Lipase activity of Lecitase® Ultra: characterization and applications in enantioselective reactions

The general properties of Lecitase® Ultra, a phospholipase manufactured and marketed by Novozymes, Denmark, have been studied after purification by ultrafiltration. The enzyme has a molecular mass of 35 KD, pH-optimum of 8.5, and appears to possess a single active site which exhibits both the lipase and phospholipase activities that increase in the presence of Ca²⁺ and Mg²⁺ ions. The enzyme is inhibited by heavy metal ions and surfactants, and does not accept p-nitrophenyl acetate and glycerol triacetate. Substrates, such as glycerol tributyrate and p-nitrophenyl palmitate, esters of N-acetyl-α-amino acids and α-hydroxy acids are readily accepted. Amino acids with aliphatic residues, such as alanine, isoleucine, and methionine, are hydrolyzed with high enantioselectivity for the l-enantiomer (E >100), but amino acids with aromatic residues such as phenylalanine and phenylglycine, and esters of α-hydroxy acids are hydrolyzed with low enantioselectivity (E = 1–5). Immobilization of the enzyme in a gelatin matrix (gelozyme) leads to a marginal improvement in the enantioselectivity for these substrates. However, a dramatic improvement in enantioselectivity is observed for ethyl 2-hydroxy-4-oxo-4-phenylbutyrate (E value increases from 4.5 to 19.5 with S-selectivity). Similarly, glycidate esters, such as ethyl trans-(±)-3-phenyl glycidate and methyl trans-(±)-3-(4-methoxyphenyl) glycidate, are selectively hydrolyzed with a remarkable selectivity towards the (2S,3R)-enantiomer providing unreacted (2R,3S)-glycidate esters (ee >99%, conversion 52–55%) by the immobilized enzyme.     

Synthesis and characterization of graft copolymer (alginate-g-poly(N,N-dimethylacrylamide))

<正>The graft copolymerization of N,N-dimethylacrylamide onto alginate by free radical polymerization using potassium peroxymonosulphate-sarbose as a redox pair in an inert atmosphere was investigated.The reaction conditions for maximum grafting have been optimized by varying the reaction variables,including the concentration of N,N-dimethylacrylamide(7×10~(-2) mol/L to 23×10~(-2) mol/L),potassium peroxymonosulphate(2×10~(-3) mol/L to 18×10~(-3) mol/L),sarbose(0.4×10~(-3) mol/L to 3.4×10~(-3) mol/L),sulphuric acid(1×10~(-3) mol/L to 8×10~(-3) mol/L) and alginic acid(0.4 g/L to 1.8 g/L) along with time duration(60 min to 180 min) and temperature(25℃to 45℃).Water swelling capacity,metal ion sorption and flocculation studies of the synthesized graft copolymer have been performed.The graft copolymer has been characterized by FTIR spectroscopy and thermogravimetric analysis.     

N,N′-Ethylene-Bridged Bis-2-Aryl-Pyrrolinium Cations to E-Diaminoalkenes: Non-Identical Stepwise Reversible Double-Redox Coupled Bond Activation Reactions

This work presents a stepwise reversible two-electron transfer induced hydrogen shift leading to the conversion of a bis-pyrrolinium cation to an E-diaminoalkene and vice versa. Remarkably, the forward and the reverse reaction, which are both reversible, follow two completely different reaction pathways. Establishing such unprecedented property in this type of processes was possible by developing a novel synthetic route towards the starting dication. All intermediates involved in both the forward and the backward reactions were comprehensively characterized by a combination of spectroscopic, crystallographic, electrochemical, spectroelectrochemical, and theoretical methods. The presented synthetic route opens up new possibilities for the generation of multi-pyrrolinium cation scaffold-based organic redox systems, which constitute decidedly sought-after molecules in contemporary chemistry.     

Statistical optimization of biodiesel production from Prunus armeniaca oil over strontium functionalized calcium oxide

Research on Chemical Intermediates - Rapid industrialisation and hike in fuel prices has led to a growing concern for the development of alternative fuel from renewable sources. Biodiesel is one of...     

Stereoselective synthesis of 2-epi-jaspine B via base-catalyzed intramolecular oxy-Michael conjugate addition approach

2-epi-Jaspine B has been synthesized starting from (−)-diethyl tartrate in 12 simple steps and 26.6% overall yield. The key intermediate was obtained via stereoselective base-catalyzed intramolecular oxy-Michael conjugate addition followed by tandem hydrogenation/hydrogenolysis.     

Efficient one-pot synthesis of α-aminophosphonates from aldehydes and ketones catalyzed by ytterbium(III) triflate

An efficient three component one-pot synthesis of N-silylated α-aminophosphonates and α,α-disubstituted α-aminophosphonates was developed using Yb(OTf)₃ as a catalyst at room temperature under mild conditions.     

RETRACTED: Asymmetric synthesis of highly enantioenriched 2-substituted piperidines and 6-substituted piperidine-2-ones by a combination enantioselective hydrazone allylation with ring closing metathesis

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the corresponding author. The corresponding author prepared a series of cinchonine derivatives and found that the structure of PCA, which was a major compound, was mistakenly assigned. The synthetic routes, physical and spectroscopic data for the products are valid. As a result the corresponding author withdraws this publication.     

Graphene oxide–gellan gum–sodium alginate nanocomposites: synthesis,characterization, and mechanical behavior

This paper reports the preparation and characterization of graphene oxide–gellan gum–sodium alginate nanocomposites (GO–GG–Alg). The nanocomposites were prepared by a simple solution mixing-evaporation method. Fourier transform infrared spectroscopy, X-ray diffractions, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and mechanical testing were conducted to study the structure and properties of the nanocomposites. The obtained findings reveal that gellan gum, sodium alginate, and graphene oxide are able to form a homogeneous mixture. Small amount of GO loading on GO–GG–Alg drastically improves its tensile strength and Young’s modulus. Detailed material characteristics of the nanocomposites are addressed.     

Homotopy Perturbation Method for Time-Fractional Shock Wave Equation

A scheme is developed to study numerical solution of the time-fractional shock wave equation and wave equation under initial conditions by the homotopy perturbation method (HPM). The fractional derivatives are taken in the Caputo sense. The solutions are given in the form of series with easily computable terms. Numerical results are illustrated through the graph.