Synergy between Printex nano-carbons and silver nanoparticles for sensitive estimation of antioxidant activity

We report on the synthesis, characterization and applications of a Printex L6 carbon-silver hybrid nanomaterial (PC-Ag), which was obtained using a polyol method. In addition, we also highlight the use of Printex L6 nano-carbon as a much cheaper alternative to the use of carbon nanotubes and graphene. The silver nanoparticles (AgNP) were prepared directly on the surface of the Printex 6L carbon “nanocarbon” material using ethylene glycol as the reducing agent. The hybrid nanomaterial was characterized by High-angle annular dark-field transmission electron microscopy (HAADF-TEM), energy–dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), Raman spectroscopy and cyclic voltammetry. Optimized electrocatalytic activity on glassy carbon electrode was reached for the architecture GC/PC-Ag, the silver nanoparticles with size ranging between 1 and 2 nm were well–distributed throughout the hybrid material. The synergy between PC nano-carbons and AgNPs was verified by detection of gallic acid (GA) at a low applied potential (0.091 V vs. Ag/AgCl). GA detection was performed in a concentration range between 5.0 × 10⁻⁷ and 8.5 × 10⁻⁶ mol L⁻¹, with a detection limit of 6.63 × 10⁻⁸ mol L⁻¹ (66.3 nmol L⁻¹), which is considerably lower than similar devices. The approach for fabricating the reproducible GC/PC-Ag electrodes is entirely generic and may be explored for other types of (bio)sensors and devices.     

Studies on the structural heterogeneities of poly(dimethylsiloxane) networks modified with poly(phenylsilsesquioxane)s using small-angle X-ray scattering and dynamical mechanical analysis

In the present investigation the morphological study of self-supported translucent films, constituted of semi-inorganic polymeric materials prepared by sol–gel process from poly(phenylsilsesquioxane) (PPSQ) and poly(dimethylsiloxane) (PDMS), modified by diphenylsilanediol (DPS), phenyltriethoxysilane (PTES) and/or tetraethoxysilane (TEOS), is reported. Small-angle X-ray scattering evidenced phase segregation between PPSQ and PDMS in the PPSQ/PDMS film (M1). The addition of TEOS to the sol, constituted by PPSQ and PDMS, led to morphological changes, characterized by nanoparticles of PPSQ and/or SiO₂ embedded in the PDMS-rich matrix. On its course, the use of diphenylsilanediol and phenyltriethoxysilane mixture, as an additive, led to more homogeneous films in comparison to PPSQ/PDMS.     

Distinguishing links up to link-homotopy by algebraic methods

In this paper we provide a complete algebraic invariant of link-homotopy, that is, an algebraic invariant that distinguishes two links if and only if they are link-homotopic. The paper establishes a connection between the “peripheral structures” approach to link-homotopy taken by Milnor, Levine and others, and the string link action approach taken by Habegger and Lin.     

Growth temperature dependence of the hysteretic behavior of Ni0.5Zn0.5Fe2O4 thin films

Herein, a discussion of the effect of deposition temperature on the magnetic behavior of Ni_0.5Zn_0.5Fe₂O₄ thin films. The thin films were grown by r.f. sputtering technique on (1 0 0) MgO single-crystal substrates at deposition temperatures ranging between 400 and 800 °C. The grain boundary microstructure was analyzed via atomic force microscopy (AFM). AFM images show that grain size (φ∼70-112 nm) increases with increasing deposition temperature, according to a diffusion growth model. From magneto-optical Kerr effect (MOKE) measurements at room temperature, coercive fields, H_c, between 37and 131 Oe were measured. The coercive field, H_c, as a function of grain size, reaches a maximum value of 131 Oe for φ ∼93 nm, while the relative saturation magnetization exhibits a minimum value at this grain size. The behaviors observed were interpreted as the existence of a critical size for the transition from single- to multi-domain regime. The saturation magnetization (21 emu/g<M_s<60 emu/g) was employed to quantify the critical magnetic intergranular correlation length (L_c≈166 nm), where a single-grain to coupled-grain behavior transition occurs. Experimental hysteresis loops were fitted by the Jiles-Atherton model (JAM). The value of the k-parameter of the JAM fitted by means of this model (k/μ_o∼50 A m²) was correlated to the domain size from the behavior of k, we observed a maximum in the density of defects for the sample with φ∼93 nm.     

Inhaltsstoffe aus Genipa americana (Rubiaceae): Mannit

Zusammenfassung Eine kristallisierte Verbindung aus dem Methanolextrakt des Holzes von Genipa americana wurde alsd-Mannit identifiziert.

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From the methanol extracts of the dried wood of Genipa americana a crystalline component was isolated and identified asd-mannitol. *** DIRECT SUPPORT *** A3615112 00027

     

Non-empirical calculations of the nuclear magnetic resonance spectra of imidazole and hydrated imidazole

The magnetic shielding constants of the ¹H, ¹³C and ¹⁵N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5-membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin-spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin-spin coupling constants are not very sensitive to solvent effects.     

Evaluation of on-line high-performance size-exclusion chromatography, differential refractometry, and multi-angle laser light scattering analysis for the monitoring of the oligomeric state of human immunodeficiency virus vaccine protein antigen

Chiron has developed a novel mutant form of the human immunodeficiency virus (HIV) envelop protein, o-gp140, that is currently entering Human Phase 1 clinical trials for testing as a prophylactic HIV vaccine. The o-gp140 protein is oligomeric and the quaternary structure is thought to play an important role in its activity as an antigen. As o-gpl40 proceeds through the clinical trial process and prior to marketing approval, analytical methods that are able to demonstrate manufacturing consistency with respect to degree of oligomerization will need to be developed and validated. On-line high-performance size-exclusion chromatography, differential refractometry, and multi-angle laser light scattering analysis (HPSEC-RI-MALLS), a method commonly used to obtain the molar mass of macromolecules based on the Rayleigh-Gans-Debye approximation, was evaluated for this purpose. The results obtained demonstrated intra- and inter-day precisions to be 0.9 and 3.6% R.S.D., respectively. Accuracy was found to be equal to, or better than, 11% when comparing the known molar masses of test proteins to that of the molar masses determined by the method. Additionally, the method compared favorably to orthogonal native polyacrylamide gel electrophoresis and ultracentrifugation analyses. R-factor analysis was used to demonstrate that HPSEC-RI-MALLS is capable of discriminating compositional differences between o-gpl40 test lots. Based on the data presented, HPSEC-RI-MALLS may be a suitable manufacturing control method.     

Nickel–cobalt hydroxide catalysts for the cycloaddition of carbon dioxide to epoxides

Research on Chemical Intermediates - Nickel and cobalt bimetallic hydroxides, in which both metal cations present the same oxidation state, were synthesized and characterized by XRD, TGA, TEM, XPS,...     

铸造铝青铜合金Cu-14Al-4Fe-Mn的摩擦磨损性能

用往复式摩擦磨损试验机考察了新型高强度、高耐磨性铸造铝青铜合金Cu-14Al-4Fe-Mn(代号HSWAB)的摩擦磨损性能,利用形貌扫描电子显微镜观察分析了合金磨损表面形貌,探讨了其磨损机理.结果表明,HSWAB合金在干摩擦和油润滑条件下的摩擦磨损性能及磨损机理存在明显差异.在干摩擦条件下,合金中脱落的硬质点及氧化物等磨粒导致较为严重的磨粒磨损,摩擦系数高、磨损率大,主要磨损机理为磨粒磨损、粘着磨损、氧化磨损及疲劳磨损.在油润滑条件下,摩擦系数和磨损率均显著降低,疲劳磨损和氧化磨损受到抑制,主要磨损机理为磨粒磨损和粘着磨损.Cu-14Al-4Fe-Mn合金在油润滑条件下的摩擦系数低达0.08,磨损率低达3.7×10-6g/m,是一种优良的耐磨材料.     

SEM-EDS probing of morphological and physiological changes produced by a porphyrin photosensitizer in Psammobatis extenta electrocytes

Morphological and physiological changes produced by the intracellular localization of an alkyl long-chain tetraphenylporphyrin photosensitizer in Psammobatis extenta electrocytes were studied by means of SEM-EDS. Immediately after photosensitizer penetration, electrocytes swell and their convex faces lose all invaginations. This effect is due to chloride and sodium ion flux into electrocytes, in accordance with energy dispersive X-ray microanalysis.