Synthesis of nanocrystalline nickel ferrite by thermal decomposition of organic precursors

Nickel ferrite powders were synthesized by thermal decomposition of the precursors obtained in the redox reaction between the mixture of Ni(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O with polyalcohol: 1,4-butanediol, polyvinyl alcohol and also with their mixture. During this reaction the primary C?COH groups were oxidized at ?CCOOH, while secondary C?COH groups at C=O groups. The carboxylic groups formed coordinate to the present Ni(II) and Fe(III) cations leading to carboxylate type compounds, further used as precursors for NiFe₂O₄. These precursors were characterized by thermal analysis and FT-IR spectrometry. All precursors thermally decomposed up to 350?°C leading to nickel ferrite weakly crystallized. By annealing at higher temperatures, nanocrystalline nickel ferrite powders were obtained, as resulted from XRD. SEM images have evidenced the formation of nanoparticulate powders; these powders present magnetic properties characteristic to the oxidic system formed by magnetic nanoparticles.     

Structure simulation into a lamellar supramolecular network and calculation of the metal ions/ligands ratio

Background

Biosensors have attracted increasing attention as reliable analytical instruments in in situ monitoring of public health and environmental pollution. For enzyme-based biosensors, the stabilization of enzymatic activity on the biological recognition element is of great importance. It is generally acknowledged that an effective immobilization technique is a key step to achieve the construction quality of biosensors.

Results

A novel disposable biosensor was constructed by immobilizing laccase (Lac) with silica spheres on the surface of multi-walled carbon nanotubes (MWCNTs)-doped screen-printed electrode (SPE). Then, it was characterized in morphology and electrochemical properties by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The characterization results indicated that a high loading of Lac and a good electrocatalytic activity could be obtained, attributing to the porous structure, large specific area and good biocompatibility of silica spheres and MWCNTs. Furthermore, the electrochemical sensing properties of the constructed biosensor were investigated by choosing dopamine (DA) as the typical model of phenolic compounds. It was shown that the biosensor displays a good linearity in the range from 1.3 to 85.5 ??M with a detection limit of 0.42 ??M (S/N = 3), and the Michaelis-Menten constant (K_m ^app) was calculated to be 3.78 ??M.

Conclusion

The immobilization of Lac was successfully achieved with silica spheres to construct a disposable biosensor on the MWCNTs-doped SPE (MWCNTs/SPE). This biosensor could determine DA based on a non-oxidative mechanism in a rapid, selective and sensitive way. Besides, the developed biosensor could retain high enzymatic activity and possess good stability without cross-linking reagents. The proposed immobilization approach and the constructed biosensor offer a great potential for the fabrication of the enzyme-based biosensors and the analysis of phenolic compounds.     

Design,synthesis and structure of new dendritic melamines. First use of a tandem C-2-substituted serinol—O,O-masked 4-piperidone as a peripheral unit in iterative synthesis

The iterative chemoselective amination of cyanuric chloride to dimers of new G-2 dendritic N-substituted-2,4,6-triamino-s-triazines (melamines) having C-2-substituted 2-aminopropane-1,3-diols (‘serinols’) in tandem with the ethylene ketal of 4-piperidone as peripheral units is reported. The structure as a function of increasing molecular size was studied by NMR spectroscopy, DFT calculation and AFM imaging. A concise nomenclature defining the restricted rotational phenomena about the newly created C(s-triazine)–N(exocyclic) partial double bonds, seen as axes of (pro)diastereomerism, is used. We propose a new form of frontier rotamerism for the dendrimer surface, which operates over a long range.     

Retro-leapfrog and related retro map operations

Operations on maps are well-known theoretical tools for transforming a given polyhedral tessellation. Several theoretical investigations of fullerenes, such as their pi-electronic structure and stability, need information on the original map which was transformed into a larger molecular structure. In this respect, retro-operations, particularly those of the most used leapfrog, chamfering, and capra operations, appear particularly useful in searching the associate graphs of fullerenes. A series of analyzed cages proved to be leapfrog transforms of smaller cages. This information was useful in understanding their closed pi-electronic structure and related properties including the local aromaticity. An index based on the optimized geometries enabled the evaluation of aromaticity of their various substructures. Pictorial images of the pi-electron distribution as the main Kekulé valence structures have been performed by the aid of the JSCHEM software package.     

Synthesis of poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) copolymers by free radical polymerization combined with oxidative coupling

Poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) triblock copolymers were synthesized for the first time by the free radical copolymerization of methyl methacrylate (MMA) and styrene (St) in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH-end groups. The apparent chain transfer constant of the thiocol SH groups in the copolymerization reaction was estimated from the rate of consumption of the thiol groups versus the overall rate of consumption of the monomers (C_T = 1.28). Based on this value, the chain transfer constant of the thiocol SH groups in St polymerization was calculated . The triblock copolymers synthesized were characterized by SEC and ¹H NMR measurements.     

Performance enhancements of mass selective axial ejection from a linear ion trap

Mass selective axial ejection (MSAE) of ions from a linear ion trap (LIT) takes advantage of the rf fringing fields at the end of the linear quadrupole to convert radial ion excitation into axial ejection. Ions gain radial amplitude via a mass selective resonance excitation process and are ejected axially over an electrostatic DC barrier. The extraction efficiency and resolution are determined by the length and shape of the extraction region in the vicinity of the exit aperture. In the work presented here, axial DC fields, created by auxiliary electrodes, were used to modify the shape of the trapping electrostatic fields along the quadrupole axis and to increase the density of the ions in the extraction region. Better confinement and ion cloud coherence increased the extraction efficiency and the spectral resolution. As a result, extraction efficiency can be increased by up to one order of magnitude at fast scan rates, i.e., 10 and 20 kTh/s, and a factor of 2–3 at the slower scan speed of 1 kTh/s. The length of the extraction region was also modified by application of a portion of the drive rf voltage to the end lens of the LIT. A comparison of the MSAE spectra at different scan rates and rf levels showed that extraction efficiencies increase at scan rates of 10 kTh/s or higher, with associated improvements in mass spectral peak widths.     

Solvability of dynamic antiplane frictional contact problems for viscoelastic cylinders

We study a mathematical model which describes the antiplane shear deformations of a cylinder in frictional contact with a rigid foundation. The process is dynamic, the material behavior is described with a linearly viscoelastic constitutive law and friction is modeled with a general subdifferential boundary condition. We derive a variational formulation of the model which is in a form of an evolutionary hemivariational inequality for the displacement field. Then we prove the existence of a weak solution to the model. The proof is based on an abstract result for second order evolutionary inclusions in Banach spaces. Also, we prove that, under additional assumptions, the weak solution to the model is unique. We complete our results with concrete examples of friction laws for which our results are valid.     

Light monotone Dialectica methods for proof mining

In view of an enhancement of our implementation on the computer, we explore the possibility of an algorithmic optimization of the various proof‐theoretic techniques employed by Kohlenbach for the synthesis of new (and better) effective uniform bounds out of established qualitative proofs in Numerical Functional Analysis. Concretely, we prove that the method (developed by the author in his thesis, as an adaptation to Dialectica interpretations of Berger's original technique for modified realizability and A‐translation) of “colouring” some of the quantifiers as “non‐computational” extends well to ε‐arithmetization, elimination‐of‐extensionality and model‐interpretation (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling and analysis of the unilateral contact of a piezoelectric body with a conductive support

We consider a mathematical model which describes the quasistatic process of contact between a piezoelectric body and an electrically conductive support, the so-called foundation. We model the material's behavior with a nonlinear electro-viscoelastic constitutive law; the contact is frictionless and is described with the Signorini condition and a regularized electrical conductivity condition. We derive a variational formulation for the problem and then we prove the existence of a unique weak solution to the model. The proof is based on arguments of nonlinear equations with multivalued maximal monotone operators and fixed point. Then we introduce a fully discrete scheme, based on the finite element method to approximate the spatial variable and the backward Euler scheme to discretize the time derivatives. We treat the unilateral contact conditions by using an augmented Lagrangian approach. We implement this scheme in a numerical code then we present numerical simulations in the study of two-dimensional test problems, together with various comments and interpretations.     

Influence of the Crystallinity of Silver Nanoparticles on Their Magnetic Properties

The magnetic properties of noble-metal nanoparticles are a puzzling phenomenon, tentatively often explained as a size effect or a ligand effect. Many experimental studies performed to date have attempted to vary these readily available parameters without reaching a definitive conclusion. In an attempt at better understanding the role of core crystallinity on these magnetic properties, we have compared the behavior of silver nanoparticles, which were either single-crystalline or multi-twinned, of almost identical sizes and with the same ligand coating. Our results indicate that single-crystalline nanoparticles tend to behave as classical paramagnetic materials, whereas multi-twinned ones exhibit a combination of para- and ferro-magnetic behaviors. Our hypothesis is that lattice defects within the core bear magnetic moments which couple through conduction electrons, with dipolar interactions also playing a local and macroscopic role.