Isolation and characterization of the monounsaturated long chain fatty acids ofMycobacterium tuberculosis

The positions of double bond in the monounsaturated C₁₅−C₃₂ fatty acids ofMycobacterium tuberculosis H37Ra were established by gas chromatography/mass spectrometry of the ozonized esters and their pyrrolidide derivatives. The monounsaturated C₁₅−C₂₁ fatty acids had the double bond primarily at the Δ⁹ position while the monounsaturated longer chain fatty acids (C₂₂−C₃₂) had the double bond in several positions. Many of the latter acids, especially the odd-numbered series, were very complex isomeric mixtures. Quantitation showed the most abundant even-numbered long chain fatty acid isomers to be as follow: C₂₂, Δ⁴; C₂₄, Δ⁵; C₂₆, Δ⁷ and Δ⁹; C₂₈, Δ⁹; C₃₀, Δ¹¹ and Δ¹³; C₃₂, Δ¹³ and Δ¹⁵.     

Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry

In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (T _o) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (T _o) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E _a), activation enthalpies (ΔH ^‡), and activation entropies (ΔS ^‡) for oxidative stability of vegetable oils were calculated. The E _a′, ΔH ^‡, and ΔS ^‡ for all vegetable oils ranged from 79 to −104 kJ mol⁻¹, from 76 to −101 kJ mol⁻¹, and from −99 to −20 J K⁻¹ mol⁻¹, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.     

Effect of solubilized amines on the structural transition of cetyltrimethylammonium bromide micelles in aqueous potassium bromide

Rod-shaped micelles were produced by mixing 0.1 M cetyltrimethylammonium bromide (CTAB) and 0.1 M KBr in aqueous solution. The effects of the addition of aliphaticn-amines (C₄, C₆, C₇ and C₈) and temperature on the shape of micelles were studied by viscosity measurements. The viscosity data show that transition of rod-shaped micelles to larger aggregates is induced by addition of higher amines (≥C₆) up to a certain concentration; a further increase in concentration produced the opposite effect. Addition of C₄-amine induces only a rod-to-sphere transition. The data were interpreted in terms of solubilization/incorporation (decrease of micellar surface charge density) of amines inside the micelles and the nature of the effective solvent (water+amine). The latter effect dominated the change from larger aggregates to smaller micelles at higher concentrations of the added amine. Increasing the temperature produced effects similar to C₄-amine addition, namely, rod-to-sphere transition. Activation free energy (ΔG^*) and enthalpy (ΔH^*) were also computed from the temperature dependence of the viscosity. ΔG^* and ΔH^* values were higher for larger aggregates (long rods) than for smaller ones (spherical micelles) and ΔH^* covered almost the total contribution to ΔG^*.     

Composition dependence of specific heat in Se80 − x Te20Sn x chalcogenide glasses

Differential Scanning Calorimetry (DSC) is performed at different heating rates under non-isothermal conditions to study the specific heat studies of glassy Se_{80 ? x} Te₂₀Sn _x (0 ≤ x ≤ 10) alloys. An extremely large increase in the specific heat values has been observed at the glass transition temperature. It has also been found that the values of C _p below glass transition temperature (C _pg ) and after glass transition (C _pe ) are highly composition dependent. This indicates that the Sn additive used in the present study influences the structure of the glassy Se₈₀Te₂₀ alloy. The results show that C _p values reveal local extrema in Se-Te-Sn glassy system at x = 4 and x = 8. The composition dependence of both parameters (C _pe and C _pg ) has been explained in terms of the glassy structure of Se-Te-Sn system.     

Thermal instability of plane poiseuille flow in the thermal entrance region

The onset of thermal convection in plane Poiseuille flow is investigated theoretically. New stability equations are derived by using the propagation theory considering the variations of disturbance amplitudes in the main flow direction. In the thermal entrance region an analytical procedure to predict the critical conditions for extremely small Prandtl-number fluids is described, based on the local similarity. For x_c≤0.01 the critical Rayleigh numbers are well represented in the whole domain of the Prandtl number by Ra_c = 200(1 + 0.123Pr^-1)Ra _C =200(1+0.123Pr⁻¹)x _C ⁻¹ under the conventional boundary layer theory. It is of much interest that the time-independent, three dimensional disturbances become more stable with a decrease in the Prandil number.     

Synthesis and thermal properties of fullerene-containing polymethacrylates

Three poly(methyl methacrylate-co-2-bromoethyl methacrylate) samples were prepared. The bromine groups in the copolymers were converted to azide groups followed by reaction with fullerene (C₆₀) to afford fullerene-containing polymethacrylates. The glass transition temperatures (T_gs) and heat capacity changes (ΔC_p) at T_g of these polymers were measured by differential scanning calorimetry. With increasing fullerene content in the polymethacrylate, the T_g value increases while the ΔC_p value decreases. The incorporation of fullerene improves the thermal stability of the polymethacrylate as shown by thermogravimetric analysis. Received: 25 February 1997/Revised: 12 May 1997/Accepted: 13 May 1997     

Phase transitions and glass transition in a hyperquenched silica‐alumina glass

We investigate phase transitions, glass transition, and dynamic behavior in the hyperquenched 69SiO₂–31Al₂O₃ (mol%) glass (SA glass). Upon reheating, the SA glass exhibits a series of thermal responses. Subsequent to the sub‐T_g enthalpy release, the glass undergoes a large jump in isobaric heat capacity (ΔC_p) during glass transition, implying the fragile nature of the SA glass. The mullite starts to form before the end of glass transition, indicating that the SA glass is extremely unstable against crystallization. After the mullite formation, the remaining glass phase exhibits an increased T_g and a suppressed ΔC_p. The formation of cristobalite at 1553 K indicates the dominance of silica in the remaining glass matrix. The cristobalite gradually re‐melts as the isothermal heat‐treatment temperature is raised from 1823 to 1853 K, which is well below the melting point of cristobalite, while the amount of the mullite remains unchanged.     

Photoelectrochemical Properties of NiO Coupled with TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Thin Film Prepared by Magnetron Sputtering Method

TiO_2−x N _x films were deposited on ITO glass by reactive dc magnetron sputtering method under different O₂/N₂ flow ratios. A NiO film was deposited by chemical bath deposition onto the as-prepared ITO/TiO_2−x N _x film to form an ITO/TiO_2−x N _x /NiO composite electrode. The morphology, crystal structure and composition of the TiO_2−x N _x films were characterized by SEM, XRD and XPS. The photoelectrochemical properties of the TiO_2−x N _x films were investigated by means of UV–Vis absorption spectra and photocurrent measurements. The results showed that the TiO_2−x N _x film sputtered under O₂/N₂ flow ratio of 1:2 exhibited a higher photocurrent response than the others. Correspondingly, the TiO_2−x N _x /NiO electrode consisting of the sputtered TiO_2−x N _x film under O₂/N₂ flow ratio of 1:2 also showed the best photoelectrochromic feature.     

Optical waveguiding in novel phosphazene polymer films

Summary Planar optical waveguides of some novel phosphazene inorganic polymers with high glass transition temperatures, T _g≥ 150°C, have been prepared by spin-coating on glass and quartz substrates. Thicknesses between 0.5 and 2 μm and index steps of about Δn∼0.2 (for quartz) and Δn∼0.1 (for glass) at λ= 0.633 μm have been achieved. From one to five modes have been observed at wavelengths ranging from the green to the near infrared. Refractive indices have been well fitted to a Sellmeier dispersion equation. Waveguide losses are estimated to be around 10 dB/cm. Received: 6 December 1999/Revised version: 20 May 2000/Accepted: 15 July 2000     

Structure and physicochemical properties of glasses in the (As2Se3)1 ? z-(SnSe2)z ? x-(Tl2Se)x and (As2Se3)1 ? z-(SnSe)z ? x-(Tl2Se)x systems

A comparative investigation of glasses in the As₂Se₃)_{1 − z} -(SnSe₂) _{z − x} -(Tl₂Se) _x and (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x systems has been performed. In both systems, the glass formation regions are shifted toward the As₂Se₃ compound. Only tin(IV) in the structure of glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system is identified by M?ssbauer spectroscopy, whereas glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system contain both Sn(II) and Sn(IV). The presence of tin in the oxidation state 2+ in the structural network of the glasses does not lead to impurity conduction. The dependences of the density, the microhardness, and the glass transition temperature on the glass composition are explained in the framework of the model according to which the structure of these glasses is built up of structural units corresponding to the As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. It is established that, for crystalline alloys in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system, there exist two compounds (Tl₂SnSe₃ and Tl₄SnSe₄), which are formed by the peritectic reactions; however, structural units of these compounds are not formed in the structural network of glasses.     

Fatty acid metabolism in marine fish: Low activity of fatty acyl Δ5 desaturation in gilthead sea bream (Sparus aurata) cells

Marine fish have an absolute dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in marine fish was either a deficiency in fatty acyl Δ5 desaturase or C_18–20 elongase activity. Recent research in turbot cells found low C_18–20 elongase but high Δ5 desaturase activity. In the present study, the fatty acid desaturase/elongase pathway was investigated in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabeled polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-¹⁴C]18∶2n−6 and [1-¹⁴C]18∶3n−3), C_18–20 elongase ([U-¹⁴C]18∶4n−3), Δ5 desaturase ([1-¹⁴C]20∶3n−6 and [1-¹⁴C]20∶5n−3), and C_20–22 elongase ([1-¹⁴C]20∶4n−6 and [1-¹⁴C]20∶5n−3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and that C_18–20 elongase and C_20–22 elongase activities were substantial. A deficiency in the desaturation/elongation pathway was clearly identified at the level of the fatty acyl Δ5 desaturase, which was very low, particularly with 20∶4n−3 as substrate. In comparison, the apparent activities of Δ6 desaturase, C_18–20 elongase, and C_20–22 elongase were approximately 94-, 27-, and 16-fold greater than that for Δ5 desaturase toward their respective n−3 polyunsaturated fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids in the marine fish the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase activity.     

Characterization of chilean hazelnut (Gevuina avellana mol) seed oil

The fatty acid composition, tocopherol and tocotrienol content, and oxidative stability of petroleum benzene-extracted Gevuina avellana Mol (Proteaceae) seed oil were determined. Positional isomers of monounsaturated fatty acids were elucidated by gas chromatography-electron impact mass spectrometry after 2-alkenyl-4,4-dimethyloxazoline derivatization. This stable oil (Rancimat induction period at 110°C: 20 h) is composed of more than 85% monounsaturated fatty acids and about equal amounts (6%) of saturated and polyunsaturated (principally linoleic) fatty acids. Unusual positional isomers of monounsaturated fatty acids, i.e., C_16:1 Δ¹¹, C_18:1 Δ¹², C_20:1 Δ¹¹, C_20:1 Δ¹⁵, C_22:1 Δ¹⁷, and presumably C_22:1 Δ¹⁹ were identified. The C_18:1 Δ¹² and C_22:1 Δ¹⁹ fatty acids are described for the first time in G. avellana seed oil. While only minute quantities of α-, γ-tocopherols and β-, γ- and δ-tocotrienols were found, the oil contained a substantial amount of α-tocotrienol (130 mg/kg). The potential nutritional value of G. avellana seed oil is discussed on the basis of its composition.     

The energetics of surfactant adsorption at the air-water interface

The standard free energy, enthalpy, and entropy changes (ΔG, ΔH, and ΔS, respectively) for the adsorption at the air-water interface of a commercial ethylene oxide (EO) adduct of straight chain nonylphenol from monomer solution at the critical micelle concentration (CMC) have been calculated from surface tension-concentration data at 21C–45C using the Gibbs equation, the standard free energy change equation ΔG=−RT (In interfacial monomer concentration/CMC), and the Gibbs-Helmholtz equation which gave ΔH directly from the slope of the (ΔG/T) vs (1/T) function. The CMC and surface tension at the CMC (γCMC) decreased, and −ΔG and molecular area increased slightly, with increasing temperature. The ΔH and ΔS values were positive, and appear explainable by the postulations applied to micellization. At ambient temperature (28C) an increase in the (EO) mol ratio of straight chain nonylphenol and C₁₃ secondary alcohol ethoxylates resulted in increases of CMC, γCMC, and molecular area, and slight decreases in −ΔG. A comparison of the 9 (EO) mol ratio adducts of C₁₃ straight chain primary and secondary alcohols showed that the CMC and molecular area of the secondary alcohol ethoxylate were larger, and the γCMC and −ΔG smaller, than the corresponding values of the primary alcohol ethoxylate.     

Unsaturated fatty acids of mycobacteria

The double bond locations have been determined for the mono-unsaturated fatty acids, C₁₄ to C₂₆ ofM. smegmatis andM. bovis BCG. The 14∶1 and 16∶1 fatty acids fromM. smegmatis are principally Δ¹⁰, while the 17∶1, 18∶1 and 19∶1 fatty acids from both organisms are Δ⁹. In the case ofM. smegmatis, the 20∶1, 22∶1 and 24∶1 fatty acids are principally Δ¹¹, Δ¹³ and Δ¹⁵, respectively, while the 22∶1, 24∶1 and 26∶1 fatty acids of BCG are principally Δ¹³, Δ¹⁵ and Δ¹⁷, respectively.     

Transformation of the crystal structure in the series of K1 ? xCsxBSi2O6 borosilicate solid solutions

The transformation of the crystal structure by isomorphous K⁺-Cs⁺ substitutions in the non-tetrahedral positions leading to the phase transition has been studied in the series of K_{1 − x} Cs _x BSi₂O₆ solid solutions. The samples have been crystallized from the glass at 850°C for 10 h. According to the data on the crystal structures refined by the Rietveld method, the compositions with 0 ≤ x ≤ 0.35 crystallize in space group I[`4]3dI\bar 43d, structural type KBSi<sub>2</sub>O<sub>6</sub>, and those with 0.37 ≤ x ≤ 1.0, crystallize in Ia[`3]dIa\bar 3d, structural type CsBSi₂O₆. The reversible cubic-cubic phase transition I[`4]3d \rightleftarrows Ia[`3]dI\bar 43d \rightleftarrows Ia\bar 3d occurs in the composition range x = 0.35–0.37.     

Density and surface tension of Se(90?0.9 x )S(10?0.1 x )Me x and Se(60?0.6 x )S(40?0.4 x )Me x (Me = Sb), Ge glass-forming meltsMe x (Me = Sb), Ge glass-forming melts

The properties of melts in the Se_(90−0.9x)S_(10−0.1x)Me _x and Se_(60−0.6x)S_(40−0.4x)Me _x (Me = Sb, Ge) systems (wherex ranges from 2.5 to 15 mol % with a step of 2.5 mol %) have been investigated. The density and surface tension of melts and the wetting angles of the PbSe semiconductor by melts are measured. The work of adhesion and adhesion strength of the glass coating are calculated. The experimental data are processed using the least-squares method, and the corresponding regression equations are derived. From the materials of the paper reported at the International Conference “Glasses and Solid Electrolytes” (St. Petersburg, 1999, May 17–19).     

Fabrication of Coaxial Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Heterostructure Nanowires by O<Subscript>2</Subscript> Flow-Induced Bifurcate Reactions

We report on bifurcate reactions on the surface of well-aligned Si_1−x Ge _x nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si_1−x Ge _x nanowires were grown in a chemical vapor transport process using SiCl₄ gas and Ge powder as a source. After the growth of nanowires, SiCl₄ flow was terminated while O₂ gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized into SiO₂ by the O₂ gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O₂ pressure without any intermediate region and enables selectively fabricated Ge/Si_1−x Ge _x or SiO₂/Si_1−x Ge _x coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion of oxygen through the oxide layer, respectively.     

Structure and properties of solid solutions of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BaCuFeO<Subscript>5 + δ</Subscript>

The effect of replacing lanthanum with praseodymium on the crystal chemistry parameters of solid solutions of La_{1 − x} Pr _x BaCuFeO_{5 + δ} has been investigated using X-ray powder diffraction analysis and IR spectroscopy. The thermal expansion, electroconductivity, and thermopower of these phases have been studied in air in the temperature range 300–1100 K. The values of linear thermal expansion coefficients (LTEC) of ceramics in different temperature ranges have been determined, and the values of electric transfer parameters in the above oxides have been calculated. It has been established that replacing lanthanum with praseodymium resulted in the compression of the elementary oxide unit La_{1 − x} Pr _x BaCuFeO_{5 + δ}, decrease in the content of labile oxygen in them (δ), decrease in nonmonotonic electroconductivity, increase in thermopower, decrease in LTEC, and difficulties in charge transfer in these phases.     

Blends of a thermotropic liquid crystalline polymer and some flexible chain polymers and the determination of the polymer-polymer interaction parameter of the two polymers

Summary Blends of a thermotropic liquid crystalline polymer (LCP) with poly(ether imide) (PEI), poly(ether ether ketone) (PEEK), polysulfone (PSF) and polyarylsulfone (PAS) prepared by screw extrusion have been investigated by differential scanning calorimeter and dynamic mechanical thermal analysis. From the measured glass transition temperature (T_g) and specific heat increment (ΔC_p) at the T_g, it appears that the LCP dissolves more in the PEI- and PEEK-rich phases than does the PEI and PEEK in the LCP-rich phase. From the DSC study of PSF-LCP and PAS-LCP blends, the T_g(PSF) and T_g(PAS) of each blends are almost constant with blend composition. Therefore, it is concluded that PSF and PAS are immiscible with LCP. The polymer-polymer interaction parameter (χ₁₂) and the degree of disorder (y/x₁) of LCP have been investigated using the Flory lattice theory in which the anisotropy of LCP is considered. The χ₁₂ values have been calculated from the T_g data and found to be 0.181 ± 0.004 at 593 K for the PEI-LCP blends and 0.069 ± 0.006 at 623 K for the PEEK-LCP blends. Using the previously presented method, the χ₁₂ and y/x₁ in partially miscible systems have been determined. Received: 6 April 1998/Revised version: 8 June 1998/Accepted: 17 June 1998     

Identification of noveltrans isomers of 20∶5n−3 in liver lipids of rats fed a heated oil

Trans polyunsaturated n−3 fatty acids are formed as a result of the heat treatment of vegetable oils. It was demonstrated previously that the 18∶3 Δ9cis, 12cis, 15trans containing acis Δ9 ethylenic bond was converted to a geometrical isomer of 20∶5n−3, the 20∶5 Δ5cis, 8cis, 11cis, 14cis, 17trans. In the present study, we have identified two new isomers of eicosapentaenoic acid, the Δ11 monotrans and the Δ11, 17 ditrans isomers in liver of rats fed a heated oil. These are formed as a result of the conversion of two of the main isomers of linolenic acid which are present in refined and frying oils, the 18∶3 Δ9trans, 12cis, 15cis and the 18∶3 Δ9trans, 12cis, 15trans.