Growth and motion of heterogeneous water droplets in laminar diffusion chambers: 2. High nanoparticle concentrations

The heterogeneous condensation of water vapor on nanoparticles and the growth of formed droplets are numerically studied under conditions of laminar diffusion chamber (LDC) of a new type with a hot porous wall. The main attention is focused on the growth of heterogeneous droplets in the gas flow at high number densities of nanoparticles exceeding 10⁸ droplet/m³. Under these conditions, there is an interrelation between the growth of droplets and processes of heat and mass transfer in LDC due to vapor depletion and the release of latent heat of phase transition on growing droplets. The efficiency of the coverage of nanoparticles with water film is studied under LDC nonuniform conditions. It is shown that, at initial number densities of nanoparticles (N _d > 10¹¹ droplet/m³), heterogeneous droplets do not grow to optically detected sizes.     

Times of metastable droplet relaxation to equilibrium states

Times of metastable droplet relaxation to their equilibrium state are calculated at saturated vapor pressures, depending on the droplet size. It is shown that for small droplets with radius R = 6 molecular diameters (or ~2 nm) the relaxation times are ~1 ns (which is comparable to the characteristic flight times of rarefied gas molecules). For large droplets with radius R ~ 800 molecular diameters, the relaxation times are as long as 10 μs. At a fixed droplet radius (6 ≤ R ≤ 800), the range of variation in relaxation time from the melting point to the critical temperature does not exceed one order of magnitude: the lower the temperature, the slower the relaxation process.     

On the applicability of Young–Laplace equation for nanoscale liquid drops

Debates continue on the applicability of the Young–Laplace equation for droplets, vapor bubbles and gas bubbles in nanoscale. It is more meaningful to find the error range of the Young–Laplace equation in nanoscale instead of making the judgement of its applicability. To do this, for seven liquid argon drops (containing 800, 1000, 1200, 1400, 1600, 1800, or 2000 particles, respectively) at T = 78 K we determined the radius of surface of tension R_s and the corresponding surface tension γ_s by molecular dynamics simulation based on the expressions of R_s and γ_s in terms of the pressure distribution for droplets. Compared with the two-phase pressure difference directly obtained by MD simulation, the results show that the absolute values of relative error of two-phase pressure difference given by the Young–Laplace equation are between 0.0008 and 0.027, and the surface tension of the argon droplet increases with increasing radius of surface of tension, which supports that the Tolman length of Lennard-Jones droplets is positive and that Lennard-Jones vapor bubbles is negative. Besides, the logic error in the deduction of the expressions of the radius and the surface tension of surface of tension, and in terms of the pressure distribution for liquid drops in a certain literature is corrected.     

Radiation-Induced Heterogeneous Processes of Water Decomposition in the Presence of Mixtures of Silica and Zirconia Nanoparticles

The radiation-induced heterogeneous processes of water decomposition on mixtures of silicon dioxide (n-SiO₂) and zirconium dioxide (n-ZrO₂) nanoparticles have been studied. The kinetics of buildup of molecular hydrogen in the radiolytic processes of water decomposition in the test systems has been examined. The reaction rates and the radiation-chemical yield of hydrogen in the radiolysis of water in the presence of n-SiO₂–n-ZrO₂ mixtures with different ratios between the components have been determined. It has been found that the rates and radiation-chemical yields decreased on going from n-ZrO₂ to n-SiO₂. The individual components (n-SiO₂ and n-ZrO₂) and the mixtures of n-SiO₂–n-ZrO₂ and n-SiO₂–n-ZrO₂ + H₂O before and after γ-irradiation have been examined by Fourier-transform IR spectroscopy in order to reveal interactions between the components and to study the mechanism of radiolytic processes. It has been found that the adsorption of water in the test systems occurs via both molecular and dissociative mechanisms. It has been shown that there is no noticeable interaction between the components of the oxide nanoparticles under the conditions of the experiments.     

Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution

Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L _ef), the radius of gyration (R _g), and the hydrodynamic radius (R _H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L _ef (or R _g or R _H) of SCMC decreased; with the increment of the DS, the L _ef of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L _ef (or R _g or R _H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L _ef, R _g, R _H, [η], and D of SCMC in NaCl solution.     

Enzymeless determination of cholesterol using gold and silver nanoparticles as electrocatalysts

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10^–5 c _chol + 5.8 × 10^–5 (R ² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5 c _chol + 3.0 × 10^–4 (R ² = 0.95) possess optimal electrocatalytic characteristics.     

Pyrrolidine synthons for β-lactams

Fused tricyclic aziridines, methyl rel-(2R,2aR,3R,4R,4aR,4bS)- and rel-(2S,2aR,3R,4R,4aR,4bS)-4-hydroxy-2,4a-dimethoxyhexahydro-1-oxa-2b-azacyclopropa[cd]pentalene-3-carboxylates, have been synthesized as possible precursors to β-lactams. The product structure has been determined by two-dimensional NMR techniques in combination with computational methods.     

Research on the Solid State Fermentation of Jerusalem Artichoke Pomace for Producing <Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">R</Emphasis>-2,3-Butanediol by <Emphasis Type="Italic">Paenibacillus polymyxa</Emphasis> ZJ-9

R,R-2,3-butanediol (R,R-2,3-BD) was produced by Paenibacillus polymyxa ZJ-9, which was capable of utilizing inulin without previous hydrolysis. The Jerusalem artichoke pomace (JAP) derived from the conversion of Jerusalem artichoke powder into inulin extract, which was usually used for biorefinery by submerged fermentation (SMF), was utilized in solid state fermentation (SSF) to produce R,R-2,3-BD. In this study, the fermentation parameters of SSF were optimized and determined in flasks. A novel bioreactor was designed and assembled for the laboratory scale-up of SSF, with a maximum yield of R,R-2,3-BD (67.90 g/kg (JAP)). This result is a 36.3% improvement compared with the flasks. Based on the same bath of Jerusalem artichoke powder, the total output of R,R-2,3-BD increased by 38.8% for the SSF of JAP combined with the SMF of inulin extraction. Overall, the utilization of JAP for R,R-2,3-BD production was beneficial to the comprehensive utilization of Jerusalem artichoke tuber.     

Dual Stereochemical Control in Reaction of Di- and Trialkyl Phosphites with Aldimines

Stereochemistry of addition of di- and trialkyl phosphites to C=N compounds was investigated. Reactions of achiral dialkyl phosphites with chiral aldimines as well as that of chiral di-(1R,2S,5R)-menthyl phosphite with achiral aldimines result in low diastereomeric enrichment of the addition compound. Reaction stereoselectivity increased when supplementary chiral inductor was introduced to the reaction system. Reaction of di-(1R,2S, 5R)-menthyl phosphite with (S)-α-methylbenzylbenzaldimine proceeds as concerted asymmetric induction to form practically one diastereomer of N-substituted aminophosphonic acid. However, reaction of di-(1R,2S, 5R)-menthyl phosphite with (R)-α-methylbenzylbenzaldimine proceeded as not concerted asymmetric induction, and diastereomeric enrichment of the product was low. By chemical extrapolation, absolute configuration of compounds formed was established. Tri-(1R,2S,5R)-menthyl phosphite reacts with C=N compounds in the presence of boron trifluoride etherate to form aminophosphonic acid derivatives with the absolute configuration opposite to that appearing in the reaction of di-(1R,2S,5R)-menthyl phosphite with the same C=N compounds.     

Structural characterization of the crystalline diastereomeric complexes of enantiopure dimethylacridino-18-crown-6 ether and the enantiomers of 1-(1-naphthyl)ethylamine hydrogen perchlorate

This paper describes the X-ray crystal structure of the diastereomeric complexes formed by enantiopure dimethyl-substituted acridino-18-crown-6 ether (R,R)-1 and the enantiomers of 1-(1-naphthyl)ethylammonium perchlorate. We found that the heterochiral complex (R,R)-1–(S)-1-NEA is more stable than the homochiral one (R,R)-1–(R)-1-NEA. In the case of the heterochiral complex, the X-ray studies revealed a strong intermolecular π–π interaction between the naphthyl unit and the acridine moiety. However, in the case of the homochiral complex, π–π interaction was not found. We suggest that the existence or absence of the π–π interaction and the difference in steric repulsions in the diastereomers is responsible for the enantiomeric discrimination.     

Synthesis and study of high-temperature heat capacity of erbium orthovanadate

Orthovanadate ErVO₄ has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V₂O₅ and chemically pure Er₂O₃ by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO₄ was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental C_p = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R³⁺ ion within the third and fourth tetrads.     

Fractal structure and microporosity of nascent particles and sintered powders based on poly(tetrafluoroethylene)

Fractal characteristics of the surface of various powders based on the suspension poly(tetrafluoroethylene) F-4 are studied by the method of low-temperature adsorption of argon. Analysis of the degree of crystallinity, density of the solid phase, and free-volume characteristics (positron-annihilation lifetime spectroscopy) makes it possible to conclude that the granules contain nanopores. Owing to the separation of the contributions from nanoporous and fractal components of the specific surface of the particles, fractal dimension d = 2.60 is estimated in the scaling relationship σ ～ R ^{d ? 3}, where σ is the specific surface and R is the radius of the particle. For this set of powders, the linear dependence of specific air permeability q of the pressed pellets with a porosity of 70 vol % on the dimensions of granules is obtained. This case corresponds to fractal dimensions of the surface of d = 2.5 in the other scaling expression, q ～ R ^{6 ? 2d} . Similar fractal parameters estimated by the adsorption and aerodynamic methods confirm that the hydrodynamic resistance of a porous layer increases owing to an irregular surface of the powder granules. The correlation between the parameters of the heterophase dispersion polymerization and the specific features of the morphology and characteristics of the polymerizate is found for three types of PTFE.     

Diastereoselective 1,3-Dipolar Cycloaddition of Nitrones to 1<Emphasis Type="Italic">H</Emphasis>-Pyrrole-2,3-diones. Synthesis of pyrrolo[3,2-<Emphasis Type="Italic">d</Emphasis>]isoxazoles

1H-pyrrol-2,3-diones react with nitrones affording substituted pyrrolо[3,2-d]isoxazoles. The structures of ethyl (3R*,3aR*,6aR*)-6-benzyl-3-(4-bromophenyl)-4,5-dioxo-2,6a-diphenylhexahydro-3aHpyrrolo[ 3,2-d]isoxazole-3a-carboxylate and dimethyl (3R*,3aR*,6aS*)-3-(4-bromophenyl)-4,5-dioxo-2,6-diphenyltetrahydro-3aH-pyrrolo[3,2-d]isoxazole-3a,6a(4H)-dicarboxylate were proved by single-crystal X-ray analysis.     

Hall effect,electrical and magnetic resistance in Cd<Subscript>3</Subscript>As<Subscript>2</Subscript> + MnAs (30%) composite at high pressures

Electrical resistivity ρ, Hall factor R _H, magnetic resistance (R _m–R ₀)/R ₀, and magnetic-field-dependent resistances were measured in 70 mol % Cd₃As₂ + 30 mol % MnAs composite at fixed values of high hydrostatic pressures (up to p ≤ 9 GPa). The ρ, R _H, and (R _m–R ₀)/R ₀ versus pressure curves feature a phase transition at p = 4–4.3 GPa. Field-dependent magnetic resistance features a negative pressure-induced trend.     

2-amino-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines: Synthesis and reactions with electrophilic reagents

The hydrogenation of 2-amino-5-R-7-R′-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines with NaBH₄ led to the formation of 2-amino-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidines. Acylation, sulfonylation, and alkylation of these compounds depending on conditions and the reagent character occur at the amino group, atoms N³ or N⁴. The treatment with alkali of 2-amino-3-benzyl-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo-[1,5-a]pyrimidinium bromide resulted in 2-amino-3-benzyl-5-R-7-R′-3,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]-pyrimidine, similar reaction of 2-acetamido-3-benzyl-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]-pyrimidinium bromide gave a mesoionic product of a hydrogen elimination from the amide nitrogen atom.     

Synthesis of Ni(II) complexes with chiral derivatives of cyclohexane-1,2-diamine,bycyclo[2.2.2]octane-2,3-diamine,and 1,2-diphenylethane-1,2-diamine

Chiral ligands—derivatives of (1R,2R)-cyclohexane-1,2-diamine, (1R,2R)-diphenylethane-1,2-diamine, and (2S,3S)-bicyclo[2.2.2]octane-2,3-diamine—and octahedral Ni(II) complexes on their basis have been synthesized.     

Crystal and Molecular Structure of (4′<Emphasis Type="Italic">R</Emphasis>,5′<Emphasis Type="Italic">R</Emphasis>,22<Emphasis Type="Italic">R</Emphasis>)-22-Hydroxy-22-(3′,4′-dimethylisoxazolin-5′-yl)-6β-methoxy-3α,5-cyclo-23,24-dinorcholane

The crystal and molecular structure of (4′R,5′R,22R)-22-hydroxy-22-(3′, 4′-dimethylisoxazolin-5′-yl)-6β-methoxy-3α,5-cyclo-23,24-dinorcholane was studied by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system, space group C2; a 19.649(7), b 7.680(2), c 17.254(6) Å; β 101.05(3)°. The only diastereomer formed by the 1,3-dipolar cycloaddition of acetonitriole oxide has the 4′R,5′R stereochemistry of the arising chiral centers. The conformation of the side chain of the molecule is additionally stabilized by an intramolecular hydrogen bond.     

Hetero-Diels–Alder Reaction of Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxalinetriones with Styrene

Hetero-Diels–Alder reaction of 3-aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones with styrene afforded diastereoisomeric (5R*,6aR*)- and (5S*,6aR*)-3,5-diaryl-5,6-dihydropyrano[4′,3′:2,3]pyrrolo[1,2-a]-quinoxaline-1,2,7(8H)-triones.     

Phospho sulfonic acid as efficient heterogeneous Brønsted acidic catalyst for one-pot synthesis of 14<Emphasis Type="Italic">H</Emphasis>-dibenzo[<Emphasis Type="Italic">a,j</Emphasis>]xanthenes and 1,8-dioxo-octahydro-xanthenes

A simple, efficient procedure for the preparation of phospho sulfonic acid PO(OSO₃H)₃ as a Brønsted acidic and recoverable heterogeneous catalyst is described, used for the one-pot synthesis of aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes. A cost-effective, simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a,j]xanthenes was developed via a one-pot condensation from substituted benzaldehydes and β-naphthol under solvent-free conditions. The one-pot condensation of substituted benzaldehydes and 5,5-dimethyl-1,3-cyclohexanedione (dimedone) under solvent-free conditions leads to 1,8-dioxo-octahydro-xanthenes. These protocols afford a number of advantages, such as: excellent yields, very short reaction times, easy procedure, simple methodology and ease of preparation and regeneration of the catalyst.