FeCl3·6H2O-catalyzed selective conjugate reduction of alkylidene-β-keto esters and alkylidene-1,3-diketones

FeCl₃·6H₂O/triethylsilane composite catalyst system is successfully developed for the selective conjugate reduction of carbon-carbon double bond of Michael acceptor-alkylidene-β-keto esters and alkylidene-1,3-diketones under mild reaction conditions to afford the corresponding saturated β-keto esters and 1,3-diketones. The process involves the iron-catalyzed hydrosilylation, followed by in situ hydrolysis of silyl enol ether. The optimal reaction conditions include 20?mol% of FeCl₃·6H₂O and triethylsilane in dichloromethane at room temperature. A broad range of substrates undergoes the reduction in 1, 4-selective manner to afford the corresponding saturated compounds in excellent yields.     

Synthesis, characterization and thermal expansion studies on europium titanate (Eu2TiO5)

The lattice thermal expansion characteristics of europium titanate (Eu₂TiO₅) have been studied by measuring the lattice parameter by high temperature X-ray diffraction technique (HT-XRD) in the temperature range 298–1573 K. Percentage linear thermal expansion and mean linear thermal expansion coefficients were computed from the lattice parameter data. The percentage linear thermal expansion in the temperature range 298–1573 K along a, b and c axes are 1.05, 1.15 and 0.95 respectively.     

Synthesis of high voltage (4.9 V) cycling LiNixCoyMn(1-x-y)O2 cathode materials for lithium rechargeable batteries

Layered mixed oxides LiNi(x)Co(y)Mn(1-x-y)O(2) (0 ≤x, y≤ 0.5) synthesized by a sol-gel method using tartaric acid as a chelating agent, and their structural and electrochemical properties are investigated by thermal analysis, XRD, SEM, FT-IR and XPS studies. The higher composition of Co leads to cation disorder and shrinks the cell volume. Electrochemical behaviour of the synthesized materials is evaluated by Galvanostatic charge/discharge studies using 2016 type coin cells. The cycling studies are carried out in the voltage limits of 2.7 to 4.6, 4.8 and 4.9 V at current rates of C/10 and C/5 respectively. The composition LiNi(0.4)Co(0.1)Mn(0.5)O(2) exhibits an average discharge capacity of 192 mA h g(-1) at the current density of 0.612 mA cm(-2) (C/5) in the voltage range of 2.7-4.9 V as compared to the discharge capacity of 155 and 175 mA h g(-1) in the potential range of 2.7-4.6 and 2.7-4.8 V over the 50 investigated cycles. The effect of higher charge voltage at 4.9 V on the electrochemical performance of LiNi(x)Co(y)Mn(1-x-y)O(2) oxide materials has not previously been reported.     

An efficient method for the N-arylation of phenylurea via copper catalyzed amidation

The coupling reaction of phenylurea with different functionalized aryl halides in the presence of air stable CuI,N,N-dimethylethylenediamine as a ligand,and K₃PO₄ as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.This method is milder than the palladium catalyzed arylation and avoids the use of toxic phosphine ligands.     

An access to α, β-unsaturated ketones via dual cooperative catalysis

A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum’s acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions.     

Metal-sensitive and thermostable trypsin from the crevalle jack (<Emphasis Type="Italic">Caranx hippos</Emphasis>) pyloric caeca: purification and characterization

Background

Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.

Results

A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-_DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K _m , k_cat, and k _cat /K _m values using BApNA as substrate were 0.689 mM, 6.9 s^-1, and 10 s^-1 mM^-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd²⁺, Al³⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ at 1 mM, revealing high sensitivity of the enzyme to metal ions.

Conclusions

Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.

     

Photoreactions in hydrophobic pockets

Organic chemists have long recognized the important role that reaction media play in controlling rates, product distributions and stereochemistry. Recently, much effort has been directed towards the use of organized media to modify reactivity as compared to that in isotropic liquids. Judicious selection of a given organized system for a given application requires sufficient understanding of the properties of the organized media themselves and those of the substrate interactions therein. The multimolecular aggregation of hydrophobic solutes in water could prove to be of immense value to the organic chemist. The aggregation of simple olefinic systems in water, would enable photocycloaddition to compete efficiently with the various other modes of dacay of the short-lived excited state. Investigations of a few systems (dimerization of coumarins, stilbenes and alkylcinnamates), in our laboratory have been successful and they bring to light the significance of the hydrophobic effect. One of the most accepted manifestations of the hydrophobic interactions is probably the formation of micellar aggregates in aqueous solutions. Micelles provide a unique interface between aqueous and non-aqueous phases at which the non-polar solute can orient itself. While intermolecular orientation at micellar interfaces can provide selectivity in dimerization reactions, intramolecular orientation can be utilized to bring about selectivity in unimolecular photo-transformations. Such examples are presented.     

129Xe NMR spectrum of xenon inside C(60)

Xenon was inserted into C(60) by heating C(60) in 3000 atm of xenon gas at 650 degrees C. The Xe@C(60) was separated from the empty C(60) by using HPLC. The (13)C resonance for Xe@C(60) is shifted downfield by 0.95 ppm (192 Hz). (129)Xe NMR showed a line 179.2 ppm downfield from xenon gas.     

ABSORBABLE SURGICAL SUTURES

Abstract

Sutures are sterile’ filaments used to close wounds and are made of either absorbable or nonabsorbable materials. The choice of suture materials for surgery is made mainly on the basis of biocompatibility and mechanical properties. The biological interaction with the tissues is considered from the point of view of the inflammatory reaction caused. An ideal suture is one that does not merely avoid negative reactions but also keeps a sterile environment and stimulates the process of healing. An absorbable suture is one which is degraded in body tissues to soluble products and disappears from the implant site, usually within 2 to 6 months. A nonabsorbable suture is resistant to biodegradation, becomes encapsulated in a fibrous sheath, and remains in the tissue as a foreign body unless it is surgically removed (e.g., skin sutures) or extruded. Sutures may be fabricated as monofilaments or multifilaments. The latter are generally braided but sometimes twisted or spun and may be coated with wax, silicone, or other polymers to decrease capillarity and improve handling properties. Hoffman [1] presented a survey on the medical applications of synthetic and natural fibrous materials made from such polymers as poly-(fluorocarbons), polyamides, polyolefins, polypeptides, and polysaccharides which are both nonbiodegradable or slowly biodegrad-ing and biodegradable fibers. Frazza [2] prepared a review on mechanical properties and sterilization of natural and synthetic absorbable and nonabsorbable suture materials. The present paper is a review on materials that have been in recent times as absorbable sutures