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1.
Dergunov AD Vorotnikova YY Visvikis S Siest G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(5):1127-1137
The self-association state of human plasma apolipoprotein E (apoE) in solution and in complexes with dimyristoylphosphatidylcholine (DMPC) varying in stoichiometry was studied in sub-micromolar concentration range by gel filtration, fluorescence anisotropy, fluorescence quenching and energy transfer measurements with apolipoprotein labeled with lysine-specific fluorescent dyes. Together, these results confirm the equilibrium scheme for various apoE structures in solution: oligomer (in aged preparations) <==> 'closed' tetramer <==> 'open' tetramer ('molten globule' state) <==> native or partially denatured monomer <==> fully denatured monomer. Within DMPC:apoE discoidal complex (125:1) the apolipoprotein association state seems to be intermediate between that in solution and in larger vesicular complex (1000:1); for both complexes, the degree of exposure of fluorescein chromophores into water phase decreased. Hetero-associates of apoA-I and apoC-III-1 in solution and in the complexes with DMPC appear to behave similarly to apoE. When extrapolated to native HDL particles, 'molten globule' state seems to be a structure responsible for the interaction of exchangeable apolipoproteins with phospholipid. For a first time, the location of various apolipoprotein molecules on disc periphery was confirmed. The lysine residue(s) seems to locate closely to reacting residue(s) within apolipoprotein molecules in associates, however, with different package constraints for discoidal versus vesicular complexes with phospholipid. 相似文献
2.
Russian Chemical Bulletin - 相似文献
3.
Reactions of mercury(II) with iminodiacetic (H2Ida), 2-hydroxyethyliminodiacetic (H2Heida), and nitrilotriacetic acids (H3Nta) were studied by spectrophotometry and pH potentiometry. The resulting complexes included [HgIda], [Hg(OH)Ida]?, [HgIda2]2?, [HgHeida], [Hg(OH)Heida]?, [Hg(Heida)2]2?, [HgNta]?, [HgNta2]4?, [Hg(Ida)Heida]2?, [Hg(Ida)Nta]3?, and [Hg(Heida)Nta]3?. The logarithms of their stability constants calculated for I = 0.1 (NaClO4) and T = 20 ± 2°C were 11.14 ± 0.07, 20.33 ± 0.08, 19.40 ± 0.10, 11.42 ± 0.04, 19.68 ± 0.11, 18.48 ± 0.09, 13.42 ± 0.05, 20.80 ± 0.08, 19.05 ± 0.06, 20.64 ± 0.11, and 20.53 ± 0.16, respectively. The experimental data were analyzed in terms of the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow one to consider only those species that are sufficient for accurate reproduction of the observed pattern. 相似文献
4.
Na2H3IO6 decomposes with water and oxygen evolution in the range of 180–250°C under the atmospheric pressure or in a dynamic vacuum. The solid residue is an equimolar mixture of NaIO3 and Na3IO5. Na3IO5 likely occurs in the form of the dimer Na6I2O10. An intermediate thermolysis stage is the elimination of a water molecule from the salt molecule with simultaneous disproportionation of the salt to trisubstituted orthoperiodate and metaperiodate: Na2H3IO6 = 0.5Na3H2IO6 + 0.5NaIO4 + H2O. Li2H3IO6 thermolysis under the atmospheric pressure proceeds in the same way; however in vacuum, the thermolysis yields LiIO3 and Li5IO6 in the ratio of 3: 1 (mol/mol). The reason for the different thermolysis routes lies in the different stability of the intermediates M3H2IO6 and MIO4. 相似文献
5.
6.
Journal of Structural Chemistry - 相似文献
7.
A. A. Reznikov V. A. Shaposhnik 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(2):179-181
The critical distances for the formation of ion pairs were calculated by a nonempirical quantum-chemical method. The results were in agreement with the Bjerrum theory. Ion pair formation in aqueous solutions of lithium and sodium chlorides was visualized, and the energies of ion pair formation calculated. 相似文献
8.
Infrared and Raman spectroscopy were used to study hydrogen-bonding interactions and the cation coordination effect in solutions of N,N-dimethylethylenediamine (DMEDA) with lithium triflate (LiTf) and sodium triflate (NaTf). A comparison of pure DMEDA with DMEDA dissolved in carbon tetrachloride enabled the separation of the relative contributions of intermolecular and intramolecular hydrogen-bonding interactions to the N-H stretching frequencies. The addition of LiTf and NaTf to DMEDA shifts the N-H stretching frequencies through two competing effects: the cation coordination effect lowers the frequencies, while the disruption of the hydrogen-bonding interactions increases the frequencies. These two effects were distinguished in a study of the concentration dependence of both salts dissolved in DMEDA; the differentiation was based on the difference in the spectral sensitivities of the symmetric and the antisymmetric stretch in both the Raman and infrared spectra. During this study, DMEDA-LiTf and DMEDA-NaTf crystals were discovered, and their structures were solved by X-ray diffraction techniques. The analysis of the vibrational spectra of these crystals was greatly enhanced by unambiguous knowledge of the structural details of cation-molecule and anion-cation interactions. These structure-spectra correlations were used to complement analogous spectroscopic studies in the solution phases. Analysis of spectral regions in both crystalline and solution phases particularly sensitive to the nature and strength of cation-molecule interactions clearly established that the interaction of the lithium ion with the nitrogen atoms of DMEDA was stronger than the sodium ion-DMEDA interaction, as expected from charge density arguments. 相似文献
9.
A. Yu. Tsivadze A. V. Dorokhov A. Yu. Masanov E. V. Nikitin N. A. Votinova 《Russian Journal of Coordination Chemistry》2007,33(8):560-565
A method for the synthesis of complexes of sodium and lithium borohydrides with crown ethers is proposed. The complexes of sodium borohydride with benzo-15-crown-5, 4′-aminobenzo-15-crown-5, dibenzo-18-crown-6, and diaza-18-crown-6 and the complexes of lithium borohydride with benzo-15-crown-5 and dibenzo-18-crown-6 are synthesized. These complexes can be used for the preparation of hydrogen in their reactions with methanol. The complex formation does not affect the purity of hydrogen formed. 相似文献
10.
M. R. Saidi R. Stan Brown A. Ziyaei-Halimjani 《Journal of the Iranian Chemical Society》2007,4(2):194-198
A one-pot high yielding reductive amination of aldehydes with primary and secondary amines using LiClO4/NaBH4 and LiClO4/LiAlH4 as reducing agents in diethyl ether is described. 相似文献
11.
C. Umfer L. Windholz M. Musso 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,25(1):23-29
Experimental and theoretical investigations of the splitting of the hyperfine structure of the sodium and lithium-D-lines in magnetic fields between 0 and 1 T were performed. In this magnetic field region the fine structure levelsJ=1/2 andJ=3/2 of the excited term2
P begin to influence each other. In case of lithium crossings and anticrossings of hyperfine states stemming from different fine structure energy levelsJ=1/2 andJ=3/2 can be observed. The measurements were performed by laseratomic-beam spectroscopy in dependence on the applied external magnetic field strength. The experimental spectra were compared with computed spectra. Spectra were simulated by calculations using for the hyperfine hamiltonian two hyperfine constantsA andB in case of sodium and four hyperfine constantsa
c
,a
d
,a
0 andb in case of lithium. Values for this constants could be derived by fitting the theoretical splittings to the experimental ones. For the first time theg
I
— factor of sodium could be determined in a purely optical way. 相似文献
12.
K. A. Yakimovich 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(7):1154-1157
A Li-LiH-type system under liquid-vapor phase equilibrium conditions was considered. Liquid is a binary infinitely dilute
solution of lithium hydride in lithium, and the coexisting vapor phase is a multi-component chemically reacting ideal mixture
of gas components. The phenomenon of the existence of azeotropy in such systems, earlier unknown, was established. The concentration
of the components was expressed in the atomic fractions of hydrogen in both phases. The temperature and concentration boundaries
of the azeotropic zone were found. The trends revealed are of importance for applications. 相似文献
13.
O. N. Kalugin V. G. Panchenko A. P. Dolgareva A. G. Nikolaichuk I. N. V’yunnik 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(9):1480-1483
The total limiting molar electrical conductivities of ions and triads of ions and the association constants of ions with the formation of ion pairs and triads of ions were calculated from the concentration dependences of the electrical conductivity of solutions of lithium and sodium perchlorates in tetrahydrofuran at 278.15–318.15 K with the use of the method specially developed earlier. The experimental total limiting electrical conductivities were used to calculate the limiting molar electrical conductivities and attraction friction factors of separate ions (Li+, Na+, ClO 4 ? , Li2ClO 4 + , Na2ClO 4 + , Li(ClO4) 2 ? , and Na(ClO4) 2 ? ). The constants of ion association into ion pairs were used to calculate the Gibbs energy of non-Coulomb interionic interaction (ΔG*+?), and the constants of association into triads of ions, to determine the a 3 distance parameter between the centers of the ion and the dipole of the ion pair. Positive ΔG*+?), values and deviations of the experimental a 3 value from the distance parameter calculated theoretically (a 3 0 ) for the triad of ions (Δa 3 = a 3 ? a 3 0 ) were related to non-Coulomb repulsion in the region of overlap of the solvation shells of ions and the influence of temperature and ion charge density on this repulsion. 相似文献
14.
Far-infrared spectra of sodium and lithium cryptates were observed in several nonaqueous solvents. The spectra are characterized by a broad band whose frequency is independent of the solvent or of the anion and which is assigned to the vibration of the cation in the cryptand cavity. The band frequencies were 234±2, 218±1, 243±3, and 348±1 cm?1 for Na+-C222, Na+-C221, Li+-C221, and Li+-C211 cryptates, respectively. These bands were found to be Raman-inactive, indicating that the cation-ligand interaction is very largely electrostatic in nature. 相似文献
15.
Allevi M Bonizzoni M Fabbrizzi L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(13):3787-3795
The tripodal system 4, in which urea fragments are appended to the three terminal amine nitrogen atoms of a tris(2-aminoethyl)amine (tren) subunit, includes a Cu(II) ion and two anions X-, according to a cascade mechanism through three well defined stepwise equilibria in a DMSO solution. The first anion X- (halide, N3-, NCS-, NO2-, H2PO4-) seeks the Cu(II) centre coordinated by the tren moiety; the second anion X- interacts with the trisurea cavity, but this occurs only if the stronger H-bond acceptors, such as N3- and H2PO4-, are used. Binding of the second X- ion is favoured by the preorganising effect exerted by the metal and disfavoured by the steric and electrostatic repulsions between the anions. Under the appropriate conditions, heterodinuclear complexes of formula [Cu(II)(4)(Cl)(H2PO4)] can be obtained in solution, in which Cl- is bound to the metal centre and H2PO4- interacts with the trisurea compartment. 相似文献
16.
Phenylstearic acid, prepared from oleic acid and benzene, using the Friedel-Crafts reaction, has been confirmed to be a reproducible mixture of twelve positional isomers. Lithium and sodium salts of this acid are semi-crystalline solids which behave in many ways like pure single substances. The thermotropic polymorphism of these soaps has been studied using DSC and polarizing microscopy (as well as X-ray diffraction and 7Li NMR spectroscopy for the former soap). Both soaps exhibit characteristic stepwise melting behaviour and form stable reversed hexagonal mesophases at elevated temperatures, in contrast to the lamellar phases exhibited by the unsubstituted soaps. 相似文献
17.
Thermodynamic functions (heat capacity, enthalpy, free energy, and entropy) were recalculated for 7LiAlF4 from new spectroscopic data. The calculations were extended to include 6LiAlF4 and NaAlF4. The calculated entropy value of S = 110.98 e. u from the data on 7LiAlF4 shows excellent agreement with the recently reported thermo dynamic value (110.9 ± 2.5 e. u.). For NaAlF4 the agreement is not so good, but the calculated value of S = 113.20 e. u. compares fairly well with the most recent thermo dynamic value (116.8 ± 2.9 e.u.). 相似文献
18.
Maria Be?towska-Brzezinska Teresa ?uczakB?a?ej Gierczyk Krystian EitnerBogumil Brzezinski Rados?aw PankiewiczGrzegorz Schroeder 《Journal of Molecular Structure》2002,607(1):77-86
The complex formation of lithium and sodium ions with silicon podand solvents: phenyl-tris(1,4-dioxapentyl) silane (PhSi23) and ethyl-tris(1,4-dioxapentyl) silane (EtSi23) has been studied by FTIR, 1H-, 13C-, 7Li- and 23Na NMR. The far FTIR spectra show that the Li+ cations fluctuate very fast whereas Na+ cations are still localised between the oxygen atoms of the oxaalkyl chains. The 7Li NMR spectra prove that one Li+ cation can be coordinated not only by one but also two silicon podand molecules. The concentration dependence of the molar conductivity of LiClO4 in the podand solvents indicates charge transfer between ion clusters. 相似文献
19.
The IR and Raman spectra of sodium oxalate and the IR spectrum of lithium oxalate are re-examined. The Raman spectrum of lithium oxalate is presented for the first time. A recent structural study is used as the basis for the first detailed vibrational study of anhydrous potassium oxalate, phase II. 相似文献
20.
S. Marković Z. Marković Ne. Begović Ne. Manojlović 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(9):1392-1397
The mechanisms of the carboxylation reactions of lithium and sodium phenoxides are investigated by means of the DFT method
with a CEP-31 + G(d) basis set. The introduction of diffusion functions does not affect the outcome of the calculations. As a consequence, the
results of this investigation are in good agreement with the findings obtained by means of the LANL2DZ basis set. Lithium
phenoxide yields only salicylic acid in the Kolbe-Schmitt reaction. The reaction of sodium phenoxide can proceed in the ortho and para positions, but the para-substituted product can be expected at a very low concentration in the reaction mixture. The deviation of lithium and sodium
phenoxides from the mechanisms of carboxylations of other alkali metals is a consequence of the small ionic radii of lithium
and sodium.
The text was submitted by the authors in English. 相似文献