共查询到20条相似文献,搜索用时 31 毫秒
1.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):941-949
Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
2.
Francisco Ros 《Monatshefte für Chemie / Chemical Monthly》2011,12(2):25-37
Abstract
The cohesion energy of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, as obtained from the change of kinetic and potential energies in the heat of sublimation of the crystal, E p,coh = −46.7 kJ mol−1 (78.6 °C), has been validated. A safe physicomathematic test based on the balance of entropy for the sublimation and Planck’s equation for changes of state, extended to entropy, was devised to ascertain the kinetic energies of the crystal and the gas molecule. Entropic equations were developed for the phase equilibrium to find precisely and with simplicity the vibrational energy of the crystal by using the vapour pressure exclusively and independently from the internal rotational and vibrational motion of the gas molecule. The heat capacity of the vapour was determined in this way, which in this case releases the solid allowing vibrational movement in the gas phase to meet the pressure of sublimation, C p (T)/J K−1 mol−1 = 1.268 T/K + 58.62 (71.1–86.1 °C). An independent variational method of deducing the vibrational entropy, energy, or heat capacity of the gas molecule from each other was compared with the equations and was shown to yield the quantities with high accuracy. Values of the Nernst–Lindemann functions are tabulated. 相似文献3.
Josiane de Lima Souza Marcelo Kobelnik Clóvis Augusto Ribeiro Jorge Manoel Vieira Capela Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):525-528
Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid
(TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear
fitting to obtain the estimation for activation energy (E
a
) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the
average activation energy, 73 ± 9 kJ mol−1 and 63 ± 1 kJ mol−1, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain.
PHB/TA show increase in the medium value of E
a, 119 ± 2 kJ mol−1 and T
c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E
a=73 ± 9 kJ mol−1, T
c = 44.8 °C at 5 °C/min). 相似文献
4.
E. Tazikeh Lemeski G. Rezaei Behbehani A. A. Saboury M. Monajjemi R. Zafar Mehrabian M. Ahmadi Golsefidi H. Rajabzadeh M. T. Baei S. Hasanzadeh 《Journal of solution chemistry》2011,40(4):575-586
The interaction of human growth hormone (hGH) with the divalent mercury ion was studied by isothermal titration calorimetry
at two temperatures of 27 °C and 37 °C in aqueous solutions. We found that there is a set of two identical and non-interacting
binding sites for Hg2+ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 4.2 mmol⋅L−1 and −14.8 kJ⋅mol−1 at 27 °C and 5.1 mmol⋅L−1 and −14.2 kJ⋅mol−1 at 37 °C, respectively. The results obtained indicate that the stability of the protein increases due to the binding of mercury
ions using the extended solvation theory. 相似文献
5.
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
6.
Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III)
in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic
acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant]
and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive
form of the oxidant was inferred to be [Cu(H3IO6)2]−. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give
a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized
by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a
fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E
a,ΔH
#,ΔS
# and ΔG
# were determined to be 51 kJ⋅mol−1,48.5 kJ⋅mol−1,−63.5 J⋅K−1⋅mol−1 and 67 kJ⋅mol−1, respectively. The value of log 10
A was calculated to be 6.8. 相似文献
7.
The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas
diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal
forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy,
DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships
are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic
stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔHf 33.1±0.2 kJ mol−1, density 1.271±0.001 g cm−3) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C,
ΔHf 32.0 ± 0.2 kJ mol−1, density 1.243±0.001 g cm−3). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically
stable at ambient conditions. Mod. III (m.p. 112 °C, ΔHf 25.1±0.5 kJ mol−1) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and
the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data.
Received September 30, 1999. Revision July 30, 2000. 相似文献
8.
Issa Yavari Mehdi Adib Hamid R. Bijanzadeh Majid M. M. Sadegi Hossein Logmani-Khouzani Javad Safari 《Monatshefte für Chemie / Chemical Monthly》2002,11(4):1109-1113
A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively, and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2 kJ · mol−1, respectively, in CDCl3. 相似文献
9.
Issa Yavari Mehdi Adib Hamid R. Bijanzadeh Majid M. M. Sadegi Hossein Logmani-Khouzani Javad Safari 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1109-1113
Summary. A dynamic NMR effect is observed in the 13C NMR spectra of anhydrous quinophthalone (quinoline yellow) and its monohydrate in the vicinity of 47°C and 0°C, respectively,
and is attributed to a restricted rotation around the polarized carbon–carbon double bond. The free energy of activation for
this process in anhydrous quinophthalone and the monohydrate is 65±2 and 55±2 kJ · mol−1, respectively, in CDCl3.
Received September 25, 2001. Accepted (revised) November 14, 2001 相似文献
10.
Ab initio HF/6-31G* and MP2/6-31G*//HF/6-31G* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C 4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C s) and twist (C 2h) conformers and requires about 22.3 kJ · mol−1. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol−1. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods. 相似文献
11.
Issa Yavari Hassan Kabiri-Fard Shahram Moradi 《Monatshefte für Chemie / Chemical Monthly》2002,133(11):1459-1468
Summary. Ab initio calculations at the HF/6-31G* level of theory for geometry optimization and the MP2/6-31G*//HF/6-31G* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C
2-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol−1 more stable than the C
S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C
S-symmetric boat-boat geometry is 19.1 kJ·mol−1. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C
1) transition state which is 43.5 kJ·mol−1 above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol−1 more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair
and boat-chair is 69.5 kJ·mol−1, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol−1. The C
S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol−1 more stable than the C
S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C
S) transition state which is 37.2 kJ·mol−1 above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol−1 less stable than the crown conformation.
Corresponding author. E-mail: isayavar@yahoo.com
Received March 25, 2002; accepted April 3, 2002 相似文献
12.
Karoline Fendler Beate Hager Heinz Falk 《Monatshefte für Chemie / Chemical Monthly》2007,138(9):859-862
Summary. Two model compounds for the tryptophane variant of the green fluorescent protein chromophore containing a 3-indolyl and 2-pyrrolyl
moiety were prepared. For the first one the (Z)-diastereomer was found to be more stable than the (E)-diastereomer by 5.7 kJ mol−1. It could be photo-diastereomerized and its thermal equilibration was studied, whereas the second one underwent photo-destruction.
From an Arrhenius plot an activation barrier for the (E) to (Z) diastereomerization of 85.6 kJ mol−1 could be determined. Thus, it could be demonstrated that in contrast to the corresponding phenyl derivative studied recently
the tyrosine- and tryptophane-derived chromophores of the green fluorescent protein are amenable to fast thermal diastereomerization,
which is of fundamental importance for the fluorescence and photoswitching processes in the corresponding proteins. 相似文献
13.
On the Chemistry of the Resveratrol Diastereomers 总被引:5,自引:0,他引:5
Summary. The (E)- and (Z)-diastereomers of resveratrol were investigated with respect to their photochemical and thermal diastereomerization reactions.
The free enthalpy difference between the two diastereomers was estimated to be in the order of common stilbenes, with the
(E)-diastereomer more stable by about 11–14 kJ mol−1. The Arrhenius activation barrier of about 280 kJ mol−1 was found to be quite high and implies that thermal equilibration cannot account for the (Z)-diastereomer found in nature. A preparative access to the (Z)-diastereomer by photodiastereomerization is described. The 1H and 13C NMR spectra of the two diastereomers were assigned and their absorption spectra and fluorescence quantum yields of the neutral
and monodeprotonated species were determined.
Corresponding author. E-mail: heinz.falk@jku.at
Received October 15, 2002; accepted November 7, 2002
Published online February 20, 2003 相似文献
14.
Summary. Ab initio HF/6-31G* and MP2/6-31G*//HF/6-31G* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C
4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C
s) and twist (C
2h) conformers and requires about 22.3 kJ · mol−1. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol−1. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries
of the title compound are in good agreement with the results of ab initio methods.
Received July 9, 2001. Accepted September 26, 2001 相似文献
15.
S. K. Tripathi Balbir Singh Patial Nagesh Thakur 《Journal of Thermal Analysis and Calorimetry》2012,107(1):31-38
Differential scanning calorimetry data at different heating rates (5, 10, 15 and 20 °C min−1) of Se70Te15In15 chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed
for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se70Te15In15 alloy has three-dimensional growth. The average values of the activation energy for glass transition, E
g, and crystallization process, E
c, are (154.16 ± 4.1) kJ mol−1 and (98.81 ± 18.1) kJ mol−1, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T
rg), Hruby’ parameter (K
gl) and fragility index (F
i) indicate that the prepared glass is obtained from a strong glass forming liquid. 相似文献
16.
It was found that the hypericinate salts of (R)-1-phenylethylamine and (S)-1-(1-naphthyl)-ethylamine display a small chiroptical signal of the same sign only at high concentrations in an apolar solvent.
No further indications of a chiral discrimination between the helical conformers of hypericinate could be found in these cases.
However, upon esterification of the 3-hydroxyl group of hypericin with (1S)-camphanic chloride, the two diastereomers were found in an 1:1 ratio equilibrating rather fast at temperatures above 30°C
with one diastereomer in excess. From the temperature dependence of the equilibrium positions (measured by means of CD and
1H NMR), a ΔG
0 value of 5.8±0.5 kJ·mol−1 was derived. Accordingly, the chiral discrimination of the (M)-configured enantiomer of the helix by the (S)-configured auxiliary occurred at an intermediate level. From the temperature dependence of the equilibration kinetics an
activation energy of E
a = 70±0.5 kJ·mol−1 was derived, which thus defines the upper limit of the helix inversion of hypericin and hypericinate. This value is by about
10 kJ·mol−1 lower than the recently estimated limit. 相似文献
17.
H. X. Ma B. Yan Y. H. Ren Y. Hu Y. L. Guan F. Q. Zhao J. R. Song R. Z. Hu 《Journal of Thermal Analysis and Calorimetry》2011,103(2):569-575
3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO4) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior
and decomposition reaction kinetics of DNAZ·HClO4 were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition
process of DNAZ·HClO4 has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E
a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO4 are f(α) = (1 − α)−1/2, 156.47 kJ mol−1, and 1015.12 s−1, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS
≠, ΔH
≠, and ΔG
≠of this reaction are 42.26 J mol−1 K−1, 154.44 kJ mol−1, and 135.42 kJ mol−1, respectively. The specific heat capacity of DNAZ·HClO4 was determined with a continuous C
p mode of microcalorimeter. 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 evaluated as 14.2 s. 相似文献
18.
Nabila M. Guindy Zeinab M. Abou-Gamra Michel F. Abdel-Messih 《Monatshefte für Chemie / Chemical Monthly》2000,131(8):857-866
Summary. The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10−5 to 1.0×10−3 molċdm−3 retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol−1 were obtained for the energy of activation and −184 and −116 Jċ K−1ċmol−1 for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1.
Received January 7, 2000. Accepted (revised) March 8, 2000 相似文献
19.
Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating
ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral,
elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol
i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction
(n = 0.96–1.49), and the energy of activation (E
a = 3.065–142.9 kJ mol−1), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK−1 mol−1), the activation enthalpy (H* = 0.380–135.15 kJ mol−1), and the free energy (G* = 33.52–222.4 kJ mol−1) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A4)(CQ)OH] · 4H2O > [Cu(A3)(CQ)OH] · 5H2O > [Cu(A1)(CQ)OH] · H2O > [Cu(A2)(CQ)OH] · 3H2O 相似文献
20.
Nabila M. Guindy Zeinab M. Abou-Gamra Michel F. Abdel-Messih 《Monatshefte für Chemie / Chemical Monthly》2000,48(2):857-866
The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10−5 to 1.0×10−3 molċdm−3 retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol−1 were obtained for the energy of activation and −184 and −116 Jċ K−1ċmol−1 for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1. 相似文献