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61.
Vinarov Z Petkova Y Tcholakova S Denkov N Stoyanov S Pelan E Lips A 《Langmuir : the ACS journal of surfaces and colloids》2012,28(21):8127-8139
An in vitro study is performed with sunflower oil-in-water emulsions to clarify the effects of type of used emulsifier, its concentration, and reaction time on the degree of oil lipolysis, α. Anionic, nonionic, and cationic surfactants are studied as emulsifiers. For all systems, three regions are observed when surfactant concentration is scaled with the critical micelle concentration, C(S)/cmc: (1) At C(S) < cmc, α ≈ 0.5 after 30 min and increases up to 0.9 after 4 h. (2) At C(S) ≈ 3 × cmc, α ≈ 0.15 after 30 min and increases steeply up to 0.9 after 2 h for the cationic and nonionic surfactants, whereas it remains around 0.2 for the anionic surfactants. (3) At C(S) above certain threshold value, α = 0 for all studied surfactants, for reaction time up to 8 h. Additional experiments show that the lipase hydrolyzes molecularly soluble substrate (tributirin) at C(S) > cmc, which is a proof that these surfactants do not denature or block the enzyme active center. Thus, we conclude that the mechanism of enzyme inhibition by these surfactants is the formation of a dense adsorption layer on an oil drop surface, which displaces the lipase from direct contact with the triglycerides. 相似文献
62.
Danov KD Stoyanov SD Vitanov NK Ivanov IB 《Journal of colloid and interface science》2012,368(1):342-355
Here we present the exact solution of two approaching spherical droplets problem, at small Reynolds and Peclet numbers, taking into account surface shear and dilatational viscosities, Gibbs elasticity, surface and bulk diffusivities due to the presence of surfactant in both disperse and continuous phases. For large interparticle distances, the drag force coefficient, f, increases only about 50% from fully mobile to tangentially immobile interfaces, while at small distances, f can differ several orders of magnitude. There is significant influence of the degree of surface coverage, θ, on hydrodynamic resistance β for insoluble surfactant monolayers. When the surfactant is soluble only in the continuous phase the bulk diffusion suppresses the Marangoni effect only for very low values of θ, while in reverse situation, the bulk diffusion from the drop phase is more efficient and the hydrodynamic resistance is lower. Surfactants with low value of the critical micelle concentration (CMC) make the interfaces tangentially immobile, while large CMC surfactants cannot suppress interfacial mobility, which lowers the hydrodynamic resistance between drops. For micron-sized droplets the interfacial viscosities practically block the surface mobility and they approach each other as solid spheres with high values of the drag coefficient. 相似文献
63.
Alexandrov NA Marinova KG Gurkov TD Danov KD Kralchevsky PA Stoyanov SD Blijdenstein TB Arnaudov LN Pelan EG Lips A 《Journal of colloid and interface science》2012,376(1):296-306
The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins. 相似文献
64.
A. G. Belov Yu. P. Gangrsky L. M. Melnikova V. Yu. Ponomarev N. Tsoneva Ch. Stoyanov A. Tonchev N. Balabanov 《Physics of Atomic Nuclei》2001,64(11):1901-1908
Isomeric ratios were measured for N=81 isotones (135Xe, 137Ba, 139Ce, 141Nd, 143Sm). In the experiment reported here, μ ν ≤3±10? J π=11/2? isomers were excited in (n, γ) and (γ, n) reactions and in the β + decay of 139Pr and 141Pm. In order to determine the reaction yields, use was made of the activation method involving measurement of the gamma-ray spectra of reaction products. It is found that, in the same reactions, isomeric ratios are different for isotones characterized by different atomic numbers Z. Isomeric ratios were calculated with the spectra of low-lying levels and radiative-transition probabilities established on the basis of the quasiparticle-phonon model. Good agreement between the experimental and calculated values of isomeric ratios is obtained for all isotopes invesigated here. The dependence of isomeric ratios on the atomic number Z of a nucleus is explained by the difference of reaction energies, which leads to different probabilities of excitation of activation levels through which the isomers being considered are populated. 相似文献
65.
E. S. Stoyanov 《Journal of Structural Chemistry》2000,41(3):440-445
It is found that cyclic trimer I and linear dimer II are the molecular states of palladium(II) acetate in its 1. 10-3-0.7 M chloroform solutions. The mole fraction of dimer II is higher in dilute solutions. Even with small acetic acid (HOAc)
additions the I↔II equilibrium is shifted toward I because of the variation of the composition of the outer-spheric solvation
shells. The content of II in the 0.1 M solution of PdAc2 in 50 vol. % HOAc+CHCl3 is 10%. However, in the thin subsurface layers of this solution at the interface CaF2 -solution, the I↔ equilibrium is slowly shifted toward II whose concentration after 60 min is 22%. This may be caused by
structuring of the liquid phase in the subsurface layers during the measured time.
Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 540-546, May–June, 2000. 相似文献
66.
State of Molecules and Ions in the Structural Channels of Synthetic Beryl with an Ammonium Impurity 总被引:1,自引:0,他引:1
The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containing solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the paramagnetic NH
3
+
and H0 radicals are stabilized in the structural channels of beryl. In addition to the known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well. For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a silicon-oxygen ring with two water molecules in adjacent cavities. 相似文献
67.
R. Schwengner W. Schauer G. Winter P. von Brentano J. Eberth J. Enders T. von Egidy M. Grinberg R.-D. Herzberg N. Huxel L. Käubler P. von Neumann-Cosel N. Nicolay J. Ott N. Pietralla H. Prade S. Raman J. Reif A. Richter C. Schlegel H. Schnare T. Servene S. Skoda C. Stoyanov H.G. Thomas I. Wiedenhöver A. Zilges 《Zeitschrift für Physik A Hadrons and Nuclei》1997,358(2):197-198
Excited states of the nuclei 122Te, 126Te and 130Te were populated via the (γ, γ') reaction at endpoint energies of the bremsstrahlung between 4.5 and 5.5 MeV. Gamma rays were detected with a EUROBALL-CLUSTER detector and a single detector. In all nuclei several dipole transitions were identified at energies around 3 MeV. The lowest corresponding J = 1 states are interpreted as two-phonon excitations. Quasiparticle-phonon-model calculations predict one 1? state arising from the coupling of the first quadrupole and the first octupole phonon and one 1+ state arising from the coupling of the first and the isovector second quadrupole phonon at about 3 MeV. The calculated transition strengths are compatible with experimental ones. 相似文献
68.
Different isoelectric buffers are analysed theoretically, taking into account a fundamental parameter, i.e., the ratio between intrinsic buffering power and conductivity (R=β/λ). For a model ampholyte, the above parameter is analysed both as a function of the pI and the pKb–pKa values. For natural pH gradients, the variation of R, connected with approaching the isoelectric point, is evaluated. A case of oligo-protic ampholytes is also considered. 相似文献
69.
A. P. Severyukhin V. V. Voronov Ch. Stoyanov N. Van Giai 《Physics of Atomic Nuclei》2004,67(9):1756-1759
A finite-rank separable approximation for the quasiparticle RPA calculations with Skyrme interactions that was proposed in our previous work is extended to take into account the coupling between one-and two-phonon terms in the wave functions of excited states. It is shown that the phonon-phonon coupling effect can be very important to reproduce experimental data. 相似文献
70.
The electrophoretic behaviors of different analytes in capillary zone electrophoresis were studied by the Whole Column Imaging Detection (WCID). For capillary zone electrophoresis (CZE) in conventional buffer systems, non-constant sample plug movement characterized by progressive decrease of peak migration velocity was observed. The appropriate velocity decrease was correlated with a degree of ionization of the analyzed ion, thus the effect observed could be explained by fast buffer composition change resulting in the development of a non-linear pH gradient. To visualize the appropriate pH gradient, the concentration profile of initially uniformly distributed amphoteric substances was also monitored. The evolution of the concentration profile exhibited very complex dynamics. In addition, it was found that the nature of the electrode solutions strongly affect changes in the background electrolyte. In the case of traditional background electrolytes with an acid-base pair for electrode solutions a non-uniform ampholyte concentration developed quickly, leading finally to a quasi-stationary profile similar to those typical of IEF. Possible approaches to suppress a negative impact of the background electrolyte composition changes during electrophoretic run on CE-separation are presented herein. In particular it was observed that zwitterionic buffers are able to withstand prolonged electrolysis much better compared to traditional buffers. 相似文献