78-98-8Relevant articles and documents
Degradation of oligosaccharides in nonenzymatic browning by formation of α-dicarbonyl compounds via a peeling off mechanism
Hollnagel, Anke,Kroh, Lothar W.
, p. 6219 - 6226 (2000)
The formation of α-dicarbonyl-containing substances and Amadori rearrangement products was studied in the glycine-catalyzed (Maillard reaction) and uncatalyzed thermal degradation of glucose, maltose, and maltotriose using o-phenylenediamine as trapping agent. Various degradation products, especially α-dicarbonyl compounds, are formed from carbohydrates with differing degrees of polymerization during nonenzymatic browning. The different Amadori rearrangement products, isomerization products, and α-dicarbonyls produced by the used carbohydrates were quantified throughout the observed reaction time, and the relevance of the different degradation pathways is discussed. In the Maillard reaction (MR) the amino-catalyzed rearrangement with subsequent elimination of water predominated, giving rise to hexosuloses with α-dicarbonyl structure, whereas under caramelization conditions more sugar fragments with an α-dicarbonyl moiety were formed. For the MR of oligosaccharides a mechanism is proposed in which 1,4-dideoxyosone is formed as the predominating α-dicarbonyl in the quasi-water-free thermolysis of di- and trisaccharides in the presence of glycine.
NiO-doped Au/Ti-powder: A catalyst with dramatic improvement in activity for gas-phase oxidation of alcohols
Zhao, Guofeng,Hu, Huanyun,Jiang, Zheng,Zhang, Shuo,Lu, Yong
, p. 171 - 177 (2013)
An active and stable NiO@Au/Ti-powder catalyst, which can be obtained by doping Au/Ti-powder (Au: 35-40 nm) with NiO, has been developed for the gas-phase oxidation of alcohols. Gold particles are found to be partially covered with tiny NiO segments to form specific NiO@Au ensembles thereby leading to a dramatic conversion improvement from only ～5% (without NiO doping) to ～94% for the benzyl alcohol oxidation at 280 C. Additionally, the selective oxidation of cyclopropyl carbinol can proceed over this catalyst at 280 C with a selectivity of 94% and a conversion of 72-80% throughout the entire 300 h test. The hybrid active-sites, Ni2O3-Au+, on the NiO@Au ensemble are identified using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS).
Methylglyoxal synthetase, enol-pyruvaldehyde, glutathione and the glyoxalase system
Rose, Irwin A.,Nowick, James S.
, p. 13047 - 13052 (2002)
enol-Pyruvaldehyde (ePY or 2-hydroxypropenal, O=C(H)-C(OH)=CH2) a transient intermediate in the alkaline decomposition of the triosephosphates to methylglyoxal is now observed by UV and 1H NMR spectroscopy as the immediate product of the methylglyoxal synthetase (MGS) reaction: dihydroxyacetone-P → Pi + ePY → methylglyoxal (MG). Analysis of ePY formed from 1-13C- and (1R, 3S)-[1,3-2H]-DHAP establishes the stereochemical course of its formation by MGS. Its rate of ketonization is much too slow to be in the sequence required for the assay of MGS by coupling of the MG produced to glyoxalase I (Glx I): MG + glutathione (GSH) → (S)-lactylglutathione (D-LG). Instead, ketonization occurs by way of the hemithioacetal (HTA) formed between ePY and GSH, and could be either an enzymatic function of Glx I or occur nonenzymatically at an activated rate. Enzymatic ketonization was ruled out because the methyl group of D-LG formed from specifically labeled ePY is achiral. Chemical ketonization of ePY is activated by general bases, such as acetate, and by thiols such as GSH and 2-mercaptoethanol, which disrupt its stabilizing double bond conjugation as hemithioacetal (HTA) adducts. 2-Mercaptoacetate combines both functions, acting as the HTA adduct of ePY with the appended carboxylate group presumably positioned to promote abstraction of the enol proton and protonation of the enolate carbon at an accelerated rate. In the MGS-Glx I system (dihydroxyacetone-P → ePY, ePY + GSH → GS-ePY, GS-ePY → GS-MG, GS-MG → D-LG), the nonenzymatic 2nd and 3rd steps describe the catalytic role of GSH in the critical ketonization process and set the stage for its participation in the glyoxalase system.
Formation of pyruvaldehyde (2-oxopropanal) by oxidative dehydrogenation of hydroxyacetone
Ai, Mamoru,Ohdan, Kyoji
, p. 2143 - 2148 (1999)
Various mixed oxides were tested as catalysts for oxidative dehydrogenation of hydroxyacetone to form pyruvaldehyde (2-oxopropanal). The best results were obtained from an iron phosphate with a P/Fe atomic ratio of 1.05. The yield of pyruvaldehyde reached 88%. The next best results were obtained from a supported heteropoly acid (H3PMo12O40). The other molybdenum- and vanadium-based oxide catalysts were not suitable. The effects of the composition and structure of iron phosphate and the effects of reaction variables on the formation of pyruvaldehyde were also studied.
Kinetics, Mechanism, and Thermodynamics of the Reversible Reaction of Methylglyoxal (CH3COCHO) with S(IV)
Betterton, Eric A.,Hoffmann, Michael R.
, p. 3011 - 3020 (1987)
At pH =/-, SO32-) is obtained: d/dt = (((k0α1+>/Ka0) + k1α1 + k2α2)0)/(1 + Kd + Kd+>/Ka0), where α1 and α2 are the fractional concentrations of HSO3- and SO32-, respectively; k0 is the rate constant for the reaction of HSO3- with the carbocation aldehyde species (CH3COC+HOH); k1 and k2 are the rate constants for the reaction of unhydrated MG with HSO3- and SO32-, respectively; kd is the dehydration constant of hydrated MG; and Ka0 is the acid dissociation constant of the carbocation.At pH =/>4 the rate of formation of HAMS is determined by the rate of dehydration of the diol form of (hydrated) MG: d/dt = kd/(1 + Kd + Kd+>/Θa0), where kd = kw + kH+> + kOH-> + kA + kB, and kw is the intrinsic (water) rate constant; kH and kOH are the specific acid and base rate constants; and kA and kB are the general acid (A) and base (B) rate constants.Between pH 2 and 4, biexponential kinetics are observed because, under our conditions, the rates of dehydration and of S(IV) addition become comparable.Over the pH range 0.7-7.0, the dissociation of HAMS follows the rate law: d/dt = ((k-0+> + k-1 + k-2Ka3/+>)Ka4+>)/(+>2 + Ka4+> + Ka3Ka4), where k-0, k-2 are the reverse of the analogous forward rate constants defined above and Ka3 and Ka4 are the acid dissociation constants of the sulfonate anion and the sulfonic acid, respectively.Experiments to determine the effect of temperature on the rate (and equilibrium) constants indicate a marked effect of ΔS(excit.) (and ΔS298) on the relative magnitude of these constants.
Reactions of aminoguanidine with a-dicarbonyl compounds studied by electrospray ionization mass spectrometry
Saraiva, Marco A.,Borges, Carlos M.,Florencio, M. Helena
, p. 385 - 397,13 (2012)
Aminoguanidine possesses extensive pharmacological properties. This drug is recognized as a powerful a-dicarbonyl scavenger. In order to better elucidate the reactivity of aminoguanidine with a-dicarbonyls, aminoguanidine was reacted with several aldehydic and diketonic a-dicarbonyls. Electrospray ionization mass spectrometry is a suitable technique to study chemical and biochemical processes and was selected for the purpose. In aminoguanidine reactions, triazines were detected and other compounds that have never been reported before were identified. Triazine precursor forms were detected, namely tetrahydrotriazines and singly dehydrated tetrahydrotriazines. Moreover, species with bicyclic ring structures and dehydrated forms were also identified in aminoguanidine reactions. These species appear to result from tetrahydrotriazines and triazines reactions with one dicarbonyl molecule. Experiments revealed that these bicyclic species, in particular the ones resulting from triazines reactivity, could exist in solution, since they were both identified in the reactions of aminoguanidine and of a selected triazine with the dicarbonyls studied. The results obtained with regard to aminoguanidine/triazines reactivities appear to support the capability of triazines to condensate and form polycyclic ring structures and also to support literature mechanistic data for dihydroimidazotriazines formation via dihydroxyimidazolidine-triazines. The data obtained in this study may prove to be valuable to complement solution information concerning the reactivity of amines with a-dicarbonyls, in particular.
Aminoacetone Metabolism by Semicarbazide-Sensitive Amine Oxidase in Rat Aorta
Lyles, Geoffrey A.,Chalmers, Janette
, p. 416 - 419 (1995)
High speed (105,000/60 min) membrane fractions from rat aorta homogenates mobilized the aliphatic amine aminoacetone (AA) to methylglyoxal (MG) with a Km of 19 +/- 3 μM, and Vmax of 510 +/- 169 nmol MG/hr/mg protein. This deaminating activity appears to be due to a semicarbazide-sensitive amine oxidase (SSAO), which is associated with smooth muscle cells in blood vessels of the rat and other species. AA was a competitive inhibitor (Ki of 28 +/- 6 μM) of the metabolism of benzylamine, a synthetic amine often used as an assay substrate for SSAO. AA is produced endogenously from mitochondrial metabolism of threonine and glycine, and thus could be a physiological substrate for SSAO, whereas the production of MG by SSAO could have cytotoxic implications for cellular function.
Aerobic oxidation of aminoacetone, a threonine catabolite: Iron catalysis and coupled iron release from ferritin
Dutra,Knudsen,Curi,Bechara
, p. 1323 - 1329 (2001)
Aminoacetone (AA) is a threonine and glycine catabolite long known to accumulate in cridu-chat and threoninemia syndromes and, more recently, implicated as a contributing source of methylglyoxal (MG) in diabetes mellitus. Oxidation of AA to MG, NH4+, and H2O2 has been reported to be catalyzed by a copper-dependent semicarbazide sensitive amine oxidase (SSAO) as well as by Cu(II) ions. We here study the mechanism of AA aerobic oxidation, in the presence and absence of iron ions, and coupled to iron release from ferritin. Aminoacetone (1-7 mM) autoxidizes in Chelex-treated phosphate buffer (pH 7.4) to yield stoichiometric amounts of MG and NH4+. Superoxide radical was shown to propagate this reaction as indicated by strong inhibition of oxygen uptake by superoxide dismutase (SOD) (1-50 units/mL; up to 90%) or semicarbazide (0.5-5 mM; up to 80%) and by EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which detected the formation of the DMPO-·OH adduct as a decomposition product from the DMPO-O2·- adduct. Accordingly, oxygen uptake by AA is accelerated upon addition of xanthine/xanthine oxidase, a well-known enzymatic source of O2·- radicals. Under Fe(II)EDTA catalysis, SOD (· enoyl radical. In the presence of iron, simultaneous (two) electron transfer from both Fe(II) and AA to O2, leading directly to H2O2 generation followed by the Fenton reaction is thought to take place. Aminoacetone was also found to induce dose-dependent Fe(II) release from horse spleen ferritin, putatively mediated by both O2·- and AA· enoyl radicals, and the co-oxidation of added hemoglobin and myoglobin, which may be viewed as the initial step for potential further iron release. It is thus tempting to propose that AA, accumulated in the blood and other tissues of diabetics, besides being metabolized by SSAO, may release iron and undergo spontaneous and iron-catalyzed oxidation with production of reactive H2O2 and O2·-, triggering pathological responses. It is noteworthy that noninsulin-dependent diabetes has been frequently associated with iron overload and oxidative stress.
Formation of arginine modifications in a model system of N α- Tert -butoxycarbonyl (Boc)-arginine with methylglyoxal
Kloepfer, Antje,Spanneberg, Robert,Glomb, Marcus A.
, p. 394 - 401 (2011)
The present study deals with the mechanistic reaction pathway of the α-dicarbonyl compound methylglyoxal with the guanidino group of arginine. Eight products were formed from the reaction of methylglyoxal with N α-tert-butoxycarbonyl (Boc)-arginine under physiological conditions (pH 7.4 and 37 °C). Isolation and purification of substances were achieved using cation-exchange chromatography and preparative high-performance liquid chromatography (HPLC). Structures were verified by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. 2-Amino-5-(2-amino-4- hydro-4-methyl-5-imidazolinone-1-yl)pentanoic acid (3) was determined as the key intermediate precursor within the total reaction scheme. Kinetic studies identified N--(5-methyl-4-oxo-5-hydroimidazolinone-2-yl)-l-ornithine and N7-carboxyethylarginine as thermodynamically more stable products from compound 3. Further mechanistic investigations revealed an acidic hydrogen at C-8 of compound 3 to trigger aldol condensations. This reactivity of compound 3 allowed for the addition of another molecule of methylglyoxal to form products, such as N--(4-carboxy-4,6-dimethyl-5,6-dihydroxy-1,4,5,6- tetrahydropyrimidine-2-yl)-l-ornithine and argpyrimidine.
Oxidations of Primary Alcohols with a Copper(II) Complex as a Possible Galactose Oxidase Model
Kitajima, Nobumasa,Whang, Kaehong,Moro-oka, Yoshihiko,Uchida, Akira,Sasada, Yoshio
, p. 1504 - 1505 (1986)
N,N'-(2-Hydroxy-propane-1,3-diyl)bis(salicylaldiminato)copper(II) was found to be an effective catalyst for the oxidation of ethanol, n-propanol, or hydroxyacetone in the presence of KOH under O2; the X-ray crystal structure shows that the co-ordination geometry of the copper is significantly distorted toward tetrahedral from square planar with two oxygens and two nitrogens from salicylaldimine moieties.
