Mössbauer study of Brazilian soapstone

Steatite mineral rocks, soapstone, have been studied by X-ray diffraction, optical microscopic analysis (modal analysis), electron probe micro analysis and Mössbauer spectroscopy for characterization, mineral percentages and chemical composition. Mössbauer spectra show both, magnetic interactions corresponding to magnetite and doublets corresponding to talc. chlorite, dolomite and tremolite. The temperature dependence of the quadrupole splitting in dolomite has been explained in terms of crystal field interaction.     

Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

New strategy for the determination of gliadins in maize- or rice-based foods matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: fractionation of gliadins from maize or rice prolamins by acidic treatment

A procedure for determining small quantities of gliadins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) in gluten-free foods containing relatively large amounts of prolamin proteins from maize or rice is described. We report for the first time that gliadins, the ethanol-soluble wheat prolamin fraction, can be quantitatively solubilized in 1.0 M acetic acid, while the corresponding ethanol-soluble maize or rice prolamin fraction remains insoluble in acetic acid. We describe a methodology for the detection of gliadins in maize and rice foods based on a two-step procedure of extraction (60% aqueous ethanol followed by 1 M acetic acid). Subsequent MALDI-TOFMS analysis of the resulting acidic extract from these gluten-free foods clearly confirms the presence of a typical mass pattern corresponding to gliadin components, ranging from 30 to 45 kDa. Depending on the percentages of maize or rice flours employed in the elaboration of these foods, the combined procedure enables levels of gliadins from 100 to 400 ppm to be detected. The efficiency of this combined procedure corroborates enzyme-linked immunosorbent assay data for a large number of maize/rice gluten-free foods by means of direct visualization of the characteristic gliadin mass pattern in maize or rice foods.     

Formation of dinuclear titanium and zirconium complexes by olefin metathesis--catalytic preparation of organometallic catalyst systems

The titanium complex [(C(5)H(4)bond;allyl)TiCl(3)] (2) undergoes olefin metathesis coupling when treated with 3 mol % of [Cl(2)(L(1))(L(2))Ru=CHPh] (L(1)=L(2)=PCy(3), 4 a; L(1)=PCy(3), L(2)=(H(2)IMes), 4 b) to yield the dimetallic complex [Cl(3)Ti(C(5)H(4))-CH(2)CH=CHCH(2)-(C(5)H(4))TiCl(3)] (5). The allyl-substituted titanocene complex [Cp(C(5)H(4)bond;allyl)TiCl(2)] (3) analogously yields the dimetallic system 6 when treated with 4. The ansa-zirconocene complex [Me(2)Si(C(5)H(4))(C(5)H(3)bond;allyl)ZrCl(2)] (7) cleanly yields the analogous dimetallic coupling product 8 (>95 % isomerically pure), when treated with catalytic amounts of 4 b in toluene. Complex 8 gives an active homogeneous ethene or propene polymerization catalyst, especially at elevated temperatures, when treated with excess methylalumoxane.     

The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography

Four poly(methyl 3,3,3-trifluoropropyl siloxanes) with trifluoro-propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases–a polydimethylsiloxane and a poly(methyl 3,3,3-trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution). Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron-donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.     

TOPS-MODE based QSARs derived from heterogeneous series of compounds. Applications to the design of new herbicides

A new application of TOPological Sub-structural MOlecular DEsign (TOPS-MODE) was carried out in herbicides using computer-aided molecular design. Two series of compounds, one containing herbicide and the other containing nonherbicide compounds, were processed by a k-Means Cluster Analysis in order to design the training and prediction sets. A linear classification function to discriminate the herbicides from the nonherbicide compounds was developed. The model correctly and clearly classified 88% of active and 94% of inactive compounds in the training set. More specifically, the model showed a good global classification of 91%, i.e., (168 cases out of 185). While in the prediction set, they showed an overall predictability of 91% and 92% for active and inactive compounds, being the global percentage of good classification of 92%. To assess the range of model applicability, a virtual screening of structurally heterogeneous series of herbicidal compounds was carried out. Two hundred eighty-four out of 332 were correctly classified (86%). Furthermore this paper describes a fragment analysis in order to determine the contribution of several fragments toward herbicidal property; also the present of halogens in the selected fragments were analyzed. It seems that the present TOPS-MODE based QSAR is the first alternate general "in silico" technique to experimentation in herbicides discovery.     

Emulsion polymerization of styrene. III. Effect of Ti(III) and Cl(1) on the polymerization of styrene initiated by potassium persulfate

The emulsion polymerization of styrene initiated by potassium persulfate catalyzed by Ti⁺³ ions was studied. Two sources of Ti⁺³ ions were used: the titanium trichloride and titanium sulfate. It was found that the titanium ions used in conjunction with potassium persulfate decrease both the reaction rate and the average molecular weight. An even greater drop of reaction rate was noted when chlorine anions (TiCl₃) were present. The presence of these ions had a stabilizing effect on the polydispersity.     

Molecular dynamics and quantum chemical approaches in the study of the hydration of protonated cyclohexyldiamines

Explicit hydration of the neutral and charged cyclohexylamine and of the cyclohexyldiamine isomers in their mono- or diprotonated forms is investigated through classical molecular dynamics (MD) simulations in aqueous solutions combined with DFT calculations in amine–water complexes. The MD studies performed in the monoamines reveal that the structure of the hydration shell around the neutral amino group (NH₂) is quite distinct from that around the charged one (NH₃⁺). On average, the number of water molecules surrounding the two groups is calculated to be ～2 and 3–4, respectively. The variation of the hydration structure prompted by the groups’ proximity is discussed based on the data found for the mono- and diprotonated diamines. To have a more detailed picture of the water molecules’ arrangement around the amino groups and of the amine–water hydrogen bonds, geometry optimisations in hydrates with up to six water molecules are carried out at the B3LYP/aug-cc-pVDZ level. Complexation energies are also computed. The main findings emerging from these calculations are found to be very helpful to rationalise the mutual influence of the amino groups and therefore to better elucidate the MD findings. The complementary nature of the two research methods is emphasised as an excellent tool in order to closely examine the hydration of polyamines, as exemplified for the cyclohexyldiamines.     

Effect of flame-sprayed Al–12Si coatings on the failure behaviour of pressurized fibre-reinforced composite tubes

Internal pressurization testing at room temperature was performed to evaluate the effect of flame-spraying aluminum-12silicon on the leakage behavior of fibre-reinforced composite tubes fabricated by filament winding, and covered with garnet sand. A group of specimens were completely coated with flame-sprayed metal particles and another set remained uncoated. t-tests were conducted at a significance level of α = 0.05 to analyze the effect of the coating on the leakage behavior of the specimens. Ultraviolet imaging was used to illustrate a characteristic leakage pattern of the composite tubes. Coated specimens exhibited slightly higher mean leakage and burst pressures than the uncoated specimens. The t-test results provided strong statistical evidence that the flame spraying process employed did not damage the filament wound tubes covered with garnet sand.     

Metal Oxide Assisted Preparation of Core–Shell Beads with Dense Metal–Organic Framework Coatings for the Enhanced Extraction of Organic Pollutants

Dense and homogeneous metal–organic framework (MOF) coatings on functional bead surfaces are easily prepared by using intermediate sacrificial metal oxide coatings containing the metal precursor of the MOF. Polystyrene (PS) beads are coated with a ZnO layer to give ZnO@PS core–shell beads. The ZnO@PS beads are reactive in the presence of 2‐methylimidazole to transform part of the ZnO coating into a porous zeolitic imidazolate framework‐8 (ZIF‐8) external shell positioned above the internal ZnO precursor shell. The obtained ZIF‐8@ZnO@PS beads can be easily packed in column format for flow‐through applications, such as the solid‐phase extraction of trace priority‐listed environmental pollutants. The prepared material shows an excellent permeance to flow when packed as a column to give high enrichment factors, facile regeneration, and excellent reusability for the extraction of the pollutant bisphenol A. It also shows an outstanding performance for the simultaneous enrichment of mixtures of endocrine disrupting chemicals (bisphenol A, 4‐tert‐octylphenol and 4‐n‐nonylphenol), facilitating their analysis when present at very low levels (<1 μg L^?1) in drinking waters. For the extraction of the pollutant bisphenol A, the prepared ZIF‐8@ZnO@PS beads also show a superior extraction and preconcentration capacity to that of the PS beads used as precursors and the composite materials obtained by the direct growth of ZIF‐8 on the surface of the PS beads in the absence of metal oxide intermediate coatings.