Spectroscopic EPR and IR studies of monomeric and dimeric species formed upon adsorption of nitric oxide on Ce0.75Zr0.25O2 and their reactivity with dioxygen

The interaction of nitric oxide with Ce_0.75Zr_0.25O₂ solid solution were investigated by means of EPR and IR spectroscopies. The influence of adsorption parameters such as adsorption temperature and pressure, presence of the O₂ co-reactant on the nature and relative surface abundance of the resultant mono- and dimeric NO species was elucidated. The thermal stability of the surface nitrosyl complexes and their reactivity toward dioxygen were also examined.     

Oxidation chemistry of indole-2-carboxylic acid: Mechanism and products formed in neutral aqueous solution

The oxidation chemistry of indole-2-carboxylic acid has been investigated in phosphate containing supporting electrolytes in the pH range 1.4-9.8 at a pyrolytic graphite electrode by voltammetric studies, spectral studies, controlled potential electrolysis and related techniques. The kinetics of decay of the UV-absorbing intermediate generated during electrooxidation was followed spectrophotometrically and the decay occurred in a pseudo-first-order reaction. The products of the electrode reaction were characterized as 2,4-, 2,6- and 2,7-dioxindoles, COC- and CC-linked dimers by using GC-MS, IR and ¹H NMR. A detailed interpretation of the redox mechanism of indole-2-carboxylic acid in neutral aqueous medium has been presented to account for the formation of various products.     

Electron-Nuclear Recoil Discrimination by Pulse Shape Analysis

In the framework of the “ULTIMA” project, we use ultra cold superfluid ³He bolometers for the direct detection of single particle events, aimed for a future use as a dark matter detector. One parameter of the pulse shape observed after such an event is the thermalization time constant τ _b . Until now it was believed that this parameter only depends on geometrical factors and superfluid ³He properties, and that it is independent of the nature of the incident particles. In this report we show new results which demonstrate that a difference for muon- and neutron events, as well as events simulated by heater pulses exist. The possibility to use this difference for event discrimination in a future dark matter detector will be discussed.      

Distribution of monomeric,dimeric and polymeric products of stigmasterol during thermo‐oxidation

When plant sterols are oxidized at moderate temperatures (≤100 °C), products mainly derive from hydroperoxides, but at temperatures close to 200 °C, thermal reactions such as dehydration and condensation become important. Although sterols are often subjected to frying conditions, very little is known of their thermal reactions. In this study, stigmasterol was thermo‐oxidized at 180 °C, and the formation of dimers and polymers and the amounts of monomers were measured by high‐performance size‐exclusion chromatography. The products were further characterized by polarity using solid‐phase extraction fractionation. During heating, the amounts of monomers decreased at a steady rate, and those of dimers and polymers increased. After 3 h of heating, 21% of the material existed in higher‐molecular‐weight products. The amount of polar monomers increased especially during the first hour, demonstrating the formation of oxides and their further reactions, while that of mid‐polar monomers decreased constantly, indicating losses of stigmasterol. Polar dimers contributed to approximately 60% of the dimers, and polar polymers to approximately 78% of the polymers, which suggests that in most higher‐molecular‐weight products at least one of the sterol moieties was oxidized. This study showed that a significant proportion of thermo‐oxidation products are not polar monomeric oxides which are commonly analyzed as oxidation products.     

Oxidative stability of sunflower oils differing in unsaturation degree during long-term storage at room temperature

The objective of this work was to study the evolution of oxidation in sunflower oils differing in unsaturation degree during long-term storage at room temperature. For this purpose, a combination of adsorption and size-exclusion chromatographies was used for quantification of oxidized triacylglycerol (TG) monomers, dimers, and polymers. Conventional sunflower oil, genetically modified high-oleic sunflower oil, and a 1∶1 mixture of the two were used. Results showed that oxidized TG monomers were the only group of oxidation compounds increasing during the early oxidation stage, and an excellent correlation was found between amounts of oxidized TG monomers and PV during the induction period, independently of the degree of oil unsaturation. Both the rate of formation and the amount of oxidized TG monomers accumulated at the end of the induction period increased as the unsaturation degree of the oils tested was higher. The end of the induction period was marked by the initiation of polymerization and exhaustion of tocopherol. Therefore, the concomitant determination of oxidized TG monomers and polymerization compounds provided a complete picture of the oxidation process.     

Quantitation and distribution of altered fatty acids in frying fats

The distribution and quantity of polar compounds and altered fatty acids in used frying oils, collected by Food Inspection Services of the Junta de Andalucía in Spain, was measured. Additional samples evaluated were sunflower oil, high-oleic sunflower oil, and palm olein that were subjected to thermoxidation and frying in laboratory experiments. A combination of adsorption and high-performance size-exclusion chromatography was applied to the oil samples both before and after transesterification. Through analysis of fatty acid methyl ester derivatives, differentiation of four groups of altered fatty acids (oxidized monomers, nonpolar dimers, oxidized dimers, and polymers) could be attained. Evaluation of real frying samples with polar compound levels around the limit for fat rejection (21.1–27.6% polar compounds) gave values of total altered fatty acids ranging from 8.1 to 11.3%, and levels higher than 20% were found in the most degradated samples. The results obtained clearly support the need for control and improvement of the quality of used fats in fried-food outlets.     

Photoreaction of Phenacyl Aryl Ether Type Lignols

Photoreactions of two dilignols, a trilignol and two tetralignols, all of which contain a phenacyl aryl ether type structure, were investigated. All lignols in ethanol yielded products showing the homolytic cleavage of a phenacyl aryl ether bond in this structure. As to tetralignols photodiscoloration was hardly observed in the absence of air, and the preexistence of a free phenolic hydroxyl groups showed no influence on discoloration even in the presence of air. Photoreaction on a filter paper revealed that main reactions are the recombination of radicals once formed by irradiation and the reaction of radicals with oxygen.     

Synthesis and characterization of oligo(heteroarylene vinylene)s incorporating furan and thiophene moieties

This article describes the synthesis and characterization of a series of homologous conjugated dimers and trimers bearing alkenyl moieties between furan and/or thiophene heterocycles, linked through their 2,5- positions, and a terminal aldehyde group. A tetramer was also isolated and characterized. These oligomers constitute:

1. useful model compounds for the corresponding conjugated homo- and co-polymers,

2. interesting molecular structures for electroluminescence and other optoelectronic applications, and

3. potential precursors to more specific compounds (e.g. liquid crystals or photosensitive species) thanks to the terminal aldehyde function.

异丁烯二聚体和三聚体的色谱分析方法

石油液化气中的烯烃(主要是碳四烯烃)在定向催化剂的作用下,选择叠合成分子量较大的聚合体。它的组成基本是异丁烯二聚体(即碳八烯烃)和三聚体(即碳十二烯烃)的同分异构体。有机化合物的同分异构体的分离和结构鉴定是比较复杂的。采用毛细柱、程序升温气相色谱技术,使异丁烯二聚体和三聚体得到良好分离,并对其中各组分进行鉴定和定量分析。