 and 0.33). Titrations were also
carried out in (water + dioxane) with ionic strengths of 0.15, 0.20 and 0.25 mol⋅dm−3 NaNO3, and the resulting dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent,
dioxane, temperature and ionic strength on the protonation processes of phenolic acids is presented and discussed to determine
the factors which control these processes.
Ahmed E. Fazary; previous address: Egyptian Organization for Biological Products and Vaccines, 51 Wezaret El-Zeraa Street,
Agouza, Giza, Egypt. Tel. +2010-3017357. 相似文献
10.
G. Xie S. P. Chen S. L. Gao X. X. Meng Q. Z. Shi 《Journal of Thermal Analysis and Calorimetry》2006,83(3):693-700
A novel solid complex, formulated as Ho(PDC)3
(o-phen), has been obtained from the reaction
of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and
1,10-phenanthroline (o-phen·H2O)
in absolute ethanol, which was characterized by elemental analysis, TG-DTG
and IR spectrum. The enthalpy change of the reaction of complex formation
from a solution of the reagents, ΔrHmθ (sol), and the molar heat capacity of the complex, cm,
were determined as being –19.161±0.051 kJ mol–1
and 79.264±1.218 J mol–1 K–1
at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy
change of complex formation from the reaction of the reagents in the solid
phase, ΔrHmθ(s), was calculated as
being (23.981±0.339) kJ mol–1 on the
basis of an appropriate thermochemical cycle and other auxiliary thermodynamic
data. The thermodynamics of reaction of formation of the complex was investigated
by the reaction in solution at the temperature range of 292.15–301.15
K. The constant-volume combustion energy of the complex, ΔcU, was determined as being –16788.46±7.74
kJ mol–1 by an RBC-II type rotating-bomb
calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHmθ, and standard enthalpy of formation,
ΔfHmθ, were calculated to be –16803.95±7.74 and –1115.42±8.94
kJ mol–1, respectively. 相似文献
11.
Thermodynamic and kinetic characteristics of liquid phase hydrogenation of substituted nitrobenzenes
Yu. V. Minenkov O. V. Lefedova I. V. Smirnova M. P. Nemtseva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(6):908-912
Quantum-chemical calculations of the thermodynamic characteristics of hydrogenation of nitrobenzoic acid isomers and nitrophenol
in the gas phase and also in aqueous and alcoholic media were performed. Correlation dependences between the calculated Δr
G
298○ values and rate constants for the reaction in various media were obtained. 相似文献
12.
V. N. Belyaev N. L. Lebedeva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(6):920-928
Sr+ + H2O ↔ SrOH+ + H equilibrium was studied spectrophotometrically. This reaction occurs in natural gas combustion products. Its enthalpy
Δr
H
○(0) = 61.4 ± 2.8 kJ/mol and bond energy D
0(Sr+-OH) = 432.6 ± 2.8 kJ/mol were determined using the third law of thermodynamics. The experimental data on this reaction obtained
earlier in hydrogen flames, Δr
H
○(0) = 55.3 ± 10.6 and D
0(Sr+-OH) = 438.7 ± 10.6 kJ/mol, were interpreted anew. The D
0(Sr+-OH) = 432.8 ± 2.7 kJ/mol value was eventually obtained. 相似文献
13.
The enthalpies of solution of L- and D-valines in water-ethanol, water-n-propanol, and water-i-propanol mixtures were measured calorimetrically at 298.15 K at alcohol mole fractions, x
2, ranging up to 0.4. Enthalpies of transfer, Δtr
H°, from water to aqueous alkanol were calculated for each of the system studied. The enthalpic coefficients, h
xy
, of the solute-cosolvent pair-wise interaction in water proved to be positive and increasing in the series: ethanol, n-propanol, and i-propanol. It was shown that both the nature of the amino acid L–L- and D–D-isomerization and dimensions of linear or branched cosolvent molecules define the energetics of interaction between valine
and alkanol molecules. 相似文献
14.
S. P. Chen X. X. Meng Q. Shuai B. J. Jiao S. L. Gao Q. Z. Shi 《Journal of Thermal Analysis and Calorimetry》2006,86(3):767-774
A
solid complex Eu(C5H8NS2)3(C12H8N2) has been obtained from reaction of
hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC)
and 1,10-phenanthroline (o-phen⋅H2O)
in absolute ethanol. IR spectrum of the complex indicated that Eu3+
in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms
from the o-phen. TG-DTG investigation provided
the evidence that the title complex was decomposed into EuS.
The
enthalpy change of the reaction of formation of the complex in ethanol, Δr
H
m
θ(l), as –22.214±0.081 kJ mol–1,
and the molar heat capacity of the complex, c
m,
as 61.676±0.651 J mol–1 K–1,
at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy
change of the reaction of formation of the complex in solid, Δr
H
m
θ(s), was calculated as 54.527±0.314 kJ mol–1
through a thermochemistry cycle. Based on the thermodynamics and kinetics
on the reaction of formation of the complex in ethanol at different temperatures,
fundamental parameters, including the activation enthalpy (ΔH
≠
θ),
the activation entropy (ΔS
≠
θ),
the activation free energy (ΔG
≠
θ),
the apparent reaction rate constant (k),
the apparent activation energy (E), the
pre-exponential constant (A) and the reaction
order (n), were obtained. The constant-volume
combustion energy of the complex, Δc
U,
was determined as –16937.88±9.79 kJ mol–1
by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy
of combustion, Δc
H
m
θ,
and standard enthalpy of formation, Δf
H
m
θ,
were calculated to be –16953.37±9.79 and –1708.23±10.69
kJ mol–1, respectively. 相似文献
15.
Paul Rademacher 《Structural chemistry》2006,17(1):19-25
The electronic and geometrical structures of fluorocyclopropanes (1–12) have been analysed using DFT B3LYP calculations. A linear relationship, Δɛω=−0.172 Δr−0.171 (n=12, R=0.931), between Δɛω (in eV), the difference of the energies of the Walsh orbitals ωS and ωA, and Δr (in pm), the difference of vicinal and distal C–C bond lengths, is established. Correcting the orbital splitting by the basic value at Δr=0.00 pm, an even better linear correlation Δɛω
eff=0.0720 Δr (n=12, R=0.984) is obtained. The results confirm the general applicability of the two-orbitals model for the relationship between geometrical and electronic structures for substituted cyclopropanes.
1For Part 4 see Ref. [17]. 相似文献
16.
T. R. Usacheva V. A. Sharnin E. Matteoli 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(11):1898-1902
Complexation of the 18-crown-6 ether (18C6) with glycine (Gly) in mixed H2O-DMSO solvents with the composition of 0.1, 0.2, and 0.25 mole fraction of DMSO (T = 298.15 K) was studied calorimetrically. Thermodynamic characteristics of the reaction of the formation of the molecular
Gly18C6 complex (Δr
G°, Δr
H°, TΔr
S°) were calculated from the calorimetric data. It was established that the change in the stability of the Gly18C6 complex
is mainly determined by the predominance of the enthalpy component of the Gibbs energy over the entropy component. It was
shown during the analysis of the enthalpy contributions of the reagents to the enthalpy of the reaction of the formation of
Gly18C6 that the change in the enthalpy of the reaction upon a change the solvent composition was due to changes in the solvation
state of 18C6. 相似文献
17.
I. N. Mezhevoi V. G. Badelin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(4):683-685
The integral enthalpies of solution (Δsol
H
m
) of L-serine in water-alcohol (ethanol, n-propanol, isopropanol) mixtures were measured over the range of alcohol concentrations up to 0.32 mole fractions. The standard
enthalpy of solution (Δsol
H°), enthalpy of transfer of L-serine from water into a mixed solvent (Δtr
H°), and enthalpy of solvation (Δsolv
H°) were calculated. The dependences of Δsol
H°, Δsolv
H°, and Δtr
H° on the composition of mixtures had extrema. The calculated enthalpy coefficients of the pair interactions of L-serine with
alcohol molecules were positive and increased along the series ethanol, n-propanol, isopropanol. The data obtained were interpreted in terms of different types of interactions in solutions and the
influence of the nature of amino acid residues on the thermochemical solution characteristics.
Original Russian Text ? I.N. Mezhevoi, V.G. Badelin, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4,
pp. 789–791. 相似文献
18.
Numerous published data on the structure and thermodynamics of formation of molecular complexes are analyzed. The enthalpies
of complexation (−ΔH) are related to the characteristic parameter Δr = [r
DA−a
1(r
D+r
A)], where r
DA is the donor-acceptor bond length determined by microwave spectroscopy and X-ray analysis, r
D and r
A are the tabulated values of the homopolar covalent radii of the heteroatoms that form the donor-acceptor bond, and a
1 is an empirical coefficient equal to 0.901±0.007. The relation between −ΔH and Δr values has the form −ΔH = a
2/Δr (a
2 = 21.6±1.6 kJ Å mol−1), with a mean relative error of approximation of about 15% and a correlation coefficient of 0.97. As the strength of the
complex increases, the donor-acceptor bond length approaches the sum of the heteropolar covalent radii of the atoms involved
in the bond (Δr tends to zero). At Δr ≫ 1, the strength of complexes is determined by weak van der Waals interactions between the complex components and the −ΔH values tend to zero.
Dedicated to the memory of E. N. Guryanova (1911–2004), a prominent scientist who formulated the basic principles elaborated
by her disciples in this review.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1869–1878, October, 2007. 相似文献
19.
W Zielenkiewicz R Swierzewski F Attanasio G Rialdi 《Journal of Thermal Analysis and Calorimetry》2006,83(3):587-595
Investigations
of lysozyme–polyethylene glycol system were made by differential scanning
calorimetry, fluorescence and density techniques. The values of unfolding
enthalpies, ΔHNU, unfolding temperatures, Tm,
excess molar heat capacities, ΔCp,
and apparent molar volumes, VΦ
, were determined as functions of PEG concentration. The three PEGs of average
molecular mass (MW) 6000, 10000, 20000
were used as macromolecular crowding agents. The concentration of polymers
was changed in the range 0–30% mass per volume (w/v). The values of ΔHNU remained
constant with no dependence on PEG concentration, while PEG addition to buffered
lysozyme solutions caused linear decrease of Tm.
The values of ΔCp
and VΦ of lysozyme
dramatically changed in the range of 8–10% of PEG concentration. The
fluorescence spectroscopy was used in order to investigate the polymer influence
on possible solvent–lysozyme interactions. The electrical properties
of polymer–water and polymer–buffer systems, the dielectric constants
of solutions were determined with use of impedance spectroscopy. 相似文献
20.
V. M. Pinchuk E. S. Kotlyarova N. V. Parkhomenko P. N. Tsybulev 《Journal of Structural Chemistry》1996,37(4):544-556
The studies concerned with the oxidation of carbon monoxide on the nickel surface are reviewed. The Eley-Rideal (ER) collision
and Langmuir-Hinshelwood (LH) adsorption mechanisms of the oxidation are analyzed. Calculations of the activation barriers
of the oxidation of carbon monoxide on the Ni (111), (100), and (110) faces were performed for the first time and involved
optimization of the reaction paths by the collision and adsorption mechanisms. It is shown that on the Ni (111) and (110)
faces the ER collision mechanism of the reaction is preferable with the activation barriers ΔE
dis
O
2=62 kJ/mole and ΔE
trans
O
A21F50012x=25 kJ/mole for Ni (111) and ΔE
dis
O
2=72 kJ/mole and ΔE
trans
O
2=20 kJ/mole for Ni (110); on the Ni (100) face, the LH adsorption mechanism with the activation barriers ΔE
dis
O
2=75 kJ/mole and ΔE
trans
O
2=42 kJ/mole is favored. Analysis of the potential barriers for the catalytic oxidation of carbon monoxide on the Ni surfaces
suggests the LH mechanism to be preferential, although insignificant differences in the activation barries can lead to the
oscillatory reaction mechanism, which is confirmed experimentally. The calculations were performed by the LCAO MO SCF method
in the MINDO/3 approximation.
Kiev Polytechnical Institute. Translated fromZhurnal Struktumoi Khimii, Vol. 37, No. 4, pp. 628–645, July–August, 1996.
Translated by I. Izvekova 相似文献