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71.
The structural and thermodynamic properties of the donor-acceptor (DA) complexes of Group 13 metal halides (MX3) with ethylenediamine and their decomposition products have been studied theoretically at the B3LYP/LANL2DZ(d,p) level of theory. Gas-phase dissociation into various components and HX elimination reactions are considered. Both processes are endothermic but favored by entropy. Complexes of 2:1 composition are predicted to be stable in the gas phase up to 640-1000 K. It is found that complexation with the second acceptor molecule lowers the HX elimination enthalpy; in turn, HX elimination increases DA bonding with a second MX3 molecule. Exceptionally high values of the dissociation enthalpies (310-390 kJ mol(-1)) and HX elimination reactions (360-420 kJ mol(-1)) of the amido compounds MX2NHC2H4NH2 and MX2NHC2H4NHMX2 make them important intermediates in the decomposition processes. Dissociation reactions of the complexes are more favorable than HX elimination reactions; however, the subsequent oligomerization and cyclization processes of coordinationally unsaturated amido and imido compounds may facilitate HX elimination. Since HI elimination reactions are predicted to be the least endothermic, and aluminum-containing compounds have the strongest M-N dissociation enthalpies, it is expected that compounds based on aluminum iodide are promising objects for experimental studies. 相似文献
72.
J. Orbán Sz. Halasi G. Papp Szilvia Barkó Beáta Bugyi 《Journal of Thermal Analysis and Calorimetry》2005,82(1):287-290
Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well. 相似文献
73.
M. I. El-Barghouthi N. A. Masoud J. K. Al-Kafawein M. B. Zughul A. A. Badwan 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):15-22
The solubility of risperidone (Risp) in aqueous buffered cyclodextrin (CD) solution was investigated for α-, β-, γ- and HP-β-CD. The effects of pH, ionic strength and temperature on complex stability were also explored. Neutral Risp tends to form
higher order complexes (1:2) with both β- and HP-β-CD, but only 1:1 type complexes with α-, and γ-CD. The tendency of Risp to complex with cyclodextrins is in the order β-CD > HP-β-CD > γ-CD > α-CD. The 1:1 complex formation constant of Risp/HP-β-CD increases with increasing ionic strength in an opposite trend to the inherent solubility (S
0) of Risp, thus indicating significant hydrophobic effect. The hydrophobic effect contributes to the extent of 72% towards
neutral Risp/HP-β-CD complex stability, while specific interactions contribute only 4.7 kJ/mol. Thermodynamic studies showed that 1:1 Risp/HP-β-CD complex formation is driven by a favorable enthalpy change (ΔH
0=−31.2 kJ/mol, ΔS
0=−7 J/mol.K) while the 1:2 complex is largely driven by entropy changes (ΔH
0=−5.0 kJ/mol, ΔS
0=42 J/mol.K). Complex stability was found to vary with pH, with a higher formation constant for neutral Risp. Molecular mechanical
computations using MM (atomic charges and bond dipole algorithms) and Amber force fields, which were carried out to explore
possible sites of interactions between Risp and CDs and to rationalize complex stoichiometry, produced similar results concerning
optimal inclusion complex geometries and stoichiometries. 相似文献
74.
Valery P. Nesterenko 《Journal of Thermal Analysis and Calorimetry》2005,80(3):575-577
Summary On the basis of calorimetric research of selenium dioxide, zirconium dioxide and zirconium diselenite dissolution reactions in the hydrofluoric acid solution under 298 K a standard enthalpy of Zr(SeO3)2 formation reaction from ZrO2 and SeO2 and a standard enthalpy of zirconium diselenite formation have been obtained. The value of enthalpy has been equal to -58.1±3.43 kJ mol-1 in ZrO2(solid)+2SeO2(solid) Zr(SeO3)2(solid) reaction. The standard enthalpy of zirconium diselenite formation is equal to Hf,2980Zr(SeO3)2(solid)= -1603.2±3.8 kJ mol-1. The Hf,2980 Zr(SeO3)2(solid) value has been determined for the first time. 相似文献
75.
John J. Lenhart Linda A. Figueroa Bruce D. Honeyman David Kaneko 《Colloids and surfaces. A, Physicochemical and engineering aspects》1997,120(1-3):243-254
This paper reports the development of a treatment system, using animal chitin as a passive biosorbent, for removing U(VI) from aqueous waste streams. An integral part of this system is a model that provides for the optimization of the treatment system through simulation of U(VI) removal efficiency based on the characteristics of the influent waste stream. The model accounts for changing solution matrix conditions through the coupling of surface complexation and mass transfer models. Complexation of U(VI) by chitin surface sites was modeled using FITEQL. Application of FITEQL in the “forward” mode provided the sorbed and aqueous phase concentrations needed for the mass transfer model. The mass transfer model was derived for both batch and continuously stirred tank reactor (CSTR) configurations using Fick's Law, reactor mass balances and rate law expressions. The coupled model was successfully validated using CSTR data at pH 6.5 and rate constants determined from batch sorption experiments. The CSTR configuration yields a steady-state, eighty percent U(VI) removal for 1 μM influent U(VI) with a solution-phase pH of 6.5 and 3.9 g l−1 chitin. 相似文献
76.
K. Ardhaoui J. Rogez A. Ben Chérifa M. Jemal P. Satre 《Journal of Thermal Analysis and Calorimetry》2006,86(2):553-559
Lanthanum-bearing silicate-oxyapatites or britholites, Ca10–xLax(PO4)6–x(SiO4)xO with 1≤x≤6, have been synthesized by solid state reaction
at high temperature. They were characterized by X-ray diffraction and IR spectroscopy.
Using two microcalorimeters, the heat of solution of these compounds have
been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained
least squares method was applied to the experimental results to obtain the
solution enthalpies at infinite dilution, and the mixing enthalpy in two steps.
In the first step the mixing enthalpy obtained is referenced to the britholite
monosubstituted and to the oxysilicate. The mixing enthalpy referenced to
the oxyapatite and to the oxysilicate is then extrapolated. In order to determine
the enthalpies of formation of all the terms of the solution, thermochemical
cycles were proposed and complementary experiments were performed. The results
obtained show a decrease of the enthalpy of formation with the amount of Si
and La introduced in the lattice. This was explained by the difference in
the bond energies of (Ca–O, P–O) and (La–O, Si–O). 相似文献
77.
Polymorphism of paracetamol 总被引:1,自引:0,他引:1
G. L. Perlovich Tatyana V. Volkova Annette Bauer-Brandl 《Journal of Thermal Analysis and Calorimetry》2007,89(3):767-774
The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature
dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured
and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications
in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG
sub298=60.0 kJ mol−1; ΔH
sub298=117.9±0.7 kJ mol−1; ΔS
sub298=190±2 J mol−1 K−1. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition
enthalpy at 298 K, ΔH
tr298(I→II)=2.0±0.4 kJ mol−1, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based
on ΔH
tr298 (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value
of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification
II were also estimated (ΔG
sub298=56.1 kJ mol−1; ΔH
sub298=115.9±0.9 kJ mol−1; ΔS
sub298=200±3 J mol−1 K−1). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported
found by classical thermochemical methods. 相似文献
78.
Wiskur SL Lavigne JJ Metzger A Tobey SL Lynch V Anslyn EV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(15):3792-3804
The thermodynamics of guanidinium and boronic acid interactions with carboxylates, alpha-hydroxycarboxylates, and diols were studied by determination of the binding constants of a variety of different guests to four different hosts (7-10). Each host contains a different combination of guanidinium groups and boronic acids. The guests included molecules with carboxylate and/or diol moieties, such as citrate, tartrate, and fructose, among others. The Gibbs free energies of binding were determined by UV/Vis absorption spectroscopy, by use of indicator displacement assays. The receptor based on three guanidinium groups (7) was selective for the tricarboxylate guest. The receptors that incorporated boronic acids (8-10) had higher affinities for guests that included alpha-hydroxycarboxylate and catechol moieties over guests containing only carboxylates or alkanediols. Isothermal titration calorimetry revealed the enthalpic and entropic contributions to the Gibbs free energies of binding. The binding of citrate and tartrate was investigated with hosts 7-10, for which all the binding events were exothermic, with positive entropy. Because of the selectivity of hosts 8-10, a simple boronic acid (14) was also investigated and determined to be selective for alpha-hydroxycarboxylates and catechols over amino acids and alkanediols. Further, the cooperativity of 8 and 9 in binding tartrate was also investigated, revealing little or no cooperativity with 8, but negative cooperativity with 9. A linear entropy/enthalpy compensation relationship for all the hosts 7-10, 14, and the carboxylate-/diol-containing guests was also obtained. This relationship indicates that increasing enthalpy of binding is offset by similar losses in entropy for molecular recognition involving guanidinium and boronic acid groups. 相似文献
79.
Kanibolotsky D. S. Bieloborodova O. A. Kotova N. V. Lisnyak V. V. 《Journal of Thermal Analysis and Calorimetry》2003,71(2):583-591
The enthalpies of mixing of liquid binary Fe-Ge (1765±5 K) and Fe-Si (1750±5 K) alloys were determined using a high-temperature
isoperibolic calorimeter. The thermodynamic properties of Fe-Ge melts were also studied by electromotive force method in the
temperature range of 1250-1580 K. The comparison of our measurement results with literature data has been performed. The extreme
negative values of integral enthalpy of mixing and alternating-sign deviations from Raoult's low for germanium can be explained
by the influence of binary clusters formation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption. 相似文献