The acid-promoted reaction of ethyl linoleate with nitrite. New insights from 15N-labelling and peculiar reactivity of a model skipped diene

The acid-promoted reaction of ethyl linoleate with nitrite ions was re-examined by an integrated approach based on the use of (NO2-)-N-15 combined with extensive GC-MS (El, NICI, PICI) and 2D H-1, N-15 and H-1, C-13 NMR analysis. The less polar products proved to be regioisomeric E-nitroalkenes, novel Z-nitroalkenes, and 3-nitro-1,5-hexadienes derivatives. A medium polarity fraction consisted mainly of stereo- and regioisomeric 1,2-nitronitrates along with 1,5-dinitro-1,3-pentadiene compounds. Novel 5-nitro-2,4-pentadienone products could be identified in the most polar fraction, which featured 1,2-nitroalcohols as the most abundant components. Under similar conditions 1,4-hexadiene gave mainly a nitrofuroxan derivative

The acid-promoted reaction of ethyl linoleate with nitrite. New insights from 15N-labelling and peculiar reactivity of a model skipped diene.

The acid-promoted reaction of ethyl linoleate with nitrite ions was re-examined by an integrated approach based on the use of (NO2-)-N-15 combined with extensive GC-MS (El, NICI, PICI) and 2D H-1, N-15 and H-1, C-13 NMR analysis. The less polar products proved to be regioisomeric E-nitroalkenes, novel Z-nitroalkenes, and 3-nitro-1,5-hexadienes derivatives. A medium polarity fraction consisted mainly of stereo- and regioisomeric 1,2-nitronitrates along with 1,5-dinitro-1,3-pentadiene compounds. Novel 5-nitro-2,4-pentadienone products could be identified in the most polar fraction, which featured 1,2-nitroalcohols as the most abundant components. Under similar conditions 1,4-hexadiene gave mainly a nitrofuroxan derivative

Acid-induced structural modifications of unsaturated fatty acids and phenolic olive oil constituents by nitrite ions: A chemical assessment

The structural modifications of the unsatd. fatty acid components of triglycerides in extra virgin olive oil (EVOO) following exposure to nitrite ions in acidic media were detd. by two-dimensional (2D) NMR spectroscopy, aided by 15N labeling and GC anal., allowing investigation of the matrix without fractionation steps. In the presence of excess nitrite ions in a 1% sulfuric acid/oil biphasic system, extensive double bond isomerization of the oleic/linoleic acid components of triglycerides was obsd. assocd. with nitration/oxidn. processes. Structurally modified species were identified as E/Z-nitroalkene, 1,2-nitrohydroxy, and 3-nitro-1-alkene(1,5-diene) derivs. based on 1H, 13C, and 15N 2D NMR anal. in comparison with model compds. Minor constituents of EVOO, including phenolic compds. and tocopherols, were also substantially modified by nitrite-derived nitrating species, even under milder reaction conditions relevant to those occurring in the gastric compartments. Novel nitrated derivs. of tyrosol, hydroxytyrosol, and oleuropein (6-8) were identified by LC/MS anal. of the polar fraction of EVOO and by comparison with synthetic samples. Overall, these results provide the first systematic description at the chem. level of the consequences of exposing EVOO to nitrite ions at acidic pH and offer an improved basis for further investigations in the field of toxic nitrosation/nitration reactions and dietary antinitrosating agents

Acid-induced structural modifications of unsaturated fatty acids and phenolic olive oil constituents by nitrite ions: A chemical assessment

The structural modifications of the unsatd. fatty acid components of triglycerides in extra virgin olive oil (EVOO) following exposure to nitrite ions in acidic media were detd. by two-dimensional (2D) NMR spectroscopy, aided by 15N labeling and GC anal., allowing investigation of the matrix without fractionation steps. In the presence of excess nitrite ions in a 1% sulfuric acid/oil biphasic system, extensive double bond isomerization of the oleic/linoleic acid components of triglycerides was obsd. assocd. with nitration/oxidn. processes. Structurally modified species were identified as E/Z-nitroalkene, 1,2-nitrohydroxy, and 3-nitro-1-alkene(1,5-diene) derivs. based on 1H, 13C, and 15N 2D NMR anal. in comparison with model compds. Minor constituents of EVOO, including phenolic compds. and tocopherols, were also substantially modified by nitrite-derived nitrating species, even under milder reaction conditions relevant to those occurring in the gastric compartments. Novel nitrated derivs. of tyrosol, hydroxytyrosol, and oleuropein (6-8) were identified by LC/MS anal. of the polar fraction of EVOO and by comparison with synthetic samples. Overall, these results provide the first systematic description at the chem. level of the consequences of exposing EVOO to nitrite ions at acidic pH and offer an improved basis for further investigations in the field of toxic nitrosation/nitration reactions and dietary antinitrosating agents

CO2 and H2O effect on propane auto-ignition delay times under mild combustion operative conditions

he auto-ignition process of propane/oxygen mixtures was experimentally and numerically studied over a range of temperatures (850-1250K) and mixture compositions (from fuel-ultra-lean to fuel-rich conditions) under MILD operative conditions. The mixtures were diluted in CO2 or H2O from 90 up to 97%. The experimental tests were realized in a Tubular Flow Reactor (TFR) at atmospheric pressure.Several combustion regimes were identified as a function of the mixture composition and inlet temperature. The experimental results showed that CO2 and H2O significantly alter the ignition process. In particular, a significant slowing of the system reactivity was observed with respect to the mixtures that were diluted in nitrogen.Numerical simulations were performed by commercial codes and detailed kinetic mechanisms. Comparisons between experimental and numerical results pointed out that kinetic models are not able to correctly reproduce system behaviors in all the experimental conditions.For CO2-diluted mixtures a good agreement between experimental and numerical analysis was obtained for fuel lean mixtures, whereas for stoichiometric and fuel-rich mixtures conditions the consistency of predicted data was less satisfactory.In the case of steam-diluted systems, the discrepancy between the experimental data and the predictions is about one order of magnitude for any mixture composition, but the model can reproduce the slight dependence of the ignition data on the mixture compositions.Further numerical analyses were performed to identify the reactions controlling the ignition process under MILD operative conditions in presence of CO2 and H2O. Results suggested that steam and carbon dioxide drastically alter the main branching mechanisms as third molecular species in termolecular reactions and/or by decomposition reactions

Copper and zinc removal from contaminated soils through soil washing process using ethylenediaminedisuccinic acid as a chelating agent: A modeling investigation

This study demonstrated that soil washing using ethylenediaminedisuccinic acid (EDDS) as a chelating agent was efficient at removing copper and zinc from real polluted soils. Only the exchangeable and reducible fractions of Cu and Zn were extracted by EDDS. Intra-particle diffusion was the main rate controlling step in this extraction of heavy metals from the solid matrix. Different contributions were found by applying the Weber and Morris intraparticle diffusion model resulting from the different roles of superficial and intra-particle diffusive processes.The diffusion coefficients of the Cu/EDDS and Zn/EDDS complexes in real contaminated soils were estimated using simplified diffusive models (based on Crank’s and Vermeulen's approximations). The relationship between the grain size and diffusion coefficient was also evaluated. In particular, the intraparticle diffusion coefficients increased with increasing the particle size, thus indicating that the smallest granulometric fractions are characterized by a higher percentage of micropores than the largest fractions

H2O and CO2 Dilution in MILD Combustion of Simple Hydrocarbons

MILD combustion is a very attractive technology because of its intrinsic features for energy production from diluted gas deriving from bio- or thermochemical degradation of biomass. An effective use of such a technology for diluted fuel requires a thorough analysis of ignition and oxidation behavior to highlight the potential effects of the different fuel components on the basis of temperature and diluent/oxygen/fuel mixture composition. In this work, ignition and oxidation of a model gas surrogate for the gaseous fraction of biomass pyrolysis products containing C1-C2 species, CO and CO2 were experimentally and numerically studied over a wide range of temperature and overall composition in the presence of large amounts of CO2 or H2O. Experimental results showed that such species significantly alter the evolution of the ignition process in dependence on temperature range and mixture composition. Several kinetic models were tested to simulate experimental results. Significant discrepancies occur, especially in the case of steam dilution. Numerical analyses suggested that such diluents acted mainly as third body species at low temperatures, conditioning both radical production pathways and the relative weight of C1 oxidation/recombination routes, while strongly interacting with the H2/O2 high temperature branching mechanisms at high temperatures. Further analyses are mandatory to improve the predictability of the models and extend the applicability of the chemical schemes to non-standard conditions

Differential Reactivity of Purified Bioactive Coffee Furans, Cafestol and Kahweol, with Acidic Nitrite: Product Characterization and Factors Controlling Nitrosation Versus Ring-Opening Pathways.

cafestol and kahweol, coffee-specific furan diterpenes, are believed to cause various physiol. effects in human subjects, including an increase in cholesterol and plasma triacylglycerol levels as well as cancer chemopreventive effects. Despite the increasing interest in these compds. raised by the diverse range of biol. activities, their reaction behavior and degrdn. pathways under physiol. relevant conditions remain uncharted. Herein, we report a detailed investigation of the structural modifications suffered by cafestol and kahweol in the presence of acidic nitrite under conditions mimicking those occurring in the stomach during digestion as well as by action of other oxidants. Prior to the chem. study, an isolation procedure for kahweol from green coffee beans was developed based on Soxhlet extn. followed by preparative HPLC. Preliminary expts. showed that kahweol is much more reactive than cafestol toward nitrite at pH 3, as evidenced by inhibition expts. with the 2,3-diaminonaphthalene assay as well as by product anal. in coffee exts. When exposed to equimolar nitrite in phosphate buffer, pH 3, kahweol gave as a main product the ring-opened dicarbonyl deriv. 1. Under more forcing conditions, cafestol reacted as well to give a main nitrogenous product identified as the 1-hydroxy-2-pyrrolinone 2. It is concluded that the conjugated double bond in kahweol is a crit. structural element, increasing the susceptibility of the furan ring to protonation rather than nitrosation and favoring ring-opening routes driven by the irreversible oxidn. steps. These results offer a useful background to assess the effects of coffee-specific lipids in assocn. with abnormally high nitrite levels from the diet

Differential Reactivity of Purified Bioactive Coffee Furans, Cafestol and Kahweol, with Acidic Nitrite: Product Characterization and Factors Controlling Nitrosation Versus Ring-Opening Pathways

cafestol and kahweol, coffee-specific furan diterpenes, are believed to cause various physiol. effects in human subjects, including an increase in cholesterol and plasma triacylglycerol levels as well as cancer chemopreventive effects. Despite the increasing interest in these compds. raised by the diverse range of biol. activities, their reaction behavior and degrdn. pathways under physiol. relevant conditions remain uncharted. Herein, we report a detailed investigation of the structural modifications suffered by cafestol and kahweol in the presence of acidic nitrite under conditions mimicking those occurring in the stomach during digestion as well as by action of other oxidants. Prior to the chem. study, an isolation procedure for kahweol from green coffee beans was developed based on Soxhlet extn. followed by preparative HPLC. Preliminary expts. showed that kahweol is much more reactive than cafestol toward nitrite at pH 3, as evidenced by inhibition expts. with the 2,3-diaminonaphthalene assay as well as by product anal. in coffee exts. When exposed to equimolar nitrite in phosphate buffer, pH 3, kahweol gave as a main product the ring-opened dicarbonyl deriv. 1. Under more forcing conditions, cafestol reacted as well to give a main nitrogenous product identified as the 1-hydroxy-2-pyrrolinone 2. It is concluded that the conjugated double bond in kahweol is a crit. structural element, increasing the susceptibility of the furan ring to protonation rather than nitrosation and favoring ring-opening routes driven by the irreversible oxidn. steps. These results offer a useful background to assess the effects of coffee-specific lipids in assocn. with abnormally high nitrite levels from the diet