AMicro-sized headspace GC technique for determination of organic volatile impurities in water-insoluble pharmaceuticals

Summary A micro-sized headspace technique is presented for determination of organic volatile impurities (OVIs) in water-insoluble pharmaceuticals. Its main features include reduction of the amounts of sample of drug and sample dissolution medium, from 100–200 mg and 1–5 mL, respectively, in the traditional headspace method to 5–30 mg and 100 μL in the micro-sized headspace method, and shortening the headspace equilibration time from 45–60 min to 5–10 min. The validity of method has been examined both experimentally and theoretically. The relative standard deviation of the analysis and the linearity of method satisfied the requirements of the United States Pharmacopoeia. It was found that headspace equilibrium conditions have little influence on the sensitivity of the method, and that the presence of different amounts of drug substance in the sampling solution has little effect on the analytical results, in contrast with the traditional headspace GC method.     

Free energy calculations offer insights into the influence of receptor flexibility on ligand–receptor binding affinities

Docking algorithms for computer-aided drug discovery and design often ignore or restrain the flexibility of the receptor, which may lead to a loss of accuracy of the relative free enthalpies of binding. In order to evaluate the contribution of receptor flexibility to relative binding free enthalpies, two host–guest systems have been examined: inclusion complexes of α-cyclodextrin (αCD) with 1-chlorobenzene (ClBn), 1-bromobenzene (BrBn) and toluene (MeBn), and complexes of DNA with the minor-groove binding ligands netropsin (Net) and distamycin (Dist). Molecular dynamics simulations and free energy calculations reveal that restraining of the flexibility of the receptor can have a significant influence on the estimated relative ligand–receptor binding affinities as well as on the predicted structures of the biomolecular complexes. The influence is particularly pronounced in the case of flexible receptors such as DNA, where a 50% contribution of DNA flexibility towards the relative ligand–DNA binding affinities is observed. The differences in the free enthalpy of binding do not arise only from the changes in ligand–DNA interactions but also from changes in ligand–solvent interactions as well as from the loss of DNA configurational entropy upon restraining.     

Chemiluminescence in the oxidation of cyclooctene by molecular oxygen

Chemiluminescence kinetics have been examined for the oxidation of cyclooctene by molecular oxygen. State University “L'vivs'ka Politekhnika,” 12 ul. S. Bandery, L'vov-13 290646, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, pp. 354–356, November–December, 1999     

Effects of nickel catalyst composition on the rate and selectivity of carbon dioxide hydrogenation

The hydrogenation of carbon dioxide has been examined in relation to the activity of catalysts containing 1–10 wt.% nickel, particularly as affected by the method of making the catalyst. Studies have been done on how alkali additives affect the activity of a nickel-aluminum catalyst. Measurements have been done on thiophen poisoning in the hydrogenation of CO₂ on nickel catalysts. N. G. Chernyshevskii Saratov State University, Saratov State University Chemical Research Institute, 83 Astrakhanskaya ul., Saratov 410026, Russia. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, pp.311–316, September–October, 1999.     

An improved version of Junmeng–Fang–Weiming–Fusheng approximation for the temperature integral

An improved version of Junmeng–Fang–Weiming–Fusheng approximation for the temperature integral has been developed. The accuracy of the improved approximation for the temperature integral has been tested by some numerical analyses. The systematic analysis of the relative errors involved in the kinetic parameters obtained from Junmeng–Fang–Weiming–Fusheng integral method and its improved version has been also carried out. The results have shown that the improved approximation is more accurate than Junmeng–Fang–Weiming–Fusheng approximation as the solution of the temperature integral, and that more accurate kinetic parameters can be determined from the integral method based on the improved temperature integral approximation.     

SPR-based immunocapture approach to creating an interfacial sensing architecture: mapping of the MRS18-2 binding site on retinoblastoma protein

Biosensor technologies based on optical readout are widely used in protein–protein interaction studies. Here we describe a fast and simple approach to the creation of oriented interfacial architectures for surface plasmon resonance (SPR) transducers, based on conventional biochemical procedures and custom reagents. The proposed protocol permits the oriented affinity-capture of GST fusion proteins by a specific antibody which is bound to protein A, which in turn has been immobilized on the transducer surface (after the surface has been modified by guanidine thiocyanate). The applicability of the method was demonstrated by studying the interaction between retinoblastoma tumor suppressor protein (pRb) and MRS18-2 proteins. The formation of the pRb–MRS18-2 protein complex was examined and the pRb binding site (A-box–spacer–B-box) was mapped. We have also shown that MRS18-2, which was detected as the Epstein–Barr virus-encoded EBNA-6 binding partner using the yeast two-hybrid system, binds to pRb in GST pull-down assays.     

Release of uranium and emission of radiation from uranium-glazed dinnerware

Samples of orange, yellow, beige, ivory and blue-green ceramic dinnerware glazed with uranium compounds have been examined. Measurements at glaze surfaces yielded exposure rates of 3.8–16 mR/h (1–4 μC/kgh) for orange glazes and rates of 0.04–1.3 mR/h (0.01–0.3 μC/kgh) for ivory beige, and yellow glazes. Whole body exposure from a shelf display of 40 orange dishes was estimated to be 0.1–0.5 mR/h (0.03–0.13 μC/kgh), or up to 50 times the room background radiation level, at a distance of 1 meter. Twenty-four hour leaching tests of orange, yellow, and ivory dishes were carried out with various concentrations of acetic and citric acids. Uranium concentrations in leachates of some orange dishes exceeded 450 mg/l. Uranium is a chemical nephrotoxin and the United States Environmental Protection Agency has proposed a maximum contaminant level for drinking water of 0.020 mg/l. Based on this value a person consuming, 2.2 l of drinking water per day would ingest 0.31 mg of uranium per week. A person eating once a week from an orange glazed dish could easily ingest 10 or more times this amount.     

Interactions of tetrakis(4-N-methylpyridyl)porphyrin with cyclodextrins and disodium phthalate in aqueous solution

In pH 7.3 buffers, the interactions of a cationic porphyrin, tetrakis(4-N-methylpyridyl)porphyrin (TMPyP), with cyclodextrins (CDs) and disodium phthalate (DSP) have been examined by means of absorption, fluorescence, and induced circular dichroism spectroscopy. α-CD, β-CD, and γ-CD form a 1:1 inclusion complex with a TMPyP monomer, which dimerizes in solution without CD. TMPyP also forms a 1:1 organic cation–organic anion complex with DSP. The 1:1 TMPyP–DSP complex forms a ternary CD–TMPyP–DSP inclusion complex with α-, β-, and γ-CD, in which a DSP molecule is not incorporated into the CD cavity. From the fluorescence intensity change, the␣equilibrium constants have been evaluated for the formation of the inclusion complexes and the organic cation–anion complexes.     

Correlation between structural and optical properties of TiO<Subscript>2</Subscript>:ZnO thin films prepared by sol–gel method

We have studied structural and optical properties of thin films of TiO₂, doped with 5% ZnO and deposited on glass substrate (by the sol–gel method). Dip-coated thin films have been examined at different annealing temperatures (350–450 °C) and for various layer thicknesses (89–289 nm). Refractive index, porosity and energy band gap were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.97–2.44, the porosity is in the range of 0.07–0.46 and the energy band gap is in the range of 3.32–3.43. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZnO, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 20.23 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range of 8.61–29.48 nm.     

Surface structure of silica gel reacted with 3-mercaptopropyltriethoxysilane and 3-aminopropyltriethoxysilane: formation of the S–S bridge structure and its characterization by Raman scattering and diffuse reflectance Fourier transform spectroscopic studies

 Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH₂SSCH₂ segment, in addition to the SH and C–S stretch modes of the CH₂SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel, a specific conformer is stabilized about the CH₂SSCH₂ segment. Received: 1 May 2001 Accepted: 16 June 2001     

Essential oil ofPeucedanum oreoselinum fruits collected near Vilnius

Fruits ofPeucedanum oreoselinum (L.) Moench, were collected at three sites in 1995–1998 and contained 1.5–5.0% essential oil. Analyses were performed using GLC and GC-MS. The main component of the essential oil is limonene (44.1–82.4%). The majority of examined samples contained more limonene than has been reported in the literature. Only in sunny locations do plants synthesize significant quantities of γ-terpinene (12.2–17.5%) and β-pinene (8.5–14.5%). Small quantities of α-pinene are present in all studied samples of essential oil (4.0–8.3%). Monoterpenes comprise 97.1–98.6% of the essential oil. The remainder consists of sesquiterpenes. Institute of Chemistry, ul. Goshtauto, 9, Vilnius, Lithuania. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 743–745, November–December, 1999.     

Obtaining calcium carbonate in a multiphase system by the use of new rotating disc precipitation reactor

Rotating disc reactor (RDR) was constructed to conduct gas–liquid–solid reactions with controlled reagent transfer from gaseous to liquid phase. The concept is based on continuous formation of thin liquid films at a surface of rotating discs where the mass transfer proceed in diffusion–convective way. The reactor was employed to run precipitation reaction of CaCO₃ via carbon dioxide absorption in lime slurry. During each reaction pH changes and Ca²⁺ concentration in time were measured. Disc rotations and gas flows were changed during the experiment and their influence on the obtained CaCO₃ powders has been examined and fully discussed.     

Relationships among the transition elements

As part of a series of contributions on patterns in the periodic table, the relationships among the transition metals are examined here in a systematic manner. It is concluded that the traditional method of categorizing transition elements by group or by period is not as valid as by using combinations thereof. From chemical similarities, it is proposed that the transition metals be considered as the [V–Cr–Mn] triad; the [Fe–Co–Ni–Cu] tetrad; the [Ti–Zr–Hf–Nb–Ta] pentad; the [Mo–W–Tc–Re] tetrad; and the [Ru–Os–Rh–Ir–Pd–Pt–Au] heptad. Silver does not fit neatly in anywhere and is better linked with thallium.     

Pt–Ru nanoparticles supported PAMAM dendrimer functionalized carbon nanofiber composite catalysts and their application to methanol oxidation

Polyamidoamine (PAMAM) dendrimers has been anchored on functionalized carbon nanofibers (CNF) and supported Pt–Ru nanoparticles have been prepared with NaBH₄ as a reducing agent. The samples were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM) analysis. It was shown that Pt–Ru particles with small average size (2.6 nm) were uniformly dispersed on PAMAM/CNF composite support and displayed the characteristic diffraction peaks of Pt face-centered cubic structure. The electrocatalytic activities of the prepared-composites (20% Pt–Ru/PAMAM-CNF) were examined by using cyclic voltammetry for oxidation of methanol. The electrocatalytic activity of the CNF-based composite (20% Pt–Ru/PAMAM-CNF) electrode for methanol oxidation showed better performance than that of commercially available Johnson Mathey 20% Pt–Ru/C catalyst. The results imply that CNF-based PAMAM composite electrodes are excellent potential candidates for application in direct methanol fuel cells.     

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N₂O stoichiometry (which is stable in a narrow temperature range of 325–425 K).     

Planar Chromatography of Cholic Acid-Derived cis—trans Isomeric bis-Steroidal Tetraoxanes

JPC – Journal of Planar Chromatography – Modern TLC - Seven pairs of cis—trans isomers of bis-steroidal tetraoxanes have been examined by both normal-phase (NP) and reversed-phase...     

Interactions of Tetrakis(4-sulfonatophenyl)porphyrin with γ-Cyclodextrin and Alkyltrimethylammonium Bromides in Aqueous Solutions

Tetrakis(4-sulfonatophenyl)porphyrin (TSPP) forms complexes with octyltrimethylammonium bromide (OTMA) and hexyltrimethylammonium bromide (HTMA) in pH 7.3 buffers. At low concentrations of OTMA (HTMA), a 1:1 TSPP–OTMA complex is formed. As the OTMA (HTMA) concentration is increased, a 1:2 TSPP–OTMA (HTMA) complex is also formed. The equilibrium constants for the formation of the TSPP–OTMA (HTMA) complexes have been evaluated from a simulation of the observed fluorescence intensity data. In the induced circular dichroism spectrum, the signal intensity of TSPP in aqueous solutions containing both γ-CD and OTMA has been similar to that containing only γ-CD, suggesting the formation of the 1:1:1 γ-CD–TSPP–OTMA (HTMA) inclusion complex. Capillary electrophoretic study has exhibited the formation of the 1:1 TSPP–OTMA (HTMA) complex, although the 1:2 TSPP–OTMA (HTMA) complex could not be observed, probably because the OTMA (HTMA) concentration used was low. The equilibrium constants for these 1:1 complexes have been evaluated from the variation in the electrophoretic mobility. The equilibrium constant for the formation of the 1:1:1 γ-CD–TSPP–OTMA or γ-CD–TSPP–HTMA complex has been evaluated from a simulation of the electrophoretic mobility change in TSPP solution containing γ-CD and OTMA or HTMA, although the equilibrium constants for the ternary inclusion complexes could not be evaluated using the fluorescence method due to the small fluorescence intensity change.     

Effect of polyelectrolyte swelling on electrical conductivity of polyaniline-polycaproamide composite films

In the example of composite films made up of polyaniline and polycaproamide [nylon-6], it has been found that the phenomenon of polyelectrolyte swelling can be used to regulate the electrical conductivity of films with a fixed content of polyaniline. The influence of the molecular conformation of the polyaniline on the film conductivity is examined critically. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Nauki Prosp., Kiev, Ukraine 252039. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 1, pp. 14–18, January–February, 1998.     

The Surface Tension and Density of Liquid Ag–Bi, Ag–Sn, and Bi–Sn Alloys

Summary. The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed.     

Algal transformation of hydrocortisone by the cyanobacterium Nostoc ellipsosporum

The potential of Nostoc ellipsosporum for biotransformation of hydrocortisone was studied. The microorganism was isolated during a screening program from soil samples collected from the paddy fields in the north of Iran and had not been previously examined for this purpose. The biotransformation yielded 11β,17α,20β, 21-tetrahydroxypregn-4-en-3-one and 11β-hydroxyandrost-4-ene-3,17-dione. Both of the metabolites were purified chromatographically and characterized using instrumental analyses. Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 572–574, November–December, 2006.