Determination of ethane and pentane in free oxygen radical-induced lipid peroxidation

It has been proposed that ethane and pentane reflect free oxygen radical-induced lipid peroxidation. However, methodological difficulties limit the use of these gases for assessment of free oxygen radical activity. In the present report we describe an improved method for the accurate analysis of picomole quantities (≥1 pmol) of ethane and pentane. They are first quantitatively trapped into an adsorbent and then heat-desorbed directly into a capillary column for gas chromatographic quantitation. During oxidation of linolenic (n−3) and linoleic (n−6) acid, ethane and pentane were formed, respectively. Nonstimulated granulocytes formed pentane. Upon addition of phorbol 13-myristate 12-acetate, the generation of pentane was increased by 540%. Addition of superoxide dismutase plus catalase inhibited lipid peroxidation in both a cell-free system and in isolated cells. The present method is useful in the evaluation of free oxygen radical induced damage.     

An apparatus for the measurement of lipoxygenase activity and pentane production

The enzyme lipoxygenase has been demonstrated to produce pentane. However, until now no apparatus has been available to measure the pentane concomitantly with the lipoxygenase activity. Such an apparatus is described by this paper. The apparatus consists of a reaction vessel which can be sealed with a rubber septum to allow sampling for pentane production and an oxygen measuring device to determine the oxygen level of the system. The apparatus is being used to conduct in-depth studies of the lipoxygenase enzyme and its possible role in food quality. Paper 4128 of the journal series of the North Carolina State University Agricultural Experiment Station, Raleigh, N.C.     

Mechanistic aspects of beta-bond-cleavage reactions of aromatic radical cations

The mesolytic cleavage of a beta-C-X bond (ArCR(2)-X(*+) --> ArCR(2)(*/+) + X(+/*)) is one of the most important reactions of alkylaromatic radical cations. In this Account, our group's results concerning some fundamental aspects of this process (cleavage mode, structural and stereoelectronic effects, competitive breaking of different beta-bonds, nucleophilic assistance, possible stereochemistry, carbon vs oxygen acidity in arylalkanol radical cations) are presented and critically discussed for reactions where X = H, CR(3), SR, and SiR(3). Several examples illustrating how this information was exploited as a tool to detect electron-transfer mechanisms in chemical and enzymatic oxidations are also reported.     

甲氰菊酯的合成

:由异丙基氯通过格氏反应、硫酸催化脱水制备了四甲基丁烯 ,进而与二氯乙酰氯反应合成了氯代四甲基环丁酮 ;它可以水解生成四甲基环丙烷羧酸。由四甲基环丙烷羧酸或氯代四甲基环丁酮合成了甲氰菊酯。     

The effect of vitamin C on in vivo lipid peroxidation in guinea pigs as measured by pentane and ethane production

Measurements of pentane and ethane as indices of in vivo lipid peroxidation were made on samples of breath from vitamin C-sufficient and vitamin C-deficient guinea pigs injected with 23 μl carbon tetrachloride (CCl₄)/100 g body wt. Vitamin C-deficient animals produced significantly more pentane and ethane after CCl₄ treatment than did vitamin C-sufficient guinea pigs. Pretreatment of vitamin C-deficient animals with 75 mg ascorbic acid/100 g body wt significantly lowered both pentane and ethane evolution. Protection against in vivo lipid peroxidation similar to that provided by ascorbic acid was also found when vitamin C-deficient guinea pigs were pretreated with isoascorbic acid, reduced glutathione, α-tocopherol or β-carotene. When animals were pretreated with the radical scavenger mannitol, a protective effect was also observed as measured by pentane evolution.     

Aerobic pentane production by soybean lipoxygenase isozymes

The effects of oxygen on production of pentane and compounds absorbing at 234 nm and 285 nm by soybean lipoxygenase isozymes I and II were examined in a model system. Aerobic conditions increased pentane production. Differences in dienone formation (A₂₈₅) and diene conjugation (A₂₃₄) indicate the reaction sequences of the 2 isozymes are not the same. Paper No. 4551, Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh North Carolina.     

Arene—onium cations—VI Electrode kinetics of the anodic formation of arene—sulphonium cations from bisarenesulphides

Electrode kinetic investigations (voltammetry at stationary electrodes, rotating ring—disc electrodes and rotating rod electrodes) of the anodic oxidation of bisanisole-, bismesitylene-, bisxylene-, bistoluene- and bisbenzenesulphide were performed in acetonitrile. Observed anodic half wave potentials increase in the given order. The S-radical cations of the bisarenesulphides form in a reversible one-electron oxidation step. The radical cations of bisanisole- and bismesitylenesulphide are unable to react, even with relatively strong bases like water, and they disproportionate to form the more reactive dications which react readily with different nucleophiles. The more reactive radical cations of bisxylene-, bistoluene- and bisbenzenesulphide react directly with nucleophiles, for instance with aromatic bases and with the more basic hydrocarbons (anisole, styrene). Participation of dications in their consecutive reactions cannot be detected. The anodic dimerization of these three bisarenesulphides is a relatively fast reaction and is due to the addition of the respective bisarenesulphide radical cation to bisarenesulphide molecules. The reason for the striking mechanistic difference for the two groups of radical cations is very likely an unfavourable disproportionation equilibrium for the more reaction bisarenesulphide radical cations.     

Photochemical behavior of intercalation compounds of layered niobates with methylvilologen

Intercalation compounds of three layered niobates with methylviologen (1, 1'-dimethyl-4,4'-bipyridinium ion) were synthesized and their photochemical behavior was investigated. All the host niobates successfully intercalated methylviologen dications, and there were structural differences among the samples. UV irradiation of the intercalation compounds caused photoinduced electron transfer from the hosts to the guest to form methylviologen radical cations. The radical cations were characterized by their high stability, which had a relation to the structure of the intercalation compounds. Co-intercalation of photochemically inactive ions (K₊ or propylammonium ions) with methylviologen extremely well stabilized the radical cations.     

溶液法合成端羧基聚丁二烯

以过氧化戊二酸为引发剂，无水乙醇或丙酮为溶剂，采用自由基型溶液法合成了端羧基聚丁二烯，并用ＩＲ对聚合物的微观结构进行了表征。结果表明当聚合反应温度为１０５￣１１５℃时，合理搭配引发剂起始用量和连续加入引发剂的递减速率，可合成满足不同应用领域的端羧基聚丁二烯产品。     

Mechanistic study of organic template removal from ZSM-5 precursors

The decomposition mechanism of tetrapropylammonium (TPA⁺) template cations in several commercial ZSM-5 precursors was studied by temperature-programmed desorption/oxidation using a mass spectrometer (TPD/TPO-MS). Different oxygen concentrations, gas flow rates and temperature ramp rates were examined to understand the effects of these factors on the organic template decomposition. The TPA⁺ template decomposition pattern is strongly dependent on the SiO₂/Al₂O₃ molar ratio (SAR) and the oxygen concentration. The TPA⁺ template cations may be associated with three different sites depending on the SAR: Lewis acid sites (surface Al–O⁻), Brønsted acid sites (framework Al–O⁻), and weakly acidic Si---O⁻ sites. The thermal decomposition of TPA⁺ templates at different sites produced different products, including water, ammonia, propylene, ethylene, methane, and n- and iso-propylamines. However, no significant heavy volatile compounds were detected, suggesting that secondary reactions (e.g., oligomerization of olefins) were extremely limited and negligible in a fixed-bed micro-reactor used for TPD/TPO. The TPD-MS results suggest that the thermal decomposition mechanism on Lewis acid sites is possibly a free radical type of reaction, while on Brønsted acid sites and Si---O⁻ sites, the decomposition undergoes both Hoffman elimination reaction and a radical type of reaction. The presence of oxygen significantly lowered the TPA⁺ decomposition temperature, which is also a function of oxygen concentration. The knowledge about the template decomposition pattern and the composition of the evolved volatiles obtained by the TPD/TPO-MS technique may be used to develop ideal organic template removal procedures for zeolites.     

Electroreduction of oxygen on glassy carbon electrodes modified with in situ generated anthraquinone diazonium cations

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with in situ generated diazonium cations of anthraquinone (AQ) has been studied using the rotating disk electrode (RDE) technique. The electrografting of the GC electrodes was carried out in two different media: in acetonitrile and in an aqueous acidic solution (0.5 M HCl). 1- and 2-Aminoanthraquinone were used as starting compounds for the formation of the corresponding diazonium derivatives. The anthraquinone diazonium cations were generated by reaction of the aminoanthraquinones with tert-butyl nitrite and sodium nitrite in acetonitrile and in 0.5 M HCl, respectively. For comparison purposes, the previously synthesised and crystallised diazonium tetrafluoroborates of anthraquinone were used for the GC surface modification. Cyclic voltammetry was employed to determine the surface concentration of AQ in O₂ free 0.1 M KOH. The electrocatalytic behaviour towards O₂ reduction was similar for all the AQ-modified electrodes studied. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model. The rate constant of the reaction between the semiquinone radical anion of AQ and molecular oxygen was virtually independent of the point of attachment of the quinone to the electrode surface.     

ESR-Spektroskopischer nachweis von radikalkationen bei der anodischen oxidation von alkylbenzolen in methylenchlorid und trifluoressigsäure

The anodic oxidation of hexaethyl- (HEB), hexa-methyl- (HMB), pentamethyl- (PMB) and 1,2,4,5-tetramethyl-benzene (TMB) on Pt in CH₂Cl₂ and CF₃COOH (TFA) is examined by cyclic voltammetry and esr spectroscopy. HEB, HMB and PMB are oxidized to the corresponding radical cations in TFA. The anodic oxidation of HMB and PMB in CH₂Cl₂ results in radical cations with one methyl group more than the starting material. The mechanism of the formation of these radical cations is discussed for HMB.     

Electrochemical studies of selected regioregular oligooctylthiophenes in solution and in thin film solid state

Electrochemical studies of a series of regioregular 3-octylthiophene oligomers with 5-8 thiophene rings, chlorine end-capped at one α terminal position, have been conducted in solution and in thin film state. Results indicate gradual coalescing of the oxidation potentials of neutral and radical cation oligomer molecule, indicative of coming close to sufficient length of the molecule to allow for two separate radical cations to exist along its chain. With increasing number of thiophene rings in the molecule, further quasi-reversible oxidation reactions upon which trication and tetracation were formed have been observed at ever decreasing potentials. It was also observed that the oxidation of radical cations comes about more easily than that of electron-paired cations, the latter process being strongly dependent on the length of oligothiophene chain. Thin film electrochemistry revealed that the processes taking place during redox reactions differ from those in solution. Sharp oxidation peaks were observed which were attributed to conformational changes taking place in the oligomer molecules upon transition to the conductive form, alongside the film's oxidative doping process. To shed some light on the issue of charge carriers appearing in the film upon its oxidation, supplemental ESR spectroelectrochemical measurements were carried out and confirmed that, radical cations are generated in the film.     

Interpretation von Moleküldiagrammen freier π-Radikalkationen — Naphthalen,Butadien, Styren, 1-Methylstyren, 1,1′Diphenylethylen

Interpretation of the MO-diagrams of Free π-Radical Cations — Naphthalene, Butadiene, Styrene, 1-Methyl-styrene, 1,1′-Diphenylethylene The reactive and spectroscopic behaviour of the radical cations of the title compounds is discussed on the basis of general structural principles by means of molecular diagrams calculated with the PPP-LHP-SCF-MO-CI-method. The greater reactivity of the monomer radicals compared with the dimers is due to the character of polymethene-like compounds, whereas the lower reactivity of the dimer radicals cations can be ascribed to the more aromatic state of these species. The experimentally determined optical absorption maxima of the radical cations can be interpreted by the same classification.     

Oxydation electrochimique de phenylhydrazones du benzaldehyde

The electrochemical oxidation of phenylhydrazone of benzaldehyde in acetonitrile leads to different dimers, stable cations, radical cations and cyano compounds when the N-benyl paramethoxyphenylhydrazone is oxidised in cyanide media.     

Zur Erfassung der endogenen Lipidperoxidation - Pentanproduktion in vivo beim Huhn

On the Registration of Endogenous Lipid Peroxidation - in vivo pentane Production in Broiler Chickens This report deals with experimental attempts to clarify the mechanism of pentane development in chicken after feeding fresh and oxidized reesterified triglycerid and different amounts of Vitamin E. In a closed system the concentration of exhaled pentane was determined and in-vivo production rates calculated. On the other hand pentane production was measured from intestinal chyme in an in-vitro preparation after killing the animals. With regard to the question of the microbial cause of pentane development, the effect of Clindamycin was tested both in the in-vitro and in-vivo experiment. In-vivo pentane production rates were increased by feeding oxidized fat, Vitamin E supplementation had no significant influence. Likewise pentane formation from chyme was significantly increased by administering oxidized fats, Vitamin E however inhibited pentane formation. Clindamycin did not suppress pentane production, suggesting that in chicken feed lipid peroxides are not broken down by microbial enzymes but by spontaneous decay, anyway intestinal processes have to be considered in pentane exhalation studies.     

Structure and Reactions of Aliphatic Bridged Bifunctional Radical Ions: Exploring Fine-Tuning in Radiation Chemistry

Bridged bifunctional molecules of general structure X (CH₂)_n Y are useful models for investigations into the effects of intra- and intermolecular interactions in primary radiation-induced processes, with a number of implications for radiation chemistry, radiobiology, and molecular electronics. This short Review presents an outline of recent studies on the structure and reactivity of aliphatic bifunctional radical ions in low-temperature matrices using EPR spectroscopy and quantum-chemical calculations. Both EPR data and DFT calculations for radical cations show that the delocalization of charge and spin density occurs if XY or X and Y have close electronic properties. If the difference in the ionization potentials between X and Y is large, localized radical cations are observed with ground-state properties close to those of the corresponding monofunctional species. Nevertheless, the remote second functional group may affect the photochemistry of such radical cations at a specific bridge length, probably due to intramolecular interactions in a certain conformation. The stabilization of bridged bifunctional radical anions containing two carbonyl groups was found to be very sensitive to the local environment, which may be described in terms of a microsolvation model at the MP2 level of theory. Two independent reactions pathways with excess electrons, yielding different types of localized radical anions, were demonstrated for asymmetrical bifunctional molecules. The obtained results and their implications are discussed in terms of fine-tuning effects in radiation-induced chemical processes in condensed phases.     

超临界沥青喷雾造粒中的戊烷闪蒸CFD模拟

重油梯级分离技术作为重油轻质化的新工艺,它通过耦合渣油萃取和沥青喷雾造粒过程,有效的简化重油处理的工艺流程,减少设备成本。在此工艺流程中,处于超临界状态的戊烷的闪蒸速率对沥青造粒质量起到了关键作用。根据其减压过程中的质量和热量传递机理,改进了戊烷闪蒸的经验模型,并将其植入到CFD软件FLUENT中,使其能较为准确的预测闪蒸雾化的非平衡热力学过程。同时对气液戊烷和沥青的三相闪蒸流动过程进行了数值模拟,结果显示喷嘴结构是控制闪蒸速率的关键,直接影响了沥青造粒的质量;此外沥青相的加入为戊烷的相变过程提供了更多能量,提高了戊烷在喷嘴内的汽化率。     

Cationic catalysis and hidden negative differential resistance in reduction of radical anion of nitrobenzene

Well-known reduction of nitrobenzene in acetonitrile yields an anion radical, which is further reduced at more negative potentials. The reduction of anion radical is strongly influenced by the nature of tetraalkylammonium salts (tetramethyl- to tetraheptylammonium) used as supporting electrolytes. At low concentration of tetrahexylammonium hexafluorophosphate the anion radical reduction occurs at extremely negative potential, however, traces of alkali metal cations yield a remarkable acceleration effect. At potentials where alkali metal cations are reduced the acceleration ceases. As a result the current-potential curves show negative or hidden negative slope. Electrochemical impedance spectroscopy sensitively indicates the presence of the negative differential resistance (NDR) or the hidden negative differential resistance (HNDR). Oscillatory behavior based on this type of cationic catalysis is currently under investigation.     

The electrochemical oxidation of phenylenediamines

Five p-phenylenediamines were oxidized electrochemically at a glassy carbon rotating ring-disk-electrode assembly. The overall reaction comprises the transfer of two electrons per molecule. At low to intermediate potentials the rate determining step for all the five compounds is the acid dissociation of the semiquinonediimine radical cation formed in a pre-equilibrium involving the transfer of one electron. Only at higher potentials can the radical cation be oxidized in parallel to the neutral semiquinone radical to form the quinonediimines. In contrast, the neutral semiquinonediimine radicals are oxidized at the same or even a lower potential than the parent phenylenediamines. The dissociation rate constants of the radical cations are in the range of 10-300 s⁻¹. The effect of the substituents on the oxidation potentials is as expected by their property to donate electrons to the mesomeric system. Their effect on the dissociation rates, however, seems to rather correlate with the inductive effect and might influence not only the electronic structure of the molecule itself but also the structure of the ions and the solvent around them. The semiquinonediimine radical cations are found to be slightly more acidic than their protonated parent phenylenediamine cations with pK_a values somewhat below 6.