Organolithium route to poly(arylsilane)s

Various poly(arylsilane)s The poly(carbosilane)s prepared in this way are of higher molecular weight than when prepared by the Wurtz-type condensation route previously reported. TG shows 40–50% overll weight loss attained at 500–600°C.     

Pyrolysis chromatography of lipids. I. Mass spectrometric identification of pyrolysis products of hydrocarbons

The products of pyrolysis at 600C of normal paraffins C₁₀−C₁₈, 2-methyl octadecane, 4-methyl octadecane, 6-methyl octadecane, cyclohexyl decane, cyclopentyl decane, 2,2,4,4,6,8,8-heptamethyl nonane, pristane and phytane were studied by means of a pyrolysis gas chromatograph directly coupled to a mass spectrometer. n-Paraffins yield a homologous series of n-olefins. Branched paraffins yield two homologous series, one of n-olefins and one of branched olefins. The n-olefin corresponding to the position of the branch is not formed. Interpretation of pyrolograms is similar in principle to the interpretation of mass spectra. Presented at the Symposium on “Mass Spectrometry of Lipids”, AOCS Cincinnati, October 1965.     

Dependence of physical properties on composition in a series of high load-bearing polyurethane foams. Part II. Effects of variations in reactant ratios

Data and interpretations are presented on the effects of chemical variations on the physical properties, and in particular, the compression–deflection characteristics of a series of high load-bearing, open-celled, shock-mitigating polyurethane foams. The load-bearing capability of the foam is considered to be a function of density and intrinsic stiffness of the polymer. Polyol components of the formulations consisted of a poly (oxypropylene triol) of approximately 4000 molecular weight and ethylene glycol. The blowing agents were water and trimerized linseed fatty acids. A solution of polymethylene polyphenylisocyanate and tolylene diisocyanate comprised the isocyanate mixture. Stannous octoate and N-ethylmorpholine were th?e dual catalysts. Load-bearing capability of the foam was raised by increasing the concentrations of the isocyanates, poly (oxypropylene triol), stannous octoate, and by employing higher ratios of polymethylene polyphenylisocyanate to tolylene diisocyanate. Decrease in compressive strength resulted from increasing the quantity of blowing agents and N-ethylmorpholine. Increasing the quantity of ethylene glycol gave load-bearing properties which increased to a maximum and then decreased. Chemical variations are analyzed in terms of their effects on the properties of the polymeric networks. These include crosslink density, number and distribution of hydrogen bonds, chain orientation and mobility, and relative selectivity of the various reactions. Effects on the overall bulk properties of the foam are discussed in terms of the chemical composition.     

A generalized equation of state for polymers

A simple, generalized equation of state has been developed that describes the pressure–volume–temperature behavior of both addition and condensation polymers. Use of the equation requires only that the polymer's glass temperature and density at 25°C. and one atmosphere be known. The equation applies to both amorphous and crystalline polymers for pressures up to 10,000 atm. It also appears to hold for copolymers. Polymer glass temperatures can also be estimated with the equation.     

A rapid method for the preparation of ganglioside Glac2 (GD3)

A method is described for the preparation of ganglioside G_lac2 [(II³(NeuAc)₂-LacCer, GD3] from cream of bovine milk using liquid-phase extraction with methanol or ethanol followed by anion exchange chromatography. The method is rapid and inexpensive; 1 kg cream, centrifuged from 14–15 L of bovine milk, yields approximately 70 mg of pure ganglioside G_lac2. The sialic acid constituent of ganglioside G_lac2 isolated from bovine milk cream consists solely of theN-acetylneuraminic acid derivative. The major components of its ceramide consist of octadecasphing-4-enine and the 22∶0 (behenic acid) and 23∶0 fatty acids. Short hand notations for gangliosides are according to Wiegandt (Ref. 1). G_lac2, (II³(NeuAc)₂-LacCer) is NeuAcα,8NeuAcα,-3Galβ,4Glcβ,1Cer; G_tet1, (II³NeuAc-Gg₄Cer) is Gal\,3GalNAcβ,-4(NeuAcα,3)Galβ,4Glcβ,1Cer.     

β-Carotene transport in human lipoproteins. Comparisons with a-tocopherol

The purpose of this study was to investigate the temporal relationships of the transport of β-carotene in human lipoproteins. We administered 60 mg β-carotene with breakfast to nine fasting subjects, then blood samples were collected at intervals of up to 75 h, lipoproteins were isolated, and β-carotene was quantitated. β-Carotene concentrations in chylomicrons and very low density lipoproteins (VLDL) peaked at 6 and 9 h, respectively. Nonetheless, at all time points the majority of plasma β-carotene was contained in low density lipoproteins (LDL), while high density lipoproteins (HDL) carried a smaller portion (at 24 h, 73±8% in LDL as compared with 23±5% in HDL). In three subjects, transport of β-carotene was compred with the results of earlier studies on the transport of stereoisomers of α-tocopherol. Unlike plasmaRRR-α-tocopherol concentrations, which are maintained by the preferential incorporation ofRRR-α-tocopherol into VLDL by the liver, β-carotene increased and decreased in VLDL similarly toSRR-α-tocopherol, a stereoisomer whose concentrations are not maintained in plasma. In conclusion, β-carotene is primarily transported in the plasma in LDL, but its incorporation by the liver into lipoproteins does not appear to be enhanced.     

Nanoscale assembly in biological systems: from neuronal cytoskeletal proteins to curvature stabilizing lipids

The review will describe experiments inspired by the rich variety of bundles and networks of interacting microtubules (MT), neurofilaments, and filamentous-actin in neurons where the nature of the interactions, structures, and structure-function correlations remain poorly understood. We describe how three-dimensional (3D) MT bundles and 2D MT bundles may assemble, in cell free systems in the presence of counter-ions, revealing structures not predicted by polyelectrolyte theories. Interestingly, experiments reveal that the neuronal protein tau, an abundant MT-associated-protein in axons, modulates the MT diameter providing insight for the control of geometric parameters in bio- nanotechnology. In another set of experiments we describe lipid-protein-nanotubes, and lipid nano-tubes and rods, resulting from membrane shape evolution processes involving protein templates and curvature stabilizing lipids. Similar membrane shape changes, occurring in cells for the purpose of specific functions, are induced by interactions between membranes and proteins. The biological materials systems described have applications in bio-nanotechnology.     

Modification of the physical properties of semiconducting MgAl2O4 by doping with a binary mixture of Co and Zn ions

The effects of doping of MgAl₂O₄ by a binary mixture of Co and Zn ions on the absorbance, electrical resistivity, capacitance, thermal conductivity, heat capacity and thermal diffusivity are reported in this paper. The materials with the nominal composition Mg_1−2x(Co,Zn)_xAl₂O₄ (x = 0.0-0.5) are synthesized by solution combustion synthesis assisted by microwave irradiation. The substituted spinels are produced with a Scherrer crystallite size of 18-23 nm, as opposed to 45 nm for undoped samples, indicated by X-ray diffraction and confirmed by transmission electron microscopy. These materials also show better thermal stability in the temperature range of 298-1773 K. Three strong absorption bands at 536, 577 and 630 nm are observed for the doped samples which are attributed to the three spin allowed (⁴A₂ (F) → ⁴T₁ (P)) electronic transitions of Co²⁺ at tetrahedral lattice sites while pure magnesium aluminate remains transparent in the whole spectral range. The semiconducting behavior of the materials is evident from the temperature dependence of the electrical resistivity. Resistivity and activation energy are higher for the substituted samples. Fitting of the resistivity data is achieved according to the hopping polaron model of solids. Both dielectric constant and loss increase on account of doping. The dielectric data are explained on the basis of space charge polarization. The thermal conductivity and diffusivity are lowered and the heat capacity is increased in the doped materials. Wiedemann-Franz's law is used to compute the electronic and lattice contributions towards the total thermal conductivity.     

Coal rank and coke reactivity

For a series of cokes prepared under identical carbonizing conditions it was shown that rates of reaction with carbon dioxide/nitrogen mixtures at about 1000°C were generally higher for the cokes prepared from coals of above 30% volatile matter. The reaction rates of cokes prepared from certain Durham coals were generally higher than anticipated. Gasification of cokes prepared from certain Durham coals were generally higher than anticipated. Gasification of the cokes resulted in loss of strength, decrease in apparent density, enlargement of pores and reduction of pore-wall thickness. It appeared that burn-off was primarily associated mineral constituents of the coke ash upon gasification rates was detected. A tentative relation was derived between gasification rates and the ratio of pore-wall thickness to pore diameter of the cokes. In turn, this latter ratio appeared to bear some relation to the oxygen content of the coal. The majority of the parameters studied were measured by established techniques. Porosity was determined by mercury pressure porosimetry and the Quantimet 720 automatic image analysis microscope was employed for structural studies. The accuracy of the measurement of pore and pore-wall dimensions was approximately ± 2%.