Mechanochemically initiated copolymerizations, 10. Kinetic data on the copolymerization of the acrylonitrile/vinyl acetate/α-methyl styrene ternary system by vibratory milling

The kinetics of mechanochemical copolymerization of the ternary system based on acrylonitrile, vinyl acetate, and α-methyl styrene, by vibratory milling activation was studied. A general relation for expressing the reaction rate is proposed as follows: Kinetics has been followed by measuring the amount of unreacted monomer by gas chromatography. Partial reaction orders – related to each comonomer, had almost unitary values, being determined from the conversion-time curves for 7 ternary systems with different comonomer ratios. The values of the reaction rate constant – taken for three temperatures – permitted the computation of the activation energy (18.82 kJ mol^-1), such a low value showing that the contribution of the thermal energy in this type of synthesis is unsignificant.     

New Amino‐Acid‐Based β‐Phosphorylated Nitroxides for Probing Acidic pH in Biological Systems by EPR Spectroscopy

There is increasing interest in measuring pH in biological samples by using nitroxides with pH‐dependent electron paramagnetic resonance (EPR) spectra. Aiming to improve the spectral sensitivity (Δa_X) of these probes (i.e., the difference between the EPR hyperfine splitting (hfs) in their protonated and unprotonated forms), we characterized a series of novel linear α‐carboxy, α′‐diethoxyphosphoryl nitroxides constructed on an amino acid core and featuring an (α or α′)‐C?H bond. In buffer, the three main hfs (a_N, a_H, and a_P) of their EPR spectra vary reversibly with pH and, from a_P or a_H titration curves, a two‐ to fourfold increase in sensitivity was achieved compared to reference imidazoline or imidazolidine nitroxides. The crystallized carboxylate 10 b (pK_a ≈3.6), which demonstrated low cytotoxicity and good resistance to bioreduction, was applied to probe stomach acidity in rats. The results pave the way to a novel generation of highly sensitive EPR pH markers.     

Does Aphid Infestation Interfere with Indirect Plant Defense against Lepidopteran Caterpillars in Wild Cabbage?

Attraction of parasitoids to plant volatiles induced by multiple herbivory depends on the specific combinations of attacking herbivore species, especially when their feeding modes activate different defense signalling pathways as has been reported for phloem feeding aphids and tissue feeding caterpillars. We studied the effects of pre-infestation with non-host aphids (Brevicoryne brassicae) for two different time periods on the ability of two parasitoid species to discriminate between volatiles emitted by plants infested by host caterpillars alone and those emitted by plants infested with host caterpillars plus aphids. Using plants originating from three chemically distinct wild cabbage (Brassica oleracea) populations, Diadegma semiclausum switched preference for dually infested plants to preference for plants infested with Plutella xylostella hosts alone when the duration of pre-aphid infestation doubled from 7 to 14 days. Microplitis mediator, a parasitoid of Mamestra brassicae caterpillars, preferred dually-infested plants irrespective of aphid-infestation duration. Separation of the volatile blends emitted by plants infested with hosts plus aphids or with hosts only was poor, based on multivariate statistics. However, emission rates of individual compounds were often reduced in plants infested with aphids plus hosts compared to those emitted by plants infested with hosts alone. This effect depended on host caterpillar species and plant population and was little affected by aphid infestation duration. Thus, the interactive effect of aphids and hosts on plant volatile production and parasitoid attraction can be dynamic and parasitoid specific. The characteristics of the multi-component volatile blends that determine parasitoid attraction are too complex to be deduced from simple correlative statistical analyses.     

Simultaneous interpenetrating networks based on castor oil polyesters and polystyrene

Simultaneous interpenetrating networks (SIN's) have been synthesized by simultaneous polymerization of a rubbery polymer based on castor oil and a second plastic forming monomer plus initiator and crosslinking agent. According to the overall composition and synthetic details, SIN's of elastomeric, leathery, or plastic behavior have been obtained. Polymers employed were the crosslinked polyester from castor oil and sebacyl chloride (a castor oil derivative) and polystyrene crosslinked with 1 percent divinyl benzene, simultaneously polymerized. Electron microscopy revealed a complex two phase morphology strongly depending on the relative gelation times of the two polymers, the polymer gelling first becoming the more continuous phase. Stress-strain curves show a SIN plastic with a well developed yield point, as well us highly toughened elastomers. Both the plastic and the elastomeric SIN's are tougher than the corresponding homopolymers. Modulus-temperature curves show a glass transition temperature around ?60°C for the elastomer component, and +100°C for the polystyrene in the SIN's.     

Properties of n‐butyl methacrylate copolymer latex films derived from crosslinked latex particles

Films obtained from copolymer latexes of n‐butyl methacrylate (BMA) with a series of crosslinking monomers [i.e., a macromonomer crosslinker (Mac), ethylene glycol dimethacrylate (EGDMA), and aliphatic urethane acrylate] exhibited differences in their tensile properties and swelling behaviors. For P(BMA‐co‐EGDMA) copolymer, a dependence on the initiator type was obtained. It is postulated that the network microstructures for the various copolymers evolved as the result of the copolymerization reactions between the monomer pairs during the synthesis in the miniemulsion free‐radical copolymerization. These network microstructures are, therefore, hypothesized to influence the mechanical properties of the resultant films. Copolymers prepared with Mac were tough in comparison with copolymers made with EGDMA. The presence of longer linear or lightly crosslinked poly(n‐butyl methacrylate) (PBMA) chains and the looseness of the crosslinked network structures in the PBMA‐co‐Mac copolymers appear to be the factors responsible for the differences. All of the copolymer films disintegrated into swollen individual microgels when they were immersed in tetrahydrofuran. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 42–49, 2003     

Viscous Flow as the Driving Force for the Densification of Low-Temperature Co-Fired Ceramics

Filled glass–ceramic composites, like low-temperature co-fired ceramics (LTCC), must densify at temperatures <900°C. The densification mechanism of LTCC is often described by liquid-phase sintering. The results of this paper clearly show that densification of ceramic-filled glass–composites with a glass content above 60 wt% can be attributed to viscous sintering, which is decisively controlled by the viscosity of the glass during the heat treatment. This is demonstrated by the experimental determination of the viscosity of a MgO–Al₂O₃–B₂O₃–SiO₂ glass dependent on temperature, by investigation of the wetting behavior of the glass on the ceramic filler mullite, and of the microstructural development. It was found that the glass does not wet the filler material in a temperature range up to 1000°C. Therefore, liquid-phase sintering can be excluded. Independent of any wetting effect and therefore in the absence of capillary forces, densification starts at a temperature of 750°C, which corresponds to a viscosity of 10^9.5 dPa·s. This densification can be attributed to viscous flow of the glass matrix composite.     

Catalytic Conversions in Water. Part 23: Steric Effects and Increased Substrate Scope in the Palladium‐Neocuproine Catalyzed Aerobic Oxidation of Alcohols in Aqueous Solvents#

The steric influence of substituents on the 2‐ and 9‐positions of phenanthroline in the (2,9‐R₂‐1,10‐phenanthroline)palladium(II)‐catalyzed aerobic oxidation of 2‐hexanol was investigated by means of high throughput experimentation. (Neocuproine)Pd(OAc)₂ (RCH₃) was found to be a highly active catalyst for alcohol oxidation in 1 : 1 water/DMSO mixtures. The catalyst is unique in that it tolerates water, polar co‐solvents and a wide variety of functional groups in the alcohol. Turn‐over frequencies of >1500 h⁻¹ were achieved and a series of alcohols was oxidised with 0.1 to 0.5 mol % of catalyst.     

Graphene–Oxide Porous Biopolymer Hybrids Enhance In Vitro Osteogenic Differentiation and Promote Ectopic Osteogenesis In Vivo

Over the years, natural-based scaffolds have presented impressive results for bone tissue engineering (BTE) application. Further, outstanding interactions have been observed during the interaction of graphene oxide (GO)-reinforced biomaterials with both specific cell cultures and injured bone during in vivo experimental conditions. This research hereby addresses the potential of fish gelatin/chitosan (GCs) hybrids reinforced with GO to support in vitro osteogenic differentiation and, further, to investigate its behavior when implanted ectopically. Standard GCs formulation was referenced against genipin (Gp) crosslinked blend and 0.5 wt.% additivated GO composite (GCsGp/GO 0.5 wt.%). Pre-osteoblasts were put in contact with these composites and induced to differentiate in vitro towards mature osteoblasts for 28 days. Specific bone makers were investigated by qPCR and immunolabeling. Next, CD1 mice models were used to assess de novo osteogenic potential by ectopic implantation in the subcutaneous dorsum pocket of the animals. After 4 weeks, alkaline phosphate (ALP) and calcium deposits together with collagen synthesis were investigated by biochemical analysis and histology, respectively. Further, ex vivo materials were studied after surgery regarding biomineralization and morphological changes by means of qualitative and quantitative methods. Furthermore, X-ray diffraction and Fourier-transform infrared spectroscopy underlined the newly fashioned material structuration by virtue of mineralized extracellular matrix. Specific bone markers determination stressed the osteogenic phenotype of the cells populating the material in vitro and successfully differentiated towards mature bone cells. In vivo results of specific histological staining assays highlighted collagen formation and calcium deposits, which were further validated by micro-CT. It was observed that the addition of 0.5 wt.% GO had an overall significant positive effect on both in vitro differentiation and in vivo bone cell recruitment in the subcutaneous region. These data support the GO bioactivity in osteogenesis mechanisms as being self-sufficient to elevate osteoblast differentiation and bone formation in ectopic sites while lacking the most common osteoinductive agents.     

Accumulation of organochlorines and brominated flame retardants in the eggs and nestlings of great tits, Parus major

Insectivorous birds may be very useful sentinels for local point-source contamination with persistent pollutants, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs). Eggs have been used extensively to monitor lipophilic contaminants, as females can pass contaminants stored in their body tissues into their eggs. Concentrations and profiles in eggs therefore relate to contamination in the female. Because nestlings are raised on food items collected locally, it is expected that the body burden in nestlings would reflect their diet and local pollution levels better than eggs. In this study we compared the accumulation and the profile of PCBs, PBDEs, and OCPs in great tit (Parus major) eggs, nestlings (5-, 10-, and 15-days old), and their food in two study sites. Our results showed that concentrations in great tit eggs were 4 to 6 times higher than those in nestlings. Concentrations in nestling great tits corresponded with concentrations predicted by a bioenergetics-based model. Most of the persistent organic pollutants in 15-day old nestlings were still from maternal origin. The profile of these persistent pollutants in eggs and nestlings also gradually changed during development. With increasing age, the proportion of the most persistent compounds decreased. This study shows that most of the persistent pollutants in fully grown nestlings may still be from maternal origin. For nestlings to be suitable as indicators of local contamination, most of the POPs they accumulate should originate from dietary sources rather than from maternal transfer via the egg. Nestling birds may therefore not be good sentinels for local contamination with persistent pollutants.     

Monitoring the Authenticity of Organic Grape Juice via Chemometric Analysis of Elemental Data

Elemental determination was carried out on 36 grape juice samples (19 organic and 17 ordinary), with the goal of identifying significant differences between the two types of juice for classification purposes. Inductively coupled plasma-mass spectrometry was used for the determination of 24 elements, Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, La, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, Se, Sn, Ti, V, and Zn. Ba, Ce, La, Mg, P, Pb, Rb, Sn, and Ti concentrations were found to be higher in organic versus ordinary samples, while Na and Va concentrations were higher in ordinary versus organic samples. The remaining investigated elements exhibited statistically equivalent concentration levels in both types of samples. Principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) statistical techniques of the elemental fingerprints were readily able to discriminate organic from ordinary samples and can be used as alternative methods for adulteration evaluation.