Acetone‐induced polymerisation of 3‐aminopropyltrimethoxysilane (APTMS) as revealed by NMR spectroscopy

We followed the reactivity of acetone with 3‐aminopropyltrimethoxysilane, a potential organosilane coupling agent, by ¹H, ¹³C and ²⁹Si NMR spectroscopy. Selective 1D and 2D‐edited NMR experiments significantly contributed to simplify the spectral complexity of reaction solution and elucidated molecular structures within progressive reaction phases. The course of the 3‐aminopropyltrimethoxysilane reaction with acetone was shown by a progressive decrease of both reactants, and a concomitant appearance of water and methanol, due to formation of imine and hydrolysis of alkoxysilane groups, respectively. The occurrence of multiple siloxane linkages in a progressively larger cross‐linked macromolecular structure was revealed by DOSY‐NMR experiments and new signals in ²⁹Si‐NMR spectra at different reaction times. The NMR approach described here may be applied to investigate the reactivity of other γ‐aminopropylalkoxysilanes and contribute to define procedures for the preparation of silica‐based materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Use of gamma-irradiation technology in combination with edible coating to produce shelf-stable foods

This research was undertaken to determine the effectiveness of low-dose gamma-irradiation combined with edible coatings to produce shelf-stable foods. Three types of commercially distributed food products were investigated: precooked shrimps, ready to cook pizzas, and fresh strawberries. Samples were coated with various formulations of protein-based solutions and irradiated at total doses between 0 and 3 kGy. Samples were stored at 4°C and evaluated periodically for microbial growth. Sensorial analysis was also performed using a nine-point hedonic scale to evaluate the organoleptic characteristics (odor, taste and appearance). The results showed significant (p0.05) combined effect of gamma-irradiation and coating on microbial growth (APCs and Pseudomonas putida). The shelf-life extension periods ranged from 3 to 10 days for shrimps and from 7 to 20 days for pizzas, compared to uncoated/unirradiated products. No significant (p>0.05) detrimental effect of gamma-irradiation on sensorial characteristics (odor, taste, appearance) was observed. In strawberries, coating with irradiated protein solutions resulted in significant reduction of the percentage of mold contamination.     

(4-Vinylpyridine-Styrene) Copolymer as Host Polymer for Chromophoric Complexes with Potential Second Order Nonlinear Optical Properties

A series of new metal containing polymers for second order nonlinear optics have been prepared by grafting Cu (II) and Pd (II) chromophoric complexes on a preformed (4-vinylpyridine-styrene) copolymeric backbone. The metallated polymers have been chemically and physically characterized. They show high glass transition temperatures, high thermal stability and good solubility. Their properties have been compared with analogous metallated poly(4-vinylpyridine) samples: variations in the polymeric backbone, as well as in ligands, metal, and metallation ratio, allow to tune their properties.     

Perturbation of Conformational Dynamics of ASCUT-1 from Ascaris lumbricoides by Temperature and Sodium Dodecyl Sulfate

ASCUT-1 is a protein found in cuticlin, the insoluble residue of the cuticles of the nematode Ascaris lumbricoides. It contains the CUT-1-like domain which is shared by members of a novel family of components of extracellular matrices. The monomeric form of ASCUT-1 contains a single tryptophan residue. An understanding of the structure-function relationship of the protein under different chemical-physical conditions is of fundamental importance for an understanding of its structure and function in cuticles. In this paper we report the effect of the temperature and sodium dodecyl sulfate on the structural stability of this protein. The structure of the protein was studied in the temperature range 25–85°C in the absence and in the presence of sodium dodecyl sulfate by frequency-domain measurements of the intrinsic fluorescence intensity and anisotropy decays. The time-resolved fluorescence data in the absence of SDS indicated that the tryptophanyl emission decays were well described by a bimodal lifetime distribution, and that the temperature increases resulted in the sharpening and in the shortening of the tryptophanyl lifetime distribution. In the presence of SDS an unimodal fluorescence lifetime distribution as well as a marked decrease in the anisotropy decay values were observed.     

Electrophilic aromatic substitution in the curing of brominated poly(isobutylene-co-4-methylstyrene): A mechanistic model study with zinc salts

The crosslinking chemistry of a new elastomer based on brominated poly(isobutylene-co-4-methylstyrene) has been investigated using model compounds. In order to mimic the conditions that prevail within the highly allphatic rubber, the study was carried out in mineral oil using catalysts that are compatible with such low polarity media. Electrophilic aromatic substitution reactions occur in a system consisting of p-isopropylbenzyl bromide and p-isopropyl toluene in the presence of zinc oxide and zinc stearate. The reaction proceeds after a significant induction period while no induction period is seen for a similar reaction with zinc bromide as the catalyst. The in situ formation of reactive species containing Zn? Br bonds appears to be an important step in the overall process. The stoichiometric ratio of zinc salt to benzylic bromide is important. High ratios lead to the accumulation of benzylic stearate or benzylic alcohol in the system which retards the alkylation reaction. The model study emphasizes the importance of stoichiometry of reagents in this reaction and provides insight into the crosslinking mechanism. © 1993 John Wiley & Sons, Inc.     

Improvement of Shack-Hartmann wave-front sensor measurement for extreme adaptive optics

The development of high-performance adaptive optics systems requires the optimization of wave-front sensors (WFSs) working in the high-order correction regime. We propose a new method to improve the wave-front slope estimation of a Shack-Hartmann WFS in such a regime. Based on a detailed analysis of the different errors in the slope estimation with a classical centroid and with the new method, the gain in terms of wave-front-sensing accuracy in both the detector and the photon noise regimes is stressed. This improvement is proposed without major system disruption.