Synthesis,characterization and properties of novel polyamides containing ferrocene unit and flexible spacers

Synthesis and characterization of ferrocene‐containing main‐chain polyamides are reported in this article. A new, interesting type of organometallic monomer (FDADO) based on ferrocene was prepared by interfacial condensation of 1,1′‐dichlorocarbonyl ferrocene with 2 mol 1,8‐diamino‐3,6‐dioxaoctane (DADO). A series of ferrocene‐based polyamides was prepared via polycondensation of the ferrocenyl diamine (FDADO) with different diacid chlorides using two different methods. The monomer and polymers were characterized by elemental analysis, infrared and NMR spectroscopy. The thermal stability and behavior of the synthesized polymers were evaluated by thermal gravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC). The crystallinity of polymers was examined by X‐ray diffraction analysis. Inherent viscosity, solubility and flame‐retardancy of the polymers were also studied. The obtained polymers showed good heat‐resistance and flame‐retardancy, and improved solubility vs generally reported polyamides in some common organic solvents. Copyright © 2007 John Wiley & Sons, Ltd.     

Relativistic effects and gold site distributions: synthesis, structure, and bonding in a polar intermetallic Na6Cd16Au7

Na(6)Cd(16)Au(7) has been synthesized via typical high-temperature reactions, and its structure refined by single crystal X-ray diffraction as cubic, Fm ?3m, a = 13.589(1) ?, Z = 4. The structure consists of Cd(8) tetrahedral star (TS) building blocks that are face capped by six shared gold (Au2) vertexes and further diagonally bridged via Au1 to generate an orthogonal, three-dimensional framework [Cd(8)(Au2)(6/2)(Au1)(4/8)], an ordered ternary derivative of Mn(6)Th(23). Linear muffin-tin-orbital (LMTO)-atomic sphere approximation (ASA) electronic structure calculations indicate that Na(6)Cd(16)Au(7) is metallic and that ～76% of the total crystal orbital Hamilton populations (-ICOHP) originate from polar Cd-Au bonding with 18% more from fewer Cd-Cd contacts. Na(6)Cd(16)Au(7) (45 valence electron count (vec)) is isotypic with the older electron-richer Mg(6)Cu(16)Si(7) (56 vec) in which the atom types are switched and bonding characteristics among the network elements are altered considerably (Si for Au, Cu for Cd, Mg for Na). The earlier and more electronegative element Au now occupies the Si site, in accord with the larger relativistic bonding contributions from polar Cd-Au versus Cu-Si bonds with the neighboring Cd in the former Cu positions. Substantial electronic differences in partial densities-of-states (PDOS) and COHP data for all atoms emphasize these. Strong contributions of nearby Au 5d(10) to bonding states without altering the formal vec are the likely origin of these effects.     

Tin Dioxide Nanowires: Evolution and Perspective of the Doped and Nondoped Systems

SnO₂ semiconductor nanowire is an extremely important technological material for use in nanophotonic and nanoelectronic devices. These semiconductor nanowires of desirable property can be achieved through a bottom-up approach to the controlled synthesis in a pure or doped state. Each of the synthetic methods offers materials with broad range structural, morphological, optical, and electrical properties. Selective doping of the SnO₂ nanowires by normal, transition or inner transition elements offer a broad variation in the optical and electrical properties and are open for further theoretical exploration of the properties as well as necessary changes possible for the improvement of the material properties. The properties of SnO₂ nanowires can be tuned either in the pure state by structural modification or doping during nanowire growth or after growth to meet most of the requirements.     

Analytical solution in 2D domain for nonlinear response of piezoelectric slabs under weak electric fields

Piezoceramic materials exhibit different types of nonlinearities depending upon the magnitude of the mechanical and electric field strength in the continuum. Some of the nonlinearities observed under weak electric fields are: presence of superharmonics in the response spectra and jump phenomena etc. especially if the system is excited near resonance. In this paper, an analytical solution (in 2D plane stress domain) for the nonlinear response of a rectangular piezoceramic slab has been obtained by use of Rayleigh–Ritz method and perturbation technique. The eigenfunction obtained from solution of the differential equation of the linear problem has been used as the shape function in the Rayleigh–Ritz method. Forced vibration experiments have been conducted on a rectangular piezoceramic slab by applying varying electric field strengths across the thickness and the results have been compared with those of analytical solution. The analytical solutions compare well with those of experimental results. These solutions should serve as a method to validate the FE formulations as well as help in the determination of nonlinear material property coefficients for these materials.     

Body- or tip-controlled reactivity of gold nanorods and their conversion to particles through other anisotropic structures

We report the shape transformation of gold nanorods to spherical nanoparticles, assisted by cupric ions. The reaction proceeds through a series of structures and could be arrested at any stage to produce particles of desired shape. In the presence of a larger concentration of cetyltrimethylammonium bromide (CTAB), selective etching of the tips of the nanorods occurs to a greater extent. The subsequent transformation is driven by the surface reconstruction of nanorods to generate more stable surfaces. As the stability of various surfaces depends on the protecting agent used, the reactivity is modified by controlling its presence at the surface. We show that the body of the rods is more susceptible for reaction at reduced CTAB concentrations. During the conversion to particles, several anisotropic transient structures were observed and were imaged using high-resolution transmission electron microscopy (HRTEM). The transformation occurs due to the hydroxyl radicals produced by Cu2+ in the presence of ascorbic acid (AA). A mechanism has been proposed and several control experiments were conducted to test it. The cupric ion induced shape transformations can be extended to other ions, and knowing the mechanism allows the control of the process to stabilize various anisotropic structures.     

Hemoprotein bioconjugates of gold and silver nanoparticles and gold nanorods: structure-function correlations

Bioconjugates of the hemoproteins, myoglobin, and hemoglobin have been synthesized by their adsorption on spherical gold and silver nanoparticles and gold nanorods. The adsorption of hemoproteins on the nanoparticle surface was confirmed by their molecular ion signatures in matrix assisted laser desorption ionization mass spectrometry and specific Raman features of the prosthetic heme b units. High-resolution transmission electron microscopy (HRTEM) and UV-visible spectroscopy showed that the particles retain their morphology and show aggregation only in the case of silver. The binding of azide ion to the Fe(III) center of the prosthetic heme b moiety caused a red shift of the Soret band, both in the case of the bioconjugates and in free hemoproteins. This was further confirmed by the characteristic signature at 2050 cm-1 in the Fourier-transform infrared spectra, which corresponds to the asymmetric stretching of the Fe(III) bound azide. The retention of the chemical behavior of the prosthetic heme group after adsorption on the nanoparticle is interesting due to its implications in nanoparticle supported enzyme catalysis. The absence of morphology changes after the reaction of bioconjugates with azide ion observed in HRTEM studies implies the stability of nanoparticles under the reaction conditions. All these studies indicate the retention of protein structure after adsorption on the nanoparticle surface.     

DNA‐Cleavage by Fullerene‐Based Synzymes

Efficient cleaving of DNA oligonucleotides by a water‐soluble fullerene main‐chain polymer is demonstrated following a facile routine of monitoring the reaction by UV‐vis spectroscopy and separating the cleaved fractions by membrane filtration. A small quantity of the fullerene derivative could cleave a large excess of the oligonucleotide under ambient light conditions, leading to cleaved DNA in quantitative yields.     

Polymerization of Acrylonitrile Initiated by the Mn(III)/Ethane Thiol Redox System

Abstract

Kinetics of vinyl polymerization of acrylonitrile initiated by the redox system Mn(III)/ethane thiol were investigated in aqueous sulfuric acid in the temperature range of 30-45°C. The rate of polymerization, rate of manganic ion disappearance, etc. were measured. The effect of certain water-miscible organic solvents, neutral electrolytes, and organic nitrogen compounds on the rate has been investigated. A mechanism involving the formation of a complex between Mn(III) and the thiol, whose decomposition yields the initiating free radical with the polymerization being terminated by mutual combination of the growing radicals, has been suggested.     

Dimensional Amplitude Response Analysis of Vibrations Produced by Defects in Rolling Contact Bearings

Usage of rolling contact bearings in variety of rotor-dynamic applications has put forth a need to develop a detailed and easy to implement techniques for the assessment of damage related features in these bearings so that before mechanical failure, maintenance actions can be planned well in advance. In accordance to this, a method based on dimensional amplitude response analysis and scaling laws is presented in this paper for the diagnosis of defects in different components of rolling contact bearings in a dimensionally scaled rotor-bearing system. Rotor, bearing, operating and defect parameters involved are detailed for dimensional analysis using frequency domain vibration data. A defect parameter for modeling all the three dimensions of the defect as well as the different shapes like square, circular, rectangular is put forth which takes into account the volume as well as the surface area of the defect. Experimental data set is generated for the ‘model’ bearing (designated as SKF30205J2/Q) using Box-Behnken design of response surface methodology for solution of the theoretical model by factorial regression approach. Obtained metamodel is then used for the prediction of the objective variable, i.e., Vibration acceleration amplitude at the defect frequency component for other types of ‘test’ bearings (designated as SKF 30305C and SKF 22220 EK) using the developed scaling laws. Confirmation experiments showed that the computable relationship amongst objective variable and the dimensionless parameters can be forecast and correlated.