Endo-inulinase Stabilization by Pyridoxal Phosphate Modification: A Kinetics, Thermodynamics, and Simulation Approach

The structural and storage and functional thermostabilization of endo-inulinase (EC 3.2.1.7) through semi-rational modification of surface accessible lysine residues by pyridoxal-5'-phosphate (PLP) and ascorbate reduction have been explored. Improved stability was observed on modifications in the absence or presence of inulin, which indicates storage or functional thermostabilization, respectively. Comparisons have been made between non-modified and modified enzyme by the determination of Tm as an indicator of structural stability, temperature-dependent half-lives (t1/2), energy barrier of the inactivation process, and thermodynamic parameters (ΔH, ΔG, and ΔS) in a storage thermostability approach. These parameters coincided well with the observed stabilization of the engineered enzyme. Moreover, relative activities with sucrose and inulin were determined for non-modified and modified endo-inulinases at different temperatures. A comparison of the sucrose-to-inulin ratios of the initial rate of hydrolysis as an indicator of substrate specificity revealed about twofold improvement in inulinase versus sucrose activity by enzyme modification. Molecular dynamics simulations and molecular docking approaches were employed to explain the observed structural and functional thermostabilization of endo-inulinase upon modification. We hypothesize the establishment of intramolecular interactions between the covalently attached PLP-Lys381 and Arg526 and Ser376 residues as a representative of modification-originated intramolecular contacts in the modified enzyme.     

Highly functionalized dihydrofuran derivatives: Synthesis by diastereoselective intramolecular Wittig reaction

3a,8a‐Dihydroxy‐1,3,3a,8a‐tetrahydro‐ indeno[1,2‐d]imidazole‐2,8‐dione 3 reacts with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine to produce some novel interesting dihydrofuran derivatives diastereoselectively. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:277–279, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20202     

Novel (thio)barbituric-phenoxy-N-phenylacetamide derivatives as potent urease inhibitors: synthesis,in vitro urease inhibition,and in silico evaluations

Structural Chemistry - A novel series of (thio)barbituric-phenoxy-N-phenylacetamide derivatives 7a-l was synthesized and evaluated against Helicobacter pylori urease. The latter assay revealed that...     

Kinetics of catalytic oxidation of benzoin to benzil by alumina supported active MnO2

The kinetics of benzoin oxidation to benzil over MnO₂/Al₂O₃ was studied by investigation of the effect of initial concentration of reactant and product, catalyst mass and also temperature on the reaction rate. On the basis of obtained experimental data a rate law for the kinetics of reaction was proposed and then the reaction rate constants and activation energy of reaction were computed. Finally a simple reaction mechanism was proposed for the reaction. Also it has been shown that the rate controlling step of oxidation of benzoin to benzil is removal of hydrogen from the α-C-atom.     

One‐pot synthesis of tetrahydroindeno[1,2‐b]pyrrolo‐3‐carboxylates derivatives

Tetrahydroindeno [1,2‐b]pyrrole‐3‐carboxylate were synthesized in a one‐pot procedure by the reaction of 1,3‐dicarbonyl and activated carbonyl compounds such as benzyl or ninhydrin in ethanol/water in the presence of ammonium acetate. J. Heterocyclic Chem., (2011).     

A Sharp Jump in Photocatalytic Activity of Elemental Sulfur for Dye Degradation in Alkaline Solution

Elemental sulfur is a low-cost and abundant substance as one of the largest by-products of the oil industry which was widely used in many industrial activities. Cyclo-octasulfur (S₈) is one of the sulfur allotropes that is a very stable substance in standard conditions. In this study, we report a low-cost and fast method for the degradation of methyl violet in water under visible light and also sunlight by using elemental sulfur (S₈). The results show that sulfur is a good photocatalyst which operates under visible light and can be utilized for degradation of methyl violet. The photocatalytic degradation of methyl violet in acidic, neutral, and alkaline media was investigated, and it was found that the photocatalytic efficiency increases dramatically in alkaline solution. The effects of the initial concentration of the dye, photocatalyst dosage, solution pH, and photocatalyst reusability were investigated. The kinetics of the reaction were studied in detail, and the photocatalytic rate equation was presented.     

Synthesis of Dialkyl Phosphorylsuccinates from the Reaction of Thiouracil Derivatives with Dialkyl Acetylenedicarboxylates in the Presence of Trialkylphosphites

Abstract

Dialkyl-2-(dialkoxyphosphonyl)-3-(1,6-dihydro-6-oxo-4-propylpyrimidin-2-ylthio) succinates and dialkyl-2-(dialkoxyphosphonyl)-3-(1,6-dihydro-6-oxopyrimidin-2-ylthio) succinates were synthesized in moderate to high yields using a novel, facile, and one-pot condensation of dialkyl acetylenedicarboxylates, trialkylphosphites, and thiouracil derivatives.

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GRAPHICAL ABSTRACT      

One-Step Synthesis of Electron-Poor Alkenes from Triphenylphosphine,Acetylenic Esters, 2,2,2-Trichloroethanol,and Ninhydrin

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 2,2,2-trichloroethanol leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce the corresponding chlorine-containing stabilized phosphorus ylides. An intermolecular Wittig reaction of the chlorine-containing stabilized phosphorus ylides with ninhydrin leads to the corresponding highly electron-poor chlorine-containing alkenes.     

CuI–Ionic Liquids as Efficient Reaction Media for the Synthesis of Pyran Skeleton via Domino Knoevenagel–Hetero–Diels–Alder Reaction with Unactivated Alkynes

The article describes ionic liquids [bmim][NO₃] in the presence of 30% mol CuI as efficient media for the domino Knoevenagel–hetero–Diels–Alder reaction of o-propargyloxy benzaldehydes as unactivated terminal alkynes with some active methylene compounds. Short reaction time, easy workup, good to excellent yields, and mild conditions are advantages of this new media.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.