Estimation of pore sizes in porous silicon by scanning electron microscopy and NMR cryoporometry

Certain possibilities of scanning electron microscopy and cryoporometry based on nuclear magnetic resonance (NMR) have been evaluated to determine pore sizes in porous silicon. The results obtained by these methods have been compared. NMR cryoporometry has been shown to be promising in the investigation of porous materials.     

Synthesis of alkenyl 3-hydroxy-2-naphthoates

Esterification of 3-hydroxy-2-naphthoic acid with homologous primary and secondary alkenyl alcohols with different chain lengths in the presence of N,N'-carbonyldiimidazole (CDI) and 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide gave the corresponding esters.     

Synthesis,some properties,and crystalline modifications of <Emphasis Type="Italic">fac</Emphasis>-[Ru(NO)(Py)<Subscript>2</Subscript>Cl<Subscript>3</Subscript>]

According to the data of ¹H NMR spectroscopy, trans-hydroxochloro complexes containing from two to four pyridine molecules in the internal sphere are formed on the heating of a dilute aqueous solution of K₂[Ru(NO)Cl₅] with pyridine. The evaporation of the reaction solution with concentrated hydrochloric acid gives fac-[Ru(NO)(Py)₂Cl₃] (I) in a yield of ~90%. The structures of two crystalline modifications of this complex are determined by X-ray diffraction analysis (CIF files ССDС nos. 1452208 (Ia) and 1452207 (Ib)). IR spectroscopy shows that the irradiation of complex I (λ ~ 450 nm, T = 80 K) results in photoisomerization with the formation of the metastable state MS1 in which the nitroso group is coordinated by the oxygen atom. The activation parameters of the photoisomerization are determined from the data of differential scanning calorimetry (DSC). Compound trans-[Ru(NO)Py₄(OH)]Cl₂ ? H₂O is isolated in a yield of ~70% on reflux of complex I with a pyridine excess in an aqueous solution, and the presence of molecules of water of crystallization in this compound is confirmed by thermal gravimetry (TG) and IR spectroscopy.     

A study of sodium bis(2-ethylhexyl) sulfosuccinate adsorption on silica from silver and gold organosols

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT) and silver and gold nanoparticles on SiO₂ from heptane solutions has been investigated by spectophotometery and CHN analysis. The adsorption isotherm of Aerosol OT is described by the Langmuir equation. Sorption capacity (2.4 × 10^–4 mol/g), sorption constant (9.0 m³/mol), and area per Aerosol OT molecule in an adsorption layer (0.83 nm²) have been determined. It has been shown that, at Aerosol OT concentrations lower than 6 × 10^–4 M, gold and silver ((0.3–6) × 10^–4 M) are simultaneously extracted by 98%; however, they have no effect on the adsorption and determination of the surfactant.     

Adsorption of hydrocarbons from solutions and gas phase on silica and alumina modified with silver and gold ions

The paper reports the immobilization of Ag⁺ cations on alumina and silica and AuCl ₄ ^? anions on amino silica and alumina. The method of inverse gas chromatography have demonstrated that Ag(I)-silica is selective for the separation of alkanes, alkenes, alkines, and arenes. The dependence of the capacitance of Ag(I) and Au(III) composites with regard to phenylacetylene (PHA) on the nature of the carriers, surface concentration, and technique of immobilizing ion metals has been considered. The isotherms of the adsorption of PHA from solutions in octane have been measured. It has been revealed that the capacitance of composites with regard to toward PHA prepared by the immobilization of ammoniates of silver nitrate on silicon dioxide is several times higher than for composites based on alumina with the same silver concentration and composites prepared by the immobilization of silver nitrate on silicon dioxide. The capacitance of the Au(III) composite based on alumina for PHA is significantly higher than for that based on aluminum oxide. The highest capacitance for PHA (0.83 and 0.88 molecules per metal ion) is observed for Ag(I) silica and the Au(III) alumina composite. In the visible region, the diffuse reflection spectra of amino silica Au(III) composites have a significant shift of the maximum of adsorption band along with the decrease in the concentration of immobilized anions of AuCl ₄ ^? , which evinces the formation of coordination bonds between free amin?propyl groups of the silica carrier and gold atom. The formation of these bonds prevents the adsorption of PHA on amino silica Au(III) composites with low gold concentrations.     

Specific Features of the Response of Cerium to Pulsed Actions

Experimental studies of cerium at high rates and nanosecond durations of action have been performed. The isomorphic phase transition was studied upon shock compression. The spall strength of cerium has been determined. Cerium demonstrates anomalous compressibility upon dynamic loading. Stress waves dampen under action of a high-current electron beam due to the energy dissipation during fragmentation and twinning.     

Nucleophilic Substitution at a Four-Coordinate Sulfur Atom: VI. Reactivity of Oximate Ions

The kinetics of the reaction of oximate ions with 2,4-dinitrophenyl p-toluenesulfonate, 4-nitrophenyl p-toluenesulfonate, diethyl 4-nitrophenyl phosphate, and ethyl 4-nitrophenyl ethylphosphonate in H₂O-DMSO mixtures (0 to 95 vol % of DMSO) cannot be described in terms of a single Bro/nsted equation. Regardless of the nature of the reaction center and leaving group, both in water and in 80% DMSO fast leveling of the reactivity of oximate ions is observed, the -effect decreases at pK _a 9.0 and disappears at pK _a 12.0 owing to difference in the solvation of weakly (pK _a 9.0) and strongly basic (pK _a 9.0) oximate ions rather than to change of the transition state. Just unfavorable solvation effects are responsible for the fact that the limiting nucleophilic reactivity of oximate ions (as typical -nucleophiles) is not higher than the reactivity of strongly basic alkoxide ions.     

Algorithm for Constructing Exact Solutions of the Problem of Unsteady Plane Motion of a Fluid with a Free Surface

JETP Letters - Unsteady plane potential flows of an ideal incompressible fluid with a free surface in the absence of external forces and capillarity are studied. An algorithm to construct exact...     

Role of the hydrophobic properties of functional detergents on micellar effects in the dissociation of environmental toxicants

1-Alkyl-3-(2-oximinopropyl)imidazolium chlorides were prepared with different alkyl chain lengths (Alk = C₁₂H₂₅, C₁₄H₂₉). Some physicochemical indices (CMC and pK _a^app) were determined. The reactivity of these compounds was studied in the dissociation of 4-nitrophenyl esters of diethylphosphonic, diethylphosphoric, and toluenesulfonic acids. The times for 50% conversion of the substrates into reaction products decrease in the series: C₁₂H₂₅ > C₁₄H₂₉ >C₁₆H₃₃. In selecting the direction of modification of the supernucleophilic functional surfactants, we should take into account not only their hydrophobic properties but also the efficiency of substrate solubilization as well as the reactivity of the oximate group in the surfactant micelles.