Aerobic biodegradation studies of nonylphenol ethoxylates in river water using liquid chromatography-electrospray tandem mass spectrometry

The aerobic biodegradation of nonylphenol ethoxylates (A9PEO) was kinetically investigated in a laboratory-scale bioreactor filled with riverwater, spiked at a concentration of 10 mg L(-1) nonionic surfactants. Analyses of the samples applying liquid chromatography-electrospray mass spectrometry (LC-ES-MS) after solid-phase enrichment revealed a relatively fast primary degradation of A9PEO with >99% degradation observed after 4 days. Contrary to the generally proposed degradation pathway of EO chain shortening, it could be shown that the initiating step of the degradation is omega-carboxylation of the individual ethoxylate chains: metabolites with long carboxylated EO chains are identified (A9PEC). Further degradation proceeds gradually into short-chain carboxylated EO with the most abundant species being AgPE2C. The oxidation of the nonyl chain proceeds concomitantly with this degradation, leading to metabolites having both a carboxylated ethoxylate and an alkyl chain of varying lengths (CAPEC). The identity of the CAPEC metabolites was confirmed by the fragmentation pattern obtained with LC-ES-MS/MS. Both A9PEC and CAPEC metabolites are still present in the bioreactor after 31 days. In the aerobic degradation pathway, A9PEO2 is formed only to a minor extent and is even further degraded in several days. The endocrine disruptor nonylphenol was not found as a metabolite in this study.     

Characterization of alkylphenol degradation gene cluster in Pseudomonas putida MT4 and evidence of oxidation of alkylphenols and alkylcatechols with medium-length alkyl chain

Alkylphenols (APs) are ubiquitous contaminants in aquatic environments and have endocrine disrupting and toxic effects on aquatic organisms. To investigate biodegradation mechanisms of APs, an AP degradation gene cluster was cloned from a butylphenol (BP)-degrading bacterium, Pseudomonas putida MT4. The gene cluster consisted of 13 genes named bupBA1A2A3A4A5A6CEHIFG. From the nucleotide sequences, bupA1A2A3A4A5A6 were predicted to encode a multicomponent phenol hydroxylase (PH), whereas bupBCEHIFG were expected to encode meta-cleavage pathway enzymes. A partial sequence of a putative NtrC-type regulatory gene, bupR, was also found upstream of the gene bupB. This result indicates that APs can be initially oxidized into alkylcatechols (ACs), followed by the meta-cleavage of the aromatic rings. To confirm this pathway, AP degradation tests were carried out using the recombinant P. putida KT2440 harboring the PH genes (bupA1A2A3A4A5A6). The recombinant strain oxidized 4-n-APs with an alkyl chain of up to C7 (< or = C7) efficiently and also several BPs including those with an alkyl chain with some degree of branching. Therefore, it was found that PH had a broad substrate specificity for APs with a medium-length alkyl chain (C3-C7). Moreover, the cell extract of a recombinant Escherichia coli harboring bupB (a catechol 2,3-dioxygenase gene) converted 4-n-ACs with an alkyl chain of < or = C9 into yellow meta-cleavage products with a maximum absorbance at 379 nm, indicating that the second step enzyme in this pathway is also responsible for the degradation of ACs with a medium-length alkyl chain. These results suggest that MT4 is a very useful strain in the biodegradation of a wide range of APs with a medium-length alkyl chain, which known nonylphenol-degrading Sphingomonas strains have never degraded.     

Chemical characterization and sorption capacity measurements of degraded newsprint from a landfill

Newsprint samples collected from 12-16 ft (top layer (TNP)), 20-24 ft (middle layer (MNP)), and 32-36 ft (bottom layer (BNP)) below the surface of the Norman Landfill (NLF) were characterized by infrared (IR) spectroscopy, cross-polarization, magic-angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopy, and tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography/mass spectrometry (GC/MS). The extent of NLF newsprint degradation was evaluated by comparing the chemical composition of NLF newsprint to that of fresh newsprint (FNP) and newsprint degraded in the laboratory under methanogenic conditions (DNP). The O-alkyl/alkyl, cellulose/lignin, and lignin/resin acid ratios showed that BNP was the most degraded, and that all three NLF newsprint samples were more degraded than DNP. 13C NMR and TMAH thermochemolysis data demonstrated selective enrichment of lignin over cellulose, and TMAH thermochemolysis further exhibited selective enrichment of resin acids over lignin. In addition, the crystallinity of cellulose in NLF newsprint samples was significantly lower relative to that of FNP and DNP as shown by 13C NMR spectra. The yield of lignin monomers from TMAH thermochemolysis suggested that hydroxyl groups were removed from the propyl side chain of lignin during the anaerobic decomposition of newsprint in the NLF. Moreover, the vanillyl acid/aldehyde ratio, which successfully describes aerobic lignin degradation, was not a good indicator of the anaerobic degradation of lignin on the basis of the TMAH data. The toluene sorption capacity increased as the degree of newsprint degradation increased or as the O-alkyl/alkyl ratio of newsprint decreased. The results of this study further verified that the sorbent O-alkyl/ alkyl ratio is useful for predicting sorption capacities of natural organic materials for hydrophobic organic contaminants.     

NP1EC degradation pathways under oxic and microxic conditions

The degradation pathway of nonylphenol ethoxyacetic acid (NP1EC) and the conditions favoring dicarboxylated alklyphenol ethoxyacetic acid (CAnP1EC; where n = the number of aliphatic carbon atoms) formation were studied in oxic microcosms constructed with organic carbon-poor soil from the Mesa soil aquifer treatment (SAT) facility (Arizona) and pristine organic carbon-rich sediments from Coyote Creek (California). Results suggest that the availability of dissolved oxygen determines the dominant biodegradation pathway; ether cleavage and the formation of NP is favored by oxic conditions, while alkyl chain oxidation and the formation of CAP1ECs is favored under microxic conditions. In the Mesa microcosms, para-NP1EC was transformed to para-nonylphenol (NP) before being rapidly transformed to nonyl alcohols via ipso-hydroxylation. In the Coyote Creek microcosms, large quantities of CAP1ECs were observed. Initially, CA8P1ECs were the dominant metabolites, but as biodegradation continued, CAP1ECs became the dominant metabolites. Compared to the CAsP1ECs, the number of CA6P1ECs peaks observed was small (< 6) even though their concentrations were high. Several novel metabolites, tentatively identified as 3-alkylchroman-4-carboxylic acids (with alkyl groups ranging from C2 to C5), were formed in the Coyote Creek microcosms. These metabolites are presumably formed from ortho-CAP1ECs by intramolecular ring closure.     

Effect of the side chain size of 1‐alkyl‐pyrroles on antioxidant activity and ‘Laba’ garlic greening

Previous studies showed that 1‐alkyl‐pyrroles not only occur in fresh food products postulated as a natural antioxidant but also might be involved in garlic greening. In the present study, a series of 1‐alkyl‐pyrroles with different side chain size were synthesised to study the relationship of structure and antioxidative activity and their effects on ‘Laba’ garlic greening. The antioxidative activity of these compounds was evaluated by the method of scavenging ABTS˙ and DPPH˙. Results showed that increasing the size of R groups on the side chain, the antioxidative activity decreased gradually against the two radicals. The 1‐alkyl‐pyrroles generally exhibited stronger scavenging activities against ABTS˙ than DPPH˙. In contrast, their corresponding amino acids except for tyrosine showed almost no antioxidative activities while pyrrole exhibited much weaker activity as compared with the 1‐alkyl‐pyrroles, suggesting that the 1‐alkyl‐pyrroles donate H‐atom from pyrrole moiety rather than side chain to quench the two radicals. On the other hand, all 1‐alkyl‐pyrroles can turn newly harvested garlic green but to a different extent. All these results suggested that these pyrrole derivatives occurring in foodstuff played an important role in either protecting foodstuff from oxidation or acting on pigment precursors during ‘Laba’ garlic greening.     

TiO2 photocatalysis of natural organic matter in surface water: impact on trihalomethane and haloacetic acid formation potential

In this study, changes in the physical and structural properties of natural organic matter (NOM) during titanium dioxide photocatalytic oxidation process were investigated using several complementary analytical techniques. Potential of the treated water to form trihalomethanes (THMs) and haloacetic acids (HAAs) was also studied. High-performance size exclusion chromatography analysis showed that NOM with apparent molecular weights of 1-4 kDa were preferentially degraded, leading to the formation of lower molecular weight organic compounds. Resin fractionation of the treated water demonstrated that the photocatalytic oxidation changed the affinity of the bulk organic character from predominantly hydrophobic to more hydrophilic. Short chain aldehydes and ketones were identified by mass spectroscopy as one of the key degradation products. The addition of hydrogen peroxide to photocatalysis was found to increase the degradation kinetics but did not affect the reaction pathway, thus producing similar degradation end products. The amount of THMs normalized per dissolved organic carbon (specific THM) formed upon chlorination of NOM treated with photocatalytic oxidation was reduced from 56 to 10 microg/mg. In contrast, the specific HAAs formation potential of the treated water remained relatively unchanged from the initial value of 38 microg/mg, which could be due to the presence of hydrophilic precursor compounds that were formed as a result of the photocatalytic oxidation process.     

Identification of degradation pathways and products of cyanidin-3-sophoroside exposed to pulsed electric field

Pulsed electric field (PEF) can induce the degradation of anthocyanins. In this study, the degradation products and postulated degradation mechanism and pathways of cyanidin-3-sophoroside (Cy-3-soph) by PEF were investigated using a combination of UV–vis spectra and HPLC-MS. Four isomers of quinonoid benzoyloxyphenylacetic acid esters resulting from the oxidative degradation of Cy-3-soph at pH 1.5 and 3.5 were detected in a model solution after PEF. The prevailing degradation pathway was different from thermal degradation. Cy-3-soph was degraded through a Baeyer–Villiger oxidation by the nucleophilic attack of hydrogen peroxide and then further oxidised by other oxidants, such as the hydroxyl free radical induced by the electrochemical reactions during PEF treatment. The thermal degradation pathways at pH 1.5 and 3.5 were also involved in the degradation of Cy-3-soph during PEF treatment.     

应用气相色谱-质谱分析竹浆Co—salen仿酶漂白机理

根据气相色谱-质谱检出产物分析了Co-salen催化漂白竹浆机理.Co-salen催化漂白使残余木素进一步氧化降解,降解的主要方式有脱甲基作用、醌型结构的产生和开环、烷基-芳基醚键和侧链碳-碳联接的氧化断裂.检测产物中,含羰基的化合物居多,这是Co-salen选择性催化氧化的结果,有利于木素大分子的碎片化溶出.     

Vc与Cu2+的耦合氧化对桑葚花色苷的降解作用

研究通过构建含Vc和Cu2+的桑葚汁模拟体系,研究这两个内源因子对花色苷的降解作用。研究表明Vc能显著促进花色苷的降解,而在果汁所含Cu2+浓度下,Cu2+对花色苷具有一定的保护作用,但当在体系中与Vc共存时,则能大大促进花色苷的降解。因此,可以得出一个花色苷被Vc和Cu2+耦合氧化的降解机制:低浓度时,Cu2+自身不催化花色苷的降解,但当有Vc存在时,它能先通过促进Vc的氧化降解,使Vc转化为对花色苷降解有显著促进作用的氢过氧化物,从而加速花色苷的降解。     

Electrochemical oxidation characteristics of p-substituted phenols using a boron-doped diamond electrode

Electrochemical oxidation of some p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) with electron-donating and -withdrawing substituents was studied to reveal the relationship between the structure and the electrochemical reactivity of p-substituted phenols using a boron-doped diamond electrode by voltammetry and bulk electrolysis. Voltammetric study shows that the oxidation peak potentials of p-substituted phenols become more positive with an increase of Hammett's constants, that is, the direct electrochemical oxidation of p-substituted phenol with an electron-withdrawing group is more difficult than that of p-substituted phenol with an electron-donating group. However,the p-substituted phenols with electron-withdrawing groups are degraded faster than those with electron-donating groups in bulk electrolysis, which is opposite to the result obtained on the Pt electrode. These results indicate that the p-substituted phenols are mainly degraded by indirect electrochemical oxidation with hydroxyl radicals on a boron-doped diamond electrode. Under the attack of hydroxyl radicals, the release of p-substituted groups from the aromatic ring is the rate-limiting step. Since electron-withdrawing groups are easy to be released, the p-substituted phenols with these groups are degraded faster than those with electron-donating groups. Therefore, the degradation rates of the p-substituted phenols rise with an increase of Hammett's constants.     

Effects of gallic acid and its alkyl esters on lipid oxidation during in vitro simulated gastrointestinal digestion of fresh and fried oysters

The process of lipid oxidation in fresh and fried oysters during in vitro digestion and the relationship between the antioxidant ability of phenolic esters with different chain lengths were investigated through co-digestion of fresh and fried oysters with gallic acid (GA) and its alkyl esters. Lipid oxidation in fresh and fried oysters during simulated digestion in vitro was observed according to increased conjugated diene value, conjugated triene value, thiobarbituric acid reactive substances and fluorescence intensity of aldehydes. Lipid oxidation in oysters was inhibited by GA and its alkyl esters during in vitro digestion effectively. As the alkyl chain length increased, the antioxidant effect first increased and then decreased, and butyl gallate achieved the highest effect among the GA and its alkyl esters we studied, which suggests that the antioxidant efficiency of GA and its alkyl esters in the digestive system may follow the ‘cut-off’ effect.     

不饱和脂肪酸室温氧化过程中自由基的变化

为探究不饱和脂肪酸室温氧化过程中自由基的变化规律,本实验以油酸、亚油酸和亚麻酸为实验材料,采用电子顺磁共振和核磁共振技术,对室温氧化及外源物质影响下不饱和脂肪酸氧化过程自由基和核磁共振氢谱变化规律进行分析。结果表明：油酸氧化0～60 min期间所含自由基以烷基自由基（R·）为主,之后以烷过氧自由基（ROO·）和烷氧自由基（RO·）为主;亚油酸、亚麻酸氧化过程所含自由基均以R·为主;氧化期间脂肪酸（RH）被引发生成R·和H·,H·与ROO·结合生成氢过氧化物,部分氢过氧化物发生分解,且亚麻酸氧化和降解程度高于亚油酸和油酸;加入生育酚（tocopherol,VE）和特丁基对苯二酚（tert-butylhydroquinone,TBHQ）均可抑制RO·、ROO·等自由基的形成;加入偶氮二异庚腈（2,2’-azobis(2,4-dimethyl)valeronitrile,ADVN）的脂肪酸中所含自由基以R·为主,同时会引入无机碳中心自由基;加入叶绿素的油酸和亚麻酸组自旋总数分别在150 min和90 min明显升高,其余时间段呈波动式变化。结论：不饱和脂肪酸室温氧化过程中,不饱和程度越高的脂肪酸生成R·数量越多;加入的VE和TBHQ会提供H·,其与脂质自由基结合从而抑制链式反应进行,尤其会抑制ROO·、RO·生成;ADVN、叶绿素具有自由基引发效应,能促进链式反应进行。     

A bench-scale constructed wetland as a model to characterize benzene biodegradation processes in freshwater wetlands

In wetlands, a variety of biotic and abiotic processes can contribute to the removal of organic substances. Here, we used compound-specific isotope analysis (CSIA), hydrogeochemical parameters and detection of functional genes to characterize in situ biodegradation of benzene in a model constructed wetland over a period of 370 days. Despite low dissolved oxygen concentrations (<30 μM), the oxidation of ammonium to nitrate and the complete oxidation of ferrous iron pointed to a dominance of aerobic processes, suggesting efficient oxygen transfer into the sediment zone by plants. As benzene removal became highly efficient after day 231 (>98% removal), we applied CSIA to study in situ benzene degradation by indigenous microbes. Combining carbon and hydrogen isotope signatures by two-dimensional stable isotope analysis revealed that benzene was degraded aerobically, mainly via the monohydroxylation pathway. This was additionally supported by the detection of the BTEX monooxygenase gene tmoA in sediment and root samples. Calculating the extent of biodegradation from the isotope signatures demonstrated that at least 85% of benzene was degraded by this pathway and thus, only a small fraction was removed abiotically. This study shows that model wetlands can contribute to an understanding of biodegradation processes in floodplains or natural wetland systems.     

Formation of toxic 2-nonyl-p-benzoquinones from α-tertiary 4-nonylphenol isomers during microbial metabolism of technical nonylphenol

In many environmental compartments, microbial degradation of α-quaternary nonylphenols proceeds along an ipso-substitution pathway. It has been reported that technical nonylphenol contains, besides α-quaternary nonylphenols, minor amounts of various α-H, α-methyl substituted tertiary isomers. Here, we show that potentially toxic metabolites of such minor components are formed during ipso-degradation of technical nonylphenol by Sphingobium xenophagum Bayram, a strain isolated from activated sewage sludge. Small but significant amounts of nonylphenols were converted to the corresponding nonylhydroquinones, which in the presence of air oxygen oxidized to the corresponding nonyl-p-benzoquinones-yielding a complex mixture of potentially toxic metabolites. Through reduction with ascorbic acid and subsequent analysis by gas chromatography-mass spectrometry, we were able to characterize this unique metabolic fingerprint and to show that its components originated for the most part from α-tertiary nonylphenol isomers. Furthermore, our results indicate that the metabolites mixture also contained several α, β-dehydrogenated derivatives of nonyl-p-benzoquinones that originated by hydroxylation induced rearrangement, and subsequent ring and side chain oxidation from α-tertiary nonylphenol isomers. We predict that in nonylphenol polluted natural systems, in which microbial ipso-degradation is prominent, 2-alkylquinone metabolites will be produced and will contribute to the overall toxicity of the remaining material.     

Influence of the chemical structure on the thermal degradation of the glucosinolates in broccoli sprouts

Glucosinolates are secondary plant metabolites occurring in Brassica vegetables. Food processing significantly reduces glucosinolate content, among other things due to thermal degradation. As there is only little information about thermal glucosinolate breakdown, the influence of the chemical structure as well as the influence of different pH to thermal degradation of individual glucosinolates was studied by analysing desulphoglucosinolates with HPLC-DAD. Thermal degradation was forced by heating broccoli sprouts at 130 °C in dry medium, whereas the influence of the pH was studied by cooking at 100 °C in aqueous medium. Within each group of glucosinolates differences in thermal degradation were revealed. Within the sulphur containing aliphatic glucosinolates the oxidative state of the sulphur atom as well as the side chain length influenced the reactivity. Among the indole glucosinolates great differences in stability were observed. A hydroxyl function in the side chain generally seems to destabilise glucosinolates. Glucosinolates were most stable towards thermal treatment in neutral and slightly acidic medium, whereas they degraded more rapidly in basic medium.     

Degradation of natural estrogen and identification of the metabolites produced by soil isolates of Rhodococcus sp. and Sphingomonas sp.

Five bacterial strains capable of utilizing 17β-estradiol (E2) and estrone (E1) were isolated from soil samples. Using their morphological and physiological features and 16S rDNA sequences, we classified these isolates into two groups: Group A (Rhodococcus sp. strains ED6, ED7, and ED10) and Group B (Sphingomonas sp. strains ED8 and ED9). All isolates used E2 and E1 as the sole carbon sources and showed high E1 and E2 degradation activities. In all strains, more than 50% of 0.8 mg of E1 or E2 was degraded in 4 mL of inorganic medium over 24 h, and 90% was degraded over 120 h. By incubating the resting ED8 cells with E2 and the meta-cleavage inhibitor 3-chlorocatechol, we identified two metabolites, 4-hydroxyestrone (4-OH-E1) and 4-hydroxyestradiol (4-OH-E2), and confirmed their identity using authentic chemicals. The 4-OH-E1 and 4-OH-E2 compounds were assumed to be intermediate metabolites formed before meta-cleavage, as they were not identified in culture without 3-chlorocatechol. Degradation of E2 by strain ED8 can be initiated by hydroxylation of the C-4 position, followed by meta-cleavage of the benzene ring. When strains ED8 degraded E2, we further identified hydroxy-E2, keto-E1 and -E2, and an additional degradation product via mass spectrometry. The presence of these compounds implied degradation through a second pathway initiated through an attack of the saturated ring.     

Trichloroethylene degradation by Ralstonia sp. KN1-10A constitutively expressing phenol hydroxylase: transformation products, NADH limitation, and product toxicity

Ralstonia sp. KN1-10A, which was constructed by inserting the tac promoter upstream of the phenol hydroxylase (PH) gene in the chromosomal DNA of the wild-type strain, Ralstonia sp. KN1, is a useful recombinant strain for eliminating trichloroethylene (TCE) from contaminated sites because it exhibits constitutive TCE oxidation activity. During TCE degradation by Ralstonia sp. KN1-10A, noxious chlorinated compounds, such as dichloroacetic acid, trichloroacetic acid, 2,2,2-trichloroethanol, and chloral, were not detected, and more than 95% of chlorine in TCE was released as chloride ions. Among the possible TCE transformation products, only carbon monoxide was detected, and its conversion percentage was 7 mol%. The addition of formate, which Ralstonia sp. KN1-10A could use as an exogenous electron donor, did not enhance the TCE degradation performance, suggesting that NADH depletion did not limit the degradation. The phenol degradation activity of Ralstonia sp. KN1-10A that previously degraded TCE was not markedly lower than that of cells not exposed to TCE, suggesting that Ralstonia sp. KN1-10A was not susceptible to product toxicity associated with TCE degradation. Furthermore, to clarify the mechanisms underlying TCE degradation by PH from Ralstonia sp. KN1, this enzyme was compared with another enzyme, a hybrid aromatic ring dioxygenase exhibiting a high TCE degradation activity in Escherichia coli and Pseudomonas sp. The initial TCE degradation rate of Ralstonia sp. KN1 (pKTP100), which produced PH, was 1 50 lower than that of Ralstonia sp. KN1 (pKTF200), which produced the hybrid aromatic ring dioxygenase. However, because of its lower product toxicity, the strain producing PH could degrade 2.3 times more TCE than that generated by the strain producing the hybrid aromatic ring dioxygenase.     

烷基链改变对吡啶类离子液体的性能影响

离子液体是一类新型软功能材料,在多相催化、萃取分离、材料制备等领域具有重要的研究意义.本文基于吡啶环上烷基链的分子结构设计,分别以溴代烷(CnH2n-1Br,n=4,8,12)、吡啶和六氟磷酸钾为反应物,获得了3种不同烷基结构的疏水性吡啶类离子液体[Cnpyr][PF6].研究表明,直链烷基吡啶类离子液体的熔点随着吡啶环上烷基链的增长,出现先降低后升高的趋势,其热分解温度在370℃左右.在室温下测定了[Cnpyr][PF6]离子液体的电导率,通过非线性最小二乘法对测得数据进行拟合,得到了[Cnpyr][PF6](n=4,8,12)的电导率与浓度之间的函数关系,其拟合的标准偏差分别为0.002 39μs/cm,0.004 47μs/cm,0.004 78μs/cm.最后,[Cnpyr][PF6]属于典型的疏水性离子液体,烷基链长度的改变对溶解性的影响相对较小.     

Oxidative degradation of glyphosate and aminomethylphosphonate by manganese oxide

Glyphosate (N-(phosphonomethyl)glycine), the most commonly used herbicide worldwide, degrades relatively rapidly in soils under most conditions, presumably by microbial processes. The most frequently detected degradation product in soil and water is AMPA (aminomethylphosphonic acid). We report the first evidence for an abiotic pathway of glyphosate and AMPA degradation under environmentally realistic conditions. Both glyphosate and AMPA degraded at 20 degrees C in dilute aqueous suspensions of birnessite, a manganese oxide common in soils, as evidenced by the accumulation of orthophosphate in solution over a period of several days. It is concluded that the abiotic degradation involved C-P bond cleavage at the Mn oxide surface, although evidence for C-N bond cleavage in the case of glyphosate and sarcosine, a likely degradation product of glyphosate, was found. The degradation of glyphosate was faster than that of AMPA, and higher temperature (50 degrees C) resulted in faster degradation of both glyphosate and AMPA. The addition of sulfate to the solution had no marked effect on the reaction rate, although Cu2+ addition inhibited degradation. As this metal ion complexes strongly with glyphosate, the inhibition can be attributed to the ability of Cu2+ to limit glyphosate coordination to reactive oxidation sites at the Mn oxide surface. Using a similar experimental design, we were unable to detect glyphosate degradation in an equimolar solution of MnCl2 (0.5 mM). However, we demonstrated that the oxidation of Mn2+ is enhanced both in solution and on an inert surface, in the presence of glyphosate (4:1 Mn-glyphosate molar ratio). This result suggests that the oxidative breakdown of glyphosate in the presence of Mn2+ may ultimately occur following the spontaneous oxygen-mediated oxidation of manganese.     

Synthesis of materials rich in pyrazines employing no sugar

The characteristics of the headspace volatiles above materials rich in pyrazines prepared with no added sugars have been determined. Formulations void of sugar and rich in branched alkyl side chain pyrazines can be prepared in a microwave oven from formulations containing hydroxyketones, selected low‐molecular‐weight aldehydes, selected amino acids and an additional nitrogen compound such as ammonium hydroxide. A relatively low temperature of 105 °C coupled with short reaction times, 60 min, affords formulations with rich aromas and relatively high concentrations of alkyl pyrazines with straight and branched alkyl side chains. The amount and type of branched chain‐containing pyrazines are a function of the amount and type of hydroxyketone, aldehyde and amino acid employed. Stepwise substitution of the hydroxyketones for high‐fructose corn syrup (HFCS) produces stepwise increases in total pyrazines. Stepwise increase in the amount of added aldehyde produces stepwise increases in the amount of pyrazines containing branched alkyl side chains. Use of 3‐hydroxy‐2‐propanone produces materials containing a set of pyrazines characterised by the presence of cis‐ and/or trans‐propenyl side chains. The semi‐quantitative yield of pyrazines, ∼3500 µg mL⁻¹, and per cent branched alkyl side chain pyrazines, ∼35%, from these formulations were determined through the use of an internal standard in the headspace measurements. Previously postulated reaction mechanisms for the formation of pyrazines are confirmed through the use of selected reagents. © 2000 Society of Chemical Industry