Enantioselective photochemistry via Lewis acid catalyzed triplet energy transfer

PubMed Central

Blum, Travis R.; Miller, Zachary D.; Bates, Desiree M.; Guzei, Ilia A.; Yoon, Tehshik P.

2017-01-01

Relatively few catalytic systems are able to control the stereochemistry of electronically excited organic intermediates. Here we report the discovery that a chiral Lewis acid complex can catalyze triplet energy transfer from an electronically excited photosensitizer. This strategy is applied to asymmetric [2+2] photocycloadditions of 2′-hydroxychalcones using tris(bipyridyl) ruthenium(II) as a sensitizer. A variety of electrochemical, computational, and spectroscopic data rule out substrate activation via photoinduced electron transfer and instead support a mechanism in which Lewis acid coordination dramatically lowers the triplet energy of the chalcone substrate. We expect that this approach will enable chemists to more broadly apply their detailed understanding of chiral Lewis acid catalysis to stereocontrol in reactions of electronically excited states. PMID:27980203

Highly efficient chemical process to convert mucic acid into adipic acid and DFT studies of the mechanism of the rhenium-catalyzed deoxydehydration.

PubMed

Li, Xiukai; Wu, Di; Lu, Ting; Yi, Guangshun; Su, Haibin; Zhang, Yugen

2014-04-14

The production of bulk chemicals and fuels from renewable bio-based feedstocks is of significant importance for the sustainability of human society. Adipic acid, as one of the most-demanded drop-in chemicals from a bioresource, is used primarily for the large-volume production of nylon-6,6 polyamide. It is highly desirable to develop sustainable and environmentally friendly processes for the production of adipic acid from renewable feedstocks. However, currently there is no suitable bio-adipic acid synthesis process. Demonstrated herein is the highly efficient synthetic protocol for the conversion of mucic acid into adipic acid through the oxorhenium-complex-catalyzed deoxydehydration (DODH) reaction and subsequent Pt/C-catalyzed transfer hydrogenation. Quantitative yields (99 %) were achieved for the conversion of mucic acid into muconic acid and adipic acid either in separate sequences or in a one-step process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rh(III)-Catalyzed Decarboxylative Coupling of Acrylic Acids with Unsaturated Oxime Esters: Carboxylic Acids Serve as Traceless Activators

PubMed Central

2015-01-01

α,β-Unsaturated carboxylic acids undergo Rh(III)-catalyzed decarboxylative coupling with α,β-unsaturated O-pivaloyl oximes to provide substituted pyridines in good yield. The carboxylic acid, which is removed by decarboxylation, serves as a traceless activating group, giving 5-substituted pyridines with very high levels of regioselectivity. Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism. PMID:24512241

Single-step synthesis of styryl phosphonic acids via palladium-catalyzed Heck coupling of vinyl phosphonic acid with aryl halides

DOE PAGES

McNichols, Brett W.; Koubek, Joshua T.; Sellinger, Alan

2017-10-27

Here, we have developed a single step palladium-catalyzed Heck coupling of aryl halides with vinyl phosphonic acid to produce functionalized (E)-styryl phosphonic acids. This pathway utilizes a variety of commercially available aryl halides, vinyl phosphonic acid and Pd(P(tBu) 3) 2 as catalyst. These conditions produce a wide range of styryl phosphonic acids with high purities and good to excellent yields (31–80%).

Single-step synthesis of styryl phosphonic acids via palladium-catalyzed Heck coupling of vinyl phosphonic acid with aryl halides

DOE Office of Scientific and Technical Information (OSTI.GOV)

McNichols, Brett W.; Koubek, Joshua T.; Sellinger, Alan

Here, we have developed a single step palladium-catalyzed Heck coupling of aryl halides with vinyl phosphonic acid to produce functionalized (E)-styryl phosphonic acids. This pathway utilizes a variety of commercially available aryl halides, vinyl phosphonic acid and Pd(P(tBu) 3) 2 as catalyst. These conditions produce a wide range of styryl phosphonic acids with high purities and good to excellent yields (31–80%).

On the Brønsted acid-catalyzed homogeneous hydrolysis of furans.

PubMed

Nikbin, Nima; Caratzoulas, Stavros; Vlachos, Dionisios G

2013-11-01

Furan affairs: Electronic structure calculations of the homogeneous Brønsted acid-catalyzed hydrolysis of 2,5-dimethylfuran show that proton transfer to the β-position is rate-limiting and provides support that the hydrolysis follows general acid catalysis. By means of projected Fukui indices, we show this to be the case for unsubstituted, 2-, and 2,5-substituted furans with electron-donating groups. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lipase-catalyzed synthesis of fattythioic acids from palm oil.

PubMed

Al-Mulla, Emad A Jaffar

2011-01-01

The present work focuses on the synthesis of fattythioic acids (FTAs) by a one-step lipase catalyzed reaction of palm oil with carbonothioic S,S-acid using Lipozyme. The product was characterized using Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance ((1)H NMR) technique and elemental analysis. The effects of various reaction parameters such as reaction time, temperature, amount of enzyme, molar ratio of substrates, and various organic solvents of the reaction system were investigated. The optimum conditions to produce FTAs were respectively, incubation time, 20 h, temperature, 40°C, amount of enzyme, 0.05 g and molar ratio of carbonothioic S,S-acid to palm oil, 5.0:1.0. Hexane was the best solvent for this reaction. The conversion of the products at optimum conditions was around 91%.

A comparative study of ozonation, iron coated zeolite catalyzed ozonation and granular activated carbon catalyzed ozonation of humic acid.

PubMed

Gümüş, Dilek; Akbal, Feryal

2017-05-01

This study compares ozonation (O 3 ), iron coated zeolite catalyzed ozonation (ICZ-O 3 ) and granular activated carbon catalyzed ozonation (GAC-O 3 ) for removal of humic acid from an aqueous solution. The results were evaluated by the removal of DOC that specifies organic matter, UV 254 absorbance, SUVA (Specific Ultraviolet Absorbance at 254 nm) and absorbance at 436 nm. When ozonation was used alone, DOC removal was 21.4% at an ozone concentration of 10 mg/L, pH 6.50 and oxidation time of 60 min. The results showed that the use of ICZ or GAC as a catalyst increased the decomposition of humic acid compared to ozonation alone. DOC removal efficiencies were 62% and 48.1% at pH 6.5, at a catalyst loading of 0.75 g/L, and oxidation time of 60 min for ICZ and GAC, respectively. The oxidation experiments were also carried out using <100 kDa and <50 kDa molecular size fractions of humic acid in the presence of ICZ or GAC. Catalytic ozonation also yielded better DOC and UV 254 reduction in both <50 kDa and <100 kDa fractions of HA compared to ozonation. Copyright © 2017 Elsevier Ltd. All rights reserved.

On-Surface Domino Reactions: Glaser Coupling and Dehydrogenative Coupling of a Biscarboxylic Acid To Form Polymeric Bisacylperoxides.

PubMed

Held, Philipp Alexander; Gao, Hong-Ying; Liu, Lacheng; Mück-Lichtenfeld, Christian; Timmer, Alexander; Mönig, Harry; Barton, Dennis; Neugebauer, Johannes; Fuchs, Harald; Studer, Armido

2016-08-08

Herein we report the on-surface oxidative homocoupling of 6,6'-(1,4-buta-1,3-diynyl)bis(2-naphthoic acid) (BDNA) via bisacylperoxide formation on different Au substrates. By using this unprecedented dehydrogenative polymerization of a biscarboxylic acid, linear poly-BDNA with a chain length of over 100 nm was prepared. It is shown that the monomer BDNA can be prepared in situ at the surface via on-surface Glaser coupling of 6-ethynyl-2-naphthoic acid (ENA). Under the Glaser coupling conditions, BDNA directly undergoes polymerization to give the polymeric peroxide (poly-BDNA) representing a first example of an on-surface domino reaction. It is shown that the reaction outcome varies as a function of surface topography (Au(111) or Au(100)) and also of the surface coverage, to give branched polymers, linear polymers, or 2D metal-organic networks. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Histochemical Demonstration of Protein-Bound Alpha-Acylamido Carboxyl Groups

PubMed Central

Barrnett, Russell J.; Seligman, Arnold M.

1958-01-01

A method has been developed to demonstrate the alpha-acylamido carboxyl groups of protein, taking advantage of the fact that acylamido carboxyl groups are converted to ketonic carbonyls by the action of acetic anhydride and absolute pyridine. The method utilizes deparaffinized sections of tissues fixed in a variety of fixatives. Following the conversion of carboxyls to the methyl ketones, the latter are stained with 2-hydroxy-3-naphthoic acid hydrazide. Control experiments have indicated that methylation of carboxyls prevented staining, as did carbonyl reagents after the carboxyls were transformed to methyl ketones. Leucofuchsin did not stain the ketonic carbonyls, and only elastic tissue stained with 2-hydroxy-3-naphthoic acid hydrazide without the previous use of the catalyzed reaction with anhydride. A brief survey of the reaction on various tissues of the albino rat was made, and the effects of various fixatives were assayed. Of particular interest were certain sites, such as acidophiles of the anterior pituitary gland, where an intense reaction occurred. The possibility exists that certain specific proteins rich in terminal acylamido carboxyl groups, by virtue of their protein side chains or low molecular weight, may be demonstrated by this method. PMID:13525430

Copper-catalyzed formic acid synthesis from CO2 with hydrosilanes and H2O.

PubMed

Motokura, Ken; Kashiwame, Daiki; Miyaji, Akimitsu; Baba, Toshihide

2012-05-18

A copper-catalyzed formic acid synthesis from CO2 with hydrosilanes has been accomplished. The Cu(OAc)2·H2O-1,2-bis(diphenylphosphino)benzene system is highly effective for the formic acid synthesis under 1 atm of CO2. The TON value approached 8100 in 6 h. The reaction pathway was revealed by in situ NMR analysis and isotopic experiments.

Regioselective Copper-Catalyzed Amination of Chlorobenzoic Acids: Synthesis and Solid-State Structures of N-Aryl Anthranilic Acid Derivatives

PubMed Central

Mei, Xuefeng; August, Adam T.; Wolf, Christian

2008-01-01

A chemo- and regioselective copper-catalyzed cross-coupling reaction for effective amination of 2-chlorobenzoic acids with aniline derivatives has been developed. The method eliminates the need for acid protection and produces a wide range of N-aryl anthranilic acid derivatives in up to 99%. The amination was found to proceed with both electron-rich and electron-deficient aryl chlorides and anilines and also utilizes sterically hindered anilines such as 2,6-dimethylaniline and 2-tert-butylaniline. The conformational isomerism of appropriately substituted N-aryl anthranilic acids has been investigated in the solid state. Crystallographic analysis of seven anthranilic acid derivatives showed formation of two distinct supramolecular architectures exhibiting trans-anti- and unprecedented trans-syn-dimeric structures. PMID:16388629

Hydrogen-bonded intermediates and transition states during spontaneous and acid-catalyzed hydrolysis of the carcinogen (+)-anti-BPDE.

PubMed

Palenik, Mark C; Rodriguez, Jorge H

2014-07-07

Understanding mechanisms of (+)-anti-BPDE detoxification is crucial for combating its mutagenic and potent carcinogenic action. However, energetic-structural correlations of reaction intermediates and transition states during detoxification via hydrolysis are poorly understood. To gain mechanistic insight we have computationally characterized intermediate and transition species associated with spontaneous and general-acid catalyzed hydrolysis of (+)-anti-BPDE. We studied the role of cacodylic acid as a proton donor in the rate limiting step. The computed activation energy (ΔG‡) is in agreement with the experimental value for hydrolysis in a sodium cacodylate buffer. Both types of, spontaneous and acid catalyzed, BPDE hydrolysis can proceed through low-entropy hydrogen bonded intermediates prior to formation of transition states whose energies determine reaction activation barriers and rates.

Kinetic mechanism and structural requirements of the amine-catalyzed decarboxylation of oxaloacetic acid.

PubMed

Thalji, Nabil K; Crowe, William E; Waldrop, Grover L

2009-01-02

The kinetic and chemical mechanism of amine-catalyzed decarboxylation of oxaloacetic acid at pH 8.0 has been reevaluated using a new and versatile assay. Amine-catalyzed decarboxylation of oxaloacetic acid proceeds via the formation of an imine intermediate, followed by decarboxylation of the intermediate and hydrolysis to yield pyruvate. The decrease in oxaloacetic acid was coupled to NADH formation by malate dehydrogenase, which allowed the rates of both initial carbinolamine formation (as part of the imination step) and decarboxylation to be determined. By comparing the rates observed for a variety of amines and, in particular, diamines, the structural and electronic requirements for diamine-catalyzed decarboxylation at pH 8.0 were identified. At pH 8.0, monoamines were found to be very poor catalysts, whereas some diamines, most notably ethylenediamine, were excellent catalysts. The results indicate that the second amino group of diamines enhances the rate of imine formation by acting as a proton shuttle during the carbinolamine formation step, which enables diamines to overcome high levels of solvation that would otherwise inhibit carbinolamine, and thus imine, formation. The presence of the second amino group may also enhance the rate of the carbinolamine dehydration step. In contrast to the findings of previous reports, the second amino group participates in the reaction by enhancing the rate of decarboxylation via hydrogen-bonding to the imine nitrogen to either stabilize the negative charge that develops on the imine during decarboxylation or preferentially stabilize the reactive imine over the unreactive enamine tautomer. These results provide insight into the precise catalytic mechanism of several enzymes whose reactions are known to proceed via an imine intermediate.

Lewis acid catalysis and ligand exchange in the asymmetric binaphthol-catalyzed propargylation of ketones.

PubMed

Grayson, Matthew N; Goodman, Jonathan M

2013-09-06

1,1'-Bi-2-naphthol (BINOL)-derived catalysts catalyze the asymmetric propargylation of ketones. Density functional theory (DFT) calculations show that the reaction proceeds via a closed six-membered transition structure (TS) in which the chiral catalyst undergoes an exchange process with the original cyclic boronate ligand. This leads to a Lewis acid type activation mode, not a Brønsted acid process, which accurately predicts the stereochemical outcome observed experimentally.

Grape skins (Vitis vinifera L.) catalyze the in vitro enzymatic hydroxylation of p-coumaric acid to caffeic acid.

PubMed

Arnous, Anis; Meyer, Anne S

2009-12-01

The ability of grape skins to catalyze in vitro conversion of p-coumaric acid to the more potent antioxidant caffeic acid was studied. Addition of different concentrations of p-coumaric to red grape skins (Cabernet Sauvignon) resulted in formation of caffeic acid. This caffeic acid formation (Y) correlated positively and linearly to p-coumaric acid consumption (X): Y = 0.5 X + 9.5; R (2) = 0.96, P < 0.0001. The kinetics of caffeic acid formation with time in response to initial p-coumaric acid levels and at different grape skin concentrations, indicated that the grape skins harboured an o-hydroxylation activity, proposedly a monophenol- or a flavonoid 3'-monooxygenase activity (EC 1.14.18.1 or EC 1.14.13.21). The K (m) of this crude o-hydroxylation activity in the red grape skin was 0.5 mM with p-coumaric acid.

Sequential aldol condensation-transition metal-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids.

PubMed

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-04-15

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. © 2011 American Chemical Society

Palladium-Catalyzed, Copper(I)-Mediated Coupling of Boronic Acids and Benzylthiocyanate. A Cyanide-Free Cyanation of Boronic Acids

PubMed Central

Zhang, Zhihui; Liebeskind, Lanny S.

2008-01-01

A new method for the synthesis of nitriles is described. As a complement to the classic cyanation of aryl halides using cyanide sources and a transition metal catalyst, the palladium-catalyzed cross-coupling of thiocyanates with boronic acids in the presence of copper(I) thiophene-2-carboxylate (CuTC) affords nitriles in good to excellent yields. PMID:16956219

Pilot-scale study on the acid-catalyzed steam explosion of rice straw using a continuous pretreatment system.

PubMed

Chen, Wen-Hua; Tsai, Chia-Chin; Lin, Chih-Feng; Tsai, Pei-Yuan; Hwang, Wen-Song

2013-01-01

A continuous acid-catalyzed steam explosion pretreatment process and system to produce cellulosic ethanol was developed at the pilot-scale. The effects of the following parameters on the pretreatment efficiency of rice straw feedstocks were investigated: the acid concentration, the reaction temperature, the residence time, the feedstock size, the explosion pressure and the screw speed. The optimal presteaming horizontal reactor conditions for the pretreatment process are as follows: 1.7 rpm and 100-110 °C with an acid concentration of 1.3% (w/w). An acid-catalyzed steam explosion is then performed in the vertical reactor at 185 °C for 2 min. Approximately 73% of the total saccharification yield was obtained after the rice straw was pretreated under optimal conditions and subsequent enzymatic hydrolysis at a combined severity factor of 0.4-0.7. Moreover, good long-term stability and durability of the pretreatment system under continuous operation was observed. Copyright © 2012 Elsevier Ltd. All rights reserved.

Conversion of Arylboronic Acids to Tetrazoles Catalyzed by ONO Pincer-Type Palladium Complex.

PubMed

Vignesh, Arumugam; Bhuvanesh, Nattamai S P; Dharmaraj, Nallasamy

2017-01-20

A convenient synthesis of a library of tetrazoles through a novel and operationally simple protocol effecting the direct conversion of arylboronic acids catalyzed by a new ONO pincer-type Pd(II) complex under mild reaction conditions using the readily available reagents is reported. The palladium complex was reused up to four cycles in an open-flask condition.

Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds**

PubMed Central

Best, Daniel; Burns, David J; Lam, Hon Wai

2015-01-01

A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N—H groups are tolerated on the barbituric acid, with no complications arising from N—H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. PMID:25959544

Indium-Catalyzed Reductive Dithioacetalization of Carboxylic Acids with Dithiols: Scope, Limitations, and Application to Oxidative Desulfurization.

PubMed

Nishino, Kota; Minato, Kohei; Miyazaki, Takahiro; Ogiwara, Yohei; Sakai, Norio

2017-04-07

In this study an InI 3 -TMDS (1,1,3,3-tetramethyldisiloxane) reducing system effectively catalyzed the reductive dithioacetalization of a variety of aromatic and aliphatic carboxylic acids with 1,2-ethanedithiol or 1,3-propanedithiol leading to the one-pot preparation of either 1,3-dithiolane derivatives or a 1,3-dithiane derivative. Also, the intact indium catalyst continuously catalyzed the subsequent oxidative desulfurization of an in situ formed 1,3-dithiolane derivative, which led to the preparation of the corresponding aldehydes.

Sequential Aldol Condensation – Transition Metal-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids

PubMed Central

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-01-01

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1′-spirobiindane-7,7′-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. PMID:21417359

β-Amino acid catalyzed asymmetric Michael additions: design of organocatalysts with catalytic acid/base dyad inspired by serine proteases.

PubMed

Yang, Hui; Wong, Ming Wah

2011-09-16

A new type of chiral β-amino acid catalyst has been computationally designed, mimicking the enzyme catalysis of serine proteases. Our catalyst approach is based on the bioinspired catalytic acid/base dyad, namely, a carboxyl and imidazole pair. DFT calculations predict that this designed organocatalyst catalyzes Michael additions of aldehydes to nitroalkenes with excellent enantioselectivities and remarkably high anti diastereoselectivities. The unusual stacked geometry of the enamine intermediate, hydrogen bonding network, and the adoption of an exo transition state are the keys to understand the stereoselectivity. © 2011 American Chemical Society

Regioselective, borinic acid-catalyzed monoacylation, sulfonylation and alkylation of diols and carbohydrates: expansion of substrate scope and mechanistic studies.

PubMed

Lee, Doris; Williamson, Caitlin L; Chan, Lina; Taylor, Mark S

2012-05-16

Synthetic and mechanistic aspects of the diarylborinic acid-catalyzed regioselective monofunctionalization of 1,2- and 1,3-diols are presented. Diarylborinic acid catalysis is shown to be an efficient and general method for monotosylation of pyranoside derivatives bearing three secondary hydroxyl groups (7 examples, 88% average yield). In addition, the scope of the selective acylation, sulfonylation, and alkylation is extended to 1,2- and 1,3-diols not derived from carbohydrates (28 examples); the efficiency, generality, and operational simplicity of this method are competitive with those of state-of-the-art protocols including the broadly applied organotin-catalyzed or -mediated reactions. Mechanistic details of the organoboron-catalyzed processes are explored using competition experiments, kinetics, and catalyst structure-activity relationships. These experiments are consistent with a mechanism in which a tetracoordinate borinate complex reacts with the electrophilic species in the turnover-limiting step of the catalytic cycle.

Kinetics of Maleic Acid and Aluminum Chloride Catalyzed Dehydration and Degradation of Glucose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ximing; Hewetson, Barron B.; Mosier, Nathan S.

We report the positive effect of maleic acid, a dicarboxylic acid, on the selectivity of hexose dehydration to 5-hydroxymethyfurfural (HMF) and subsequent hydrolysis to levulinic and formic acids. We also describe the kinetic analysis of a Lewis acid (AlCl3) alone and in combination with HCl or maleic acid to catalyze the isomerization of glucose to fructose, dehydration of fructose to HMF, hydration of HMF to levulinic and formic acids, and degradation of these compounds to humins. The results show that AlCl3 significantly enhances the rate of glucose conversion to HMF and levulinic acid in the presence of both maleic acidmore » and HCl. In addition, the degradation of HMF to humins, rather than levulinic and formic acids, is reduced by 50% in the presence of maleic acid and AlCl3 compared to HCl combined with AlCl3. The results suggest different reaction mechanisms for the dehydration of glucose and rehydration of HMF between maleic acid and HCl.« less

Copper(II)-Catalyzed Conversion of Aryl/Heteroaryl Boronic Acids, Boronates, and Trifluoroborates into the Corresponding Azides: Substrate Scope and Limitations.

PubMed

Grimes, Kimberly D; Gupte, Amol; Aldrich, Courtney C

2010-05-01

We report the copper(II)-catalyzed conversion of organoboron compounds into the corresponding azide derivatives. A systematic series of phenylboronic acid derivatives is evaluated to examine the importance of steric and electronic effects of the substituents on reaction yield as well as functional group compatibility. Heterocyclic substrates are also shown to participate in this mild reaction while compounds incorporating B-C(sp(3)) bonds are unreactive under the reaction conditions. The copper(II)-catalyzed boronic acid-azide coupling reaction is further extended to both boronate esters and potassium organotrifluoroborate salts. The method described herein complements existing procedures for the preparation of aryl azides from the respective amino, triazene, and halide derivatives and we expect that it will greatly facilitate copper- and ruthenium-catalyzed azide-alkyne cycloaddition reactions for the preparation of diversely functionalized 1-aryl- or 1-heteroaryl-1,2,3-triazoles derivatives.

Alkali-catalyzed low temperature wet crosslinking of plant proteins using carboxylic acids.

PubMed

Reddy, Narendra; Li, Ying; Yang, Yiqi

2009-01-01

We report the development of a new method of alkali-catalyzed low temperature wet crosslinking of plant proteins to improve their breaking tenacity without using high temperatures or phosphorus-containing catalysts used in conventional poly(carboxylic acid) crosslinking of cellulose and proteins. Carboxylic acids are preferred over aldehyde-containing crosslinkers for crosslinking proteins and cellulose because of their low toxicity and cost and ability to improve the desired properties of the materials. However, current knowledge in carboxylic acid crosslinking of proteins and cellulose requires the use of carboxylic acids with at least three carboxylic groups, toxic phosphorous-containing catalysts and curing at high temperatures (150-185 degrees C). The use of high temperatures and low pH in conventional carboxylic acid crosslinking has been reported to cause substantial strength loss and/or undesired changes in the properties of the crosslinked materials. In this research, gliadin, soy protein, and zein fibers have been crosslinked with malic acid, citric acid, and butanetetracarboxylic acid to improve the tenacity of the fibers without using high temperatures and phosphorus-containing catalysts. The new method of wet crosslinking using carboxylic acids containing two or more carboxylic groups will be useful to crosslink proteins for various industrial applications.

Ru (III) Catalyzed Oxidation of Aliphatic Ketones by N-Bromosuccinimide in Aqueous Acetic Acid: A Kinetic Study

PubMed Central

Giridhar Reddy, P.; Ramesh, K.; Shylaja, S.; Rajanna, K. C.; Kandlikar, S.

2012-01-01

Kinetics of Ru (III) catalyzed oxidation of aliphatic ketones such as acetone, ethyl methyl ketone, diethyl ketone, iso-butylmethyl ketone by N-bromosuccinimide in the presence of Hg(II) acetate have been studied in aqueous acid medium. The order of [N-bromosuccinimide] was found to be zero both in catalyzed as well as uncatalyzed reactions. However, the order of [ketone] changed from unity to a fractional one in the presence of Ru (III). On the basis of kinetic features, the probable mechanisms are discussed and individual rate parameters evaluated. PMID:22654610

Identification of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid in Pseudomonas sp. strain E-3.

PubMed

Okuyama, H; Enari, D; Shibahara, A; Yamamoto, K; Morita, N

1996-06-01

A cell-free extract of Pseudomonas sp. strain E-3 catalyzed the conversion of 9-cis-hexadecenoic acid [16:1(9c)] to 9-trans-hexadecenoic acid [16:1(9t)] in the free acid form and when 16:1(9c) was esterified to phosphatidylethanolamine (PE). The cytosolic fraction catalyzed the isomerizations of free 16:1(9c) by itself and of 16:1(9c) esterified to PE in the presence of the membrane fraction. Tracer experiments using [2,2-2H2]16:1(9c) demonstrated that the isomerization of free 16:1(9c) occurred independently of the isomerization of 16:1(9c) esterified to PE, indicating that this bacterium has two types of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid.

The CYP88A cytochrome P450, ent-kaurenoic acid oxidase, catalyzes three steps of the gibberellin biosynthesis pathway

PubMed Central

Helliwell, Chris A.; Chandler, Peter M.; Poole, Andrew; Dennis, Elizabeth S.; Peacock, W. James

2001-01-01

We have shown that ent-kaurenoic acid oxidase, a member of the CYP88A subfamily of cytochrome P450 enzymes, catalyzes the three steps of the gibberellin biosynthetic pathway from ent-kaurenoic acid to GA12. A gibberellin-responsive barley mutant, grd5, accumulates ent-kaurenoic acid in developing grains. Three independent grd5 mutants contain mutations in a gene encoding a member of the CYP88A subfamily of cytochrome P450 enzymes, defined by the maize Dwarf3 protein. Mutation of the Dwarf3 gene gives rise to a gibberellin-responsive dwarf phenotype, but the lesion in the gibberellin biosynthesis pathway has not been identified. Arabidopsis thaliana has two CYP88A genes, both of which are expressed. Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA12. Sequence comparison suggests that the maize Dwarf3 locus also encodes ent-kaurenoic acid oxidase. PMID:11172076

Electrochemical synthesis of formic acid from CO2 catalyzed by Shewanella oneidensis MR-1 whole-cell biocatalyst.

PubMed

Le, Quang Anh Tuan; Kim, Hee Gon; Kim, Yong Hwan

2018-09-01

The electro-biocatalytic conversion of CO 2 into formic acid using whole-cell and isolated biocatalysts is useful as an alternative route for CO 2 sequestration. In this study, Shewanella oneidensis MR-1 (S. oneidensis MR-1), a facultative aerobic bacterium that has been extensively studied for its utility as biofuel cells as well as for the detoxification of heavy metal oxides (i.e., MnO 2 , uranium), has been applied for the first time as a whole-cell biocatalyst for formic acid synthesis from gaseous CO 2 and electrons supplied from an electrode. S. oneidensis MR-1, when aerobically grown in Luria-Bertani (LB) medium, exhibited its ability as a whole-cell biocatalyst for the conversion of CO 2 into formic acid with moderate productivity of 0.59 mM h -1 for 24 h. In addition, an optimization of growth conditions of S. oneidensis MR-1 resulted in a remarkable increase in productivity. The CO 2 reduction reaction catalyzed by S. oneidensis MR-1, when anaerobically grown in newly optimized LB medium supplemented with fumarate and nitrate, exhibited 3.2-fold higher productivity (1.9 mM h -1 for 72 h) compared to that grown aerobically in only LB medium. Furthermore, the average conversion rate of formic acid synthesis catalyzed by S. oneidensis MR-1 when grown in the optimal medium over a period of 72 h was 3.8 mM h -1  g -1 wet-cell, which is 9.6-fold higher than that catalyzed by Methylobacterium extorquens AM1 whole-cells in our previous study. Copyright © 2018 Elsevier Inc. All rights reserved.

Stereochemical analysis of the elimination reaction catalyzed by D-amino-acid oxidase.

PubMed

Cheung, Y F; Walsh, C

1976-06-01

The stereochemistry of the intramolecular proton transfer catalyzed by the flavoenzyme, D-amino-acid oxidase, during the elimination reaction of beta-chloro-alpha-amino acid substrates (Walsh et al. (1973), J. Biol. Chem. 248, 1964) has been established. Both D-erythro- and D-threo-2-amino-3-chloro(2-3H) butyrate have been shown to yield (3R)-2-keto (3-3H)-2- butyrate predominantly. Tritium kinetic isotope effects on the rate of the reaction (4.7 for the D-erythro, and 3.8 for the D-threo compound) and percentages of intramolecular triton transfer (7.2% for the D-erythro- and 2.6% for the D-threo compound) have been measured. Their implications on the mechanism of this unusual elimination reaction are discussed.

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols.

PubMed

Tait, Katrina; Horvath, Alysia; Blanchard, Nicolas; Tam, William

2017-01-01

The acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicylic alkene using alcohol nucleophiles were investigated. Although this acid-catalyzed ring-opening reaction did not cleave the cyclopropane unit as planned, this represent the first examples of ring-openings of cyclopropanated 3-aza-2-oxabicyclo[2.2.1]alkenes that lead to the cleavage of the C-O bond instead of the N-O bond. Different acid catalysts were tested and it was found that pyridinium toluenesulfonate in methanol gave the best yields in the ring-opening reactions. The scope of the reaction was successfully expanded to include primary, secondary, and tertiary alcohol nucleophiles. Through X-ray crystallography, the stereochemistry of the product was determined which confirmed an S N 2-like mechanism to form the ring-opened product.

Behaviors of glucose decomposition during acid-catalyzed hydrothermal hydrolysis of pretreated Gelidium amansii.

PubMed

Jeong, Tae Su; Choi, Chang Ho; Lee, Ji Ye; Oh, Kyeong Keun

2012-07-01

Acid-catalyzed hydrothermal hydrolysis is one path to cellulosic glucose and subsequently to its dehydration end products such as hydroxymethyl furfural (HMF), formic acid and levulinic acid. The effect of sugar decomposition not only lowers the yield of fermentable sugars but also forms decomposition products that inhibit subsequent fermentation. The present experiments were conducted with four different acid catalysts (H(2)SO(4), HNO(3), HCl, and H(3)PO(4)) at various acid normalities (0.5-2.1N) in batch reactors at 180-210 °C. From the results, H(2)SO(4) was the most suitable catalyst for glucose production, but glucose decomposition occurred during the hydrolysis. The glucose production was maximized at 160.7 °C, 2.0% (w/v) H(2)SO(4), and 40 min, but resulted in a low glucan yield of 33.05% due to the decomposition reactions, which generated formic acid and levulinic acid. The highest concentration of levulinic acid, 7.82 g/L, was obtained at 181.2 °C, 2.0% (w/v) H(2)SO(4), and 40 min. Copyright © 2012 Elsevier Ltd. All rights reserved.

Silver-catalyzed double-decarboxylative cross-coupling of α-keto acids with cinnamic acids in water: a strategy for the preparation of chalcones.

PubMed

Zhang, Ning; Yang, Daoshan; Wei, Wei; Yuan, Li; Nie, Fafa; Tian, Laijin; Wang, Hua

2015-03-20

A silver-catalyzed double-decarboxylative protocol has been proposed for the construction of chalcone derivatives via cascade coupling of substituted α-keto acids with cinnamic acids under the mild aqueous conditions. The developed method for constructing C-C bonds via double-decarboxylative reactions is efficient, practical, and environmentally benign by using the readily available starting materials. It should provide a promising synthesis candidate for the formation of diverse and useful chalcone derivatives in the fields of synthetic and pharmaceutical chemistry.

Late-Stage Functionalization of Arylacetic Acids by Photoredox-Catalyzed Decarboxylative Carbon-Heteroatom Bond Formation.

PubMed

Sakakibara, Yota; Ito, Eri; Fukushima, Tomohiro; Murakami, Kei; Itami, Kenichiro

2018-05-02

The rapid transformation of pharmaceuticals and agrochemicals enables access to unexplored chemical space and thus has accelerated the discovery of novel bioactive molecules. Because arylacetic acids are regarded as key structures in bioactive compounds, new transformations of these structures could contribute to drug/agrochemical discovery and chemical biology. This work reports carbon-nitrogen and carbon-oxygen bond formation through the photoredox-catalyzed decarboxylation of arylacetic acids. The reaction shows good functional group compatibility without pre-activation of the nitrogen- or oxygen-based coupling partners. Under similar reaction conditions, carbon-chlorine bond formation was also feasible. This efficient derivatization of arylacetic acids makes it possible to synthesize pharmaceutical analogues and bioconjugates of pharmaceuticals and natural products. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Biotechnological Production of Caffeic Acid by Bacterial Cytochrome P450 CYP199A2

PubMed Central

Arai, Yuka; Kino, Kuniki

2012-01-01

Caffeic acid is a biologically active molecule that has various beneficial properties, including antioxidant, anticancer, and anti-inflammatory activities. In this study, we explored the catalytic potential of a bacterial cytochrome P450, CYP199A2, for the biotechnological production of caffeic acid. When the CYP199A2 enzyme was reacted with p-coumaric acid, it stoichiometrically produced caffeic acid. The crystal structure of CYP199A2 shows that Phe at position 185 is situated directly above, and only 6.35 Å from, the heme iron. This F185 residue was replaced with hydrophobic or hydroxylated amino acids using site-directed mutagenesis to create mutants with novel and improved catalytic properties. In whole-cell assays with the known substrate of CYP199A2, 2-naphthoic acid, only the wild-type enzyme hydroxylated 2-naphthoic acid at the C-7 and C-8 positions, whereas all of the active F185 mutants exhibited a preference for C-5 hydroxylation. Interestingly, several F185 mutants (F185V, F185L, F185I, F185G, and F185A mutants) also acquired the ability to hydroxylate cinnamic acid, which was not hydroxylated by the wild-type enzyme. These results demonstrate that F185 is an important residue that controls the regioselectivity and the substrate specificity of CYP199A2. Furthermore, Escherichia coli cells expressing the F185L mutant exhibited 5.5 times higher hydroxylation activity for p-coumaric acid than those expressing the wild-type enzyme. By using the F185L whole-cell catalyst, the production of caffeic acid reached 15 mM (2.8 g/liter), which is the highest level so far attained in biotechnological production of this compound. PMID:22729547

Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.

PubMed

Jain, Siddharth; Sharma, M P

2010-10-01

Out of various non-edible oil resources, Jatropha curcas oil (JCO) is considered as future feedstock for biodiesel production in India. Limited work is reported on the kinetics of transesterification of high free fatty acids containing oil. The present study reports the results of kinetic study of two-step acid base catalyzed transesterification process carried out at an optimum temperature of 65 °C and 50 °C for esterification and transesterification respectively under the optimum methanol to oil ratio of 3:7 (v/v), catalyst concentration 1% (w/w) for H₂SO₄ and NaOH. The yield of methyl ester (ME) has been used to study the effect of different parameters. The results indicate that both esterification and transesterification reaction are of first order with reaction rate constant of 0.0031 min⁻¹ and 0.008 min⁻¹ respectively. The maximum yield of 21.2% of ME during esterification and 90.1% from transesterification of pretreated JCO has been obtained. Copyright © 2010 Elsevier Ltd. All rights reserved.

Synthesis of 2-monoacylglycerols and structured triacylglycerols rich in polyunsaturated fatty acids by enzyme catalyzed reactions.

PubMed

Rodríguez, Alicia; Esteban, Luis; Martín, Lorena; Jiménez, María José; Hita, Estrella; Castillo, Beatriz; González, Pedro A; Robles, Alfonso

2012-08-10

This paper studies the synthesis of structured triacylglycerols (STAGs) by a four-step process: (i) obtaining 2-monoacylglycerols (2-MAGs) by alcoholysis of cod liver oil with several alcohols, catalyzed by lipases Novozym 435, from Candida antartica and DF, from Rhizopus oryzae, (ii) purification of 2-MAGs, (iii) formation of STAGs by esterification of 2-MAGs with caprylic acid catalyzed by lipase DF, from R. oryzae, and (iv) purification of these STAGs. For the alcoholysis of cod liver oil, absolute ethanol, ethanol 96% (v/v) and 1-butanol were compared; the conditions with ethanol 96% were then optimized and 2-MAG yields of around 54-57% were attained using Novozym 435. In these 2-MAGs, DHA accounted for 24-31% of total fatty acids. In the operational conditions this lipase maintained a stable level of activity over at least 11 uses. These results were compared with those obtained with lipase DF, which deactivated after only three uses. The alcoholysis of cod liver oil and ethanol 96% catalyzed by Novozym 435 was scaled up by multiplying the reactant amounts 100-fold and maintaining the intensity of treatment constant (IOT=3g lipase h/g oil). In these conditions, the 2-MAG yield attained was about 67%; these 2-MAGs contained 36.6% DHA. The synthesized 2-MAGs were separated and purified from the alcoholysis reaction products by solvent extraction using solvents of low toxicity (ethanol and hexane); 2-MAG recovery yield and purity of the target product were approximately 96.4% and 83.9%, respectively. These 2-MAGs were transformed to STAGs using the optimal conditions obtained in a previous work. After synthesis and purification, 93% pure STAGs were obtained, containing 38% DHA at sn-2 position and 60% caprylic acid (CA) at sn-1,3 positions (of total fatty acids at these positions), i.e. the major TAG is the STAG with the structure CA-DHA-CA. Copyright © 2012 Elsevier Inc. All rights reserved.

Brønsted acid-catalyzed decarboxylative redox amination: formation of N-alkylindoles from azomethine ylides by isomerization.

PubMed

Mao, Hui; Wang, Sichang; Yu, Peng; Lv, Huiqing; Xu, Runsheng; Pan, Yuanjiang

2011-02-18

A Brønsted acid-catalyzed decarboxylative redox amination involving aldehydes with 2-carboxyindoline for the synthesis of N-alkylindoles is described. The decarboxylative condensations of aldehydes with 2-carboxyindoline produce azomethine ylides in situ, which then transform into N-alkylindoles by isomerization. © 2011 American Chemical Society

Copper(II)-catalyzed hydroxylation of aryl halides using glycolic acid as a ligand.

PubMed

Xiao, Yan; Xu, Yongnan; Cheon, Hwan-Sung; Chae, Junghyun

2013-06-07

Copper(II)-catalyzed hydroxylation of aryl halides has been developed to afford functionalized phenols. The protocol utilizes the reagent combination of Cu(OH)2, glycolic acid, and NaOH in aqueous DMSO, all of which are cheap, readily available, and easily removable after the reaction. A broad range of aryl iodides and activated aryl bromides were transformed into the corresponding phenols in excellent yields. Moreover, it has been shown that C-O(alkyl)-coupled product, instead of phenol, can be predominantly formed under similar reaction conditions.

Chemical Inactivation of the Cinnamate 4-Hydroxylase Allows for the Accumulation of Salicylic Acid in Elicited Cells1

PubMed Central

Schoch, Guillaume A.; Nikov, Georgi N.; Alworth, William L.; Werck-Reichhart, Danièle

2002-01-01

The cinnamate (CA) 4-hydroxylase (C4H) is a cytochrome P450 that catalyzes the second step of the main phenylpropanoid pathway, leading to the synthesis of lignin, pigments, and many defense molecules. Salicylic acid (SA) is an essential trigger of plant disease resistance. Some plant species can synthesize SA from CA by a mechanism not yet understood. A set of specific inhibitors of the C4H, including competitive, tight-binding, mechanism-based irreversible, and quasi-irreversible inhibitors have been developed with the main objective to redirect cinnamic acid to the synthesis of SA. Competitive inhibitors such as 2-hydroxy-1-naphthoic acid and the heme-coordinating compound 3-(4-pyridyl)-acrylic acid allowed strong inhibition of C4H activity in a tobacco (Nicotiana tabacum cv Bright Yellow [BY]) cell suspension culture. This inhibition was however rapidly relieved either because of substrate accumulation or because of inhibitor metabolism. Substrate analogs bearing a methylenedioxo function such as piperonylic acid (PIP) or a terminal acetylene such as 4-propynyloxybenzoic acid (4PB), 3-propynyloxybenzoic acid, and 4-propynyloxymethylbenzoic acid are potent mechanism-based inactivators of the C4H. PIP and 4PB, the best inactivators in vitro, were also efficient inhibitors of the enzyme in BY cells. Inhibition was not reversed 46 h after cell treatment. Cotreatment of BY cells with the fungal elicitor β-megaspermin and PIP or 4PB led to a dramatic increase in SA accumulation. PIP and 4PB do not trigger SA accumulation in nonelicited cells in which the SA biosynthetic pathway is not activated. Mechanism-based C4H inactivators, thus, are promising tools for the elucidation of the CA-derived SA biosynthetic pathway and for the potentiation of plant defense. PMID:12376665

Direct Synthesis of 5-Aryl Barbituric Acids by Rhodium(II)-Catalyzed Reactions of Arenes with Diazo Compounds.

PubMed

Best, Daniel; Burns, David J; Lam, Hon Wai

2015-06-15

A commercially available rhodium(II) complex catalyzes the direct arylation of 5-diazobarbituric acids with arenes, allowing straightforward access to 5-aryl barbituric acids. Free N-H groups are tolerated on the barbituric acid, with no complications arising from N-H insertion processes. This method was applied to the concise synthesis of a potent matrix metalloproteinase (MMP) inhibitor. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Synthesis of 24-phenyl-24-oxo steroids derived from bile acids by palladium-catalyzed cross coupling with phenylboronic acid. NMR characterization and X-ray structures.

PubMed

Mayorquín-Torres, Martha C; Romero-Ávila, Margarita; Flores-Álamo, Marcos; Iglesias-Arteaga, Martin A

2013-11-01

Palladium-catalyzed cross coupling of phenyboronic acid with acetylated bile acids in which the carboxyl functions have been activated by formation of a mixed anhydride with pivalic anhydride afforded moderate to good yield of 24-phenyl-24-oxo-steroids. Unambiguous assignments of the NMR signals were made with the aid of combined 1D and 2D NMR techniques. X-ray diffraction studies confirmed the obtained structures. Copyright © 2013 Elsevier Inc. All rights reserved.

General synthesis of C-glycosyl amino acids via proline-catalyzed direct electrophilic alpha-amination of C-glycosylalkyl aldehydes.

PubMed

Nuzzi, Andrea; Massi, Alessandro; Dondoni, Alessandro

2008-10-16

Non-natural axially and equatorially linked C-glycosyl alpha-amino acids (glycines, alanines, and CH2-serine isosteres) with either S or R alpha-configuration were prepared by D- and L-proline-catalyzed (de >95%) alpha-amination of C-glycosylalkyl aldehydes using dibenzyl azodicarboxylate as the electrophilic reagent.

Imidazole catalyzes chlorination by unreactive primary chloramines

PubMed Central

Roemeling, Margo D.; Williams, Jared; Beckman, Joseph S.; Hurst, James K.

2015-01-01

Hypochlorous acid and simple chloramines (RNHCl) are stable biologically-derived chlorinating agents. In general, the chlorination potential of HOCl is much greater than that of RNHCl, allowing it to oxidize or chlorinate a much wider variety of reaction partners. However, in this study we demonstrate by kinetic analysis that the reactivity of RNHCl can be dramatically promoted by imidazole and histidyl model compounds via intermediary formation of the corresponding imidazole chloramines. Two biologically relevant reactions were investigated—loss of imidazole-catalyzed chlorinating capacity and phenolic ring chlorination using fluorescein and the tyrosine analog, 4-hydroxyphenylacetic acid (HPA). HOCl reacted stoichiometrically with imidazole, N-acetylhistidine (NAH), or imidazoleacetic acid to generate the corresponding imidazole chloramines which subsequently decomposed. Chloramine (NH2Cl) also underwent a markedly accelerated loss in chlorinating capacity when NAH was present, although in this case NAHCl did not accumulate, indicating that the catalytic intermediate must be highly reactive. Mixing HOCl with 1-methylimidazole (MeIm) led to very rapid loss in chlorinating capacity via formation of a highly reactive chlorinium ion (MeImCl+) intermediate; this behavior suggests that the reactive forms of the analogous imidazole chloramines are their conjugate acids, e.g., the imidazolechlorinium ion (HImCl+). HOCl-generated imidazole chloramine (ImCl) reacted rapidly with fluorescein in a specific acid-catalyzed second order reaction to give 3′-monochloro and 3′,5′-dichloro products. Equilibrium constants for the transchlorination reactions: HOCl + HIm = H2O + ImCl and NH2Cl + HIm = NH3 + ImCl were estimated from the dependence of the rate constants upon [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl+; consistent with this interpretation, MeIm markedly catalyzed fluorescein chlorination by HOCl

Asymmetric synthesis of 5-arylcyclohexenones by rhodium(I)-catalyzed conjugate arylation of racemic 5-(trimethylsilyl)cyclohexenone with arylboronic acids.

PubMed

Chen, Qian; Kuriyama, Masami; Soeta, Takahiro; Hao, Xinyu; Yamada, Ken-ichi; Tomioka, Kiyoshi

2005-09-29

[reaction: see text] A catalytic asymmetric conjugate arylation of racemic 5-(trimethylsilyl)cyclohex-2-enone with arylboronic acids was catalyzed by 3 mol % chiral amidophosphane- or BINAP-Rh(I) in dioxane-water (10:1) to afford trans- and cis-3-aryl-5-(trimethylsilyl)cyclohexanones in high enantioselectivity. Dehydrosilylation of the product mixture with cupric chloride in DMF gave 5-arylcyclohex-2-enones with up to 93% ee in good yield. Enantiofacial selectivity with chiral phosphane-Rh(I) exceeds the trans-diastereoselectivity that is maintained in the achiral or racemic phosphane-Rh(I)-catalyzed conjugate arylation of 5-(trimethylsilyl)cyclohexenone.

Kinetics and mechanism of S-nitrosothiol acid-catalyzed hydrolysis: sulfur activation promotes facile NO+ release.

PubMed

Moran, Ernesto E; Timerghazin, Qadir K; Kwong, Elizabeth; English, Ann M

2011-03-31

The denitrosation of three primary S-nitrosothiols (RSNO; S-nitrosocysteine, S-nitroso-N-acetylcysteine, and S-nitrosoglutathione) and two tertiary RSNOs (S-nitrosopenicillamine and S-nitroso-N-acetylpenicillamine) was investigated in 3.75 M H(2)SO(4) to probe the mechanism of acid-catalyzed RSNO hydrolysis and its dependence on RSNO structure. This reversible reaction was forced to proceed in the denitrosation direction by trapping the nitrosating agent with HN(3). The primary RSNOs exhibited hydrolysis k(obs) values of ∼2 × 10(-4) s(-1), and the tertiary RSNO k(obs) values were an order of magnitude higher. Product analysis by HPLC revealed that the parent thiols (RSHs) were formed in 90-100% yield on 79-99% RSNO denitrosation. Possible hydrolysis mechanisms were studied computationally at the CBS-QB3 level using S-nitrosomethanethiol (MeSNO) as a model RSNO. Consideration of RSNOs as a combination of conventional R-S-N═O, zwitterionic R-S(+)═N-O(-), and RS(-)/NO(+) ion-pair resonance structures was key in understanding the mechanistic details of acid-catalyzed hydrolysis. Protonation of the S-nitroso oxygen or nitrogen activates the sulfur and nucleophilic attack by H(2)O at this atom leads to the formation of the sulfoxide-protonated N-hydroxysulfinamide, MeS(+)(OH)NHOH, with barriers of 19 and 29 kcal/mol, respectively. Proton loss and reprotonation at the nitrogen lead to secondary hydrolysis that produces the sulfinic acid MeS(═O)OH and NH(2)OH. Notably, no low-energy RSNO hydrolysis pathway for HNO release was found in the computational analysis. Protonation of the S-nitroso sulfur gives rise to NO(+) release with a low activation barrier (ΔH(double dagger)(calc) ≈ 6 kcal/mol) and the formation of MeSH in agreement with experiment. The experimental k(obs) can be expressed as K(a)k(1), where K(a) is the acid dissociation constant for protonation of the S-nitroso sulfur and k(1) the pseudo-first-order hydrolysis rate constant. Given the low �

Fractionation of lignocellulosic biopolymers from sugarcane bagasse using formic acid-catalyzed organosolv process.

PubMed

Suriyachai, Nopparat; Champreda, Verawat; Kraikul, Natthakorn; Techanan, Wikanda; Laosiripojana, Navadol

2018-05-01

A one-step formic acid-catalyzed organosolv process using a low-boiling point acid-solvent system was studied for fractionation of sugarcane bagasse. Compared to H 2 SO 4 , the use of formic acid as a promoter resulted in higher efficiency and selectivity on removals of hemicellulose and lignin with increased enzymatic digestibility of the cellulose-enriched solid fraction. The optimal condition from central composite design analysis was determined as 40 min residence time at 159 °C using water/ethanol/ethyl acetate/formic acid in the respective ratios of 43:20:16:21%v/v. Under this condition, a 94.6% recovery of cellulose was obtained in the solid with 80.2% cellulose content while 91.4 and 80.4% of hemicellulose and lignin were removed to the aqueous-alcohol-acid and ethyl acetate phases, respectively. Enzymatic hydrolysis of the solid yielded 84.5% glucose recovery compared to available glucan in the raw material. Physicochemical analysis revealed intact cellulose fibers with decreased crystallinity while the hemicellulose was partially recovered as mono- and oligomeric sugars. High-purity organosolv lignin with < 1% sugar cross-contamination was obtained with no major structural modification according to Fourier-transform infrared spectroscopy. The work represents an alternative process for efficient fractionation of lignocellulosic biomass in biorefineries.

Asymmetric Synthesis of Hydrocarbazoles Catalyzed by an Octahedral Chiral-at-Rhodium Lewis Acid.

PubMed

Huang, Yong; Song, Liangliang; Gong, Lei; Meggers, Eric

2015-12-01

A bis-cyclometalated chiral-at-metal rhodium complex catalyzes the Diels-Alder reaction between N-Boc-protected 3-vinylindoles (Boc = tert-butyloxycarbonyl) and β-carboxylic ester-substituted α,β-unsaturated 2-acyl imidazoles with good-to-excellent regioselectivity (up to 99:1) and excellent diastereoselectivity (>50:1 d.r.) as well as enantioselectivity (92-99% ee) under optimized conditions. The rhodium catalyst serves as a chiral Lewis acid to activate the 2-acyl imidazole dienophile by two-point binding and overrules the preferred regioselectivity of the uncatalyzed reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enzyme-catalyzed cationic epoxide rearrangements in quinolone alkaloid biosynthesis.

PubMed

Zou, Yi; Garcia-Borràs, Marc; Tang, Mancheng C; Hirayama, Yuichiro; Li, Dehai H; Li, Li; Watanabe, Kenji; Houk, K N; Tang, Yi

2017-03-01

Epoxides are highly useful synthons and biosynthons for the construction of complex natural products during total synthesis and biosynthesis, respectively. Among enzyme-catalyzed epoxide transformations, a reaction that is notably missing, in regard to the synthetic toolbox, is cationic rearrangement that takes place under strong acid. This is a challenging transformation for enzyme catalysis, as stabilization of the carbocation intermediate upon epoxide cleavage is required. Here, we discovered two Brønsted acid enzymes that can catalyze two unprecedented epoxide transformations in biology. PenF from the penigequinolone pathway catalyzes a cationic epoxide rearrangement under physiological conditions to generate a quaternary carbon center, while AsqO from the aspoquinolone pathway catalyzes a 3-exo-tet cyclization to forge a cyclopropane-tetrahydrofuran ring system. The discovery of these new epoxide-modifying enzymes further highlights the versatility of epoxides in complexity generation during natural product biosynthesis.

Isotope Effects and Mechanism of the Asymmetric BOROX Brønsted Acid Catalyzed Aziridination Reaction

PubMed Central

Vetticatt, Mathew J.; Desai, Aman A.; Wulff, William D.

2013-01-01

The mechanism of the chiral VANOL-BOROX Brønsted acid catalyzed aziridination reaction of imines and ethyldiazoacetate has been studied using a combination of experimental kinetic isotope effects and theoretical calculations. A stepwise mechanism where reversible formation of a diazonium ion intermediate precedes rate-limiting ring-closure to form the cis-aziridine is implicated. A revised model for the origin of enantio- and diastereoselectivity is proposed based on relative energies of the ring closing transition structures. PMID:23687986

Semicontinuous measurements of organic carbon and acidity during the Pittsburgh air quality study: implications for acid-catalyzed organic aerosol formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. Takahama; C.I. Davidson; S.N. Pandis

2006-04-01

Laboratory evidence suggests that inorganic acid seed particles may increase secondary organic aerosol yields secondary organic aerosol (SOA) through heterogeneous chemistry. Additional laboratory studies, however, report that organic acidity generated in the same photochemical process by which SOA is formed may be sufficient to catalyze these heterogeneous reactions. Understanding the interaction between inorganic acidity and SOA mass is important when evaluating emission controls to meet PM2.5 regulations. Semicontinuous measurements of organic carbon (OC), elemental carbon (EC), and inorganic species from the Pittsburgh Air Quality Study were examined to determine if coupling in the variations of inorganic acidity and OC couldmore » be detected. Significant enhancements of SOA production could not be detected due to inorganic acidity in Western Pennsylvania most of the time, but its signal might have been lost in the noise. If a causal relationship between inorganic acidity and OC is assumed, reductions in OC for Western Pennsylvania that might result from drastic reductions in inorganic acidity were estimated to be 2 {+-} 4% by a regression technique, and an upper bound for this geographic area was estimated to be 5 {+-} 8% based on calculations from laboratory measurements. 48 refs., 7 figs., 3 tabs.« less

Computational Study of Formic Acid Dehydrogenation Catalyzed by Al(III)-Bis(imino)pyridine.

PubMed

Lu, Qian-Qian; Yu, Hai-Zhu; Fu, Yao

2016-03-18

The mechanism of formic acid dehydrogenation catalyzed by the bis(imino)pyridine-ligated aluminum hydride complex (PDI(2-))Al(THF)H (PDI=bis(imino)pyridine) was studied by density functional theory calculations. The overall transformation is composed of two stages: catalyst activation and the catalytic cycle. The catalyst activation begins with O-H bond cleavage of HCOOH promoted by aluminum-ligand cooperation, followed by HCOOH-assisted Al-H bond cleavage, and protonation of the imine carbon atom of the bis(imino)pyridine ligand. The resultant doubly protonated complex ((H,H) PDI)Al(OOCH)3 is the active catalyst for formic acid dehydrogenation. Given this, the catalytic cycle includes β-hydride elimination of ((H,H) PDI)Al(OOCH)3 to produce CO2, and the formed ((H,H) PDI)Al(OOCH)2 H mediates HCOOH to release H2. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Aryl Ketone Synthesis via Tandem Orthoplatinated Triarylphosphite-Catalyzed Addition Reactions of Arylboronic Acids with Aldehydes Followed by Oxidation

PubMed Central

Liao, Yuan-Xi; Hu, Qiao-Sheng

2010-01-01

Tandem orthoplatinated triarylphosphite-catalyzed addition reactions of arylboronic acids with aldehydes followed by oxidation to yield aryl ketones is described. 3-Pentanone was identified as a suitable oxidant for the tandem aryl ketone formation reaction. By using microwave energy, aryl ketones were obtained in high yields with the catalyst loading as low as 0.01%. PMID:20849092

Copper-catalyzed aerobic decarboxylative sulfonylation of cinnamic acids with sodium sulfinates: stereospecific synthesis of (E)-alkenyl sulfones.

PubMed

Jiang, Qing; Xu, Bin; Jia, Jing; Zhao, An; Zhao, Yu-Rou; Li, Ying-Ying; He, Na-Na; Guo, Can-Cheng

2014-08-15

A copper-catalyzed aerobic decarboxylative sulfonylation of alkenyl carboxylic acids with sodium sulfinates is developed. This study offers a new and expedient strategy for stereoselective synthesis of (E)-alkenyl sulfones that are widely present in biologically active natural products and therapeutic agents. Moreover, the transformation is proposed to proceed via a radical process and exhibits a broad substrate scope and good functional group tolerance.

Remarkable co-catalysis by copper(I) oxide in the palladium catalyzed cross-coupling of arylboronic acids with ethyl bromoacetate.

PubMed

Liu, Xing-xin; Deng, Min-zhi

2002-03-21

Copper(I) oxide can effectively co-catalyze the Suzuki type cross-coupling reactions of arylboronic acids with ethyl bromoacetate. As an alternative protocol for introducing the methylenecarboxy group into functionalized molecules, this reaction occurs in the absence of highly toxic thallium compounds or special ligands and should be convenient and practical.

Additional Nucleophile-Free FeCl3-Catalyzed Green Deprotection of 2,4-Dimethoxyphenylmethyl-Protected Alcohols and Carboxylic Acids.

PubMed

Sawama, Yoshinari; Masuda, Masahiro; Honda, Akie; Yokoyama, Hiroki; Park, Kwihwan; Yasukawa, Naoki; Monguchi, Yasunari; Sajiki, Hironao

2016-01-01

The deprotection of the methoxyphenylmethyl (MPM) ether and ester derivatives can be generally achieved by the combinatorial use of a catalytic Lewis acid and stoichiometric nucleophile. The deprotections of 2,4-dimethoxyphenylmethyl (DMPM)-protected alcohols and carboxylic acids were found to be effectively catalyzed by iron(III) chloride without any additional nucleophile to form the deprotected mother alcohols and carboxylic acids in excellent yields. Since the present deprotection proceeds via the self-assembling mechanism of the 2,4-DMPM protective group itself to give the hardly-soluble resorcinarene derivative as a precipitate, the rigorous purification process by silica-gel column chromatography was unnecessary and the sufficiently-pure alcohols and carboxylic acids were easily obtained in satisfactory yields after simple filtration.

A Highly Stereocontrolled, One-Pot Approach toward Pyrrolobenzoxazinones and Pyrroloquinazolinones through a Lewis Acid-Catalyzed [3 + 2]-Cycloannulation Process.

PubMed

Boomhoff, Michael; Ukis, Rostyslav; Schneider, Christoph

2015-08-21

We report herein a stereocontrolled [3 + 2]-cycloheteroannulation of bis-silyl dienediolate 1 with 2-aminobenzoic acid- and 2-aminobenzamide-derived imines to furnish highly substituted pyrrolo[1,2-a]benzoxazinones 3 and pyrrolo[1,2-a]quinazolinones 4, respectively, in good overall yields. This one-pot process rapidly generates molecular complexity and comprises a Lewis acid-catalyzed, vinylogous Mannich reaction of 1 followed by an intramolecular N,O-acetal- and N,N-aminal formation, respectively, which proceeds with good to excellent stereocontrol.

Improved Synthesis of 5-Substituted 1H-Tetrazoles via the [3+2] Cycloaddition of Nitriles and Sodium Azide Catalyzed by Silica Sulfuric Acid

PubMed Central

Du, Zhenting; Si, Changmei; Li, Youqiang; Wang, Yin; Lu, Jing

2012-01-01

A silica supported sulfuric acid catalyzed [3+2] cycloaddition of nitriles and sodium azide to form 5-substituted 1H-tetrazoles is described. The protocol can provide a series of 5-substituted 1H-tetrazoles using silica sulfuric acid from nitriles and sodium azide in DMF in 72%–95% yield. PMID:22606004

Acid-catalyzed hydrogenation during kerosene hydrodewaxing over H/ZSM-5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Longstaff, D.C.; Hanson, F.V.

1996-11-01

Hydrogen addition to the products derived from cracking kerosene over H/ZSM-5 was observed at hydrogen pressures between 4.1-8.7 MPa and at 373-390{degrees}C. At low pressures, kerosene cracking over H/ZSM-5 yielded typical cracked products: aromatics, as well as low molecular weight saturates and olefins. Endothermic reactor temperature profiles were also observed, indicative of cracking reactions. At high hydrogen partial pressures product selectivity was altered in that kerosene cracking gave high yields of low molecular weight paraffins and low yields of olefins and aromatics. Reactor temperature profiles were exothermic, indicative of hydrocracking reactions. A mechanism for acid catalyzed hydrogenation is suggested. Althoughmore » hydrogenation was not observed at lower hydrogen pressures, hydrogen proved beneficial in maintaining catalyst activity at a stable level. Lost catalyst activity was restored by maintaining the catalyst under static hydrogen at 1.4 MPa and 370{degrees}C for 16h. 36 refs., 14 figs., 3 tabs.« less

Selective Formation of Secondary Amides via the Copper-Catalyzed Cross-Coupling of Alkylboronic Acids with Primary Amides

PubMed Central

Rossi, Steven A.; Shimkin, Kirk W.; Xu, Qun; Mori-Quiroz, Luis M.; Watson, Donald A.

2014-01-01

For the first time, a general catalytic procedure for the cross coupling of primary amides and alkylboronic acids is demonstrated. The key to the success of this reaction was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the mono-alkylation of amides. PMID:23611591

Cu-catalyzed formal methylative and hydrogenative carboxylation of alkynes with carbon dioxide: efficient synthesis of α,β-unsaturated carboxylic acids.

PubMed

Takimoto, Masanori; Hou, Zhaomin

2013-08-19

The sequential hydroalumination or methylalumination of various alkynes catalyzed by different catalyst systems, such those based on Sc, Zr, and Ni complexes, and the subsequent carboxylation of the resulting alkenylaluminum species with CO2 catalyzed by an N-heterocyclic carbene (NHC)-copper catalyst have been examined in detail. The regio- and stereoselectivity of the overall reaction relied largely on the hydroalumination or methylalumination reactions, which significantly depended on the catalyst and alkyne substrates. The subsequent Cu-catalyzed carboxylation proceeded with retention of the stereoconfiguration of the alkenylaluminum species. All the reactions could be carried out in one-pot to afford efficiently a variety of α,β-unsaturated carboxylic acids with well-controlled configurations, which are difficult to construct by previously reported methods. This protocol could be practically useful and attractive because of its high regio- and stereoselectivity, simple one-pot reaction operation, and the use of CO2 as a starting material. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed Asymmetric Allylic Alkylation of 4-Substituted Isoxazolidin-5-ones: Straightforward Access to β2,2 -Amino Acids.

PubMed

Nascimento de Oliveira, Marllon; Arseniyadis, Stellios; Cossy, Janine

2018-04-03

We report here an unprecedented and highly enantioselective palladium-catalyzed allylic alkylation applied to 4-substituted isoxazolidin-5-ones. Ultimately, the process provides a straightforward access to β 2,2 -amino acids bearing an all-carbon quaternary stereogenic center in great yields and a high degree of enantioselectivity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Asymmetric synthesis of all-carbon benzylic quaternary stereocenters via Cu-catalyzed conjugate addition of dialkylzinc reagents to 5-(1-arylalkylidene) Meldrum's acids.

PubMed

Fillion, Eric; Wilsily, Ashraf

2006-03-08

The asymmetric synthesis of all-carbon benzylic quaternary stereocenters has been successfully achieved through copper-catalyzed addition of dialkylzinc reagents to 5-(1-arylalkylidene) and 5-(dihydroindenylidene) Meldrum's acids in the presence of phosphoramidite ligand. The resulting benzyl-substituted Meldrum's acids and 1,1-disubstituted indanes were obtained in good yields and up to 99% ee. The significance of substituting the position para, meta, and ortho to the electrophilic benzylic center was highlighted. A benzyl Meldrum's acid product was further transformed to a 3,3-disubstituted 1-indanone and a beta,beta-disubstituted pentanoic acid.

Characterization of a Cross-Linked Protein–Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

PubMed Central

2015-01-01

RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate to detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl-13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process. PMID:24806349

Characterization of a Cross-Linked Protein-Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silakov, Alexey; Grove, Tyler L.; Radle, Matthew I.

2014-08-14

RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate tomore » detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl- 13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process« less

Characterization and optimization of carboxylesterase-catalyzed esterification between capric acid and glycerol for the production of 1-monocaprin in reversed micellar system.

PubMed

Park, Kyung Min; Kwon, Oh Taek; Ahn, Seon Min; Lee, JaeHwan; Chang, Pahn-Shick

2010-02-28

Calotropis procera R. Br. carboxylesterase (EC 3.1.1.1) solubilized in reversed micellar glycerol droplets containing a very small amount of water (less than 5ppm) and stabilized by a surfactant effectively catalyzed the esterification between glycerol and capric acid to produce 1-monocaprin. Reaction variables including surfactant types, organic solvent media, reaction time, G-value ([glycerol]/[capric acid]), R-value ([water]/[surfactant]), pH, temperature, and types of metal ion inhibitors on the carboxylesterase-catalyzed esterification were characterized and optimized to efficiently produce 1-monocaprin. Bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and isooctane were the most effective surfactant and organic solvent medium, respectively, for 1-monocaprin formation in reversed micelles. The optimum G- and R-values were 3.0 and 0.05, respectively, and the optimum pH and temperature were determined to be 10.0 and 60 degrees C, respectively. K(m,app.) and V(max,app.) were calculated from a Hanes-Woolf plot, and the values were 9.64 mM and 2.45 microM/min mg protein, respectively. Among various metal ions, Cu(2+) and Fe(2+) severely inhibited carboxylesterase-catalyzed esterification activity (less than 6.0% of relative activity). Copyright 2009 Elsevier B.V. All rights reserved.

Nickel-Catalyzed Coupling of Alkenes, Aldehydes, and Silyl Triflates

PubMed Central

Ng, Sze-sze; Ho, Chun-Yu; Jamison, Timothy F.

2011-01-01

A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed. PMID:16939275

An Iterative O-Methyltransferase Catalyzes 1,11-Dimethylation of Aspergillus fumigatus Fumaric Acid Amides.

PubMed

Kalb, Daniel; Heinekamp, Thorsten; Schieferdecker, Sebastian; Nett, Markus; Brakhage, Axel A; Hoffmeister, Dirk

2016-10-04

S-adenosyl-l-methionine (SAM)-dependent methyltransfer is a common biosynthetic strategy to modify natural products. We investigated the previously uncharacterized Aspergillus fumigatus methyltransferase FtpM, which is encoded next to the bimodular fumaric acid amide synthetase FtpA. Structure elucidation of two new A. fumigatus natural products, the 1,11-dimethyl esters of fumaryl-l-tyrosine and fumaryl-l-phenylalanine, together with ftpM gene disruption suggested that FtpM catalyzes iterative methylation. Final evidence that a single enzyme repeatedly acts on fumaric acid amides came from an in vitro biochemical investigation with recombinantly produced FtpM. Size-exclusion chromatography indicated that this methyltransferase is active as a dimer. As ftpA and ftpM homologues are found clustered in other fungi, we expect our work will help to identify and annotate natural product biosynthesis genes in various species. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acid-catalyzed conversion of mono- and poly-sugars into platform chemicals: effects of molecular structure of sugar substrate.

PubMed

Hu, Xun; Wu, Liping; Wang, Yi; Song, Yao; Mourant, Daniel; Gunawan, Richard; Gholizadeh, Mortaza; Li, Chun-Zhu

2013-04-01

Hydrolysis/pyrolysis of lignocellulosic biomass always produces a mixture of sugars with distinct structures as intermediates or products. This study tried to elucidate the effects of molecular structure of sugars on their acid-catalyzed conversions in ethanol/water. Location of carbonyl group in sugars (fructose versus glucose) and steric configuration of hydroxyl groups (glucose versus galactose) significantly affected yields of levulinic acid/ester (fructose>glucose>galactose). The dehydration of fructose to 5-(hydroxymethyl)furfural produces much less soluble polymer than that from glucose and galactose, which results in high yields of levulinic acid/ester from fructose. Anhydrate sugar such as levoglucosan tends to undergo the undesirable decomposition to form less levulinic acid/ester. Catalytic behaviors of the poly-sugars (sucrose, maltose, raffinose, β-cyclodextrins) were determined much by their basic units. However, their big molecular sizes create the steric hindrance that significantly affects their followed conversion over solid acid catalyst. Copyright © 2013 Elsevier Ltd. All rights reserved.

Mechanistic insights into iron catalyzed dehydrogenation of formic acid: β-hydride elimination vs. direct hydride transfer.

PubMed

Yang, Xinzheng

2013-09-07

Density functional theory calculations reveal a complete reaction mechanism with detailed energy profiles and transition state structures for the dehydrogenation of formic acid catalyzed by an iron complex, [P(CH2CH2PPh2)3FeH](+). In the cationic reaction pathway, a β-hydride elimination process is confirmed to be the rate-determining step in this catalytic reaction. A potential reaction pathway starting with a direct hydride transfer from HCOO(-) to Fe is found to be possible, but slightly less favorable than the catalytic cycle with a β-hydride elimination step.

Brönsted Acid-Catalyzed One-Pot Synthesis of Indoles from o-Aminobenzyl Alcohols and Furans

PubMed Central

Kuznetsov, Alexey; Makarov, Anton; Rubtsov, Alexandr E.; Butin, Alexander V.; Gevorgyan, Vladimir

2013-01-01

Brönsted acid-catalyzed one-pot synthesis of indoles from o-aminobenzyl alcohols and furans has been developed. This method operates via the in situ formation of aminobenzylfuran, followed by its recyclization into the indole core. The method proved to be efficient for substrates possessing different functional groups, including -OMe, -CO2Cy, and -Br. The resulting indoles can easily be transformed into diverse scaffolds, including 2,3- and 1,2-fused indoles, and indole possessing an α,β-unsaturated ketone moiety at the C-2 position. PMID:24255969

Roles of the Lewis acid and base in the chemical reduction of CO2 catalyzed by frustrated Lewis pairs.

PubMed

Lim, Chern-Hooi; Holder, Aaron M; Hynes, James T; Musgrave, Charles B

2013-09-03

We employ quantum chemical calculations to discover how frustrated Lewis pairs (FLP) catalyze the reduction of CO2 by ammonia borane (AB); specifically, we examine how the Lewis acid (LA) and Lewis base (LB) of an FLP activate CO2 for reduction. We find that the LA (trichloroaluminum, AlCl3) alone catalyzes hydride transfer (HT) to CO2 while the LB (trimesitylenephosphine, PMes3) actually hinders HT; inclusion of the LB increases the HT barrier by ∼8 kcal/mol relative to the reaction catalyzed by LAs only. The LB hinders HT by donating its lone pair to the LUMO of CO2, increasing the electron density on the C atom and thus lowering its hydride affinity. Although the LB hinders HT, it nonetheless plays a crucial role by stabilizing the active FLP·CO2 complex relative to the LA dimer, free CO2, and free LB. This greatly increases the concentration of the reactive complex in the form FLP·CO2 and thus increases the rate of reaction. We expect that the principles we describe will aid in understanding other catalytic CO2 reductions.

Development of a Lewis Base Catalyzed Selenocyclization Reaction

ERIC Educational Resources Information Center

Collins, William

2009-01-01

The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

Mechanistic Study on Cu(II)-Catalyzed Oxidative Cross-Coupling Reaction between Arenes and Boronic Acids under Aerobic Conditions.

PubMed

Zhang, Qian; Liu, Yang; Wang, Ting; Zhang, Xinhao; Long, Chao; Wu, Yun-Dong; Wang, Mei-Xiang

2018-04-25

Substantial attention has been given to modern organocopper chemistry in recent years since copper salts are naturally abundant, cheap, and less toxic in comparison to precious metals. Copper salts also exhibit versatility in catalyzing and mediating carbon-carbon and carbon-heteroatom bond forming reactions. Despite the wide applications of copper salts in catalysis, reaction mechanisms have remained elusive. Using azacalix[1]arene[3]pyridine, an arene-embedded macrocycle, and its isolated and structurally well-defined ArCu(II) and ArCu(III) compounds as molecular tools, we now report an in-depth experimental and computational study on the mechanism of a Cu(II)-catalyzed oxidative cross-coupling reaction between arenes and boronic acids with air as the oxidant. Stoichiometric reaction of organocopper compounds with p-tolylboronic acid validated arylcopper(II) rather than arylcopper(III) as a reactive organometallic intermediate. XPS, EPR, 1 H NMR, HRMS, and UV-vis spectroscopic evidence along with the isolation and quantification of all products and copper speciation, combined with computational analysis of the electronic structure and energetics of the transient intermediates, suggested a reaction sequence involving electrophilic metalation of arene by Cu(II), transmetalation of arylboronate to ArCu(II), the redox reaction between the resulting ArCu(II)Ar' and ArCu(II) to form respectively ArCu(III)Ar' and ArCu(I), and finally reductive elimination of ArCu(III)Ar'. Under aerobic catalytic conditions, all Cu(I) ions released from reductive elimination of ArCu(III)Ar' and from protolysis of ArCu(I) were oxidized by oxygen to regenerate Cu(II) species that enters into the next catalytic cycle. The unraveled reactivity of arylcopper(II) compounds and the catalytic cycle would enrich our knowledge of modern organocopper chemistry and provide useful information in the design of copper-catalyzed reactions.

Recovery of slaughterhouse Animal Fatty Wastewater Sludge by conversion into Fatty Acid Butyl Esters by acid-catalyzed esterification.

PubMed

Wallis, Christopher; Cerny, Muriel; Lacroux, Eric; Mouloungui, Zéphirin

2017-02-01

Two types of Animal Fatty Wastewater Sludges (AFWS 1 and 2) were analyzed and fully characterized to determine their suitability for conversion into biofuel. AFWS 1 was determined to be unsuitable as it contains 68.8wt.% water and only 32.3wt.% dry material, of which only around 80% is lipids to be converted. AFWS 2 has only 15.7wt.% water and 84.3wt.% dry material of which is assumed to 100% lipids as the protein and ash contents were determined to be negligible. The 4-dodecylbenzenesulfonic acid (DBSA) catalyzed esterification of AFWS with 1-butanol was performed in a novel batch reactor fitted with a drying chimney for the "in situ" removal of water and optimized using a non-conventional Doehlert surface response methodology. The optimized condition was found to be 1.66mol equivalent of 1-butanol (with respect to total fatty acid chains), 10wt.% of DBSA catalyst (with respect to AFWS) at 105°C for 3h. Fatty Acid Butyl Esters (FABEs) were isolated in good yields (95%+) as well as a blend of FABEs with 1-butanol (16%). The two potential biofuels were analyzed in comparison with current and analogous biofuels (FAME based biodiesel, and FABE products made from vegetable oils) and were found to exhibit high cetane numbers and flash point values. Copyright © 2016 Elsevier Ltd. All rights reserved.

Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes

PubMed Central

Kondoh, Azusa; Jamison, Timothy F.

2010-01-01

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki-Miyaura cross-coupling applications are also presented. PMID:20107646

Peroxygenase-Catalyzed Fatty Acid Epoxidation in Cereal Seeds (Sequential Oxidation of Linoleic Acid into 9(S),12(S),13(S)-Trihydroxy-10(E)-Octadecenoic Acid).

PubMed Central

Hamberg, M.; Hamberg, G.

1996-01-01

Peroxygenase-catalyzed epoxidation of oleic acid in preparations of cereal seeds was investigated. The 105,000g particle fraction of oat (Avena sativa) seed homogenate showed high peroxygenase activity, i.e. 3034 [plus or minus] 288 and 2441 [plus or minus] 168 nmol (10 min)-1 mg-1 protein in two cultivars, whereas the corresponding fraction obtained from barley (Hordeum vulgare and Hordeum distichum), rye (Secale cereale), and wheat (Triticum aestivum) showed only weak activity, i.e. 13 to 138 nmol (10 min)-1 mg-1 protein. In subcellular fractions of oat seed homogenate, peroxygenase specific activity was highest in the 105,000g particle fraction, whereas lipoxygenase activity was more evenly distributed and highest in the 105,000g supernatant fraction. Incubation of [1-14C]linoleic acid with the 105,000g supernatant of oat seed homogenate led to the formation of several metabolites, i.e. in order of decreasing abundance, 9(S)-hydroxy-10(E),12(Z)-octadecadienoic acid, 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid, cis-9,10-epoxy-12(Z)-octadecenoic acid [mainly the 9(R),10(S) enantiomer], cis-12,13-epoxy-9(Z)-octadecenoic acid [mainly the 12(R),13(S) enantiomer], threo-12,13-dihydroxy-9(Z)-octadecenoic acid, and 12(R),13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoic acid. Incubation of linoleic acid with the 105,000g particle fraction gave a similar, but not identical, pattern of metabolites. Conversion of linoleic acid into 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid, a naturally occurring oxylipin with antifungal properties, took place by a pathway involving sequential catalysis by lipoxygenase, peroxygenase, and epoxide hydrolase. PMID:12226220

Ultra-sensitive EUV resists based on acid-catalyzed polymer backbone breaking

NASA Astrophysics Data System (ADS)

Manouras, Theodoros; Kazazis, Dimitrios; Koufakis, Eleftherios; Ekinci, Yasin; Vamvakaki, Maria; Argitis, Panagiotis

2018-03-01

The main target of the current work was to develop new sensitive polymeric materials for lithographic applications, focusing in particular to EUV lithography, the main chain of which is cleaved under the influence of photogenerated acid. Resist materials based on the cleavage of polymer main chain are in principle capable to create very small structures, to the dimensions of the monomers that they consist of. Nevertheless, in the case of the commonly used nonchemically amplified materials of this type issues like sensitivity and poor etch resistance limit their areas of application, whereas inadequate etch resistance and non- satisfactory process reliability are the usual problems encountered in acid catalysed materials based on main chain scission. In our material design the acid catalyzed chain cleavable polymers contain very sensitive moieties in their backbone while they remain intact in alkaline ambient. These newly synthesized polymers bear in addition suitable functional groups for the achievement of desirable lithographic characteristics (thermal stability, acceptable glass transition temperature, etch resistance, proper dissolution behavior, adhesion to the substrate). Our approach for achieving acceptable etch resistance, a main drawback in other main chain cleavable resists, is based on the introduction of polyaromatic hydrocarbons in the polymeric backbone, whereas the incorporation of an inorganic component further enhances the etch resistance. Single component systems can also be designed following the proposed approach by the incorporation of suitable PAGs and base quencher molecules in the main chain. Resist formulations based on a random copolymer designed according to the described rules evaluated in EUV exhibit ultrahigh sensitivity, capability for high resolution patterning and overall processing characteristics that make them strong candidates for industrial use upon further optimization.

Iridium-Catalyzed Asymmetric Hydrogenation of Ketones with Accessible and Modular Ferrocene-Based Amino-phosphine Acid (f-Ampha) Ligands.

PubMed

Yu, Jianfei; Long, Jiao; Yang, Yuhong; Wu, Weilong; Xue, Peng; Chung, Lung Wa; Dong, Xiu-Qin; Zhang, Xumu

2017-02-03

A series of tridentate ferrocene-based amino-phosphine acid (f-Ampha) ligands have been successfully developed. The f-Ampha ligands are extremely air stable and exhibited excellent performance in the Ir-catalyzed asymmetric hydrogenation of ketones (full conversions, up to >99% ee, and 500 000 TON). DFT calculations were performed to elucidate the reaction mechanism and the importance of the -COOH group. Control experiments also revealed that the -COOH group played a key role in this reaction.

Triphenylphosphine as Ligand for Room Temperature Ni(0)-Catalyzed Cross-Coupling Reactions of Aryl Chlorides with Arylboronic Acids

PubMed Central

Tang, Zhen-Yu; Hu, Qiao-Sheng

2008-01-01

Room temperature Ni(0)-catalyzed cross-coupling reactions of deactivated aryl chlorides with arylboronic acids with inexpensive triphenylphosphine (PPh3) as a supporting ligand have been accomplished in good to excellent yields. Air-stable Ni(PPh3)2Cl2 has also been established as catalyst precursor and highly active nickel catalysts were obtained when the reduction of Ni(PPh3)2Cl2 with n-BuLi was carried out in presence of an aryl chloride. PMID:16497011

Lipase-catalyzed production of short-chain acids terpenyl esters of interest to the food industry.

PubMed

Laboret, F; Perraud, R

1999-12-01

The production of low molecular weight esters as flavor compounds by biotechnological processes has a potential interest for the food industry. The use of natural available substrates and enzymes is an essential part of the process design, because the products may obtain natural label. In this study, direct esterification of citronellol and geraniol with short-chain fatty acids catalyzed by free lipase from Mucor miehei was performed with high yields in n-hexane. The effects of the acid:alcohol ratio on the bioconversion rate of increasing chain length esters was investigated. To reach the optimum yield, substrates and enzyme concentration were determined. The inhibiting effects of acid are strongly attenuated by reducing the quantity of acid and increasing the amount of enzyme in media following the optimum values. Improvements have been made to increase the ester purity. The consumption of excess substrate by adding calculated amounts of acid gives a 10% yield enhancement, and leads to 100% pure terpenyl esters. The first steps to a scale-up application were attempted using a reactor that allowed us to produce ester quantities up to 100 cm3. Separation and purification of the products were treated with success, underlining the lipase stability and efficiency under the conditions of this study. The ability to recover the enzyme, and reusing it in bioconversions, plays a major role in reducing the cost of the overall process.

Novel Enzyme Family Found in Filamentous Fungi Catalyzing trans-4-Hydroxylation of l-Pipecolic Acid

PubMed Central

Hibi, Makoto; Mori, Ryosuke; Miyake, Ryoma; Kawabata, Hiroshi; Kozono, Shoko; Takahashi, Satomi

2016-01-01

Hydroxypipecolic acids are bioactive compounds widely distributed in nature and are valuable building blocks for the organic synthesis of pharmaceuticals. We have found a novel hydroxylating enzyme with activity toward l-pipecolic acid (l-Pip) in a filamentous fungus, Fusarium oxysporum c8D. The enzyme l-Pip trans-4-hydroxylase (Pip4H) of F. oxysporum (FoPip4H) belongs to the Fe(II)/α-ketoglutarate-dependent dioxygenase superfamily, catalyzes the regio- and stereoselective hydroxylation of l-Pip, and produces optically pure trans-4-hydroxy-l-pipecolic acid (trans-4-l-HyPip). Amino acid sequence analysis revealed several fungal enzymes homologous with FoPip4H, and five of these also had l-Pip trans-4-hydroxylation activity. In particular, the homologous Pip4H enzyme derived from Aspergillus nidulans FGSC A4 (AnPip4H) had a broader substrate specificity spectrum than other homologues and reacted with the l and d forms of various cyclic and aliphatic amino acids. Using FoPip4H as a biocatalyst, a system for the preparative-scale production of chiral trans-4-l-HyPip was successfully developed. Thus, we report a fungal family of l-Pip hydroxylases and the enzymatic preparation of trans-4-l-HyPip, a bioactive compound and a constituent of secondary metabolites with useful physiological activities. PMID:26801577

Efficient production of fermentable sugars from oil palm empty fruit bunch by combined use of acid and whole cell culture-catalyzed hydrolyses.

PubMed

Li, Qingxin; Ng, Wei Ting; Puah, Sze Min; Bhaskar, Ravindran Vijay; Soh, Loon Siong; MacBeath, Calum; Parakattil, Pius; Green, Phil; Wu, Jin Chuan

2014-01-01

Empty fruit bunch (EFB) of oil palm trees was converted to fermentable sugars by the combined use of dilute acids and whole fungal cell culture-catalyzed hydrolyses. EFB (5%, w/v) was hydrolyzed in the presence of 0.5% H2 SO4 and 0.2% H3 PO4 at 160 °C for 10 Min. The solid fraction was separated from the acid hydrolysate by filtration and subjected to enzymatic hydrolysis at 50 °C using the whole cell culture of Trichoderma reesei RUT-C30 (2%, w/v), which was prepared by cultivation at 30 °C for 7 days to reach its maximal cellulase activity. The combined hydrolyses of EFB gave a total sugar yield of 82.0%. When used as carbon sources for cultivating Escherichia coli in M9 medium at 37 °C, the combined EFB hydrolysates were shown to be more favorable or at least as good as pure glucose for cell growth in terms of the higher (1.1 times) optical density of E. coli cells. The by-products generated during the acid-catalyzed hydrolysis did not seem to obviously affect cell growth. The combined use of acid and whole cell culture hydrolyses might be a commercially promising method for pretreatment of lignocellulose to get fermentable sugars. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

Convenient synthesis of benzothiazoles and benzimidazoles through Brønsted acid catalyzed cyclization of 2-amino thiophenols/anilines with β-diketones.

PubMed

Mayo, Muhammad Shareef; Yu, Xiaoqiang; Zhou, Xiaoyu; Feng, Xiujuan; Yamamoto, Yoshinori; Bao, Ming

2014-02-07

Brønsted acid catalyzed cyclization reactions of 2-amino thiophenols/anilines with β-diketones under oxidant-, metal-, and radiation-free conditions are described. Various 2-substituted benzothiazoles/benzimidazoles are obtained in satisfactory to excellent yields. Different groups such as methyl, chloro, nitro, and methoxy linked on benzene rings were tolerated under the optimized reaction conditions.

N-Boc amines to oxazolidinones via Pd(II)/bis-sulfoxide/Brønsted acid co-catalyzed allylic C-H oxidation.

PubMed

Osberger, Thomas J; White, M Christina

2014-08-06

A Pd(II)/bis-sulfoxide/Brønsted acid catalyzed allylic C-H oxidation reaction for the synthesis of oxazolidinones from simple N-Boc amines is reported. A range of oxazolidinones are furnished in good yields (avg 63%) and excellent diastereoselectivities (avg 15:1) to furnish products regioisomeric from those previously obtained using allylic C-H amination reactions. Mechanistic studies suggest the role of the phosphoric acid is to furnish a Pd(II)bis-sulfoxide phosphate catalyst that promotes allylic C-H cleavage and π-allylPd functionalization with a weak, aprotic oxygen nucleophile and to assist in catalyst regeneration.

N-Boc Amines to Oxazolidinones via Pd(II)/Bis-sulfoxide/Brønsted Acid Co-Catalyzed Allylic C–H Oxidation

PubMed Central

2015-01-01

A Pd(II)/bis-sulfoxide/Brønsted acid catalyzed allylic C–H oxidation reaction for the synthesis of oxazolidinones from simple N-Boc amines is reported. A range of oxazolidinones are furnished in good yields (avg 63%) and excellent diastereoselectivities (avg 15:1) to furnish products regioisomeric from those previously obtained using allylic C–H amination reactions. Mechanistic studies suggest the role of the phosphoric acid is to furnish a Pd(II)bis-sulfoxide phosphate catalyst that promotes allylic C–H cleavage and π-allylPd functionalization with a weak, aprotic oxygen nucleophile and to assist in catalyst regeneration. PMID:24999765

Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

PubMed

Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

2014-12-01

The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of α,β-unsaturated ketones (Michael acceptor substrates) and α-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and α-keto acids, resulting in 2-hydroxy ketones.

Cytochrome P450 CYP716A254 catalyzes the formation of oleanolic acid from β-amyrin during oleanane-type triterpenoid saponins biosynthesis in Anemone flaccida.

PubMed

Zhan, Chuansong; Ahmed, Shakeel; Hu, Sheng; Dong, Shuang; Cai, Qian; Yang, Tewu; Wang, Xuekui; Li, Xiaohua; Hu, Xuebo

2018-01-01

Anemone flaccida Fr. Shmidt (Ranunculaceae), known as 'Di Wu' in China, is a perennial herb which has long been used to treat arthritis. The rhizome of A. flaccida contains pharmacologically active components i.e. oleanane-type triterpenoid saponins. Oleanolic acid is natural triterpenoid in plants with diverse biological activities. The biosynthesis of oleanolic acid involves cyclization of 2,3-oxidosqualene to the oleanane-type triterpenoid skeleton, followed by a series of oxidation reactions catalyzed by cytochrome P450 monooxygenase (CYP450). Previously, we identified four possible cytochrome P450 genes belonging to CYP716A subfamily from the transcriptome of A. flaccida. In this study, we identified one of those genes "CYP716A254" encoding a cytochrome P450 monooxygenase from A. flaccida that catalyzes the conversion of the β-amyrin into oleanolic acid. The heterologous expression of CYP716A254 in yeast resulted in oxidation of β-amyrin at the C-18 position to oleanolic acid production. These results provide an important basis for further studies of oleanane-type triterpenoid saponins synthesis in A. flaccida. Copyright © 2017 Elsevier Inc. All rights reserved.

Radical scavenging activity of lipophilized products from lipase-catalyzed transesterification of triolein with cinnamic and ferulic acids.

PubMed

Choo, Wee-Sim; Birch, Edward John

2009-02-01

Lipase-catalyzed transesterification of triolein with cinnamic and ferulic acids using an immobilized lipase from Candida antarctica (E.C. 3.1.1.3) was conducted to evaluate the antioxidant activity of the lipophilized products as model systems for enhanced protection of unsaturated oil. The lipophilized products were identified using ESI-MS. Free radical scavenging activity was determined using the DPPH radical method. The polarity of the solvents proved important in determining the radical scavenging activity of the substrates. Ferulic acid showed much higher radical scavenging activity than cinnamic acid, which has limited activity. The esterification of cinnamic acid and ferulic acid with triolein resulted in significant increase and decrease in the radical scavenging activity, respectively. These opposite effects were due to the effect of addition of electron-donating alkyl groups on the predominant mechanism of reaction (hydrogen atom transfer or electron transfer) of a species with DPPH. The effect of esterification of cinnamic acid was confirmed using ethyl cinnamate which greatly enhances the radical scavenging activity. Although, compared to the lipophilized cinnamic acid product, the activity was lower. The radical scavenging activity of the main component isolated from lipophilized cinnamic acid product using solid phase extraction, monocinnamoyl dioleoyl glycerol, was as good as the unseparated mixture of lipophilized product. Based on the ratio of a substrate to DPPH concentration, lipophilized ferulic acid was a much more efficient radical scavenger than lipophilized cinnamic acid.

A novel on-line gold nanoparticle-catalyzed luminol chemiluminescence detector for high-performance liquid chromatography.

PubMed

Zhang, Qun Lin; Wu, Liang; Lv, Chen; Zhang, Xiao Yue

2012-06-15

A novel on-line gold nanoparticle-catalyzed luminol-H(2)O(2) chemiluminescence (CL) detector for high-performance liquid chromatography (HPLC) was established, in which gold nanoparticles were produced by the on-line reaction of H(2)O(2), NaHCO(3)-Na(2)CO(3) (buffer solution of luminol), and HAuCl(4). Eight phenolic compounds (gallic acid, protocatechuic acid, protocatechuic aldehyde, 2,5-dihydroxybenzoic acid, caffeic acid, 2,3-dihydroxybenzoic acid, (+)-catechin, and (-)-epicatechin) were chosen as the model compounds. Every separated phenolic compound in the column eluent strongly enhanced the CL signal of on-line gold nanoparticle-catalyzed luminol system. The CL and UV-visible absorption spectra and transmission electron microscopy studies were carried out, and the CL enhancement mechanism was ascribed to that the presence of phenolic compound promoted the on-line formation of 38-nm-diameter gold nanoparticles, which better catalyzed the luminol-H(2)O(2) CL reaction. The effects of methanol and phosphoric acid in the proposed HPLC configuration were performed by two gradient elution programs, and the baseline profile revealed that on-line gold nanoparticle-catalyzed luminol-H(2)O(2) CL detector had better compatibility than 38 nm gold colloids-luminol-H(2)O(2) CL detector. The proposed CL detector exhibits excellent analytical performance with the low detection limit (S/N=3) of 0.53-0.97 ng/mL (10.6-19.4 pg) phenolic compounds, and offers a new strategy for developing on-line nanoparticle-catalyzed CL detector for HPLC with sensitive analysis. Copyright © 2012 Elsevier B.V. All rights reserved.

Difference analysis of the enzymatic hydrolysis performance of acid-catalyzed steam-exploded corn stover before and after washing with water.

PubMed

Zhu, Junjun; Shi, Linli; Zhang, Lingling; Xu, Yong; Yong, Qiang; Ouyang, Jia; Yu, Shiyuan

2016-10-01

The difference in the enzymatic hydrolysis yield of acid-catalyzed steam-exploded corn stover (ASC) before and after washing with water reached approximately 15 % under the same conditions. The reasons for the difference in the yield between ASC and washed ASC (wASC) were determined through the analysis of the composition of ASC prehydrolyzate and sugar concentration of enzymatic hydrolyzate. Salts produced by neutralization (CaSO4, Na2SO4, K2SO4, and (NH4)2SO4), sugars (polysaccharides, oligosaccharides, and monosaccharides), sugar-degradation products (weak acids and furans), and lignin-degradation products (ethyl acetate extracts and nine main lignin-degradation products) were back-added to wASC. Results showed that these products, except furans, exerted negative effect on enzymatic hydrolysis. According to the characteristics of acid-catalyzed steam explosion pretreatment, the five sugar-degradation products' mixture and salts [Na2SO4, (NH4)2SO4] showed minimal negative inhibition effect on enzymatic hydrolysis. By contrast, furans demonstrated a promotion effect. Moreover, soluble sugars, such as 13 g/L xylose (decreased by 6.38 %), 5 g/L cellobiose (5.36 %), 10 g/L glucose (3.67 %), as well as lignin-degradation products, and ethyl acetate extracts (4.87 %), exhibited evident inhibition effect on enzymatic hydrolysis. Therefore, removal of soluble sugars and lignin-degradation products could effectively promote the enzymatic hydrolysis performance.

Preparation of an amphiphilic resin-supported BINAP ligand and its use for rhodium-catalyzed asymmetric 1,4-addition of phenylboronic acid in water.

PubMed

Otomaru, Yusuke; Senda, Taichi; Hayashi, Tamio

2004-09-16

[reaction: see text] The axially chiral bisphosphine ligand, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap), was supported on a polystyrene-poly(ethylene glycol) copolymer (PS-PEG) resin and was used successfully for the rhodium-catalyzed asymmetric 1,4-addition of phenylboronic acid to alpha,beta-unsaturated ketones in water.

Stereospecific Palladium-Catalyzed C-H Arylation of Pyroglutamic Acid Derivatives at the C3 Position Enabled by 8-Aminoquinoline as a Directing Group.

PubMed

Verho, Oscar; Maetani, Micah; Melillo, Bruno; Zoller, Jochen; Schreiber, Stuart L

2017-09-01

An efficient and stereospecific Pd-catalyzed protocol for the C-H arylation of pyroglutamic acid derivatives that uses 8-aminoquinoline as a directing group is described. The reaction was shown to proceed efficiently with a variety of aryl and heteroaryl iodides bearing different functional groups, giving C3-arylated cis products in good to high yields. Removal of the 8-aminoquinoline unit from these C-H arylation products enables access to synthetically useful cis and trans pyroglutamic acid-based building blocks.

Palladium-atom catalyzed formic acid decomposition and the switch of reaction mechanism with temperature.

PubMed

He, Nan; Li, Zhen Hua

2016-04-21

Formic acid decomposition (FAD) reaction has been an innovative way for hydrogen energy. Noble metal catalysts, especially palladium-containing nanoparticles, supported or unsupported, perform well in this reaction. Herein, we considered the simplest model, wherein one Pd atom is used as the FAD catalyst. With high-level theoretical calculations of CCSD(T)/CBS quality, we investigated all possible FAD pathways. The results show that FAD catalyzed by one Pd atom follows a different mechanism compared with that catalyzed by surfaces or larger clusters. At the initial stage of the reaction, FAD follows a dehydration route and is quickly poisoned by CO due to the formation of very stable PdCO. PdCO then becomes the actual catalyst for FAD at temperatures approximately below 1050 K. Beyond 1050 K, there is a switch of catalyst from PdCO to Pd atom. The results also show that dehydration is always favoured over dehydrogenation on either the Pd-atom or PdCO catalyst. On the Pd-atom catalyst, neither dehydrogenation nor dehydration follows the formate mechanism. In contrast, on the PdCO catalyst, dehydrogenation follows the formate mechanism, whereas dehydration does not. We also systematically investigated the performance of 24 density functional theory methods. We found that the performance of the double hybrid mPW2PLYP functional is the best, followed by the B3LYP, B3PW91, N12SX, M11, and B2PLYP functionals.

Protection of ascorbic acid from copper(II)-catalyzed oxidative degradation in the presence of flavonoids: quercetin, catechin and morin.

PubMed

Beker, Bilge Yildoğan; Sönmezoğlu, Inci; Imer, Filiz; Apak, Reşat

2011-08-01

Protection of ascorbic acid (AA) (vitamin C) from Cu(II)-catalyzed autoxidation is an important aspect of antioxidant chemistry. The autoxidation of AA in the absence and presence of Cu(II) ions was investigated in aerated solution at room temperature and I = 0.1 ionic strength (KNO(3)); the effects of three different flavonoids of similar structure (quercetin, morin and catechin) and their mixtures on the AA system were studied. The concentration of unoxidized AA remaining in solution was measured with the modified cupric ion reducing antioxidant capacity spectrophotometric method. The Cu(II)-catalyzed oxidation at pH 4.5 followed first-order kinetics with respect to AA concentration. Catalytic autoxidation of AA was inhibited to a greater extent by stable quercetin and morin complexes of Cu(II) than by catechin complex. The inhibitive effectiveness order of mixtures gives information about possible synergistic or antagonistic combinations of flavonoid antioxidants, which should be further confirmed with other antioxidant tests.

Synthesis of structured triacylglycerols containing caproic acid by lipase-catalyzed acidolysis: optimization by response surface methodology.

PubMed

Zhou, D; Xu, X; Mu, H; Høy, C E; Adler-Nissen, J

2001-12-01

Production in a batch reactor with a solvent-free system of structured triacylglycerols containing short-chain fatty acids by Lipozyme RM IM-catalyzed acidolysis between rapeseed oil and caproic acid was optimized using response surface methodology (RSM). Reaction time (t(r)), substrate ratio (S(r)), enzyme load (E(l), based on substrate), water content (W(c), based on enzyme), and reaction temperature (T(e)), the five most important parameters for the reaction, were chosen for the optimization. The range of each parameter was selected as follows: t(r) = 5-17 h; E(l) = 6-14 wt %; T(e) = 45-65 degrees C; S(r) = 2-6 mol/mol; and W(c) = 2-12 wt %. The biocatalyst was Lipozyme RM IM, in which Rhizomucor miehei lipase is immobilized on a resin. The incorporation of caproic acid into rapeseed oil was the main monitoring response. In addition, the contents of mono-incorporated structured triacylglycerols and di-incorporated structured triacylglycerols were also evaluated. The optimal reaction conditions for the incorporation of caproic acid and the content of di-incorporated structured triacylglycerols were as follows: t(r) = 17 h; S(r) = 5; E(l) = 14 wt %; W(c) = 10 wt %; T(e) = 65 degrees C. At these conditions, products with 55 mol % incorporation of caproic acid and 55 mol % di-incorporated structured triacylglycerols were obtained.

Improving fatty acid methyl ester production yield in a lipase-catalyzed process using waste frying oils as feedstock.

PubMed

Azócar, Laura; Ciudad, Gustavo; Heipieper, Hermann J; Muñoz, Robinson; Navia, Rodrigo

2010-06-01

The application of waste frying oil (WFO) mixed with rapeseed oil as a feedstock for the effective production of fatty acid methyl esters (FAME) in a lipase-catalyzed process was investigated. The response surface methodology (RSM) was used to optimize the interaction of four variables: the percentage of WFO in the mixed feedstock, the methanol-to-oil ratio, the dosage of Novozym 435 as a catalyst and the temperature. Furthermore, the addition of methanol to the reaction mixture in a second step after 8 h was shown to effectively diminish enzyme inhibition. Using this technique, the model predicted the optimal conditions that would reach 100% FAME, including a methanol-to-oil molar ratio of 3.8:1, 100% (wt) WFO, 15% (wt) Novozym 435 and incubation at 44.5 degrees C for 12 h with agitation at 200 rpm, and verification experiments confirmed the validity of the model. According to the model, the addition of WFO increased FAME production yield, which is largely due to its higher contents of monoacylglycerols, diacylglycerols and free fatty acids (in comparison to rapeseed oil), which are more available substrates for the enzymatic catalysis. Therefore, the replacement of rapeseed oil with WFO in Novozym 435-catalyzed processes could diminish biodiesel production costs since it is a less expensive feedstock that increases the production yield and could be a potential alternative for FAME production on an industrial scale. (c) 2009 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Detection of Nucleic Acids in Complex Samples via Magnetic Microbead-assisted Catalyzed Hairpin Assembly and "DD-A" FRET.

PubMed

Fang, Hongmei; Xie, Nuli; Ou, Min; Huang, Jin; Li, Wenshan; Wang, Qing; Liu, Jianbo; Yang, Xiaohai; Wang, Kemin

2018-05-21

Nucleic acids, as one kind of significant biomarkers, have attracted tremendous attention and exhibited immense value in fundamental studies and clinical applications. In this work, we developed a fluorescent assay for detecting nucleic acids in complex samples based on magnetic microbead (MMB)-assisted catalyzed hairpin assembly (CHA) and donor donor-acceptor fluorescence resonance energy transfer ("DD-A" FRET) signaling mechanism. Three types of DNA hairpin probes were employed in this system, including Capture, H1 (double FAM-labelled probe as FRET donor) and H2 (TAMRA-labelled probe as FRET acceptor). Firstly, the Captures immobilized on MMBs bound to targets in complex samples, and the sequences in Captures that could trigger catalyzed hairpin assembly (CHA) were exposed. Then, target-enriched MMBs complexes were separated and resuspended in the reaction buffer containing H1 and H2. As a result, numerous H1-H2 duplexes were formed during CHA process, inducing an obvious FRET signal. In contrast, CHA could not be trigger and the FRET signal was weak while target was absent. With the aid of magnetic separation and "DD-A" FRET, it was demonstrated to effectively eliminate errors from background interference. Importantly, this strategy realized amplified detection in buffer, with detection limits of microRNA as low as 34 pM. Furthermore, this method was successfully applied to detect microRNA-21 in serum and cell culture media. The results showed that our method has the potential for biomedical research and clinical application.

Influence of Pb 2+ ions in the H 2 oxidation on Pt catalyzed hydrogen diffusion anodes in sulfuric acid: presence of oscillatory phenomena

NASA Astrophysics Data System (ADS)

Expósito, E.; Sánchez-Sánchez, C. M.; Solla-Gullón, J.; Montiel, V.

The influence of Pb 2+ ions in sulfuric acid medium on the behavior of a platinum catalyzed hydrogen diffusion electrode (HDE) in a filter press reactor has been studied. A voltammetric study of the H 2 oxidation reaction on a polyoriented platinum electrode and a platinum rotating disk electrode (RDE) in presence of lead ions in solution has also been carried out. Potential oscillations were found in galvanostatic experiments of H 2 oxidation using a HDE catalyzed with platinum when Pb 2+ ions are present in solution. This oscillatory phenomenon was also observed when hydrogen oxidation was carried out in presence of Pb 2+ ions using a platinum RDE. The oscillatory behavior observed has been attributed to an adsorption-oxidation-desorption process of lead on the platinum surface. Due to the low solubility of Pb 2+ in sulfuric acid, at high values of coverage, lead is oxidised to insoluble lead sulfate that blocks the Pt surface. The coupling of the dissolution of lead sulfate and the Pb electrochemical adsorption-oxidation processes cause the oscillatory phenomenon.

Rhodium-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds: large accelerating effects of bases and ligands.

PubMed

Itooka, Ryoh; Iguchi, Yuki; Miyaura, Norio

2003-07-25

The effects of ligands and bases in the rhodium(I)-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds were reinvestigated to carry out the reaction under mild conditions. Rhodium(I) complexes possessing a 1,5-cyclooctadiene (cod) and a hydroxo ligand such as [RhOH(cod)](2) exhibited excellent catalyst activities compared to those of the corresponding rhodium-acac or -chloro complexes and their phosphine derivatives. The reaction was further accelerated in the presence of KOH, thus allowing the 1,4-addition even at 0 degrees C. A cationic rhodium(I)-(R)-binap complex, [Rh(R-binap)(nbd)]BF(4), catalyzed the reaction at 25-50 degrees C in the presence of Et(3)N with high enantioselectivities of up to 99% ee for alpha,beta-unsaturated ketones, 92% for aldehydes, 94% for esters, and 92% for amides.

A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Nan; Ferrer, Jean-Luc; Moon, Hong S

2012-01-01

Known SABATH methyltransferases, all of which were identified from seed plants, catalyze methylation of either the carboxyl group of a variety of low molecular weight metabolites or the nitrogen moiety of precursors of caffeine. In this study, the SABATH family from the bryophyte Physcomitrella patens was identified and characterized. Four SABATH-like sequences (PpSABATH1, PpSABATH2, PpSABATH3, and PpSABATH4) were identified from the P. patens genome. Only PpSABATH1 and PpSABATH2 showed expression in the leafy gametophyte of P. patens. Full-length cDNAs of PpSABATH1 and PpSABATH2 were cloned and expressed in soluble form in Escherichia coli. Recombinant PpSABATH1 and PpSABATH2 were tested formore » methyltransferase activity with a total of 75 compounds. While showing no activity with carboxylic acids or nitrogen-containing compounds, PpSABATH1 displayed methyltransferase activity with a number of thiols. PpSABATH2 did not show activity with any of the compounds tested. Among the thiols analyzed, PpSABATH1 showed the highest level of activity with thiobenzoic acid with an apparent Km value of 95.5 lM, which is comparable to those of known SABATHs. Using thiobenzoic acid as substrate, GC MS analysis indicated that the methylation catalyzed by PpSABATH1 is on the sulfur atom. The mechanism for S-methylation of thiols catalyzed by PpSABATH1 was partially revealed by homology-based structural modeling. The expression of PpSABATH1 was induced by the treatment of thiobenzoic acid. Further transgenic studies showed that tobacco plants overexpressing PpSABATH1 exhibited enhanced tolerance to thiobenzoic acid, suggesting that PpSABATH1 have a role in the detoxification of xenobiotic thiols.« less

Caffeine-catalyzed gels.

PubMed

DiCiccio, Angela M; Lee, Young-Ah Lucy; Glettig, Dean L; Walton, Elizabeth S E; de la Serna, Eva L; Montgomery, Veronica A; Grant, Tyler M; Langer, Robert; Traverso, Giovanni

2018-07-01

Covalently cross-linked gels are utilized in a broad range of biomedical applications though their synthesis often compromises easy implementation. Cross-linking reactions commonly utilize catalysts or conditions that can damage biologics and sensitive compounds, producing materials that require extensive post processing to achieve acceptable biocompatibility. As an alternative, we report a batch synthesis platform to produce covalently cross-linked materials appropriate for direct biomedical application enabled by green chemistry and commonly available food grade ingredients. Using caffeine, a mild base, to catalyze anhydrous carboxylate ring-opening of diglycidyl-ether functionalized monomers with citric acid as a tri-functional crosslinking agent we introduce a novel poly(ester-ether) gel synthesis platform. We demonstrate that biocompatible Caffeine Catalyzed Gels (CCGs) exhibit dynamic physical, chemical, and mechanical properties, which can be tailored in shape, surface texture, solvent response, cargo release, shear and tensile strength, among other potential attributes. The demonstrated versatility, low cost and facile synthesis of these CCGs renders them appropriate for a broad range of customized engineering applications including drug delivery constructs, tissue engineering scaffolds, and medical devices. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Glycerol Dehydration to Acrolein Catalyzed by ZSM‐5 Zeolite in Supercritical Carbon Dioxide Medium

PubMed Central

Zou, Bin; Ren, Shoujie

2016-01-01

Abstract Supercritical carbon dioxide (SC‐CO2) has been used for the first time as a reaction medium for the dehydration of glycerol to acrolein catalyzed by a solid acid. Unprecedented catalyst stability over 528 hours of time‐on‐stream was achieved and the rate of coke deposition on the zeolite catalyst was the lowest among extensive previous studies, showing potential for industrial application. Coking pathways in SC‐CO2 were also elucidated for future development. The results have potential implications for other dehydration reactions catalyzed by solid acids. PMID:27796088

Dehydrogenation, disproportionation and transfer hydrogenation reactions of formic acid catalyzed by molybdenum hydride compounds.

PubMed

Neary, Michelle C; Parkin, Gerard

2015-03-01

The cyclopentadienyl molybdenum hydride compounds, Cp R Mo(PMe 3 ) 3- x (CO) x H (Cp R = Cp, Cp*; x = 0, 1, 2 or 3), are catalysts for the dehydrogenation of formic acid, with the most active catalysts having the composition Cp R Mo(PMe 3 ) 2 (CO)H. The mechanism of the catalytic cycle is proposed to involve (i) protonation of the molybdenum hydride complex, (ii) elimination of H 2 and coordination of formate, and (iii) decarboxylation of the formate ligand to regenerate the hydride species. NMR spectroscopy indicates that the nature of the resting state depends on the composition of the catalyst. For example, (i) the resting states for the CpMo(CO) 3 H and CpMo(PMe 3 )(CO) 2 H systems are the hydride complexes themselves, (ii) the resting state for the CpMo(PMe 3 ) 3 H system is the protonated species [CpMo(PMe 3 ) 3 H 2 ] + , and (iii) the resting state for the CpMo(PMe 3 ) 2 (CO)H system is the formate complex, CpMo(PMe 3 ) 2 (CO)(κ 1 -O 2 CH), in the presence of a high concentration of formic acid, but CpMo(PMe 3 ) 2 (CO)H when the concentration of acid is low. While CO 2 and H 2 are the principal products of the catalytic reaction induced by Cp R Mo(PMe 3 ) 3- x (CO) x H, methanol and methyl formate are also observed. The generation of methanol is a consequence of disproportionation of formic acid, while methyl formate is a product of subsequent esterification. The disproportionation of formic acid is a manifestation of a transfer hydrogenation reaction, which may also be applied to the reduction of aldehydes and ketones. Thus, CpMo(CO) 3 H also catalyzes the reduction of a variety of ketones and aldehydes to alcohols by formic acid, via a mechanism that involves ionic hydrogenation.

Membrane protein complexes catalyze both 4- and 3-hydroxylation of cinnamic acid derivatives in monolignol biosynthesis

PubMed Central

Chen, Hsi-Chuan; Li, Quanzi; Shuford, Christopher M.; Liu, Jie; Muddiman, David C.; Sederoff, Ronald R.; Chiang, Vincent L.

2011-01-01

The hydroxylation of 4- and 3-ring carbons of cinnamic acid derivatives during monolignol biosynthesis are key steps that determine the structure and properties of lignin. Individual enzymes have been thought to catalyze these reactions. In stem differentiating xylem (SDX) of Populus trichocarpa, two cinnamic acid 4-hydroxylases (PtrC4H1 and PtrC4H2) and a p-coumaroyl ester 3-hydroxylase (PtrC3H3) are the enzymes involved in these reactions. Here we present evidence that these hydroxylases interact, forming heterodimeric (PtrC4H1/C4H2, PtrC4H1/C3H3, and PtrC4H2/C3H3) and heterotrimeric (PtrC4H1/C4H2/C3H3) membrane protein complexes. Enzyme kinetics using yeast recombinant proteins demonstrated that the enzymatic efficiency (Vmax/km) for any of the complexes is 70–6,500 times greater than that of the individual proteins. The highest increase in efficiency was found for the PtrC4H1/C4H2/C3H3-mediated p-coumaroyl ester 3-hydroxylation. Affinity purification-quantitative mass spectrometry, bimolecular fluorescence complementation, chemical cross-linking, and reciprocal coimmunoprecipitation provide further evidence for these multiprotein complexes. The activities of the recombinant and SDX plant proteins demonstrate two protein-complex–mediated 3-hydroxylation paths in monolignol biosynthesis in P. trichocarpa SDX; one converts p-coumaric acid to caffeic acid and the other converts p-coumaroyl shikimic acid to caffeoyl shikimic acid. Cinnamic acid 4-hydroxylation is also mediated by the same protein complexes. These results provide direct evidence for functional involvement of membrane protein complexes in monolignol biosynthesis. PMID:22160716

Novel Dextranase Catalyzing Cycloisomaltooligosaccharide Formation and Identification of Catalytic Amino Acids and Their Functions Using Chemical Rescue Approach*

PubMed Central

Kim, Young-Min; Kiso, Yoshiaki; Muraki, Tomoe; Kang, Min-Sun; Nakai, Hiroyuki; Saburi, Wataru; Lang, Weeranuch; Kang, Hee-Kwon; Okuyama, Masayuki; Mori, Haruhide; Suzuki, Ryuichiro; Funane, Kazumi; Suzuki, Nobuhiro; Momma, Mitsuru; Fujimoto, Zui; Oguma, Tetsuya; Kobayashi, Mikihiko; Kim, Doman; Kimura, Atsuo

2012-01-01

A novel endodextranase from Paenibacillus sp. (Paenibacillus sp. dextranase; PsDex) was found to mainly produce isomaltotetraose and small amounts of cycloisomaltooligosaccharides (CIs) with a degree of polymerization of 7–14 from dextran. The 1,696-amino acid sequence belonging to the glycosyl hydrolase family 66 (GH-66) has a long insertion (632 residues; Thr451–Val1082), a portion of which shares identity (35% at Ala39–Ser1304 of PsDex) with Pro32–Ala755 of CI glucanotransferase (CITase), a GH-66 enzyme that catalyzes the formation of CIs from dextran. This homologous sequence (Val837–Met932 for PsDex and Tyr404–Tyr492 for CITase), similar to carbohydrate-binding module 35, was not found in other endodextranases (Dexs) devoid of CITase activity. These results support the classification of GH-66 enzymes into three types: (i) Dex showing only dextranolytic activity, (ii) Dex catalyzing hydrolysis with low cyclization activity, and (iii) CITase showing CI-forming activity with low dextranolytic activity. The fact that a C-terminal truncated enzyme (having Ala39–Ser1304) has 50% wild-type PsDex activity indicates that the C-terminal 392 residues are not involved in hydrolysis. GH-66 enzymes possess four conserved acidic residues (Asp189, Asp340, Glu412, and Asp1254 of PsDex) of catalytic candidates. Their amide mutants decreased activity (11,500 to 140,000 times), and D1254N had 36% activity. A chemical rescue approach was applied to D189A, D340G, and E412Q using α-isomaltotetraosyl fluoride with NaN3. D340G or E412Q formed a β- or α-isomaltotetraosyl azide, respectively, strongly indicating Asp340 and Glu412 as a nucleophile and acid/base catalyst, respectively. Interestingly, D189A synthesized small sized dextran from α-isomaltotetraosyl fluoride in the presence of NaN3. PMID:22461618

Theoretical study on the mechanism of aqueous synthesis of formic acid catalyzed by [Ru3+]-EDTA complex.

PubMed

Chen, Zhe-Ning; Chan, Kwong-Yu; Pulleri, Jayasree K; Kong, Jing; Hu, Hao

2015-02-16

Because formic acid can be effectively decomposed by catalysis into very pure hydrogen gas, the synthesis of formic acid, especially using CO and H2O as an intermediate of the water gas shift reaction (WGSR), bears important application significance in industrial hydrogen gas production. Here we report a theoretical study on the mechanism of efficient preparation of formic acid using CO and H2O catalyzed by a water-soluble [Ru(3+)]-EDTA complex. To determine the feasibility of using the [Ru(3+)]-EDTA catalyst to produce CO-free hydrogen gas in WGSR, two probable reaction paths have been examined: one synthesizes formic acid, while the other converts the reactants directly into CO2 and H2, the final products of WGSR. Our calculation results provide a detailed mechanistic rationalization for the experimentally observed selective synthesis of HCOOH by the [Ru(3+)]-EDTA catalyst. The results support the applicability of using the [Ru(3+)]-EDTA catalyst to efficiently synthesize formic acid for hydrogen production. Careful analyses of the electronic structure and interactions of different reaction complexes suggest that the selectivity of the reaction processes is achieved through the proper charge/valence state of the metal center of the [Ru(3+)]-EDTA complex. With the catalytic roles of the ruthenium center and the EDTA ligand being carefully understood, the detailed mechanistic information obtained in this study will help to design more efficient catalysts for the preparation of formic acid and further to produce CO-free H2 at ambient temperature.

Acid-catalyzed condensed-phase reactions of limonene and terpineol and their impacts on gas-to-particle partitioning in the formation of organic aerosols.

PubMed

Li, Yong Jie; Cheong, Gema Y L; Lau, Arthur P S; Chan, Chak K

2010-07-15

We investigated the condensed-phase reactions of biogenic VOCs with C double bond C bonds (limonene, C(10)H(16), and terpineol, C(10)H(18)O) catalyzed by sulfuric acid by both bulk solution (BS) experiments and gas-particle (GP) experiments using a flow cell reactor. Product analysis by gas chromatography-mass spectrometry (GC-MS) showed that cationic polymerization led to dimeric and trimeric product formation under conditions of relative humidity (RH) <20% (in the GP experiments) and a sulfuric acid concentration of 57.8 wt % (in the BS experiments), while hydration occurred under conditions of RH > 20% (in the GP experiments) and sulfuric acid concentrations of 46.3 wt % or lower (in the BS experiments). Apparent partitioning coefficients (K(p,rxn)) were estimated from the GP experiments by including the reaction products. Only under extremely low RH conditions (RH < 5%) did the values of K(p,rxn) ( approximately 5 x 10(-6) m(3)/microg for limonene and approximately 2 x 10(-5) m(3)/microg for terpineol) substantially exceed the physical partitioning coefficients (K(p) = 6.5 x 10(-8) m(3)/microg for limonene and =2.3 x 10(-6) m(3)/microg for terpineol) derived from the absorptive partitioning theory. At RH higher than 5%, the apparent partitioning coefficients (K(p,rxn)) of both limonene and terpineol were in the same order of magnitude as the K(p) values derived from the absorptive partitioning theory. Compared with other conditions including VOC concentration and degree of neutralization (by ammonium) of acidic particles, RH is a critical parameter that influences both the reaction mechanisms and the uptake ability (K(p,rxn) values) of these processes. The finding suggests that RH needs to be considered when taking the effects of acid-catalyzed reactions into account in estimating organic aerosol formation from C double bond C containing VOCs.

Glycerol Dehydration to Acrolein Catalyzed by ZSM-5 Zeolite in Supercritical Carbon Dioxide Medium.

PubMed

Zou, Bin; Ren, Shoujie; Ye, X Philip

2016-12-08

Supercritical carbon dioxide (SC-CO 2 ) has been used for the first time as a reaction medium for the dehydration of glycerol to acrolein catalyzed by a solid acid. Unprecedented catalyst stability over 528 hours of time-on-stream was achieved and the rate of coke deposition on the zeolite catalyst was the lowest among extensive previous studies, showing potential for industrial application. Coking pathways in SC-CO 2 were also elucidated for future development. The results have potential implications for other dehydration reactions catalyzed by solid acids. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Aromatic aldehyde-catalyzed gas-phase decarboxylation of amino acid anion via imine intermediate: An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Xiang, Zhang

2013-10-01

It is generally appreciated that carbonyl compound can promote the decarboxylation of the amino acid. In this paper, we have performed the experimental and theoretical investigation into the gas-phase decarboxylation of the amino acid anion catalyzed by the aromatic aldehyde via the imine intermediate on the basis of the tandem mass spectrometry (MS/MS) technique and density functional theory (DFT) calculation. The results show that the aromatic aldehyde can achieve a remarkable catalytic effect. Moreover, the catalytic mechanism varies according to the type of amino acid: (i) The decarboxylation of α-amino acid anion is determined by the direct dissociation of the Csbnd C bond adjacent to the carboxylate, for the resulting carbanion can be well stabilized by the conjugation between α-carbon, Cdbnd N bond and benzene ring. (ii) The decarboxylation of non-α-amino acid anion proceeds via a SN2-like transition state, in which the dissociation of the Csbnd C bond adjacent to the carboxylate and attacking of the resulting carbanion to the Cdbnd N bond or benzene ring take place at the same time. Specifically, for β-alanine, the resulting carbanion preferentially attacks the benzene ring leading to the benzene anion, because attacking the Cdbnd N bond in the decarboxylation can produce the unstable three or four-membered ring anion. For the other non-α-amino acid anion, the Cdbnd N bond preferentially participates in the decarboxylation, which leads to the pediocratic nitrogen anion.

Impact of Zeolite Aging in Hot Liquid Water on Activity for Acid-Catalyzed Dehydration of Alcohols.

PubMed

Vjunov, Aleksei; Derewinski, Miroslaw A; Fulton, John L; Camaioni, Donald M; Lercher, Johannes A

2015-08-19

The location and stability of Brønsted acid sites catalytically active in zeolites during aqueous phase dehydration of alcohols were studied on the example of cyclohexanol. The catalytically active hydronium ions originate from Brønsted acid sites (BAS) of the zeolite that are formed by framework tetrahedral Si atom substitution by Al. Al K-edge extended X-ray absorption fine structure (EXAFS) and (27)Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopies in combination with density functional theory (DFT) calculations are used to determine the distribution of tetrahedral Al sites (Al T-sites) both qualitatively and quantitatively for both parent and HBEA catalysts aged in water prior to catalytic testing. The aging procedure leads to partial degradation of the zeolite framework evidenced from the decrease of material crystallinity (XRD) as well as sorption capacity (BET). With the exception of one commercial zeolite sample, which had the highest concentration of framework silanol-defects, there is no evidence of Al coordination modification after aging in water. The catalyst weight-normalized dehydration rate correlated best with the sum of strong and weak Brønsted acidic protons both able to generate the hydrated hydronium ions. All hydronium ions were equally active for the acid-catalyzed reactions in water. Zeolite aging in hot water prior to catalysis decreased the weight normalized dehydration reaction rate compared to that of the parent HBEA, which is attributed to the reduced concentration of accessible Brønsted acid sites. Sites are hypothesized to be blocked due to reprecipitation of silica dissolved during framework hydrolysis in the aging procedure.

PhdA Catalyzes the First Step of Phenazine-1-Carboxylic Acid Degradation in Mycobacterium fortuitum.

PubMed

Costa, Kyle C; Moskatel, Leon S; Meirelles, Lucas A; Newman, Dianne K

2018-05-15

Phenazines are a class of bacterially produced redox-active metabolites that are found in natural, industrial, and clinical environments. In Pseudomonas spp., phenazine-1-carboxylic acid (PCA)-the precursor of all phenazine metabolites-facilitates nutrient acquisition, biofilm formation, and competition with other organisms. While the removal of phenazines negatively impacts these activities, little is known about the genes or enzymes responsible for phenazine degradation by other organisms. Here, we report that the first step of PCA degradation by Mycobacterium fortuitum is catalyzed by a ph enazine- d egrading decarboxylase (PhdA). PhdA is related to members of the UbiD protein family that rely on a prenylated flavin mononucleotide cofactor for activity. The gene for PhdB, the enzyme responsible for cofactor synthesis, is present in a putative operon with the gene encoding PhdA in a region of the M. fortuitum genome that is essential for PCA degradation. PhdA and PhdB are present in all known PCA-degrading organisms from the Actinobacteria M. fortuitum can also catabolize other Pseudomonas -derived phenazines such as phenazine-1-carboxamide, 1-hydroxyphenazine, and pyocyanin. On the basis of our previous work and the current characterization of PhdA, we propose that degradation converges on a common intermediate: dihydroxyphenazine. An understanding of the genes responsible for degradation will enable targeted studies of phenazine degraders in diverse environments. IMPORTANCE Bacteria from phylogenetically diverse groups secrete redox-active metabolites that provide a fitness advantage for their producers. For example, phenazines from Pseudomonas spp. benefit the producers by facilitating anoxic survival and biofilm formation and additionally inhibit competitors by serving as antimicrobials. Phenazine-producing pseudomonads act as biocontrol agents by leveraging these antibiotic properties to inhibit plant pests. Despite this importance, the fate of phenazines in

Kinetics of non-catalyzed hydrolysis of tannin in high temperature liquid water*

PubMed Central

Lu, Li-li; Lu, Xiu-yang; Ma, Nan

2008-01-01

High temperature liquid water (HTLW) has drawn increasing attention as an environmentally benign medium for organic chemical reactions, especially acid-/base-catalyzed reactions. Non-catalyzed hydrolyses of gallotannin and tara tannin in HTLW for the simultaneous preparation of gallic acid (GA) and pyrogallol (PY) are under investigation in our laboratory. In this study, the hydrolysis kinetics of gallotannin and tara tannin were determined. The reaction is indicated to be a typical consecutive first-order one in which GA has formed as a main intermediate and PY as the final product. Selective decomposition of tannin in HTLW was proved to be possible by adjusting reaction temperature and time. The present results provide an important basic data and reference for the green preparation of GA and PY. PMID:18500780

Enantiomerically pure 3-aryl- and 3-hetaryl-2-hydroxypropanoic acids by chemoenzymatic reduction of 2-oxo acids.

PubMed

Sivanathan, Sivatharushan; Körber, Florian; Tent, Jannis Aron; Werner, Svenja; Scherkenbeck, Jürgen

2015-03-06

Phenyllactic acids are found in numerous natural products as well as in active substances used in medicine or plant protection. Enantiomerically pure phenyllactic acids are available by transition-metal-catalyzed hydrogenations or chemoenzymatic reductions of the corresponding 3-aryl-2-oxopropanoic acids. We show here that d-lactate dehydrogenase from Staphylococcus epidermidis reduces a broad spectrum of 2-oxo acids, which are difficult substrates for transition-metal-catalyzed reactions, with excellent enantioselectivities in a simple experimental setup.

[Inhibiting properties of stable nitroxyl radicals in reactions of linoleic acid and linoleyl alcohol oxidation catalyzed by 5-lipoxygenase].

PubMed

Kharchenko, O V; Kharitonenko, A I; Vovk, A I; Kukhar', V P; Babiĭ, L V; Khil'chevskiĭ, A N; Mel'nik, A K

2005-01-01

The inhibiting effects of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its 4-substituted derivatives in reactions of linoleyl acid or linoleyl alcohol oxidation catalyzed by potato tuber 5-lipoxygenase were investigated. Inhibiting properties of stable nitroxyl radicals in presence of lubrol and SDS were reduced at the transition from TEMPO to 4-hydroxy-TEMPO or 4-amino-TEMPO and increased at use of adamantane-1-carboxylic or 3-methyladamantane-1-carboxylic acid 1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl esters. Enzyme activity at saturating concentrations of inhibitor was not suppressed completely, and decreased up to the certain level determined by the substrate nature. The dependence of partial inhibition efficiency on rotational correlation time of stable nitroxides in model micellar systems were analysed. It was supposed that 5-lipoxygenase inhibition includes the interaction of hydrophobic nitroxide with radical intermediate formed in enzymatic process.

H NMR studies of substrate hydrogen exchange reactions catalyzed by L-methionine gamma-lyase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esaki, N.; Nakayama, T.; Sawada, S.

Hydrogen exchange reactions of various L-amino acids catalyzed by L-methionine gamma-lyase (EC 4.4.1.11) have been studied. The enzyme catalyzes the rapid exchange of the alpha- and beta-hydrogens of L-methionine and S-methyl-L-cysteine with deuterium from the solvent. The rate of alpha-hydrogen exchange was about 40 times faster than that of the enzymatic elimination reaction of the sulfur-containing amino acids. The enzyme also catalyzes the exchange reaction of alpha- and beta-hydrogens of the straight-chain L-amino acids which are not susceptible to elimination. The exchange rates of the alpha-hydrogen and the total beta-hydrogens of L-alanine and L-alpha-aminobutyrate with deuterium followed first-order kinetics. Formore » L-norvaline, L-norleucine, S-methyl-L-cysteine, and L-methionine, the rate of alpha-hydrogen exchange followed first-order kinetics, but the rate of total beta-hydrogen exchange decreased due to a primary isotope effect at the alpha-position. L-Phenylalanine and L-tryptophan slowly underwent alpha-hydrogen exchange. The pro-R hydrogen of glycine was deuterated stereospecifically.« less

Lipase-catalyzed enantioselective synthesis of (R,R)-lactide from alkyl lactate to produce PDLA (poly D-lactic acid) and stereocomplex PLA (poly lactic acid).

PubMed

Jeon, Byoung Wook; Lee, Jumin; Kim, Hyun Sook; Cho, Dae Haeng; Lee, Hyuk; Chang, Rakwoo; Kim, Yong Hwan

2013-10-20

R-lactide, a pivotal monomer for the production of poly (D-lactic acid) (PDLA) or stereocomplex poly (lactic acid) (PLA) was synthesized from alkyl (R)-lactate through a lipase-catalyzed reaction without racemization. From among several types of lipase, only lipase B from Candida antarctica (Novozym 435; CAL-B) was effective in the reaction that synthesized (R,R)-lactide. Enantiopure (R,R)-lactide, which consisted of over 99% enantiomeric excess, was synthesized from methyl (R)-lactate through CAL-B catalysis. Removal of the methanol by-product was critical to obtain a high level of lactide conversion. The (R,R)-lactide yield was 56% in a reaction containing 100 mg of Novozym 435, 10 mM methyl (R)-lactate and 1500 mg of molecular sieve 5A in methyl tert-butyl ether (MTBE). The important monomer (R,R)-lactide that is required for the production of the widely recognized bio-plastic PDLA and the PLA stereocomplex can be obtained using this novel synthetic method. Copyright © 2013 Elsevier B.V. All rights reserved.

Direct amidation of carboxylic acids catalyzed by ortho-iodo arylboronic acids: catalyst optimization, scope, and preliminary mechanistic study supporting a peculiar halogen acceleration effect.

PubMed

Gernigon, Nicolas; Al-Zoubi, Raed M; Hall, Dennis G

2012-10-05

The importance of amides as a component of biomolecules and synthetic products motivates the development of catalytic, direct amidation methods employing free carboxylic acids and amines that circumvent the need for stoichiometric activation or coupling reagents. ortho-Iodophenylboronic acid 4a has recently been shown to catalyze direct amidation reactions at room temperature in the presence of 4A molecular sieves as dehydrating agent. Herein, the arene core of ortho-iodoarylboronic acid catalysts has been optimized with regards to the electronic effects of ring substitution. Contrary to the expectation, it was found that electron-donating substituents are preferable, in particular, an alkoxy substituent positioned para to the iodide. The optimal new catalyst, 5-methoxy-2-iodophenylboronic acid (MIBA, 4f), was demonstrated to be kinetically more active than the parent des-methoxy catalyst 4a, providing higher yields of amide products in shorter reaction times under mild conditions at ambient temperature. Catalyst 4f is recyclable and promotes the formation of amides from aliphatic carboxylic acids and amines, and from heteroaromatic carboxylic acids and other functionalized substrates containing moieties like a free phenol, indole and pyridine. Mechanistic studies demonstrated the essential role of molecular sieves in this complex amidation process. The effect of substrate stoichiometry, concentration, and measurement of the catalyst order led to a possible catalytic cycle based on the presumed formation of an acylborate intermediate. The need for an electronically enriched ortho-iodo substituent in catalyst 4f supports a recent theoretical study (Marcelli, T. Angew. Chem. Int. Ed.2010, 49, 6840-6843) with a purported role for the iodide as a hydrogen-bond acceptor in the orthoaminal transition state.

Effect of polyvinylpyrrolidone on mesoporous silica morphology and esterification of lauric acid with 1-butanol catalyzed by immobilized enzyme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jinyu; Zhou, Guowei, E-mail: guoweizhou@hotmail.com; Jiang, Bin

2014-05-01

Mesoporous silica materials with a range of morphology evolution, i.e., from curved rod-shaped mesoporous silica to straight rod-shaped mesoporous silica, were successfully prepared using polyvinylpyrrolidone (PVP) and triblock copolymer as dual template. The effects of PVP molecular weight and concentration on mesoporous silica structure parameters were studied. Results showed that surface area and pore volume continuously decreased with increased PVP molecular weight. Mesoporous silica prepared with PVP K30 also possessed larger pore diameter, interplanar spacing (d{sub 100}), and cell parameter (a{sub 0}) than that prepared with PVP K15 and PVP K90. In addition, with increased PVP concentration, d{sub 100} andmore » a{sub 0} continuously decreased. The mechanism of morphology evolution caused by the change in PVP concentration was investigated. The conversion rate of lauric acid with 1-butanol catalyzed by immobilized Porcine pancreatic lipase (PPL) was also evaluated. Results showed that PPL immobilized on amino-functionalized straight rod-shaped mesoporous silica maintained 50% of its esterification conversion rate even after five cycles of use with a maximum conversion rate was about 90.15%. - Graphical abstract: Curved rod-shaped mesoporous silica can be obtained at low and the highest PVP concentration, while straight rod-shaped mesoporous silica can be obtained at higher PVP concentration. - Highlights: • Mesoporous silica with morphology evolution from CRMS to SRMS were prepared. • Effects of PVP molecular weight and concentration on silica morphology were studied. • A possible mechanism for the formation of morphology evolution SiO{sub 2} was proposed. • Esterification of lauric acid with 1-butanol catalyzed by immobilized PPL.« less

Phosphine-Catalyzed Doubly Stereoconvergent γ-Additions of Racemic Heterocycles to Racemic Allenoates: The Catalytic Enantioselective Synthesis of Protected α,α-Disubstituted α-Amino Acid Derivatives.

PubMed

Kalek, Marcin; Fu, Gregory C

2015-07-29

Methods have recently been developed for the phosphine-catalyzed asymmetric γ-addition of nucleophiles to readily available allenoates and alkynoates to generate useful α,β-unsaturated carbonyl compounds that bear a stereogenic center in either the γ or the δ position (but not both) with high stereoselectivity. The utility of this approach would be enhanced considerably if the stereochemistry at both termini of the new bond could be controlled effectively. In this report, we describe the achievement of this objective, specifically, that a chiral phosphepine can catalyze the stereoconvergent γ-addition of a racemic nucleophile to a racemic electrophile; through the choice of an appropriate heterocycle as the nucleophilic partner, this new method enables the synthesis of protected α,α-disubstituted α-amino acid derivatives in good yield, diastereoselectivity, and enantioselectivity.

A simple colorimetric chemosensor bearing a carboxylic acid group with high selectivity for CN-

NASA Astrophysics Data System (ADS)

Park, Gyeong Jin; Choi, Ye Won; Lee, Dongkuk; Kim, Cheal

2014-11-01

A new simple ‘naked eye' chemosensor 1 (sodium (E)-2-((2-(3-hydroxy-2-naphthoyl)hydrazono)methyl)benzoate) has been synthesized for detection of CN- in a mixture of DMF/H2O (9:1). The sensor 1 comprises of a naphthoic hydrazide as efficient hydrogen bonding donor group and a benzoic acid as the moiety with the water solubility. The receptor 1 showed high selectivity toward cyanide ions in a 1:1 stoichiometric manner, which induces a fast color change from colorless to yellow for CN- over other anions. Therefore, receptor 1 could be useful for cyanide detection in aqueous environment, displaying a high distinguishable selectivity from hydrogen bonded anions and being clearly visible to the naked eye.

Heteropoly acid-catalyzed microwave-assisted three-component aza-Diels-Alder cyclizations: diastereoselective synthesis of potential drug candidates for Alzheimer's disease.

PubMed

Borkin, Dmitry; Morzhina, Elena; Datta, Silpi; Rudnitskaya, Aleksandra; Sood, Abha; Török, Marianna; Török, Béla

2011-03-07

A highly diastereoselective microwave-assisted three component synthesis of azabicyclo[2.2.2]octan-5-ones by a silicotungstic acid-catalyzed aza-Diels-Alder cyclization is described. The one-pot process involves the formation of the in situ generated Schiff base and its immediate cyclization with cyclohex-2-enone. The short reaction times, good yields and excellent diastereoselectivity make this annulation a practical and environmentally attractive method for the synthesis of the target compounds. Preliminary assays were carried out to determine the activity of the products in AChE as well as in amyloid β fibrillogenesis inhibition.

Conversion of nicotinic acid to trigonelline is catalyzed by N-methyltransferase belonged to motif B′ methyltransferase family in Coffea arabica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizuno, Kouichi, E-mail: koumno@akita-pu.ac.jp; Matsuzaki, Masahiro; Kanazawa, Shiho

Graphical abstract: Trigonelline synthase catalyzes the conversion of nicotinic acid to trigonelline. We isolated and characterized trigonelline synthase gene(s) from Coffea arabica. - Highlights: • Trigonelline is a major compound in coffee been same as caffeine is. • We isolated and characterized trigonelline synthase gene. • Coffee trigonelline synthases are highly homologous with coffee caffeine synthases. • This study contributes the fully understanding of pyridine alkaloid metabolism. - Abstract: Trigonelline (N-methylnicotinate), a member of the pyridine alkaloids, accumulates in coffee beans along with caffeine. The biosynthetic pathway of trigonelline is not fully elucidated. While it is quite likely that themore » production of trigonelline from nicotinate is catalyzed by N-methyltransferase, as is caffeine synthase (CS), the enzyme(s) and gene(s) involved in N-methylation have not yet been characterized. It should be noted that, similar to caffeine, trigonelline accumulation is initiated during the development of coffee fruits. Interestingly, the expression profiles for two genes homologous to caffeine synthases were similar to the accumulation profile of trigonelline. We presumed that these two CS-homologous genes encoded trigonelline synthases. These genes were then expressed in Escherichiacoli, and the resulting recombinant enzymes that were obtained were characterized. Consequently, using the N-methyltransferase assay with S-adenosyl[methyl-{sup 14}C]methionine, it was confirmed that these recombinant enzymes catalyzed the conversion of nicotinate to trigonelline, coffee trigonelline synthases (termed CTgS1 and CTgS2) were highly identical (over 95% identity) to each other. The sequence homology between the CTgSs and coffee CCS1 was 82%. The pH-dependent activity curve of CTgS1 and CTgS2 revealed optimum activity at pH 7.5. Nicotinate was the specific methyl acceptor for CTgSs, and no activity was detected with any other nicotinate

A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines.

PubMed

Unhale, Rajshekhar A; Sadhu, Milon M; Ray, Sumit K; Biswas, Rayhan G; Singh, Vinod K

2018-04-03

A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-hydroxyisoindolinones has been demonstrated in this communication. A variety of isoindolinone-based α-amino diazo esters bearing a quaternary stereogenic center were afforded in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). Furthermore, the synthetic utility of the products has been depicted by the hydrogenation of the diazo moiety of adducts.

One-step production of biodiesel from rice bran oil catalyzed by chlorosulfonic acid modified zirconia via simultaneous esterification and transesterification.

PubMed

Zhang, Yue; Wong, Wing-Tak; Yung, Ka-Fu

2013-11-01

Due to the high content (25-50%) of free fatty acid (FFA), crude rice bran oil usually requires a two steps conversion or one step conversion with very harsh condition for simultaneous esterification and transesterification. In this study, chlorosulfonic acid modified zirconia (HClSO3-ZrO2) with strong acidity and durability is prepared and it shows excellent catalytic activity toward simultaneous esterification and transesterification. Under a relative low reaction temperature of 120 °C, HClSO3-ZrO2 catalyzes a complete conversion of simulated crude rice bran oil (refined oil with 40 wt% FFA) into biodiesel and the conversion yield keep at above 92% for at least three cycles. Further investigation on the tolerance towards FFA and water reveals that it maintains high activity even with the presence of 40 wt% FFA and 3 wt% water. It shows that HClSO3-ZrO2 is a robust and durable catalyst which shows high potential to be commercial catalyst for biodiesel production from low grade feedstock. Copyright © 2013 Elsevier Ltd. All rights reserved.

3-Hydroxylaminophenol Mutase from Ralstonia eutropha JMP134 Catalyzes a Bamberger Rearrangement

PubMed Central

Schenzle, Andreas; Lenke, Hiltrud; Spain, Jim C.; Knackmuss, Hans-Joachim

1999-01-01

3-Hydroxylaminophenol mutase from Ralstonia eutropha JMP134 is involved in the degradative pathway of 3-nitrophenol, in which it catalyzes the conversion of 3-hydroxylaminophenol to aminohydroquinone. To show that the reaction was really catalyzed by a single enzyme without the release of intermediates, the corresponding protein was purified to apparent homogeneity from an extract of cells grown on 3-nitrophenol as the nitrogen source and succinate as the carbon and energy source. 3-Hydroxylaminophenol mutase appears to be a relatively hydrophobic but soluble and colorless protein consisting of a single 62-kDa polypeptide. The pI was determined to be at pH 4.5. In a database search, the NH2-terminal amino acid sequence of the undigested protein and of two internal sequences of 3-hydroxylaminophenol mutase were found to be most similar to those of glutamine synthetases from different species. Hydroxylaminobenzene, 4-hydroxylaminotoluene, and 2-chloro-5-hydroxylaminophenol, but not 4-hydroxylaminobenzoate, can also serve as substrates for the enzyme. The enzyme requires no oxygen or added cofactors for its reaction, which suggests an enzymatic mechanism analogous to the acid-catalyzed Bamberger rearrangement. PMID:10049374

Degradation of Perfluorooctanoic Acid and Perfluoroctane Sulfonate by Enzyme Catalyzed Oxidative Humification Reactions

NASA Astrophysics Data System (ADS)

Huang, Q.

2016-12-01

Poly- and perfluoroalkyl substances (PFASs) are alkyl based chemicals having multiple or all hydrogens replaced by fluorine atoms, and thus exhibit high thermal and chemical stability and other unusual characteristics. PFASs have been widely used in a wide variety of industrial and consumer products, and tend to be environmentally persistent. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two representative PFASs that have drawn particular attention because of their ubiquitous presence in the environment, resistance to degradation and toxicity to animals. This study examined the decomposition of PFOA and PFOS in enzyme catalyzed oxidative humification reactions (ECOHR), a class of reactions that are ubiquitous in the environment involved in natural organic humification. Reaction rates and influential factors were examined, and high-resolution mass spectrometry was used to identify possible products. Fluorides and partially fluorinated compounds were identified as likely products from PFOA and PFOS degradation, which were possibly formed via a combination of free radical decomposition, rearrangements and coupling processes. The findings suggest that PFOA and PFOS may be transformed during humification, and ECOHR can potentially be used for the remediation of these chemicals.

Acetylation of bacterial cellulose catalyzed by citric acid: Use of reaction conditions for tailoring the esterification extent.

PubMed

Ávila Ramírez, Jhon Alejandro; Gómez Hoyos, Catalina; Arroyo, Silvana; Cerrutti, Patricia; Foresti, María Laura

2016-11-20

Bacterial cellulose (BC) nanoribbons were partially acetylated by a simple direct solvent-free route catalyzed by citric acid. The assay of reaction conditions within chosen intervals (i.e. esterification time (0.5-7h), catalyst content (0.08-1.01mmol/mmol AGU), and temperature (90-140°C)), illustrated the flexibility of the methodology proposed, with reaction variables which can be conveniently manipulated to acetylate BC to the required degree of substitution (DS) within the 0.20-0.73 interval. Within this DS interval, characterization results indicated a surface-only process in which acetylated bacterial cellulose with tunable DS, preserved fibrous structure and increased hydrophobicity could be easily obtained. The feasibility of reusing the catalyst/excess acylant in view of potential scale-up was also illustrated. Copyright © 2016 Elsevier Ltd. All rights reserved.

Synthesis and characterization of poly(lactic acid)/ montmorillonite nanocomposites by in situ polycondensation catalyzed by non-metal-based compound.

PubMed

Kaewprapan, Kulwadee; Phattanarudee, Siriwan

2012-01-01

Poly(lactic acid)/montmorillonite nanocomposites were prepared by using non-toxic catalysts, i.e., phthalic acid and succinimide, via in situ polycondensation in presence of silicate. Concentrations of catalysts and clay were varied in a range of 0-3% wt and 0-0.5% wt, respectively. The reaction condition was controlled at 180 degrees C for 24 hr under a reduced pressure. Viscosity average molecular weight of the synthesized polymers and nanocomposites were characterized and compared using an Ubbelohde viscometer. Pattern of silicate distribution in the composites was investigated by X-ray diffraction to correlate with thermal properties evaluated by differential scanning calorimetry and thermogravimetric analysis. The results showed that the addition of catalysts at 2% wt gave the highest product yield (55-60%). The presence of silicate affected on molecular weight reduction, and the diffracted patterns suggested an intercalated structure. With a small amount of added filler, a significant improvement in thermal property and crystallinity of the resultant composites was obtained compared to those of the catalyzed polymers, in which the composites with succinimide exhibited overall better thermal stability and higher crystallinity than the ones prepared with phthalic acid.

Solvent effects in acid-catalyzed dehydration of the Diels-Alder cycloadduct between 2,5-dimethylfuran and maleic anhydride

NASA Astrophysics Data System (ADS)

Salavati-fard, Taha; Caratzoulas, Stavros; Doren, Douglas J.

2017-03-01

Dehydration of the cycloadduct produced from the Diels-Alder reaction between 2,5-dimethylfuran and maleic anhydride to 3,6-dimethylphthalic anhydride exemplifies an important step in producing platform chemicals from biomass. The mechanisms of dehydration and catalytic effects of Lewis and Brønsted acids are investigated with density functional theory. The uncatalyzed reaction has a very high activation barrier (68.7 kcal/mol) in the gas phase and it is not significantly affected by solvation. With a Lewis acid catalyst, modeled as an alkali ion, the activation barriers are reduced, but intermediates are also stabilized. The net effect in vacuum is that the energetic span, or apparent activation energy of the catalytic cycle, is 77.9 kcal/mol, even higher than the barrier in the uncatalyzed case. In solution, however, the energetic span is reduced by as much as 20 kcal/mol, due to differences in the solvation energy of the transition states and intermediates. In the case of a Brønsted acid catalyst, modeled as a proton, the gas phase transition state energies are reduced even more than in the Lewis acid case, and there is no strong stabilization of the intermediates. The energetic span in vacuum is only 13.8 kcal/mol and is reduced even further in solution. Brønsted acid catalysis appears to be the preferred mechanism for dehydration of this cycloadduct. Since the Diels-Alder reaction that produced the molecule has previously been shown to be catalyzed by Brønsted acids, this suggests that a single catalyst could be used to accelerate both steps.

Thermodynamics of enzyme-catalyzed esterifications: II. Levulinic acid esterification with short-chain alcohols.

PubMed

Altuntepe, Emrah; Emel'yanenko, Vladimir N; Forster-Rotgers, Maximilian; Sadowski, Gabriele; Verevkin, Sergey P; Held, Christoph

2017-10-01

Levulinic acid was esterified with methanol, ethanol, and 1-butanol with the final goal to predict the maximum yield of these equilibrium-limited reactions as function of medium composition. In a first step, standard reaction data (standard Gibbs energy of reaction Δ R g 0 ) were determined from experimental formation properties. Unexpectedly, these Δ R g 0 values strongly deviated from data obtained with classical group contribution methods that are typically used if experimental standard data is not available. In a second step, reaction equilibrium concentrations obtained from esterification catalyzed by Novozym 435 at 323.15 K were measured, and the corresponding activity coefficients of the reacting agents were predicted with perturbed-chain statistical associating fluid theory (PC-SAFT). The so-obtained thermodynamic activities were used to determine Δ R g 0 at 323.15 K. These results could be used to cross-validate Δ R g 0 from experimental formation data. In a third step, reaction-equilibrium experiments showed that equilibrium position of the reactions under consideration depends strongly on the concentration of water and on the ratio of levulinic acid: alcohol in the initial reaction mixtures. The maximum yield of the esters was calculated using Δ R g 0 data from this work and activity coefficients of the reacting agents predicted with PC-SAFT for varying feed composition of the reaction mixtures. The use of the new Δ R g 0 data combined with PC-SAFT allowed good agreement to the measured yields, while predictions based on Δ R g 0 values obtained with group contribution methods showed high deviations to experimental yields.

Ruthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 C-H bond and Lewis acid catalysis.

PubMed

Wang, Ming-Zhong; Zhou, Cong-Ying; Wong, Man-Kin; Che, Chi-Ming

2010-05-17

Ruthenium porphyrins (particularly [Ru(2,6-Cl(2)tpp)CO]; tpp=tetraphenylporphinato) and RuCl(3) can act as oxidation and/or Lewis acid catalysts for direct C-3 alkylation of indoles, giving the desired products in high yields (up to 82% based on 60-95% substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron-withdrawing or electron-donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N-arylindoles to 3-{[(N-aryl-N-alkyl)amino]methyl}indoles (yield: up to 82%, conversion: up to 95%) and the alkylation of N-alkyl or N-H indoles to 3-[p-(dialkylamino)benzyl]indoles (yield: up to 73%, conversion: up to 92%). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp(3) C-H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N-arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three-component coupling reaction of the in situ generated formaldehyde with an N-alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium-labeling experiments are consistent with the alkylation of N-alkylindoles via pathway B. The relative reaction rates of [Ru(2,6-Cl(2)tpp)CO]-catalyzed oxidative coupling reactions of 4-X-substituted N,N-dimethylanilines with N-phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants sigma (R(2)=0.989), giving a rho value of -1.09. This rho value and the magnitudes of the intra- and intermolecular deuterium isotope effects (k(H)/k(D)) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4-X-substituted N,N-dimethylanilines. Ruthenium-catalyzed three-component reaction of N-alkyl/N-H indoles

Methyl Ester Production via Heterogeneous Acid-Catalyzed Simultaneous Transesterification and Esterification Reactions

NASA Astrophysics Data System (ADS)

Indrayanah, S.; Erwin; Marsih, I. N.; Suprapto; Murwani, I. K.

2017-05-01

The heterogeneous acid catalysts (MgF2 and ZnF2) have been used to catalyze the simultaneous transesterification and esterification reactions of crude palm oil (CPO) with methanol. Catalysts were synthesized by sol-gel method (combination of fluorolysis and hydrolysis). The physicochemical, structural, textural, thermal stability of the prepared catalysts was investigated by N2 adsorption-desorption, XRD, FT-IR, SEM and TG/DTG. Both MgF2 and ZnF2 have rutile structures with a different phase. The surface area of ZnF2 is smaller than that of MgF2, but the pore size and volume of ZnF2 are larger than those of MgF2. However, these materials are thermally stable. The performance of the catalysts is determined from the yield of catalysts toward the formation of methyl ester determined based on the product of methyl ester obtained from the reaction. The catalytic activity of ZnF2 is higher than MgF2 amounted to 85.21% and 26.82% with the optimum condition. The high activity of ZnF2 could be attributed to its pore diameter and pore volume but was not correlated with its surface area. The yield of methyl ester decreased along with the increase in molar ratio of methanol/CPO from 85.21 to 80.99 for ZnF2, respectively.

Muon Catalyzed Fusion

NASA Technical Reports Server (NTRS)

Armour, Edward A.G.

2007-01-01

Muon catalyzed fusion is a process in which a negatively charged muon combines with two nuclei of isotopes of hydrogen, e.g, a proton and a deuteron or a deuteron and a triton, to form a muonic molecular ion in which the binding is so tight that nuclear fusion occurs. The muon is normally released after fusion has taken place and so can catalyze further fusions. As the muon has a mean lifetime of 2.2 microseconds, this is the maximum period over which a muon can participate in this process. This article gives an outline of the history of muon catalyzed fusion from 1947, when it was first realised that such a process might occur, to the present day. It includes a description of the contribution that Drachrnan has made to the theory of muon catalyzed fusion and the influence this has had on the author's research.

Biodiesel from Citrullus colocynthis Oil: Sulfonic-Ionic Liquid-Catalyzed Esterification of a Two-Step Process

PubMed Central

Ali Elsheikh, Yasir; Hassan Akhtar, Faheem

2014-01-01

Biodiesel was prepared from Citrullus colocynthis oil (CCO) via a two-step process. The first esterification step was explored in two ionic liquids (ILs) with 1,3-disulfonic acid imidazolium hydrogen sulfate (DSIMHSO4) and 3-methyl-1-sulfonic acid imidazolium hydrogen sulfate (MSIMHSO4). Both ILs appeared to be good candidates to replace hazardous acidic catalyst due to their exceptional properties. However, the two sulfonic chains existing in DSIMHSO4 were found to increase the acidity to the IL than the single sulfonic chain in MSIMHSO4. Based on the results, 3.6 wt% of DSIMHSO4, methanol/CCO molar ratio of 12 : 1, and 150°C offered a final FFA conversion of 95.4% within 105 min. A 98.2% was produced via second KOH-catalyzed step in 1.0%, 6 : 1 molar ratio, 600 rpm, and 60°C for 50 min. This new two-step catalyzed process could solve the corrosion and environmental problems associated with the current acidic catalysts. PMID:24987736

Separation and determination of citrinin in corn using HPLC fluorescence detection assisted by molecularly imprinted solid phase extraction clean-up

USDA-ARS?s Scientific Manuscript database

A liquid chromatography based method to detect citrinin in corn was developed using molecularly imprinted solid phase extraction (MISPE) sample clean-up. Molecularly imprinted polymers were synthesized using 1,4-dihydroxy-2-naphthoic acid as the template and an amine functional monomer. Density func...

Palladium-catalyzed stereoretentive olefination of unactivated C(sp3)-H bonds with vinyl iodides at room temperature: synthesis of β-vinyl α-amino acids.

PubMed

Wang, Bo; Lu, Chengxi; Zhang, Shu-Yu; He, Gang; Nack, William A; Chen, Gong

2014-12-05

A method is reported for palladium-catalyzed N-quinolyl carboxamide-directed olefination of the unactivated C(sp(3))-H bonds of phthaloyl alanine with a broad range of vinyl iodides at room temperature. This reaction represents the first example of the stereoretentive installation of multisubstituted terminal and internal olefins onto unactivated C(sp(3))-H bonds. These methods enable access to a wide range of challenging β-vinyl α-amino acid products in a streamlined and controllable fashion, beginning from simple precursors.

Mechanistic Insight Facilitates Discovery of a Mild and Efficient Copper-Catalyzed Dehydration of Primary Amides to Nitriles Using Hydrosilanes.

PubMed

Liu, Richard Y; Bae, Minwoo; Buchwald, Stephen L

2018-02-07

Metal-catalyzed silylative dehydration of primary amides is an economical approach to the synthesis of nitriles. We report a copper-hydride(CuH)-catalyzed process that avoids a typically challenging 1,2-siloxane elimination step, thereby dramatically increasing the rate of the overall transformation relative to alternative metal-catalyzed systems. This new reaction proceeds at ambient temperature, tolerates a variety of metal-, acid-, or base-sensitive functional groups, and can be performed using a simple ligand, inexpensive siloxanes, and low catalyst loading.

The Aerobic Oxidation of Bromide to Dibromine Catalyzed by Homogeneous Oxidation Catalysts and Initiated by Nitrate in Acetic Acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Partenheimer, Walt; Fulton, John L.; Sorensen, Christina M.

A small amount of nitrate, ~0.002 molal, initiates the Co/Mn catalyzed aerobic oxidation of bromide compounds (HBr,NaBr,LiBr) to dibromine in acetic acid at room temperature. At temperatures 40oC or less , the reaction is autocatalytic. Co(II) and Mn(II) themselves and mixed with ionic bromide are known homogeneous oxidation catalysts. The reaction was discovered serendipitously when a Co/Br and Co/Mn/Br catalyst solution was prepared for the aerobic oxidation of methyaromatic compounds and the Co acetate contained a small amount of impurity i.e. nitrate. The reaction was characterized by IR, UV-VIS, MALDI and EXAFS spectroscopies and the coordination chemistry is described. Themore » reaction is inhibited by water and its rate changed by pH. The change in these variables, as well as others, are identical to those observed during homogeneous, aerobic oxidation of akylaromatics. A mechanism is proposed. Accidental addition of a small amount of nitrate compound into a Co/Mn/Br/acetic acid mixture in a large, commercial feedtank is potentially dangerous.« less

Iron Catalyzed Hydroformylation of Alkenes under Mild Conditions: Evidence of an Fe(II) Catalyzed Process.

PubMed

Pandey, Swechchha; Raj, K Vipin; Shinde, Dinesh R; Vanka, Kumar; Kashyap, Varchaswal; Kurungot, Sreekumar; Vinod, C P; Chikkali, Samir H

2018-03-28

Earth abundant, first row transition metals offer a cheap and sustainable alternative to the rare and precious metals. However, utilization of first row metals in catalysis requires harsh reaction conditions, suffers from limited activity, and fails to tolerate functional groups. Reported here is a highly efficient iron catalyzed hydroformylation of alkenes under mild conditions. This protocol operates at 10-30 bar syngas pressure below 100 °C, utilizes readily available ligands, and applies to an array of olefins. Thus, the iron precursor [HFe(CO) 4 ] - [Ph 3 PNPPh 3 ] + (1) in the presence of triphenyl phosphine catalyzes the hydroformylation of 1-hexene (S2), 1-octene (S1), 1-decene (S3), 1-dodecene (S4), 1-octadecene (S5), trimethoxy(vinyl)silane (S6), trimethyl(vinyl)silane (S7), cardanol (S8), 2,3-dihydrofuran (S9), allyl malonic acid (S10), styrene (S11), 4-methylstyrene (S12), 4- iBu-styrene (S13), 4- tBu-styrene (S14), 4-methoxy styrene (S15), 4-acetoxy styrene (S16), 4-bromo styrene (S17), 4-chloro styrene (S18), 4-vinylbenzonitrile (S19), 4-vinylbenzoic acid (S20), and allyl benzene (S21) to corresponding aldehydes in good to excellent yields. Both electron donating and electron withdrawing substituents could be tolerated and excellent conversions were obtained for S11-S20. Remarkably, the addition of 1 mol % acetic acid promotes the reaction to completion within 16-24 h. Detailed mechanistic investigations revealed in situ formation of an iron-dihydride complex [H 2 Fe(CO) 2 (PPh 3 ) 2 ] (A) as an active catalytic species. This finding was further supported by cyclic voltammetry investigations and intermediacy of an Fe(0)-Fe(II) species was established. Combined experimental and computational investigations support the existence of an iron-dihydride as the catalyst resting state, which then follows a Fe(II) based catalytic cycle to produce aldehyde.

Selective heterogeneous acid catalyzed esterification of N-terminal sulfyhdryl fatty acids

USDA-ARS?s Scientific Manuscript database

Our interest in thiol fatty acids lies in their antioxidative, free radical scavenging, and metal ion scavenging capabilities as applied to cosmeceutical and skin care formulations. The retail market is filled with products containing the disulfide-containing free fatty acid, lipoic acid. These pr...

Application of a new amidophosphite ligand to Rh-catalyzed asymmetric hydrogenation of β-dehydroamino acid derivatives in supercritical carbon dioxide: activation effect of protic Co-solvents.

PubMed

Lyubimov, Sergey E; Rastorguev, Eugenie A; Davankov, Vadim A

2011-09-01

New chiral amidophosphite ligand was synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of (Z)-β-(acylamino)acrylates in protic solvents and supercritical carbon dioxide (scCO(2) ) The catalytic performance is affected greatly by the acidity of the solvents. Better enantioselectivity (up to 88% ee) was achieved in scCO(2) containing 1,1,1,3,3,3-hexafluoro-2-propanol, compared to neat protic solvents. Copyright © 2011 Wiley-Liss, Inc.

Exploratory development of foams from liquid crystal polymers

NASA Technical Reports Server (NTRS)

Chung, T. S.

1985-01-01

Two types of liquid crystal polymer (LCP) compositions were studied and evaluated as structural foam materials. One is a copolymer of 6-hydroxy-2-naphthoic acid, terephthalic acid, and p-acetoxyacetanilide (designed HNA/TA/AAA), and the other is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (designated HBA/HNA). Experimental results showed that the extruded HNA/TA/AA foams have better mechanical quality and appearance than HBA/HNA foams. Heat treatment improved foam tensile strength and break elongation, but reduced their modulus. The injection molding results indicated that nitrogen foaming agents with a low-pressure process gave better void distribution in the injection molded LCP foams than those made by the conventional injection-molding machine and chemical blowing agents. However, in comparing LCP foams with other conventional plastic foams, HBA/HNA foams have better mechanical properties than foamed ABS and PS, but are comparable to PBT and inferior to polycarbonate foams, especially in heat-deflection temperature and impact resistance energy. These deficiencies are due to LCP molecules not having been fully oriented during the Union-Carbide low-pressure foaming process.

The Isomerization of (-)-Menthone to (+)-Isomenthone Catalyzed by an Ion-Exchange Resin

ERIC Educational Resources Information Center

Ginzburg, Aurora L.; Baca, Nicholas A.; Hampton, Philip D.

2014-01-01

A traditional organic chemistry laboratory experiment involves the acid-catalyzed isomerization of (-)-menthone to (+)-isomenthone. This experiment generates large quantities of organic and aqueous waste, and only allows the final ratio of isomers to be determined. A "green" modification has been developed that replaces the mineral acid…

An efficient synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and thiones catalyzed by a novel Brønsted acidic ionic liquid under solvent-free conditions.

PubMed

Zhang, Yonghong; Wang, Bin; Zhang, Xiaomei; Huang, Jianbin; Liu, Chenjiang

2015-02-26

We report here an efficient and green method for Biginelli condensation reaction of aldehydes, β-ketoesters and urea or thiourea catalyzed by Brønsted acidic ionic liquid [Btto][p-TSA] under solvent-free conditions. Compared to the classical Biginelli reaction conditions, the present method has the advantages of giving good yields, short reaction times, near room temperature conditions and the avoidance of the use of organic solvents and metal catalyst.

Prostaglandin H synthase-catalyzed oxidation of all-trans- and 13-cis-retinoic acid to carbon-centered and peroxyl radical intermediates.

PubMed

Freyaldenhoven, M A; Lloyd, R V; Samokyszyn, V M

1996-06-01

Due to the importance of all-trans-retinoic acid (RA) in the treatment of various dermatological conditions and the wide distribution of prostaglandin H synthase (PGHS) in tissues, we have further examined the mechanisms involved in the hydroperoxide-dependent cooxidation of RA and its isomer, 13-cis-retinoic acid ((13Z)-RA), by PGHS. Hydroperoxide-dependent, PGHS-catalyzed oxidation of RA and (13Z)-RA was shown to form free radical adducts, using electron spin resonance (ESR) spin trapping techniques and 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) or 13-hydroperoxy-9-cis-11-trans-octadecadienoic acid (13-OOH-18:2) as hydroperoxide substrates. Utilization of the spin trap alpha-phenyl-N-tert-butylnitrone (PBN) resulted in the detection of (13Z)-RA-PBN and RA-PBN adducts whose spectra were characterized by hyperfine coupling constants of aH = 4.16/aN = 15.69 and aH = 3.01/aN =15.92, respectively. Identical experiments under anaerobic conditions were carried out using the spin trap 2-methyl-2-nitrosopropane (NtB) which yielded nitroxide adducts whose spectra were characterized by a triplet of doublets with values of aH = 3.49/aN = 15.84 for the (13Z)-RA adduct and aH = 3.49/aN = 15.88 for the RA adduct. These results are indicative of secondary carbon-centered radical formation. We also used (+)-benzo[a]pyrene 7(S),8(S)-dihydrodiol ((+)-BP-7,8-diol) as a peroxyl radical probe. The results demonstrated the formation of (+)-BP-7,8-diol-derived tetrols, with the trans-anti tetrol representing the major oxidation product in systems undergoing PPHP-dependent, PGHS-catalyzed oxidation of (13Z)-RA or RA. These results are consistent with the formation of peroxyl radicals in these systems. In all experiments, the (13Z)-RA isomer appeared to be a better substrate for the enzyme compared to the all-trans isomer. Collectively these results provide further evidence to support the previously proposed mechanism for retinoid oxidation by PGHS involving the intermediacy of C4 carbon

Structural and stereoelectronic insights into oxygenase-catalyzed formation of ethylene from 2-oxoglutarate.

PubMed

Zhang, Zhihong; Smart, Tristan J; Choi, Hwanho; Hardy, Florence; Lohans, Christopher T; Abboud, Martine I; Richardson, Melodie S W; Paton, Robert S; McDonough, Michael A; Schofield, Christopher J

2017-05-02

Ethylene is important in industry and biological signaling. In plants, ethylene is produced by oxidation of 1-aminocyclopropane-1-carboxylic acid, as catalyzed by 1-aminocyclopropane-1-carboxylic acid oxidase. Bacteria catalyze ethylene production, but via the four-electron oxidation of 2-oxoglutarate to give ethylene in an arginine-dependent reaction. Crystallographic and biochemical studies on the Pseudomonas syringae ethylene-forming enzyme reveal a branched mechanism. In one branch, an apparently typical 2-oxoglutarate oxygenase reaction to give succinate, carbon dioxide, and sometimes pyrroline-5-carboxylate occurs. Alternatively, Grob-type oxidative fragmentation of a 2-oxoglutarate-derived intermediate occurs to give ethylene and carbon dioxide. Crystallographic and quantum chemical studies reveal that fragmentation to give ethylene is promoted by binding of l-arginine in a nonoxidized conformation and of 2-oxoglutarate in an unprecedented high-energy conformation that favors ethylene, relative to succinate formation.

Rhodium-Catalyzed Acyloxy Migration of Propargylic Esters in Cycloadditions, Inspiration from Recent “Gold Rush”

PubMed Central

Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M.

2012-01-01

Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most π-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed. PMID:22895533

Regioselective Ni-Catalyzed Carboxylation of Allylic and Propargylic Alcohols with Carbon Dioxide.

PubMed

Chen, Yue-Gang; Shuai, Bin; Ma, Cong; Zhang, Xiu-Jie; Fang, Ping; Mei, Tian-Sheng

2017-06-02

An efficient Ni-catalyzed reductive carboxylation of allylic alcohols with CO 2 has been successfully developed, providing linear β,γ-unsaturated carboxylic acids as the sole regioisomer with generally high E/Z stereoselectivity. In addition, the carboxylic acids can be generated from propargylic alcohols via hydrogenation to give allylic alcohol intermediates, followed by carboxylation. A preliminary mechanistic investigation suggests that the hydrogenation step is made possible by a Ni hydride intermediate produced by a hydrogen atom transfer from water.

N-triflylthiophosphoramide catalyzed enantioselective Mukaiyama aldol reaction of aldehydes with silyl enol ethers of ketones.

PubMed

Cheon, Cheol Hong; Yamamoto, Hisashi

2010-06-04

The first Brønsted acid catalyzed asymmetric Mukaiyama aldol reaction of aldehydes using silyl enol ethers of ketones as nucleophiles has been reported. A variety of aldehydes and silyl enol ethers of ketones afforded the aldol products in excellent yields and good to excellent enantioselectivities. Mechanistic studies revealed that the actual catalyst may be changed from the silylated Brønsted acid to the Brønsted acid itself depending on the reaction temperature.

Myeloperoxidase-catalyzed incorporation of amines into proteins: role of hypochlorous acid and dichloramines.

PubMed

Thomas, E L; Jefferson, M M; Grisham, M B

1982-11-23

Myeloperoxidase-catalyzed oxidation of chloride (Cl-) to hypochlorous acid (HOCl) resulted in formation of mono- and dichloramine derivatives (RNHCl and RNCl2) of primary amines. The RNCl2 derivatives could undergo a reaction that resulted in incorporation of the R moiety into proteins. The probable mechanism was attack of RNCl2 or an intermediate formed in the decomposition of RNCl2 on histidine, tyrosine, and cystine residues and on lysine residues at high pH. Incorporation of radioactivity from labeled amines into stable, high molecular weight derivatives of proteins was measured by acid or acetone precipitation and by gel chromatography and electrophoresis. Whereas formation of RNCl2 was favored at low pH, the subsequent incorporation reaction was favored at high pH. Up to several hours were required for the maximum amount of incorporation, which was less than 10% of the label in RNCl2. For the amines tested, incorporation was in the order histamine greater than 1,2-diaminoethane greater than putrescine greater than taurine greater than lysine greater than glucosamine greater than leucine greater than methylamine. Initiation of the reaction required HOCl, and oxidized forms of bromide, iodide, or thiocyanate did not substitute. Inhibitors of incorporation fell into three classes. First, ammonia or amines competed with the labeled amine for reaction with HOCl, so that larger amounts of HOCl were required. Second, readily oxidized substances such as sulfhydryl or diketo compounds or thioethers (methionine) reduced RNCl2. Third, certain compounds competed with protein as the acceptor for the incorporation reaction. The amount required to block incorporation into protein depended on protein concentration. Among these inhibitors were imidazole compounds (histidine), phenols (tyrosine), and disulfides (glutathione disulfide, GSSG). Low yields of derivatives of histidine, tyrosine, and GSSG were detected by thin-layer chromatography. Acid-precipitable derivatives were

Sonochemical enzyme-catalyzed regioselective acylation of flavonoid glycosides.

PubMed

Ziaullah; Rupasinghe, H P Vasantha

2016-04-01

This work compares a highly efficient and alternative method of sonication-assisted lipase catalyzed acylation of quercetin-3-O-glucoside and phloretin-2'-glucoside, using Candida antarctica lipase B (Novozyme 435(®)), with a range of fatty acids. In this study, sonication-assisted irradiation coupled with stirring has been found to be more efficient and economical than conventional reaction conditions. Sonication-assisted acylation accelerated the reactions and reduced the time required by 4-5 folds. Copyright © 2016 Elsevier Inc. All rights reserved.

Pyruvate Decarboxylase Catalyzes Decarboxylation of Branched-Chain 2-Oxo Acids but Is Not Essential for Fusel Alcohol Production by Saccharomyces cerevisiae

PubMed Central

ter Schure, Eelko G.; Flikweert, Marcel T.; van Dijken, Johannes P.; Pronk, Jack T.; Verrips, C. Theo

1998-01-01

The fusel alcohols 3-methyl-1-butanol, 2-methyl-1-butanol, and 2-methyl-propanol are important flavor compounds in yeast-derived food products and beverages. The formation of these compounds from branched-chain amino acids is generally assumed to occur via the Ehrlich pathway, which involves the concerted action of a branched-chain transaminase, a decarboxylase, and an alcohol dehydrogenase. Partially purified preparations of pyruvate decarboxylase (EC 4.1.1.1) have been reported to catalyze the decarboxylation of the branched-chain 2-oxo acids formed upon transamination of leucine, isoleucine, and valine. Indeed, in a coupled enzymatic assay with horse liver alcohol dehydrogenase, cell extracts of a wild-type Saccharomyces cerevisiae strain exhibited significant decarboxylation rates with these branched-chain 2-oxo acids. Decarboxylation of branched-chain 2-oxo acids was not detectable in cell extracts of an isogenic strain in which all three PDC genes had been disrupted. Experiments with cell extracts from S. cerevisiae mutants expressing a single PDC gene demonstrated that both PDC1- and PDC5-encoded isoenzymes can decarboxylate branched-chain 2-oxo acids. To investigate whether pyruvate decarboxylase is essential for fusel alcohol production by whole cells, wild-type S. cerevisiae and an isogenic pyruvate decarboxylase-negative strain were grown on ethanol with a mixture of leucine, isoleucine, and valine as the nitrogen source. Surprisingly, the three corresponding fusel alcohols were produced in both strains. This result proves that decarboxylation of branched-chain 2-oxo acids via pyruvate decarboxylase is not an essential step in fusel alcohol production. PMID:9546164

The first characterization of free radicals formed from cellular COX-catalyzed peroxidation.

PubMed

Gu, Yan; Xu, Yi; Law, Benedict; Qian, Steven Y

2013-04-01

Through free radical-mediated peroxidation, cyclooxygenase (COX) can metabolize dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA) to form well-known bioactive metabolites, namely, the 1-series of prostaglandins (PGs1) and the 2-series of prostaglandins (PGs2), respectively. Unlike PGs2, which are generally viewed as proinflammatory and procarcinogenic PGs, PGs1 may possess anti-inflammatory and anti-cancer activity. Previous studies using ovine COX along with spin trapping and the LC/ESR/MS technique have shown that certain exclusive free radicals are generated from different free radical reactions in DGLA and AA peroxidation. However, it has been unclear whether the differences were associated with the contrasting bioactivity of DGLA vs AA. The aim of this study was to refine the LC/MS and spin trapping technique to make it possible for the association between free radicals and cancer cell growth to be directly tested. Using a colon cancer cell line, HCA-7 colony 29, and LC/MS along with a solid-phase extraction, we were able to characterize the reduced forms of radical adducts (hydroxylamines) as the free radicals generated from cellular COX-catalyzed peroxidation. For the first time, free radicals formed in the COX-catalyzed peroxidation of AA vs DGLA and their association with cancer cell growth were assessed (cell proliferation via MTS and cell cycle distribution via propidium iodide staining) in the same experimental setting. The exclusive free radicals formed from the COX-catalyzed peroxidation of AA and DGLA were shown to be correlated with the cell growth response. Our results indicate that free radicals generated from the distinct radical reactions in COX-catalyzed peroxidation may represent the novel metabolites of AA and DGLA that correspond to their contrasting bioactivity. Copyright © 2012 Elsevier Inc. All rights reserved.

The First Characterization of Free Radicals Formed From Cellular COX-Catalyzed Peroxidation

PubMed Central

Gu, Yan; Xu, Yi; Law, Benedict; Qian, Steven Y.

2014-01-01

Through free radical-mediated peroxidation, cyclooxygenase (COX) can metabolize dihomo-γ-linolenic acid (DGLA) and arachidonic acid(AA) to form well-known bioactive metabolites, namely, the 1-series of prostaglandins (PGs1) and 2-series of prostaglandins(PGs2), respectively. Unlike PGs2, which are generally viewed as pro-inflammatory and pro-carcinogenic PGs, PGs1 may possess anti-inflammatory and anti-cancer activity. Previous studies using ovine COX along with spin trapping and the LC/ESR/MS technique have shown that certain exclusive free radicals are generated from different free radical reactions in DGLA and AA peroxidation. However, it has been unclear whether the differences were associated with the contrasting bioactivity of DGLA vs. AA. The aim of this study was to refine the LC/MS and spin-trapping technique to make it possible for the association between free radicals and cancer cell growth to be directly tested. Using a colon cancer cell line, HCA-7 colony 29, and LC/MS along with a solid phase extraction, we were able to characterize the reduced forms of radical adducts (hydroxylamines) as the free radicals generated from cellular COX-catalyzed peroxidation. For the first time, free radicals formed in the COX-catalyzed peroxidation of AA vs. DGLA and their association with cancer cell growth was assessed (cell proliferation via MTS and cell cycle distribution via PI staining) in the same experimental setting. The exclusive free radicals formed from the COX-catalyzed peroxidation of AA and DGLA were shown to be correlated with the cell growth response. Our results indicate that free radicals generated from the distinct radical reactions in COX-catalyzed peroxidation may represent the novel metabolites of AA and DGLA that correspond to their contrasting bioactivity. PMID:23261941

Copper-Catalyzed Oxidative Dehydrogenative Carboxylation of Unactivated Alkanes to Allylic Esters via Alkenes

PubMed Central

2015-01-01

We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV–vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C–H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C–H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper–carboxylate, copper–amidate, and copper–imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)–amidate > Cu(II)–imidate > Cu(II)–benzoate. Consistent with this trend, Cu(II)–amidates and Cu(II)–benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products. PMID:25389772

Cox-2 inhibitory effects of naturally occurring and modified fatty acids.

PubMed

Ringbom, T; Huss, U; Stenholm , A; Flock, S; Skattebøl, L; Perera, P; Bohlin, L

2001-06-01

In the search for new cyclooxygenase-2 (COX-2) selective inhibitors, the inhibitory effects of naturally occurring fatty acids and some of their structural derivatives on COX-2-catalyzed prostaglandin biosynthesis were investigated. Among these fatty acids, linoleic acid (LA), alpha-linolenic acid (alpha-LNA), myristic acid, and palmitic acid were isolated from a CH(2)Cl(2) extract of the plant Plantago major by bioassay-guided fractionation. Inhibitory effects of other natural, structurally related fatty acids were also investigated: stearic acid, oleic acid, pentadecanoic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Further, the inhibitory effects of these compounds on COX-2- and COX-1-catalyzed prostaglandin biosynthesis was compared with the inhibition of some synthesized analogues of EPA and DHA with ether or thioether functions. The most potent COX-2-catalyzed prostaglandin biosynthesis inhibitor was all-(Z)-5-thia-8,11,14,17-eicosatetraenoic acid (2), followed by EPA, DHA, alpha-LNA, LA, (7E,11Z,14Z,17Z)-5-thiaeicosa-7,11,14,17-tetraenoic acid, all-(Z)-3-thia-6,9,12,15-octadecatetraenoic acid, and (5E,9Z,12Z,15Z,18Z)-3-oxaheneicosa-5,9,12,15,18-pentaenoic acid, with IC(50) values ranging from 3.9 to180 microM. The modified compound 2 and alpha-LNA were most selective toward COX-2, with COX-2/COX-1 ratios of 0.2 and 0.1, respectively. This study shows that several of the natural fatty acids as well as all of the semisynthetic thioether-containing fatty acids inhibited COX-2-catalyzed prostaglandin biosynthesis, where alpha-LNA and compound 2 showed selectivity toward COX-2.

Iron-Catalyzed Enantioselective Cross-Coupling Reactions of α-Chloroesters with Aryl Grignard Reagents.

PubMed

Jin, Masayoshi; Adak, Laksmikanta; Nakamura, Masaharu

2015-06-10

The first iron-catalyzed enantioselective cross-coupling reaction between an organometallic compound and an organic electrophile is reported. Synthetically versatile racemic α-chloro- and α-bromoalkanoates were coupled with aryl Grignard reagents in the presence of catalytic amounts of an iron salt and a chiral bisphosphine ligand, giving the products in high yields with acceptable and synthetically useful enantioselectivities (er up to 91:9). The produced α-arylalkanoates were readily converted to the corresponding α-arylalkanoic acids with high optical enrichment (er up to >99:1) via simple deprotections/recrystallizations. The results of radical probe experiments are consistent with a mechanism that involves the formation of an alkyl radical intermediate, which undergoes subsequent enantioconvergent arylation in an intermolecular manner. The developed asymmetric coupling offers not only facile and practical access to various chiral α-arylalkanoic acid derivatives, which are of significant pharmaceutical importance, but also a basis of controlling enantioselectivity in an iron-catalyzed organometallic transformation.

Spontaneous, Metal-Catalyzed, and Enzyme-Catalyzed Decarboxylation of Oxalosuccinic Acid.

DTIC Science & Technology

1980-01-01

acid, 2,4- dinitrophenylhydrazine was added. This yielded a hydrazone which, after two recrystallizations, melted at 2200C. A sample of the a...accurately determined to be 24,500 at a wavelength of 352 nm (46). 34 2,4- Dinitrophenylhydrazine . Obtained from the Eastman Kodak Chemicals Division...reaction with 2,4- dinitrophenylhydrazine (57). The reaction mixture was sampled hourly during the daytime for a period of three days. The concentration of a

Rhodium enalcarbenoids: direct synthesis of indoles by rhodium(II)-catalyzed [4+2] benzannulation of pyrroles.

PubMed

Dawande, Sudam Ganpat; Kanchupalli, Vinaykumar; Kalepu, Jagadeesh; Chennamsetti, Haribabu; Lad, Bapurao Sudam; Katukojvala, Sreenivas

2014-04-14

Disclosed herein is the design of an unprecedented electrophilic rhodium enalcarbenoid which results from rhodium(II)-catalyzed decomposition of a new class of enaldiazo compounds. The synthetic utility of these enalcarbenoids has been successfully demonstrated in the first transition-metal-catalyzed [4+2] benzannulation of pyrroles, thus leading to substituted indoles. The new benzannulation has been applied to the efficient synthesis of the natural product leiocarpone as well as a potent adipocyte fatty-acid binding protein inhibitor. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Silica, Alumina and Clay Catalyzed Peptide Bond Formation: Enhanced Efficiency of Alumina Catalyst

NASA Astrophysics Data System (ADS)

Bujdák, Juraj; Rode, Bernd M.

1999-10-01

Catalytic efficiencies of clay (hectorite), silica and alumina were tested in peptide bond formation reactions of glycine (Gly), alanine (Ala), proline (Pro), valine (Val) and leucine (Leu). The reactions were performed as drying/wetting (hectorite) and temperature fluctuation (silica and alumina) experiments at 85 °C. The reactivity of amino acids decreased in order Gly > Ala > Pro ~ Val ~ Leu. The highest catalytic efficiency was observed for alumina, the only catalyst producing oligopeptides in all investigated reaction systems. The peptide bond formation on alumina is probably catalyzed by the same sites and via similar reaction mechanisms as some alumina-catalyzed dehydration reactions used in industrial chemistry.

Gold-Catalyzed Formal C-C Bond Insertion Reaction of 2-Aryl-2-diazoesters with 1,3-Diketones.

PubMed

Ren, Yuan-Yuan; Chen, Mo; Li, Ke; Zhu, Shou-Fei

2018-06-29

The transition-metal-catalyzed formal C-C bond insertion reaction of diazo compounds with monocarbonyl compounds is well established, but the related reaction of 1,3-diketones instead gives C-H bond insertion products. Herein, we report a protocol for a gold-catalyzed formal C-C bond insertion reaction of 2-aryl-2-diazoesters with 1,3-diketones, which provides efficient access to polycarbonyl compounds with an all-carbon quaternary center. The aryl ester moiety plays a crucial role in the unusual chemoselectivity, and the addition of a Brønsted acid to the reaction mixture improves the yield of the C-C bond insertion product. A reaction mechanism involving cyclopropanation of a gold carbenoid with an enolate and ring-opening of the resulting donor-acceptor-type cyclopropane intermediate is proposed. This mechanism differs from that of the traditional Lewis-acid-catalyzed C-C bond insertion reaction of diazo compounds with monocarbonyl compounds, which involves a rearrangement of a zwitterion intermediate as a key step. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-Triflylthiophosphoramide Catalyzed Enantioselective Mukaiyama Aldol Reaction of Aldehydes with Silyl Enol Ethers of Ketones

PubMed Central

Cheon, Cheol Hong; Yamamoto, Hisashi

2010-01-01

The first Brønsted acid catalyzed asymmetric Mukaiyama aldol reaction of aldehydes using silyl enol ethers of ketones as nucleophiles has been reported. A variety of aldehydes and silyl enol ethers of ketones afforded the aldol products in excellent yields and good to excellent enantioselectivities. Mechanistic studies revealed that the actual catalyst may be changed from the silylated Brønsted acid to Brønsted acid itself depending on the reaction temperature. PMID:20465277

Enantioselective oxidation of racemic lactic acid to D-lactic acid and pyruvic acid by Pseudomonas stutzeri SDM.

PubMed

Gao, Chao; Qiu, Jianhua; Li, Jingchen; Ma, Cuiqing; Tang, Hongzhi; Xu, Ping

2009-03-01

D-lactic acid and pyruvic acid are two important building block intermediates. Production of D-lactic acid and pyruvic acid from racemic lactic acid by biotransformation is economically interesting. Biocatalyst prepared from 9 g dry cell wt l(-1) of Pseudomonas stutzeri SDM could catalyze 45.00 g l(-1)DL-lactic acid into 25.23 g l(-1)D-lactic acid and 19.70 g l(-1) pyruvic acid in 10h. Using a simple ion exchange process, D-lactic acid and pyruvic acid were effectively separated from the biotransformation system. Co-production of d-lactic acid and pyruvic acid by enantioselective oxidation of racemic lactic acid is technically feasible.

Acid-catalyzed rearrangements of flavan-4-phloroglucinol derivatives to novel 6-hydroxyphenyl-6a,llb-dihydro-6H-[1]benzofuro[2,3-c]-chromenes and hydroxyphenyl-3,2'-spirobi[dihydro[l]benzofurans

Treesearch

Petrus J. Steynberg; Jan P. Steynberg; Richard W. Hemingway; Daneel Ferreira; G. Wayne McGraw

1997-01-01

Acetic acid-catalyzed cleavage of proanthocyanidins in the presence of phloroglucinol gives a series of 2R procyanidin- and prodelphinidin-phloroglucinol adducts together with a novel 2S all-cis derivative implicating cleavage of the pyran ring and subsequent inversion of stereochernistry at C-2c. These flavan-4-phloroglucinol adducts also suffer dehydration to...

Synthesis of ω-Oxo Amino Acids and trans-5-Substituted Proline Derivatives Using Cross-Metathesis of Unsaturated Amino Acids.

PubMed

Salih, Nabaz; Adams, Harry; Jackson, Richard F W

2016-09-16

A range of 7-oxo, 8-oxo, and 9-oxo amino acids, analogues of 8-oxo-2-aminodecanoic acid, one of the key components of the cyclic tetrapeptide apicidin, have been prepared by a three-step process involving copper-catalyzed allylation of serine-, aspartic acid-, and glutamic acid-derived organozinc reagents, followed by cross-metathesis of the resulting terminal alkenes with unsaturated ketones and hydrogenation. The intermediate 7-oxo-5-enones underwent a highly diastereoselective (dr ≥96:4) acid-catalyzed aza-Michael reaction to give trans-2,5-disubstituted pyrrolidines, 5-substituted proline derivatives. The aza-Michael reaction was first observed when the starting enones were allowed to stand in solution in deuterochloroform but can be efficiently promoted by catalytic amounts of dry HCl.

An enhanced procedure for measuring organic acids and methyl esters in PM2.5

NASA Astrophysics Data System (ADS)

Liu, F.; Duan, F. K.; He, K. B.; Ma, Y. L.; Rahn, K. A.; Zhang, Q.

2015-11-01

A solid-phase extraction (SPE) pretreatment procedure allowing organic acids to be separated from methyl esters in fine aerosol has been developed. The procedure first separates the organic acids from fatty acid methyl esters (FAMEs) and other nonacid organic compounds by aminopropyl-based SPE cartridge and then quantifies them by gas chromatography/mass spectrometry. The procedure prevents the fatty acids and dimethyl phthalate from being overestimated, and so allows us to accurately quantify the C4-C11 dicarboxylic acids (DCAs) and the C8-C30 monocarboxylic acids (MCAs). Results for the extraction of DCAs, MCAs, and AMAs in eluate and FAMEs in effluate by SAX and NH2 SPE cartridges exhibited that the NH2 SPE cartridge gave higher extraction efficiency than the SAX cartridge. The recoveries of analytes ranged from 67.5 to 111.3 %, and the RSD ranged from 0.7 to 10.9 %. The resulting correlations between the aliphatic acids and FAMEs suggest that the FAMEs had sources similar to those of the carboxylic acids, or were formed by esterifying carboxylic acids, or that aliphatic acids were formed by hydrolyzing FAMEs. Through extraction and cleanup using this procedure, 17 aromatic acids in eluate were identified and quantified by gas chromatography/tandem mass spectrometry, including five polycyclic aromatic hydrocarbon (PAH): acids 2-naphthoic, biphenyl-4-carboxylic, 9-oxo-9H-fluorene-1-carboxylic, biphenyl-4,4´-dicarboxylic, and phenanthrene-1-carboxylic acid, plus 1,8-naphthalic anhydride. Correlations between the PAH acids and the dicarboxylic and aromatic acids suggested that the first three acids and 1,8-naphthalic anhydride were secondary atmospheric photochemistry products and the last two mainly primary.

Palladium- and Copper-Catalyzed Arylation of Carbon-Hydrogen Bonds

PubMed Central

Daugulis, Olafs; Do, Hien-Quang; Shabashov, Dmitry

2010-01-01

The transition-metal-catalyzed functionalization of C-H bonds is a powerful method for generating carbon-carbon bonds. Although significant advances to this field have been reported during the last decade, many challenges remain. First, most of the methods are substrate-specific and thus cannot be generalized. Second, conversions of unactivated (i.e. not benzylic or alpha to heteroatom) sp3 C–H bonds to C–C bonds are rare, with most examples limited to t-butyl groups—a conversion that is inherently simple because there are no β-hydrogens that can be eliminated. Finally, the palladium, rhodium, and ruthenium catalysts routinely used for the conversion of C–H bonds to C–C bonds are expensive. Catalytically active metals that are cheaper and less exotic (e.g. copper, iron, and manganese) are rarely used. This Account describes our attempts to provide solutions to these three problems. We have developed a general method for directing-group-containing arene arylation by aryl iodides. Using palladium acetate as the catalyst, we arylated anilides, benzamides, benzoic acids, benzylamines, and 2-substituted pyridine derivatives under nearly identical conditions. We have also developed a method for the palladium-catalyzed auxiliary-assisted arylation of unactivated sp3 C–H bonds. This procedure allows for the β-arylation of carboxylic acid derivatives and the γ-arylation of amine derivatives. Furthermore, copper catalysis can be used to mediate the arylation of acidic arene C–H bonds (i.e. those with pKa values <35 in DMSO). Using a copper iodide catalyst in combination with a base and a phenanthroline ligand, we successfully arylated electron-rich and electron-deficient heterocycles and electron-poor arenes possessing at least two electron-withdrawing groups. The reaction exhibits unusual regioselectivity: arylation occurs at the most hindered position. This copper-catalyzed method supplements the well-known C–H activation/borylation methodology, in which

Palladium- and copper-catalyzed arylation of carbon-hydrogen bonds.

PubMed

Daugulis, Olafs; Do, Hien-Quang; Shabashov, Dmitry

2009-08-18

The transition-metal-catalyzed functionalization of C-H bonds is a powerful method for generating carbon-carbon bonds. Although significant advances to this field have been reported during the past decade, many challenges remain. First, most of the methods are substrate-specific and thus cannot be generalized. Second, conversions of unactivated (i.e., not benzylic or alpha to heteroatom) sp(3) C-H bonds to C-C bonds are rare, with most examples limited to t-butyl groups, a conversion that is inherently simple because there are no beta-hydrogens that can be eliminated. Finally, the palladium, rhodium, and ruthenium catalysts routinely used for the conversion of C-H bonds to C-C bonds are expensive. Catalytically active metals that are cheaper and less exotic (e.g., copper, iron, and manganese) are rarely used. This Account describes our attempts to provide solutions to these three problems. We have developed a general method for directing-group-containing arene arylation by aryl iodides. Using palladium acetate as the catalyst, we arylated anilides, benzamides, benzoic acids, benzylamines, and 2-substituted pyridine derivatives under nearly identical conditions. We have also developed a method for the palladium-catalyzed auxiliary-assisted arylation of unactivated sp(3) C-H bonds. This procedure allows for the beta-arylation of carboxylic acid derivatives and the gamma-arylation of amine derivatives. Furthermore, copper catalysis can be used to mediate the arylation of acidic arene C-H bonds (i.e., those with pK(a) values <35 in DMSO). Using a copper iodide catalyst in combination with a base and a phenanthroline ligand, we successfully arylated electron-rich and electron-deficient heterocycles and electron-poor arenes possessing at least two electron-withdrawing groups. The reaction exhibits unusual regioselectivity: arylation occurs at the most hindered position. This copper-catalyzed method supplements the well-known C-H activation/borylation methodology, in

Copper/amino acid catalyzed cross-couplings of aryl and vinyl halides with nucleophiles.

PubMed

Ma, Dawei; Cai, Qian

2008-11-18

Copper-assisted Ullmann-type coupling reactions are valuable transformations for organic synthesis. Researchers have extensively applied these reactions in both academic and industrial settings. However, two important issues, the high reaction temperatures (normally above 150 degrees C) and the stoichiometric amounts of copper necessary, have greatly limited the reaction scope. To solve these problems, we and other groups have recently explored the use of special ligands to promote these coupling reactions. We first showed that the structure of alpha-amino acids can accelerate Cu-assisted Ullmann reactions, leading to the coupling reactions of aryl halides and alpha-amino acids at 80-90 degrees C. In response to these encouraging results, we also discovered that an l-proline ligand facilitated the following transformations: (1) coupling of aryl halides with primary amines, cyclic secondary amines, and N-containing heterocycles at 40-90 degrees C; (2) coupling of aryl halides with sulfinic acid salts at 80-95 degrees C; (3) azidation of aryl halides and vinyl halides with sodium azide at 40-95 degrees C; (4) coupling of aryl halides with activated methylene compounds at 25-50 degrees C. In addition, we found that N,N-dimethylglycine as a ligand facilitated Cu-catalyzed biaryl ether formation at 90 degrees C. Moreover, Sonogashira reactions worked in the absence of palladium and phosphine ligands, forming enamides from vinyl halides and amides at temperatures ranging from ambient temperature up to 80 degrees C. Furthermore, we discovered that an ortho-amide group can accelerate some Ullmann-type reactions. This functional group in combination with other ligand effects allowed for aryl amination or biaryl ether formation at ambient temperature. The coupling between aryl halides and activated methylene compounds even proceeded at -45 degrees C to enantioselectively form a quaternary carbon center. Taking advantage of these results, we developed several novel approaches

The ferroin-catalyzed Belousov-Zhabotinskii system with a "clock" behaviour

NASA Astrophysics Data System (ADS)

Melicherčík, Milan; Treindl, L̆udovít

1991-07-01

The ferroin-catalyzed Belousov-Zhabotinskii oscillatory system with methyl-, ethyl-, or isopropyl-ester of 3-oxobutanoic acid exhibits a "clock" behaviour and subsequent two-frequency oscillations. The influence of oxygen on the "clock" behaviour is assumed to be caused by an interaction of oxygen as a scavenger with intermediary radicals. A mechanism of the "clock" behaviour together with two-frequency oscillations of the Belousov-Zhabotinskii type will be developed later.

Iron-catalyzed olefin epoxidation in the presence of acetic acid: insights into the nature of the metal-based oxidant.

PubMed

Mas-Ballesté, Rubén; Que, Lawrence

2007-12-26

The iron complexes [(BPMEN)Fe(OTf)2] (1) and [(TPA)Fe(OTf)2] (2) [BPMEN = N,N'-bis-(2-pyridylmethyl)-N,N'-dimethyl-1,2-ethylenediamine; TPA = tris-(2-pyridylmethyl)amine] catalyze the oxidation of olefins by H2O2 to yield epoxides and cis-diols. The addition of acetic acid inhibits olefin cis-dihydroxylation and enhances epoxidation for both 1 and 2. Reactions carried out at 0 degrees C with 0.5 mol % catalyst and a 1:1.5 olefin/H2O2 ratio in a 1:2 CH3CN/CH3COOH solvent mixture result in nearly quantitative conversions of cyclooctene to epoxide within 1 min. The nature of the active species formed in the presence of acetic acid has been probed at low temperature. For 2, in the absence of substrate, [(TPA)FeIII(OOH)(CH3COOH)]2+ and [(TPA)FeIVO(NCCH3)]2+ intermediates can be observed. However, neither is the active epoxidizing species. In fact, [(TPA)FeIVO(NCCH3)]2+ is shown to form in competition with substrate oxidation. Consequently, it is proposed that epoxidation is mediated by [(TPA)FeV(O)(OOCCH3)]2+, generated from O-O bond heterolysis of the [(TPA)FeIII(OOH)(CH3COOH)]2+ intermediate, which is promoted by the protonation of the terminal oxygen atom of the hydroperoxide by the coordinated carboxylic acid.

The rhodium catalyzed three-component reaction of diazoacetates, titanium(IV) alkoxides and aldehydes.

PubMed

Lu, Chong-Dao; Liu, Hui; Chen, Zhi-Yong; Hu, Wen-Hao; Mi, Ai-Qiao

2005-05-28

The rhodium(II)-catalyzed three-component reaction of diazoacetates, titanium alkoxides and aldehydes is shown to give alpha-alkoxyl-beta-hydroxyl acid derivatives; the novel C-C bond formation reaction is proposed to occur through oxonium ylides derived from diazo compounds and titanium alkoxides, and followed by intermolecular trapping by aldehydes.

Silica metal-oxide vesicles catalyze comprehensive prebiotic chemistry.

PubMed

Bizzarri, Bruno Mattia; Botta, Lorenzo; Pérez-Valverde, Maritza Iveth; Saladino, Raffaele; Di Mauro, Ernesto; Garcia Ruiz, Juan Manuel

2018-03-30

It has recently been demonstrated that mineral self-assembled structures catalyzing prebiotic chemical reactions may form in natural waters derived from serpentinization, a geological process widespread in the early stages of Earth-like planets. We have synthesized self-assembled membranes by mixing microdrops of metal solutions with alkaline silicate solutions in the presence of formamide (NH2CHO), a single carbon molecule, at 80ºC. We found that these bilayer membranes, made of amorphous silica and metal oxide-hydroxide nanocrystals, catalyze the condensation of formamide, yielding the four nucleobases of RNA, three aminoacids and several carboxylic acids in a single pot experiment. Besides manganese, iron and magnesium, two abundant elements in the earliest Earth crust that are key in serpentinization reactions, are enough to produce all these biochemical compounds. These results suggest that the transition from inorganic geochemistry to prebiotic organic chemistry is common on a universal scale and, most probably, earlier than ever thought for our planet. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of new β-amidodehydroaminobutyric acid derivatives and of new tyrosine derivatives using copper catalyzed C-N and C-O coupling reactions.

PubMed

Pereira, G; Vilaça, H; Ferreira, P M T

2013-02-01

Several β-amidodehydroaminobutyric acid derivatives were prepared from N,C-diprotected β-bromodehydroaminobutyric acids and amides by a copper catalyzed C-N coupling reaction. The best reaction conditions include the use of a catalytic amount of CuI, N,N'-dimethylethylenediamine as ligand and K(2)CO(3) as base in toluene at 110 °C. The stereochemistry of the products was determined using NOE difference experiments and the results obtained are in agreement with an E-stereochemistry. Thus, the stereochemistry is maintained in the case of the E-isomers of β-bromodehydroaminobutyric acid derivatives, but when the Z-isomers were used as substrates the reaction proceeds with inversion of configuration. The use of β-bromodehydrodipeptides as substrates was also tested. It was found that the reaction outcome depend on the stereochemistry of the β-bromodehydrodipeptide and on the nature of the first amino acid residue. The products isolated were the β-amidodehydrodipeptide derivatives and/or the corresponding dihydropyrazines. The same catalytic system (CuI/N,N'-dimethylethylene diamine) was used in the C-O coupling reactions between a tyrosine derivative and aryl bromides. The new O-aryltyrosine derivatives were isolated in moderate to good yields. The photophysical properties of two of these compounds were studied in four solvents of different polarity. The results show that these compounds after deprotection can be used as fluorescence markers.

Molybdenum Nitrogenase Catalyzes the Reduction and Coupling of CO to Form Hydrocarbons*♦

PubMed Central

Yang, Zhi-Yong; Dean, Dennis R.; Seefeldt, Lance C.

2011-01-01

The molybdenum-dependent nitrogenase catalyzes the multi-electron reduction of protons and N2 to yield H2 and 2NH3. It also catalyzes the reduction of a number of non-physiological doubly and triply bonded small molecules (e.g. C2H2, N2O). Carbon monoxide (CO) is not reduced by the wild-type molybdenum nitrogenase but instead inhibits the reduction of all substrates catalyzed by nitrogenase except protons. Here, we report that when the nitrogenase MoFe protein α-Val70 residue is substituted by alanine or glycine, the resulting variant proteins will catalyze the reduction and coupling of CO to form methane (CH4), ethane (C2H6), ethylene (C2H4), propene (C3H6), and propane (C3H8). The rates and ratios of hydrocarbon production from CO can be adjusted by changing the flux of electrons through nitrogenase, by substitution of other amino acids located near the FeMo-cofactor, or by changing the partial pressure of CO. Increasing the partial pressure of CO shifted the product ratio in favor of the longer chain alkanes and alkenes. The implications of these findings in understanding the nitrogenase mechanism and the relationship to Fischer-Tropsch production of hydrocarbons from CO are discussed. PMID:21454640

High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis.

PubMed

Cui, Yanyan; Liang, Xinmiao; Chai, Jingchao; Cui, Zili; Wang, Qinglei; He, Weisheng; Liu, Xiaochen; Liu, Zhihong; Cui, Guanglei; Feng, Jiwen

2017-11-01

It is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self-catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte (C-PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li + and considerable ionic conductivity of 8.9 × 10 -5 S cm -1 at ambient temperature. Moreover, the LiFePO 4 /C-PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self-catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes.

Behavior of S.A.P. in the Mercury Catalyzed Nitric Acid Dissolution; COMPORTAMENTO DEL S.A.P. ALL'ATTACCO DI SOLUZIONI DI ACIDO NITRICO E NITRATO MERCURICO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beone, G.

1963-10-01

Plates of S.A.P. (sintered Aluminum Powder) were dissolved under different conditions in a nitric acid solution containing mercuric nitrate as a catalyst. These experiments nim at establishing a head-end dissolution process for S.A.P. cladded uranium oxide fuels. The results of preliminary dissolution experiments on simulated fuel rods are also described. The behavior of S.A.P. in the mercury catalyzed nitric acid dissolutions differs strongly from the behavior of aluminum: reaction rates are very low for S.A.P. and the dissolution time borders on being unacceptable in an industrial process. Settling rates of suspended alumina are however favorable. A tentative head end flowsheetmore » lay out for PRO second core fuel elements is included. (auth)« less

Transglutaminase catalyzed cross-linking of sodium caseinate improves oxidative stability of flaxseed oil emulsion.

PubMed

Ma, Hairan; Forssell, Pirkko; Kylli, Petri; Lampi, Anna-Maija; Buchert, Johanna; Boer, Harry; Partanen, Riitta

2012-06-20

Sodium caseinate was modified by transglutaminase catalyzed cross-linking reaction prior to the emulsification process in order to study the effect of cross-linking on the oxidative stability of protein stabilized emulsions. The extent of the cross-linking catalyzed by different dosages of transglutaminase was investigated by following the ammonia production during the reaction and using SDS-PAGE gel. O/W emulsions prepared with the cross-linked and non-cross-linked sodium caseinates were stored for 30 days under the same conditions. Peroxide value measurement, oxygen consumption measurement, and headspace gas chromatography analysis were used to study the oxidative stability of the emulsions. The emulsion made of the cross-linked sodium caseinate showed an improved oxidative stability with reduced formation of fatty acid hydroperoxides and volatiles and a longer period of low rate oxygen consumption. The improving effect of transglutaminase catalyzed cross-linking could be most likely attributed to the enhanced physical stability of the interfacial protein layer against competitive adsorption by oil oxidation products.

Carbon Isotope Measurements of Experimentally-Derived Hydrothermal Mineral-Catalyzed Organic Products by Pyrolysis-Isotope Ratio Mass Spectrometry

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Fu, Qi; Niles, Paul B.

2011-01-01

We report results of experiments to measure the C isotope composition of mineral catalyzed organic compounds derived from high temperature and high pressure synthesis. These experiments make use of an innovative pyrolysis technique designed to extract and measure C isotopes. To date, our experiments have focused on the pyrolysis and C isotope ratio measurements of low-molecular weight intermediary hydrocarbons (organic acids and alcohols) and serve as a proof of concept for making C and H isotope measurements on more complicated mixtures of solid-phase hydrocarbons and intermediary products produced during high temperature and high pressure synthesis on mineral-catalyzed surfaces. The impetus for this work stems from recently reported observations of methane detected within the Martian atmosphere [1-4], coupled with evidence showing extensive water-rock interaction during Martian history [5-7]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization reactions [8,9]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [10-12]. Further, recent experiments by Fu et al. [13] focus on examining detailed C isotope measurements of hydrocarbons produced by surface-catalyzed mineral reactions. Work described in this paper details the experimental techniques used to measure intermediary organic reaction products (alcohols and organic acids).

Ligand-Promoted Rh(III)-Catalyzed Coupling of Aryl C-H Bonds with Arylboron Reagents.

PubMed

Wang, Huai-Wei; Cui, Pei-Pei; Lu, Yi; Sun, Wei-Yin; Yu, Jin-Quan

2016-04-15

Rhodium(III)-catalyzed C-H arylation of arenes with phenylboronic acid pinacol esters has been achieved using a readily removable N-pentafluorophenylbenzamide directing group for the first time. The use of a bidentate phosphine ligand (Binap) significantly increased the yield of the cross-coupling of C-H bonds with organoboron reagents.

Characterization of thermal and mechanical properties of opligo(glycerol-glutaric acid)s

USDA-ARS?s Scientific Manuscript database

Dibutyltin oxide was used to catalyze the synthesis of oligo(glycerol-glutaric acid)s in the absence and presence of solvent. Reaction times were either 10h or 24h for reactions performed in DMF and 24h for the neat reaction. The oligomers were obtained on average in 84% yield and were characteriz...

The initial step in the archaeal aspartate biosynthetic pathway catalyzed by a monofunctional aspartokinase

PubMed Central

Faehnle, Christopher R.; Liu, Xuying; Pavlovsky, Alexander; Viola, Ronald E.

2006-01-01

The activation of the β-carboxyl group of aspartate catalyzed by aspartokinase is the commitment step to amino-acid biosynthesis in the aspartate pathway. The first structure of a microbial aspartokinase, that from Methanococcus jannaschii, has been determined in the presence of the amino-acid substrate l-­aspartic acid and the nucleotide product MgADP. The enzyme assembles into a dimer of dimers, with the interfaces mediated by both the N- and C-terminal domains. The active-site functional groups responsible for substrate binding and specificity have been identified and roles have been proposed for putative catalytic functional groups. PMID:17012784

Identification of non-heme diiron proteins that catalyze triple bond and epoxy group formation.

PubMed

Lee, M; Lenman, M; Banaś, A; Bafor, M; Singh, S; Schweizer, M; Nilsson, R; Liljenberg, C; Dahlqvist, A; Gummeson, P O; Sjödahl, S; Green, A; Stymne, S

1998-05-08

Acetylenic bonds are present in more than 600 naturally occurring compounds. Plant enzymes that catalyze the formation of the Delta12 acetylenic bond in 9-octadecen-12-ynoic acid and the Delta12 epoxy group in 12,13-epoxy-9-octadecenoic acid were characterized, and two genes, similar in sequence, were cloned. When these complementary DNAs were expressed in Arabidopsis thaliana, the content of acetylenic or epoxidated fatty acids in the seeds increased from 0 to 25 or 15 percent, respectively. Both enzymes have characteristics similar to the membrane proteins containing non-heme iron that have histidine-rich motifs.

Transition metal-catalyzed oxidation of sulfur(IV) oxides. Atmospheric-relevant processes and mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brandt, C.; Eldik, R. van

1995-01-01

The transition metal-catalyzed oxidation of sulfur(IV) oxides has been known for more than 100 years. There is a significant lack of information on the actual role of the transition metal-catalyzed reactions, and much of the earlier work was performed without a detailed knowledge of the chemical system. For this reason attention is focused on the role of transition metal ions in the oxidation of sulfur(IV) oxides in terms of the coordination chemistry involved, as well as the stability and chemical behavior of the various participating species. The oxidation process of sulfur(IV) oxides plays an important role in atmospheric chemistry (e.g.more » acid rain formation) as well as industrial processes (e.g. desulfurization of plume gases and ore). The present report deals with the mechanism of the transition metal-catalyzed oxidation of sulfur(IV) oxides with the aim to discuss this in terms of atmospheric and chemical processes. In addition, the authors would like to emphasize the key role of oxygen in these processes. 1,076 refs.« less

Iodine-Catalyzed Isomerization of Dimethyl Muconate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Settle, Amy E.; Berstis, Laura; Zhang, Shuting

cis,cis-Muconic acid is a platform biobased chemical that can be upgraded to drop-in commodity and novel monomers. Among the possible drop-in products, dimethyl terephthalate can be synthesized via esterification, isomerization, Diels-Alder cycloaddition, and dehydrogenation. The isomerization of cis,cis-dimethyl muconate ( ccDMM) to the trans,trans-form ( ttDMM) can be catalyzed by iodine; however, studies have yet to address (i) the mechanism and reaction barriers unique to DMM, and (ii) the influence of solvent, potential for catalyst recycle, and recovery of high-purity ttDMM. To address this gap, we apply a joint computational and experimental approach to investigate iodine-catalyzed isomerization of DMM. Densitymore » functional theory calculations identified unique regiochemical considerations due to the large number of halogen-diene coordination schemes. Both transition state theory and experiments estimate significant barrier reductions with photodissociated iodine. Solvent selection was critical for rapid kinetics, likely due to solvent complexation with iodine. Under select conditions, ttDMM yields of 95% were achieved in <1 h with methanol, followed by high purity recovery (>98%) with crystallization. Lastly, post-reaction iodine can be recovered and recycled with minimal loss of activity. Altogether, these findings provide new insight into the mechanism and conditions necessary for DMM isomerization with iodine to advance the state-of-the-art for biobased chemicals.« less

Iodine-Catalyzed Isomerization of Dimethyl Muconate

DOE PAGES

Settle, Amy E.; Berstis, Laura; Zhang, Shuting; ...

2018-04-16

cis,cis-Muconic acid is a platform biobased chemical that can be upgraded to drop-in commodity and novel monomers. Among the possible drop-in products, dimethyl terephthalate can be synthesized via esterification, isomerization, Diels-Alder cycloaddition, and dehydrogenation. The isomerization of cis,cis-dimethyl muconate ( ccDMM) to the trans,trans-form ( ttDMM) can be catalyzed by iodine; however, studies have yet to address (i) the mechanism and reaction barriers unique to DMM, and (ii) the influence of solvent, potential for catalyst recycle, and recovery of high-purity ttDMM. To address this gap, we apply a joint computational and experimental approach to investigate iodine-catalyzed isomerization of DMM. Densitymore » functional theory calculations identified unique regiochemical considerations due to the large number of halogen-diene coordination schemes. Both transition state theory and experiments estimate significant barrier reductions with photodissociated iodine. Solvent selection was critical for rapid kinetics, likely due to solvent complexation with iodine. Under select conditions, ttDMM yields of 95% were achieved in <1 h with methanol, followed by high purity recovery (>98%) with crystallization. Lastly, post-reaction iodine can be recovered and recycled with minimal loss of activity. Altogether, these findings provide new insight into the mechanism and conditions necessary for DMM isomerization with iodine to advance the state-of-the-art for biobased chemicals.« less

High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self‐Catalyzed Strategy toward Facile Synthesis

PubMed Central

Cui, Yanyan; Liang, Xinmiao; Chai, Jingchao; Cui, Zili; Wang, Qinglei; He, Weisheng; Liu, Xiaochen; Feng, Jiwen

2017-01-01

Abstract It is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self‐catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether‐based solid polymer electrolyte (C‐PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether‐based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li+ and considerable ionic conductivity of 8.9 × 10−5 S cm−1 at ambient temperature. Moreover, the LiFePO4/C‐PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self‐catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes. PMID:29201612

Yield of 1,6-anhydro-3,4-dideoxy-β-D-glycero-hex-3-enopyranos-2-ulose (levoglucosenone) on the acid-catalyzed pyrolysis of cellulose and 1,6-anhydro-β-D-glucopyranose (levoglucosan)

Treesearch

Abraham Broido; Malcolm Evett; Craig C. Hodges

1975-01-01

Although 1,6-anhydro-3,4-dideoxy-β-D-glycero-hex-3-enopyranos-2-ulose (2) is produced by the acid-catalyzed pyrolysis of both cellulose and 1,6-anhydro-β-D-glucopyranose (1), data presented here show that the principal mechanism of its formation in the pyrolysis of cellulose is not via 1. Furthermore, the data provide evidence that 1 itself is not...

Iodide-ion-induced oscillations of the ferroin-catalyzed Belousov—Zhabotinskii reaction

NASA Astrophysics Data System (ADS)

Melicherčík, Milan; Treindl, Ľudovít

1992-08-01

Contrary to "classical" Belousov—Zhabotinskii (BZ) oscillatory systems, consisting of malonic acid, Ce(IV)—Ce(III) or Mn(III)—Mn(II) redox catalyst and KBrO 3 in solutions of H 2SO 4, where in an interval of added iodide initial concentrations 10 -4 mol dm -3 < [I -] 0 < 10 -3 mol dm -3 the oscillations have the same frequency and amplitude as in the absence of iodide, the effect of added iodide on the ferroin-catalyzed BZ system with methyl ester of 3-oxobutanoic acid leads to an increase in the number of oscillations and in the time of their duration. The dependence of this effect on substrate, bromate, iodide, sulfuric acid and ferroin concentrations has been studied. The observations may be explained by a mechanism involving direct reduction of ferroin by iodide, oxidation of iodide to iodate by bromate with a bromide production and eventual faster bromination and iodination of methyl ester of 3-oxobutanoic acid in relation to malonic acid.

Lipase-catalyzed synthesis of fatty acid amide (erucamide) using fatty acid and urea.

PubMed

Awasthi, Neeraj Praphulla; Singh, R P

2007-01-01

Ammonolysis of fatty acids to the corresponding fatty acid amides is efficiently catalysed by Candida antartica lipase (Novozym 435). In the present paper lipase-catalysed synthesis of erucamide by ammonolysis of erucic acid and urea in organic solvent medium was studied and optimal conditions for fatty amides synthesis were established. In this process erucic acid gave 88.74 % pure erucamide after 48 hour and 250 rpm at 60 degrees C with 1:4 molar ratio of erucic acid and urea, the organic solvent media is 50 ml tert-butyl alcohol (2-methyl-2-propanol). This process for synthesis is economical as we used urea in place of ammonia or other amidation reactant at atmospheric pressure. The amount of catalyst used is 3 %.

Ruthenium(III) catalyzed oxidation of sugar alcohols by dichloroisocyanuric acid—A kinetic study

NASA Astrophysics Data System (ADS)

Lakshman Kumar, Y.; Venkata Nadh, R.; Radhakrishnamurti, P. S.

2016-02-01

Kinetics of ruthenium(III) catalyzed oxidation of biologically important sugar alcohols (myo-inositol, D-sorbitol, and D-mannitol) by dichloroisocyanuric acid was carried out in aqueous acetic acid—perchloric medium. The reactions were found to be first order in case of oxidant and ruthenium(III). Zero order was observed with the concentrations of sorbitol and mannitol whereas, a positive fractional order was found in the case of inositol concentration. An inverse fractional order was observed with perchloric acid in oxidation of three substrates. Arrhenius parameters were calculated and a plausible mechanism was proposed.

Copper-Catalyzed, Directing Group-Assisted Fluorination of Arene and Heteroarene C-H Bonds

PubMed Central

Truong, Thanh; Klimovica, Kristine; Daugulis, Olafs

2013-01-01

We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of β-sp2 C-H bonds of benzoic acid derivatives and γ-sp2 C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs CuI catalyst, AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids. PMID:23758609

Thermodynamics of Enzyme-Catalyzed Reactions Database

National Institute of Standards and Technology Data Gateway

SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

Oligomerization of L-gamma-carboxyglutamic acid

NASA Technical Reports Server (NTRS)

Hill, A. R. Jr; Orgel, L. E.; Bada, J. L. (Principal Investigator)

1999-01-01

Unlike glutamic acid, L-gamma-carboxyglutamic acid does not oligomerize efficiently when treated with carbonyldiimidazole in aqueous solution. However, divalent ions such as Mg2+ catalyze the reaction, and lead to the formation of oligomers in good yield. In the presence of hydroxylapatite, L-gamma-carboxyglutamic acid oligomerizes efficiently in a reaction that proceeds in the absence of divalent ions but is further catalyzed when they are present. After 'feeding' 50 times with activated amino acid in the presence of the Mg2+ ion, oligomers longer than the 20-mer could be detected. The effect of hydroxylapatite on peptide elongation is very sensitive to the nature of the activated amino acid and the acceptor peptide. Glutamic acid oligomerizes more efficiently than L-gamma-carboxyglutamic acid on hydroxylapatite and adds more efficiently to decaglutamic acid in solution. One might, therefore, expect that glutamic acid would add more efficiently than L-gamma-carboxyglutamic acid to decaglutamic acid on hydroxylapatite. The contrary is true--the addition of L-gamma-carboxyglutamic acid is substantially more efficient. This suggests that oligomerization on the surface of hydroxylapatite depends on the detailed match between the structure of the surface of the mineral and the structure of the oligomer.

Total synthesis of (+)-achalensolide based on the rh(i)-catalyzed allenic Pauson-Khand-type reaction.

PubMed

Hirose, Toshiyuki; Miyakoshi, Naoki; Mukai, Chisato

2008-02-01

The first total synthesis of (+)-achalensolide was achieved from a commercially available d-(-)-isoascorbic acid. The known epoxide, derived from d-(-)-isoascorbic acid, was converted into the allenyne, the Rh(I)-catalyzed Pauson-Khand-type reaction of which directly provided the bicyclo[5.3.0]decane system, a core framework of the title natural product. The construction of the gamma-lactone moiety and some chemical modifications resulted in the completion of the total synthesis of (+)-achalensolide.

Lipase-catalyzed highly enantioselective kinetic resolution of boron-containing chiral alcohols.

PubMed

Andrade, Leandro H; Barcellos, Thiago

2009-07-16

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained.

Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins

ERIC Educational Resources Information Center

Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines

2011-01-01

A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The…

Chemo- and regioselective homogeneous rhodium-catalyzed hydroamidomethylation of terminal alkenes to N-alkylamides.

PubMed

Raoufmoghaddam, Saeed; Drent, Eite; Bouwman, Elisabeth

2013-09-01

A rhodium/xantphos homogeneous catalyst system has been developed for direct chemo- and regioselective mono-N-alkylation of primary amides with 1-alkenes and syngas through catalytic hydroamidomethylation with 1-pentene and acetamide as model substrates. For appropriate catalyst performance, it appears to be essential that catalytic amounts of a strong acid promoter, such as p-toluenesulfonic acid (HOTs), as well as larger amounts of a weakly acidic protic promoter, particularly hexafluoroisopropyl alcohol (HOR(F) ) are applied. Apart from the product N-1-hexylacetamide, the isomeric unsaturated intermediates, hexanol and higher mass byproducts, as well as the corresponding isomeric branched products, can be formed. Under optimized conditions, almost full alkene conversion can be achieved with more than 80% selectivity to the product N-1-hexylamide. Interestingly, in the presence of a relatively high concentration of HOR(F) , the same catalyst system shows a remarkably high selectivity for the formation of hexanol from 1-pentene with syngas, thus presenting a unique example of a selective rhodium-catalyzed hydroformylation-hydrogenation tandem reaction under mild conditions. Time-dependent product formation during hydroamidomethylation batch experiments provides evidence for aldehyde and unsaturated intermediates; this clearly indicates the three-step hydroformylation/condensation/hydrogenation reaction sequence that takes place in hydroamidomethylation. One likely role of the weakly acidic protic promoter, HOR(F) , in combination with the strong acid HOTs, is to establish a dual-functionality rhodium catalyst system comprised of a neutral rhodium(I) hydroformylation catalyst species and a cationic rhodium(III) complex capable of selectively reducing the imide and/or ene-amide intermediates that are in a dynamic, acid-catalyzed condensation equilibrium with the aldehyde and amide in a syngas environment. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-catalyzed hydroaminocarbonylation of alkenes with amines: a strategy to overcome the basicity barrier imparted by aliphatic amines.

PubMed

Zhang, Guoying; Gao, Bao; Huang, Hanmin

2015-06-22

A novel and efficient palladium-catalyzed hydroaminocarbonylation of alkenes with aminals has been developed under mild reaction conditions, and allows the synthesis of a wide range of N-alkyl linear amides in good yields with high regioselectivity. On the basis of this method, a cooperative catalytic system operating by the synergistic combination of palladium, paraformaldehyde, and acid was established for promoting the hydroaminocarbonylation of alkenes with both aromatic and aliphatic amines, which do not react well under conventional palladium-catalyzed hydroaminocarbonylation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oligomerization of glycine and alanine catalyzed by iron oxides: implications for prebiotic chemistry.

PubMed

Shanker, Uma; Bhushan, Brij; Bhattacharjee, G; Kamaluddin

2012-02-01

Iron oxide minerals are probable constituents of the sediments present in geothermal regions of the primitive earth. They might have adsorbed different organic monomers (amino acids, nucleotides etc.) and catalyzed polymerization processes leading to the formation of the first living cell. In the present work we tested the catalytic activity of three forms of iron oxides (Goethite, Akaganeite and Hematite) in the intermolecular condensation of each of the amino acids glycine and L-alanine. The effect of zinc oxide and titanium dioxide on the oligomerization has also been studied. Oligomerization studies were performed for 35 days at three different temperatures 50, 90 and 120°C without applying drying/wetting cycling. The products formed were characterized by HPLC and ESI-MS techniques. All three forms of iron oxides catalyzed peptide bond formation (23.2% of gly2 and 10.65% of ala2). The reaction was monitored every 7 days. Formation of peptides was observed to start after 7 days at 50°C. Maximum yield of peptides was found after 35 days at 90°C. Reaction at 120°C favors formation of diketopiperazine derivatives. It is also important to note that after 35 days of reaction, goethite produced dimer and trimer with the highest yield among the oxides tested. We suggest that the activity of goethite could probably be due to its high surface area and surface acidity.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones.

PubMed

Takaki, Ken; Hino, Makoto; Ohno, Akira; Komeyama, Kimihiro; Yoshida, Hiroto; Fukuoka, Hiroshi

2017-01-01

Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.

Microbial degradation of poly(amino acid)s.

PubMed

Obst, Martin; Steinbüchel, Alexander

2004-01-01

Natural poly(amino acid)s are a group of poly(ionic) molecules (ionomers) with various biological functions and putative technical applications and play, therefore, an important role both in nature and in human life. Because of their biocompatibility and their synthesis from renewable resources, poly(amino acid)s may be employed for many different purposes covering a broad spectrum of medical, pharmaceutical, and personal care applications as well as the domains of agriculture and of environmental applications. Biodegradability is one important advantage of naturally occurring poly(amino acid)s over many synthetic polymers. The intention of this review is to give an overview about the enzyme systems catalyzing the initial steps in poly(amino acid) degradation. The focus is on the naturally occurring poly(amino acid)s cyanophycin, poly(epsilon-L-lysine) and poly(gamma-glutamic acid); but biodegradation of structurally related synthetic polyamides such as poly(aspartic acid) and nylons, which are known from various technical applications, is also included.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

PubMed Central

Hino, Makoto; Ohno, Akira; Komeyama, Kimihiro; Yoshida, Hiroto; Fukuoka, Hiroshi

2017-01-01

Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products. PMID:28904625

[Ru/AC catalyzed ozonation of recalcitrant organic compounds].

PubMed

Wang, Jian-Bing; Hou, Shao-Pei; Zhou, Yun-Rui; Zhu, Wan-Peng; He, Xu-Wen

2009-09-15

Ozonation and Ru/AC catalyzed ozonation of dimethyl phthalate (DMP), phenols and disinfection by-products precursors were studied. It shows that Ru/AC catalyst can obviously enhance the mineralization of organic compounds. In the degradation of DMP, TOC removal was 28.84% by ozonation alone while it was 66.13% by catalytic ozonation. In the oxidation of 23 kinds of phenols, TOC removals were 9.57%-56.08% by ozonation alone while they were 41.81%-82.32% by catalytic ozonation. Compared to ozonation alone, Ru/AC catalyzed ozonation was more effective for the reduction of disinfection by-products formation potentials in source water. The reduction of haloacetic acids formation potentials was more obvious than thichlomethane formation potentials. After the treatment by catalytic ozonation, the haloacetic acids formation potentials decreased from 144.02 microg/L to 58.50 microg/L, which was below the standard value of EPA. However ozonation alone could not make it reach the standard. The treatments of source water by BAC, O3 + BAC, O3/AC + BAC and Ru/AC + O3 + BAC were also studied. In the four processes, TOC removal was 3.80%, 20.14%, 27.45% and 48.30% respectively, COD removal was 4.37%, 27.22%, 39.91% and 50.00% respectively, UV254 removal was 8.16%, 62.24%, 67.03% and 84.95% respectively. Ru/AC + O3 + BAC process is more effective than the other processes for the removal of TOC, COD and UV254 and no ruthenium leaching observed in the solution. It is a promising process for the treatment of micro polluted source water.

DNA-Catalyzed Amide Hydrolysis.

PubMed

Zhou, Cong; Avins, Joshua L; Klauser, Paul C; Brandsen, Benjamin M; Lee, Yujeong; Silverman, Scott K

2016-02-24

DNA catalysts (deoxyribozymes) for a variety of reactions have been identified by in vitro selection. However, for certain reactions this identification has not been achieved. One important example is DNA-catalyzed amide hydrolysis, for which a previous selection experiment instead led to DNA-catalyzed DNA phosphodiester hydrolysis. Subsequent efforts in which the selection strategy deliberately avoided phosphodiester hydrolysis led to DNA-catalyzed ester and aromatic amide hydrolysis, but aliphatic amide hydrolysis has been elusive. In the present study, we show that including modified nucleotides that bear protein-like functional groups (any one of primary amino, carboxyl, or primary hydroxyl) enables identification of amide-hydrolyzing deoxyribozymes. In one case, the same deoxyribozyme sequence without the modifications still retains substantial catalytic activity. Overall, these findings establish the utility of introducing protein-like functional groups into deoxyribozymes for identifying new catalytic function. The results also suggest the longer-term feasibility of deoxyribozymes as artificial proteases.

Iodine-Catalyzed Isomerization of Dimethyl Muconate.

PubMed

Settle, Amy E; Berstis, Laura; Zhang, Shuting; Rorrer, Nicholas A; Hu, Haiming; Richards, Ryan M; Beckham, Gregg T; Crowley, Michael F; Vardon, Derek R

2018-06-11

cis,cis-Muconic acid is a platform bio-based chemical that can be upgraded to drop-in commodity and novel monomers. Among the possible drop-in products, dimethyl terephthalate can be synthesized via esterification, isomerization, Diels-Alder cycloaddition, and dehydrogenation. The isomerization of cis,cis-dimethyl muconate (ccDMM) to the trans,trans-form (ttDMM) can be catalyzed by iodine; however, studies have yet to address (i) the mechanism and reaction barriers unique to DMM, and (ii) the influence of solvent, potential for catalyst recycle, and recovery of high-purity ttDMM. To address this gap, we apply a joint computational and experimental approach to investigate iodine-catalyzed isomerization of DMM. Density functional theory calculations identified unique regiochemical considerations owing to the large number of halogen-diene coordination schemes. Both transition state theory and experiments estimate significant barrier reductions with photodissociated iodine. Solvent selection was critical for rapid kinetics, likely because of solvent complexation with iodine. Under select conditions, ttDMM yields of 95 % were achieved in <1 h with methanol, followed by high purity recovery (>98 %) with crystallization. Lastly, post-reaction iodine can be recovered and recycled with minimal loss of activity. Overall, these findings provide new insight into the mechanism and conditions necessary for DMM isomerization with iodine to advance the state-of-the-art for bio-based chemicals. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Engineering entropy-driven reactions and networks catalyzed by DNA.

PubMed

Zhang, David Yu; Turberfield, Andrew J; Yurke, Bernard; Winfree, Erik

2007-11-16

Artificial biochemical circuits are likely to play as large a role in biological engineering as electrical circuits have played in the engineering of electromechanical devices. Toward that end, nucleic acids provide a designable substrate for the regulation of biochemical reactions. However, it has been difficult to incorporate signal amplification components. We introduce a design strategy that allows a specified input oligonucleotide to catalyze the release of a specified output oligonucleotide, which in turn can serve as a catalyst for other reactions. This reaction, which is driven forward by the configurational entropy of the released molecule, provides an amplifying circuit element that is simple, fast, modular, composable, and robust. We have constructed and characterized several circuits that amplify nucleic acid signals, including a feedforward cascade with quadratic kinetics and a positive feedback circuit with exponential growth kinetics.

Oxidative metabolism of phenanthrene and anthracene by soil pseudomonads. The ring-fission mechanism

PubMed Central

Evans, W. C.; Fernley, H. N.; Griffiths, E.

1965-01-01

1. Phenanthrene is oxidatively metabolized by soil pseudomonads through trans-3,4-dihydro-3,4-dihydroxyphenanthrene to 3,4-dihydroxyphenanthrene, which then undergoes cleavage. 2. Some properties of the ring-fission product, cis-4-(1-hydroxynaphth-2-yl)-2-oxobut-3-enoic acid, are described. The Fe2+-dependent oxygenase therefore disrupts the bond between C-4 and the angular C of the phenanthrene nucleus. 3. An enzyme of the aldolase type converts the fission product into 1-hydroxy-2-naphthaldehyde (2-formyl-1-hydroxynaphthalene). An NAD-specific dehydrogenase is also present in the cell-free extract, which oxidizes the aldehyde to 1-hydroxy-2-naphthoic acid. This is then oxidatively decarboxylated to 1,2-dihydroxynaphthalene, thus allowing continuation of metabolism via the naphthalene pathway. 4. Anthracene is similarly metabolized, through 1,2-dihydro-1,2-dihydroxyanthracene to 1,2-dihydroxyanthracene, in which ring-fission occurs to give cis-4-(2-hydroxynaphth-3-yl)-2-oxobut-3-enoic acid. The position of cleavage is again at the bond between the angular C and C-1 of the anthracene nucleus. 5. Enzymes that convert the fission product through 2-hydroxy-3-naphthaldehyde into 2-hydroxy-3-naphthoic acid were demonstrated. The further metabolism of this acid is discussed. 6. The Fe2+-dependent oxygenase responsible for cleavage of all the o-dihydroxyphenol derivatives appears to be catechol 2,3-oxygenase, and is a constitutive enzyme in the Pseudomonas strains used. PMID:14342521

Substituted naphthoquinones as novel amino acid sensitive reagents for the detection of latent fingermarks on paper surfaces.

PubMed

Jelly, R; Lewis, S W; Lennard, C; Lim, K F; Almog, J

2010-10-15

In this paper, we present our preliminary studies into naphthoquinones as novel reagents for the detection of latent fingermarks on paper. Latent fingermarks deposited on paper substrates were treated with solutions of selected naphthoquinones in ethyl acetate/HFE-7100, with subsequent heating. The selected compounds were 1,4-dihydroxy-2-naphthoic acid, 1,2-naphthoquinone-4-sulfonate, 2-methoxy-1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone. All of the tested compounds yielded purple-brown visible fingermarks, which also exhibited photoluminescence when illuminated with a high intensity filtered light source at 555 nm and viewed through red goggles. Indirect heat using an oven at 150°C for 1h was found to be superior to direct heat with an iron, which while providing faster development lead to increased levels of background colouration. Luminescence spectrophotometry revealed differences in photoluminescence characteristics for fingermarks developed with the different naphthoquinones, with excitation over the range 530-590 nm. Luminescence spectrophotometry of developed lysine, glycine and serine spots on paper was used to confirm that the naphthoquinones were reacting with amino acids in the latent fingermark. Copyright © 2010 Elsevier B.V. All rights reserved.

Soft Ultraviolet (UV) Photopatterning and Metallization of Self-Assembled Monolayers (SAMs) Formed from the Lipoic Acid Ester of α-Hydroxy-1-acetylpyrene: The Generality of Acid-Catalyzed Removal of Thiol-on-Gold SAMs using Soft UV Light.

PubMed

Pukenas, Laurynas; Prompinit, Panida; Nishitha, Boda; Tate, Daniel J; Singh, N D Pradeep; Wälti, Christoph; Evans, Stephen D; Bushby, Richard J

2017-05-31

Under a layer of 0.1 M HCl in isopropanol, soft ultraviolet (UV) (365 nm) photolysis of the thiol-on-gold self-assembled monolayer (SAM) derived from the lipoic acid ester of α-hydroxy-1-acetylpyrene results in the expected removal of the acetylpyrene protecting group. When photolyzing through a mask, this can be used to produce a patterned surface and, at a controlled electrochemical potential, it is then possible to selectively and reversibly electrodeposit copper on the photolyzed regions. Rather surprisingly, under these photolysis conditions, there is not only the expected photodeprotection of the ester but also partial removal of the lipoic acid layer which has been formed. In further studies, it is shown that this type of acid-catalyzed photoremoval of SAM layers by soft UV is a rather general phenomenon and results in the partial removal of the thiol-on-gold SAM layers derived from other ω-thiolated carboxylic acids. However, this phenomenon is chain-length dependent. Under conditions in which there is a ∼60% reduction in the thickness of the SAM derived from dithiobutyric acid, the SAM derived from mercaptoundecanoic acid is almost unaffected. The process by which the shorter-chain SAM layers are partially removed is not fully understood because these compounds do not absorb significantly in the 365 nm region of the spectrum! Significantly, this study shows that acid catalysis photolysis of thiol-on-gold SAMs needs to be used with caution.

Inhibitors of amino acids biosynthesis as antifungal agents.

PubMed

Jastrzębowska, Kamila; Gabriel, Iwona

2015-02-01

Fungal microorganisms, including the human pathogenic yeast and filamentous fungi, are able to synthesize all proteinogenic amino acids, including nine that are essential for humans. A number of enzymes catalyzing particular steps of human-essential amino acid biosynthesis are fungi specific. Numerous studies have shown that auxotrophic mutants of human pathogenic fungi impaired in biosynthesis of particular amino acids exhibit growth defect or at least reduced virulence under in vivo conditions. Several chemical compounds inhibiting activity of one of these enzymes exhibit good antifungal in vitro activity in minimal growth media, which is not always confirmed under in vivo conditions. This article provides a comprehensive overview of the present knowledge on pathways of amino acids biosynthesis in fungi, with a special emphasis put on enzymes catalyzing particular steps of these pathways as potential targets for antifungal chemotherapy.

Spliceostatin hemiketal biosynthesis in Burkholderia spp. is catalyzed by an iron/α-ketoglutarate–dependent dioxygenase

PubMed Central

Eustáquio, Alessandra S.; Janso, Jeffrey E.; Ratnayake, Anokha S.; O’Donnell, Christopher J.; Koehn, Frank E.

2014-01-01

Spliceostatins are potent spliceosome inhibitors biosynthesized by a hybrid nonribosomal peptide synthetase−polyketide synthase (NRPS−PKS) system of the trans-acyl transferase (AT) type. Burkholderia sp. FERM BP-3421 produces hemiketal spliceostatins, such as FR901464, as well as analogs containing a terminal carboxylic acid. We provide genetic and biochemical evidence for hemiketal biosynthesis by oxidative decarboxylation rather than the previously hypothesized Baeyer–Villiger oxidative release postulated to be catalyzed by a flavin-dependent monooxygenase (FMO) activity internal to the last module of the PKS. Inactivation of Fe(II)/α-ketoglutarate–dependent dioxygenase gene fr9P led to loss of hemiketal congeners, whereas the mutant was still able to produce all major carboxylic acid-type compounds. FMO mutants, on the other hand, produced both hemiketal and carboxylic acid analogs containing an exocyclic methylene instead of an epoxide, indicating that the FMO is involved in epoxidation rather than Baeyer–Villiger oxidation. Moreover, recombinant Fr9P enzyme was shown to catalyze hydroxylation to form β-hydroxy acids, which upon decarboxylation led to hemiketal FR901464. Finally, a third oxygenase activity encoded in the biosynthetic gene cluster, the cytochrome P450 monooxygenase Fr9R, was assigned as a 4-hydroxylase based on gene inactivation results. Identification and deletion of the gene involved in hemiketal formation allowed us to generate a strain—the dioxygenase fr9P− mutant—that accumulates only the carboxylic acid-type spliceostatins, which are as potent as the hemiketal analogs, when derivatized to increase cell permeability, but are chemically more stable. PMID:25097259

Enhancement effects of chelating agents on the degradation of tetrachloroethene in Fe(III) catalyzed percarbonate system

PubMed Central

Miao, Zhouwei; Gu, Xiaogang; Lu, Shuguang; Brusseau, Mark L.; Zhang, Xiang; Fu, Xiaori; Danish, Muhammad; Qiu, Zhaofu; Sui, Qian

2015-01-01

The performance of Fe(III)-based catalyzed sodium percarbonate (SPC) for stimulating the oxidation of tetrachloroethene (PCE) for groundwater remediation applications was investigated. The chelating agents citric acid monohydrate (CIT), oxalic acid (OA), and Glutamic acid (Glu) significantly enhanced the degradation of PCE. Conversely, ethylenediaminetetraacetic acid (EDTA) had a negative impact on PCE degradation, which may due to its strong Fe chelation and HO• scavenging abilities. However, excessive SPC or chelating agent will retard PCE degradation. In addition, investigations using free radical probe compounds and radical scavengers revealed that PCE was primarily degraded by HO• radical oxidation in both the chelated and non-chelated systems, while O2•− also participated in the non-chelated system and the OA and Glu modified systems. According to the electron paramagnetic resonance (EPR) studies, the presence of HO• in the Fe(III)/SPC system was maintained much longer than that in the Fe(II)/SPC system. The results indicated that the addition of CIT, OA or Glu indeed enhanced the generation of HO• in the first 10 min and promoted degradation efficiency by increasing the amount of Fe(III) and maintaining the concentration of HO• radicals in solution. In conclusion, chelated Fe(III)-based catalyzed SPC oxidation is a promising method for the remediation of PCE-contaminated groundwater. PMID:26549979

Chemo-enzymatic synthesis of furfuralcohol from chestnut shell hydrolysate by a sequential acid-catalyzed dehydration under microwave and Escherichia coli CCZU-Y10 whole-cells conversion.

PubMed

Di, Junhua; Ma, Cuiluan; Qian, Jianghao; Liao, Xiaolong; Peng, Bo; He, Yucai

2018-08-01

In this study, chemo-enzymatic synthesis of furfuralcohol from biomass-derived xylose was successfully demonstrated by a sequential acid-catalyzed dehydration under microwave and whole-cells reduction. After dry dewaxed chestnut shells (CNS, 75 g/L) was acid-hydrolyzed with dilute oxalic acid (0.5 wt%) at 140 °C for 40 min, the obtained CNS-derived xylose (17.9 g/L xylose) could be converted to furfural at 78.8% yield with solid acid SO 4 2- /SnO 2 -Attapulgite (2.0 wt% catalyst loading) in the dibutyl phthalate-water (1:1, v:v) under microwave (600 W) at 180 °C for 10 min. In the dibutyl phthalate-water (1:1, v/v) media at 30 °C and pH 6.5, the furfural liquor (47.0 mM furfural) was biologically converted to furfuralcohol by recombinant Escherichia coli CCZU-Y10 whole-cells harboring an NADH-dependent reductase (PgCR) without extra addition of NAD + and glucose, and furfural was completely converted to furfuralcohol after 2.5 h. Clearly, this one-pot synthesis strategy can be effectively used for furfuralcohol production. Copyright © 2018 Elsevier Ltd. All rights reserved.

Thermo-kinetics of lipase-catalyzed synthesis of 6-O-glucosyldecanoate.

PubMed

Gumel, A M; Annuar, M S M; Heidelberg, T; Chisti, Y

2011-10-01

Lipase-catalyzed synthesis of 6-O-glucosyldecanoate from d-glucose and decanoic acid was performed in dimethyl sulfoxide (DMSO), a mixture of DMSO and tert-butanol and tert-butanol alone with a decreasing order of polarity. The highest conversion yield (> 65%) of decanoic acid was obtained in the blended solvent of intermediate polarity mainly because it could dissolve relatively large amounts of both the reactants. The reaction obeyed Michaelis-Menten type of kinetics. The affinity of the enzyme towards the limiting substrate (decanoic acid) was not affected by the polarity of the solvent, but increased significantly with temperature. The esterification reaction was endothermic with activation energy in the range of 60-67 kJ mol⁻¹. Based on the Gibbs energy values, in the solvent blend of DMSO and tert-butanol the position of the equilibrium was shifted more towards the products compared to the position in pure solvents. Monoester of glucose was the main product of the reaction. Copyright © 2011 Elsevier Ltd. All rights reserved.

Imino-Oxy Acetic Acid Dealkylation as Evidence for an Inner-Sphere Alcohol Intermediate in the Reaction Catalyzed by Peptidylglycine α-Hydroxylating Monooxygenase (PHM)

PubMed Central

McIntyre, Neil R.; Lowe, Edward W.; Merkler, David J.

2009-01-01

Peptidylglycine α-hydroxylating monooxygenase (PHM, EC 1.14.17.3) catalyzes the stereospecific hydroxylation of a glycyl α-carbon in a reaction that requires O2 and ascorbate. Subsequent dealkylation of the α-hydroxyglycine by another enzyme, peptidylamidoglycolate lyase (PAL. EC 4.3.2.5), yields a bioactive amide and glyoxylate. PHM is a non-coupled, type II dicopper monooxygenase which activates O2 at only a single copper atom, CuM. In this study, the PHM mechanism was probed using a non-natural substrate, benzaldehyde imino-oxy acetic acid (BIAA). PHM catalyzes the O-oxidative dealkylation of BIAA to benzaldoxime and glyoxylate with no involvement of PAL. The minimal kinetic mechanism for BIAA was shown to be steady-state ordered using primary deuterium kinetic isotope effects. The D(V/K)APPARENT, BIAA decreased from 14.7 ± 1.0 as [O2] → 0 to 1.0 ± 0.2 as [O2] → ∞ suggesting the dissociation rate constant from the PHM·BIAA complex decreases as [O2] increases; thereby, reducing the steady-state concentration of [PHM]free. BIAA was further used to differentiate between potential oxidative Cu/O species using a QM/MM reaction coordinate simulation to determine which species could yield product O-dealkylation that matched our experimental data. The results of this study provided compelling evidence for the presence of a covalently linked CuII-alkoxide intermediate with a quartet spin state responsible BIAA oxidation. PMID:19569683

Ionic Liquid Catalyzed Electrolyte for Electrochemical Polyaniline Supercapacitors

NASA Astrophysics Data System (ADS)

Inamdar, A. I.; Im, Hyunsik; Jung, Woong; Kim, Hyungsang; Kim, Byungchul; Yu, Kook-Hyun; Kim, Jin-Sang; Hwang, Sung-Min

2013-05-01

The effect of different wt.% of ionic liquid "1,6-bis (trimethylammonium-1-yl) hexane tetrafluoroborate" in 0.5 M LiClO4+PC electrolyte on the supercapacitor properties of polyaniline (PANI) thin film are investigated. The PANI film is synthesized using electropolymerization of aniline in the presence of sulfuric acid. The electrochemical properties of the PANI thin film are studied by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) measurements. The optimum amount of the ionic liquid is found to be 2 wt.% which provides better ionic conductivity of the electrolyte. The highest specific capacitance of 259 F/g is obtained using the 2 wt.% electrolyte. This capacitance remains at up to 208 F/g (80% capacity retention) after 1000 charge-discharge cycles at a current density of 0.5 mA/g. The PANI film in the 2 wt.% ionic liquid catalyzed 0.5 M LiClO4+PC electrolyte shows small electrochemical resistance, better rate performance and higher cyclability. The increased ionic conductivity of the 2 wt.% ionic liquid catalyzed electrolyte causes a reduction in resistance at the electrode/electrolyte interface, which can be useful in electrochemically-preferred power devices for better applicability.

Fe0 catalyzed photo-Fenton process to detoxify the biodegraded products of azo dye Mordant Yellow 10.

PubMed

Brindha, R; Muthuselvam, P; Senthilkumar, S; Rajaguru, P

2018-06-01

Inspired by the efficiency of the photo-Fenton process on oxidation of organic pollutants, we herein present the feasibility of visible light driven photo-Fenton process as a post treatment of biological method for the effective degradation and detoxification of monoazo dye Mordant Yellow 10 (MY10). Anaerobic degradation of MY10 by Pseudomonas aeroginosa formed aromatic amines which were further degraded in the subsequent Fe catalyzed photo-Fenton process carried out at pH 3.0, with iron shavings and H 2 O 2 under blue LED light illumination. LC-MS and stoichiometric analysis confirmed that reductive azo bond cleavage was the major reaction in anaerobic bacterial degradation of MY10 producing 4-amino benzene sulfonic acid (4-ABS) and 5-amino salicylic acid (5-ASA) which were further degraded into hydroxyl amines, nitroso and di/tri carboxylic acids by the photo-Fenton process. Toxicity studies with human small cell lung cancer A549 cells provide evidence that incorporation of Fe 0 catalyzed photo-Fenton step after anaerobic bacterial treatment improved the mineralization and detoxification of MY10 dye. Copyright © 2018 Elsevier Ltd. All rights reserved.

Copper-catalyzed C(sp3)-OH cleavage with concomitant C-C coupling: synthesis of 3-substituted isoindolinones.

PubMed

Rao, H Surya Prakash; Rao, A Veera Bhadra

2015-02-06

Copper(II) trifluoromethanesulfonate (Cu(OTf)2) efficiently catalyzes the C-C coupling of 3-hydoxyisoindolinones with a variety of aryl-, heteroaryl-, and alkenylboronic acids to furnish C(3) aryl-, heteroaryl-, and alkenyl-substituted isoindolinones. The coupling reactions work smoothly in 1,2-dicholoroethane (DCE) reflux, to effect both inter- and intramolecular versions. This is the first report on C(sp(3))-OH cleavage with concomitant C-C coupling. The photolabile 2-nitrobenzyl protecting group is most appropriate for promotion of the coupling reaction and for deprotection. The tetracyclic ring motif of the alkaloid neuvamine was prepared by applying the newly developed copper-catalyzed C-C coupling.

Nickel-Catalyzed, Carbonyl-Ene-Type Reactions: Selective for Alpha Olefins and More Efficient with Electron-Rich Aldehydes

PubMed Central

Ho, Chun-Yu; Ng, Sze-Sze; Jamison, Timothy F.

2011-01-01

Described are several classes of unusual or unprecedented carbonyl-ene-type reactions, including those between alpha olefins and aromatic aldehydes. Catalyzed by nickel, these processes complement existing Lewis acid-catalyzed methods in several respects. Not only are monosubstituted alkenes, aromatic aldehydes, and tert-alkyl aldehydes effective substrates, but monosubstituted olefins also react faster than those that are more substituted, and large or electron-rich aldehydes are more effective than small or electron-poor ones. Conceptually, in the presence of a nickel-phosphine catalyst, the combination of off-the-shelf alkenes, silyl triflates, and triethylamine functions as a replacement for an allylmetal reagent. PMID:16620106

Whey protein isolate with improved film properties through cross-linking catalyzed by small laccase from Streptomyces coelicolor.

PubMed

Quan, Wei; Zhang, Chong; Zheng, Meixia; Lu, Zhaoxin; Lu, Fengxia

2018-08-01

The effects of small laccase (SLAC) from Streptomyces coelicolor on the properties of whey protein isolate (WPI) films were studied. WPI was catalyze by SLAC without phenolic acid assistance. Particle size distribution results showed that some complexes with higher relative molecular weight formed in WPI samples treated with SLAC. The content of α-helixes decreased while those of β-sheets and random coils increased following SLAC treatment according to circular dichroism results. Fourier transform infrared spectral analysis suggested that some conformational changes occurred in WPI following SLAC treatment. Analysis of WPI films prepared by casting after SLAC treatment indicated that their film properties were all improved, including mechanical properties, solubility, water vapor, oxygen and carbon dioxide barrier properties, film color, light transmission, transparency and thermal properties. Compared with that of the control film, some obvious differences in the morphology of the WPI films were observed following SLAC treatment. This report demonstrates that laccase can directly catalyze protein cross-linking, which may be useful to improve the performance of protein films. In this study, SLAC was applied to WPI edible film during the film-making process. The results showed that SLAC can catalyze WPI cross-linking without phenolic acid assistance, and WPI film properties were improved after SLAC treatment. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industry.

Rhodium-catalyzed chemo-, regio-, and enantioselective addition of 2-pyridones to terminal allenes.

PubMed

Li, Changkun; Kähny, Matthias; Breit, Bernhard

2014-12-08

A rhodium-catalyzed chemo-, regio-, and enantioselective addition of 2-pyridones to terminal allenes to give branched N-allyl 2-pyridones is reported. Preliminary mechanistic studies support the hypothesis that the reaction was initiated from the more acidic 2-hydroxypyridine form, and the initial kinetic O-allylation product was finally converted into the thermodynamically more stable N-allyl 2-pyridones. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

NASA Technical Reports Server (NTRS)

Bohler, Christof; Hill, Aubrey R., Jr.; Orgel, Leslie E.

1996-01-01

Treatment of relatively concentrated aqueous solutions of 0-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

NASA Technical Reports Server (NTRS)

Boehler, Christof; Hill, Aubrey R., Jr.; Orgel, Leslie E.

1996-01-01

Treatment of relatively concentrated aqueous solutions of O-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Engineering an ATP-dependent D-Ala:D-Ala ligase for synthesizing amino acid amides from amino acids.

PubMed

Miki, Yuta; Okazaki, Seiji; Asano, Yasuhisa

2017-05-01

We successfully engineered a new enzyme that catalyzes the formation of D-Ala amide (D-AlaNH 2 ) from D-Ala by modifying ATP-dependent D-Ala:D-Ala ligase (EC 6.3.2.4) from Thermus thermophilus, which catalyzes the formation of D-Ala-D-Ala from two molecules of D-Ala. The new enzyme was created by the replacement of the Ser293 residue with acidic amino acids, as it was speculated to bind to the second D-Ala of D-Ala-D-Ala. In addition, a replacement of the position with Glu performed better than that with Asp with regards to specificity for D-AlaNH 2 production. The S293E variant, which was selected as the best enzyme for D-AlaNH 2 production, exhibited an optimal activity at pH 9.0 and 40 °C for D-AlaNH 2 production. The apparent K m values of this variant for D-Ala and NH 3 were 7.35 mM and 1.58 M, respectively. The S293E variant could catalyze the synthesis of 9.3 and 35.7 mM of D-AlaNH 2 from 10 and 50 mM D-Ala and 3 M NH 4 Cl with conversion yields of 93 and 71.4 %, respectively. This is the first report showing the enzymatic formation of amino acid amides from amino acids.

Nicotinic Acid Metabolism, V. A Cobamide Coenzyme-Dependent Conversion of α-Methyleneglutaric Acid to Dimethylmaleic Acid

PubMed Central

Kung, H. F.; Cederbaum, S.; Tsai, L.; Stadtman, T. C.

1970-01-01

A new B12-coenzyme-dependent isomerization, catalyzed by extracts of a nicotinate-fermenting clostridium, results in the conversion of α-methyleneglutaric acid to dimethylmaleic acid. These two acids are intermediates in the multistep anaerobic process wherein nicotinate is converted, ultimately, to one mole each of propionate, acetate, carbon dioxide, and ammonia. Dimethylmaleic acid reacts in its anhydride form with 2,4-dinitrophenylhydrazine to form N-2′,4′-dinitrophenyl-anilino-3,4-dimethylmaleimide. The characteristic reddish color exhibited by the latter derivative in alkaline solution serves as a convenient quantitative assay for dimethylmaleic acid. Comparison of the 2,4-dinitrophenylhydrazine derivatives of the product of the enzymic reaction and of synthetic dimethylmaleic anhydride showed them to be identical in every respect. PMID:5266166

Gas-phase hydration of glyoxylic acid: Kinetics and atmospheric implications.

PubMed

Liu, Ling; Zhang, Xiuhui; Li, Zesheng; Zhang, Yunhong; Ge, Maofa

2017-11-01

Oxocarboxylic acids are one of the most important organic species found in secondary organic aerosols and can be detected in diverse environments. But the hydration of oxocarboxylic acids in the atmosphere has still not been fully understood. Neglecting the hydration of oxocarboxylic acids in atmospheric models may be one of the most important reasons for the significant discrepancies between field measurements and abundance predictions of atmospheric models for oxocarboxylic acids. In the present paper, glyoxylic acid, as the most abundant oxocarboxylic acids in the atmosphere, has been selected as an example to study whether the hydration process can occur in the atmosphere and what the kinetic process of hydration is. The gas-phase hydration of glyoxylic acid to form the corresponding geminal diol and those catalyzed by atmospheric common substances (water, sulfuric acid and ammonia) have been investigated at the CCSD(T)-F12/cc-pVDZ-F12//M06-2X/6-311++G(3df,3pd) level of theory. The contour map of electron density difference of transition states have been further analyzed. It is indicated that these atmospheric common substances can all catalyze on the hydration to some extent and sulfuric acid is the most effective reducing the Gibbs free energy of activation to 9.48 kcal/mol. The effective rate constants combining the overall rate constants and concentrations of the corresponding catalysts have shown that water and sulfuric acid are both important catalysts and the catalysis of sulfuric acid is the most effective for the gas-phase hydration of glyoxylic acid. This catalyzed processes are potentially effective in coastal regions and polluted regions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Understanding the hydrolysis mechanism of ethyl acetate catalyzed by an aqueous molybdocene: a computational chemistry investigation.

PubMed

Tílvez, Elkin; Cárdenas-Jirón, Gloria I; Menéndez, María I; López, Ramón

2015-02-16

A thoroughly mechanistic investigation on the [Cp2Mo(OH)(OH2)](+)-catalyzed hydrolysis of ethyl acetate has been performed using density functional theory methodology together with continuum and discrete-continuum solvation models. The use of explicit water molecules in the PCM-B3LYP/aug-cc-pVTZ (aug-cc-pVTZ-PP for Mo)//PCM-B3LYP/aug-cc-pVDZ (aug-cc-pVDZ-PP for Mo) computations is crucial to show that the intramolecular hydroxo ligand attack is the preferred mechanism in agreement with experimental suggestions. Besides, the most stable intermediate located along this mechanism is analogous to that experimentally reported for the norbornenyl acetate hydrolysis catalyzed by molybdocenes. The three most relevant steps are the formation and cleavage of the tetrahedral intermediate immediately formed after the hydroxo ligand attack and the acetic acid formation, with the second one being the rate-determining step with a Gibbs energy barrier of 36.7 kcal/mol. Among several functionals checked, B3LYP-D3 and M06 give the best agreement with experiment as the rate-determining Gibbs energy barrier obtained only differs 0.2 and 0.7 kcal/mol, respectively, from that derived from the experimental kinetic constant measured at 296.15 K. In both cases, the acetic acid elimination becomes now the rate-determining step of the overall process as it is 0.4 kcal/mol less stable than the tetrahedral intermediate cleavage. Apart from clarifying the identity of the cyclic intermediate and discarding the tetrahedral intermediate formation as the rate-determining step for the mechanism of the acetyl acetate hydrolysis catalyzed by molybdocenes, the small difference in the Gibbs energy barrier found between the acetic acid formation and the tetrahedral intermediate cleavage also uncovers that the rate-determining step could change when studying the reactivity of carboxylic esters other than ethyl acetate substrate specific toward molybdocenes or other transition metal complexes. Therefore

Synthesis of antiviral tetrahydrocarbazole derivatives by photochemical and acid-catalyzed C-H functionalization via intermediate peroxides (CHIPS).

PubMed

Gulzar, Naeem; Klussmann, Martin

2014-06-20

The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Here, we describe a two-step procedure to functionalize indole derivatives, more specifically tetrahydrocarbazoles, by C-H amination using only elemental oxygen as oxidant. The reaction uses the principle of C-H functionalization via Intermediate PeroxideS (CHIPS). In the first step, a hydroperoxide is generated oxidatively using visible light, a photosensitizer and elemental oxygen. In the second step, the N-nucleophile, an aniline, is introduced by Brønsted-acid catalyzed activation of the hydroperoxide leaving group. The products of the first and second step often precipitate and can be conveniently filtered off. The synthesis of a biologically active compound is shown.

Facile and Promising Method for Michael Addition of Indole and Pyrrole to Electron-Deficient trans-β-Nitroolefins Catalyzed by a Hydrogen Bond Donor Catalyst Feist's Acid and Preliminary Study of Antimicrobial Activity

PubMed Central

Al Majid, Abdullah M. A.; Islam, Mohammad Shahidul; Barakat, Assem; Al-Agamy, Mohamed H. M.; Naushad, Mu.

2014-01-01

The importance of cooperative hydrogen-bonding effects has been demonstrated using novel 3-methylenecyclopropane-1,2-dicarboxylic acid (Feist's acid (FA)) as hydrogen bond donor catalysts for the addition of indole and pyrrole to trans-β-nitrostyrene derivatives. Because of the hydrogen bond donor (HBD) ability, Feist's acid (FA) has been introduced as a new class of hydrogen bond donor catalysts for the activation of nitroolefin towards nucleophilic substitution reaction. It has effectively catalyzed the Michael addition of indoles and pyrrole to β-nitroolefins under optimum reaction condition to furnish the corresponding Michael adducts in good to excellent yields (up to 98%). The method is general, atom-economical, convenient, and eco-friendly and could provide excellent yields and regioselectivities. Some newly synthesized compounds were for examined in vitro antimicrobial activity and their preliminary results are reported. PMID:24574906

Improved synthesis of isostearic acid using zeolite catalysts

USDA-ARS?s Scientific Manuscript database

Isostearic acids are unique and important biobased products with superior properties. Unfortunately, they are not widely utilized in industry because they are produced as byproducts from a process called clay-catalyzed oligomerization of tall oil fatty acids. Generally, this clay method results in...

Dynamic kinetic asymmetric transformation (DYKAT) by combined amine- and transition-metal-catalyzed enantioselective cycloisomerization.

PubMed

Zhao, Gui-Ling; Ullah, Farman; Deiana, Luca; Lin, Shuangzheng; Zhang, Qiong; Sun, Junliang; Ibrahem, Ismail; Dziedzic, Pawel; Córdova, Armando

2010-02-01

The first examples of one-pot highly chemo- and enantioselective dynamic kinetic asymmetric transformations (DYKATs) involving alpha,beta-unsaturated aldehydes and propargylated carbon acids are presented. These DYKATs, which proceed by a combination of catalytic iminium activation, enamine activation, and Pd(0)-catalyzed enyne cycloisomerization, give access to functionalized cyclopentenes with up to 99 % ee and can be used for the generation of all-carbon quaternary stereocenters.

Cobalt-catalyzed hydrogenation of esters to alcohols: unexpected reactivity trend indicates ester enolate intermediacy.

PubMed

Srimani, Dipankar; Mukherjee, Arup; Goldberg, Alexander F G; Leitus, Gregory; Diskin-Posner, Yael; Shimon, Linda J W; Ben David, Yehoshoa; Milstein, David

2015-10-12

The atom-efficient and environmentally benign catalytic hydrogenation of carboxylic acid esters to alcohols has been accomplished in recent years mainly with precious-metal-based catalysts, with few exceptions. Presented here is the first cobalt-catalyzed hydrogenation of esters to the corresponding alcohols. Unexpectedly, the evidence indicates the unprecedented involvement of ester enolate intermediates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly efficient Cu(I)-catalyzed oxidation of alcohols to ketones and aldehydes with diaziridinone.

PubMed

Zhu, Yingguang; Zhao, Baoguo; Shi, Yian

2013-03-01

A novel and efficient Cu(I)-catalyzed oxidation of alcohols has been achieved with di-tert-butyldiaziridinone as the oxidant under mild conditions. A wide variety of primary and secondary alcohols with various functional groups can be oxidized to aldehydes and ketones in high yields. The reaction proceeds under neutral conditions making it compatible with acid- or base-sensitive substrates, and it is amenable to gram scale.

Silver-Catalyzed Cyclopropanation of Alkenes Using N-Nosylhydrazones as Diazo Surrogates.

PubMed

Liu, Zhaohong; Zhang, Xinyu; Zanoni, Giuseppe; Bi, Xihe

2017-12-15

An efficient silver-catalyzed [2 + 1] cyclopropanation of sterically hindered internal alkenes with diazo compounds in which room-temperature-decomposable N-nosylhydrazones are used as diazo surrogates is reported. The unexpected unique catalytic activity of silver was ascribed to its dual role as a Lewis acid activating alkene substrates and as a transition metal forming silver carbenoids. A wide range of internal alkenes, including challenging diarylethenes, were suitable for this protocol, thereby affording a variety of cyclopropanes with high efficiency in a stereoselective manner under mild conditions.

An endogenous factor enhances ferulic acid decarboxylation catalyzed by phenolic acid decarboxylase from Candida guilliermondii

PubMed Central

2012-01-01

The gene for a eukaryotic phenolic acid decarboxylase of Candida guilliermondii was cloned, sequenced, and expressed in Escherichia coli for the first time. The structural gene contained an open reading frame of 504 bp, corresponding to 168 amino acids with a calculated molecular mass of 19,828 Da. The deduced amino sequence exhibited low similarity to those of functional phenolic acid decarboxylases previously reported from bacteria with 25-39% identity and to those of PAD1 and FDC1 proteins from Saccharomyces cerevisiae with less than 14% identity. The C. guilliermondii phenolic acid decarboxylase converted the main substrates ferulic acid and p-coumaric acid to the respective corresponding products. Surprisingly, the ultrafiltrate (Mr 10,000-cut-off) of the cell-free extract of C. guilliermondii remarkably activated the ferulic acid decarboxylation by the purified enzyme, whereas it was almost without effect on the p-coumaric acid decarboxylation. Gel-filtration chromatography of the ultrafiltrate suggested that an endogenous amino thiol-like compound with a molecular weight greater than Mr 1,400 was responsible for the activation. PMID:22217315

Delineation of the Caffeine C-8 Oxidation Pathway in Pseudomonas sp. Strain CBB1 via Characterization of a New Trimethyluric Acid Monooxygenase and Genes Involved in Trimethyluric Acid Metabolism

PubMed Central

Mohanty, Sujit Kumar; Yu, Chi-Li; Das, Shuvendu; Louie, Tai Man; Gakhar, Lokesh

2012-01-01

The molecular basis of the ability of bacteria to live on caffeine via the C-8 oxidation pathway is unknown. The first step of this pathway, caffeine to trimethyluric acid (TMU), has been attributed to poorly characterized caffeine oxidases and a novel quinone-dependent caffeine dehydrogenase. Here, we report the detailed characterization of the second enzyme, a novel NADH-dependent trimethyluric acid monooxygenase (TmuM), a flavoprotein that catalyzes the conversion of TMU to 1,3,7-trimethyl-5-hydroxyisourate (TM-HIU). This product spontaneously decomposes to racemic 3,6,8-trimethylallantoin (TMA). TmuM prefers trimethyluric acids and, to a lesser extent, dimethyluric acids as substrates, but it exhibits no activity on uric acid. Homology models of TmuM against uric acid oxidase HpxO (which catalyzes uric acid to 5-hydroxyisourate) reveal a much bigger and hydrophobic cavity to accommodate the larger substrates. Genes involved in the caffeine C-8 oxidation pathway are located in a 25.2-kb genomic DNA fragment of CBB1, including cdhABC (coding for caffeine dehydrogenase) and tmuM (coding for TmuM). Comparison of this gene cluster to the uric acid-metabolizing gene cluster and pathway of Klebsiella pneumoniae revealed two major open reading frames coding for the conversion of TM-HIU to S-(+)-trimethylallantoin [S-(+)-TMA]. The first one, designated tmuH, codes for a putative TM-HIU hydrolase, which catalyzes the conversion of TM-HIU to 3,6,8-trimethyl-2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (TM-OHCU). The second one, designated tmuD, codes for a putative TM-OHCU decarboxylase which catalyzes the conversion of TM-OHCU to S-(+)-TMA. Based on a combination of enzymology and gene-analysis, a new degradative pathway for caffeine has been proposed via TMU, TM-HIU, TM-OHCU to S-(+)-TMA. PMID:22609920

Diazo compounds and N-tosylhydrazones: novel cross-coupling partners in transition-metal-catalyzed reactions.

PubMed

Xiao, Qing; Zhang, Yan; Wang, Jianbo

2013-02-19

Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo

Detection of choline and phosphatidic acid (PA) catalyzed by phospholipase D (PLD) using MALDI-QIT-TOF/MS with 9-aminoacridine matrix.

PubMed

Park, Kyung-Eui; Kim, Jun-Dal; Nagashima, Yusuke; Kako, Koichiro; Daitoku, Hiroaki; Matsui, Motoki; Park, Gwi Gun; Fukamizu, Akiyoshi

2014-01-01

Phospholipase D (PLD) catalyzes the hydrolysis of phosphatidylcholine (PC), the most abundant phospholipids of plasma membrane, resulting in the production of choline and phosphatidic acid (PA). Choline is a precursor of the neurotransmitter acetylcholine, whereas PA functions as an intracellular lipid mediator of diverse biological functions. For assessing PLD activity in vitro, PLD-derived choline has been often analyzed with radioactive or non-radioactive methods. In this study, we have developed a new method for detecting choline and PA with MALDI-QIT-TOF/MS by using 9-aminoacridine as a matrix. The standard calibration curves showed that choline and PA could be detected with linearity over the range from 0.05 and 1 pmol, respectively. Importantly, this method enables the concomitant detection of choline and PA as a reaction product of PC hydrolysis by PLD2 proteins. Thus, our simple and direct method would be useful to characterize the enzymatic properties of PLD, thereby providing insight into mechanisms of PLD activation.

Synthesis of δ- and α-Carbolines via Nickel-Catalyzed [2 + 2 + 2] Cycloaddition of Functionalized Alkyne-Nitriles with Alkynes.

PubMed

Wang, Gaonan; You, Xu; Gan, Yi; Liu, Yuanhong

2017-01-06

A new method for the synthesis of δ- and α-carbolines through Ni-catalyzed [2 + 2 + 2] cycloaddition of ynamide-nitriles or alkyne-cyanamides with alkynes has been developed. The catalytic system of NiCl 2 (DME)/dppp/Zn with a low-cost Ni(II)-precursor was first utilized in Ni-catalyzed [2 + 2 + 2] cycloaddition reactions, and the in situ generated Lewis acid may play an important role for the successful transformation. Not only internal alkynes but also terminal alkynes undergo the desired cycloaddition reactions efficiently to furnish the carboline derivatives with wide diversity and functional group tolerance.

Lysophosphatidylcholine synthesis by lipase-catalyzed ethanolysis.

PubMed

Yang, Guolong; Yang, Ruoxi; Hu, Jingbo

2015-01-01

Lysophosphatidylcholine (LPC) is amphiphilic substance, and possesses excellent physiological functions. In this study, LPC was prepared through ethanolysis of phosphatidylcholine (PC) in n-hexane or solvent free media catalyzed by Novozym 435 (from Candida antarctica), Lipozyme TLIM (from Thermomcyces lanuginosus) and Lipozyme RMIM (from Rhizomucor miehei). The results showed that three immobilized lipases from Candida Antarctica, Thermomcyces lanuginosus and Rhizomucor miehei could catalyze ethanolysis of PC efficiently. In n-hexane, the LPC conversions of ethanolysis of PC catalyzed by Novozyme 435, Lipozyme TLIM and Lipozyme RMIM could reach to 98.5 ± 1.6%, 94.6 ± 1.4% and 93.7 ± 1.8%, respectively. In solvent free media, the highest LPC conversions of ethanolysis of PC catalyzed by Novozyme 435, Lipozyme TL IM and Lipozyme RM IM were 97.7 ± 1.7%, 93.5 ± 1.2% and 93.8 ± 1.9%, respectively. The catalytic efficiencies of the three lipases were in the order of Novozyme 435 > Lipozyme TLIM > Lipozyme RMIM. Furthermore, their catalytic efficiencies in n-hexane were better than those in solvent free media.

Novel syn intramolecular pathway in base-catalyzed 1,2-elimination reactions of beta-acetoxy esters.

PubMed

Mohrig, Jerry R; Carlson, Hans K; Coughlin, Jane M; Hofmeister, Gretchen E; McMartin, Lea A; Rowley, Elizabeth G; Trimmer, Elizabeth E; Wild, Andrew J; Schultz, Steve C

2007-02-02

As part of a comprehensive investigation of electronic effects on the stereochemistry of base-catalyzed 1,2-elimination reactions, we observed a new syn intramolecular pathway in the elimination of acetic acid from beta-acetoxy esters and thioesters. 1H and 2H NMR investigation of reactions using stereospecifically labeled tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanoate (1) and its (2R*,3S*) diastereomer (2) shows that 23 +/- 2% syn elimination occurs. The elimination reactions were catalyzed with KOH or (CH3)4NOH in ethanol/water under rigorously non-ion-pairing conditions. By contrast, the more sterically hindered beta-trimethylacetoxy ester produces only 6 +/- 1% syn elimination. These data strongly support an intramolecular (Ei) syn path for elimination of acetic acid, most likely through the oxyanion produced by nucleophilic attack at the carbonyl carbon of the beta-acetoxy group. The analogous thioesters, S-tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanethioate (3) and its (2R*,3S*) diastereomer (4), showed 18 +/- 2% syn elimination, whereas the beta-trimethylacetoxy substrate gave 5 +/- 1% syn elimination. The more acidic thioester substrates do not produce an increased amount of syn stereoselectivity even though their elimination reactions are at the E1cb interface.

Dipeptide derivative synthesis catalyzed by Pseudomonas aeruginosa elastase.

PubMed

Rival, S; Besson, C; Saulnier, J; Wallach, J

1999-02-01

Pseudomonas aeruginosa elastase was used to synthesize various N-protected dipeptide amides. The identity of the products was confirmed by FAB(+)-MS. After recrystallization, the yield of their synthesis was calculated, their purity was checked by RP-HPLC and their melting point was measured. With regard to the hydrolysis, it is well-established that the enzyme prefers hydrophobic amino acids in P'1 position and it has a wide specificity for the P1 position. This specificity was demonstrated to be quite unchanged when comparing the initial rates of peptide bond formation between different carboxyl donors (Z-aa) and nucleophiles (aa-NH2). The elastase, but not the thermolysin, was notably able to incorporate tyrosine and tryptophan in P'1 position. Furthermore, synthesis initial rates were at least 100 times faster with the elastase. To overcome the problematic condensation of some amino acids during chemical peptide synthesis, it has been previously suggested that enzymatic steps can combine with a chemical strategy. We demonstrated that the elastase readily synthesizes dipeptide derivatives containing various usual N-protecting groups. It was especially able to condense phenylalaninamide to Fmoc- and Boc-alanine. Increasing interest in peptides containing unnatural amino acids led us to try the elastase-catalyzed synthesis of Z-dipeptide amides including those amino acids in the P1 position. A synthesis was demonstrated with alphaAbu, Nle, Nva and Phg.

Thermostable Lipoxygenase, a Key Enzyme in the Conversion of Linoleic Acid into Thrihydroxy-octadecenoic Acid by Pseudomonas aeruginosa PR3

USDA-ARS?s Scientific Manuscript database

Lipoxygenases (LOX) constitute a family of lipid-peroxidizing enzymes catalyzing the oxidation of unsaturated fatty acid with (1Z,4Z)-pentadiene structural unit, leading to formation of the conjugated (Z,E)-hydroperoxydienoic acid. LOXs have been known to be widely distributed in plants and animals...

A General Method for Copper-Catalyzed Arene Cross-Dimerization

PubMed Central

Do, Hien-Quang; Daugulis, Olafs

2011-01-01

A general method for a highly regioselective, copper-catalyzed cross-coupling of two aromatic compounds by using iodine oxidant has been developed. The reactions involve an initial iodination of one arene followed by arylation of the most acidic C-H bond of the other coupling component. Cross-coupling of electron-rich arenes, electron-poor arenes, five- and six-membered heterocycles is possible in many combinations. Typically, 1/1.5 to 1/3 ratio of coupling components is used in contrast to existing methodology that often employs a large excess of one of the arenes. Common functionalities such as ester, ketone, aldehyde, ether, nitrile, nitro, and amine are well-tolerated. PMID:21823581

Kinetics of acid-catalyzed cleavage of procyanindins

Treesearch

Richard W. Hemingway; Gerald W. McGraw

1983-01-01

Comparison of the rates of cleavage of isomeric procyanidin dimers in the presence of excess phenylmethane thiol and acetic acid showed that compounds with a C(4)-C(8) interflavanoid bond were cleaved more rapidly than their C(4)-C(6) linked isomers, that 2,3-cis isomers with an axial flavan substituent were cleaved more-rapidly than a 2,3-...

Enhancement of nitric oxide release and hemocompatibility by surface chirality of D-tartaric acid grafting

NASA Astrophysics Data System (ADS)

Han, Honghong; Wang, Ke; Fan, Yonghong; Pan, Xiaxin; Huang, Nan; Weng, Yajun

2017-12-01

Nitric Oxide (NO) generation from endogenous NO-donors catalyzed by diselenide modified biomaterials has been reported. Here we reported surface chirality by L-tartaric acid and D-tartaric acid grafting on the outermost showed a significant impact on diselenide modified biomaterials, which modulated protein adsorption, NO release and anti-platelet adhesion properties. D-tartaric acid grafted surface showed more blood protein adsorption than that of L-surfaces by QCM analysis, however, ELISA analysis disclosed less fibrinogen denatured on the D surfaces. Due to the surface ratio of selenium decreasing, NO release catalyzed by L-tartaric acid grafting on the outermost significantly decreased in comparison to that of only selenocystamine immobilized surfaces. While NO release catalyzed by D-tartaric acid grafting on the outermost didn't decrease and was similar with that of selenocystamine immobilized surfaces. Surface chirality combined with NO release had synergetic effects on platelet adhesion, and it showed the lowest number of platelets adhered on the D-tartaric acid grafted surfaces. Thus surface chirality from D-tartaric acid grafting enhanced hemocompatibility of the surface in this study. Our work provides new insights into engineering novel blood contacting biomaterials by taking into account surface chirality.

Cytochromes P450 Catalyze the Reduction of α,β-Unsaturated Aldehydes

PubMed Central

Amunom, Immaculate; Dieter, Laura J.; Tamasi, Viola; Cai, Jan; Conklin, Daniel J.; Srivastava, Sanjay; Martin, Martha V.; Guengerich, F. Peter; Prough, Russell A.

2011-01-01

The metabolism of α,β-unsaturated aldehydes, e.g. 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O2, and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ≅ P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 & rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions, but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and α-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of reduction of α,β-unsaturated aldehydes in liver. PMID:21766881

Carbon Isotope Systematics in Mineral-Catalyzed Hydrothermal Organic Synthesis Processes at High Temperature and Pressures

NASA Technical Reports Server (NTRS)

Fu, Qi; Socki, R. A.; Niles, Paul B.

2011-01-01

Observation of methane in the Martian atmosphere has been reported by different detection techniques. Reduction of CO2 and/or CO during serpentization by mineral surface catalyzed Fischer-Tropsch Type (FTT) synthesis may be one possible process responsible for methane generation on Mars. With the evidence a recent study has discovered for serpentinization in deeply buried carbon rich sediments, and more showing extensive water-rock interaction in Martian history, it seems likely that abiotic methane generation via serpentinization reactions may have been common on Mars. Experiments involving mineral-catalyzed hydrothermal organic synthesis processes were conducted at 750 C and 5.5 Kbars. Alkanes, alcohols and carboxylic acids were identified as organic compounds. No "isotopic reversal" of delta C-13 values was observed for alkanes or carboxylic acids, suggesting a different reaction pathway than polymerization. Alcohols were proposed as intermediaries formed on mineral surfaces at experimental conditions. Carbon isotope data were used in this study to unravel the reaction pathways of abiotic formation of organic compounds in hydrothermal systems at high temperatures and pressures. They are instrumental in constraining the origin and evolution history of organic compounds on Mars and other planets.

Highly Efficient Cu(I)-Catalyzed Oxidation of Alcohols to Ketones and Aldehydes with Diaziridinone

PubMed Central

Zhu, Yingguang; Zhao, Baoguo

2013-01-01

A novel and efficient Cu(I)-catalyzed oxidation of alcohols has been achieved with di-tert-butyldiaziridinone as oxidant under mild conditions. A wide variety of primary and secondary alcohols with various functional groups can be oxidized to aldehydes and ketones in high yields. The reaction proceeds under neutral conditions making it compatible with acid or base-sensitive substrates, and it is amenable to gram scale. PMID:23413952

Mesoepitaxy: A Universal Route to Oriented Materials

DTIC Science & Technology

1993-06-14

naphthoic acid) (VecuaZ, Hoechst-Celanese], a perfluorinated copolymer of ethylene and propylene (FEP TI00, Du Pont], poly(butylene terephthalate) (PBT...189 meV). In ferences are evident in the vibronic character of the ab- addition, the zero-phonon emission line, now at 2.09 eV, sorption and emission...the ab- sorption spectra is disorder-induced localization. To model the photoluminescence spectrum, we con- Qualitatively, the disordered -,r-electron

Preparation of activated petroleum coke for removal of naphthenic acids model compounds: Box-Behnken design optimization of KOH activation process.

PubMed

Niasar, Hojatallah Seyedy; Li, Hanning; Das, Sreejon; Kasanneni, Tirumala Venkateswara Rao; Ray, Madhumita B; Xu, Chunbao Charles

2018-04-01

This study employed Box-Behnken design and response surface methodology to optimize activation parameters for the production of activated petroleum coke (APC) adsorbent from petroleum coke (PC) to achieve highest adsorption capacity for three model naphthenic acids. Activated petroleum coke (APC) adsorbent with a BET surface area of 1726 m 2 /g and total pore volume of 0.85 cc/g was produced at the optimum activation conditions (KOH/coke mass ratio) of 3.0, activation temperature 790 °C, and activation time 3.47 h). Effects of the activation parameters on the adsorption pefromances (adsortion capaciy and kinetics) were investigated. With the APC obtained at the optimum activation condition, the maximum adsorption capacity of 451, 362, and 320 (mg/g) was achieved for 2-naphthoic acid, diphenylacetic acid and cyclohexanepentanoic acid (CP), respectively. Although, generally APC adsorbents with a higher specific surface area and pore volume provide better adsorption capacity, the textural properties (surface areas and pore volume) are not the only parameters determining the APC adsorbents' adsorption capacity. Other parameters such as surface functionalities play effective roles on the adsorption capacity of the produced APC adsorbents for NAs. The KOH activation process, in particular the acid washing step, distinctly reduced the sulfur and metals contents in the raw PC, decreasing the leaching potential of metals from APC adsorbents during adsorption. Copyright © 2018 Elsevier Ltd. All rights reserved.

Catalyzed and Electrocatalyzed Oxidation of l-Tyrosine and l-Phenylalanine to Dopachrome by Nanozymes.

PubMed

Hou, Jianwen; Vázquez-González, Margarita; Fadeev, Michael; Liu, Xia; Lavi, Ronit; Willner, Itamar

2018-06-13

Catalyzed oxygen insertion into C-H bonds represents a continuous challenge in chemistry. Particularly, driving this process at ambient temperature and aqueous media represents a "holy grail" in catalysis. We report on the catalyzed cascade transformations of l-tyrosine or l-phenylalanine to dopachrome in the presence of l-ascorbic acid/H 2 O 2 as oxidizing mixture and CuFe-Prussian Blue-like nanoparticles, Fe 3 O 4 nanoparticles or Au nanoparticles as catalysts. The process involves the primary transformation of l-tyrosine to l-DOPA that is further oxidized to dopachrome. The transformation of l-phenylalanine to dopachrome in the presence of CuFe-Prussian Blue-like nanoparticles and l-ascorbic acid/H 2 O 2 involves in the first step the formation of l-tyrosine and, subsequently, the operation of the catalytic oxidation cascade of l-tyrosine to l-DOPA and dopachrome. Electron spin resonance experiments demonstrate that ascorbate radicals and hydroxyl radicals play cooperative functions in driving the different oxygen-insertion processes. In addition, the aerobic elecrocatalyzed oxidation of l-tyrosine to dopachrome in the presence of naphthoquinone-modified Fe 3 O 4 nanoparticles and l-ascorbic acid is demonstrated. In this system, magnetic-field attraction of the naphthoquinone-modified Fe 3 O 4 nanoparticles onto the electrode allows the quinone-mediated electrocatalyzed reduction of O 2 to H 2 O 2 (bias potential -0.5 V vs SCE). The electrogenerated H 2 O 2 is then utilized to promote the transformation of l-tyrosine to dopachrome in the presence of l-ascorbic acid and Fe 3 O 4 catalyst.

Biodiesel production from used cooking oil by two-step heterogeneous catalyzed process.

PubMed

Srilatha, K; Prabhavathi Devi, B L A; Lingaiah, N; Prasad, R B N; Sai Prasad, P S

2012-09-01

The present study demonstrates the production of biodiesel from used cooking oil containing high free fatty acid by a two-step heterogeneously catalyzed process. The free fatty acids were first esterified with methanol using a 25 wt.% TPA/Nb(2)O(5) catalyst followed by transesterification of the oil with methanol over ZnO/Na-Y zeolite catalyst. The catalysts were characterized by XRD, FT-IR, BET surface area and CO(2)-TPD. In the case of transesterification the effect of reaction parameters, such as catalyst concentration, methanol to oil molar ratio and reaction temperature, on the yield of ester were investigated. The catalyst with 20 wt.% ZnO loading on Na-Y exhibited the highest activity among the others. Both the solid acid and base catalysts were found to be reusable for several times indicating their efficacy in the two-step process. Copyright © 2012 Elsevier Ltd. All rights reserved.

Benz[a]anthracene Biotransformation and Production of Ring Fission Products by Sphingobium sp. Strain KK22

PubMed Central

Kunihiro, Marie; Ozeki, Yasuhiro; Nogi, Yuichi; Hamamura, Natsuko

2013-01-01

A soil bacterium, designated strain KK22, was isolated from a phenanthrene enrichment culture of a bacterial consortium that grew on diesel fuel, and it was found to biotransform the persistent environmental pollutant and high-molecular-weight polycyclic aromatic hydrocarbon (PAH) benz[a]anthracene. Nearly complete sequencing of the 16S rRNA gene of strain KK22 and phylogenetic analysis revealed that this organism is a new member of the genus Sphingobium. An 8-day time course study that consisted of whole-culture extractions followed by high-performance liquid chromatography (HPLC) analyses with fluorescence detection showed that 80 to 90% biodegradation of 2.5 mg liter−1 benz[a]anthracene had occurred. Biodegradation assays where benz[a]anthracene was supplied in crystalline form (100 mg liter−1) confirmed biodegradation and showed that strain KK22 cells precultured on glucose were equally capable of benz[a]anthracene biotransformation when precultured on glucose plus phenanthrene. Analyses of organic extracts from benz[a]anthracene biodegradation by liquid chromatography negative electrospray ionization tandem mass spectrometry [LC/ESI(−)-MS/MS] revealed 10 products, including two o-hydroxypolyaromatic acids and two hydroxy-naphthoic acids. 1-Hydroxy-2- and 2-hydroxy-3-naphthoic acids were unambiguously identified, and this indicated that oxidation of the benz[a]anthracene molecule occurred via both the linear kata and angular kata ends of the molecule. Other two- and single-aromatic-ring metabolites were also documented, including 3-(2-carboxyvinyl)naphthalene-2-carboxylic acid and salicylic acid, and the proposed pathways for benz[a]anthracene biotransformation by a bacterium were extended. PMID:23686261

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C-H carbenoid functionalization.

PubMed

Patel, Pitambar; Borah, Gongutri

2016-12-22

Herein we disclose the first report on the synthesis of oxindole derivatives from acetanilide via Ir(iii)-catalyzed intermolecular C-H functionalization with diazotized Meldrum's acid. A broad range of substituted anilides were found to react smoothly under the Ir(iii)-catalytic system to afford the corresponding N-protected oxindoles. The N-protecting groups, such as Ac, Bz or Piv, can be easily removed to furnish the oxindole. Various synthetic applications of the synthesized oxindole were also demonstrated.

Dinuclear Zinc-Prophenol-Catalyzed Enantioselective α-Hydroxyacetate Aldol Reaction with Activated Ester Equivalents

PubMed Central

Trost, Barry M.; Michaelis, David J.; Truica, Mihai I.

2013-01-01

An enantioselective α-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc Prophenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting α,β-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Metallaphotoredox-Catalyzed sp3–sp3 Cross-Coupling of Carboxylic Acids with Alkyl Halides

PubMed Central

Johnston, Craig P.; Smith, Russell T.; Allmendinger, Simon; MacMillan, David W. C.

2017-01-01

Over the last half-century, transition metal-mediated cross-coupling reactions have changed the way in which complex organic molecules are synthesized. Indeed, the predictable and chemoselective nature of these transformations has led to their widespread adoption across a vast array of chemical research areas1. However, the construction of sp3–sp3 bonds, a fundamental unit of organic chemistry, remains an important yet elusive objective for cross-coupling reaction engineering2. In comparison to related procedures with sp2-hybridized species, the development of methods for sp3–sp3 bond formation via transition metal catalysis has been historically hampered by deleterious side-reactions, such as β-hydride elimination with Pd-catalysis, and the reluctance of alkyl halides to undergo oxidative addition3,4. To address this issue, a number of research groups have demonstrated the feasibility of nickel-catalyzed cross-coupling processes to form sp3–sp3 bonds that utilize organometallic nucleophiles and alkyl electrophiles5–7. In particular, the coupling of alkyl halides with pregenerated organozinc8–10, Grignard11,12, and organoborane13 species has been used to furnish diverse molecular structures. However, the poor step and atom economies along with the operational difficulties associated with making, carrying, and using these sensitive coupling partners has hindered their widespread adoption. The prospect of establishing a generically useful sp3–sp3 coupling technology that employs bench-stable, native organic functional groups, without the need for pre-functionalization or substrate derivatization, would therefore be a valuable addition to fields of research that rely on organic molecule construction. Here, we demonstrate that the synergistic merger of photoredox and nickel catalysis enables the direct formation of sp3–sp3 bonds using only simple carboxylic acids and alkyl halides as the nucleophilic and electrophilic coupling partners, respectively. The

Lactic Acid Production from Pretreated Hydrolysates of Corn Stover by a Newly Developed Bacillus coagulans Strain.

PubMed

Jiang, Ting; Qiao, Hui; Zheng, Zhaojuan; Chu, Qiulu; Li, Xin; Yong, Qiang; Ouyang, Jia

2016-01-01

An inhibitor-tolerance strain, Bacillus coagulans GKN316, was developed through atmospheric and room temperature plasma (ARTP) mutation and evolution experiment in condensed dilute-acid hydrolysate (CDH) of corn stover. The fermentabilities of other hydrolysates with B. coagulans GKN316 and the parental strain B. coagulans NL01 were assessed. When using condensed acid-catalyzed steam-exploded hydrolysate (CASEH), condensed acid-catalyzed liquid hot water hydrolysate (CALH) and condensed acid-catalyzed sulfite hydrolysate (CASH) as substrates, the concentration of lactic acid reached 45.39, 16.83, and 18.71 g/L by B. coagulans GKN316, respectively. But for B. coagulans NL01, only CASEH could be directly fermented to produce 15.47 g/L lactic acid. The individual inhibitory effect of furfural, 5-hydroxymethylfurfural (HMF), vanillin, syringaldehyde and p-hydroxybenzaldehyde (pHBal) on xylose utilization by B. coagulans GKN316 was also studied. The strain B. coagulans GKN316 could effectively convert these toxic inhibitors to the less toxic corresponding alcohols in situ. These results suggested that B. coagulans GKN316 was well suited to production of lactic acid from undetoxified lignocellulosic hydrolysates.

Lactic Acid Production from Pretreated Hydrolysates of Corn Stover by a Newly Developed Bacillus coagulans Strain

PubMed Central

Jiang, Ting; Qiao, Hui; Zheng, Zhaojuan; Chu, Qiulu; Li, Xin; Yong, Qiang; Ouyang, Jia

2016-01-01

An inhibitor-tolerance strain, Bacillus coagulans GKN316, was developed through atmospheric and room temperature plasma (ARTP) mutation and evolution experiment in condensed dilute-acid hydrolysate (CDH) of corn stover. The fermentabilities of other hydrolysates with B. coagulans GKN316 and the parental strain B. coagulans NL01 were assessed. When using condensed acid-catalyzed steam-exploded hydrolysate (CASEH), condensed acid-catalyzed liquid hot water hydrolysate (CALH) and condensed acid-catalyzed sulfite hydrolysate (CASH) as substrates, the concentration of lactic acid reached 45.39, 16.83, and 18.71 g/L by B. coagulans GKN316, respectively. But for B. coagulans NL01, only CASEH could be directly fermented to produce 15.47 g/L lactic acid. The individual inhibitory effect of furfural, 5-hydroxymethylfurfural (HMF), vanillin, syringaldehyde and p-hydroxybenzaldehyde (pHBal) on xylose utilization by B. coagulans GKN316 was also studied. The strain B. coagulans GKN316 could effectively convert these toxic inhibitors to the less toxic corresponding alcohols in situ. These results suggested that B. coagulans GKN316 was well suited to production of lactic acid from undetoxified lignocellulosic hydrolysates. PMID:26863012

Rhodium-catalyzed asymmetric hydrogenation of tetrasubstituted β-acetoxy-α-enamido esters and efficient synthesis of droxidopa.

PubMed

Guan, Yu-Qing; Gao, Min; Deng, Xu; Lv, Hui; Zhang, Xumu

2017-07-18

A rhodium-catalyzed asymmetric hydrogenation of challenging tetrasubstituted β-acetoxy-α-enamido esters was developed, giving chiral β-acetoxy-α-amido esters in high yields with excellent enantioselectivities (up to >99% ee). The products could be easily transformed to β-hydroxy-α-amino acid derivatives which are valuable chiral building blocks and a novel route for the synthesis of droxidopa was also developed.

Biodiesel production from Nannochloropsis gaditana lipids through transesterification catalyzed by Rhizopus oryzae lipase.

PubMed

Navarro López, Elvira; Robles Medina, Alfonso; González Moreno, Pedro Antonio; Esteban Cerdán, Luis; Martín Valverde, Lorena; Molina Grima, Emilio

2016-03-01

Biodiesel (fatty acid methyl esters, FAMEs) was produced from saponifiable lipids (SLs) extracted from wet Nannochloropsis gaditana biomass using methanolysis catalyzed by Rhizopus oryzae intracellular lipase. SLs were firstly extracted with ethanol to obtain 31 wt% pure SLs. But this low SL purity also gave a low biodiesel conversion (58%). This conversion increased up to 80% using SLs purified by crystallization in acetone (95 wt% purity). Polar lipids play an important role in decreasing the reaction velocity - using SLs extracted with hexane, which have lower polar lipid content (37.4% versus 49.0% using ethanol), we obtained higher reaction velocities and less FAME conversion decrease when the same lipase batch was reused. 83% of SLs were transformed to biodiesel using a 70 wt% lipase/SL ratio, 11:1 methanol/SL molar ratio, 10 mL t-butanol/g SLs after 72 h. The FAME conversion decreased to 71% after catalyzing three reactions with the same lipase batch. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synthesis, chemical characterization, and economical feasibility of poly-phenolic-branched-chain fatty acids: Synthesis of poly-phenolic-branched-chain fatty acids

USDA-ARS?s Scientific Manuscript database

New poly-phenolic branched-chain fatty acid (poly-PBC-FA) products were synthesized from a combination of soybean fatty acids and phenolic materials through a highly efficient zeolite catalyzed arylation method. These poly-PBC-FAs are liquid at room temperature and do not have the unpleasant odor li...

Multistep divergent synthesis of benzimidazole linked benzoxazole/benzothiazole via copper catalyzed domino annulation.

PubMed

Liao, Jen-Yu; Selvaraju, Manikandan; Chen, Chih-Hau; Sun, Chung-Ming

2013-04-21

An efficient, facile synthesis of structurally diverse benzimidazole integrated benzoxazole and benzothiazoles has been developed. In a multi-step synthetic sequence, 4-fluoro-3-nitrobenzoic acid was converted into benzimidazole bis-heterocycles, via the intermediacy of benzimidazole linked ortho-chloro amines. The amphiphilic reactivity of this intermediate was designed to achieve the title compounds by the reaction of various acid chlorides and isothiocyanates in a single step through the in situ formation of ortho-chloro anilides and thioureas under microwave irradiation. A versatile one pot domino annulation reaction was developed to involve the reaction of benzimidazole linked ortho-chloro amines with acid chlorides and isothiocyanates. The initial acylation and urea formation followed by copper catalyzed intramolecular C-O and C-S cross coupling reactions furnished the angularly oriented bis-heterocycles which bear a close resemblance to the streptomyces antibiotic UK-1.

Palladium-catalyzed domino C,N-coupling/carbonylation/Suzuki coupling reaction: an efficient synthesis of 2-aroyl-/heteroaroylindoles.

PubMed

Arthuis, Martin; Pontikis, Renée; Florent, Jean-Claude

2009-10-15

A convenient one-pot synthesis of 2-aroylindoles using a domino palladium-catalyzed C,N-coupling/carbonylation/C,C-coupling sequence is described. The reaction involved easily prepared 2-gem-dibromovinylanilines and boronic acids under carbon monoxide. Optimized reaction conditions allowed the construction of a wide variety of highly functionalized 2-aroyl-/heteroaroylindoles in satisfactory yields.

Regioselective lipase-catalyzed synthesis of 3-o-acyl derivatives of resveratrol and study of their antioxidant properties.

PubMed

Torres, Pamela; Poveda, Ana; Jimenez-Barbero, Jesús; Ballesteros, Antonio; Plou, Francisco J

2010-01-27

One of the approaches to increasing the bioavailability of resveratrol is to protect its 3-OH phenolic group. In this work, regioselective acylation of resveratrol at 3-OH was achieved by transesterification with vinyl acetate catalyzed by immobilized lipase from Alcaligenes sp. (lipase QLG). The maximum yield of 3-O-acetylresveratrol was approximately 75%, as the lipase also catalyzes its further acetylation affording the diester 3,4'-di-O-acetylresveratrol and finally the peracetylated derivative. Long saturated and unsaturated fatty acid vinyl esters were also effective as acyl donors with similar regioselectivity. In contrast, lipase B from Candida antarctica catalyzes the acylation of the phenolic group 4'-OH with 80% yield and negligible formation of higher esters. The analysis of the antioxidant properties showed that the Trolox equivalent antioxidant capability (TEAC) values for the acetyl and stearoyl derivatives at 3-OH were, respectively, 40% and 25% referred to resveratrol. The addition of an acyl chain in the 3-OH position caused a higher loss of activity compared with that at the 4'-OH.

Enantioselective Synthesis of Chiral Cyclopent-2-enones by Nickel-Catalyzed Desymmetrization of Malonate Esters.

PubMed

Karad, Somnath Narayan; Panchal, Heena; Clarke, Christopher; Lewis, William; Lam, Hon Wai

2018-05-16

The enantioselective synthesis of highly functionalized chiral cyclopent-2-enones by the reaction of alkynyl malonate esters with arylboronic acids is described. These desymmetrizing arylative cyclizations are catalyzed by a chiral phosphinooxazoline-nickel complex, and cyclization is enabled by the reversible E/Z isomerization of alkenylnickel species. The general methodology is also applicable to the synthesis of 1,6-dihydropyridin-3(2H)-ones. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atom-Economical Dimerization Strategy by the Rhodium-Catalyzed Addition of Carboxylic Acids to Allenes: Protecting-Group-Free Synthesis of Clavosolide A and Late-Stage Modification.

PubMed

Haydl, Alexander M; Breit, Bernhard

2015-12-14

Natural products of polyketide origin with a high level of symmetry, in particular C2 -symmetric diolides as a special macrolactone-based product class, often possess a broad spectrum of biological activity. An efficient route to this important structural motif was developed as part of a concise and highly convergent synthesis of clavosolide A. This strategy features an atom-economic "head-to-tail" dimerization by the stereoselective rhodium-catalyzed addition of carboxylic acids to terminal allenes with the simultaneous construction of two new stereocenters. The excellent efficiency and selectivity with which the C2 -symmetric core structures were obtained are remarkable considering the outcome under classical dimerization conditions. Furthermore, this approach facilitates late-stage modification and provides ready access to potential new lead structures. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A general method for copper-catalyzed arene cross-dimerization.

PubMed

Do, Hien-Quang; Daugulis, Olafs

2011-08-31

A general method for a highly regioselective copper-catalyzed cross-coupling of two aromatic compounds using iodine as an oxidant has been developed. The reactions involve an initial iodination of one arene followed by arylation of the most acidic C-H bond of the other coupling component. Cross-coupling of electron-rich arenes, electron-poor arenes, and five- and six-membered heterocycles is possible in many combinations. Typically, a 1/1.5 to 1/3 ratio of coupling components is used, in contrast to existing methodology that often employs a large excess of one of the arenes. Common functionalities such as ester, ketone, aldehyde, ether, nitrile, nitro, and amine are well-tolerated.

Detoxification of acidic catalyzed hydrolysate of Kappaphycus alvarezii (cottonii).

PubMed

Meinita, Maria Dyah Nur; Hong, Yong-Ki; Jeong, Gwi-Taek

2012-01-01

Red seaweed, Kappaphycus alvarezii, holds great promise for use in biofuel production due to its high carbohydrate content. In this study, we investigated the effect of fermentation inhibitors to the K. alvarezii hydrolysate on cell growth and ethanol fermentation. In addition, detoxification of fermentation inhibitors was performed to decrease the fermentation inhibitory effect. 5-Hydroxymethylfurfural and levulinic acid, which are liberated from acidic hydrolysis, was also observed in the hydrolysate of K. alvarezii. These compounds inhibited ethanol fermentation. In order to remove these inhibitors, activated charcoal and calcium hydroxide were introduced. The efficiency of activated charcoals was examined and over-liming was used to remove the inhibitors. Activated charcoal was found to be more effective than calcium hydroxide to remove the inhibitors. Detoxification by activated charcoal strongly improved the fermentability of dilute acid hydrolysate in the production of bioethanol from K. alvarezii with Saccharomyces cerevisiae. The optimal detoxifying conditions were found to be below an activated charcoal concentration of 5%.

Lewis Acid-Induced Change from Four- to Two-Electron Reduction of Dioxygen Catalyzed by Copper Complexes Using Scandium Triflate

PubMed Central

Kakuda, Saya; Rolle, Clarence; Ohkubo, Kei; Siegler, Maxime A.; Karlin, Kenneth D.; Fukuzumi, Shunichi

2015-01-01

Mononuclear copper complexes, [(tmpa)CuII(CH3CN)](ClO4)2 (1, tmpa = tris(2-pyridylmethyl)amine) and [(BzQ)CuII(H2O)2](ClO4)2 (2, BzQ = bis(2-quinolinylmethyl)benzylamine)], act as efficient catalysts for the selective two-electron reduction of O2 by ferrocene derivatives in the presence of scandium triflate (Sc(OTf)3), in acetone, whereas 1 catalyzes the four-electron reduction of O2 by the same reductant in the presence of Brønsted acids such as triflic acid. Following formation of the peroxo-bridged dicopper(II) complex [(tmpa)CuII(O2)CuII(tmpa)]2+, the two-electron reduced product of O2 with Sc3+ is observed to be scandium peroxide ([Sc3+(O22−)]+). In the presence of three equiv of hexamethylphosphoric triamide (HMPA), [Sc3+(O22−)]+ was oxidized by [Fe(bpy)3]3+ (bpy = 2,2′-bipyridine) to the known superoxide species [(HMPA)3Sc3+(O2•−)]2+ as detected by EPR spectroscopy. A kinetic study revealed that the rate-determining step of the catalytic cycle for the two-electron reduction of O2 with 1 is electron transfer from Fc* to 1 to give a cuprous complex which is highly reactive toward O2, whereas the rate-determining step with 2 is changed to the reaction of the cuprous complex with O2 following electron transfer from ferrocene derivatives to 2. The explanation for the change in catalytic O2-reaction stoichiometry from four-electron with Brønsted acids to two-electron reduction in the presence of Sc3+ and also for the change in the rate-determining step is clarified based on a kinetics interrogation of the overall catalytic cycle as well as each step of the catalytic cycle with study of the observed effects of Sc3+ on copper-oxygen intermediates. PMID:25659416

Retinoic acid biosynthesis catalyzed by retinal dehydrogenases relies on a rate-limiting conformational transition associated with substrate recognition

PubMed Central

Bchini, Raphaël; Vasiliou, Vasilis; Branlant, Guy; Talfournier, François; Rahuel-Clermont, Sophie

2012-01-01

Retinoic acid (RA), a metabolite of vitamin A, exerts pleiotropic effects throughout life in vertebrate organisms. Thus, RA action must be tightly regulated through the coordinated action of biosynthetic and degradating enzymes. The last step of retinoic acid biosynthesis is irreversibly catalyzed by the NAD-dependent retinal dehydrogenases (RALDH), which are members of the aldehyde dehydrogenase (ALDH) superfamily. Low intracellular retinal concentrations imply efficient substrate molecular recognition to ensure high affinity and specificity of RALDHs for retinal. This study addresses the molecular basis of retinal recognition in human ALDH1A1 (or RALDH1) and rat ALDH1A2 (or RALDH2), through the comparison of the catalytic behavior of retinal analogs and use of the fluorescence properties of retinol. We show that, in contrast to long chain unsaturated substrates, the rate-limiting step of retinal oxidation by RALDHs is associated with acylation. Use of the fluorescence resonance energy transfer upon retinol interaction with RALDHs provides evidence that retinal recognition occurs in two steps: binding into the substrate access channel, and a slower structural reorganization with a rate constant of the same magnitude as the kcat for retinal oxidation: 0.18 vs. 0.07 s−1 and 0.25 vs. 0.1 s−1 for ALDH1A1 and ALDH1A2, respectively. This suggests that the conformational transition of the RALDH-retinal complex significantly contributes to the rate-limiting step that controls the kinetics of retinal oxidation, as a prerequisite for the formation of a catalytically competent Michaelis complex. This conclusion is consistent with the general notion that structural flexibility within the active site of ALDH enzymes has been shown to be an integral component of catalysis. PMID:23220587

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies

NASA Technical Reports Server (NTRS)

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

RNA-Catalyzed RNA Ligation on an External RNA Template

NASA Technical Reports Server (NTRS)

McGinness, Kathleen E.; Joyce, Gerald F.

2002-01-01

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

Iodine-catalyzed diazo activation to access radical reactivity.

PubMed

Li, Pan; Zhao, Jingjing; Shi, Lijun; Wang, Jin; Shi, Xiaodong; Li, Fuwei

2018-05-17

Transition-metal-catalyzed diazo activation is a classical way to generate metal carbene, which are valuable intermediates in synthetic organic chemistry. An alternative iodine-catalyzed diazo activation is disclosed herein under either photo-initiated or thermal-initiated conditions, which represents an approach to enable carbene radical reactivity. This metal-free diazo activation strategy were successfully applied into olefin cyclopropanation and epoxidation, and applying this method to pyrrole synthesis under thermal-initiated conditions further demonstrates the unique reactivity using this method over typical metal-catalyzed conditions.

Catalytic and inhibiting effect of amino acids on the porphyrin metallation reactions

NASA Astrophysics Data System (ADS)

Mamardashvili, Galina M.; Zhdanova, Daria Yu.; Mamardashvili, Nugzar Zh.; Koifman, Oskar I.; Dehaen, Wim

In the present work, using the interaction of tetra-(4-sulfophenyl)porphyrin with copper(II) chloride as an example, it has been shown how different amino acid additives (glycine, valine, leucine and tryptophan) catalyze or inhibit the formation of Cu-porphyrin as a function of the chemical environment (borate buffer (pH7.4), DMSO) and the concentration of the additive. It has been demonstrated that the type of amino acid affects the complexation reaction rate. Possible mechanisms of metalloporphyrin formation and the ways of their acceleration are discussed. Ways in which different amino acid additives catalyze or inhibit the interaction of tetra-(4-sulfophenyl)porphyrin with copper(II) chloride are examined.

Simultaneous detoxification, saccharification, and ethanol fermentation of weak-acid hydrolyzates

USDA-ARS?s Scientific Manuscript database

Lignocellulosic feedstocks can be prepared for ethanol fermentation by pre-treatment with a dilute mineral acid catalyst that hydrolyzes the hemicellulose and opens up the plant cell wall fibers for subsequent enzymatic saccharification. The acid catalyzed reaction scheme is sequential whereby rele...

The Pyruvate and α-Ketoglutarate Dehydrogenase Complexes of Pseudomonas aeruginosa Catalyze Pyocyanin and Phenazine-1-carboxylic Acid Reduction via the Subunit Dihydrolipoamide Dehydrogenase*

PubMed Central

Glasser, Nathaniel R.; Wang, Benjamin X.; Hoy, Julie A.; Newman, Dianne K.

2017-01-01

Phenazines are a class of redox-active molecules produced by diverse bacteria and archaea. Many of the biological functions of phenazines, such as mediating signaling, iron acquisition, and redox homeostasis, derive from their redox activity. Although prior studies have focused on extracellular phenazine oxidation by oxygen and iron, here we report a search for reductants and catalysts of intracellular phenazine reduction in Pseudomonas aeruginosa. Enzymatic assays in cell-free lysate, together with crude fractionation and chemical inhibition, indicate that P. aeruginosa contains multiple enzymes that catalyze the reduction of the endogenous phenazines pyocyanin and phenazine-1-carboxylic acid in both cytosolic and membrane fractions. We used chemical inhibitors to target general enzyme classes and found that an inhibitor of flavoproteins and heme-containing proteins, diphenyleneiodonium, effectively inhibited phenazine reduction in vitro, suggesting that most phenazine reduction derives from these enzymes. Using natively purified proteins, we demonstrate that the pyruvate and α-ketoglutarate dehydrogenase complexes directly catalyze phenazine reduction with pyruvate or α-ketoglutarate as electron donors. Both complexes transfer electrons to phenazines through the common subunit dihydrolipoamide dehydrogenase, a flavoprotein encoded by the gene lpdG. Although we were unable to co-crystallize LpdG with an endogenous phenazine, we report its X-ray crystal structure in the apo-form (refined to 1.35 Å), bound to NAD+ (1.45 Å), and bound to NADH (1.79 Å). In contrast to the notion that phenazines support intracellular redox homeostasis by oxidizing NADH, our work suggests that phenazines may substitute for NAD+ in LpdG and other enzymes, achieving the same end by a different mechanism. PMID:28174304

The Pyruvate and α-Ketoglutarate Dehydrogenase Complexes of Pseudomonas aeruginosa Catalyze Pyocyanin and Phenazine-1-carboxylic Acid Reduction via the Subunit Dihydrolipoamide Dehydrogenase.

PubMed

Glasser, Nathaniel R; Wang, Benjamin X; Hoy, Julie A; Newman, Dianne K

2017-03-31

Phenazines are a class of redox-active molecules produced by diverse bacteria and archaea. Many of the biological functions of phenazines, such as mediating signaling, iron acquisition, and redox homeostasis, derive from their redox activity. Although prior studies have focused on extracellular phenazine oxidation by oxygen and iron, here we report a search for reductants and catalysts of intracellular phenazine reduction in Pseudomonas aeruginosa Enzymatic assays in cell-free lysate, together with crude fractionation and chemical inhibition, indicate that P. aeruginosa contains multiple enzymes that catalyze the reduction of the endogenous phenazines pyocyanin and phenazine-1-carboxylic acid in both cytosolic and membrane fractions. We used chemical inhibitors to target general enzyme classes and found that an inhibitor of flavoproteins and heme-containing proteins, diphenyleneiodonium, effectively inhibited phenazine reduction in vitro , suggesting that most phenazine reduction derives from these enzymes. Using natively purified proteins, we demonstrate that the pyruvate and α-ketoglutarate dehydrogenase complexes directly catalyze phenazine reduction with pyruvate or α-ketoglutarate as electron donors. Both complexes transfer electrons to phenazines through the common subunit dihydrolipoamide dehydrogenase, a flavoprotein encoded by the gene lpdG Although we were unable to co-crystallize LpdG with an endogenous phenazine, we report its X-ray crystal structure in the apo-form (refined to 1.35 Å), bound to NAD + (1.45 Å), and bound to NADH (1.79 Å). In contrast to the notion that phenazines support intracellular redox homeostasis by oxidizing NADH, our work suggests that phenazines may substitute for NAD + in LpdG and other enzymes, achieving the same end by a different mechanism. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Et3B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

PubMed Central

Abidi, Ahlem; Oueslati, Yosra

2016-01-01

A practical and efficient palladium-catalyzed direct allylation of β-dicarbonyl compounds with both cyclic and acyclic Morita–Baylis–Hillman (MBH) alcohols, using Et3B as a Lewis acid promoter, is described herein. A wide range of the corresponding functionalized allylated derivatives have been obtained in good yields and with high selectivity. PMID:28144308

Two new compounds from Helichrysum arenarium (L.).

PubMed

Zhang, Yu-Wei; Sun, Wu-Xing; Li, Xian; Zhao, Chun-Chao; Meng, Da-Li; Li, Ning

2009-01-01

Two new compounds were isolated from the whole plant of Helichrysum arenarium (L.) Moench. By means of spectroscopic data (IR, UV, 1D and 2D NMR, HR-MS, ESI-MS, and NOESY) and chemical evidence, the structures were established as 6,7-dimethoxy-4-hydroxy-1-naphthoic acid (1) and (Z)-5-hydroxy-7-methoxy-4-[3-methyl-4-(O-beta-D-xylopyranosyl)but-2-enyl]isobenzofuran-1(3H)-one (2).

Pyrimidine Nucleosides with a Reactive (β-Chlorovinyl)sulfone or (β-Keto)sulfone Group at the C5 Position, Their Reactions with Nucleophiles and Electrophiles, and Their Polymerase-Catalyzed Incorporation into DNA

PubMed Central

2018-01-01

Transition-metal-catalyzed chlorosulfonylation of 5-ethynylpyrimidine nucleosides provided (E)-5-(β-chlorovinyl)sulfones A, which undergo nucleophilic substitution with amines or thiols affording B. The treatment of vinyl sulfones A with ammonia followed by acid-catalyzed hydrolysis of the intermediary β-sulfonylvinylamines gave 5-(β-keto)sulfones C. The latter reacts with electrophiles, yielding α-carbon-alkylated or -sulfanylated analogues D. The 5′-triphosphates of A and C were incorporated into double-stranded DNA, using open and one-nucleotide gap substrates, by human or Escherichia coli DNA-polymerase-catalyzed reactions. PMID:29732453

Synergistic Heterobimetallic Manifold for Expedient Manganese(I)-Catalyzed C-H Cyanation.

PubMed

Liu, Weiping; Richter, Sven C; Mei, Ruhuai; Feldt, Milica; Ackermann, Lutz

2016-12-12

The manganese-catalyzed cyanation of inert C-H bonds was achieved within a heterobimetallic catalysis regime. The manganese(I) catalysis proved widely applicable and enabled C-H cyanations on indoles, pyrroles and thiophenes by facile C-H manganesation. The robustness of the manganese catalyst set the stage for the racemization-free C-H cyanation of amino acids with excellent levels of positional and chemo selectivity by the new cyanating agent NCFS. Experimental and computational mechanistic studies provided strong support for a synergistic heterobimetallic activation mode, facilitating the key C-C formation. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Representing Rate Equations for Enzyme-Catalyzed Reactions

ERIC Educational Resources Information Center

Ault, Addison

2011-01-01

Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

Mechanism of xanthine oxidase catalyzed biotransformation of HMX under anaerobic conditions.

PubMed

Bhushan, Bharat; Paquet, Louise; Halasz, Annamaria; Spain, Jim C; Hawari, Jalal

2003-06-27

Enzyme catalyzed biotransformation of the energetic chemical octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is not known. The present study describes a xanthine oxidase (XO) catalyzed biotransformation of HMX to provide insight into the biodegradation pathway of this energetic chemical. The rates of biotransformation under aerobic and anaerobic conditions were 1.6+/-0.2 and 10.5+/-0.9 nmolh(-1)mgprotein(-1), respectively, indicating that anaerobic conditions favored the reaction. The biotransformation rate was about 6-fold higher using NADH as an electron-donor compared to xanthine. During the course of reaction, the products obtained were nitrite (NO(2)(-)), methylenedinitramine (MDNA), 4-nitro-2,4-diazabutanal (NDAB), formaldehyde (HCHO), nitrous oxide (N(2)O), formic acid (HCOOH), and ammonium (NH(4)(+)). The product distribution gave carbon and nitrogen mass-balances of 91% and 88%, respectively. A comparative study with native-, deflavo-, and desulfo-XO and the site-specific inhibition studies showed that HMX biotransformation occurred at the FAD-site of XO. Nitrite stoichiometry revealed that an initial single N-denitration step was sufficient for the spontaneous decomposition of HMX.

Free radical derivatives formed from cyclooxygenase-catalyzed dihomo-γ-linolenic acid peroxidation can attenuate colon cancer cell growth and enhance 5-fluorouracil's cytotoxicity.

PubMed

Xu, Yi; Qi, Jin; Yang, Xiaoyu; Wu, Erxi; Qian, Steven Y

2014-01-01

Dihomo-γ-linolenic acid (DGLA) and its downstream fatty acid arachidonic acid (AA) are both nutritionally important ω-6 polyunsaturated fatty acids (ω-6s). Evidence shows that, via COX-mediated peroxidation, DGLA and its metabolites (1-series prostaglandins) are associated with anti-tumor activity, while AA and its metabolites (2-series prostaglandins) could be tightly implicated in various cancer diseases. However, it still remains a mystery why DGLA and AA possess contrasting bioactivities. Our previous studies showed that DGLA could go through an exclusive C-8 oxygenation pathway during COX-catalyzed lipid peroxidation in addition to a C-15 oxygenation pathway shared by both DGLA and AA, and that the exclusive C-8 oxygenation could lead to the production of distinct DGLA׳s free radical derivatives that may be correlated with DGLA׳s anti-proliferation activity. In the present work, we further investigate the anti-cancer effect of DGLA׳s free radical derivatives and their associated molecular mechanisms. Our study shows that the exclusive DGLA׳s free radical derivatives from C-8 oxygenation lead to cell growth inhibition, cell cycle arrest and apoptosis in the human colon cancer cell line HCA-7 colony 29, probably by up-regulating the cancer suppressor p53 and the cell cycle inhibitor p27. In addition, these exclusive radical derivatives were also able to enhance the efficacy of 5-Fluorouracil (5-FU), a widely used chemo-drug for colon cancer. For the first time, we show how DGLA׳s radical pathway and metabolites are associated with DGLA׳s anti-cancer activities and able to sensitize colon cancer cells to chemo-drugs such as 5-FU. Our findings could be used to guide future development of a combined chemotherapy and dietary care strategy for colon cancer treatment.

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Qinhua

2004-12-19

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I 2, ICl, PhSeCl, PhSCl and p-O 2NC 6H 4SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellentmore » yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these

Theoretical study on the reaction mechanisms of Michael chirality addition between propionaldehyde and nitroalkene catalyzed by an enantioselective catalyst.

PubMed

Zhou, Xinming; Li, Ling; Sun, Xuejun; Wang, Yajun; Du, Dongmei; Fu, Hui

2018-06-01

The asymmetric Michael addition between propionaldehyde and nitroalkene catalyzed by 8-(ethoxycarbonyl)-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid has obtained relatively high yields and excellent enantioselectivities at room temperature. In this study, the molecular structures and optical activity of the most stable conformation I are optimized at B3LYP/6-311++ G(d,p) level. We find that levorotatory conformation I catalyzing the same Michael addition can produce laevo-product A and dextrorotatory conformation I' can obtain the dextral-product A'. These results have guiding significance for further studying on the new chemzymes and the mechanism of the obtained different chiral products. © 2018 Wiley Periodicals, Inc.

Didehydroaspartate Modification in Methyl-Coenzyme M Reductase Catalyzing Methane Formation.

PubMed

Wagner, Tristan; Kahnt, Jörg; Ermler, Ulrich; Shima, Seigo

2016-08-26

All methanogenic and methanotrophic archaea known to date contain methyl-coenzyme M reductase (MCR) that catalyzes the reversible reduction of methyl-coenzyme M to methane. This enzyme contains the nickel porphinoid F430 as a prosthetic group and, highly conserved, a thioglycine and four methylated amino acid residues near the active site. We describe herein the presence of a novel post-translationally modified amino acid, didehydroaspartate, adjacent to the thioglycine as revealed by mass spectrometry and high-resolution X-ray crystallography. Upon chemical reduction, the didehydroaspartate residue was converted into aspartate. Didehydroaspartate was found in MCR I and II from Methanothermobacter marburgensis and in MCR of phylogenetically distantly related Methanosarcina barkeri but not in MCR I and II of Methanothermobacter wolfeii, which indicates that didehydroaspartate is dispensable but might have a role in fine-tuning the active site to increase the catalytic efficiency. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Proline/pipecolinic acid-promoted copper-catalyzed P-arylation.

PubMed

Huang, Cheng; Tang, Xu; Fu, Hua; Jiang, Yuyang; Zhao, Yufen

2006-06-23

We have developed a convenient and efficient approach for P-arylation of organophosphorus compounds containing P-H. Using commercially available and inexpensive proline and pipecolinic acid as the ligands greatly improved the efficiency of the coupling reactions, so the method can provide an entry to arylphosphonates, arylphosphinates and arylphosphine oxides.

Hybrid carbon nanoparticles modified core-shell silica: a high efficiency carbon-based phase for hydrophilic interaction liquid chromatography.

PubMed

Ibrahim, Mohammed E A; Wahab, M Farooq; Lucy, Charles A

2014-04-11

Hydrophilic interaction liquid chromatography (HILIC) is a fast growing separation technique for hydrophilic and polar analytes. In this work, we combine the unique selectivity of carbon surfaces with the high efficiency of core-shell silica. First, 5 μm core-shell silica is electrostatically coated with 105 nm cationic latex bearing quaternary ammonium groups. Then 50 nm anionic carbon nanoparticles are anchored onto the surface of the latex coated core-shell silica particles to produce a hybrid carbon-silica phase. The hybrid phase shows different selectivity than ten previously classified HILIC column chemistries and 36 stationary phases. The hybrid HILIC phase has shape selectivity for positional isomeric pairs (phthalic/isophthalic and 1-naphthoic/2-naphthoic acids). Fast and high efficiency HILIC separations of biologically important carboxylates, phenols and pharmaceuticals are reported with efficiencies up to 85,000 plates m(-1). Reduced plate height of 1.9 (95,000 plates m(-1)) can be achieved. The hybrid phase is stable for at least 3 months of usage and storage under typical HILIC eluents. Copyright © 2014 Elsevier B.V. All rights reserved.

Preparative resolution of D,L-threonine catalyzed by immobilized phosphatase.

PubMed

Scollar, M P; Sigal, G; Klibanov, A M

1985-03-01

Hydrolysis of L- and D-O-phosphothreonines catalyzed by four different phosphatases, alkaline phosphatases from calf intestine and E. coli and acid phosphatases from wheat germ and potato, has been kinetically studied. Alkaline phosphatases were found to have comparable reactivities towards the optical isomers. On the other hand, both acid phosphatases displayed a marked stereoselectivity, hydrolyzing the L-ester much faster than its D counterpart. Wheat germ acid phosphatase was the most stereoselective enzyme: V(L)/V(D) = 24 and K(m,L)/K(m,D) = 0.17. This enzyme was immobilized (in k-carrageenan gel, followed by crosslinking with glutaraldehyde) and used for the preparative resolution of D,L-threonine: the latter was first chemically O-phosphorylated and then asymmetrically hydrolyzed by the immobilized phosphatase. As a result, gram quantities of L-threonine of high optical purity and O-phospho-D-threonine were prepared. Immobilized wheat germ phosphatase has been tested for the resolution of other racemic alcohols: serine, 2-amino-1-butanol, 1-amino-2-propanol, 2-octanol, and menthol. In all those cases, the enzyme was either not sufficiently stereoselective or too slow for preparative resolutions.

Graphene oxide for acid catalyzed-reactions: Effect of drying process

NASA Astrophysics Data System (ADS)

Gong, H. P.; Hua, W. M.; Yue, Y. H.; Gao, Z.

2017-03-01

Graphene oxides (GOs) were prepared by Hummers method through various drying processes, and characterized by XRD, SEM, FTIR, XPS and N2 adsorption. Their acidities were measured using potentiometric titration and acid-base titration. The catalytic properties were investigated in the alkylation of anisole with benzyl alcohol and transesterification of triacetin with methanol. GOs are active catalysts for both reaction, whose activity is greatly affected by their drying processes. Vacuum drying GO exhibits the best performance in transesterification while freezing drying GO is most active for alkylation. The excellent catalytic behavior comes from abundant surface acid sites as well as proper surface functional groups, which can be obtained by selecting appropriate drying process.

Autoinduced catalysis and inverse equilibrium isotope effect in the frustrated Lewis pair catalyzed hydrogenation of imines.

PubMed

Tussing, Sebastian; Greb, Lutz; Tamke, Sergej; Schirmer, Birgitta; Muhle-Goll, Claudia; Luy, Burkhard; Paradies, Jan

2015-05-26

The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol(-1)) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Factors influencing inapplicability of cosolvency-induced model on organic acid sorption onto humic substance from methanol mixture.

PubMed

Kim, Minhee; Kim, Juhee; Kim, Jeong-Gyu; Hyun, Seunghun

2015-10-01

Applicability of cosolvency model for describing the sorption of organic acids to humic substance was investigated by analyzing dataset of sorption (K m) and solubility (S m) of selected solutes (benzoic acid, 1-naphthoic acid, 2,4-dichlorophenoxyacetic acid, and 2,4,6-trichlorophenol (2,4,6-TCP)) as a function of pH(appCME) (apparent pH of liquid phase) and f c (methanol volume fractions). For all solutes, the K m decreased with f c with the K m reduction being less than the S m-based prediction. The slope of log K m-f c plot in the three organic carboxylic acids was well correlated with their cosolvency power, whereas the data of organic phenolic acid (2,4,6-TCP) was placed above the trend, indicating the different actions of functional groups. The occurrence of Ca(2+) bridge between carboxylate and negatively charged humic surface may explain this phenomenon. Normalizing the K m to the corresponding S m (α' = K m/S m) was not in unity over the pH(app)-f c range but decreased with f c, indicating a possible structural modification of sorption domain favoring extra sorption. For a given solute, the α' of neutral species was always greater than that of anionic species, showing that extra interaction will be likely at pH(app) acids by humic substance in methanol/water mixtures. Modification of humic structure and hydrophilic interaction (such as Ca(2+) bridge and same-charge repulsion) is considered a relevant process that possibly restricts the applicability of the cosolvency model.

Paper microfluidic-based enzyme catalyzed double microreactor.

PubMed

Ferrer, Ivonne M; Valadez, Hector; Estala, Lissette; Gomez, Frank A

2014-08-01

We describe a paper microfluidic-based enzyme catalyzed double microreactor assay using fluorescent detection. Here, solutions of lactate dehydrogenase (LDH) and diaphorase (DI) were directly spotted onto the microfluidic paper-based analytical device (μPAD). Samples containing lactic acid, resazurin, and nicotinamide adenine dinucleotide oxidized form (NAD(+) ), potassium chloride (KCl), and BSA, in MES buffer were separately spotted onto the μPAD and MES buffer flowed through the device. A cascade reaction occurs upon the sample spot overlapping with LDH to form pyruvate and nicotinamide adenine dinucleotide reduced form (NADH). Subsequently, NADH is used in the conversion of resazurin to fluorescent resorufin by DI. The μPAD avoids the need of surface functionalization or enzyme immobilization steps. These microreactor devices are low cost and easy to fabricate and effect reaction based solely on buffer capillary action. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of Two Derivatization Methods for the Analysis of Fatty Acids and Trans Fatty Acids in Bakery Products Using Gas Chromatography

PubMed Central

Salimon, Jumat; Omar, Talal A.; Salih, Nadia

2014-01-01

Two different procedures for the methylation of fatty acids (FAs) and trans fatty acids (TFAs) in food fats were compared using gas chromatography (GC-FID). The base-catalyzed followed by an acid-catalyzed method (KOCH3/HCl) and the base-catalyzed followed by (trimethylsilyl)diazomethane (TMS–DM) method were used to prepare FA methyl esters (FAMEs) from lipids extracted from food products. In general, both methods were suitable for the determination of cis/trans FAs. The correlation coefficients (r) between the methods were relatively small (ranging from 0.86 to 0.99) and had a high level of agreement for the most abundant FAs. The significant differences (P = 0.05) can be observed for unsaturated FAs (UFAs), specifically for TFAs. The results from the KOCH3/HCl method showed the lowest recovery values (%R) and higher variation (from 84% to 112%), especially for UFAs. The TMS-DM method had higher R values, less variation (from 90% to 106%), and more balance between variation and %RSD values in intraday and interday measurements (less than 4% and 6%, resp.) than the KOCH3/HCl method, except for C12:0, C14:0, and C18:0. Nevertheless, the KOCH3/HCl method required shorter time and was less expensive than the TMS-DM method which is more convenient for an accurate and thorough analysis of rich cis/trans UFA samples. PMID:24719581

Comparison of two derivatization methods for the analysis of fatty acids and trans fatty acids in bakery products using gas chromatography.

PubMed

Salimon, Jumat; Omar, Talal A; Salih, Nadia

2014-01-01

Two different procedures for the methylation of fatty acids (FAs) and trans fatty acids (TFAs) in food fats were compared using gas chromatography (GC-FID). The base-catalyzed followed by an acid-catalyzed method (KOCH3/HCl) and the base-catalyzed followed by (trimethylsilyl)diazomethane (TMS-DM) method were used to prepare FA methyl esters (FAMEs) from lipids extracted from food products. In general, both methods were suitable for the determination of cis/trans FAs. The correlation coefficients (r) between the methods were relatively small (ranging from 0.86 to 0.99) and had a high level of agreement for the most abundant FAs. The significant differences (P = 0.05) can be observed for unsaturated FAs (UFAs), specifically for TFAs. The results from the KOCH3/HCl method showed the lowest recovery values (%R) and higher variation (from 84% to 112%), especially for UFAs. The TMS-DM method had higher R values, less variation (from 90% to 106%), and more balance between variation and %RSD values in intraday and interday measurements (less than 4% and 6%, resp.) than the KOCH3/HCl method, except for C12:0, C14:0, and C18:0. Nevertheless, the KOCH3/HCl method required shorter time and was less expensive than the TMS-DM method which is more convenient for an accurate and thorough analysis of rich cis/trans UFA samples.

Rhodium-catalyzed asymmetric construction of quaternary carbon stereocenters: ligand-dependent regiocontrol in the 1,4-addition to substituted maleimides.

PubMed

Shintani, Ryo; Duan, Wei-Liang; Hayashi, Tamio

2006-05-03

A rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to substituted maleimides has been described. The regioselectivity in this reaction is controlled by the choice of ligand (dienes or bisphosphines), and 1,4-adducts with a quaternary stereocenter can be obtained with high regio- and enantioselectivity by the use of (R)-H8-binap.

Stereoselective synthesis of functionalized cyclic amino acid derivatives via a [2,3]-Stevens rearrangement and ring-closing metathesis.

PubMed

Nash, Aaron; Soheili, Arash; Tambar, Uttam K

2013-09-20

Unnatural cyclic amino acids are valuable tools in biomedical research and drug discovery. A two-step stereoselective strategy for converting simple glycine-derived aminoesters into unnatural cyclic amino acid derivatives has been developed. The process includes a palladium-catalyzed tandem allylic amination/[2,3]-Stevens rearrangement followed by a ruthenium-catalyzed ring-closing metathesis. The [2,3]-rearrangement proceeds with high diastereoselectivity through an exo transition state. Oppolzer's chiral auxiliary was utilized to access an enantiopure cyclic amino acid by this approach, which will enable future biological applications.

Dual chemistry catalyzed by human acireductone dioxygenase

PubMed Central

Deshpande, Aditi R.; Pochapsky, Thomas C.; Petsko, Gregory A.

2017-01-01

Abstract Acireductone dioxygenase (ARD) from the methionine salvage pathway of Klebsiella oxytoca is the only known naturally occurring metalloenzyme that catalyzes different reactions in vivo based solely on the identity of the divalent transition metal ion (Fe2+ or Ni2+) bound in the active site. The iron-containing isozyme catalyzes the cleavage of substrate 1,2-dihydroxy-3-keto-5-(thiomethyl)pent-1-ene (acireductone) by O2 to formate and the ketoacid precursor of methionine, whereas the nickel-containing isozyme uses the same substrates to catalyze an off-pathway shunt to form methylthiopropionate, carbon monoxide and formate. This dual chemistry was recently demonstrated in vitro by ARD from Mus musculus (MmARD), providing the first example of a mammalian ARD exhibiting metal-dependent catalysis. We now show that human ARD (HsARD) is also capable of metal-dependent dual chemistry. Recombinant HsARD was expressed and purified to obtain a homogeneous enzyme with a single transition metal ion bound. As with MmARD, the Fe2+-bound HsARD shows the highest activity and catalyzes on-pathway chemistry, whereas Ni2+, Co2+ or Mn2+ forms catalyze off-pathway chemistry. The thermal stability of the HsARD isozymes is a function of the metal ion identity, with Ni2+-bound HsARD being the most stable followed by Co2+ and Fe2+, and Mn2+-bound HsARD being the least stable. As with the bacterial ARD, solution NMR data suggest that HsARD isozymes can have significant structural differences depending upon the metal ion bound. PMID:28062648

The Roles of Acids and Bases in Enzyme Catalysis

ERIC Educational Resources Information Center

Weiss, Hilton M.

2007-01-01

Many organic reactions are catalyzed by strong acids or bases that protonate or deprotonate neutral reactants leading to reactive cations or anions that proceed to products. In enzyme reactions, only weak acids and bases are available to hydrogen bond to reactants and to transfer protons in response to developing charges. Understanding this…

Metalloenzyme-like catalyzed isomerizations of sugars by Lewis acid zeolites

PubMed Central

Bermejo-Deval, Ricardo; Assary, Rajeev S.; Nikolla, Eranda; Moliner, Manuel; Román-Leshkov, Yuriy; Hwang, Son-Jong; Palsdottir, Arna; Silverman, Dorothy; Lobo, Raul F.; Curtiss, Larry A.; Davis, Mark E.

2012-01-01

Isomerization of sugars is used in a variety of industrially relevant processes and in glycolysis. Here, we show that hydrophobic zeolite beta with framework tin or titanium Lewis acid centers isomerizes sugars, e.g., glucose, via reaction pathways that are analogous to those of metalloenzymes. Specifically, experimental and theoretical investigations reveal that glucose partitions into the zeolite in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center, isomerizes into the acyclic form of fructose, and finally ring closes to yield the furanose product. The zeolite catalysts provide processing advantages over metalloenzymes such as an ability to work at higher temperatures and in acidic conditions that allow for the isomerization reaction to be coupled with other important conversions. PMID:22665778

Palladium catalyzed hydrogenation of bio-oils and organic compounds

DOEpatents

Elliott, Douglas C [Kennewick, WA; Hu, Jianli [Richland, WA; Hart,; Todd, R [Kennewick, WA; Neuenschwander, Gary G [Burbank, WA

2011-06-07

The invention provides palladium-catalyzed hydrogenations of bio-oils and certain organic compounds. Experimental results have shown unexpected and superior results for palladium-catalyzed hydrogenations of organic compounds typically found in bio-oils.

Palladium catalyzed hydrogenation of bio-oils and organic compounds

DOEpatents

Elliott, Douglas C [Richland, WA; Hu, Jianli [Kennewick, WA; Hart, Todd R [Kennewick, WA; Neuenschwander, Gary G [Burbank, WA

2008-09-16

The invention provides palladium-catalyzed hydrogenations of bio-oils and certain organic compounds. Experimental results have shown unexpected and superior results for palladium-catalyzed hydrogenations of organic compounds typically found in bio-oils.

Stereoselective Formation of Trisubstituted Vinyl Boronate Esters by the Acid-Mediated Elimination of α-Hydroxyboronate Esters

PubMed Central

2015-01-01

The copper-catalyzed diboration of ketones followed by an acid-catalyzed elimination leads to the formation of 1,1-disubstituted and trisubstituted vinyl boronate esters with moderate to good yields and selectivity. Addition of tosic acid to the crude diboration products provides the corresponding vinyl boronate esters upon elimination. The trisubstituted vinyl boronate esters are formed as the (Z)-olefin isomer, which was established by subjecting the products to a Suzuki–Miyaura coupling reaction to obtain alkenes of known geometry. PMID:24915498

Acid-catalyzed rearrangements of flavans to novelbenzofuran derivatives

Treesearch

Richard W. Hemingway; Weiling Peng; Anthony H. Conner; Petrus J. Steynberg; Jan P. Steynberg

1998-01-01

The objective of this work was to define reactions that occur when proanthocyanidins and their derivatives are reacted in the presence of acid catalysts. Pure compounds (either as the free phenols, the methyl ether, or the methyl ether-acetate derivatives) were isolated by a variety of chromatographic methods. Proof of their structure was based mainly on 2D-NMR, as...

Zinc-catalyzed allenylations of aldehydes and ketones.

PubMed

Fandrick, Daniel R; Saha, Jaideep; Fandrick, Keith R; Sanyal, Sanjit; Ogikubo, Junichi; Lee, Heewon; Roschangar, Frank; Song, Jinhua J; Senanayake, Chris H

2011-10-21

The general zinc-catalyzed allenylation of aldehydes and ketones with an allenyl boronate is presented. Preliminary mechanistic studies support a kinetically controlled process wherein, after a site-selective B/Zn exchange to generate a propargyl zinc intermediate, the addition to the electrophile effectively competes with propargyl-allenyl zinc equilibration. The utility of the methodology was demonstrated by application to a rhodium-catalyzed [4+2] cycloaddition. © 2011 American Chemical Society

Synthesis of 1-methyleneindenes via palladium-catalyzed tandem reactions.

PubMed

Ye, Shengqing; Gao, Ke; Zhou, Haibo; Yang, Xiaodi; Wu, Jie

2009-09-28

Palladium-catalyzed tandem reactions of 2-alkenylphenyl-acetylenes with CuCl2 or CuBr2 afforded 3-chloro- or 3-bromo-1-methyleneindenes in good yields; these compounds could be further elaborated via palladium-catalyzed coupling reactions.

Diastereoselective synthesis of furanose and pyranose substituted glycine and alanine derivatives via proline-catalyzed asymmetric α-amination of aldehydes.

PubMed

Petakamsetty, Ramu; Ansari, Anas; Ramapanicker, Ramesh

2016-11-29

A concise organocatalytic route toward the synthesis of furanose and pyranose substituted glycine and alanine derivatives is reported. These compounds are core structural units of some of the naturally available antibiotics and antifungal agents. Proline-catalyzed asymmetric α-amination of aldehydes derived from sugars is used as the key reaction to synthesize twelve sugar amino acid derivatives. The asymmetric transformations proceeded in good yields and with good to excellent diastereoselectivity. The application of the synthesized amino acids is demonstrated by synthesizing a tripeptide containing one of them. Copyright © 2016 Elsevier Ltd. All rights reserved.

Temperature regulated Brønsted acidic ionic liquid-catalyze esterification of oleic acid for biodiesel application

NASA Astrophysics Data System (ADS)

Rafiee, Ezzat; Mirnezami, Fakhrosadat

2017-02-01

By combining phosphotungstic acid (PW) and SO3H- functioned zwitterion, heteropoly anion-based Brønsted acidic ionic liquids (HPA-ILs) were successfully obtained. Scanning electron microscopy and energy dispersive X-ray spectroscopy were provided the morphology and composition of the prepared material. Catalytic performance and reusability of the catalysts were evaluated through an esterification reaction between oleic acid and methanol for production of biodiesel. Relationship between catalytic activities and acidity of the catalysts have been discussed by potentiometric titration. The results showed that HPA-ILs had good activity and reusability. HPA-ILs dissolved in the reaction mixture during the reaction process and could be precipitated and separated from products at lower temperature.

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

PubMed Central

Hintermann, Lukas; Perseghini, Mauro

2011-01-01

Summary Titanium-based Lewis acids catalyze the α-fluorination of β-ketoesters by electrophilic N–F-fluorinating reagents. Asymmetric catalysis with TADDOLato–titanium(IV) dichloride (TADDOL = α,α,α',α'-tetraaryl-(1,3-dioxolane-4,5-diyl)-dimethanol) Lewis acids produces enantiomerically enriched α-fluorinated β-ketoesters in up to 91% enantiomeric excess, with either F–TEDA (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)) in acetonitrile solution or NFSI (N-fluorobenzenesulfonimide) in dichloromethane solution as fluorinating reagents. The effects of various reaction parameters and of the TADDOL ligand structure on the catalytic activity and enantioselectivity were investigated. The absolute configuration of several fluorination products was assigned through correlation. Evidence for ionization of the catalyst complex by chloride dissociation, followed by generation of titanium β-ketoenolates as key reaction intermediates, was obtained. Based on the experimental findings, a general mechanistic sketch and a steric model of induction are proposed. PMID:22043253

Existence of efficient divalent metal ion-catalyzed and inefficient divalent metal ion-independent channels in reactions catalyzed by a hammerhead ribozyme

PubMed Central

Zhou, Jing-Min; Zhou, De-Min; Takagi, Yasuomi; Kasai, Yasuhiro; Inoue, Atsushi; Baba, Tadashi; Taira, Kazunari

2002-01-01

The hammerhead ribozyme is generally accepted as a well characterized metalloenzyme. However, the precise nature of the interactions of the RNA with metal ions remains to be fully defined. Examination of metal ion-catalyzed hammerhead reactions at limited concentrations of metal ions is useful for evaluation of the role of metal ions, as demonstrated in this study. At concentrations of Mn2+ ions from 0.3 to 3 mM, addition of the ribozyme to the reaction mixture under single-turnover conditions enhances the reaction with the product reaching a fixed maximum level. Further addition of the ribozyme inhibits the reaction, demonstrating that a certain number of divalent metal ions is required for proper folding and also for catalysis. At extremely high concentrations, monovalent ions, such as Na+ ions, can also serve as cofactors in hammerhead ribozyme-catalyzed reactions. However, the catalytic efficiency of monovalent ions is extremely low and, thus, high concentrations are required. Furthermore, addition of monovalent ions to divalent metal ion-catalyzed hammerhead reactions inhibits the divalent metal ion-catalyzed reactions, suggesting that the more desirable divalent metal ion–ribozyme complexes are converted to less desirable monovalent metal ion–ribozyme complexes via removal of divalent metal ions, which serve as a structural support in the ribozyme complex. Even though two channels appear to exist, namely an efficient divalent metal ion-catalyzed channel and an inefficient monovalent metal ion-catalyzed channel, it is clear that, under physiological conditions, hammerhead ribozymes are metalloenzymes that act via the significantly more efficient divalent metal ion-dependent channel. Moreover, the observed kinetic data are consistent with Lilley’s and DeRose’s two-phase folding model that was based on ground state structure analyses. PMID:12034824

Lipase-catalyzed acylation of microbial mannosylerythritol lipids (biosurfactants) and their characterization.

PubMed

Recke, Verena K; Beyrle, Catharina; Gerlitzki, Melanie; Hausmann, Rudolf; Syldatk, Christoph; Wray, Victor; Tokuda, Harukuni; Suzuki, Nobutaka; Lang, Siegmund

2013-05-24

Culturing Pseudozyma aphidis on glucose as main carbon source and soybean oil as co-substrate the mannosylerythritol lipids MEL-A and MEL-B were produced. Based on their excellent surface/interfacial active behavior they possess a high potential among all known biosurfactants. The components of a microbial MEL mixture were purified by medium pressure liquid chromatography (MPLC) and were used as substrates for in vitro enzymatic modifications. Lipase-catalyzed acylations of MEL-A and MEL-B with uncommon fatty acids from other microbial glycolipids-3-hydroxydecanoic acid from rhamnolipids and 17-hydroxyoctadecanoic acid from classical sophorolipids-yielded functionalized products at the C-1 position of the erythritol. The novel products were purified by MPLC and their structures elucidated by (1)H and (13)C nuclear magnetic resonance spectroscopy and mass spectrometry. In physicochemical characterization experiments two of the three new glycoconjugates lowered the surface tension of water from 72 mN m(-1) to 27-38 mN m(-1). Moreover the novel compounds inhibited the growth of gram-positive bacteria and showed a potential for anti-tumor-promoting activity. Copyright © 2013 Elsevier Ltd. All rights reserved.

Transformation of Unsaturated Fatty Acids/Esters to Corresponding Keto Fatty Acids/Esters by Aerobic Oxidation with Pd(II)/Lewis Acid Catalyst.

PubMed

Senan, Ahmed M; Zhang, Sicheng; Zeng, Miao; Chen, Zhuqi; Yin, Guochuan

2017-08-16

Utilization of renewable biomass to partly replace the fossil resources in industrial applications has attracted attention due to the limited fossil feedstock with the increased environmental concerns. This work introduced a modified Wacker-type oxidation for transformation of unsaturated fatty acids/esters to the corresponding keto fatty acids/esters, in which Cu 2+ cation was replaced with common nonredox metal ions, that is, a novel Pd(II)/Lewis acid (LA) catalyst. It was found that adding nonredox metal ions can effectively promote Pd(II)-catalyzed oxidation of unsaturated fatty acids/esters to the corresponding keto fatty acids/esters, even much better than Cu 2+ , and the promotional effect is highly dependent on the Lewis acidity of added nonredox metal ions. The improved catalytic efficiency is attributed to the formation of heterobimetallic Pd(II)/LA species, and the oxidation mechanism of this Pd(II)/LA catalyst is also briefly discussed.

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules.

PubMed

Guo, Lin; Rueping, Magnus

2018-05-15

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel

Facile access to amides and hydroxamic acids directly from nitroarenes.

PubMed

Jain, Shreyans K; Aravinda Kumar, K A; Bharate, Sandip B; Vishwakarma, Ram A

2014-09-07

A new method for synthesis of amides and hydroxamic acids from nitroarenes and aldehydes is described. The MnO2 catalyzed thermal deoxygenation of nitrobenzene resulted in formation of a reactive nitroso intermediate which on reaction with aldehydes provided amides and hydroxamic acids. The thermal neat reaction in the presence of 0.01 mmol KOH predominantly led to formation of hydroxamic acid whereas reaction in the presence of 1 mmol acetic acid produced amides as the only product.

New bis(alkythio) fatty acid methyl esters

USDA-ARS?s Scientific Manuscript database

The addition reaction of dimethyl disulfide (DMDS) to mono-unsaturated fatty acid methyl esters is well-known for analytical purposes to determine the position of double bonds by mass spectrometry. In this work, the classical iodine-catalyzed reaction is expanded to other dialkyl disulfides (RSSR), ...

Facile conversion of a coordinated nitro group into an aqua group: acid-induced nitro-to-nitro rearrangement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, W.G.

1987-11-18

The nitro complex (NH/sub 3/)/sub 5/CoNO/sub 2//sup 2 +/ reacts rapidly and completely with neat anhydrous trifluoromethanesulfonic acid to generate the aqua species (NH/sub 3/)/sub 5/CoOH/sub 2//sup 3 +/. Oxygen-17 NMR results show that the oxygen in the bound water is derived from the original nitro group. A mechanism involving acid-catalyzed nitrogen-to-oxygen nitrite rearrangement is considered. The relationship between the mechanisms for oxygen scrambling and acid-catalyzed loss of NO/sup +/ from the nitrito linkage isomer is discussed, together with the mechanism for the present reaction. 20 references, 1 figure.

Sol-gel preparation of hydrophobic silica antireflective coatings with low refractive index by base/acid two-step catalysis.

PubMed

Cai, Shuang; Zhang, Yulu; Zhang, Hongli; Yan, Hongwei; Lv, Haibing; Jiang, Bo

2014-07-23

Hydrophobic antireflective coatings with a low refractive index were prepared via a base/acid-catalyzed two-step sol-gel process using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors, respectively. The base-catalyzed hydrolysis of TEOS leads to the formation of a sol with spherical silica particles in the first step. In the second step, the acid-catalyzed MTES hydrolysis and condensation occur at the surface of the initial base-catalyzed spherical silica particles, which enlarge the silica particle size from 12.9 to 35.0 nm. By a dip-coating process, this hybrid sol gives an antireflective coating with a refractive index of about 1.15. Moreover, the water contact angles of the resulted coatings increase from 22.4 to 108.7° with the increases of MTES content, which affords the coatings an excellent hydrophobicity. A "core-shell" particle growth mechanism of the hybrid sol was proposed and the relationship between the microstructure of silica sols and the properties of AR coatings was investigated.

Preferential amino acid sequences in alumina-catalyzed peptide bond formation.

PubMed

Bujdák, J; Rode, B M

2002-05-21

The catalytic effect of activated alumina on amino acid condensation was investigated. The readiness of amino acids to form peptide sequences was estimated on the basis of the yield of dipeptides and was found to decrease in the order glycine (Gly), alanine (Ala), leucine (Leu), valine (Val), proline (Pro). For example, approximately 15% Gly was converted to the dipeptide (Gly(2)), 5% to cyclic anhydride (cyc(Gly(2))) and small amounts of tri- (Gly(3)) and tetrapeptide (Gly(4)) were formed after 28 days. On the other hand, only trace amounts of Pro(2) were formed from proline under the same conditions. Preferential formation of certain sequences was observed in the mixed reaction systems containing two amino acids. For example, almost ten times more Gly-Val than Val-Gly was formed in the Gly+Val reaction system. The preferred sequences can be explained on the basis of an inductive effect that side groups have on the nucleophilicity and electrophilicity, respectively, of the amino and carboxyl groups. A comparison with published data of amino acid reactions in other reaction systems revealed that the main trends of preferential sequence formation were the same as those described for the salt-induced peptide formation (SIPF) reaction. The results of this work and other previously published papers show that alumina and related mineral surfaces might have played a crucial role in the prebiotic formation of the first peptides on the primitive earth.

Molecular Active Sites in Heterogeneous Ir-La/C-Catalyzed Carbonylation of Methanol to Acetates.

PubMed

Kwak, Ja Hun; Dagle, Robert; Tustin, Gerald C; Zoeller, Joseph R; Allard, Lawrence F; Wang, Yong

2014-02-06

We report that when Ir and La halides are deposited on carbon, exposure to CO spontaneously generates a discrete molecular heterobimetallic structure, containing an Ir-La covalent bond that acts as a highly active, selective, and stable heterogeneous catalyst for the carbonylation of methanol to produce acetic acid. This catalyst exhibits a very high productivity of ∼1.5 mol acetyl/mol Ir·s with >99% selectivity to acetyl (acetic acid and methyl acetate) without detectable loss in activity or selectivity for more than 1 month of continuous operation. The enhanced activity can be mechanistically rationalized by the presence of La within the ligand sphere of the discrete molecular Ir-La heterobimetallic structure, which acts as a Lewis acid to accelerate the normally rate-limiting CO insertion in Ir-catalyzed carbonylation. Similar approaches may provide opportunities for attaining molecular (single site) behavior similar to homogeneous catalysis on heterogeneous surfaces for other industrial applications.

Production of Odd-Carbon Dicarboxylic Acids in Escherichia coli Using an Engineered Biotin-Fatty Acid Biosynthetic Pathway.

PubMed

Haushalter, Robert W; Phelan, Ryan M; Hoh, Kristina M; Su, Cindy; Wang, George; Baidoo, Edward E K; Keasling, Jay D

2017-04-05

Dicarboxylic acids are commodity chemicals used in the production of plastics, polyesters, nylons, fragrances, and medications. Bio-based routes to dicarboxylic acids are gaining attention due to environmental concerns about petroleum-based production of these compounds. Some industrial applications require dicarboxylic acids with specific carbon chain lengths, including odd-carbon species. Biosynthetic pathways involving cytochrome P450-catalyzed oxidation of fatty acids in yeast and bacteria have been reported, but these systems produce almost exclusively even-carbon species. Here we report a novel pathway to odd-carbon dicarboxylic acids directly from glucose in Escherichia coli by employing an engineered pathway combining enzymes from biotin and fatty acid synthesis. Optimization of the pathway will lead to industrial strains for the production of valuable odd-carbon diacids.

Tetrachloroethene degradation by reducing-agent enhanced Fe(II)/Fe(III) catalyzed percarbonate

NASA Astrophysics Data System (ADS)

Miao, Z.; Brusseau, M. L.; Lu, S.; Gu, X.; Yan, N.; Qiu, Z.; Sui, Q.

2015-12-01

This project investigated the effect of reducing agents on the degradation of tetrachloroethene(PCE) by Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC). SPC possesses similar function as liquid H2O2, such that free H2O2 is released into solution when percarbonate is mixed with water. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redoxcycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations.The results of chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO● was the predominant radical in the system and that O2●-played a minor role. This was further confirmed by the results of electron paramagnetic resonance measurements and salicylic acid hydroxylationanalysis by high performance liquid chromatography(HPLC). PCE degradation decreased significantly with the addition of isopropanol, a strong HO● scavenger, supporting the hypothesis that HO● was primarily responsible for PCE degradation. It should be noted that the release of Cl- was slightly delayed in the first 20 mins, indicating that intermediate products were produced. However, gas chromatography mass spectrometry (GC/MS) analysis did not detect any chlorinated organic compound except PCE, indicating these intermediates were quickly degraded, which resulted in the complete conversion of PCE to CO2. In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater.

Cooperative Effects Between Arginine and Glutamic Acid in the Amino Acid-Catalyzed Aldol Reaction.

PubMed

Valero, Guillem; Moyano, Albert

2016-08-01

Catalysis of the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde by mixtures of L-Arg and of L-Glu in wet dimethyl sulfoxide (DMSO) takes place with higher enantioselectivity (up to a 7-fold enhancement in the anti-aldol for the 1:1 mixture) than that observed when either L-Glu or L-Arg alone are used as the catalysts. These results can be explained by the formation of a catalytically active hydrogen-bonded complex between both amino acids, and demonstrate the possibility of positive cooperative effects in catalysis by two different α-amino acids. Chirality 28:599-605, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Studies of reaction variables for lipase-catalyzed production of alpha-linolenic acid enriched structured lipid and oxidative stability with antioxidants.

PubMed

Mitra, Kanika; Shin, Jung-Ah; Lee, Jeung-Hee; Kim, Seong-Ai; Hong, Soon-Taek; Sung, Chang-Keun; Xue, Cheng Lian; Lee, Ki-Teak

2012-01-01

Alpha-linolenic acid (ALA) enriched structured lipid (SL) was produced by lipase-catalyzed interesterification from perilla oil (PO) and corn oil (CO). The effects of different reaction conditions (substrate molar ratio [PO/CO 1:1 to 1:3], reaction time [0 to 24 h], and reaction temperature [55 to 65 °C]) were studied. Lipozyme RM IM from Rhizomucor miehei was used as biocatalyst. We obtained 32.39% of ALA in SL obtained under the optimized conditions (molar ratio-1:1 [PO:CO], temperature-60 °C, reaction time-15 h). In SL, the major triacylglycerol (TAG) species (linolenoyl-linolenoyl-linolenoyl glycerol [LnLnLn], linolenoyl-linolenoyl-linoleoyl glycerol [LnLnL]) mainly from PO and linoleoyl-linoleoyl-oleoyl glycerol (LLO), linoleoyl-oleoyl-oleoyl glycerol (LOO), palmitoyl-linoleoyl-oleoyl glycerol (PLO) from CO decreased while linolenoyl-linolenoyl-oleoyl glycerol (LnLnO) (18.41%), trilinolein (LLL) (9.06%), LLO (16.66%), palmitoyl-linoleoyl-linoleoyl glycerol (PLL) (9.69%) were increased compared to that of physical blend. Total tocopherol content (28.01 mg/100 g), saponification value (SV) (192.2), and iodine value (IV) (161.9) were obtained. Furthermore, oxidative stability of the SL was also investigated by addition of 3 different antioxidants (each 200 ppm of rosemary extract [SL-ROS], BHT [SL-BHT], catechin [SL-CAT]) was added into SL and stored in 60 °C oven for 30 d. 2-Thiobabituric acid-reactive substances (TBARS) value was 0.16 mg/kg in SL-CAT and 0.18 mg/kg in SL-ROS as compared with 0.22 mg/kg in control (SL) after oxidation. The lowest peroxide value (POV, 200.9 meq/kg) and longest induction time (29.88 h) was also observed in SL-CAT. © 2011 Institute of Food Technologists®

Simple citric acid-catalyzed surface esterification of cellulose nanocrystals.

PubMed

Ávila Ramírez, Jhon Alejandro; Fortunati, Elena; Kenny, José María; Torre, Luigi; Foresti, María Laura

2017-02-10

A simple straightforward route for the surface esterification of cellulose nanocrystals (CNC) is herein proposed. CNC obtained from microcrystalline cellulose were acetylated using as catalyst citric acid, a α-hydroxy acid present in citrus fruits and industrially produced by certain molds in sucrose or glucose-containing medium. No additional solvent was added to the system; instead, the acylant (acetic anhydride) was used in sufficient excess to allow CNC dispersion and proper suspension agitation. By tuning the catalyst load, CNC with two different degree of substitution (i.e. DS=0.18 and 0.34) were obtained. Acetylated cellulose nanocrystals were characterized in terms of chemical structure, crystallinity, morphology, thermal decomposition and dispersion in a non-polar solvent. Results illustrated for the first time the suitability of the protocol proposed for the simple surface acetylation of cellulose nanocrystals. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ozonation of clofibric acid catalyzed by titanium dioxide.

PubMed

Rosal, Roberto; Gonzalo, María S; Rodríguez, Antonio; García-Calvo, Eloy

2009-09-30

The removal of clofibric acid from aqueous solution has been investigated in catalytic and non-catalytic semicontinuous ozonation runs. Kinetic data were analyzed using second order expressions for the reaction between organics and ozone or hydroxyl radicals. Catalytic runs used a commercial titanium dioxide catalyst consisting of fumed colloidal particles. The kinetic constant of the non-catalytic ozonation of clofibric acid at pH 3 was 8.16 x 10(-3)+/-3.4 x 10(-4)L mmol(-1)s(-1). The extent of mineralization during non-catalytic runs ranged from 50% at pH 7 to 20% at pH 3 in a reaction that essentially took place during the first 10-20 min. The catalyst increased the total extent of mineralization, its effect being more important during the first part of the reaction. The pseudo-homogeneous catalytic rate constant was 2.17 x 10(-2) L mmol(-1)s(-1) at pH 3 and 6.80 x 10(-1)L mmol(-1)s(-1) at pH 5, with up to a threefold increase with respect to non-catalytic constants using catalyst load of 1g/L. A set of stopped-flow experiments were designed to elucidate the role of catalyst, whose effect was probably due to the adsorption of organics on catalytic sites rather than to the promotion of ozone decomposition.

Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes: the accelerating effect of certain alcohols and amines.

PubMed

Munshi, Pradip; Main, A Denise; Linehan, John C; Tai, Chih-Cheng; Jessop, Philip G

2002-07-10

A trace amount of alcohol cocatalyst and a stoichiometric amount of base are required during the hydrogenation of CO(2) to formic acid catalyzed by ruthenium trimethylphosphine complexes. Variation of the choice of alcohol and base causes wide variation in the rate of reaction. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, use of DBU rather than NEt(3) increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h(-1) have now been obtained, and even higher rates should be possible using the cocatalyst and amine combinations identified herein. Preliminary in situ NMR spectroscopic observations are described, and the possible roles of the alcohol and base are discussed.

Practical Alkoxythiocarbonyl Auxiliaries for Iridium(I)-Catalyzed C-H Alkylation of Azacycles.

PubMed

Tran, Anh T; Yu, Jin-Quan

2017-08-21

The development of new and practical 3-pentoxythiocarbonyl auxiliaries for Ir I -catalyzed C-H alkylation of azacycles is described. This method allows for the α-C-H alkylation of a variety of substituted pyrrolidines, piperidines, and tetrahydroisoquinolines through alkylation with alkenes. While the practicality of these simple carbamate-type auxiliaries is underscored by the ease of installation and removal, the method's utility is demonstrated in its ability to functionalize biologically relevant l-proline and l-trans-hydroxyproline, delivering unique 2,5-dialkylated amino acid analogues that are not accessible by other C-H functionalization methods. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper-catalyzed oxidative desulfurization-oxygenation of thiocarbonyl compounds using molecular oxygen: an efficient method for the preparation of oxygen isotopically labeled carbonyl compounds.

PubMed

Shibahara, Fumitoshi; Suenami, Aiko; Yoshida, Atsunori; Murai, Toshiaki

2007-06-21

A novel copper-catalyzed oxidative desulfurization reaction of thiocarbonyl compounds, using molecular oxygen as an oxidant and leading to formation of carbonyl compounds, has been developed, and the utility of the process is demonstrated by its application to the preparation of a carbonyl-18O labeled sialic acid derivative.

Understanding Self-Catalyzed Epitaxial Growth of III-V Nanowires toward Controlled Synthesis.

PubMed

Zi, Yunlong; Suslov, Sergey; Yang, Chen

2017-02-08

The self-catalyzed growth of III-V nanowires has drawn plenty of attention due to the potential of integration in current Si-based technologies. The homoparticle-assisted vapor-liquid-solid growth mechanism has been demonstrated for self-catalyzed III-V nanowire growth. However, the understandings of the preferred growth sites of these nanowires are still limited, which obstructs the controlled synthesis and the applications of self-catalyzed nanowire arrays. Here, we experimentally demonstrated that thermally created pits could serve as the preferred sites for self-catalyzed InAs nanowire growth. On that basis, we performed a pregrowth annealing strategy to promote the nanowire density by enhancing the pits formation on the substrate surface and enable the nanowire growth on the substrate that was not capable to facilitate the growth. The discovery of the preferred self-catalyzed nanowire growth sites and the pregrowth annealing strategy have shown great potentials for controlled self-catalyzed III-V nanowire array growth with preferred locations and density.

Functional characterization of two microsomal fatty acid desaturases from Jatropha curcas L.

PubMed

Wu, Pingzhi; Zhang, Sheng; Zhang, Lin; Chen, Yaping; Li, Meiru; Jiang, Huawu; Wu, Guojiang

2013-10-15

Linoleic acid (LA, C18:2) and α-linolenic acid (ALA, C18:3) are polyunsaturated fatty acids (PUFAs) and major storage compounds in plant seed oils. Microsomal ω-6 and ω-3 fatty acid (FA) desaturases catalyze the synthesis of seed oil LA and ALA, respectively. Jatropha curcas L. seed oils contain large proportions of LA, but very little ALA. In this study, two microsomal desaturase genes, named JcFAD2 and JcFAD3, were isolated from J. curcas. Both deduced amino acid sequences possessed eight histidines shown to be essential for desaturases activity, and contained motif in the C-terminal for endoplasmic reticulum localization. Heterologous expression in Saccharomyces cerevisiae and Arabidopsis thaliana confirmed that the isolated JcFAD2 and JcFAD3 proteins could catalyze LA and ALA synthesis, respectively. The results indicate that JcFAD2 and JcFAD3 are functional in controlling PUFA contents of seed oils and could be exploited in the genetic engineering of J. curcas, and potentially other plants. Copyright © 2013 Elsevier GmbH. All rights reserved.

Manganese Catalyzed C–H Halogenation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Groves, John T.

2015-06-16

The remarkable aliphatic C–H hydroxylations catalyzed by the heme-containing enzyme, cytochrome P450, have attracted sustained attention for more than four decades. The effectiveness of P450 enzymes as highly selective biocatalysts for a wide range of oxygenation reactions of complex substrates has driven chemists to develop synthetic metalloporphyrin model compounds that mimic P450 reactivity. Among various known metalloporphyrins, manganese derivatives have received considerable attention since they have been shown to be versatile and powerful mediators for alkane hydroxylation and olefin epoxidation. Mechanistic studies have shown that the key intermediates of the manganese porphyrin-catalyzed oxygenation reactions include oxo- and dioxomanganese(V) species thatmore » transfer an oxygen atom to the substrate through a hydrogen abstraction/oxygen recombination pathway known as the oxygen rebound mechanism. Application of manganese porphyrins has been largely restricted to catalysis of oxygenation reactions until recently, however, due to ultrafast oxygen transfer rates. In this Account, we discuss recently developed carbon–halogen bond formation, including fluorination reactions catalyzed by manganese porphyrins and related salen species. We found that biphasic sodium hypochlorite/manganese porphyrin systems can efficiently and selectively convert even unactivated aliphatic C–H bonds to C–Cl bonds. An understanding of this novel reactivity derived from results obtained for the oxidation of the mechanistically diagnostic substrate and radical clock, norcarane. Significantly, the oxygen rebound rate in Mn-mediated hydroxylation is highly correlated with the nature of the trans-axial ligands bound to the manganese center (L–Mn V$=$O). Based on the ability of fluoride ion to decelerate the oxygen rebound step, we envisaged that a relatively long-lived substrate radical could be trapped by a Mn–F fluorine source, effecting carbon–fluorine bond

Glutamic acid as anticancer agent: An overview

PubMed Central

Dutta, Satyajit; Ray, Supratim; Nagarajan, K.

2013-01-01

The objective of the article is to highlight various roles of glutamic acid like endogenic anticancer agent, conjugates to anticancer agents, and derivatives of glutamic acid as possible anticancer agents. Besides these emphases are given especially for two endogenous derivatives of glutamic acid such as glutamine and glutamate. Glutamine is a derivative of glutamic acid and is formed in the body from glutamic acid and ammonia in an energy requiring reaction catalyzed by glutamine synthase. It also possesses anticancer activity. So the transportation and metabolism of glutamine are also discussed for better understanding the role of glutamic acid. Glutamates are the carboxylate anions and salts of glutamic acid. Here the roles of various enzymes required for the metabolism of glutamates are also discussed. PMID:24227952

Glutamic acid as anticancer agent: An overview.

PubMed

Dutta, Satyajit; Ray, Supratim; Nagarajan, K

2013-10-01

The objective of the article is to highlight various roles of glutamic acid like endogenic anticancer agent, conjugates to anticancer agents, and derivatives of glutamic acid as possible anticancer agents. Besides these emphases are given especially for two endogenous derivatives of glutamic acid such as glutamine and glutamate. Glutamine is a derivative of glutamic acid and is formed in the body from glutamic acid and ammonia in an energy requiring reaction catalyzed by glutamine synthase. It also possesses anticancer activity. So the transportation and metabolism of glutamine are also discussed for better understanding the role of glutamic acid. Glutamates are the carboxylate anions and salts of glutamic acid. Here the roles of various enzymes required for the metabolism of glutamates are also discussed.

Characterization and antioxidant activity of gallic acid derivative

NASA Astrophysics Data System (ADS)

Malinda, Krissan; Sutanto, Hery; Darmawan, Akhmad

2017-11-01

Peroxidase enzyme was used to catalyze the dimerization process of gallic acid. The structure of the dimerization product was characterized by 1H NMR and LC-MS-MS. The mechanism of gallic acid dimerization was also discussed. It was proposed that ellagic acid was formed through an oxidative coupling mechanism that lead to the formation of a C-C bond and followed by an intramolecular Fischer esterification mechanism that lead to the formation of two C-O bonds. Moreover, the antioxidant activity of gallic acid and ellagic acid were also studied. Gallic acid and ellagic acid exhibited the DPPH radical scavenging activity with IC50 values of 13.2 μM and 15.9 μM, respectively.

Hydrothermal-acid treatment for effectual extraction of eicosapentaenoic acid (EPA)-abundant lipids from Nannochloropsis salina.

PubMed

Lee, Ilgyu; Han, Jong-In

2015-09-01

Hydrothermal acid treatment, was adopted to extract eicosapentaenoic acid (EPA) from wet biomass of Nannochloropsis salina. It was found that sulfuric acid-based treatment increased EPA yield from 11.8 to 58.1 mg/g cell in a way that was nearly proportional to its concentration. Nitric acid exhibited the same pattern at low concentrations, but unlike sulfuric acid its effectiveness unexpectedly dropped from 0.5% to 2.0%. The optimal and minimal conditions for hydrothermal acid pretreatment were determined using a statistical approach; its maximum EPA yield (predicted: 43.69 mg/g cell; experimental: 43.93 mg/g cell) was established at a condition of 1.27% of sulfuric acid, 113.34 °C of temperature, and 36.71 min of reaction time. Our work demonstrated that the acid-catalyzed cell disruption, accompanied by heat, can be one potentially promising option for ω-3 fatty acids extraction. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Enantiomers of 4-Amino-3-fluorobutanoic Acid as Substrates for γ-Aminobutyric Acid Aminotransferase. Conformational Probes for GABA Binding†

PubMed Central

Clift, Michael; Ji, Haitao; Deniau, Gildas P.; O’Hagan, David; Silverman, Richard B.

2008-01-01

γ-Aminobutyric acid aminotransferase (GABA-AT), a pyridoxal 5’-phosphate dependent enzyme, catalyzes the degradation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) to succinic semialdehyde with concomitant conversion of pyridoxal 5’-phosphate (PLP) to pyridoxamine 5’-phosphate (PMP). The enzyme then catalyzes the conversion of α-ketoglutarate to the excitatory neurotransmitter L-glutamate. Racemic 4-amino-3-fluorobutanoic acid (3-F-GABA) was shown previously to act as a substrate for GABA-AT, not for transamination, but for HF elimination. Here we report studies of the reaction catalyzed by GABA-AT on (R)- and (S)-3-F-GABA. Neither enantiomer is a substrate for transamination. Very little elimination from the (S)-enantiomer was detected using a coupled enzyme assay; The rate of elimination of HF from the (R)-enantiomer is at least 10 times greater than that for the (S)-enantiomer. The (R)-enantiomer is about 20 times more efficient as a substrate for GABA-AT catalyzed HF elimination than GABA is a substrate for transamination. The (R)-enantiomer also inhibits the transamination of GABA 10 times more effectively than the (S)-enantiomer. Using a combination of computer modeling and the knowledge that vicinal C-F and C-NH3+ bonds have a strong preference to align gauche rather than anti to each other, it is concluded that on binding of free 3-F-GABA to GABA-AT the optimal conformation places the C-NH3+ and C-F bonds gauche in the (R)-enantiomer but anti in the (S)-enantiomer. Furthermore, the dynamic binding process and the bioactive conformation of GABA bound to GABA-AT have been inferred based on the different biological behavior of the two enantiomers of 3-F-GABA when they bind to the enzyme. The present study suggests that the C-F bond can be utilized as a conformational probe to explore the dynamic binding process and provide insight into the bioactive conformation of substrates, which cannot be easily determined by other biophysical

Analysis and properties of the decarboxylation products of oleic acid by catalytic triruthenium dodecacarbonyl

USDA-ARS?s Scientific Manuscript database

Recently, ruthenium-catalyzed isomerization-decarboxylation of fatty acids to give alkene mixtures was reported. When the substrate was oleic acid, the reaction yielded a mixture consisting of heptadecene isomers. In this work, we report the compositional analysis of the mixture obtained by triruthe...

Heterogeneous catalytic esterification of omega-sulfhydryl fatty acids: Avoidance of thioethers, thioesters, and disulfides

USDA-ARS?s Scientific Manuscript database

Two mesoporous silicas functionalized with propylsulfonic (SBA-15-PSA) and arenesulfonic (SBA-15-ASA) acid groups, and a highly acidic, functionalized styrene divinylbenzene copolymer ion exchange resin (Amberlyst-15) were examined for their ability to catalyze the ethanolic esterification of the N-...

Iron-Catalyzed Intramolecular C(sp(2))-N Cyclization of 1-(N-Arylpyrrol-2-yl)ethanone O-Acetyl Oximes toward Pyrrolo[1,2-a]quinoxaline Derivatives.

PubMed

Zhang, Zhiguo; Li, Junlong; Zhang, Guisheng; Ma, Nana; Liu, Qingfeng; Liu, Tongxin

2015-07-02

An efficient and convenient iron-catalyzed protocol has been developed for the synthesis of substituted pyrrolo[1,2-a]quinoxalines from 1-(N-arylpyrrol-2-yl)ethanone O-acetyl oximes through N-O bond cleavage and intramolecular directed C-H arylation reactions in acetic acid.

Iridium-Catalyzed Hydrogen Transfer Reactions

NASA Astrophysics Data System (ADS)

Saidi, Ourida; Williams, Jonathan M. J.

This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst "borrows" hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C-C bonds where the only by-product is typically water.

Naturally occurring alkaline amino acids function as efficient catalysts on Knoevenagel condensation at physiological pH: a mechanistic elucidation.

PubMed

Li, Weina; Fedosov, Sergey; Tan, Tianwei; Xu, Xuebing; Guo, Zheng

2014-05-01

To maintain biological functions, thousands of different reactions take place in human body at physiological pH (7.0) and mild conditions, which is associated with health and disease. Therefore, to examine the catalytic function of the intrinsically occurring molecules, such as amino acids at neutral pH, is of fundamental interests. Natural basic α-amino acid of L-lysine, L-arginine, and L-histidine neutralized to physiological pH as salts were investigated for their ability to catalyze Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate. Compared with their free base forms, although neutralized alkaline amino acid salts reduced the catalytic activity markedly, they were still capable to perform an efficient catalysis at physiological pH as porcine pancreatic lipase (PPL), one of the best enzymes that catalyze Knoevenagel condensation. In agreement with the fact that the three basic amino acids were well neutralized, stronger basic amino acid Arg and Lys showed more obvious variation in NH bend peak from the FTIR spectroscopy study. Study of ethanol/water system and quantitative kinetic analysis suggested that the microenvironment in the vicinity of amino acid salts and protonability/deprotonability of the amine moiety may determine their catalytic activity and mechanism. The kinetic study of best approximation suggested that the random binding might be the most probable catalytic mechanism for the neutralized alkaline amino acid salt-catalyzed Knoevenagel condensation.

Production of Odd-Carbon Dicarboxylic Acids in Escherichia coli Using an Engineered Biotin–Fatty Acid Biosynthetic Pathway

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haushalter, Robert W.; Phelan, Ryan M.; Hoh, Kristina M.

Dicarboxylic acids are commodity chemicals used in the production of plastics, polyesters, nylons, fragrances, and medications. Bio-based routes to dicarboxylic acids are gaining attention due to environmental concerns about petroleum-based production of these compounds. Some industrial applications require dicarboxylic acids with specific carbon chain lengths, including odd-carbon species. Biosynthetic pathways involving cytochrome P450-catalyzed oxidation of fatty acids in yeast and bacteria have been reported, but these systems produce almost exclusively even-carbon species. Here in this paper we report a novel pathway to odd-carbon dicarboxylic acids directly from glucose in Escherichia coli by employing an engineered pathway combining enzymes from biotinmore » and fatty acid synthesis. Optimization of the pathway will lead to industrial strains for the production of valuable odd-carbon diacids.« less

ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT: ENVIROFUELS DIESEL FUEL CATALYZER FUEL ADDITIVE

EPA Science Inventory

EPA's Environmental Technology Verification Program has tested EnviroFuels diesel fuel additive, called the Diesel Fuel Catalyzer. EnviroFuels has stated that heavy-duty on and off road diesel engines are the intended market for the catalyzer. Preliminary tests conducted indicate...

The sugar model: catalysis by amines and amino acid products

NASA Technical Reports Server (NTRS)

Weber, A. L.

2001-01-01

Ammonia and amines (including amino acids) were shown to catalyze the formation of sugars from formaldehyde and glycolaldehyde, and the subsequent conversion of sugars to carbonylcontaining products under the conditions studied (pH 5.5 and 50 degrees C). Sterically unhindered primary amines were better catalysts than ammonia, secondary amines, and sterically hindered primary amines (i.e. alpha-aminoisobutyric acid). Reactions catalyzed by primary amines initially consumed formaldehyde and glycolaldehyde about 15-20 times faster than an uncatalyzed control reaction. The amine-catalyzed reactions yielded aldotriose (glyceraldehyde), ketotriose (dihydroxyacetone), aldotetroses (erythrose and threose), ketotetrose (erythrulose), pyruvaldehyde, acetaldehyde, glyoxal, pyruvate, glyoxylate, and several unindentified carbonyl products. The concentrations of the carbonyl products, except pyruvate and ketotetrose, initially increased and then declined during the reaction, indicating their ultimate conversion to other products (like larger sugars or pyruvate). The uncatalyzed control reaction yielded no pyruvate or glyoxylate, and only trace amounts of pyruvaldehyde, acetaldehyde and glyoxal. In the presence of 15 mM catalytic primary amine, such as alanine, the rates of triose and pyruvaldehyde of synthesis were about 15-times and 1200-times faster, respectively, than the uncatalyzed reaction. Since previous studies established that alanine is synthesized from glycolaldehyde and formaldehyde via pyruvaldehyde as its direct precursor, the demonstration that the alanine catalyzes the conversion of glycolaldehyde and formaldehyde to pyruvaldehyde indicates that this synthetic pathway is capable of autocatalysis. The relevance of this synthetic process, named the Sugar Model, to the origin of life is discussed.

Lipase catalyzed epoxidation of fatty acid methyl esters derived from unsaturated vegetable oils in absence of carboxylic acid.

PubMed

Sustaita-Rodríguez, Alejandro; Ramos-Sánchez, Víctor H; Camacho-Dávila, Alejandro A; Zaragoza-Galán, Gerardo; Espinoza-Hicks, José C; Chávez-Flores, David

2018-04-11

Nowadays the industrial chemistry reactions rely on green technologies. Enzymes as lipases are increasing its use in diverse chemical processes. Epoxidized fatty acid methyl esters obtained from transesterification of vegetable oils have recently found applications as polymer plasticizer, agrochemical, cosmetics, pharmaceuticals and food additives. In this research article, grapeseed, avocado and olive oils naturally containing high percents of mono and poly unsaturations were used as starting materials for the production of unsaturated fatty acid methyl esters. The effect of lauric acid as an active oxygen carrier was studied on epoxidation reactions where unsaturated fatty acid methyl esters were converted to epoxy fatty acid methyl esters using immobilized Candida antarctica Lipase type B as catalyst and hydrogen peroxide as oxygen donor at mild temperature and pressure conditions. After this study it was confirmed by 1 H NMR, 13 C NMR and GC-MS that the addition of lauric acid to the enzymatic reaction is unnecessary to transform the alkenes in to epoxides. It was found that quantitative conversions were possible in despite of a carboxylic acid absence.

Stop-catalyzed baryogenesis beyond the MSSM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katz, Andrey; Perelstein, Maxim; Ramsey-Musolf, Michael J.

2015-11-19

Nonminimal supersymmetric models that predict a tree-level Higgs mass above the minimal supersymmetric standard model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. Here, we also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside themore » gauge sector drive the electroweak phase transition.« less

Transition metal-catalyzed carboxylation reactions with carbon dioxide.

PubMed

Martin, Ruben; Tortajada, Andreu; Juliá-Hernández, Francisco; Borjesson, Marino; Moragas, Toni

2018-05-03

Driven by the inherent synthetic potential of CO2 as an abundant, inexpensive and renewable C1 chemical feedstock, the recent years have witnessed renewed interest in devising catalytic CO2 fixations into organic matter. Although the formation of C-C bonds via catalytic CO2 fixation remained rather limited for a long period of time, a close look into the recent literature data indicates that catalytic carboxylation reactions have entered a new era of exponential growth, evolving into a mature discipline that allows for streamlining the synthesis of carboxylic acids, building blocks of utmost relevance in industrial endeavours. These strategies have generally proven broadly applicability and convenient to perform. However, substantial challenges still need to be addressed reinforcing the need to cover metal-catalyzed carboxylation arena in a conceptual and concise manner, delineating the underlying new principles that are slowly emerging in this vibrant area of expertise. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ethanosolv Pretreatment of Bamboo with Dilute Acid for Efficient Enzymatic Saccharification

Treesearch

Zhiqiang Li; Zehui Jiang; Benhua Fei; Zhiyong Cai; Xuejun Pan

2012-01-01

Bamboo is a potential lignocellulosic biomass for the production of bioethanol because of its high cellulose and hemicelluloses content. In this research, ethanosolv pretreatment catalyzed by sulfuric acid was studied in order to enhance enzymatic saccharification of moso bamboo. The addition of 2% (w/w on bamboo) sulfuric acid in water or 75% (v/v) ethanol was...

Extraction of microalgal lipids and the influence of polar lipids on biodiesel production by lipase-catalyzed transesterification.

PubMed

Navarro López, Elvira; Robles Medina, Alfonso; González Moreno, Pedro Antonio; Esteban Cerdán, Luis; Molina Grima, Emilio

2016-09-01

In order to obtain microalgal saponifiable lipids (SLs) fractions containing different polar lipid (glycolipids and phospholipids) contents, SLs were extracted from wet Nannochloropsis gaditana microalgal biomass using seven extraction systems, and the polar lipid contents of some fractions were reduced by low temperature acetone crystallization. We observed that the polar lipid content in the extracted lipids depended on the polarity of the first solvent used in the extraction system. Lipid fractions with polar lipid contents between 75.1% and 15.3% were obtained. Some of these fractions were transformed into fatty acid methyl esters (FAMEs, biodiesel) by methanolysis, catalyzed by the lipases Novozym 435 and Rhizopus oryzae in tert-butanol medium. We observed that the reaction velocity was higher the lower the polar lipid content, and that the final FAME conversions achieved after using the same lipase batch to catalyze consecutive reactions decreased in relation to an increase in the polar lipid content. Copyright © 2016 Elsevier Ltd. All rights reserved.

Convenient divergent strategy for the synthesis of TunePhos-type chiral diphosphine ligands and their applications in highly enantioselective Ru-catalyzed hydrogenations.

PubMed

Sun, Xianfeng; Zhou, Le; Li, Wei; Zhang, Xumu

2008-02-01

A convenient, divergent strategy for the synthesis of a series of modular and fine-tunable C3-TunePhos-type chiral diphosphine ligands and their applications in highly efficient Ru-catalyzed asymmetric hydrogenations were explored. Up to 97 and 99% ee values were achieved for the enantioselective synthesis of beta-methyl chiral amines and alpha-hydroxy acid derivatives, respectively.

Enhancement of lipase catalyzed-fatty acid methyl esters production from waste activated bleaching earth by nullification of lipase inhibitors.

PubMed

Dwiarti, Lies; Ali, Ehsan; Park, Enoch Y

2010-01-01

This study sought to identify inhibitory factors of lipase catalyzed-fatty acid methyl esters (FAME) production from waste activated bleaching earth (wABE). During the vegetable oil refinery process, activated bleaching earth (ABE) is used for removing the impure compounds, but adsorbs vegetable oil up to 35-40% as on a weight basis, and then the wABE is discarded as waste material. The impurities were extracted from the wABE with methanol and evaluated by infra-red (IR) spectroscopy, which revealed that some were chlorophyll-plant pigments. The chlorophylls inhibited the lipase during FAME conversion from wABE. The inhibition by a mixture of chlorophyll a and b was found to be competitive. The inhibition of the enzymatic hydrolysis of waste vegetable oil contained in wABE by chlorophyll a alone was competitive, while the inhibition by chlorophyll b alone was non-competitive. Furthermore, the addition of a small amount of alkali nullified this inhibitory effect and accelerated the FAME production rate. When 0.9% KOH (w/w wABE) was added to the transesterification reaction with only 0.05% lipase (w/w wABE), the maximum FAME production rate improved 120-fold, as compared to that without the addition of KOH. The alkali-combined lipase significantly enhanced the FAME production rate from wABE, in spite of the presence of the plant pigments, and even when a lower amount of lipase was used as a catalyst.

Catalyzed sodium chlorate candles

NASA Technical Reports Server (NTRS)

Malich, C. W.; Wydeven, T.

1972-01-01

The catalytic effect of cobalt powder on chlorate decomposition has been confirmed. Catalysis is enhanced by oxidation of the metal during burning. Catalysts other than cobalt compounds should also be effective; the complete elimination of fuel has shown that the oxidation of cobalt during decomposition is not a vital factor in the improved performance of catalyzed candles.

Applications of Iridium-Catalyzed Asymmetric Allylic Substitution Reactions in Target-Oriented Synthesis.

PubMed

Qu, Jianping; Helmchen, Günter

2017-10-17

Metal catalyzed allylic substitution is a cornerstone of organometallic and synthetic chemistry. Enantioselective versions have been developed with catalysts derived from transition metals, most notably molybdenum, nickel, ruthenium, rhodium, iridium, palladium, and copper. The palladium- and the iridium-catalyzed versions have turned out to be particularly versatile in organic synthesis because of the very broad scope of the nucleophile and great functional group compatibility. Assets of the iridium-catalyzed reaction are the formation of branched, chiral products from simple monosubstituted allylic substrates, high degrees of regio- and enantioselectivity, and use of modular, readily available chiral ligands. The possibility to use carbon, nitrogen, oxygen, and sulfur compounds as well as fluoride as nucleophiles allows a wide range of chiral building blocks to be prepared. Our Account begins with the presentation of fundamental reaction schemes and chiral ligands. We will focus our discussion on reactions promoted by phosphoramidite ligands, though numerous chiral ligands have been employed. The subsequent section presents a brief overview of reaction mechanism and experimental conditions. Two versions of the iridium-catalyzed allylic substitution have emerged. In type 1 reactions (introduced in 1997), linear allylic esters are commonly used as substrates under basic reaction conditions. In type 2 reactions (introduced in 2007), environmentally friendly branched allylic alcohols can be reacted under acidic conditions; occasionally, derivatives of allylic alcohols have also been applied. A unique feature of the type 2 reactions is that highly electrophilic allylic intermediates can be brought to reaction with weakly activated alkenes. The subsequent text is ordered according to the strategies followed to transform allylic substitution products to desired targets, most of which are natural products or drugs. Syntheses starting with an intermolecular allylic

A Lipoxygenase from Red Alga Pyropia haitanensis, a Unique Enzyme Catalyzing the Free Radical Reactions of Polyunsaturated Fatty Acids with Triple Ethylenic Bonds

PubMed Central

Zhu, Zhujun; Qian, Feijian; Yang, Rui; Chen, Juanjuan; Luo, Qijun; Chen, Haimin; Yan, Xiaojun

2015-01-01

Lipoxygenases (LOXs) are key enzymes to regulate the production of hormones and defensive metabolites in plants, animals and algae. In this research, a full length LOX gene has been cloned and expressed from the red alga Pyropia haitanensis (Bangiales, Rhodophyta) gametophyte (PhLOX2). Subsequent phylogenetic analysis showed that such LOX enzymes are separated at the early stage of evolution, establishing an independent branch. The LOX activity was investigated at the optimal pH of 8.0. It appears that PhLOX2 is a multifunctional enzyme featuring both lipoxygenase and hydroperoxidase activities. Additionally, PhLOX2 exhibits remarkable substrate and position flexibility, and it can catalyze an array of chemical reactions involving various polyunsaturated fatty acids, ranging from C18 to C22. As a matter of fact, mono-hydroperoxy, di-hydroperoxy and hydroxyl products have been obtained from such transformations, and eicosapentaenoic acid seem to be the most preferred substrate. It was found that at least triple ethylenic bonds are required for PhLOX2 to function as a LOX, and the resulting hydroxy products should be originated from the PhLOX2 mediated reduction of mono-hydroperoxides, in which the hydrogen abstraction occurs on the carbon atom between the second and third double bond. Most of the di-hydroperoxides observed seem to be missing their mono-position precursors. The substrate and position flexibility, as well as the function versatility of PhLOXs represent the ancient enzymatic pathway for organisms to control intracellular oxylipins. PMID:25658744

Palladium-catalyzed heteroannulation of 1,3-dienes to form alpha-alkylidene-gamma-butyrolactones.

PubMed

Gagnier, S V; Larock, R C

2000-03-10

alpha-Alkylidene-gamma-butyrolactones are readily prepared by the palladium-catalyzed heteroannulation of a variety of 1,3-dienes by alpha-iodo and alpha-bromo acrylic acids. The best results are obtained by employing a catalytic amount of the sterically hindered chelating alkyl phosphine D-t-BPF [(di-tert-butylphosphino)ferrocene]. In most cases, this process is highly regioselective. The reaction is believed to proceed via (1) oxidative addition of the vinylic halide to Pd(0), (2) organopalladium addition to the less hindered end of the 1,3-diene to form a pi-allylpalladium intermediate, and (3) nucleophilic displacement of the palladium by the carboxylate ion.

Selective Inactivation of Functional RNAs by Ribozyme-Catalyzed Covalent Modification.

PubMed

Poudyal, Raghav R; Benslimane, Malak; Lokugamage, Melissa P; Callaway, Mackenzie K; Staller, Seth; Burke, Donald H

2017-03-17

The diverse functions of RNA provide numerous opportunities for programming biological circuits. We describe a new strategy that uses ribozyme K28min to covalently tag a specific nucleobase within an RNA or DNA target strand to regulate and selectively inactivate those nucleic acids. K28min variants with appropriately reprogrammed internal guide sequences efficiently tagged multiple sites from an mRNA and from aptamer and ribozyme targets. Upon covalent modification by the corresponding K28min variant, an ATP-binding aptamer lost all affinity for ATP, and the fluorogenic Mango aptamer lost its ability to activate fluorescence of its dye ligand. Modifying a hammerhead ribozyme near the catalytic core led to loss of almost all of its substrate-cleaving activity, but modifying the same hammerhead ribozyme within a tertiary stabilizing element that reduces magnesium dependence only impaired substrate cleavage at low magnesium concentration. Thus, ribozyme-mediated covalent modification can be used both to selectively inactivate and to fine-tune the activities of targeted functional RNAs, analogous to the effects of post-translational modifications of proteins. Ribozyme-catalyzed covalent modification could therefore be developed to regulate nucleic acids components of synthetic and natural circuits.

Zeolite-catalyzed hydrogenation of carbon dioxide and ethene.

PubMed

Chan, Bun; Radom, Leo

2008-07-30

Ab initio molecular orbital theory and density functional theory calculations have been used to study the three-stage zeolite-catalyzed hydrogenation of CO2 to methanol and the hydrogenation of C2H 4 to ethane, with the aim of designing an effective zeolite catalyst for these reactions. Both Brønsted acid (XH) and alkali metal (XM) sites in model zeolites (-X-Al-XH- or -X-Al-XM-) have been examined. It is found that appropriately designed zeolites can provide excellent catalysis for these reactions, particularly for the hydrogenation of CO2, HCO2H and CH2O, with uncatalyzed barriers of more than 300 kJ mol(-1) being reduced to as little as 17 kJ mol(-1) (in the case of CH2O). The reaction barrier depends on the acidity of the XH moiety or the nature of the metal cation M in the XM moiety, and the basicity of the adjacent X group in the catalyst. For a catalyst based on alkali metal zeolites (XM), the catalytic activity is relatively insensitive to the nature of X in the XM group. As a result, the catalytic activity for these types of zeolites increases as X becomes more basic. We propose that alkali metal zeolites with Ge and N incorporated into the framework could be very effective catalysts for hydrogenation processes.

Synthesis and Biological Evaluation of Non-Hydrolizable 1,2,3-Triazole Linked Sialic Acid Derivatives as Neuraminidase Inhibitors

PubMed Central

Weïwer, Michel; Chen, Chi-Chang; Kemp, Melissa M.; Linhardt, Robert J.

2013-01-01

α-Sialic acid azide 1 has been used as a substrate for the efficient preparation of 1,2,3-triazole derivatives of sialic acid using the copper-catalyzed azide-alkyne Huisgen cycloaddition (“click chemistry”). Our approach is to generate non-natural N-glycosides of sialic acid that are resistant to neuraminidase catalyzed hydrolysis as opposed to the natural O-glycosides. These N-glycosides would act as neuraminidase inhibitors to prevent the release of new virions. As a preliminary study, a small library of 1,2,3-triazole-linked sialic acid derivatives has been synthesized in 71-89% yield. A disaccharide mimic of sialic acid has also been prepared using the α-sialic acid azide 1 and a C-8 propargyl sialic acid acceptor in 68% yield. A model sialic acid coated dendrimer was also synthesized from a per-propargylated pentaerythritol acceptor. These novel sialic acid derivatives were then evaluated as potential neuraminidase inhibitors using a 96-well plate fluorescence assay; micromolar IC50 values were observed, comparable to the known sialidase inhibitor Neu5Ac2en. PMID:24223493

A review on production of biodiesel using catalyzed transesterification

NASA Astrophysics Data System (ADS)

Dash, Santosh Kumar; Lingfa, Pradip

2017-07-01

Biodiesel is arguably an important fuel for compression ignition engine as far as sustainability and environmental issues are concerned. It can be produced from both edible and non-edible vegetable oils and animal fats. Owing to higher viscosity, the utilization of crude vegetable oil is not advisable as it results engine failure. For reducing the viscosity and improving the other fuel characteristics comparable to that of diesel fuel, different approaches have been developed. However, transesterification process is very reliable, less costly and easy method compared to other methods. Due to more free fatty acids content in most of the non-edible vegetable oils, a pretreatment is employed to convert the acids to ester, then transesterified with suitable alcohol. Primarily yield of biodiesel depends upon the molar ratio of oil/alcohol, reaction temperature, reaction time, amount of catalyst, type of catalyst, stirring speed. Both homogeneous and heterogeneous catalysts are used for synthesis purposes. Heterogeneous catalysts are less costly, environmental benign and can be derived from natural resources. Enzymatic catalysts are more environmental benign than heterogeneous catalysts but are costly, which hinders its widespread research and utilization. This article reviews the results of prominent works and researches in the field of production of biodiesel via catalyzed transesterification process.

Pd/C Synthesized with Citric Acid: An Efficient Catalyst for Hydrogen Generation from Formic Acid/Sodium Formate

PubMed Central

Wang, Zhi-Li; Yan, Jun-Min; Wang, Hong-Li; Ping, Yun; Jiang, Qing

2012-01-01

A highly efficient hydrogen generation from formic acid/sodium formate aqueous solution catalyzed by in situ synthesized Pd/C with citric acid has been successfully achieved at room temperature. Interestingly, the presence of citric acid during the formation and growth of the Pd nanoparticles on carbon can drastically enhance the catalytic property of the resulted Pd/C, on which the conversion and turnover frequency for decomposition of formic acid/sodium formate system can reach the highest values ever reported of 85% within 160 min and 64 mol H2 mol−1 catalyst h−1, respectively, at room temperature. The present simple, low cost, but highly efficient CO-free hydrogen generation system at room temperature is believed to greatly promote the practical application of formic acid system on fuel cells. PMID:22953041

Recent advances in copper-catalyzed asymmetric coupling reactions

PubMed Central

2015-01-01

Summary Copper-catalyzed (or -mediated) asymmetric coupling reactions have received significant attention over the past few years. Especially the coupling reactions of aryl or alkyl halides with nucleophiles became a very powerful tool for the formation of C–C, C–N, C–O and other carbon–heteroatom bonds as well as for the construction of heteroatom-containing ring systems. This review summarizes the recent progress in copper-catalyzed asymmetric coupling reactions for the formation of C–C and carbon–heteroatom bonds. PMID:26734106

Pyrolysis of oil palm mesocarp fiber catalyzed with steel slag-derived zeolite for bio-oil production.

PubMed

Kabir, G; Mohd Din, A T; Hameed, B H

2018-02-01

The pyrolysis of oil palm mesocarp fiber (OPMF) was catalyzed with a steel slag-derived zeolite (FAU-SL) in a slow-heating fixed-bed reactor at 450 °C, 550 °C, and 600 °C. The catalytic pyrolysis of OPMF produced a maximum yield of 47 wt% bio-oil at 550 °C, and the crude pyrolysis vapor (CPV) of this process yielded crude pyrolysis oil with broad distribution of bulky oxygenated organic compounds. The bio-oil composition produced at 550 °C contained mainly light and stable acid-rich carbonyls at a relative abundance of 48.02% peak area and phenolic compounds at 12.03% peak area. The FAU-SL high mesoporosity and strong surface acidity caused the conversion of the bulky CPV molecules into mostly light acid-rich carbonyls and aromatics through secondary reactions. The secondary reactions mechanisms facilitated by FAU-SL reduced the distribution of the organic compounds in the bio-oil to mostly acid-rich carbonyls and aromatic in contrast to other common zeolite. Copyright © 2017. Published by Elsevier Ltd.

Cu-catalyzed aerobic oxidative cyclizations of 3-N-hydroxyamino-1,2-propadienes with alcohols, thiols, and amines to form α-O-, S-, and N-substituted 4-methylquinoline derivatives.

PubMed

Sharma, Pankaj; Liu, Rai-Shung

2015-03-16

A one-pot, two-step synthesis of α-O-, S-, and N-substituted 4-methylquinoline derivatives through Cu-catalyzed aerobic oxidations of N-hydroxyaminoallenes with alcohols, thiols, and amines is described. This reaction sequence involves an initial oxidation of N-hydroxyaminoallenes with NuH (Nu = OH, OR, NHR, and SR) to form 3-substituted 2-en-1-ones, followed by Brønsted acid catalyzed intramolecular cyclizations of the resulting products. Our mechanistic analysis suggests that the reactions proceed through a radical-type mechanism rather than a typical nitrone-intermediate route. The utility of this new Cu-catalyzed reaction is shown by its applicability to the synthesis of several 2-amino-4-methylquinoline derivatives, which are known to be key precursors to several bioactive molecules. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DFT study of the molybdenum-catalyzed deoxydehydration of vicinal diols.

PubMed

Lupp, Daniel; Christensen, Niels Johan; Dethlefsen, Johannes R; Fristrup, Peter

2015-02-16

The mechanism of the molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an Mo(VI) oxo complex, oxidative cleavage of the diol resulting in an Mo(IV) complex, and extrusion of the alkene. We have compared the proposed pathway with several alternatives, and the results have been corroborated by comparison with the molybdenum-catalyzed sulfoxide reduction recently published by Sanz et al. and with experimental observations for the DODH itself. Improved understanding of the mechanism should expedite future optimization of molybdenum-catalyzed biomass transformations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CYP98A6 from Lithospermum erythrorhizon encodes 4-coumaroyl-4'-hydroxyphenyllactic acid 3-hydroxylase involved in rosmarinic acid biosynthesis.

PubMed

Matsuno, Michiyo; Nagatsu, Akito; Ogihara, Yukio; Ellis, Brian E; Mizukami, Hajime

2002-03-13

Rosmarinic acid is the dominant hydroxycinnamic acid ester accumulated in Boraginaceae and Lamiaceae plants. A cytochrome P450 cDNA was isolated by differential display from cultured cells of Lithospermum erythrorhizon, and the gene product was designated CYP98A6 based on the deduced amino acid sequence. After expression in yeast, the P450 was shown to catalyze the 3-hydroxylation of 4-coumaroyl-4'-hydroxyphenyllactic acid, one of the final two steps leading to rosmarinic acid. The expression level of CYP98A6 is dramatically increased by addition of yeast extract or methyl jasmonate to L. erythrorhizon cells, and its expression pattern reflected the elicitor-induced change in rosmarinic acid production, indicating that CYP98A6 plays an important role in regulation of rosmarinic acid biosynthesis.

Hydrolysis of Ketene Catalyzed by Formic Acid: Modification of Reaction Mechanism, Energetics, and Kinetics with Organic Acid Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Louie, Matthew K.; Francisco, Joseph S.; Verdicchio, Marco

2015-05-14

The hydrolysis of ketene (H2C=C=O) to form acetic acid involving two water molecules and also separately in the presence of one to two water molecules and formic acid (FA) was investigated. Our results show that, while the currently accepted indirect mechanism, involving addition of water across the carbonyl C=O bond of ketene to form an ene-diol followed by tautomerization of the ene-diol to form acetic acid, is the preferred pathway when water alone is present, with formic acid as catalyst, addition of water across the ketene C=C double bond to directly produce acetic acid becomes the kinetically favored pathway formore » temperatures below 400 K. We find not only that the overall barrier for ketene hydrolysis involving one water molecule and formic acid (H2C2O + H2O + FA) is significantly lower than that involving two water molecules (H2C2O + 2H(2)O) but also that FA is able to reduce the barrier height for the direct path, involving addition of water across the C=C double bond, so that it is essentially identical with (6.4 kcal/mol) that for the indirect ene-diol formation path involving addition of water across the C=O bond. For the case of ketene hydrolysis involving two water molecules and formic acid (H2C2O + 2H(2)O + FA), the barrier for the direct addition of water across the C=C double bond is reduced even further and is 2.5 kcal/mol lower relative to the ene-diol path involving addition of water across the C=O bond. In fact, the hydrolysis barrier for the H2C2O + 2H(2)O + FA reaction through the direct path is sufficiently low (2.5 kcal/mol) for it to be an energetically accessible pathway for acetic acid formation under atmospheric conditions. Given the structural similarity between acetic and formic acid, our results also have potential implications for aqueous-phase chemistry. Thus, in an aqueous environment, even in the absence of formic acid, though the initial mechanism for ketene hydrolysis is expected to involve addition of water across the

Effects of swelling on the viscoelastic properties of polyester films made from glycerol and glutaric acid

USDA-ARS?s Scientific Manuscript database

Viscoelastic properties have been determined for poly(glycerol-co-glutaric acid) films synthesized from Lewis acid-catalyzed polyesterifications. The polymers were prepared by synthesizing polymer gels that were subsequently cured at 125 degrees C to form polymer films. The polymers were evaluated ...

Synthesis of "trans"-4,5-Bis-dibenzylaminocyclopent-2-Enone from Furfural Catalyzed by ErCl[subscript 3]·6H[subscript 2]O

ERIC Educational Resources Information Center

Estevão, Mónica S.; Martins, Ricardo J. V.; Alfonso, Carlos A. M.

2017-01-01

An experiment exploring the chemistry of the carbonyl group for the one-step synthesis of "trans"-4,5- dibenzylaminocyclopent-2-enone is described. The reaction of furfural and dibenzylamine in the environmentally friendly solvent ethanol and catalyzed by the Lewis acid ErCl[subscript 3]·6H[subscript 2]O afforded the product in high…

Gold-Catalyzed Solid-Phase Synthesis of 3,4-Dihydropyrazin-2(1H)-ones: Relevant Pharmacophores and Peptide Backbone Constraints.

PubMed

Přibylka, Adam; Krchňák, Viktor

2017-11-13

Here, we report the efficient solid-phase synthesis of N-propargyl peptides using Fmoc-amino acids and propargyl alcohol as key building blocks. Gold-catalyzed nucleophilic addition to the triple bond induced C-N bond formation, which triggered intramolecular cyclization, yielding 1,3,4-trisubstituted-5-methyl-3,4-dihydropyrazin-2(1H)-ones. Conformations of acyclic and constrained peptides were compared using a two-step conformer distribution analysis at the molecular mechanics level and density functional theory. The results indicated that the incorporation of heterocyclic molecular scaffold into a short peptide sequence adopted extended conformation of peptide chain. The amide bond adjacent to the constraint did not show significant preference for either cis or trans isomerism. Prepared model compounds demonstrate a proof of concept for gold-catalyzed polymer-supported synthesis of variously substituted 3,4-dihydropyrazin-2(1H)-ones for applications in drug discovery and peptide backbone constraints.

Adipic acid production catalyzed by a combination of a solid acid and an iodide salt from biomass-derived tetrahydrofuran-2,5-dicarboxylic acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilkey, Matthew J.; Balakumar, Rachana; Vlachos, Dionisios G.

We recently reported biomass-derived tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) as a potential renewable feedstock for adipic acid (AA) production by combining HI and molecular H 2 in organic acid solvents.

Adipic acid production catalyzed by a combination of a solid acid and an iodide salt from biomass-derived tetrahydrofuran-2,5-dicarboxylic acid

DOE PAGES

Gilkey, Matthew J.; Balakumar, Rachana; Vlachos, Dionisios G.; ...

2018-01-01

We recently reported biomass-derived tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) as a potential renewable feedstock for adipic acid (AA) production by combining HI and molecular H 2 in organic acid solvents.

Evidence for the Involvement of Acid/Base Chemistry in the Reaction Catalyzed by the Type II Isopentenyl Diphosphate/Dimethylallyl Diphosphate Isomerase from Staphylococcus aureus†

PubMed Central

Thibodeaux, Christopher J.; Mansoorabadi, Steven O.; Kittleman, William; Chang, Wei-chen; Liu, Hung-wen

2011-01-01

The type II isopentenyl diphosphate/dimethylallyl diphosphate isomerase (IDI-2) is a flavin mononucleotide (FMN)-dependent enzyme that catalyzes the reversible isomerization of isopentenyl pyrophosphate (IPP) to dimethylallyl pyrophosphate (DMAPP), a reaction with no net change in redox state of the coenzyme or substrate. Here, UV-vis spectral analysis of the IDI-2 reaction revealed the accumulation of a reduced neutral dihydroflavin intermediate when the reduced enzyme was incubated with IPP or DMAPP. When IDI-2 was reconstituted with 1-deazaFMN and 5-deazaFMN, similar reduced neutral forms of the deazaflavin analogues were observed in the presence of IPP. Single turnover stopped-flow absorbance experiments indicated that this flavin intermediate formed and decayed at kinetically competent rates in the pre-steady-state and, thus, most likely represents a true intermediate in the catalytic cycle. UV-vis spectra of the reaction mixtures reveal trace amounts of a neutral semiquinone, but evidence for the presence of IPP-based radicals could not be obtained by EPR spectroscopy. Rapid-mix chemical quench experiments show no burst in DMAPP formation, suggesting that the rate determining step in the forward direction (IPP to DMAPP) occurs prior to DMAPP formation. A solvent deuterium kinetic isotope effect (D2OVmax = 1.5) was measured on vo in steady-state kinetic experiments at saturating substrate concentrations. A substrate deuterium kinetic isotope effect was also measured on the initital velocity (DVmax = 1.8) and on the decay rate of the flavin intermediate (Dks = 2.3) in single-turnover stopped-flow experiments using (R)-[2-2H]-IPP. Taken together, these data suggest that the C2–H bond of IPP is cleaved in the rate determining step and that general acid/base catalysis may be involved during turnover. Possible mechanisms for the IDI-2 catalyzed reaction are presented and discussed in terms of the available X-ray crystal structures. PMID:18229948

Rhodium-Catalyzed Asymmetric 1,4-Additions, in Water at Room Temperature, with In-Flask Catalyst Recycling

PubMed Central

Lipshutz, Bruce H.; Isley, Nicholas A.; Moser, Ralph; Ghorai, Subir; Leuser, Helena; Taft, Benjamin R.

2013-01-01

Using the newly introduced designer surfactant polyethyleneglycol ubiquinol sebacate (PQS), as the platform for micellar catalysis, nonracemic BINAP has been covalently attached and rhodium(I) inserted to form PQS-BINAP-Rh. This species, the first example of a nonracemically-ligated transition metal catalyst-tethered amphiphile, can be utilized for Rh-catalyzed asymmetric conjugate addition reactions of arylboronic acids to acyclic and cyclic enones. These are performed in water at room temperature, while the catalyst can be recycled without its removal from water in the reaction vessel. PMID:24659941

Enzymes involved in branched-chain amino acid metabolism in humans.

PubMed

Adeva-Andany, María M; López-Maside, Laura; Donapetry-García, Cristóbal; Fernández-Fernández, Carlos; Sixto-Leal, Cristina

2017-06-01

Branched-chain amino acids (leucine, isoleucine and valine) are structurally related to branched-chain fatty acids. Leucine is 2-amino-4-methyl-pentanoic acid, isoleucine is 2-amino-3-methyl-pentanoic acid, and valine is 2-amino-3-methyl-butanoic acid. Similar to fatty acid oxidation, leucine and isoleucine produce acetyl-coA. Additionally, leucine generates acetoacetate and isoleucine yields propionyl-coA. Valine oxidation produces propionyl-coA, which is converted into methylmalonyl-coA and succinyl-coA. Branched-chain aminotransferase catalyzes the first reaction in the catabolic pathway of branched-chain amino acids, a reversible transamination that converts branched-chain amino acids into branched-chain ketoacids. Simultaneously, glutamate is converted in 2-ketoglutarate. The branched-chain ketoacid dehydrogenase complex catalyzes the irreversible oxidative decarboxylation of branched-chain ketoacids to produce branched-chain acyl-coA intermediates, which then follow separate catabolic pathways. Human tissue distribution and function of most of the enzymes involved in branched-chain amino acid catabolism is unknown. Congenital deficiencies of the enzymes involved in branched-chain amino acid metabolism are generally rare disorders. Some of them are associated with reduced pyruvate dehydrogenase complex activity and respiratory chain dysfunction that may contribute to their clinical phenotype. The biochemical phenotype is characterized by accumulation of the substrate to the deficient enzyme and its carnitine and/or glycine derivatives. It was established at the beginning of the twentieth century that the plasma level of the branched-chain amino acids is increased in conditions associated with insulin resistance such as obesity and diabetes mellitus. However, the potential clinical relevance of this elevation is uncertain.

Transition metal catalyzed borylation of functional π-systems

PubMed Central

SHINOKUBO, Hiroshi

2014-01-01

Borylated functional π-systems are useful building blocks to enable efficient synthesis of novel molecular architectures with beautiful structures, intriguing properties and unique functions. Introduction of boronic ester substituents to a variety of extended π-systems can be achieved through either iridium-catalyzed direct C–H borylation or the two-step procedure via electrophilic halogenation followed by palladium-catalyzed borylation. This review article focuses on our recent progress on borylation of large π-conjugated systems such as porphyrins, perylene bisimides, hexabenzocoronenes and dipyrrins. PMID:24492644

Solution-phase parallel synthesis of hexahydro-1H-isoindolone libraries via tactical combination of Cu-catalyzed three-component coupling and Diels-Alder reactions.

PubMed

Zhang, Lei; Lushington, Gerald H; Neuenswander, Benjamin; Hershberger, John C; Malinakova, Helena C

2008-01-01

Parallel solution-phase synthesis of combinatorial libraries of hexahydro-1 H-isoindolones exploiting a novel "tactical combination" of Cu-catalyzed three-component coupling and Diels-Alder reactions was accomplished. Three distinct libraries consisting of 24 members (library I), 60 members (library II), and 32 members (library III) were constructed. Variation of three substituents on the isoindolone scaffold in library I was exclusively achieved by the choice of the building blocks. In the syntheses of libraries II and III, sublibraries of isoindolone scaffolds were prepared initially in a one-pot/two-step process and were further diversified via Pd-catalyzed Suzuki cross-coupling reaction with boronic acids at two different diversification points. The Lipinski profiles and calculated ADME properties of the compounds are also reported.

Mild partial deoxygenation of esters catalyzed by an oxazolinylborate-coordinated rhodium silylene

DOE PAGES

Xu, Songchen; Boschen, Jeffery S.; Biswas, Abhranil; ...

2015-08-17

An electrophilic, coordinatively unsaturated rhodium complex supported by borate-linked oxazoline, oxazoline-coordinated silylene, and N-heterocyclic carbene donors [{κ³-N,Si,C-PhB(Ox Me²)(Ox Me²SiHPh)Im Mes}Rh(H)CO][HB(C₆F₅)₃] (2, Ox Me² = 4,4-dimethyl-2-oxazoline; Im Mes = 1-mesitylimidazole) is synthesized from the neutral rhodium silyl {PhB(Ox Me²)₂Im Mes}RhH(SiH 2Ph)CO (1) and B(C 6F 5) 3. The unusual oxazoline-coordinated silylene structure in 2 is proposed to form by rearrangement of an unobserved isomeric cationic rhodium silylene species [{PhB(Ox Me²)₂Im Mes}RhH(SiHPh)CO][HB(C₆F₅)₃] generated by H abstraction. Complex 2 catalyzes reductions of organic carbonyl compounds with silanes to give hydrosilylation products or deoxygenation products. The pathway to these reactions is primarily influenced bymore » the degree of substitution of the organosilane. Reactions with primary silanes give deoxygenation of esters to ethers, amides to amines, and ketones and aldehydes to hydrocarbons, whereas tertiary silanes react to give 1,2-hydrosilylation of the carbonyl functionality. In contrast, the strong Lewis acid B(C₆F₅)₃ catalyzes the complete deoxygenation of carbonyl compounds to hydrocarbons with PhSiH₃ as the reducing agent.« less

Mild partial deoxygenation of esters catalyzed by an oxazolinylborate-coordinated rhodium silylene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Songchen; Boschen, Jeffery S.; Biswas, Abhranil

An electrophilic, coordinatively unsaturated rhodium complex supported by borate-linked oxazoline, oxazoline-coordinated silylene, and N-heterocyclic carbene donors [{κ³-N,Si,C-PhB(Ox Me²)(Ox Me²SiHPh)Im Mes}Rh(H)CO][HB(C₆F₅)₃] (2, Ox Me² = 4,4-dimethyl-2-oxazoline; Im Mes = 1-mesitylimidazole) is synthesized from the neutral rhodium silyl {PhB(Ox Me²)₂Im Mes}RhH(SiH 2Ph)CO (1) and B(C 6F 5) 3. The unusual oxazoline-coordinated silylene structure in 2 is proposed to form by rearrangement of an unobserved isomeric cationic rhodium silylene species [{PhB(Ox Me²)₂Im Mes}RhH(SiHPh)CO][HB(C₆F₅)₃] generated by H abstraction. Complex 2 catalyzes reductions of organic carbonyl compounds with silanes to give hydrosilylation products or deoxygenation products. The pathway to these reactions is primarily influenced bymore » the degree of substitution of the organosilane. Reactions with primary silanes give deoxygenation of esters to ethers, amides to amines, and ketones and aldehydes to hydrocarbons, whereas tertiary silanes react to give 1,2-hydrosilylation of the carbonyl functionality. In contrast, the strong Lewis acid B(C₆F₅)₃ catalyzes the complete deoxygenation of carbonyl compounds to hydrocarbons with PhSiH₃ as the reducing agent.« less

Self-Catalyzing Chemiluminescence of Luminol-Diazonium Ion and Its Application for Catalyst-Free Hydrogen Peroxide Detection and Rat Arthritis Imaging.

PubMed

Zhao, Chunxin; Cui, Hongbo; Duan, Jing; Zhang, Shenghai; Lv, Jiagen

2018-02-06

We report the unique self-catalyzing chemiluminescence (CL) of luminol-diazonium ion (N 2 + -luminol) and its analytical potential. Visual CL emission was initially observed when N 2 + -luminol was subjected to alkaline aqueous H 2 O 2 without the aid of any catalysts. Further experimental investigations found peroxidase-like activity of N 2 + -luminol on the cleavage of H 2 O 2 into OH • radical. Together with other experimental evidence, the CL mechanism is suggested as the activation of N 2 + -luminol and its dediazotization product 3-hydroxyl luminol by OH • radical into corresponding intermediate radicals, and then further oxidation to excited-state 3-N 2 + -phthalic acid and 3-hydroxyphthalic acid, which finally produce 415 nm CL. The self-catalyzing CL of N 2 + -luminol provides us an opportunity to achieve the attractive catalyst-free CL detection of H 2 O 2 . Experiments demonstrated the 10 -8 M level detection sensitivity to H 2 O 2 as well as to glucose or uric acid if presubjected to glucose oxidase or uricase. With the exampled determination of serum glucose and uric acid, N 2 + -luminol shows its analytical potential for other analytes linking the production or consumption of H 2 O 2 . Under physiological condition, N 2 + -luminol exhibits highly selective and sensitive CL toward 1 O 2 among the common reactive oxygen species. This capacity supports the significant application of N 2 + -luminol for detecting 1 O 2 in live animals. By imaging the arthritis in LEW rats, N 2 + -luminol CL is demonstrated as a potential tool for mapping the inflammation-relevant biological events in a live body.

Horseradish-Peroxidase-Catalyzed Tyrosine Click Reaction.

PubMed

Sato, Shinichi; Nakamura, Kosuke; Nakamura, Hiroyuki

2017-03-02

The efficiency of protein chemical modification on tyrosine residues with N-methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H 2 O 2 , oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N-methylluminol derivatives with a minimum amount of H 2 O 2 prevented the occurrence of oxidative side reactions under HRP-catalyzed conditions. As probes for HRP-catalyzed protein modification, N-methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β-nicotinamide adenine dinucleotide (NADH, H 2 O 2 -free conditions). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Alkylation of acetohydroxyacid synthase I from Escherichia coli K-12 by 3-bromopyruvate: evidence for a single active site catalyzing acetolactate and acetohydroxybutyrate synthesis.

PubMed Central

Silverman, P M; Eoyang, L

1987-01-01

Acetohydroxyacid synthase I (AHAS I) purified from Escherichia coli K-12 was irreversibly inactivated by incubation with 3-bromopyruvate. Inactivation was specific, insofar as bromoacetate and iodoacetate were much less effective than bromopyruvate. Inactivation was accompanied by incorporation of radioactivity from 3-bromo[2-14C]pyruvate into acid-insoluble material. More than 95% of the incorporated radioactivity coelectrophoresed with the 60-kilodalton IlvB subunit of the enzyme through a sodium dodecyl sulfate-polyacrylamide gel; less than 5% coelectrophoresed with the 11.2-kilodalton IlvN subunit. The stoichiometry of incorporation at nearly complete inactivation was 1 mol of 14C per mol of IlvB polypeptide. These data indicate that bromopyruvate inactivates AHAS I by alkylating an amino acid at or near a single active site located in the IlvB subunit of the enzyme. We confirmed that this alkylation inactivated both AHAS reactions normally catalyzed by AHAS I. These results provide the first direct evidence that AHAS I catalyzes both acetohydroxybutyrate and acetolactate synthesis from the same active site. Images PMID:3294793

Pretreatment efficiency and structural characterization of rice straw by an integrated process of dilute-acid and steam explosion for bioethanol production.

PubMed

Chen, Wen-Hua; Pen, Ben-Li; Yu, Ching-Tsung; Hwang, Wen-Song

2011-02-01

The combined pretreatment of rice straw using dilute-acid and steam explosion followed by enzymatic hydrolysis was investigated and compared with acid-catalyzed steam explosion pretreatment. In addition to measuring the chemical composition, including glucan, xylan and lignin content, changes in rice straw features after pretreatment were investigated in terms of the straw's physical properties. These properties included crystallinity, surface area, mean particle size and scanning electron microscopy imagery. The effect of acid concentration on the acid-catalyzed steam explosion was studied in a range between 1% and 15% acid at 180°C for 2 min. We also investigated the influence of the residence time of the steam explosion in the combined pretreatment and the optimum conditions for the dilute-acid hydrolysis step in order to develop an integrated process for the dilute-acid and steam explosion. The optimum operational conditions for the first dilute-acid hydrolysis step were determined to be 165°C for 2 min with 2% H(2)SO(4) and for the second steam explosion step was to be carried out at 180°C for 20 min; this gave the most favorable combination in terms of an integrated process. We found that rice straw pretreated by the dilute-acid/steam explosions had a higher xylose yield, a lower level of inhibitor in the hydrolysate and a greater degree of enzymatic hydrolysis; this resulted in a 1.5-fold increase in the overall sugar yield when compared to the acid-catalyzed steam explosion. Copyright © 2010 Elsevier Ltd. All rights reserved.

Indium-catalyzed direct chlorination of alcohols using chlorodimethylsilane-benzil as a selective and mild system.

PubMed

Yasuda, Makoto; Yamasaki, Satoshi; Onishi, Yoshiyuki; Baba, Akio

2004-06-16

The InCl3-catalyzed reaction of alcohols with chlorodimethylsilane (HSiMe2Cl) in the presence of benzil gave the corresponding organic chlorides under mild conditions. Benzil significantly changes the reaction course because the reducing product through dehydroxyhydration was obtained in the absence of benzil. The secondary or tertiary alcohols were effectively chlorinated. The substrates bearing acid-sensitive functional groups were also applied to this system. The highly selective chlorination of the tertiary site was observed in the competitive reaction between tertiary and primary alcohols. The highly coordinated hydrosilane generated from benzil and HSiMe2Cl is an important intermediate.

Bioorthogonal Diversification of Peptides through Selective Ruthenium(II)-Catalyzed C-H Activation.

PubMed

Schischko, Alexandra; Ren, Hongjun; Kaplaneris, Nikolaos; Ackermann, Lutz

2017-02-01

Methods for the chemoselective modification of amino acids and peptides are powerful techniques in biomolecular chemistry. Among other applications, they enable the total synthesis of artificial peptides. In recent years, significant momentum has been gained by exploiting palladium-catalyzed cross-coupling for peptide modification. Despite major advances, the prefunctionalization elements on the coupling partners translate into undesired byproduct formation and lengthy synthetic operations. In sharp contrast, we herein illustrate the unprecedented use of versatile ruthenium(II)carboxylate catalysis for the step-economical late-stage diversification of α- and β-amino acids, as well as peptides, through chemo-selective C-H arylation under racemization-free reaction conditions. The ligand-accelerated C-H activation strategy proved water-tolerant and set the stage for direct fluorescence labelling as well as various modes of peptide ligation with excellent levels of positional selectivity in a bioorthogonal fashion. The synthetic utility of our approach is further demonstrated by twofold C-H arylations for the complexity-increasing assembly of artificial peptides within a multicatalytic C-H activation manifold. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation

PubMed Central

Serganov, Alexander; Keiper, Sonja; Malinina, Lucy; Tereshko, Valentina; Skripkin, Eugene; Höbartner, Claudia; Polonskaia, Anna; Phan, Anh Tuân; Wombacher, Richard; Micura, Ronald; Dauter, Zbigniew; Jäschke, Andres; Patel, Dinshaw J

2015-01-01

The majority of structural efforts addressing RNA’s catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with a reaction product. The RNA adopts a λ-shaped nested pseudoknot architecture whose preformed hydrophobic pocket is precisely complementary in shape to the reaction product. RNA folding and product binding are dictated by extensive stacking and hydrogen bonding, whereas stereoselection is governed by the shape of the catalytic pocket. Catalysis is apparently achieved by a combination of proximity, complementarity and electronic effects. We observe structural parallels in the independently evolved catalytic pocket architectures for ribozyme- and antibody-catalyzed Diels-Alder carbon-carbon bond-forming reactions. PMID:15723077

Selective Conversion of Biorefinery Lignin into Dicarboxylic Acids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Ruoshui; Guo, Mond; Zhang, Xiao

The emerging biomass-to-biofuel conversion industry has created an urgent need for identifying new applications for biorefinery lignin. This paper demonstrates a new route to producing dicarboxylic acids from biorefinery lignin through chalcopyrite-catalyzed oxidation in a highly selective process. Up to 95 % selectivity towards stable dicarboxylic acids was obtained for several types of biorefinery lignin and model compounds under mild, environmentally friendly reaction conditions. The findings from this study paved a new avenue to biorefinery lignin conversions and applications.

Developing Ligands for Palladium(II)-Catalyzed C–H Functionalization: Intimate Dialogue between Ligand and Substrate

PubMed Central

Engle, Keary M.; Yu, Jin-Quan

2013-01-01

Homogeneous transition metal–catalyzed reactions are indispensable to all facets of modern chemical synthesis. It is thus difficult to imagine that for much of the early 20th century, the reactivity and selectivity of all known homogeneous metal catalysts paled in comparison to their heterogeneous and biological counterparts. In the intervening decades, advances in ligand design bridged this divide, such that today some of the most demanding bond-forming events are mediated by ligand-supported homogeneous metal species. While ligand design has propelled many areas of homogeneous catalysis, in the field of Pd(II)-catalyzed C–H functionalization, suitable ligand scaffolds are lacking, which has hampered the development of broadly practical transformations based on C–H functionalization logic. In this review, we offer an account of our research employing three ligand scaffolds, mono-N-protected amino acids, 2,6-disubstituted pyridines, and 2,2′-bipyridines, to address challenges posed by several synthetically versatile substrate classes. Drawing on this work, we discuss principles of ligand design, such as the need to match a ligand to a particular substrate class, and how ligand traits such as tunability and modularity can be advantageous in reaction discovery. PMID:23565982

A new sol-gel synthesis of 45S5 bioactive glass using an organic acid as catalyst.

PubMed

Faure, J; Drevet, R; Lemelle, A; Ben Jaber, N; Tara, A; El Btaouri, H; Benhayoune, H

2015-02-01

In this paper a new sol-gel approach was explored for the synthesis of the 45S5 bioactive glass. We demonstrate that citric acid can be used instead of the usual nitric acid to catalyze the sol-gel reactions. The substitution of nitric acid by citric acid allows to reduce strongly the concentration of the acid solution necessary to catalyze the hydrolysis of silicon and phosphorus alkoxides. Two sol-gel powders with chemical compositions very close to that of the 45S5 were obtained by using either a 2M nitric acid solution or either a 5mM citric acid solution. These powders were characterized and compared to the commercial Bioglass®. The surface properties of the two bioglass powders were assessed by scanning electron microscopy (SEM) and by Brunauer-Emmett-Teller method (BET). The Fourier transformed infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) revealed a partial crystallization associated to the formation of crystalline phases on the two sol-gel powders. The in vitro bioactivity was then studied at the key times during the first hours of immersion into acellular Simulated Body Fluid (SBF). After 4h immersion into SBF we clearly demonstrate that the bioactivity level of the two sol-gel powders is similar and much higher than that of the commercial Bioglass®. This bioactivity improvement is associated to the increase of the porosity and the specific surface area of the powders synthesized by the sol-gel process. Moreover, the nitric acid is efficiently substituted by the citric acid to catalyze the sol-gel reactions without alteration of the bioactivity of the 45S5 bioactive glass. Copyright © 2014 Elsevier B.V. All rights reserved.

Inhibition kinetics and molecular simulation of p-substituted cinnamic acid derivatives on tyrosinase.

PubMed

Cui, Yi; Hu, Yong-Hua; Yu, Feng; Zheng, Jing; Chen, Lin-Shan; Chen, Qing-Xi; Wang, Qin

2017-02-01

This study was to investigate the inhibition effects of para-substituted cinnamic acid derivatives (4-chlorocinnamic acid, 4-ethoxycinnamic acid and 4-nitrocinnamic acid) on tyrosinase catalyzing the substrates, with the purpose of elucidating the inhibition mechanism of the tested derivatives on tyrosinase by the UV-vis spectrum, fluorescence spectroscopy, copper interacting and molecular docking, respectively. The native-PAGE results showed that 4-chlorocinnamic acid (4-CCA), 4-ethoxycinnamic acid (4-ECA) and 4-nitrocinnamic acid (4-NCA) had inhibitory effects on tyrosinase. Spectrophotometric analysis used to determine the inhibition capabilities of these compounds on tyrosinase catalyzing L-tyrosine (L-Tyr) and L-3,4-Dihydroxyphenylalanine (L-DOPA) as well. The IC 50 values and inhibition constants were further determined. Moreover, quenching mechanisms of tested compounds to tyrosinase belonged to static type and a red shift on fluorescence emission peak occurred when 4-NCA added. Copper interacting and molecular docking demonstrated that 4-CCA could not bind directly to the copper, but it could interact with residues in the active center of tyrosinase. Meanwhile, 4-ECA and 4-NCA could chelate a copper ion of tyrosinase. Anti-tyrosinase activities of para-substituted cinnamic acid derivatives would lay scientific foundation for their utilization in designing of novel tyrosinase inhibitors. Copyright © 2016 Elsevier B.V. All rights reserved.

Structurally divergent lysophosphatidic acid acyltransferases with high selectivity for saturated medium chain fatty acids from Cuphea seeds.

PubMed

Kim, Hae Jin; Silva, Jillian E; Iskandarov, Umidjon; Andersson, Mariette; Cahoon, Rebecca E; Mockaitis, Keithanne; Cahoon, Edgar B

2015-12-01

Lysophosphatidic acid acyltransferase (LPAT) catalyzes acylation of the sn-2 position on lysophosphatidic acid by an acyl CoA substrate to produce the phosphatidic acid precursor of polar glycerolipids and triacylglycerols (TAGs). In the case of TAGs, this reaction is typically catalyzed by an LPAT2 from microsomal LPAT class A that has high specificity for C18 fatty acids containing Δ9 unsaturation. Because of this specificity, the occurrence of saturated fatty acids in the TAG sn-2 position is infrequent in seed oils. To identify LPATs with variant substrate specificities, deep transcriptomic mining was performed on seeds of two Cuphea species producing TAGs that are highly enriched in saturated C8 and C10 fatty acids. From these analyses, cDNAs for seven previously unreported LPATs were identified, including cDNAs from Cuphea viscosissima (CvLPAT2) and Cuphea avigera var. pulcherrima (CpuLPAT2a) encoding microsomal, seed-specific class A LPAT2s and a cDNA from C. avigera var. pulcherrima (CpuLPATB) encoding a microsomal, seed-specific LPAT from the bacterial-type class B. The activities of these enzymes were characterized in Camelina sativa by seed-specific co-expression with cDNAs for various Cuphea FatB acyl-acyl carrier protein thioesterases (FatB) that produce a variety of saturated medium-chain fatty acids. CvLPAT2 and CpuLPAT2a expression resulted in accumulation of 10:0 fatty acids in the Camelina sativa TAG sn-2 position, indicating a 10:0 CoA specificity that has not been previously described for plant LPATs. CpuLPATB expression generated TAGs with 14:0 at the sn-2 position, but not 10:0. Identification of these LPATs provides tools for understanding the structural basis of LPAT substrate specificity and for generating altered oil functionalities. © 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.

Terrestrial evolution of polymerization of amino acids - Heat to ATP

NASA Technical Reports Server (NTRS)

Fox, S. W.; Nakashima, T.

1981-01-01

Sets of amino acids containing sufficient trifunctional monomer are thermally polymerized at temperatures such as 65 deg; the amino acids order themselves. Various polymers have diverse catalytic activities. The polymers aggregate, in aqueous solution, to cell-like structures having those activities plus emergent properties, e.g. proliferatability. Polyamino acids containing sufficient lysine catalyze conversion of free amino acids, by ATP, to small peptides and a high molecular weight fraction. The lysine-rich proteinoid is active in solution, within suspensions of cell-like particles, or in other particles composed of lysine-rich proteinoid and homopolyribonucleotide. Selectivities are observed. An archaic polyamino acid prelude to coded protein synthesis is indicated.

Copper-Catalyzed Alkoxycarbonylation of Alkanes with Alcohols.

PubMed

Li, Yahui; Wang, Changsheng; Zhu, Fengxiang; Wang, Zechao; Dixneuf, Pierre H; Wu, Xiao-Feng

2017-04-10

Esters are important chemicals widely used in various areas, and alkoxycarbonylation represents one of the most powerful tools for their synthesis. In this communication, a new copper-catalyzed carbonylative procedure for the synthesis of aliphatic esters from cycloalkanes and alcohols was developed. Through direct activation of the Csp3 -H bond of alkanes and with alcohols as the nucleophiles, the desired esters were prepared in moderate-to-good yields. Paraformaldehyde could also be applied for in situ alcohol generation by radical trapping, and moderate yields of the corresponding esters could be produced. Notably, this is the first report on copper-catalyzed alkoxycarbonylation of alkanes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly regioselective Lewis acid-catalyzed [3+2] cycloaddition of alkynes with donor-acceptor oxiranes by selective carbon-carbon bond cleavage of epoxides.

PubMed

Liu, Renrong; Zhang, Mei; Zhang, Junliang

2011-12-28

A novel, efficient, highly regioselective Sc(OTf)(3)-catalyzed [3+2] cycloaddition of electron-rich alkynes with donor-acceptor oxiranes via highly chemoselective C-C bond cleavage under mild conditions was developed. This journal is © The Royal Society of Chemistry 2011

Metal-catalyzed Decarboxylative Fluoroalkylation Reactions.

PubMed

Ambler, Brett R; Yang, Ming-Hsiu; Altman, Ryan A

2016-12-01

Metal-catalyzed decarboxylative fluoroalkylation reactions enable the conversion of simple O-based substrates into biologically relevant fluorinated analogs. Herein, we present decarboxylative methods that facilitate the synthesis of trifluoromethyl- and difluoroketone-containing products. We highlight key mechanistic aspects that are critical for efficient catalysis, and that inspired our thinking while developing the reactions.

Highly enantioselective synthesis of γ-, δ-, and ε-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)–Cu- or Pd-catalyzed cross-coupling

PubMed Central

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

2014-01-01

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (≥99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (≥99% ee) and catalytic synthesis of various γ- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)–Cu- or Pd-catalyzed cross-coupling. ZACA–in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ω-alkene-1-ols produced both (R)- and (S)-α,ω-dioxyfunctional intermediates (3) in 80–88% ee, which were readily purified to the ≥99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These α,ω-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of γ-, δ-, and ε-chiral 1-alkanols of ≥99% ee. The MαNP ester analysis has been applied to the determination of the enantiomeric purities of δ- and ε-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Lipase-catalyzed synthesis of palmitanilide: Kinetic model and antimicrobial activity study.

PubMed

Liu, Kuan-Miao; Liu, Kuan-Ju

2016-01-01

Enzymatic syntheses of fatty acid anilides are important owing to their wide range of industrial applications in detergents, shampoo, cosmetics, and surfactant formulations. The amidation reaction of Mucor miehei lipase Lipozyme IM20 was investigated for direct amidation of triacylglycerol in organic solvents. The process parameters (reaction temperature, substrate molar ratio, enzyme amount) were optimized to achieve the highest yield of anilide. The maximum yield of palmitanilide (88.9%) was achieved after 24 h of reaction at 40 °C at an enzyme concentration of 1.4% (70 mg). Kinetics of lipase-catalyzed amidation of aniline with tripalmitin has been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The kinetic constants were estimated by using non-linear regression method using enzyme kinetic modules. The enzyme operational stability study showed that Lipozyme IM20 retained 38.1% of the initial activity for the synthesis of palmitanilide (even after repeated use for 48 h). Palmitanilide, a fatty acid amide, exhibited potent antimicrobial activity toward Bacillus cereus. Copyright © 2015 Elsevier Inc. All rights reserved.

Enantioselective Rhodium Enolate Protonations. A New Methodology for the Synthesis of β2-Amino Acids

PubMed Central

Sibi, Mukund P.; Tatamidani, Hiroto; Patil, Kalyani

2008-01-01

Rhodium catalyzed conjugate addition of an aryl boronic acid to α-methylamino acrylates followed by enantioselective protonation of the oxa-π-allylrhodium intermediate provides access to aryl substituted β2-amino acids. The impact of the different variables of the reaction on the levels of enantioselectivity has been assessed. PMID:15957893

Palladium-catalyzed Suzuki-Miyaura coupling of amides by carbon-nitrogen cleavage: general strategy for amide N-C bond activation.

PubMed

Meng, Guangrong; Szostak, Michal

2016-06-15

The first palladium-catalyzed Suzuki-Miyaura cross-coupling of amides with boronic acids for the synthesis of ketones by sterically-controlled N-C bond activation is reported. The transformation is characterized by operational simplicity using bench-stable, commercial reagents and catalysts, and a broad substrate scope, including substrates with electron-donating and withdrawing groups on both coupling partners, steric-hindrance, heterocycles, halides, esters and ketones. The scope and limitations are presented in the synthesis of >60 functionalized ketones. Mechanistic studies provide insight into the catalytic cycle of the cross-coupling, including the first experimental evidence for Pd insertion into the amide N-C bond. The synthetic utility is showcased by a gram-scale cross-coupling and cross-coupling at room temperature. Most importantly, this process provides a blueprint for the development of a plethora of metal catalyzed reactions of typically inert amide bonds via acyl-metal intermediates. A unified strategy for amide bond activation to enable metal insertion into N-C amide bond is outlined ().

Ligand-Controlled Regioselective Copper-Catalyzed Trifluoromethylation To Generate (Trifluoromethyl)allenes.

PubMed

Ambler, Brett R; Peddi, Santosh; Altman, Ryan A

2015-05-15

"Cu-CF3" species have been used historically for a broad spectrum of nucleophilic trifluoromethylation reactions. Although recent advancements have employed ligands to stabilize and harness the reactivity of this key organometallic intermediate, the ability of a ligand to differentiate a regiochemical outcome of a Cu-CF3-mediated or -catalyzed reaction has not been previously reported. Herein, we report the first example of a Cu-catalyzed trifluoromethylation reaction in which a ligand controls the regiochemical outcome. More specifically, we demonstrate the ability of bipyridyl-derived ligands to control the regioselectivity of the Cu-catalyzed nucleophilic trifluoromethylation reactions of propargyl electrophiles to generate (trifluoromethyl)allenes. This method provides a variety of di-, tri-, and tetrasubstituted (trifluoromethyl)allenes, which can be further modified to generate complex fluorinated substructures.

Desaturation reactions catalyzed by soluble methane monooxygenase.

PubMed

Jin, Y; Lipscomb, J D

2001-09-01

Soluble methane monooxygenase (MMO) is shown to be capable of catalyzing desaturation reactions in addition to the usual hydroxylation and epoxidation reactions. Dehydrogenated products are generated from MMO-catalyzed oxidation of certain substrates including ethylbenzene and cyclohexadienes. In the reaction of ethylbenzene, desaturation of ethyl C-H occurred along with the conventional hydroxvlations of ethyl and phenyl C-Hs. As a result, styrene is formed together with ethylphenols and phenylethanols. Similarly, when 1,3- and 1,4-cyclohexadienes were used as substrates, benzene was detected as a product in addition to the corresponding alcohols and epoxides. In all cases, reaction conditions were found to significantly affect the distribution among the different products. This new activity of MMO is postulated to be associated with the chemical properties of the substrates rather than fundamental changes in the nature of the oxygen and C-H activation chemistries. The formation of the desaturated products is rationalized by formation of a substrate cationic intermediate, possibly via a radical precursor. The cationic species is then proposed to partition between recombination (alcohol formation) and elimination (alkene production) pathways. This novel function of MMO indicates close mechanistic kinship between the hydroxylation and desaturation reactions catalyzed by the nonheme diiron clusters.

Identification of the enzymes catalyzing metabolism of methoxyflurane.

PubMed

Waskell, L; Canova-Davis, E; Philpot, R; Parandoush, Z; Chiang, J Y

1986-01-01

The hepatic microsomal metabolism of methoxyflurane in rabbits is markedly stimulated by treatment with phenobarbital. However, the increased rate of metabolism cannot be completely accounted for by the activity of the purified phenobarbital-inducible cytochrome P-450 isozyme 2, even in the presence of cytochrome b5. The discovery of a second hepatic phenobarbital-inducible cytochrome P-450, isozyme 5, led us to undertake experiments to determine in hepatic and pulmonary preparations the portion of microsomal metabolism of methoxyflurane catalyzed by cytochrome P-450 isozymes 2 and 5. We report herein that isozyme 2 accounts for 25% and 29%, respectively, of the O-demethylation of methoxyflurane in hepatic microsomes from untreated and phenobarbital-treated rabbits, and for 25% of the methoxyflurane metabolism in pulmonary microsomes. Results for isozyme 5 indicate that it catalyzes 19% and 27% of methoxyflurane metabolism in control and phenobarbital-induced liver, and 47% of O-demethylation in the lung. In summary, we demonstrate that methoxyflurane O-demethylation in lung, phenobarbital-induced liver, and control liver microsomes is catalyzed by cytochrome P-450 isozymes 2 and 5. Results with purified cytochrome P-450 isozyme 5 are consistent with those obtained using microsomal preparations. Furthermore, metabolism of methoxyflurane by purified isozyme 5 is markedly stimulated by cytochrome b5. A role for cytochrome b5 in cytochrome P-450 isozyme 5-catalyzed metabolism of methoxyflurane was also demonstrated in microsomes. Antibody to isozyme 5 was unable to inhibit methoxyflurane metabolism in the presence of maximally inhibiting concentrations of cytochrome b5 antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

γ-Sultam-cored N,N-ligands in the ruthenium(ii)-catalyzed asymmetric transfer hydrogenation of aryl ketones.

PubMed

Rast, Slavko; Modec, Barbara; Stephan, Michel; Mohar, Barbara

2016-02-14

The synthesis of new enantiopure syn- and anti-3-(α-aminobenzyl)-benzo-γ-sultam ligands 6 and their application in the ruthenium(ii)-catalyzed asymmetric transfer hydrogenation (ATH) of ketones using formic acid/triethylamine is described. In particular, benzo-fused cyclic ketones afforded excellent enantioselectivities in reasonable time employing a low loading of the syn ligand-containing catalyst. A never-before-seen dynamic kinetic resolution (DKR) during reduction of a γ-keto carboxylic ester (S7) derivative of 1-indanone is realized leading as well to excellent induction.

Reuse performance of granular-activated carbon and activated carbon fiber in catalyzed peroxymonosulfate oxidation.

PubMed

Yang, Shiying; Li, Lei; Xiao, Tuo; Zhang, Jun; Shao, Xueting

2017-03-01

Recently, activated carbon was investigated as an efficient heterogeneous metal-free catalyst to directly activate peroxymonosulfate (PMS) for degradation of organic compounds. In this paper, the reuse performance and the possible deactivation reasons of granular-activated carbon (GAC) and activated carbon fiber (ACF) in PMS activation were investigated. As results indicated, the reusability of GAC, especially in the presence of high PMS dosage, was relatively superior to ACF in catalyzed PMS oxidation of Acid Orange 7 (AO7), which is much more easily adsorbed by ACF than by GAC. Pre-oxidation experiments were studied and it was demonstrated that PMS oxidation on ACF would retard ACF's deactivation to a big extent. After pre-adsorption with AO7, the catalytic ability of both GAC and ACF evidently diminished. However, when methanol was employed to extract the AO7-spent ACF, the catalytic ability could recover quite a bit. GAC and ACF could also effectively catalyze PMS to degrade Reactive Black 5 (RB5), which is very difficult to be adsorbed even by ACF, but both GAC and ACF have poor reuse performance for RB5 degradation. The original organic compounds or intermediate products adsorbed by GAC or ACF would be possibly responsible for the deactivation.

Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism

PubMed Central

Camilloni, Carlo; Sahakyan, Aleksandr B.; Holliday, Michael J.; Isern, Nancy G.; Zhang, Fengli; Eisenmesser, Elan Z.; Vendruscolo, Michele

2014-01-01

Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions. Different families of enzymes, known as “peptidyl-prolyl isomerases” (PPIases), catalyze this reaction, which involves the interconversion between the cis and trans isomers of the N-terminal amide bond of the amino acid proline. However, complete descriptions of the mechanisms by which these enzymes function have remained elusive. We show here that cyclophilin A, one of the most common PPIases, provides a catalytic environment that acts on the substrate through an electrostatic handle mechanism. In this mechanism, the electrostatic field in the catalytic site turns the electric dipole associated with the carbonyl group of the amino acid preceding the proline in the substrate, thus causing the rotation of the peptide bond between the two residues. We identified this mechanism using a combination of NMR measurements, molecular dynamics simulations, and density functional theory calculations to simultaneously determine the cis-bound and trans-bound conformations of cyclophilin A and its substrate as the enzymatic reaction takes place. We anticipate that this approach will be helpful in elucidating whether the electrostatic handle mechanism that we describe here is common to other PPIases and, more generally, in characterizing other enzymatic processes. PMID:24982184

Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism.

PubMed

Camilloni, Carlo; Sahakyan, Aleksandr B; Holliday, Michael J; Isern, Nancy G; Zhang, Fengli; Eisenmesser, Elan Z; Vendruscolo, Michele

2014-07-15

Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions. Different families of enzymes, known as "peptidyl-prolyl isomerases" (PPIases), catalyze this reaction, which involves the interconversion between the cis and trans isomers of the N-terminal amide bond of the amino acid proline. However, complete descriptions of the mechanisms by which these enzymes function have remained elusive. We show here that cyclophilin A, one of the most common PPIases, provides a catalytic environment that acts on the substrate through an electrostatic handle mechanism. In this mechanism, the electrostatic field in the catalytic site turns the electric dipole associated with the carbonyl group of the amino acid preceding the proline in the substrate, thus causing the rotation of the peptide bond between the two residues. We identified this mechanism using a combination of NMR measurements, molecular dynamics simulations, and density functional theory calculations to simultaneously determine the cis-bound and trans-bound conformations of cyclophilin A and its substrate as the enzymatic reaction takes place. We anticipate that this approach will be helpful in elucidating whether the electrostatic handle mechanism that we describe here is common to other PPIases and, more generally, in characterizing other enzymatic processes.

EFFECTS OF AQUATIC HUMIC SUBSTANCES ON ANALYSIS FOR HYDROGEN PEROXIDE USING PEROXIDASE-CATALYZED OXIDATIONS OF TRIARYLMETHANES OR P-HYDROXYPENYLACETIC ACID (JOURNAL VERSION)

EPA Science Inventory

A sensitive procedure is described for trace analysis of hydrogen peroxide in water. The process involves the peroxide-catalyzed oxidation of the leuco forms of two dyes, crystal violet and malachite green. The sensitivity of this procedure, as well as of another procedure based ...

Activation Energies for an Enzyme-Catalyzed and Acid-Catalyzed Hydrolysis: An Introductory Interdisciplinary Experiment for Chemists and Biochemists.

ERIC Educational Resources Information Center

Adams, K. R.; Meyers, M. B.

1985-01-01

Background information, procedures used, and typical results obtained are provided for an experiment in which students determine and compare the Arrhenius activation energies (Ea) for the hydrolysis of salicin. This reaction is subject to catalysis both by acid and by the enzyme emulsin (beta-d-glucoside glycohydrolase). (JN)

Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels-Alder Reaction of Styrene-ynes.

PubMed

Mun, Hyeon Jin; Seong, Eun Young; Ahn, Kwang-Hyun; Kang, Eun Joo

2018-02-02

The intramolecular didehydro-Diels-Alder reaction of styrene-ynes was catalyzed by Fe(II) and Fe(III) to produce various naphthalene derivatives under microwave heating conditions. Mechanistic calculations found that the Fe(II) catalyst activates the styrenyl diene in an inverse-electron-demand Diels-Alder reaction, and the consecutive dehydrogenation reaction can be promoted by either Fe(II)-catalyzed direct dehydrogenation or an Fe(III)-catalyzed rearomatization/dehydrogenation pathway.

Copper-Catalyzed Carbonylative Coupling of Cycloalkanes and Amides.

PubMed

Li, Yahui; Dong, Kaiwu; Zhu, Fengxiang; Wang, Zechao; Wu, Xiao-Feng

2016-06-13

Carbonylation reactions are a most powerful method for the synthesis of carbonyl-containing compounds. However, most known carbonylation procedures still require noble-metal catalysts and the use of activated compounds and good nucleophiles as substrates. Herein, we developed a copper-catalyzed carbonylative transformation of cycloalkanes and amides. Imides were prepared in good yields by carbonylation of a C(sp(3) )-H bond of the cycloalkane with the amides acting as weak nucleophiles. Notably, this is the first report of copper-catalyzed carbonylative C-H activation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cascade Production of Lactic Acid from Universal Types of Sugars Catalyzed by Lanthanum Triflate.

PubMed

Liu, Dajiang; Kim, Kwang Ho; Sun, Jian; Simmons, Blake A; Singh, Seema

2018-02-09

Lignocellulosic biomass conversion into value-added platform chemicals in the non-toxic, water-tolerant Lewis acid, and water solutions bears the hallmark of green chemistry. Lactic acid derived from biomass is an important chemical building block for biodegradable polymers such as polylactide. Herein, a universal method of converting lignocellulosic sugars into lactic acid using catalytic amount of water-stable Lewis acid La(OTf) 3 is demonstrated. The lignocellulosic sugars studied in this work include 1) pyrolytic sugars from pyrolysis oil, and 2) sugars derived from ionic liquid (IL)-pretreated biomass. Under moderate conditions (250 °C, 1 h), levoglucosan (major pyrolytic sugar), glucose, and xylose were converted into lactic acid with carbon-based molar yields of 75, 74, and 61 %, respectively. Furthermore, roughly 49 mol % (based on levoglucosan) and 74 wt % (relative to pretreated biomass) of lactic acid were obtained from the conversion of pyrolytic sugars and sugar-rich fraction after lignin removal from switchgrass, respectively. To our knowledge, this is the first reported conversion of pyrolytic sugar into lactic acid by chemocatalysis and also lignocellulosic sugars are converted into lactic acid without hydrolysis. This approach could potentially be extended to other lignocellulosic sugars after simple removal of lignin from biomass pretreatment, rendering moderate to high yields of lactic acid. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A highly efficient synthesis of the FGH ring of micrandilactone A. Application of thioureas as ligands in the Co-catalyzed Pauson-Khand reaction and Pd-catalyzed carbonylative annulation.

PubMed

Tang, Yefeng; Zhang, Yandong; Dai, Mingji; Luo, Tuoping; Deng, Lujiang; Chen, Jiahua; Yang, Zhen

2005-03-03

The functionalized FGH ring system of micrandilactone A was successfully constructed in high selectivity and good yields. The key reactions in our strategy are the Co-thiourea-catalyzed stereoselective, intramolecular Pauson-Khand reaction and Pd-thiourea-catalyzed stereoselective, intramolecular annulation. [structure: see text

Synthesis and acid catalysis of cellulose-derived carbon-based solid acid

NASA Astrophysics Data System (ADS)

Suganuma, Satoshi; Nakajima, Kiyotaka; Kitano, Masaaki; Yamaguchi, Daizo; Kato, Hideki; Hayashi, Shigenobu; Hara, Michikazu

2010-06-01

SO 3H-bearing amorphous carbon, prepared by partial carbonization of cellulose followed by sulfonation in fuming H 2SO 4, was applied as a solid catalyst for the acid-catalyzed hydrolysis of β-1,4 glucan, including cellobiose and crystalline cellulose. Structural analyses revealed that the resulting carbon material consists of graphene sheets with 1.5 mmol g -1 of SO 3H groups, 0.4 mmol g -1 of COOH, and 5.6 mmol g -1 of phenolic OH groups. The carbon catalyst showed high catalytic activity for the hydrolysis of β-1,4 glycosidic bonds in both cellobiose and crystalline cellulose. Pure crystalline cellulose was not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, Nafion ® NR-50, and Amberlyst-15, whereas the carbon catalyst efficiently hydrolyzes cellulose into water-soluble saccharides. The catalytic performance of the carbon catalyst is due to the large adsorption capacity for hydrophilic reactants and the adsorption ability of β-1,4 glucan, which is not adsorbed to other solid acids.

Removal of emerging pollutants by Ru/TiO2-catalyzed permanganate oxidation.

PubMed

Zhang, Jing; Sun, Bo; Xiong, Xinmei; Gao, Naiyun; Song, Weihua; Du, Erdeng; Guan, Xiaohong; Zhou, Gongming

2014-10-15

TiO2 supported ruthenium nanoparticles, Ru/TiO2 (0.94‰ as Ru), was synthesized to catalyze permanganate oxidation for degrading emerging pollutants (EPs) with diverse organic moieties. The presence of 1.0 g L(-1) Ru/TiO2 increased the second order reaction rate constants of bisphenol A, diclofenac, acetaminophen, sulfamethoxazole, benzotriazole, carbamazepine, butylparaben, diclofenac, ciprofloxacin and aniline at mg L(-1) level (5.0 μM) by permanganate oxidation at pH 7.0 by 0.3-119 times. The second order reaction rate constants of EPs with permanganate or Ru/TiO2-catalyzed permanganate oxidation obtained at EPs concentration of mg L(-1) level (5.0 μM) underestimated those obtained at EPs concentration of μg L(-1) level (0.050 μM). Ru/TiO2-catalyzed permanganate could decompose a mixture of nine EPs at μg L(-1) level efficiently and the second order rate constant for each EP was not decreased due to the competition of other EPs. The toxicity tests revealed that Ru/TiO2-catalyzed permanganate oxidation was effective not only for elimination of EPs but also for detoxification. The removal rates of sulfamethoxazole by Ru/TiO2-catalyzed permanganate oxidation in ten successive cycles remained almost constant in ultrapure water and slightly decreased in Songhua river water since the sixth run, indicating the satisfactory stability of Ru/TiO2. Ru/TiO2-catalyzed permanganate oxidation was selective and could remove selected EPs spiked in real waters more efficiently than chlorination. Therefore, Ru/TiO2-catalyzed permanganate oxidation is promising for removing EPs with electron-rich moieties. Copyright © 2014 Elsevier Ltd. All rights reserved.

Purification and characterization of 9-hexadecenoic acid cis-trans isomerase from pseudomonas sp. strain E-3

PubMed

Okuyama; Ueno; Enari; Morita; Kusano

1998-01-01

A 9-hexadecenoic acid cis-trans isomerase (9-isomerase) that catalyzed the cis-to-trans isomerization of the double bond of free 9-cis-hexadecenoic acid [16:1(9c)] was purified to homogeneity from an extract of Pseudomonas sp. strain E-3 and characterized. Electrophoresis of the purified enzyme on both incompletely denaturing and denaturing polyacrylamide gels yielded a single band of a protein with a molecular mass of 80 kDa, suggesting that the isomerase is a monomeric protein of 80 kDa. The 9-isomerase, assayed with 16:1(9c) as a substrate, had a specific activity of 22.8 &mgr;mol h-1 (mg protein)-1 and a Km of 117.6 mM. The optimal pH and temperature for catalysis were approximately pH 7-8 and 30 degrees C, respectively. The 9-isomerase catalyzed the cis-to-trans conversion of a double bond at positions 9, 10, or 11, but not that of a double bond at position 6 or 7 of cis-mono-unsaturated fatty acids with carbon chain lengths of 14, 15, 16, and 17. Octadecenoic acids with a double bond at position 9 or 11 were not susceptible to isomerization. These results suggest that 9-isomerase has a strict specificity for both the position of the double bond and the chain length of the fatty acid. The enzyme catalyzed the cis-to-trans isomerization of fatty acids in a free form, and in the presence of a membrane fraction it was also able to isomerize 16:1(9c) esterified to phosphatidylethanolamine. The 9-isomerase was strongly inhibited by catecholic antioxidants such as alpha-tocopherol and nordihydroguaiaretic acid, but was not inhibited by 1, 10-phenanthroline or EDTA or under anoxic conditions. Based on these results, the possible mechanism of catalysis by this enzyme is discussed.

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review.

PubMed

He, Jie; Yang, Xiaofang; Men, Bin; Wang, Dongsheng

2016-01-01

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals (OH) from reactions between recyclable solid catalysts and H2O2 at acidic or even circumneutral pH. Hence, it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology. Due to the complex reaction system, the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating, and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies. Iron-based materials usually possess high catalytic activity, low cost, negligible toxicity and easy recovery, and are a superior type of heterogeneous Fenton catalysts. Therefore, this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials. OH, hydroperoxyl radicals/superoxide anions (HO2/O2(-)) and high-valent iron are the three main types of reactive oxygen species (ROS), with different oxidation reactivity and selectivity. Based on the mechanisms of ROS generation, the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron, the heterogeneous catalysis mechanism, and the heterogeneous reaction-induced homogeneous mechanism. Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed. Finally, related future research directions are also suggested. Copyright © 2015. Published by Elsevier B.V.

Iron-catalyzed intermolecular cycloaddition of diazo surrogates with hexahydro-1,3,5-triazines.

PubMed

Liu, Pei; Zhu, Chenghao; Xu, Guangyang; Sun, Jiangtao

2017-09-26

We report here an unprecedented iron-catalyzed cycloaddition reaction of diazo surrogates with hexahydro-1,3,5-triazines, providing five-membered heterocycles in moderate to high yields under mild reaction conditions. This cycloaddition features C-N and C-C bond formation using a cheap iron catalyst. Importantly, different to our former report on a gold-catalyzed system, both donor/donor and donor/acceptor diazo substrates are tolerated in this iron-catalyzed protocol.

Decarboxylation of fatty acids with triruthenium dodecacarbonyl: Influence of the compound structure and analysis of the product mixtures

USDA-ARS?s Scientific Manuscript database

Recently, the decarboxylation of oleic acid (9(Z)-octadecenoic acid) catalyzed by triruthenium dodecacarbonyl, Ru3(CO)12, to give a mixture of heptadecenes with concomitant formation of other hydrocarbons, heptadecane and C17 alkylbenzenes, was reported. The product mixture, consisting of about 77% ...

Using ruthenium sawhorse based decarboxylation to produce industrial materials from oleic acid

USDA-ARS?s Scientific Manuscript database

Ruthenium catalyzed isomerization and decarboxylation of 9-cis-octadecenoic acid are reported as part of the effort to produce valuable industrial materials from biobased sources. Initial studies have demonstrated the efficacy of ruthenium sawhorse materials and further mechanistic studies uncovered...

Ligand- and base-free copper(II)-catalyzed C-N bond formation: cross-coupling reactions of organoboron compounds with aliphatic amines and anilines.

PubMed

Quach, Tan D; Batey, Robert A

2003-11-13

[reaction: see text] A ligandless and base-free Cu-catalyzed protocol for the cross-coupling of arylboronic acids and potassium aryltrifluoroborate salts with primary and secondary aliphatic amines and anilines is described. The process utilizes catalytic copper(II) acetate monohydrate and 4 A molecular sieves in dichloromethane at slightly elevated temperatures under an atmosphere of oxygen. A broad range of functional groups are tolerated on both of the cross-coupling partners.

Efficient water removal in lipase-catalyzed esterifications using a low-boiling-point azeotrope.

PubMed

Yan, Youchun; Bornscheuer, Uwe T; Schmid, Rolf D

2002-04-05

High conversions in lipase-catalyzed syntheses of esters from free acyl donors and an alcohol requires efficient removal of water preferentially at temperatures compatible to enzyme activity. Using a lipase B from Candida antarctica (CAL-B)-mediated synthesis of sugar fatty-acid esters, we show that a mixture of ethyl methylketone (EMK) and hexane (best ratio: 4:1, vo/vo) allows efficient removal of water generated during esterification. Azeotropic distillation of the solvent mixture (composition: 26% EMK, 55% hexane, 19% water) takes place at 59 degrees C, which closely matches the optimum temperature reported for CAL-B. Water is then removed from the azeotrope by membrane vapor permeation. In case of glucose stearate, 93% yield was achieved after 48 h using an equimolar ratio of glucose and stearic acid. CAL-B could be reused for seven reaction cycles, with 86% residual activity after 14 d total reaction time at 59 degrees C. A decrease in fatty-acid chain length as well as increasing temperatures (75 degrees C) resulted in lower conversions. In addition, immobilization of CAL-B on a magnetic polypropylene carrier (EP 100) facilitated separation of the biocatalyst. Copyright 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 31--34, 2002; DOI 10.1002/bit.10084

Titanocene(III)-Catalyzed Three-Component Reaction of Secondary Amides, Aldehydes, and Electrophilic Alkenes.

PubMed

Zheng, Xiao; He, Jiang; Li, Heng-Hui; Wang, Ao; Dai, Xi-Jie; Wang, Ai-E; Huang, Pei-Qiang

2015-11-09

An umpolung Mannich-type reaction of secondary amides, aliphatic aldehydes, and electrophilic alkenes has been disclosed. This reaction features the one-pot formation of C-N and C-C bonds by a titanocene-catalyzed radical coupling of the condensation products, from secondary amides and aldehydes, with electrophilic alkenes. N-substituted γ-amido-acid derivatives and γ-amido ketones can be efficiently prepared by the current method. Extension to the reaction between ketoamides and electrophilic alkenes allows rapid assembly of piperidine skeletons with α-amino quaternary carbon centers. Its synthetic utility has been demonstrated by a facile construction of the tricyclic core of marine alkaloids such as cylindricine C and polycitorol A. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DETOX{sup SM} catalyzed wet oxidation as a highly suitable pretreatment for vitrification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogers, T.W.; Dhooge, P.M.; Goldblatt, S.D.

1995-11-01

A catalyzed wet oxidation process has been developed which uses ferric iron in an acidic water solution to oxidize organic compounds in the presence of platinum ion and/or ruthenium ion catalysts. The process is capable of oxidizing a wide range of organic compounds to carbon dioxide and water with great efficiency. The process has been tested in the bench-scale with many different types of organics. Conceptual engineering for application of the process to treatment of liquid and solid organic waste materials has been followed by engineering design for a demonstration unit. Fabrication of the unit and demonstration on hazardous andmore » mixed wastes at two Department of Energy sites is planned in 1995 through 1997.« less

Glycoproteomics enabled by tagging sialic acid- or galactose-terminated glycans

PubMed Central

Ramya, T N C; Weerapana, Eranthie; Cravatt, Benjamin F; Paulson, James C

2013-01-01

In this paper, we present two complementary strategies for enrichment of glycoproteins on living cells that combine the desirable attributes of “robust enrichment” afforded by covalent-labeling techniques and “specificity for glycoproteins” typically provided by lectin or antibody affinity reagents. Our strategy involves the selective introduction of aldehydes either into sialic acids by periodate oxidation (periodate oxidation and aniline-catalyzed oxime ligation (PAL)) or into terminal galactose and N-acetylgalactosamine residues by galactose oxidase (galactose oxidase and aniline-catalyzed oxime ligation (GAL)), followed by aniline-catalyzed oxime ligation with aminooxy-biotin to biotinylate the glycans of glycoprotein subpopulations with high efficiency and cell viability. As expected, the two methods exhibit reciprocal tagging efficiencies when applied to fully sialylated cells compared with sialic acid-deficient cells. To assess the utility of these labeling methods for glycoproteomics, we enriched the PAL- and GAL-labeled (biotinylated) glycoproteome by adsorption onto immobilized streptavidin. Glycoprotein identities (IDs) and N-glycosylation site information were then obtained by liquid chromatography-tandem mass spectrometry on total tryptic peptides and on peptides subsequently released from N-glycans still bound to the beads using peptide N-glycosidase F. A total of 175 unique N-glycosylation sites were identified, belonging to 108 nonredundant glycoproteins. Of the 108 glycoproteins, 48 were identified by both methods of labeling and the remainder was identified using PAL on sialylated cells (40) or GAL on sialic acid-deficient cells (20). Our results demonstrate that PAL and GAL can be employed as complementary methods of chemical tagging for targeted proteomics of glycoprotein subpopulations and identification of glycosylation sites of proteins on cells with an altered sialylation status. PMID:23070960

Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s

PubMed Central

Tsuji, Hideto; Eto, Takehiko; Sakamoto, Yuzuru

2011-01-01

Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic acid (HA), and DL-2-hydroxydecanoic acid (DA), respectively. The hydrolytic degradation behavior was investigated in phosphate-buffered solution at 80 and 37 °C by gravimetry and gel permeation chromatography. It was found that the reactivity of monomers during polycondensation as monitored by the degree of polymerization (DP) decreased in the following order: LA > DA > BA > HA. The hydrolytic degradation rate traced by DP and weight loss at 80 °C decreased in the following order: PLA > PDA > PHA > PBA and that monitored by DP at 37 °C decreased in the following order: PLA > PDA > PBA > PHA. LA and PLA had the highest reactivity during polymerization and hydrolytic degradation rate, respectively, and were followed by DA and PDA. BA, HA, PBA, and PHA had the lowest reactivity during polymerization and hydrolytic degradation rate. The findings of the present study strongly suggest that inter-chain interactions play a major role in the reactivity of non-substituted and substituted LA monomers and degradation rate of the non-substituted and substituted PLA, along with steric hindrance of the side chains as can be expected. PMID:28824149

Hydrogenation of carboxylic acids with a homogeneous cobalt catalyst.

PubMed

Korstanje, Ties J; van der Vlugt, Jarl Ivar; Elsevier, Cornelis J; de Bruin, Bas

2015-10-16

The reduction of esters and carboxylic acids to alcohols is a highly relevant conversion for the pharmaceutical and fine-chemical industries and for biomass conversion. It is commonly performed using stoichiometric reagents, and the catalytic hydrogenation of the acids previously required precious metals. Here we report the homogeneously catalyzed hydrogenation of carboxylic acids to alcohols using earth-abundant cobalt. This system, which pairs Co(BF4)2·6H2O with a tridentate phosphine ligand, can reduce a wide range of esters and carboxylic acids under relatively mild conditions (100°C, 80 bar H2) and reaches turnover numbers of up to 8000. Copyright © 2015, American Association for the Advancement of Science.

Mechanistic Comparison Between Pd-Catalyzed Ligand Directed C-H Chlorination and C-H Acetoxylation

PubMed Central

Stowers, Kara J.; Sanford, Melanie S.

2009-01-01

This communication describes detailed investigations of the mechanism of the Pd-catalyzed C-H chlorination and acetoxylation of 2-ortho-tolylpyridine. Under the conditions examined, both reactions proceed via rate limiting cyclopalladation. However, substrate and catalyst order as well as Hammett data indicate that the intimate mechanism of cyclopalladation differs significantly between PdCl2-catalyzed chlorination and Pd(OAc)2-catalyzed acetoxylation. PMID:19754074

Production of Fatty Acid Methyl Esters via the In Situ Transesterification of Soybean Oil in Carbon Dioxide-Expanded Methanol

USDA-ARS?s Scientific Manuscript database

The production of fatty acid methyl esters (FAME) by direct alkali- and acid-catalyzed in situ transesterification of soybean flakes in CO2-expanded methanol was examined at various temperatures and pressures. Attempts to synthesize FAME from soy flakes via alkaline catalysis, using sodium methoxid...

Palladium-Catalyzed Reductive Insertion of Alcohols into Aryl Ether Bonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Meng; Gutiérrez, Oliver Y.; Camaioni, Donald M.

Pd/C catalyzes C-O bond cleavage of aryl ethers (diphenyl ether and cyclohexyl phenyl ether) by methanol in H2. The aromatic C-O bond is cleaved by reductive methanolysis, which is initiated by Pd-catalyzed partial hydrogenation of one phenyl ring to form an enol ether. The enol ether reacts rapidly with methanol to form a ketal, which generates methoxycyclohexene by eliminating phenol or an alkanol. Subsequent hydrogenation leads to methoxycyclohexane.

Acid-Functionalized Mesoporous Carbon: An Efficient Support for Ruthenium-Catalyzed γ-Valerolactone Production

DOE PAGES

Villa, Alberto; Schiavoni, Marco; Chan-Thaw, Carine E.; ...

2015-06-18

The hydrogenation of levulinic acid has been studied using Ru supported on ordered mesoporous carbons (OMCs) prepared by soft-templating. P- and S-containing acid groups were introduced by postsynthetic functionalization before the addition of 1% Ru by incipient wetness impregnation. These functionalities and the reaction conditions mediate the activity and selectivity of the levulinic acid hydrogenation. The presence of Scontaining groups (Ru/OMC-S and Ru/OMC-P/S) deactivates the Ru catalysts strongly, whereas the presence of P-containing groups (Ru/OMC-P) enhances the activity compared to that of pristine Ru/OMC. Under mild conditions (70 8C and 7 bar H2) the catalyst shows high selectivity to g-valerolactonemore » (GVL; >95%) and high stability on recycling. However, under more severe conditions (200 8C and pH2=40 bar) Ru/OMC-P is particularly able to promote GVL ring-opening and the consecutive hydrogenation to pentanoic acid.« less

Meteorite-catalyzed syntheses of nucleosides and of other prebiotic compounds from formamide under proton irradiation

PubMed Central

Saladino, Raffaele; Carota, Eleonora; Botta, Giorgia; Kapralov, Mikhail; Timoshenko, Gennady N.; Rozanov, Alexei Y.; Krasavin, Eugene; Di Mauro, Ernesto

2015-01-01

Liquid formamide has been irradiated by high-energy proton beams in the presence of powdered meteorites, and the products of the catalyzed resulting syntheses were analyzed by mass spectrometry. Relative to the controls (no radiation, or no formamide, or no catalyst), an extremely rich, variegate, and prebiotically relevant panel of compounds was observed. The meteorites tested were representative of the four major classes: iron, stony iron, chondrites, and achondrites. The products obtained were amino acids, carboxylic acids, nucleobases, sugars, and, most notably, four nucleosides: cytidine, uridine, adenosine, and thymidine. In accordance with theoretical studies, the detection of HCN oligomers suggests the occurrence of mechanisms based on the generation of radical cyanide species (CN·) for the synthesis of nucleobases. Given that many of the compounds obtained are key components of extant organisms, these observations contribute to outline plausible exogenous high-energy–based prebiotic scenarios and their possible boundary conditions, as discussed. PMID:25870268

Redox Chemistry in Laccase-Catalyzed Oxidation of N-Hydroxy Compounds

PubMed Central

Xu, Feng; Kulys, Juozas J.; Duke, Kyle; Li, Kaichang; Krikstopaitis, Kastis; Deussen, Heinz-Josef W.; Abbate, Eric; Galinyte, Vilija; Schneider, Palle

2000-01-01

1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an “outer-sphere” type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation. PMID:10788380

Identification of an itaconic acid degrading pathway in itaconic acid producing Aspergillus terreus.

PubMed

Chen, Mei; Huang, Xuenian; Zhong, Chengwei; Li, Jianjun; Lu, Xuefeng

2016-09-01

Itaconic acid, one of the most promising and flexible bio-based chemicals, is mainly produced by Aspergillus terreus. Previous studies to improve itaconic acid production in A. terreus through metabolic engineering were mainly focused on its biosynthesis pathway, while the itaconic acid-degrading pathway has largely been ignored. In this study, we used transcriptomic, proteomic, bioinformatic, and in vitro enzymatic analyses to identify three key enzymes, itaconyl-CoA transferase (IctA), itaconyl-CoA hydratase (IchA), and citramalyl-CoA lyase (CclA), that are involved in the catabolic pathway of itaconic acid in A. terreus. In the itaconic acid catabolic pathway in A. terreus, itaconic acid is first converted by IctA into itaconyl-CoA with succinyl-CoA as the CoA donor, and then itaconyl-CoA is hydrated into citramalyl-CoA by IchA. Finally, citramalyl-CoA is cleaved into acetyl-CoA and pyruvate by CclA. Moreover, IctA can also catalyze the reaction between citramalyl-CoA and succinate to generate succinyl-CoA and citramalate. These results, for the first time, identify the three key enzymes, IctA, IchA, and CclA, involved in the itaconic acid degrading pathway in itaconic acid producing A. terreus. The results will facilitate the improvement of itaconic acid production by metabolically engineering the catabolic pathway of itaconic acid in A. terreus.

Catalyzed D-D stellarator reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheffield, John; Spong, Donald A.

The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusionmore » program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, F R = 0.9 to 1.15, ≈ 8.0% to 11.5%, Z eff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, B m ≈ 14 to 16 T, and R ≈ 18 to 24 m.« less

Catalyzed D-D stellarator reactor

DOE PAGES

Sheffield, John; Spong, Donald A.

2016-05-12

The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusionmore » program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, F R = 0.9 to 1.15, ≈ 8.0% to 11.5%, Z eff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, B m ≈ 14 to 16 T, and R ≈ 18 to 24 m.« less

Organometallic catalysts for primary phosphoric acid fuel cells

NASA Technical Reports Server (NTRS)

Walsh, Fraser

1987-01-01

A continuing effort by the U.S. Department of Energy to improve the competitiveness of the phosphoric acid fuel cell by improving cell performance and/or reducing cell cost is discussed. Cathode improvement, both in performance and cost, available through the use of a class of organometallic cathode catalysts, the tetraazaannulenes (TAAs), was investigated. A new mixed catalyst was identified which provides improved cathode performance without the need for the use of a noble metal. This mixed catalyst was tested under load for 1000 hr. in full cell at 160 to 200 C in phosphoric acid H3PO4, and was shown to provide stable performance. The mixed catalyst contains an organometallic to catalyze electroreduction of oxygen to hydrogen peroxide and a metal to catalyze further electroreduction of the hydrogen peroxide to water. Cathodes containing an exemplar mixed catalyst (e.g., Co bisphenyl TAA/Mn) operate at approximately 650 mV vs DHE in 160 C, 85% H3PO4 with oxygen as reactant. In developing this mixed catalyst, a broad spectrum of TAAs were prepared, tested in half-cell and in a rotating ring-disk electrode system. TAAs found to facilitate the production of hydrogen peroxide in electroreduction were shown to be preferred TAAs for use in the mixed catalyst. Manganese (Mn) was identified as a preferred metal because it is capable of catalyzing hydrogen peroxide electroreduction, is lower in cost and is of less strategic importance than platinum, the cathode catalyst normally used in the fuel cell.

Kinetic fractionation of stable nitrogen isotopes during amino acid transamination

NASA Astrophysics Data System (ADS)

Macko, Stephen A.; Estep, Marilyn L. Fogel; Engel, Michael H.; Hare, P. E.

1986-10-01

This study evaluates a kinetic isotope effect involving 15N, during the transamination reactions catalyzed by glutamic oxalacetic transaminase. During the transfer of amino nitrogen from glutamic acid to oxaloacetate to form aspartic acid, 14NH 2 reacted 1.0083 times faster than 14NH 2. In the reverse reaction transferring NH 2 from aspartic acid to α-ketoglutarate, 14NH 2 was incorporated 1.0017 times faster than 15NH 2. Knowledge of the magnitude and sign of these isotope effects will be useful in the interpretation of the distribution of 15N in biological and geochemical systems.

Gas phase hydrolysis of formaldehyde to form methanediol: impact of formic acid catalysis.

PubMed

Hazra, Montu K; Francisco, Joseph S; Sinha, Amitabha

2013-11-21

We find that formic acid (FA) is very effective at facilitating diol formation through its ability to reduce the barrier for the formaldehyde (HCHO) hydrolysis reaction. The rate limiting step in the mechanism involves the isomerization of a prereactive collision complex formed through either the HCHO···H2O + FA and/or HCHO + FA···H2O pathways. The present study finds that the effective barrier height, defined as the difference between the zero-point vibrational energy (ZPE) corrected energy of the transition state (TS) and the HCHO···H2O + FA and HCHO + FA···H2O starting reagents, are respectively only ∼1 and ∼4 kcal/mol. These barriers are substantially lower than the ∼17 kcal/mol barrier associated with the corresponding step in the hydrolysis of HCHO catalyzed by a single water molecule (HCHO + H2O + H2O). The significantly lower barrier heights for the formic acid catalyzed pathway reveal a new important role that organic acids play in the gas phase hydrolysis of atmospheric carbonyl compounds.

Transesterification of oil mixtures catalyzed by microencapsulated cutinase in reversed micelles.

PubMed

Badenes, Sara M; Lemos, Francisco; Cabral, Joaquim M S

2010-03-01

Recombinant cutinase from Fusarium solani pisi was used to catalyze the transesterification reaction between a mixture of triglycerides (oils) and methanol in reversed micelles of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane for the purposes of producing biodiesel. The use of a bi-phase lipase-catalyzed system brings advantages in terms of catalyst re-use and the control of water activity in the medium and around the enzyme micro-environment. Small-scale batch studies were performed to study the influence of the initial enzyme and alcohol concentrations, and the substrates molar ratio. Conversions in excess of 75 were obtained with reaction times under 24 h, which makes this enzymatic process highly competitive when compared to similar lipase catalyzed reactions for biodiesel production using methanol.

Identification, Purification, and Characterization of a Novel Amino Acid Racemase, Isoleucine 2-Epimerase, from Lactobacillus Species

PubMed Central

Mutaguchi, Yuta; Ohmori, Taketo; Wakamatsu, Taisuke; Doi, Katsumi

2013-01-01

Accumulation of d-leucine, d-allo-isoleucine, and d-valine was observed in the growth medium of a lactic acid bacterium, Lactobacillus otakiensis JCM 15040, and the racemase responsible was purified from the cells and identified. The N-terminal amino acid sequence of the purified enzyme was GKLDKASKLI, which is consistent with that of a putative γ-aminobutyrate aminotransferase from Lactobacillus buchneri. The putative γ-aminobutyrate aminotransferase gene from L. buchneri JCM 1115 was expressed in recombinant Escherichia coli and then purified to homogeneity. The enzyme catalyzed the racemization of a broad spectrum of nonpolar amino acids. In particular, it catalyzed at high rates the epimerization of l-isoleucine to d-allo-isoleucine and d-allo-isoleucine to l-isoleucine. In contrast, the enzyme showed no γ-aminobutyrate aminotransferase activity. The relative molecular masses of the subunit and native enzyme were estimated to be about 49 kDa and 200 kDa, respectively, indicating that the enzyme was composed of four subunits of equal molecular masses. The Km and Vmax values of the enzyme for l-isoleucine were 5.00 mM and 153 μmol·min−1·mg−1, respectively, and those for d-allo-isoleucine were 13.2 mM and 286 μmol·min−1·mg−1, respectively. Hydroxylamine and other inhibitors of pyridoxal 5′-phosphate-dependent enzymes completely blocked the enzyme activity, indicating the enzyme requires pyridoxal 5′-phosphate as a coenzyme. This is the first evidence of an amino acid racemase that specifically catalyzes racemization of nonpolar amino acids at the C-2 position. PMID:24039265

Antiproton catalyzed microfission/fusion propulsion

NASA Technical Reports Server (NTRS)

Chiang, Pi-Ren; Lewis, Raymond A.; Smith, Gerald A.; Newton, Richard; Dailey, James; Werthman, W. Lance; Chakrabarti, Suman

1994-01-01

Inertial confinement fusion (ICF) utilizing an antiproton catalyzed hybrid fission/fusion target is discussed as a potential energy source for interplanetary propulsion. A proof-of-principle experiment underway at Phillips Laboratory, Kirtland AFB and antiproton trapping experiments at CERN, Geneva, Switzerland, are presented. The ICAN propulsion concept is described and results of performance analyses are reviewed. Future work to further define the ICAN concept is outlined.

Copper-catalyzed trifluoromethylthiolation of aryl halides with diverse directing groups.

PubMed

Xu, Jiabin; Mu, Xin; Chen, Pinhong; Ye, Jinxing; Liu, Guosheng

2014-08-01

The expansion of cross-coupling components in Cu-catalyzed C-X bond forming reactions have received much attention recently. A novel Cu-catalyzed trifluoromethylthiolation of aryl bromides and iodides with the assistance of versatile directing groups such as pyridyl, methyl ester, amide, imine and oxime was reported. CuBr was used as the catalyst, and 1,10-phenanthroline as the ligand. By changing the solvent from acetonitrile to DMF, the coupling process could even take place at room temperature.

Products and kinetics of the liquid-phase reaction of glyoxal catalyzed by ammonium ions (NH4(+)).

PubMed

Nozière, Barbara; Dziedzic, Pawel; Córdova, Armando

2009-01-08

Glyoxal, a common atmospheric gas, has been reported to be depleted in some regions of the atmosphere. The corresponding sink could be accounted for by reactions in or at the surface of atmospheric particles, but these reactions were not identified. Recently, we showed that inorganic ammonium ions, NH(4)(+), are efficient catalysts for reactions of carbonyl compounds, including glyoxal, in the liquid phase. To determine whether ammonium-catalyzed reactions can contribute to depletion of glyoxal in the atmosphere, the reactivity of this compound in aqueous solutions containing ammonium salts (ammonium sulfate, chloride, fluoride, and phosphate) at 298 K has been studied. The products identified by LC-HRMS and UV absorption revealed a mechanism involving two distinct pathways: a Bronsted acid pathway and an iminium pathway. The kinetics of the iminium pathway was studied by monitoring formation of a specific product. This pathway was second order in glyoxal in most of the solutions studied and should therefore be second order in most ammonium-containing aerosols in the atmosphere. The corresponding rate constant, k(II) (M(-1) s(-1)), increased strongly with ammonium ion activity, a(NH(4)(+)), and pH: k(II) (M(-1) s(-1)) = (2 +/- 1) x 10(-10) exp((1.5 +/- 0.8)aNH(4)(+)) exp((2.5 +/- 0.2)pH). This iminium pathway is a lower limit for the ammonium-catalyzed consumption of glyoxal, but the contribution of the acid pathway is expected to be small in tropospheric aerosols. With these results the reactive uptake of glyoxal on ammonium-containing aerosols was estimated and shown to be a possible explanation for depletion of this compound in Mexico City.

NHC-Catalyzed Asymmetric Benzoin Reaction in Water.

PubMed

Yan, Jun; Sun, Rong; Shi, Kuangxi; Li, Kai; Yang, Limin; Zhong, Guofu

2018-06-11

A chiral NHC-catalyzed benzoin condensation reaction in water was developed, thereby affording α-hydroxy ketones in good to high yields and high enantioselectivities. Water was proposed as a proton shuttle in the aqueous asymmetric condensation reaction.

Ruthenium-Catalyzed Cascade C—H Functionalization of Phenylacetophenones**

PubMed Central

Mehta, Vaibhav P; García-López, José-Antonio; Greaney, Michael F

2014-01-01

Three orthogonal cascade C—H functionalization processes are described, based on ruthenium-catalyzed C—H alkenylation. 1-Indanones, indeno indenes, and indeno furanones were accessed through cascade pathways by using arylacetophenones as substrates under conditions of catalytic [{Ru(p-cymene)Cl2}2] and stoichiometric Cu(OAc)2. Each transformation uses C—H functionalization methods to form C—C bonds sequentially, with the indeno furanone synthesis featuring a C—O bond formation as the terminating step. This work demonstrates the power of ruthenium-catalyzed alkenylation as a platform reaction to develop more complex transformations, with multiple C—H functionalization steps taking place in a single operation to access novel carbocyclic structures. PMID:24453063

Optimization of lipase-catalyzed synthesis of ginsenoside Rb1 esters using response surface methodology.

PubMed

Hu, Jiang-Ning; Lee, Jeung-Hee; Zhu, Xue-Mei; Shin, Jung-Ah; Adhikari, Prakash; Kim, Jae-Kyung; Lee, Ki-Teak

2008-11-26

In the lipase (Novozyme 435)-catalyzed synthesis of ginsenoside Rb1 esters, different acyl donors were found to affect not only the degree of conversion but also the regioselectivity. The reaction of acyl donors with short carbon chain was more effective, showing higher conversion than those with long carbon chain. Among the three solvent systems, the reaction in tert-amyl alcohol showed the highest conversion rate, while the reaction in the mixed solvent of t-BuOH and pyridine (1:1) had the lowest conversion rate. To allow the increase of GRb1 lipophilicity, we decided to further study the optimal condition of synthesis of GRb1 with vinyl decanoate with 10 carbon chain fatty acids in tert-amyl alcohol. Response surface methodology (RSM) was employed to optimize the synthesis condition. From the ridge analysis with maximum responses, the maximum GRb1 conversion was predicted to be 61.51% in a combination of factors (40.2 h, 52.95 degrees C, substrate mole ratio 275.57, and enzyme amount 39.81 mg/mL). Further, the adequacy of the predicted model was examined by additional independent experiments at the predicted maximum synthesis conditions. Results showed that the RSM was effective to optimize a combination of factors for lipase-catalyzed synthesis of ginsenoside Rb1 with vinyl decanoate.

Polymerization of euphorbia oil with Lewis acid in carbon dioxide media

USDA-ARS?s Scientific Manuscript database

Boron trifluoride diethyl etherate (BF3-OEt2) Lewis acid catalyzed ring-opening polymerization of euphorbia oil (EO), a natural epoxy oil, in liquid carbon dioxide was conducted in an effort to develop useful vegetable oil based polymers. The resulting polymers (RPEO) were characterized by FTIR, 1H-...

Cytochrome P450 family member CYP704B2 catalyzes the {omega}-hydroxylation of fatty acids and is required for anther cutin biosynthesis and pollen exine formation in rice.

PubMed

Li, Hui; Pinot, Franck; Sauveplane, Vincent; Werck-Reichhart, Danièle; Diehl, Patrik; Schreiber, Lukas; Franke, Rochus; Zhang, Ping; Chen, Liang; Gao, Yawei; Liang, Wanqi; Zhang, Dabing

2010-01-01

The anther cuticle and microspore exine act as protective barriers for the male gametophyte and pollen grain, but relatively little is known about the mechanisms underlying the biosynthesis of the monomers of which they are composed. We report here the isolation and characterization of a rice (Oryza sativa) male sterile mutant, cyp704B2, which exhibits a swollen sporophytic tapetal layer, aborted pollen grains without detectable exine, and undeveloped anther cuticle. In addition, chemical composition analysis indicated that cutin monomers were hardly detectable in the cyp704B2 anthers. These defects are caused by a mutation in a cytochrome P450 family gene, CYP704B2. The CYP704B2 transcript is specifically detected in the tapetum and the microspore from stage 8 of anther development to stage 10. Heterologous expression of CYP704B2 in yeast demonstrated that CYP704B2 catalyzes the production of omega -hydroxylated fatty acids with 16 and 18 carbon chains. Our results provide insights into the biosynthesis of the two biopolymers sporopollenin and cutin. Specifically, our study indicates that the omega -hydroxylation pathway of fatty acids relying on this ancient CYP704B family, conserved from moss to angiosperms, is essential for the formation of both cuticle and exine during plant male reproductive and spore development.

Study of Silicidation Process of Tungsten Catalyzer during Silicon Film Deposition in Catalytic Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Honda, Kazuhiro; Ohdaira, Keisuke; Matsumura, Hideki

2008-05-01

In catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD, source gases are decomposed by catalytic cracking reactions with heated catalyzing metal wires. In the case of silicon (Si) film deposition, such metal wires are often converted to silicide, which shortens the lifetime of catalyzing wires. As a catalyzer, tungsten (W) is widely used. Thus, the process of silicidation of a W catalyzer at temperatures over 1650 °C, which is the temperature used in Cat-CVD for Si film deposition, was studied extensively in various experiments. It is found that two phases of tungsten-silicide, WSi2 and W5Si3, are formed at this temperature, and that the radiation emissivity of WSi2 is 1.2 to 1.7 times higher than that of W5Si3 and pure W. The increase of surface emissivity due to the formation of WSi2 decreases the catalyzer surface temperature which induces further growth of the tungsten-silicide layer. It is also found that the suppression of WSi2 formation by elevating catalyzer temperatures over 1750 °C is a key to extending the lifetime of the W catalyzer in Cat-CVD.

Kinetic Behavior of Exchange-Driven Growth with Catalyzed-Birth Processes

NASA Astrophysics Data System (ADS)

Wang, Hai-Feng; Lin, Zhen-Quan; Kong, Xiang-Mu

2006-12-01

Two catalyzed-birth models of n-species (n>=2) aggregates with exchange-driven growth processes are proposed and compared. In the first one, the exchange reaction occurs between any two aggregates Amk and Amj of the same species with the rate kernels Km(k,j) = Kmkj (m = 1,2,...,n, n>=2), and aggregates of An species catalyze a monomer-birth of Al species (l = 1,2,...,n-1) with the catalysis rate kernel Jl(k,j) = Jlkjυ. The kinetic behaviors are investigated by means of the mean-field theory. We find that the evolution behavior of aggregate-size distribution alk(t) of Al species depends crucially on the value of the catalysis rate parameter υ: (i) alk(t) obeys the conventional scaling law in the case of υ<=0, (ii) alk(t) satisfies a modified scaling form in the case of υ>0. In the second model, the mechanism of monomer-birth of An-species catalyzed by Al species is added on the basis of the first model, that is, the aggregates of Al and An species catalyze each other to cause monomer-birth. The kinetic behaviors of Al and An species are found to fall into two categories for the different υ: (i) growth obeying conventional scaling form with υ<=0, (ii) gelling at finite time with υ>0.

Stereospecific Synthesis of threo- and erythro-β-Hydroxyglutamic Acid During Kutzneride Biosynthesis

PubMed Central

Strieker, Matthias; Nolan, Elizabeth M.; Walsh, Christopher T.; Marahiel, Mohamed A.

2009-01-01

The antifungal and antimicrobial kutznerides, hexadepsipeptides comprised of one α-hydroxy acid and five non-proteinogenic amino acids, are remarkable examples of the structural diversity found in nonribosomally-produced natural products. They contain D-3-hydroxyglutamic acid, which is found in the threo and erythro isomers in mature kutznerides. In this study, two putative non-heme iron oxygenase enzymes, KtzO and KtzP, were recombinantly expressed, characterized biochemically in vitro, and found to stereospecifically hydroxylate the β-position of glutamic acid. KtzO generates threo-L-hydroxyglutamic acid and KtzP catalyzes the formation of the erythro-isomer bound to the peptidyl carrier protein of the third module of the nonribosomal peptide synthetase KtzH. This module has a truncated adenylation domain and is unable to activate and incorporate glutamic acid. The lack of a functional adenylation domain in the third KtzH module is compensated in trans by the stand-alone adenylation domain KtzN, which activates and transfers glutamic acid onto the carrier of KtzH in the presence of the truncated adenylation domain and either KtzO or KtzP. A method that employs non-hydrolyzable coenzyme A analogs was developed and used to determine the kinetic parameters for KtzO- and KtzP-catalyzed hydroxylation of glutamic acid bound to the carrier protein. A detailed mechanism for the in trans compensation of the truncated adenylation domain and the stereospecific hydroxyglutamic acid generation and incorporation is presented. These insights may guide the use of KtzO/KtzP and KtzN or other in trans modification/restoration tools in biocombinatorial engineering approaches. PMID:19722489

Electrophoresis-chemiluminescence detection of phenols catalyzed by hemin.

PubMed

Shu, Lu; Zhu, Jinkun; Wang, Qingjiang; He, Pingang; Fang, Yuzhi

2014-09-01

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis-chemiluminescence (CE-CL) detection method for phenols using a hemin-luminol-hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br(-) and F(-) could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE-CL detection system because of the self-polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin-luminol afforded a stable CE-CL baseline. The indirect CE-CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10(-8) mol/L (o-sec-butylphenol), 4.9 × 10(-8) mol/L (o-cresol), 5.4 × 10(-8) mol/L (m-cresol), 5.3 × 10(-8) mol/L (2,4-dichlorophenol) and 7.1 × 10(-8) mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.

Nickel-catalyzed amination of aryl chlorides with ammonia or ammonium salts.

PubMed

Green, Rebecca A; Hartwig, John F

2015-03-16

The nickel-catalyzed amination of aryl chlorides to form primary arylamines occurs with ammonia or ammonium sulfate and a well-defined single-component nickel(0) precatalyst containing a Josiphos ligand and an η(2)-bound benzonitrile ligand. This system also catalyzes the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling and optimization of phospholipase A₁-catalyzed hydrolysis of phosphatidylcholine using response surface methodology for lysophosphatidylcholine production.

PubMed

Lim, Chang Wan; Kim, Byung Hee; Kim, In-Hwan; Lee, Moon-Won

2015-01-01

Modeling the phospholipase A1 (PLA1 )-catalyzed partial hydrolysis of soy phosphatidylcholine (PC) in hexane for the production of lysophosphatidylcholine (LPC) and optimizing the reaction conditions using response surface methodology were described. The reaction was performed with 4 g of PC in a stirred batch reactor using a commercial PLA1 (Lecitase Ultra) as the biocatalyst. The effects of temperature, reaction time, water content, and enzyme loading on LPC and glycerylphosphorylcholine (GPC) content in the reaction products were elucidated using the models established. Optimal reaction conditions for maximizing the LPC content while suppressing acyl migration, which causes GPC formation, were as follows: temperature, 60°C; reaction time, 3 h; water content, 10% of PC; and enzyme loading, 1% of PC. When the reaction was conducted with 40 g of PC under these conditions, the reaction products contained 83.7 mol % LPC and were free of GPC. LPC had a higher total unsaturated fatty acid content than original PC had and was mainly composed of linoleic acid (78.0 mol % of the total fatty acids). © 2014 American Institute of Chemical Engineers.

Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.

ERIC Educational Resources Information Center

Polichnowski, S. W.

1986-01-01

Presents a study of the rhodium-catalyzed, ioding-promoted carbonylation of methyl acetate. This study provides an interesting contrast between the carbonylation of methyl acetate and the carbonylation of methanol when similar rhodium/iodine catalyst systems are used. (JN)