Dynamic mechanical analysis on modified bismaleimide resins

Polyaminobismaleimides (PAMBI) with diphenyl methane, diphenyl ether and hexamethylene segments were synthesized according to Michael type addition reaction. The modification of PAMBIs with 2-glycidyl-phenyl-ether (GPE) was performed in order to ameliorate the toughness of the products. Dynamic mechanical analysis allowed the study of the processes that concur in the material through curing by tracking the storage modulus (E′) and loss factor (tanδ) changes. The small drop of E′ with increasing temperature in the glass transition region argues for crosslinked structures. The viscoelastic behavior revealed complex processes, i.e., overlapping of glass transition temperature range with intra-and inter-crosslinking.     

Inclusion complexes of cyclodextrins with biradicals linked by a polyether chain--an EPR study

Complexation of beta-cyclodextrin with flexible nitroxide biradicals linked by a polyethylene glycol chain was monitored by EPR spectroscopy. The EPR spectra of the uncomplexed biradicals show an exchange interaction due to the flexibility of the polyethylene glycol chain. Complexation with cyclodextrin leads to the disappearance of the exchange interaction in the EPR spectra. The complexation can be reversed by the addition of competing guests (e.g., adamantane derivatives). At high concentration, the inclusion complexes precipitate, and differential scanning calorimetry (DSC) of the precipitates proved the formation of complexes. Elemental analysis data revealed that the complexes contain several cyclodextrin units per biradical but that the composition was not stoichiometric.     

The influence of the halide ions on the photochemical reaction cycle of pharaonis halorhodopsin

Sodium salt of chloride, bromide and iodide were used to elucidate the effect of the size of the anion on the binding to pharaonis halorhodopsin and its transport during the photocycle of this retinal protein. Spectroscopic titration revealed an apparent strong binding constant of 2 mM for chloride, 0.23 mM for bromide and 5 mM for iodide. In the case of iodide a second, week binding constant of about 10 M could be estimated. This second binding constant was similar to that observed earlier for nitrate. By changing the halide ions, only the transitions in the second half of the photocycle were affected, which contained intermediates N, O, and HR'. The O to HR' transition becomes faster with increasing ion volume, meaning that the ion uptake is accelerated. This effect shows a direct correlation with the ion radius. With increasing ion concentration the N-O-HR' equilibrium changed in such a way that the accumulated O tended to decrease. This tendency was overruled in iodide, by the appearance of the second binding constant. The increasing iodide concentration, up to 100mM decreases the accumulation of the intermediate O, due to kinetic reasons, but at higher ion concentration the amount of O increases, although its decay becomes faster. This effect correlates with the appearance of the second iodide bound to the protein.     

Radioactive waste treatment products studied by Mössbauer spectroscopy

Mössbauer effect was used for the characterization of the radioactive waste treatment products, e.g. precipitate formed during the treatment of LLAW (Low Level Active Waste) using iron compounds and their conditioned matrix obtained by cementation.     

Analysis of classes of compounds of environmental concern: III. Organochlorine pesticides

Forty five organochlorine pesticides (currently listed in EPA Method 8081A) have been chromatographed on DB-5/DB-1701 and SPB-5/SPB-1701 column pairs which were in each case connected to an inlet splitter and separate electron capture detectors. Thirteen additional compounds were evaluated for their suitability as internal standards or surrogate compounds for incorporation into Method 8081A. Method reproducibility and linearity are discussed, and results are presented for extracts of six real samples spiked with fifteen organochlorine pesticides and analyzed using the dual-column, dual-detector arrangement.     

Characterization and catalytic-hydrogenation behavior of SiO2-embedded nanoscopic Pd, Au, and Pd-Au alloy colloids

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au M?ssbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.     

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 μM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.     

Determination of ceruloplasmin in human serum by SEC-ICPMS

This paper describes an analytical method for the determination of ceruloplasmin (Cp) in human serum. The method uses immunoaffinity chromatography and size-exclusion chromatography (SEC) to “purify” the serum sample prior to analysis of ⁶³Cu and ⁶⁵Cu by inductively-coupled plasma mass spectrometry (ICPMS). By removing the six most abundant proteins from serum with immunoaffinity chromatography and by using SEC to separate Cu bound by Cp from any free Cu that might be present in the serum sample, we demonstrated that SEC-ICPMS can accurately and reproducibly measure Cp in the ERM DA470 reference serum. Cp identification is based on retention time match of the unknown in the serum sample with the Cp external standard and the presence of ⁶³Cu and ⁶⁵Cu at a ratio of 2.2±0.1. This method was used to analyze a reference serum certified for Cp, 47 serum samples from four different diseases and a set of normal controls. The reference serum and a serum sample from a patient with myocardial infarction, as well as a Cp standard, were also analyzed by electrospray mass spectrometry to confirm the presence of Cp in the SEC fraction known to contain ⁶³Cu.     

Synthesis and Characterization of New α,ω-Bis(Maleimide-Ester) Substituted Siloxane Oligomers

Abstract

Organofunctional siloxane oligomers containing maleimide were synthesized by condensation reaction of α. ω-hydroxypropylsiloxane oligomers with n-[4-(chlorocarbonyl)phenyl]maleimide. A model compound [bis(maleimide-ester)disiloxane] was obtained to facilitate the characerization of the oligomers. Then, the heterogeneous catalyzed ring-opening cationic polymerization technique was applied to obtain an oligomer starting from the model compound and octamethylcyclotetrasiloxane.

The structures of the resulting oligomers were confirmed by elemental analysis, IR and ¹H-NMR spectroscopy. They were characterized by determining softening points, solubility and studying their thermal behavior by thermogravimetric (TGA and differential scanning calorimetry (DSC) measurements.