Cleavage Of Carbon Chain Research Articles

O2-H2O2 high-efficient co-oxidation of carbohydrate biomass to formic acid via Co3O4/C nanocatalyst

The conversion of biomass to chemicals/fuels has emerged as a valuable solution that offers both environmental and economic benefits, with the transformation of carbohydrate into formic acid garnering escalating scholar interest. However, the relative limited efficiency of catalyzed-oxidation or expensive cost of H2O2 and alkali in wet hydrothermal oxidation impose limitations on industrialization. This paper proposed a new idea for formic acid production by O2-H2O2 co-oxidation of carbohydrate. A two-step reaction method was developed, where the initial step is engineered to regulate the carbon chain cleavage of carbohydrates to augment the production of active intermediate. Oxygen was employed in the subsequent step as effective oxidant through free radical mechanism, resulting in a formic acid yield of 82.6%. Theoretical calculation, intermediates detection and real time EPR confirmed the reaction mechanism. Finally, the universality of the reaction was verified by using disaccharides and polysaccharides such as cellulose as substrates.

The thermal transformation mechanism of chlorinated paraffins: An experimental and density functional theory study.

The increasing production and usage of chlorinated paraffins (CPs) correspondently increase the amount of CPs that experience thermal processes. Our previous study revealed that a significant amount of medium-chain chlorinated paraffins (MCCPs), short-chain chlorinated paraffins (SCCPs) as well as aromatic and chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) were formed synergistically during the thermal decomposition of CP-52 (a class of CP products). However, the transformation mechanisms of CP-52 to these compounds are still not very clear. This article presents a mechanistic analysis on the decomposition of CP-52 experimentally and theoretically. It was found that CP-52 initially undergoes dehydrochlorination and carbon chain cleavage and it transformed into chlorinated and unsaturated hydrocarbons. Cyclization and aromatization were the most accessible pathways at low temperatures (200-400°C), both of which produce mostly aromatic hydrocarbons. As the temperature exceeds 400°C, the hydrocarbons could decompose into small molecules, and the subsequent radical-induced reactions become the predominant pathways, leading to the formation of Cl-PAHs. The decomposition of CP-52 was investigated by using density functional theory and calculations demonstrating the feasibility and rationality of PCB and PCN formation from chlorobenzene. The results improve the understanding of the transformation processes from CP-52 to SCCPs and Cl-PAHs as well as provide data for reducing their emissions during thermal-related processes.

A Kinetic and Mechanismic Study of Plasma-Induced Degradation of Monochloropropionic Acids in Water by Means of Anodic Contact Glow Discharge Electrolysis

Decomposition of aqueous monochloropropionic acids (MCPAs) was investigated by means of anodic contact glow discharge electrolysis (CGDE). With the decay of MCPAs, the corresponding total organic carbon (TOC) also decreased smoothly. Furthermore, it was found that chlorine atoms in the MCPAs were released as chloride ions. As the main by-products, oxalic acid and formic acid were detected. The acetic acid (CA), monochloroacetic acid (MCA), and propanedioic acid (PDA) were also detected as the primary intermediates for decomposition of the corresponding MCPAs. The decay of both MCPAs and TOC obeyed the first-order kinetics, respectively. The apparent rate constant for the decay of MCPAs increased with the increase inpKavalues of MCPAs, while that for the decay of TOC was substantially unaffected. The reaction pathway involving the successive attack of hydroxyl radical and the carbon chain cleavage were discussed based on the products and kinetics.

Radical acylation of L-lysine derivatives and L-lysine-containing peptides by peroxynitrite-treated diacetyl and methylglyoxal

Highly electrophilic α-dicarbonyls such as diacetyl, methylglyoxal, 3-deoxyglucosone, and4,5-dioxovaleric acid have been characterized as secondary catabolites that can aggregate proteins and form DNA nucleobase adducts in several human maladies, including Alzheimer's disease, rheumatoid arthritis, diabetes, sepsis, renal failure, and respiratory distress syndrome. In vitro, diacetyl and methylglyoxal have also been shown to rapidly add up the peroxynitrite anion (k2 ˜ 104–105 M−1 s−1), a potent biological nucleophile, oxidant and nitrosating agent, followed by carbon chain cleavage to carboxylic acids via acetyl radical intermediate that can modify amino acids. In this study, we used the amino acid derivatives Ac-Lys-OMe and Z-Lys-OMe and synthesized the tetrapeptides H-KALA-OH, Ac-KALA-OH, and H-K(Boc)ALA-OH to reveal the preferential Lys amino group targeted by acyl radical generated by the α-dicarbonyl/peroxynitrite system. The pH profiles of the reactions are bell-shaped, peaking at approximately 7.5; hence, they are close to the pKa values of ONOOH and of the catalytic H2PO4− anion. RP-HPLC and ESI-MS analyses of reaction products confirmed αN- and ϵN-acetylation of Lys by diacetyl as well as acetylation and formylation by methylglyoxal, with preference for the α-amino group. These data suggest the possibility of radical acylation of proteins in epigenetic processes, where enzymatic acetylation of these biomolecules is a well-documented event, recently reported to be as critical to the cell cycle as phosphorylation. Also noteworthy is the observed formylation of L-Lys containing peptides by methylglyoxal never reported to occur in amino acid residues of peptides and proteins.

Intermolecular Peroxyl Radical Reactions during Autoxidation of Hydroxy and Hydroperoxy Arachidonic Acids Generate a Novel Series of Epoxidized Products

We report on the identification of novel epoxide products formed during the autoxidative transformation of 15 S-hydroxy- and 15 S-hydroperoxy-eicosatetra-5 Z,8 Z,11 Z,13 E-enoic acids (15 S-HETE and 15 S-HPETE). These epoxides account for about 20-30% of the polar compounds detected during the early stages of autoxidation. Their common structural features are retention of the original 15 S-hydroxy or 15 S-hydroperoxy moiety with epoxidation of the 11 Z or 13 E double bonds in the conjugated diene of the starting material. Four main epoxyalcohol isomers were characterized from the hydroxy fatty acid 15 S-HETE, comprising two pairs of diastereomers with either an 11,12- trans or 13,14- trans epoxide functionality. Four main epoxyhydroperoxides identified from 15 S-HPETE comprised two pairs with cis or trans epoxide configuration at the 11,12 position. To account for these transformations, we propose a mechanism involving peroxyl radical dependent dimerization or oligomerization of the fatty acid hydroxy or hydroperoxy derivatives into covalent intermediates resulting in intermolecular transfer of oxygen from the peroxyl radical to the epoxide group. Autoxidation of [ (18)O 2]-15 S-HPETE carrying an O-18 labeled hydroperoxide showed that the 11,12- cis epoxy oxygen of the epoxy-hydroperoxide product was enriched in the labeled oxygen, providing evidence that in part it was derived directly from the starting hydroperoxide and not from molecular oxygen. Thus, intermediate dimerization and possibly oligomerization of fatty acid peroxyl radicals provides a mechanism of epoxidation of fatty acid derivatives during lipid peroxidation and a potential route to other products including aldehydes formed via carbon chain cleavage.

Molecular Cloning and Functional Characterization of Psoralen Synthase, the First Committed Monooxygenase of Furanocoumarin Biosynthesis

Ammi majus L. accumulates linear furanocoumarins by cytochrome P450 (CYP)-dependent conversion of 6-prenylumbelliferone via (+)-marmesin to psoralen. Relevant activities, i.e. psoralen synthase, are induced rapidly from negligible background levels upon elicitation of A. majus cultures with transient maxima at 9-10 h and were recovered in labile microsomes. Expressed sequence tags were cloned from elicited Ammi cells by a nested DD-RT-PCR strategy with CYP-specific primers, and full-size cDNAs were generated from those fragments correlated in abundance with the induction profile of furanocoumarin-specific activities. One of these cDNAs representing a transcript of maximal abundance at 4 h of elicitation was assigned CYP71AJ1. Functional expression in Escherichia coli or yeast cells initially failed but was accomplished eventually in yeast cells after swapping the N-terminal membrane anchor domain with that of CYP73A1. The recombinant enzyme was identified as psoralen synthase with narrow substrate specificity for (+)-marmesin. Psoralen synthase catalyzes a unique carbon-chain cleavage reaction concomitantly releasing acetone by syn-elimination. Related plants, i.e. Heracleum mantegazzianum, are known to produce both linear and angular furanocoumarins by analogous conversion of 8-prenylumbelliferone via (+)-columbianetin to angelicin, and it was suggested that angelicin synthase has evolved from psoralen synthase. However, (+)-columbianetin failed as substrate but competitively inhibited psoralen synthase activity. Analogy modeling and docked solutions defined the conditions for high affinity substrate binding and predicted the minimal requirements to accommodate (+)-columbianetin in the active site cavity. The studies suggested that several point mutations are necessary to pave the road toward angelicin synthase evolution.

Synthesis of dihydroperoxides of linoleic and linolenic acids and studies on their transformation to 4‐hydroperoxynonenal

The cytotoxic aldehydes 4-hydroxynonenal, 4-hydroperoxynonenal (4-HPNE), and 4-oxononenal are formed during lipid peroxidation via oxidative transformation of the hydroxy or hydroperoxy precursor fatty acids, respectively. The mechanism of the carbon chain cleavage reaction leading to the aldehyde fragments is not known, but Hock-cleavage of a suitable dihydroperoxide derivative was implicated to account for the fragmentation [Schneider, C., Tallman, K.A., Porter, N.A., and Brash, A.R. (2001) Two Distinct Pathways of Formation of 4-Hydroxynonenal. Mechanisms of Nonenzymatic Transformation of the 9- and 13-Hydroperoxides of Linoleic Acid to 4-Hydroxyalkenals, J. Biol. Chem. 275, 20831-20838]. Both 8,13- and 10,13-dihydroperoxyoctadecadienoic acids (diHPODE) could serve as precursors in a Hock-cleavage leading to 4-HPNE via two different pathways. Here, we synthesized diastereomeric 9,12-, 10,12-, and 10,13-diHPODE using singlet oxidation of linoleic acid. 8,13-Dihydroperoxyoctadecatrienoic acid was synthesized by vitamin E-controlled autoxidation of gamma-linolenic acid followed by reaction with soybean lipoxygenase. The transformation of these potential precursors to 4-HPNE was studied under conditions of autoxidation, hematin-, and acid-catalysis. In contrast to 9- or 13-HPODE, neither of the dihydroperoxides formed 4-HPNE on autoxidation (lipid film, 37 degrees C), regardless of whether the free acid or the methyl ester derivative was used. Acid treatment of 10,13-diHPODE led to the expected formation of 4-HPNE as a significant product, in accord with a Hock-type cleavage reaction. We conclude that, although the suppression of 4-H(P)NE formation from monohydroperoxides by alpha-tocopherol indicates peroxyl radical reactions in the major route of carbon chain cleavage, the dihydroperoxides previously implicated are not intermediates in the autoxidative transformation of monohydroperoxy fatty acids to 4-HPNE and related aldehydes.

Synthesis of isofagomine, a novel glycosidase inhibitor

(3R, 4R, 5R)-3,4-Dihydroxy-5-hydroxymethyl-piperidine (Isofagomine, 1) a potent β-glucosidase inhibitor was synthesised in a 6 step synthesis in an overall yield of 34% starting from 1,6:2,3-dianhydro-4- O-benzyl-β- d-mannopyranose (7). A hydroxymethyl group was introduced at C-2 in 7 by epoxide opening with vinylmagnesium bromide followed by ozonolysis with reductive workup to give 1,6-anhydro-4- O- benzyl-2-deoxy-2- C-hydroxymethyl-β- d-glucopyranose, 9. Hydrolysis of the anhydro bond and subsequent oxidative carbon chain cleavage gave a pentodialdose, which was cyclised by reductive amination with ammonia affording the 4- O-benzyl derivative of 1. After the removing the protecting group by hydrogenation under acidic conditions 1 was isolated as its hydrochloride. Synthesis of 1 was also attempted from its lactam precursur. For this purpose 5-amino-2,3-anhydro-5-deoxy-4- O- tert-butyl-dimethylsily- d-lyxono-1,5-lactam 6 was synthesised in the 5 steps from d-galactose. However, epoxide opening of 6 or 7 with the α-alkoxy cuprate dilithium benzoxymethyl-2-thienylcyanocuprate was unsuccessful.

The enzyme activity of bovine adrenocortical cytochrome P-450 producing pregnenolone from cholesterol: Kinetic and electrophoretic studies on the reactivity of hydroxycholesterol intermediates

Electrofocusing of a highly-purified preparation of bovine adrenocortical cytochrome P-450(scc) showed a single peak of enzyme activity at pH 6.8, when either cholesterol, [20S]-20-hydroxycholesterol, [22R]-22-hydroxycholesterol or [20R, 22R]-20, 22-dihydroxycholesterol was used as the substrate for the side chain cleavage reaction. The formation of pregnenolone from these hydroxycholesterols was inhibited by [20R, 22S]-20, 22-epoxycholesterol similarly in a competitive manner and the Ki value for the epoxide was found to be 12–15 μM for all these substrates. When one of the above mentioned substrates was incubated in a concentration sufficient for maximal reaction velocity, the addition of another hydroxycholesterol did not result in further increase of pregnenolone production. These results support the assumption that a single species of enzyme catalyzes all the three steps of the reaction, i.e., 20-hydroxylation, 22-hydroxylation and cleavage of carbon chain between carbon-20 and carbon-22.

Mass spectrometry of hydroxy dicarboxylic acids as trimethylsilyl derivatives. Rearrangement fragmentations

AbstractGas chromatography—mass spectrometry offers a convenient method for the separation and identification of hydroxy dicarboxylic acids as open‐chain trimethylsilyl (TMS) derivatives. Mass spectra were studied of aldaric (tartronic, tartaric, pentaric and hexaric) acids and deoxyaldaric (malic, 2‐deoxypentaric, 2‐deoxyhexaric, 3‐deoxypentaric and 3‐deoxyhexaric) acids. The different structural types can be readily identified from their characteristic spectra.The most prominent fragmentations involving the rupture of one bond are the loss of a siliconlinked methyl group and the formation of α‐cleavage ions by carbon chain cleavage. The further decay is characterized by a number of significant rearrangements specific of TMS derivatives. Several of these can be classified as involving migration of a TMS group to an oxygen atom or migration of an ester OTMS group to a silicon atom. Concomitant loss of a stable molecule often provides a driving force.Prominent odd‐electron ions are formed by a McLafferty‐type rearrangement of a TMS group. The decomposition of several even‐electron ions can be regarded as analogous to that rearrangement.