Effects of the nature and composition of the solvent on the thermodynamic characteristics of the individual forms of hydrogen adsorbed on the surface of porous nickel

The effects of the nature and composition of solvents on the thermodynamic characteristics of the adsorption states of hydrogen on nickel were studied. The adsorption can be described in terms of the thermodynamic model of a surface with a discrete nonhomogeneity for three individual forms of adsorbed hydrogen. The thermodynamic characteristics of the individual forms of hydrogen adsorbed on porous nickel from aqueous solutions of sodium hydroxide, dimethylformamide, methanol, and ethanol were determined.     

On the direct calculation of the time evolution of excited molecular states in the presence of nonadiabatic interactions

The possibility is explored of calculating the time evolution of a given initial molecular state, in the presence of sufficiently strong nonadiabatic interactions, with a fully quantum-mechanical approach. Two methods are presented. The first one is based on the determination of the molecular eigenstates, with expansion of the nuclear wavefunctions on a Hermite basis. The second method is based on the Padé 1,1 approximation of the time evolution operator and on a finite difference representation of the time-dependent nuclear wavefunctions. Both methods are applied to simple models of a diatomic molecule.     

Simulation of a monolayer adsorbed on a heterogeneous surface: effect of the size and shape of the adsorbate on the structure of the interface and the distribution of the adsorption energies

At the low temperature limit, the effect on the size and shape factors of the adsorbate molecule is shown in a simulation of a monomolecular phase adsorbed on a heterogeneous surface. This factor is reflected both in the theoretical distribution of the adsorption energies and the packing of the adsorbed phase.     

Effect of the nature of the active component and support on the activity of catalysts for the hydrolysis of sodium borohydride

The effect of the nature of an active component and a support on the rate of hydrolysis of aqueous sodium borohydride solutions was studied. It was found that the activity of supported catalysts, which were reduced in a reaction medium of sodium borohydride, decreased in the order Rh > Pt ≈ Ru ? Pd regardless of the nature of the support (γ-Al₂O₃, a Sibunit carbon material, or TiO₂). The catalysts based on TiO₂ exhibited the highest activity. As found by UV-vis diffuse reflectance spectroscopy, the composition and structure of the supported precursor of an active component depend on the nature of the support. It is likely that rhodium clusters with different reaction properties were formed on various supports under the action of a reaction medium.     

Enhancement of the third-order nonlinear optical properties in open-shell singlet transition-metal dinuclear systems: effects of the group, of the period, and of the charge of the metal atom

Metal-metal multiply bonded complexes in their singlet state have been predicted to form a novel class of "σ-dominant" third-order nonlinear optical compounds based on the results of dichromium(II) and dimolybdenum(II) systems (H. Fukui et al. J. Phys. Chem. Lett.2011, 2, 2063) whose second hyperpolarizabilities (γ) are enhanced by the contribution of the dσ electrons with an intermediate diradical character. In this study, using the spin-unrestricted coupled-cluster method with singles and doubles as well as with perturbative triples, we investigate the dependences of γ on the group and on the period of the transition metals as well as on their atomic charges in several open-shell singlet dimetallic systems. A significant enhancement of γ is observed in those dimetallic systems composed of (i) transition metals with a small group number, (ii) transition metals with a large periodic number, and (iii) transition metals with a small positive charge. From the decomposition of the γ values into the contributions of dσ, dπ, and dδ electrons, the γ enhancements are shown to originate from the dσ contribution, because it corresponds to the intermediate diradical character region. Furthermore, the amplitude of dσ contribution turns out to be related to the size of the d(z(2)) atomic orbital of the transition metal, which accounts for the dependence of γ on the group, on the period, and on the charge of the metal atoms. These dependences provide a guideline for an effective molecular design of highly efficient third-order nonlinear optical (NLO) systems based on the metal-metal bonded systems.     

The effect of the order of the autocatalysis on the transverse stability of reaction fronts

A linear stability analysis of planar reaction fronts to transverse perturbations is considered for a system based on an autocatalytic reaction of general order p. Dispersion curves, plots of the growth rate sigma against a transverse wavenumber k, are obtained for a range of values of p and D, where D is the ratio of the diffusion coefficients of autocatalyst and substrate. A value D(0) of D, dependent on p, is found at which sigma(max), the maximum value of sigma in the unstable regime, is largest, with D(0) increasing as p is increased. An asymptotic analysis for small wavenumbers is derived, which enables the region in the (p, D) parameter space for instability to be determined. An analysis for D small is undertaken, which leads to upper bounds on the wavenumber for a possible instability.     

On the investigation of the low-energy conformational space of molecules

A new perspective on traditional energy minimization problems is provided by a connection between statistical thermodynamics and combinatorial optimization (finding the minimum of a function depending on many variables). The joint use of a new method for uncovering the global minimum of intramolecular potential energy functions, based on following the asymptotic behavior of a system of stochastic differential equations, and an iterative-improvement technique, whereby a search for relative minima is made by carrying out local quasi-Newton minimizations starting from many distinct points of the energy hypersurface, proved most effective for investigating the low-energy conformational space of molecules.     

Effect of the shape of human erythrocytes on the evaluation of the passive electrical properties of the cell membrane

The possible influence of the cell shape on the derivation of the passive electrical parameters of a biological cell membrane is discussed in light of two different models which describe the cell as a shelled ellipsoidal particle and as a biconcave disk obtained by the revolution of the Cassini oval, respectively. Whereas within the first model, the Laplace equation can be solved analytically, in the second one a numerical algorithm based on the boundary element method has been employed. We have compared the results obtained by these two different models in the case of normal human erythrocyte cell membrane, using radiowave dielectric spectroscopy measurements. Our findings show that, although in principle the cell shape might deeply affect the evaluation of the passive electrical parameters of the cell membrane, in the case of the erythrocyte shape modelled by the Cassini curve, only small deviations are evidenced in comparison to the values derived, as usually done in the dielectric spectroscopy of biological cell suspensions, from an ellipsoidal model analysis. This result gives further support to the reliability of the data reported in the literature based on an ellipsoidal shape erythrocyte model.     

Influence of the structure of the alcoholic modifier on the enantioselective separation of nadolol

The influence of the structure of the alcoholic modifier of the mobile phase on the liquid chromatographic separation of the optical isomers of nadolol on a Pirkle-type chiral stationary phase was investigated. The isomers were separated as their chiral 1-naphthylureides on a column consisting of 3,5-dinitrobenzoyl- -leucine covalently bound to 3-μm aminopropylsilica, using an eluent consisting of n-hexane modified with an alcohol. A number of straight-chain, branched and unsaturated alcohols with carbon numbers ranging from 1 to 8 were evaluated. The choice of alcohol influenced both retention and selectivity, with optimum stereoselectivity being observed for C₃. The alcoholic modifiers selectively affected the retention and resolution of the two pairs of enantiomers that constitute nadolol. Thus chromatograms displaying two, three or four peaks could be obtained, depending on which modifier was employed. The best separation of all four isomers was achieved with ethanol as the modifier.     

Characteristics of the cholinesterase of the venom of the central Asian cobra

Summary 1. By rechromatography on sulfoethyl-Sephadex C-50, an electrophoretically homogeneous preparation of cholinesterase has been obtained from the venom ofNaja oxiana Eichwald.2. The activity of the cholinesterase isolated depends on the concentration of the enzyme and the time and temperature of incubation, and also on the pH. The following must be considered the optimum conditions: time of incubation of the enzyme with the substrate 20–30 min, pH 8.0–8.5, temperature 37–38°C.3. Diisopropyl phosphorofluoridate (DIPF) in a concentration of 2 µM completely suppresses the activity of the cobra venom cholinesterase.4. The venom cholinesterase hydrolyzes acetylcholine chloride and acetylthiocholine bromide but has no effect on butyrylthiocholine bromide, in which respect it resembles the true cholinesterases.5. Preparations of cobra venom cholinesterase do not possess a lethal action and do not potentiate the activity of the neurotoxins of the same venom.Institute of Biochemistry, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 783–789, November–December, 1972.     

Influence of the structure of boundary layers and the nature of counterions on the position of the isoelectric point of silica surfaces

Dependences of electrokinetic potentials of different silica materials (nano-and ultraporous glasses, a quartz glass plane-parallel capillary, and monodisperse spherical particles of silicon oxide) on the pH of solutions containing single-, double-, and triple-charged cations have been compared. It has been shown that the degree of hydration of a single-charged cation and the structure of an interface substantially affect the position of the isoelectric point (IEP). The most hydrated Na⁺ ions have virtually no effect on the position of the IEP up to their concentration of 0.1 M irrespective of the thickness of an ion-permeable layer at the surface of a solid phase. A reduction in the radius of a hydrated cation (K⁺, Cs⁺) enables its penetration into an ion-permeable layer and, as a consequence, causes the IEP to shift toward larger pH values depending on the parameters of this layer. Two IEPs are observed in LaCl₃ solutions: one at a pH value close to pH_IEP in NaCl solutions and another at a higher pH value corresponding to the charge reversal of the Stern layer.     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

Influence of the errors made in the measurement of the extra-column volume on the accuracies of estimates of the column efficiency and the mass transfer kinetics parameters

The influences of the errors made in the measurement of the extra-column volume of an instrument on the accuracies of the estimates made of the column efficiency and of the parameters of the mass transfer kinetics were investigated from an experimental point of view. A standard HP1090 apparatus (extra-column volume, approximately 50 micro L) was used to measure the efficiency of a Sunfire-C(18) RPLC column (column hold-up volume, approximately 1.50 mL). The first and second moments of the peaks of phenol (a retained compound) and of thiourea (a practically non-retained compound) were measured at six different temperatures between 22 and 78 degrees C, for flow rates between 0.10 and 4.70 mL/min (i.e., for linear velocities between 0.025 and 1.179 cm/s). Each series of measurements was successively made with the instrument being fitted with and without the column. The experimental HETP data must be corrected for the solute dispersion in the connected tubes in order properly to assess the true column efficiency. Even with a modern, high performance instrument, the dispersion of a non-retained compound is essentially due to the band broadening phenomena that take place in the extra-column volumes, the sum of all these extra-column band broadening contributions accounting for more than 80% of the total band broadening measured. The contribution of the sampling device is particularly deleterious since, for a 2 mu L injection, the maximum solute concentration in the peak that enters into the column is nearly ten-fold lower than that of the sample. Nevertheless, the impact of the extra-column volumes on the estimates of the kinetic parameters (e.g., molecular diffusion coefficient D(m) and effective particle diffusivity D(e)) remains negligible. Obviously, the relative error made on the column efficiency of a retained compound depends much on its retention factor. It decreases from 8 to 1% when the retention factor increases from 5 to 17.     

Investigations on the influence of the substrate on the crystal structure of sputtered LiCoO2

The influence of the uppermost substrate layer on the structural properties of sputtered lithium cobalt oxide (LiCoO₂) is discussed in this work. For this purpose, bare, oxidized, and platinum-coated silicon wafers, as well as stainless steel and titanium sheets, were used as substrates. The resulting crystal structure of LiCoO₂ deposited on these substrates was analyzed and discussed. The LiCoO₂ thin films were deposited by RF magnetron sputtering with different film thicknesses. A subsequent annealing step at 700 °C was performed to induce the crystallinity of LiCoO₂. The crystal orientation was determined by X-ray diffraction. The obtained results show a strong dependency of LiCoO₂'s crystal structure on the surface the film is deposited on. However, the strong influence of the film thickness reported in previous publications could not be observed. If LiCoO₂ is deposited on the substrates with a metallic surface, a strong (003) preferential orientation is obtained for a wide range of film thicknesses. In contrast, sputtering of LiCoO₂ on bare and on oxidized silicon wafers results in a (101) dominated crystal structure for the different film thicknesses. These experiments show the importance of the characterization of LiCoO₂'s crystal structure in the intended battery setup.     

Amplification of chirality of the majority-rules type in helical supramolecular polymers: the impact of the presence of achiral monomers

We present a theoretical treatment describing the conformational state of helical supramolecular polymers that consist of three types of monomer: right-handed and left-handed chiral monomers and achiral ones. We find that chirality amplification of the majority-rules type, that is, a disproportionately large shift in the helix screw sense due to a small enantiomeric excess, can occur in these polymers. The strength of the chirality amplification depends on the free-energy penalty of a helix reversal along the self-assembled chain and on that of a mismatch between the conformation of a bond and the preferred conformation of the preceding monomer. It turns out that the impact of achiral monomers also depends on these two parameters. For high values of these free energies, the net helicity does not change much from the situation where no achiral material is present. However, if the free-energy penalties are not both large, the impact of the achiral monomers on the conformational state of the aggregates can be quite substantial.     

Influence of the structure of the double layer on the polarographic behavior of nitro compounds

Summary The structure of the double electrical layer has a considerable effect on the half-wave potential of the logarithmic wave of the reduction of nitrocompounds, the change in the effective potential jump exerting the main influence; the increase in the pH in the peri-electrodic layer on increasing the ionic strength of the solution has a considerably smaller effect.     

Improvement of the Composition of Detergent Solutions for the Removal of Deposits on the Axial-Compressor Blades of Gas-Turbine Units

During the operation of gas-turbine units deposits, which have the form of a conglomerate of hydraulic oil and contaminations from atmosphere air, are accumulated on the axial-compressor blades. Deposits are occasionally removed using solid abrasive or detergent solutions. Only detergent solutions are employed on modern units, because abrasive substances damage the protective sputtering of blades. The detergent solutions that are used have a high cost and are unsafe in use. In this work, a high-performance detergent solution is suggested, which is able to dissolve deposits on the axial-compressor blades of gas-turbine units.     

Dependence of the composition of the lipids of the seeds ofPlectranthus glaucocalyx on the conditions of growth

A change in the geographical growth zone and in the density of the soil has a substantial influence on the amount of lipids in the seeds ofPlectranthus glaucocalyx Maxim. and their degree of unsaturation, and also on the structure of the triacylglycerols.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 30–35, January–February, 1984.     

From the Micro- to the Macro-: Managing the Conservation of the Warship,Vasa

Sweden's famous warship, Vasa, sank on her maiden voyage in August 1628, and remained on the bottom of Stockholm harbour for 333 years. Raised in 1961, she became the first large-scale wooden object to be treated with polyethylene glycol (PEG). In the summer of 2000 a number of acidic salt precipitations were noticed on the surface of the ship and on wooden artefacts in the storerooms. An international research project has been established to look into the causes of this problem and suggest possible re-treatments. Meanwhile projects are underway to monitor movements in the ship, to build a better support system, and to replace the thousands of iron bolts holding the structure together, while a sophisticated new climate system has recently been installed in the museum.