Various Combinations Of Substrates Research Articles

Asymmetric Syn-Selective Vinylogous Addition of Butenolides to Chromones via Al-Li-BINOL Catalysis

A gram-scale syn-selective asymmetric vinylogous addition of butenolides to chromones, catalyzed by an Al-Li-BINOL (ALB) complex, was developed in this study. For various combinations of substrates, the observed diastereoselectivity approached 20:1 with 84-98% ee. This protocol is complementary to previously reported ones and improves the selectivity for several chromones. This methodology can be applied to a quinolone substrate, affording another type of heterocyclic scaffolds substituted with five-membered lactones. Computational studies support the role of ALB as a bifunctional catalyst in this reaction and provide insights into the origin of the observed stereoselectivity.

Particle-Reinforced Ceramic Matrix Composites—Selected Examples

This paper presents some examples of ceramic matrix composites (CMCs) reinforced with metal or intermetallic phases fabricated by powder consolidation without a liquid phase (melted metal). Composites with a complex structure, which are an advanced group of CMCs called hybrid composites, were described in contrast to conventional composites with a ceramic matrix. In advanced CMCs, their complex structures make it possible to achieve the synergistic effect of the micro- and nanoparticles of the metallic, intermetallic, and ceramic phases on the composite properties, which is not possible in conventional materials. Various combinations of substrates in the form of powder as more than one metal and ceramics with different powder sizes that are used to form hybrid composites were analyzed. The types of CMC microstructures, together with their geometrical schemas and some examples of real ceramic matrix composites, were described. The schemas of composite microstructures showed the possible location of the ceramic, metallic, or intermetallic phases in composites. A new concept of an advanced ceramic–intermetallic composite fabricated by the consolidation of pre-composite powder mixed with ceramic powder was also presented. This concept is based on the selection of substrates, two metals in the form of powder, which will form a new compound, intermetallic material, during processing. Metal powders were milled with ceramic powders to obtain a pre-composite powder consisting of intermetallic material and ceramics. In the next step, the consolidation of pre-composite powder with ceramic powder allows the creation of composites with complex microstructures. Selected examples of real particle-reinforced conventional and hybrid microstructures based on our own investigations were presented. In addition to microstructures, the properties and possible applications of CMCs were analyzed.

Organocatalytic Synthesis and Antitumor Activity of Novel 1,2,3-triazoles Derived from Fatty β-ketoesters.

Developing methods to synthesize highly functionalized and complex 1,2,3- triazoles from various combinations of substrates remains a significant challenge in organic synthesis. Thus, to the best of our knowledge, an organocatalytic approach to synthesize 1,2,3-triazoles derived from fatty acids has not been explored. In this sense, we describe here the organocatalyzed synthesis and preliminary results of antitumor and cytotoxic activity of a range of 1,2,3-triazoles derived from fatty esters. To synthesize 1,2,3-triazoles 3 derived from fatty β-ketoesters, we performed the reaction of appropriate aryl azides 2a-j with β -ketoesters 1a-c in the presence of 5 mol% of DBU using DMSO as a solvent at 70 °C for 24 h. The viability of 5637 cells was determined by measuring the reduction of soluble MTT to water-insoluble formazan. The IC50 concentration that inhibits 50% of cell growth and the results were obtained by at least three independent experiments in triplicate for each test. Through enolate-mediated organocatalysis, 1,2,3-triazoles 3 derived from fatty β-ketoesters were synthesized in moderate to excellent yields by reacting fatty esters 1 with aryl azides 2 in the presence of a catalytic amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (5 mol%). All compounds derived from palmitic acetoacetate 1a were evaluated regarding induced cytotoxicity in vitro in a human bladder cancer cell line, and compounds 3a, 3d, 3e, and 3g were shown to be promising alternatives for bladder cancer treatment and presented the lowest inhibitory concentration of IC50. We described a synthetic procedure to prepare 1,2,3-triazoles derived from fatty β - ketoesters by DBU-catalyzed 1,3-dipolar cycloaddition reactions of fatty esters with different aryl azides. Compounds derived from palmitic acetoacetate were screened for antitumor and cytotoxic activity in vitro in human bladder cancer cell lines, and compounds 3a, 3d, 3e, and 3g showed potential to treat bladder cancer.

Effect of different microbial seeds on batch anaerobic digestion of fish waste

Initial microbial compositions would be the precursor for the efficient anaerobic digestion (AD) of fish waste (FW). A mesophilic batch test was conducted using four seeds collected from different digesters treating various combinations of substrates to investigate their effects on FW degradation. Key microbial groups were identified by 16s rRNA gene-based metagenomics analysis. Among four, the seed from the digester co-digesting livestock manure, food waste, and food wastewater showed the best performance and obtained the highest methane yield (350.5 ± 5.2 mL/gVSadded) and lowest lag phase (0.6 ± 0.1 d). Proteiniphilum, Aminobacterium, dgA-11 gut group, and Syntrophomonas were dominant bacterial genera identified in FW degradation. Methanosaeta was the dominant methanogen in the best performing seed and microbial network analysis revealed its contribution to achieving the highest CH4 yield. Obtained results could be useful in selecting microbial seed sources to avoid system imbalance in full-scale digesters that treat FW.

Quantitative analysis of the interaction of ethanol metabolism with gluconeogenesis and fatty acid oxidation in the perfused liver of fasted rats

Ethanol is known to significantly affect gluconeogenesis and lipid metabolism in the liver, primarily by altering the redox ratio in both cytosol and mitochondria. The effect of ethanol was analyzed using a comprehensive, dynamic model of liver metabolism that takes into account sub-cellular compartmentation, detailed kinetics for the citric acid cycle, ethanol and acetaldehyde oxidation, and gluconeogenesis, and inter-compartmental transport of metabolites, including the malate-aspartate shuttle. The kinetic expression for alcohol dehydrogenase takes into account inhibition by ethanol and NADH. Simulations of perfusions of the rat liver were performed with various combinations of substrates (lactate, pyruvate, and fatty acids), with subsequent addition of ethanol to the perfusate. The model successfully predicts NADH/NAD+, in both cytosol and mitochondria, the expected directional flux of reducing equivalents between the two compartments during perfusion with different gluconeogenic precursors, and the effect of ethanol on glucose and ketone body production. This model can serve as a platform for in silico experiments investigating the effects of ethanol on the many dehydrogenases, and thus the major carbohydrate and lipid metabolic pathways in the liver, as well as potential effects of various drugs that may interact with ethanol.

ChemInform Abstract: Acid‐Catalyzed Direct Conjugate Alkenylation of α,β‐Unsaturated Ketones.

AbstractTreatment of the product (IIIa) with HBF4 gives the compound (IV) via 1,4‐phenyl shift.

Acid‐Catalyzed Direct Conjugate Alkenylation of α,β‐Unsaturated Ketones

New tricks, old reaction: The title reaction proceeds under mild and transition-metal-free conditions (see scheme; Tf=trifluoromethanesulfonyl). Various combinations of substrates are applicable to the synthesis of γ,δ-unsaturated ketones by employing silicon substituents at the β-position of the enones. The silicon substituents play a key role in stabilization of the cationic intermediate by hyperconjugation.

Microbial fuel cell: technology for harvesting energy from biomass

Microbial fuel cells (MFCs) are an emerging technology that has gained considerable attention in the recent years because they provide new opportunities for sustainable production of energy from a wide range of soluble complex organic wastes and renewable biomass. The driving force for research in this field has been the apprehension over the energy climate crisis and environment pollution. MFCs are bioreactors that can convert the chemical energy present in organic compounds into electrical energy. Presently, the literature shows that current and power yields are relatively low, but improvements in the technology can enhance these parameters as well as the efficiency of these cells. Sediment MFCs in powering low-powered electronic monitoring devices is one of the practical uses of MFCs. Additionally, MFCs can be used in implantable medical devices and wastewater treatment plants. This review discusses the factors governing the performance of these cells and the maximum power density that can be obtained using various combinations of substrates and microorganisms.

Highly modular P-OP ligands in asymmetric allylic substitution

A library of highly modular P-OP ligands have been evaluated in Pd-catalysed allylic substitutions with C- and N-nucleophiles. Catalyst optimisation via a variation of the phosphino and phosphite substituents led to a ‘lead’ catalyst, which efficiently mediated the allylic substitutions when various combinations of substrates and nucleophiles were tested. Ground-state calculations were carried out and these allowed a clearer understanding of the stereochemical outcome of the reaction.

1,3-Dipolar Cycloaddition of Organic Azides to Alkynes by a Dicopper-Substituted Silicotungstate

The dicopper-substituted gamma-Keggin silicotungstate TBA 4[gamma-H2SiW10O36Cu2(mu-1,1-N3)2] (I, TBA = tetra- n-butylammonium) could act as an efficient precatalyst for the regioselective 1,3-dipolar cycloaddition of organic azides to alkynes. Various combinations of substrates (four azides and eight alkynes) were efficiently converted to the corresponding 1,2,3-triazole derivatives in excellent yields without any additives. The present system was applicable to a larger-scale cycloaddition of benzyl azide to phenylacetylene under solvent-free conditions (100 mmol scale) in which 21.5 g of the analytically pure corresponding triazole could be isolated. In this case, the turnover frequency and the turnover number reached up to 14,800 h(-1) and 91,500, respectively, and these values were the highest among those reported for the copper-mediated systems so far. In addition, I could be applied to the one-pot synthesis of 1-benzyl-4-phenyl-1H-1,2,3-triazole from benzyl chloride, sodium azide, and phenylacetylene. The catalyst effect, kinetic, mechanistic, and computational studies show that the reduced dicopper core plays an important role in the present 1,3-dipolar cycloaddition.

Ruthenium-Catalyzed Addition of Terminal Alkynes to Alkynylstannanes with Migration of the Stannyl Group

Abstract In the presence of a catalytic amount of a ruthenium complex coordinated with PBu3, alkynylstannanes (R1C≡CSnBu3) were found to accept the addition of terminal alkynes (R2C≡CH) with a 1,2-shift of the stannyl group to give (E)- and (Z)-1-tributylstannylbut-1-en-3-ynes (Bu3SnC(R1)=CHC≡CR2). Various combinations of substrates having an aromatic and/or aliphatic substituent can be used, and the stereochemical outcome depends largely on the character of these substituents. The reaction of aliphatic terminal alkynes proceeds stereoselectively, and substituent R1 on the alkynylstannanes determines the configuration: E for R1 = alkyl and Z for R1 = aryl. In contrast, the reaction of arylacetylenes gave a mixture of stereoisomers irrespective of the character of substituent R1 on the alkynylstannane. Ruthenium–β-stannylvinylidene complexes generated from a ruthenium complex and an alkynylstannane with migration of the stannyl group are likely to be key intermediates, which accept addition of the C–H bond of terminal alkynes to give the corresponding stannylenynes. DFT calculation clearly shows that the 1,2-shift of the stannyl group on formation of ruthenium–β-stannylvinylidene complexes is more facile than the corresponding 1,2-hydrogen shift of the coordinating terminal alkynes. The effect of the substituents on the stereoselectivity also is discussed based on the calculation.

On the Performance of Thin Hard Coatings for Gearing Applications

Thin hard coatings are possible candidates for the enhancement of scuffing and micro-pitting performance of gears. They exhibit very high levels of surface hardness (typically 1000 HV) combined with a low traction coefficient (typically 0.2) against dry steel. The paper presents the results of an experimental program carried out in order to assess the scuffing performance of thin hard coatings for various combinations of substrates and surface finish under realistic engineering conditions of sliding speed, oil temperature and contact pressure. Two types of coating were assessed: diamond like carbon (DLC) coatings and boron carbide coatings. Although the overall performance improvement is promising, caution may be required when using thin hard coatings with case carburised substrates where adhesion problems may occur. Their use with nitrided steel as a substrate seems to be particularly advantageous, possibly because a higher process temperature may be used. The coatings tested also gave better performance at relatively low sliding speeds (≤ 16 m/s). At higher levels of sliding the predominant effect is one of lubrication failure, the material parameter becoming secondary.

Inactivation of 1-aminocyclopropane-1-carboxylate oxidase involves oxidative modifications.

1-Aminocyclopropane-1-carboxylate (ACC) oxidase catalyzes the final step in the biosynthesis of the plant signaling molecule ethylene. It is a member of the ferrous iron dependent family of oxidases and dioxygenases and is unusual in that it displays a very short half-life under catalytic conditions, typically less than 20 min, and a requirement for CO2 as an activator. The rates of inactivation of purified, recombinant ACC oxidase from tomato under various combinations of substrates and cofactors were measured. Inactivation was relatively slow in the presence of buffer alone (t1/2 > 1 h), but fast in the presence of ferrous iron and ascorbate (t1/2 approximately 10 min). The rate of iron/ascorbate-mediated inactivation was increased by the addition of ACC, unaffected by the addition of CO2 at saturation (supplied as bicarbonate) but decreased by the addition of catalase or ACC + CO2 at saturation (supplied as bicarbonate). Iron/ascorbate-mediated inactivation was accompanied by partial proteolysis as observed by SDS-PAGE analysis. The fragmentation pattern was altered when ACC was also included, suggesting that ACC can bind to ACC oxidase in the absence of bicarbonate. N-terminal sequencing of fragments resulted in identification of an internal cleavage site which we propose is proximate to active-site bound iron. Thus, ACC oxidase inactivates via relatively slow partial unfolding of the catalytically active conformation, oxidative damage mediated via hydrogen peroxide which is catalase protectable and oxidative damage to the active site which results in partial proteolysis and is not catalase protectable.

Identification of Amino Acid Residues Modified by Pyridoxal 5′-Phosphate in Escherichia coli Glutamine Synthetase

Chemical modification studies with pyridoxal 5'-phosphate have indicated that lysine(s) appear to be at or near the active site of Escherichia coli glutamine synthetase (Colanduoni, J., and Villafranca, J. J. (1985) J. Biol. Chem. 260, 15042-15050; Whitley, E. J., Jr., and Ginsburg, A. (1978) J. Biol. Chem. 253, 7017-7025). Enzyme samples were prepared that contained approximately 1, approximately 2, and approximately 3 pyridoxamine 5'-phosphate residues/50,000-Da monomer; the activity of each sample was 100, 25, and 14% of the activity of unmodified enzyme, respectively. Cyanogen bromide cleavage of each enzyme sample was performed, the peptides were separated by high performance liquid chromatography, and the peptides containing pyridoxamine 5'-phosphate were identified by their absorbance at 320 nm. These isolated peptides were analyzed for amino acid composition and sequenced. The N terminus of the protein (a serine residue) was modified by pyridoxal 5'-phosphate at a stoichiometry of approximately 1/50,000 Da and this modified enzyme had full catalytic activity. Beyond a stoichiometry of approximately 1, lysines 383 and 352 reacted with pyridoxal 5'-phosphate and each modification results in a partial loss of activity. When various combinations of substrates and substrate analogs (ADP/Pi or L-methionine-SR-sulfoximine phosphate/ADP) were used to protect the enzyme from modification, Lys-352 was protected from modification indicating that this residue is at the active site. Under all experimental conditions employed, Lys-47, which reacts with the ATP analog 5'-p-fluorosulfonylbenzoyl-adenosine does not react with pyridoxal 5'-phosphate.

Multiple requirements for glycogen synthesis by hepatocytes isolated from fasted rats.

Glycogen synthesis from various combinations of substrates by hepatocytes isolated from rats fasted 24 h was studied. As reported by Katz et al. (Katz, J., Golden, S., and Wals, P. A. (1976) Proc. Natl. Acad. Sci. U. S. A. 73, 3433-3437), appreciable rates of glycogen synthesis occurred only in the presence of gluconeogenic precursors and one of several amino acids, which includes L-glutamine. L-Leucine had negligible effects on glycogen synthesis from 20 mM dihydroxyacetone and/or 15 mM glucose when L-glutamine was not added to the medium. In the presence of 10 mM L-glutamine, L-leucine greatly increased glycogen synthesis from these substrates. alpha-Ketoisocaproate was ineffective, as was oleate. NH4Cl depressed glycogen synthesis from 10 mM glucose plus 20 mM dihydroxyacetone in the absence of added L-glutamine and enhanced that in its presence, but these effects were weak compared to those of L-leucine. The amino acid analogues L-norvaline and L-norleucine exerted effects that were similar to those exerted by L-leucine. Under all conditions studied, cycloheximide and puromycin inhibited net glycogen synthesis. Cycloheximide did not stimulate gluconeogenesis from dihydroxyacetone, or phosphorylase in hepatocytes from starved rats, or glycogenolysis in hepatocytes from fed rats. Puromycin, however, stimulated glycogenolysis in hepatocytes from fed rats. Glycogen synthesis from 20 mM dihydroxyacetone proceeds with a pronounced initial lag phase that can be shortened by incubation of cells with glutamine plus leucine before addition of dihydroxyacetone. Concurrent measurements of glycogen synthesis, glycogen synthase, and gluconeogenesis under different conditions reveal that in addition to protein synthesis, activation of glycogen synthase, which must occur to allow glycogen synthesis in hepatocytes, requires a second component which can be satisfied by addition of dihydroxyacetone or fructose to the cells.

Cyanide and methylisocyanide: Probes for nitrogenase reactivity

Nitrogenase (N 2ase) is composed of two separately purified proteins, the molybdenum-iron (MoFe) protein and the iron (Fe) protein. Nitrogen fixation requires both proteins, a reductant, protons and MgATP. The Fe protein is generally accepted as a specific one-electron donor for the MoFe protein, which is believed to contain the substrate-reduction site. Besides, N 2, N 2ase catalyzes the reduction of protons and a number of alternative substrates [ e.g. 1], including the two six-electron substrates, cyanide and methylisocyanide, we have recently studied. The rate-limiting step for N 2ase turnover occurs prior to substrate reduction. Thus, total electron flow through the enzyme should be essentially independent of the substrate being reduced. Although this appears true N 2 fixation, H 2 evolution and C 2H 2 reduction [2], both CN − [3] and CH 3NC dramatically inhibit the rate of total electron flow through N 2ase. Inhibition by both substrates is completely reversed by CO. Not only do CN− and CH 3NC inhibit nitrogenase turnover, they also reduce the enzyme's efficiency by increasing the amount of MgATP hydrolyzed for each electron pair used to reduce substrate. These data are interpreted in terms of CN− or CH 3NC binding to the MoFE protein in such a way as to prevent electron transfer to substrate. With nowhere to go, the electrons fall back to the Fe protein to complete a futile cycle. Are the substrates N 2, HCN and CH 3NC reduced in one six-electron step or via a series of lesser reduced intermediates? Previously, we proposed that N 2 is reduced to ammonia via the two-electron intermediates N 2H 2 and N 2H 4 [4]. For the six-electron reductions of HCN to CH 4 + NH 3 and CH 3NC to CH 4 + CH 3NH 2, we have definitely identified the four-electron products, CH 3NH 2 (for HCN) and CH 3NHCH 3 (for CH 3NC), and suggest them as intermediates. The formation of two-electron reduced intermediates for both HCN and CH 3NC is suggested by the product ratio of NH 3-to-CH 4 (for HCN) and CH 3NHCH 2-to-CH 4 (for CH 3NC) being greater than one. The data support mechanisms whereby the six-electron reduction of N 2, HCN and CH 3NC occur via a series of analogous two- and four-electron reduced intermediates. Thus, a common phenomenon is likely as an intimate part of the mechanisms of N 2, HCN and CH 3NC reduction. Although H 2 evolution is suggested as an obligatory part of the N 2-fixation mechanism, it is not required for either HCN or CH 3NC reduction. This apparent anomaly might be explained if N 2, HCN or CH 3NC were either reduced at different sites or bound and reduced by different redox states of the MoFe protein. So, as increasing the ratio of Fe protein-to-MoFe protein increases electron flow, component protein ratio titration experiments in the presence of N 2,HCN and CH 3NC were used. They indicate that HCN and CH 3NC bind to and are reduced at a redox state of the MoFe protein more oxidized than that responsible for either N 2 fixation or H 2 evolution. Do all substrates and inhibitors of nitrogenase bind to the same site on nitrogenase? Experiments with various combinations of substrates (N 2, HCN, CH 3NC, C 2H 2, N 2O, N − 3 and inhibitors (H 2, CO, CN −, CH 3NC) indicate that either C 2H 2 or N 2O stimulate HCN reduction and influence its product distribution, implying simultaneous binding and at least two interaction sites on N 2ase. CH 3NC appears to act as both substrate and inhibitor on binding to the same N 2ase site, implying productive and non-productive modes of binding.

Cysteine in the manganous-isocitrate binding site of pig heart TPN-specific isocitrate dehydrogenase: II. Identification of a critical cysteine-containing tryptic peptide derived from the thiocyano enzyme

The pig heart TPN-speciftc isocitrate dehydrogenase was reacted successively with 5,5′-dithiobis(2-nitrobenzoic acid) and K 14CN in the presence of various combinations of substrates and/or inhibitors to produce thiocyano derivatives of the reactive cysteine residues. The thiocyano-enzyme preparations, after cyclization and cleavage to yield iminothiazolidine derivatives, were digested with trypsin and the resultant tryptic digests were fractionated by two-dimensional paper chromatography and high-voltage electrophoresis. The 14C-labeled peptides were located by a two-dimensional radioscanner. The distribution of radioactivity in the tryptic digests of inactive enzyme, obtained by reaction with 5,5′-dithiobis(2-nitrobenzoate) and K 14CN in the absence of ligands, was compared with that of enzyme obtained by reaction in the presence of ligands such as Mn 2+ and isocitrate or Ca 2+ and isocitrate which protect against inactivation. The results suggest that modification of one cysteine-containing peptide, termed Peptide 2, leads to inactivation. Peptide 2 has been purified and its amino acid composition determined. Evidence from this and the preceding paper indicates that this peptide participates in the metal-isocitrate binding site. The amino acid composition of the intact pig heart TPN-specific isocitrate dehydrogenase is also presented.

Inactivation of human gamma-glutamylcysteine synthetase by cystamine. Demonstration and quantification of enzyme-ligand complexes.

Human erythrocyte gamma-glutamylcysteine synthetase is inactivated by the disulfide cystamine (2,2'-dithiobis-(ethylamine)) at pH 8.2 with a rate constant of 1020 min-1 mM-1. Magnesium ion and various combinations of substrates and products confer differing degrees of protection against cystamine inactivation, thus allowing the detection and quantification of certain enzyme-ligand interactions. By measuring inactivation rates as a function of ligand concentrations in incomplete reaction mixtures, we have obtained evidence for the following complexes: enzyme . Mg2+; enzyme . Mg2+ . MgATP2-; enzyme . Mg2+ . L-glutamate; enzyme . Mg2+ . MgATP2- . L-glutamate; enzyme . Mg2+ . L-gamma-glutamyl-L-alpha-aminobutyrate. The data also imply the existence of enzyme . (Mg2+)2 . MgATP2- . L-glutamate and several enzyme forms resulting from the weak binding to L-alpha-aminobutyrate. The methods used permit the calculation of cystamine inactivation rates for most of these enzyme forms and also give values for the equilibrium constants describing their formation.

The Interaction of Phosphoglucomutase with Nucleotide Inhibitors

Phosphoglucomutases from rabbit muscle and Escherichia coli are inhibited by several nucleotides, the more potent of which are GDP, GTP, dTDP, Coenzyme A, and several CoA derivatives. Phosphoglucomutase from E. coli is somewhat more sensitive to the inhibitors than is the rabbit muscle enzyme. All of the inhibitors are noncompetitive with glucose 1,6-diphosphate and almost uncompetitive with glucose 1-phosphate as the varied substrates. Measurements of the relaxation rate of the solvent water protons in the presence of manganese complex of phosphoglucomutase from rabbit muscle and various combinations of substrates and inhibitors confirm observations in the literature that the relaxation enhancement due to the manganese-enzyme complex is greatly decreased when saturating amounts of glucose 1-phosphate and glucose 6-phosphate are added. When either ATP or acetyl-CoA is also present with the substrates, the decrease in relaxation enhancement is not as marked as in the presence of substrates alone. It is concluded from these studies and from titrations of the enzyme-manganese-substrate complexes with acetyl-CoA or GTP measuring the water proton relaxation rate that the inhibitors probably bind at a site on the enzyme surface which is distinct from the substrate binding site(s).

Spectrophotometric studies of interactions between various substrates in their binding to microsomal cytochrome P-450

The question of whether liver microsomes contain a single cytochrome P-450 with broad substrate specificity or a multitude of different cytochromes P-450 with high substrate specificity has been examined by determining the patterns of spectral changes in the presence of various combinations of substrates. The results can be explained in terms of the existence of two spectrally distinguishable forms of cytochrome P-450, which can associate with various substrates to form complexes which are spectrally similar to, but not necessarily identical to, one or the other of these forms.