Hydroxyapatite nanoparticle prepared by controlled precipitation from aqueous phase

Hydroxyapatite nanoparticles (NPs) were prepared by controlled precipitation in the presence of stabilizers that confined growth and inhibited the aggregation of nanoparticles. Electrostatically stabilized NPs were prepared in the presence of sodium citrate; Tween 80 was used for steric stabilization. At low stabilizer concentrations, nanorods were formed of grown together, spheroidal hydroxyapatite NPs of ~20 nm in diameter. The rod length decreased as ether sodium citrate or Tween 80 concentration increased. When Cit^3–/Ca²⁺ = 3mol/mol, platelike NPs were formed 20–45 nm long and ~10 nm wide; for Cit^3–/Ca²⁺ = 4 mol/mol, NPs had sizes of 10–15 nm. At relatively high Tween 80 concentrations (>0.05 mol/L), foamlike structures were obtained.     

Thermodynamic parameters of reactions of Cd2+ ion complexation with L-aspartic acid in aqueous solutions

Calorimetric enthalpies of complexation of L-aspartic acid (H₂Asp) with Cd²⁺ ion at 298.15 K and ionic strengths of 0.5, 0.75, and 1.0 (KNO₃) were determined. The thermodynamic parameters of complex formation reactions (for CdAsp and CdAsp ₂ ^2? complexes) at zero and nonzero ionic strength were calculated.     

Analysis of humic acids from various soils using acid hydrolysis

Structural changes in humic acids from various soils, produced by acid hydrolysis, are studied by elemental and thermal analyses and by IR and NMR spectroscopy.     

Determination of sulfur in organic compounds using a barium-selective electrode

A procedure was developed for determining sulfur (>1.5 abs %) in sulfur-containing organic compounds. The procedure was based on the combustion of a sample portion in a flask filled with oxygen followed by the potentiometric titration of sulfate ions with barium nitrate in a water-acetone solution. In distinction from analogous procedures, halogens and metals contained in the analyzed compound did not interfere with the determination of sulfur. The error of determination was below 3 rel %.     

Separation of Multicomponent Mixture of Naphthalene Derivatives by Reversed-Phase High-Performance Liquid Chromatography

Separation of a mixture of naphthalene derivatives by reversed-phase high-performance liquid chromatography with UV detection was studied. Chromatographic characteristics were calculated for nine compounds, including naphthalene.     

Composition and structure of fluorinated graphite compounds with camphor

Intercalation compounds of fluorinated graphite (ICFG) with camphor are investigated by IR spectroscopy, chromatography, and X-ray phase and element analyses. It is shown that camphor ICFG of first-degree filling (identity period ～11.6 Å) can exist at room temperature.     

Fluorescence probing of temperature-dependent dynamics and friction in ionic liquid local environments

The solvation dynamics and local orientational friction for a series of four ionic liquids have been probed using coumarin 153 (C153) as a function of temperature. These ionic liquids are comprised of nonaromatic organic cations paired with a common anion, bis(trifluoromethylsulfonyl)imide (NTf(2)-). The specific liquids are as follows: N-methyl-tri-N-butylammonium NTf(2)- (N(1444)+/NTf(2)-), N-hexyl-tri-N-butylammonium NTf(2)- (N(6444)+/NTf(2)-), N-methyl-N-butylpyrrolidinium NTf(2)- (Pyrr(14)+/NTf(2)-), and N-methyl-N-ethoxyethylpyrrolidinium NTf(2)- (Pyrr(1(2O2))+/NTf(2)-). The observed solvation dynamics and fluorescence depolarization dynamics occur over a broad range of time scales that can only be adequately fit by functions including three or more exponential components. Stretched exponential distributions cannot adequately fit our data. The solvation and reorientational dynamics of the C153 probe are studied over a range of temperatures from 278.2 to 353.2 K. For both the solvation dynamics and the probe reorientational dynamics, the observed temperature dependence is well fit by a Vogel-Tammann-Fulcher law. To correlate the observed microscopic dynamics with macroscopic physical properties, temperature-dependent viscosities are also measured. Differential scanning calorimetry is used to study the thermodynamics of the phase transitions from the liquid to supercooled liquid to glassy states. For the two tetraalkylammonium liquids, the observed melting transitions occur near 300 K, so we are able to study the dynamics in a clearly supercooled regime. Very long time scale orientational relaxation time constants dynamics on the order of 100 ns are observed in the C153 fluorescence anisotropy. These are interpreted to arise from long-lived local structures in the environment surrounding the C153 probe.