Kinetics of the reactions of OH radicals with 2- and 3-methylfuran, 2,3- and 2,5-dimethylfuran, and E- and Z-3-hexene-2,5-dione, and products of OH + 2,5-dimethylfuran

Furan and alkylfurans are present in the atmosphere from direct emissions and in situ formation from other volatile organic compounds. The OH radical-initiated reactions of furan and alkylfurans have been proposed as relatively clean in situ sources of unsaturated 1,4-dicarbonyls, some of which are otherwise not readily available. Using a relative rate method, rate constants at 296 ± 2 K for the gas-phase reactions of OH radicals with 2- and 3-methylfuran, 2,3- and 2,5-dimethylfuran, and Z- and E-3-hexene-2,5-dione have been measured, of (in units of 10(-11) cm(3) molecule(-1) s(-1)): 2-methylfuran, 7.31 ± 0.35; 3-methylfuran, 8.73 ± 0.18; 2,3-dimethylfuran, 12.6 ± 0.4; 2,5-dimethylfuran, 12.5 ± 0.4; Z-3-hexene-2,5-dione, 5.90 ± 0.57; and E-3-hexene-2,5-dione, 4.14 ± 0.02. Products of the OH radical-initiated reaction of 2,5-dimethylfuran were investigated, with 3-hexene-2,5-dione being formed with molar yields of 24 ± 3% in the presence of NO and 34 ± 3% in the absence of NO. Direct air sampling atmospheric pressure ionization mass spectrometry showed the formation of additional products of molecular weight 114, attributed to CH(3)C(O)CH ═ CHC(O)OH and/or 5-hydroxy-5-methyl-2-furanone, and 128, attributed to CH(3)C(O)OC(CH(3)) = CHCHO.     

High correlation of methylglyoxal with acrylamide formation in glucose/asparagine Maillard reaction model

α-Dicarbonyl compounds were highly reactive intermediates formed in Maillard reaction (MR), and o-phenylenediamine (OPD) was widely used as a trapping agent for α-dicarbonyl compounds. Both aqueous glucose/asparagine (Glc/Asn) and glucose/asparagine/o-phenylenediamine (Glc/Asn/OPD) model systems were heated at 150 °C for up to 30 min. The α-dicarbonyl compounds formed in MR were identified by HPLC/MS in our particular model system, indicating that 3-deoxy-2-hexosulose, 2,3-butanedione and methylglyoxal (MG) were three main α-dicarbonyl compounds. In this work, MG was chosen as a representative of α-dicarbonyl compound in MR to investigate the influence on the formation of acrylamide (AA). The concentrations of AA, MG and Asn were detected during MR by HPLC method. The results indicated that the formation of AA increased with the heating time, and nearly 80% of AA formed through participation of α-dicarbonyl compounds. These results were consistent with the changes of amounts of MG. The amounts of formation and consumption of MG increased with heating time, and from 9 min of reaction, the consumed amounts of MG accounted for 73–88% on basis of total amounts of MG formed in MR, suggesting that most of MG take part in the next reaction steps. Meanwhile, the Asn concentration decreased with heating time in both models. The formation of AA and consumption of Asn were highly correlated with MG. Indeed, as MG concentration in MG/Asn model system decreased during heating at 150 °C, the concentration of AA significantly increased. The coefficient of correlation between consumed amounts of MG and the formed amounts of AA is 0.931, again demonstrating that MG does play a role in AA formation.     

Correlation of methylglyoxal with acrylamide formation in fructose/asparagine Maillard reaction model system

α-Dicarbonyl compounds were highly reactive intermediates formed in Maillard reaction (MR), and o-phenylenediamine (OPD) was widely used as a trapping agent for α-dicarbonyl compounds. Both aqueous fructose/asparagine (Fru/Asn) and fructose/asparagine/o-phenylenediamine (Fru/Asn/OPD) model systems were heated at 150 °C for up to 30 min. Methylglyoxal (MG) was the main α-dicarbonyl compounds formed in MR, which was chosen as a representative of α-dicarbonyl compound to investigate the influence on acrylamide (AA) formation. The concentrations of AA, MG and Asn were detected during MR by HPLC method. The results indicated that the formation of AA increased with the heating time, and nearly 75% of AA was formed through the participation of α-dicarbonyl compounds. The amounts of formation and consumption of MG increased with heating time, and from 12 min of reaction, the consumed amounts of MG accounted for 62.1–90.3% on the basis of total amounts of MG formed in MR, suggesting that most of the MG took part in further reactions. Meanwhile, Asn concentration decreased with heating time in both models. The formation of AA and consumption of Asn were highly correlated with MG. Indeed, as MG concentration in MG/Asn model system decreased during heating at 150 °C, the concentration of AA significantly increased. The coefficient of correlation between consumed amounts of MG and the formed amounts of AA was 0.931, demonstrating that MG plays a role in AA formation.     

Dicarbonyl products of the OH radical-initiated reactions of naphthalene and the Cl- and C2-alkylnaphthalenes

Naphthalene and the C1- and C2-alkylnaphthalenes are the most abundant polycyclic aromatic hydrocarbons (PAHs) in urban atmospheres. Their major atmospheric loss process is by gas-phase reaction with hydroxyl (OH) radicals. In this study, we have used in situ direct air sampling atmospheric pressure ionization mass spectrometry (API-MS) as well as gas chromatography-mass spectrometry (GC/MS) techniques to investigate the products of the gas-phase reactions of OH radicals with naphthalene, naphthalene-ds, 1- and 2-methylnaphthalene (MN), 1- and 2-MN-dio, 1- and 2-ethylnaphthalene (EN), and the 10 isomeric dimethylnaphthalenes (DMNs). The major reaction products are ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two P-carbons and associated alkyl groups, and ring-containing compounds that may be epoxides. Phthalic anhydride and alkyl-substituted phthalic anhydrides were observed as second generation products. The position of alkyl-substitution on the naphthalene ring is a key factor determining the ring cleavage site and the isomeric product distribution.     

Effects of o-phenylenediamine on methylglyoxal generation from monosaccharide: Comment on “correlation of methylglyoxal with acrylamide formation in fructose/asparagine Maillard reaction model system”

Methylglyoxal (MG), a reactive carbonyl compound, has recently garnered much attention because of its ability to modify proteins over time and yield advanced glycation end products (AGEs) that are thought to contribute to the development of diabetes mellitus and its complications. In a recent paper published in Food Chemistry by Yuan et al. [Yuan, Y., Zhao, G. H., Hu, X. S., Wu, J. H., Liu, J., & Chen, F. (2007a). Correlation of methylglyoxal with acrylamide formation in fructose/asparagines Maillard reaction model system. Food Chemistry, 108(3), 885–890] authors showed a high correlation between methylglyoxal formation and acrylamide formation. However, in their study, model systems of aqueous fructose/asparagines (Fru/Asn) and fructose/asparagines/o-phenylenediamine (Fru/Asn/OPD) heating at 150 °C were used. The validity of these models relies on the assumption that OPD will only serve the role of a trapping agent for MG. In this short communication, we would like to call to attention that MG can also have a strong catalytic effect in the generation of MG from fructose. Therefore, it is concluded that the concentration of MG obtained in Fru/Asn/OPD model system cannot correspond to the total amount of MG formed by Maillard reaction of Fru and Asn as claimed by Yuan et al. [Yuan, Y., Zhao, G. H., Hu, X. S., Wu, J. H., Liu, J., & Chen, F. (2007a). Correlation of methylglyoxal with acrylamide formation in fructose/asparagines Maillard reaction model system. Food Chemistry, 108(3), 885–890, Yuan, Y., Zhao, G. H., Hu X. S., Wu, J. H., Liu, J., & Chen. F. (2007b). High correlation of methylglyoxal with acrylamide formation in glucose/asparagine Maillardreaction model. European Food Research and Technology. doi:10.1007/s00217-007-0658-0].     

Amino acid-dependent formation pathways of 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone in the Maillard reaction

The formation pathways of two furanoids, 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone (DMHF) were studied by GC–MS in the Maillard-type model system based on glucose and selected amino acids. The reaction was performed in 0.01 M phosphate buffer by heating a 1:1 mixture of [¹³C6] glucose and [¹²C6] glucose with amino acid. There is only one major formation pathway for DMHF in which the glucose carbon skeleton stayed intact. Formation pathways for 2-acetylfuran were more complicated. They formed either from glucose or from glucose and glycine. In the presence of glycine, the [C-5] unit of glucose combined with formaldehyde from glycine leads to 2-acetylfuran. For other amino acids, either cyclisation of intact glucose or recombination of glucose fragments can lead to 2-acetylfuran formation. These results indicate a competitive trend in controlling Maillard reaction. Therefore, besides changing Miallard reaction impact factors (temperature, time, pH etc.), inhibiting or preventing the competitive reaction cascade may direct desired pathways of Maillard reaction.     

Heterogeneous reactions of methylglyoxal in acidic media: implications for secondary organic aerosol formation

Recent environmental chamber studies have suggested that acid-catalyzed particle-phase reactions of organic carbonyls contribute to the formation of secondary organic aerosol (SOA). We report the first measurements of uptake of methylglyoxal on liquid H2SO4 over the temperature range of 250-298 K and acidic range of 55-85 wt %. From the time-dependent uptake the effective Henry's law solubility constant (H*) was determined. Heterogeneous reactions of methylglyoxal are shown to decrease with acidity and involve negligible formation of sulfate esters. Hydration and polymerization likely explain the measured uptake of methylglyoxal on H2SO4 and the measurements do not support an acid-catalyzed uptake of methylglyoxal. The results imply that heterogeneous reactions of methylglyoxal contribute to organic aerosol formation in less acidic media and hydration and polymerization of methylglyoxal in the atmospheric aerosol-phase are dependent on the hygroscopicity, rather than the acidity of the aerosols.     

Kinetics and products of the reaction of OH radicals with 3-methoxy-3-methyl-1-butanol

3-Methoxy-3-methyl-1-butanol [CH(3)OC(CH(3))(2)CH(2)CH(2)OH] is used as a solvent for paints, inks, and fragrances and as a raw material for the production of industrial detergents. A rate constant of (1.64 ± 0.18) × 10(-11) cm(3) molecule(-1) s(-1) for the reaction of 3-methoxy-3-methyl-1-butanol with OH radicals has been measured at 296 ± 2 K using a relative rate method, where the indicated error is the estimated overall uncertainty. Acetone, methyl acetate, glycolaldehyde, and 3-methoxy-3-methylbutanal were identified as products of the OH radical-initiated reaction, with molar formation yields of 3 ± 1%, 35 ± 9%, 13 ± 3%, and 33 ± 7%, respectively, at an average NO concentration of 1.3 × 10(14) molecules cm(-3). Using a 12-h average daytime OH radical concentration of 2 × 10(6) molecules cm(-3), the calculated lifetime of 3-methoxy-3-methyl-1-butanol with respect to reaction with OH radicals is 8.5 h. Potential reaction mechanisms are discussed.     

Acetone-h6 or -d6 + OH reaction products: evidence for heterogeneous formation of acetic acid in a simulation chamber

Simulation chamber experiments have been carried out at room temperature to investigate the products of the acetone + OH and acetone-d6 + OH reactions using two photoreactors made of Teflon or Pyrex and coupled to GC-FTIR-FID analytical techniques. In the Pyrex chamber, the results demonstrated that the channel forming acetic acid is a minor oxidation route in the atmospheric acetone-h6 + OH reaction (yield <5%), whereas a higher yield of about 20% was obtained in the case of the acetone-d6 + OH reaction, in good agreement with previous studies. Existence of a heterogeneous way of formation of acetic acid has also been identified in the Teflon photoreactor.     

L-Rhamnose: progenitor of 2,5-dimethyl-4-hydroxy-3 [2H]-furanone formation by Pichia capsulata?

 2,5-Dimethyl-4-hydroxy-3[2H]-furanone (Furaneol, 1), an important aroma constituent, was detected at concentrations of up to 2 mg/l after 4 days of growth of Pichia capsulata on casein peptone culture medium containing L-(+)-rhamnose (2). Blank samples without yeast contained no 1 after the incubation period. In parallel experiments five samples of 2 exhibiting different [¹³C] abundance were given to P. capsulata. The volatile compounds formed were isolated and analysed for their [¹³C]/[¹²C] ratios by on-line gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). A positive correlation between the isotopes in 1 and 2 was observed; thus, 2 served as the carbon source for 1. However, 1 was formed from a postulated intermediate of 2 generated during thermal sterilization, as 1 was neither detected after sterile filtration of the culture medium nor after separate thermal sterilization of the casein peptone and 2. This observation was confirmed by an experiment investigating the time course of the formation of 1. Received: 4 June 1996     

Detection and identification of a protein-bound imidazolone resulting from the reaction of arginine residues and methylglyoxal

A ninhydrin-positive compound was detected in acid hydrolysates of various alkali-treated bakery products (pretzels, snack bars), eluting immediately after pyridosine in amino acid chromatograms. Following preparative isolation from a food sample and independent synthesis, the compound was unequivocally identified by fast-atom bombardement-mass spectrometry,¹H- and¹³C-nuclear magnetic resonance as a protein-bound imidazolone, existing in two tautomeric forms, namelyN -(5-methyl-4-oxo-5-hydroimidazol-2-yl) -L-ornithine andN -(4-methyl-5-oxo-4-hydroimidazol-2-yl) -L-ornithine. The acid-labile amino acid derivative is formed by direct condensation of the guanido group of arginine and methylglyoxal, a sugar degradation product, and represents a previously unknown post-translational protein modification. For a number of commercially available alkali-treated bakery products, the amounts of the imidazolone after complete enzymic digestion ranged between 900 and 1300 mg per 100g protein, indicating that between 20 and 30% of the arginyl residues might react with methylglyoxal during the bakery process.

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Nachweis und Identifizierung eines proteingebundenen Imidazolons aus der Reaktion zwischen Argininresten und Methylglyoxal

Zusammenfassung In Säurehydrolysaten verschiedener Laugenbackwaren (Brezeln, Knabberartikel) wurde eine im Aminosäurechromatogramm unmittelbar nach Pyridosin eluierende ninhydrinpositive Verbindung nachgewiesen. Sie konnte nach präparativer Isolierung aus einer Lebensmittelprobe sowie nach unabhängiger Synthese mittels FAB-MS,¹H- und¹³C-NMR eindeutig als proteingebundenes Imidazolon identifiziert werden, welches in den zwei tautomeren FormenN -(5-Methyl-4-oxo-5-hydroimidazol-2-yl)-l-ornithin undN -(4-Methyl-5-oxo-4-hydroimidazol-2-yl)-l-ornithin vorliegt. Das säurelabile Aminosäurederivat entsteht durch direkte Kondensation der Guanidinogruppe von Arginin mit dem Zuckerabbauprodukt Methylglyoxal und ist Vertreter einer neuen Form posttranslationaler Proteinmodifikationen. Für eine Anzahl handelsüblicher Laugenbackwaren lagen die nach enzymatischer Totalhydrolyse bestimmbaren Gehalte des Imidazolons zwischen 900 und 1300 mg pro 100g Protein. Während des Backprozesses werden somit zwischen 20 und 30% der Argininreste mit Methylglyoxal umgesetzt.

     

Atmospheric chemistry of N-methyl perfluorobutane sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: kinetics and mechanism of reaction with OH

Relative rate methods were used to measure the gas-phase reaction of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE) with OH radicals, giving k(OH + NMeFBSE) = (5.8 +/- 0.8) x 10(-12) cm3 molecule(-1) s(-1) in 750 Torr of air diluent at 296 K. The atmospheric lifetime of NMeFBSE is determined by reaction with OH radicals and is approximately 2 days. Degradation products were identified by in situ FTIR spectroscopy and offline GC-MS and LC-MS/MS analysis. The primary carbonyl product C4F9SO2N(CH3)CH2CHO, N-methyl perfluorobutane sulfonamide (C4F9SO2NH(CH3)), perfluorobutanoic acid (C3F7C(O)OH), perfluoropropanoic acid (C2F5C(O)OH), trifluoroacetic acid (CF3C(O)OH), carbonyl fluoride (COF2), and perfluorobutane sulfonic acid (C4F9SO3H) were identified as products. A mechanism involving the addition of OH to the sulfone double bond was proposed to explain the production of perfluorobutane sulfonic acid and perfluorinated carboxylic acids in yields of 1 and 10%, respectively. The gas-phase N-dealkylation product, N-methyl perfluorobutane sulfonamide (NMeFBSA), has an atmospheric lifetime (>20 days) which is much longer than that of the parent compound, NMeFBSE. Accordingly,the production of NMeFBSA exposes a mechanism by which NMeFBSE may contribute to the burden of perfluorinated contamination in remote locations despite its relatively short atmospheric lifetime. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.     

First direct detection of HONO in the reaction of methylnitrite (CH3ONO) with OH radicals

We report on the development of a new environmental simulation chamber coupled with an in situ continuous wave cavity ring-down spectrometer operating in the near IR (～1.5 μm). The first application reported in this paper dealt with the chemical mechanism of UV photolysis of methyl nitrite (CH(3)ONO) in air. HONO has been detected for the first time and shown to be formed in the OH + CH(3)ONO reaction. A dense spectrum of cis-HONO absorption lines has been observed near 1.5 μm, in agreement with a previous study (Guilmot et al.). CH(2)O has been measured as primary product with good sensitivity and time resolution. In contrast to Zhao et al., we did not detect any NO(2) absorption features in this wavelength range. Calibration experiments provided very low NO(2) absorption cross sections in this region (～10(-25) cm(2)), leading to conclude that NO(2) cannot be observed in this wavelength range in the presence of equal amounts of CH(2)O.     

Formation and reaction of hydroxycarbonyls from the reaction of OH radicals with 1,3-butadiene and isoprene

1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are emitted into the atmosphere in vehicle exhaust and, in the case of isoprene, from vegetation. We have investigated the formation and further reaction of products of their hydroxyl radical-initiated reactions using atmospheric pressure ionization mass spectrometry (API-MS) and solid-phase microextraction fibers precoated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for on-fiber derivatization of carbonyl compounds, with subsequent analysis by thermal desorption and gas chromatography with flame ionization detection (SPME/GC-FID) or MS detection. Products attributed as HOCH2CH=CHCHO and HOCH2CH=CHCH2ONO2 (and isomers) from 1,3-butadiene; HOCD2CD=CDCDO and HOCD2CD=CDCD2ONO2 (and isomers) from 1,3-butadiene-d6; HOCH2C(CH3)=CHCHO and/or HOCH2CH=C(CH3)CHO, and HOCH2C(CH3)=CHCH2ONO2 (and isomers) from isoprene; and HOCD2C(CD3)=CDCDO and/or HOCD2CD=C(CD3)CDO, and HOCD2C(CD3)=CDCD2ONO2 (and isomers) from isoprene-d8 were observed as their NO2- adducts in the API-MS analyses. The hydroxycarbonyls were observed from SPME/GC-FID analyses of the 1,3-butadiene and isoprene reactions as their oximes, together with acrolein, glycolaldehyde, and glyoxal from the 1,3-butadiene reaction. A rate constant for the reaction of OH radicals with 4-hydroxy-2-butenal of (5.7 +/- 1.4) x 10(-11) cm3 molecule(-1) s(-1) at 298 +/- 2 K was derived, and formation yields of acrolein and 4-hydroxy-2-butenal from the 1,3-butadiene reaction of 58 +/- 10% and 25 (+15/-10)%, respectively, were determined. Analogous experiments showed that the two C5-hydroxycarbonyls formed from isoprene have rate constants for their reactions with OH radicals of (1.0 +/- 0.3) x 10(-10) cm3 molecule(-1) s(-1) and (4 +/- 2) x 10(-11) cm3 molecule(-1) s(-1) and a combined yield of approximately 15%, although isomer-specific identification of the hydroxycarbonyls was not achieved.     

Tropospheric reaction of OH with selected linear ketones: kinetic studies between 228 and 405 K

The absolute rate coefficients for the tropospheric reactions of hydroxyl radical (OH) with a series of linear aliphatic ketones (2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4)) were measured as a function of temperature (228-405 K) and pressure (45-600 Torr of He) by the pulsed laser photolysis/laser induced fluorescence technique. These studies are essential to model the atmospheric chemistry of these ketones and their impact in the air quality. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k1(298 K) (x10(-12) cm3 molecule(-1) s(-1)) were averaged over the pressure range studied yielding the following: (1.04+/-0.74), (3.14+/-0.40), (6.37+/-1.40), and (8.22+/-1.10), for 2-butanone (k1), 2-pentanone (k2), 2-hexanone (k3), and 2-heptanone (k4), respectively. k1 exhibits a slightly positive temperature dependence over the temperature range studied. A conventional Arrhenius expression describes the observed behavior. In contrast, the temperature dependence of k2-k4 shows a distinct deviation from the Arrhenius behavior. The best fit to our data was found to be described by the three-parameter expression: k(T) = A + B exp(-C/T) in cm3 molecule(-1) s(-1). This work constitutes the first determination of the temperature dependence of k2-k4. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions are also discussed.