Absolute Configuration Determination and Convenient Asymmetric Synthesis of cis-3-(9-Anthryl)cyclohexanol with Proline as a Catalyst

cis‐(3R)‐(9‐anthryl) derivative of cyclohexanol was conveniently obtained in enantiomerically pure form from 2‐cyclohexenone using asymmetric Michael addition of anthrone catalyzed by l ‐proline in a key step. The absolute configuration of the addition product was unequivocally determined by means of electronic circular dichroism measurements combined with calculation of the circular dichroism spectrum by using a density functional theory method. Chirality 24:833–839, 2012. © 2012 Wiley Periodicals, Inc.     

Synthesis of new pryridyl alcohols and their use as catalysts in the asymmetric addition of diethylzinc to aldehydes.

Optically active new pyridyl alcohols 1-4, which can be easily synthesized by the reaction of (+)-camphor or (-)-menthone with lithiated pyridine derivatives, were applied as chiral ligands in the asymmetric addition of diethylzinc to aldehydes. Good yields with up to 94.0% enantiomeric excesses were observed in these reactions.     

Recombinant peptide fusion construction for protein-templated catalytic palladium nanoparticles

Although peptide-enabled synthesis of nanostructures has garnered considerable interest for use in catalytic applications, it has so far been achieved mostly via Fmoc based solid phase peptide synthesis. Consequently, the potential of longer peptides in nanoparticle synthesis have not been explored largely due to the complexities and economic constraints of this chemical synthesis route. This study examines the potential of a 45-amino acid long peptide expressed as fusion to green fluorescence protein (GFPuv) in Escherichia coli for use in palladium nanoparticle synthesis. Fed-batch fermentation with E. coli harboring an arabinose-inducible plasmid produced a product containing three copies of Pd4 peptide fused to N-terminus of GFPuv ((Pd4)₃-GFPuv). Using the intrinsic fluorescence of GFPuv, expression and enrichment of the fusion product was easily monitored. Crude lysate, desalted lysate, and an ion-exchange enriched fraction containing (Pd4)₃-GFPuv were used to test the hypothesis that high purity of the biologic material used as the nanoparticle synthesis template may not be necessary. Nanoparticles were characterized using a variety of material science techniques and used to catalyze a model Suzuki–Miyaura coupling reaction. Results demonstrated that palladium nanoparticles can be synthesized using the soluble cell extract containing (Pd4)₃-GFPuv without extensive purification or cleavage steps, and as a catalyst the crude mixture is functional.     

Synthesis of d‐mannitol‐based crown ethers and their application as catalyst in asymmetric phase transfer reactions

A few new d ‐mannitol‐based monoaza‐15‐crown‐5 type chiral lariat ethers and 18‐crown‐6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans‐chalcone, in the addition of diethyl acetamidomalonate to ß‐nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2‐benzylidene‐1,3‐indandione, and in the Darzens condensation of α‐chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d ‐mannitol‐based macrocycles as the catalysts.     

Characterisation of silver nanoparticles synthesised by Bacillus thuringiensis as a nanobiopesticide for insect pest control

Nanotechnology has become one of the most promising new approaches for pest control in recent years. In this research, biocompatible silver nanoparticles (Btk-AgNPs) were synthesised by using the entomopathogenic bacterium, Bacillus thuringiensis kurstaki (Btk) as a low-cost and eco-friendly production system. The AgNP samples exhibited a brownish-yellow colour that is characteristic for silver nanoparticles synthesis. Btk-synthesised AgNPs were produced using both the supernatant and pellet of Bt culture at various concentrations and AgNP particles were characterised by UV-Vis spectrophotometer and Dynamic Light Scattering (DLS). The variation of hydrodynamic diameter (D_h) and UV-Vis spectra of silver particles produced by various concentration of culture showed that production of AgNPs was maximised when using 20% for either supernatant or pellet treatments of Bt of culture and the size of particles was around 85?nm for both. The insecticidal efficacy of Btk-synthesised AgNPs against larvae of the cabbage looper, Trichoplusia ni (Hübner) and black cutworm, Agrotis ipsilon (Hufnagel) was tested. Results demonstrated that the treatments of either Btk-synthesised AgNP(s) made with Bt supernatant or Btk-synthesised AgNP(p) using Bt pellet were found to be significantly more virulent toward larvae of T. ni than to A. ipsilon.     

High-efficient and synergetic antibacterial nanocomposite hydrogel with quaternized chitosan/Ag nanoparticles prepared by one-pot UV photochemical synthesis

Hydrogel dressings have significant advantages such as absorption of tissue exudate, maintenance of proper moist environment, and promotion of cell proliferation. However, facile preparation method and high-efficient antibacterial hydrogel dressings are still a great challenge. In this study, a facile approach to prepare antibacterial nanocomposite hydrogel dressing to accelerate healing was explored. The hydrogels consisted of quaternized chitosan and chemically cross-linked polyacrylamide, as well as silver nanoparticles (AgNPs) stabilized by chitosan. The synthesis of the hydrogels including the formation of AgNPs and polymerization of acrylamide was accomplished simultaneously under UV irradiation in 1 hour without adding initiator. The hydrogels showed favorable tensile strength of ∼100 kPa with elongation at break over 1000% and shear modulus of ∼10⁴ Pa as well as suitable swelling ratio, which were appropriate for wound dressing. The combination of quaternized chitosan and AgNPs exhibited high-efficient and synergetic antibacterial performance with low cytotoxicity. In vivo animal experiments showed that the hydrogel can effectively prevent wound infection and promote wound healing. This study provides a facile method to produce antibacterial hydrogel wound dressing materials.     

First asymmetric synthesis of chiral beta-iodo Baylis-Hillman esters via tandem 1,4-conjugate addition/carbonyl coupling reactions

A new asymmetric approach to chiral beta-iodo Baylis-Hillman hydroxy esters was developed via a tandem asymmetric I-C/C-C formation reaction. The reaction was conveniently carried out by slow addition of diethylaluminum iodide into a mixture of aldehyde and alpha,beta-acetylenic menthyl ester in dichloromethane at -23 degrees C. Excellent geometric selectivity, promising diastereoselectivity and modest to high yields (up to 91%) were obtained.     

Synthesis of xylal- and arabinal-based crown ethers and their application as asymmetric phase transfer catalysts

New xylal- and arabinal-based monoaza-15-crown-5 ethers were synthesized starting from l - and d -xylose, and l - and d -arabinose, respectively. These monosaccharide-based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal-based crown compounds proved to be efficient catalysts in a few liquid-liquid phase reactions. The epoxidation of trans-chalcone and the Darzens condensation of α-chloroacetophenone with benzaldehyde took place with complete diastereoselectivity and up to 77% ee and 58% ee, respectively. It was found that the substituents in the aromatic ring of the chalcone and the α-chloroacetophenone had an influence on the enantioselectivity. The highest ee values were obtained in the epoxidation of 4-chlorochalcone (81% ee) and in the reaction of a 2-naphthyl analogue (96% ee), while in the Darzens condensation of 4-phenyl-α-chloroacetophenone with benzaldehyde, a maximum ee of 91% was detected. The configuration of the monosaccharide unit in the crown ring influenced the absolute configuration of the epoxyketones synthesized.     

A novel L-neopentylglycine derivative as auxiliary for copper-catalyzed asymmetric Michael reactions

L-Neopentylglycine diethylamide (4a). was prepared from the new unnatural amino acid L-neopentylglycine (1). The utilization of amide 4a as a chiral auxiliary in the copper(II)-catalyzed asymmetric Michael reaction was investigated in comparison with L-valine diethylamide (4b). Cyclic beta-oxocarboxylates 7 react with 4a and 4b to give the respective enaminoesters 8, which were converted with methyl vinyl ketone (9) in the presence of 10 mol% Cu(OAc)(2). H2O at room temperature in acetone to yield the optically active Michael addition products (R)-10a, b with high selectivity independent of the starting enamine. In the case of the seven-membered beta-oxocarboxylate 7c, however, the valine-derived enamine 8f led to higher enantioselectivity for product 10c. Despite the bulkiness of the neopentyl group, the isopropyl group with an alpha-branch has a better stereoinducing effect.     

Synthesis and application of 3‐substituted (S)‐BINOL as chiral ligands for the asymmetric ethylation of aldehydes

A series of (S)‐BINOL ligands substituted at the 3 position with some five‐membered nitrogen‐containing aromatic heterocycles were effectively prepared and their catalytic abilities were evaluated in the asymmetric addition of diethylzinc to benzaldehyde in the presence of titanium tetraisopropoxide. Under the optimized reaction conditions, titanium complex of (S)‐3‐(1H‐benzimidazol‐1‐yl)‐1,1′‐bi‐2‐naphthol was found to be the most efficient catalyst for asymmetric ethylation of various aldehydes to generate the corresponding secondary alcohols in up to 99% yield and 91% ee. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Alpha-aminophosphonates as novel organocatalysts for asymmetric Michael addition of carbonyl compounds to nitroolefins

A cyclic alpha-aminophosphonate was found to be a novel organocatalyst for Michael type addition reactions of carbonyl compounds to nitroolefins to afford the corresponding adducts in high enantio- and diastereoselectivities.     

Functionalization of cotton fabrics with titanium oxide doped silver nanoparticles: Antimicrobial and UV protection activities

The target of our current work was designed to prepare titanium oxide doped silver nanoparticles (Ag/TiO₂NPs) and their impact on the functionalization of cotton fabrics. Additionally, the effect of Ag/TiO₂NPs was compared with the individually prepared silver nanoparticles (AgNPs) and titanium oxide nanoparticles (TiO₂NPs). In this work, AgNPs were prepared in the solid state using arabic gum as efficient stabilizing and reducing agent. Then, two concentrations of the as-synthesized nanoparticles were used to functionalize the cotton fabrics by pad-dry-cure treatment in the presence of fixing agent to increase the durability of treated cotton fabrics against vigorous washing cycles. The findings implied that the as-prepared nanoparticles were successfully synthesized in nano-size with spherical shape and homogeneity. The efficacy of the functionalized cotton fabrics with those nanoparticles were evaluated in terms of multifunctional properties including antimicrobial and ultraviolet protection factor (UPF) and the mechanical features before and after many washing cycles; 10, 15 and 20 times. The resultant also proved that Ag/TiO₂NPs-treated cotton fabrics exhibited the greater values of both antimicrobial and UPF properties with enhancement in the tensile strength and elongation features. Thus, the combination between these two nanoparticles through doping reaction is suitable for imparting superior antimicrobial properties against the four tested microbial species (Staphylococcus aureus, Escherichia coli, Candida albicans, and Aspergillus niger) and good UPF properties. Depending on the promising obtained results of the multi-finishing fabrics, these nanoparticles of Ag/TiO₂NPs can be applied for the production of an efficient medical clothes for doctors, nurses and bed sheets for patients in order to kill and prevent the spread of bacteria and then, reduce the transmission of infection to others.     

Silver nanoparticles from Prosopis glandulosa and their potential application as biocontrol of Acinetobacter calcoaceticus and Bacillus cereus

In the present study the characterization and properties of silver nanoparticles from Prosopis glandulosa leaf extract (AgNPs) were investigated using UV–Vis spectroscopic techniques, energy dispersive X-ray spectrometers (EDS), zeta potential and dynamic light scattering. The UV–Vis spectroscopic analysis showed the absorbance peaked at 487 nm, which indicated the synthesis of silver nanoparticles. The experimental results showed silver nanoparticles had Z-average diameter of 421 nm with higher stability (?200 mV). The EDS analysis also exhibited presentation of silver element. Additionally, the different concentrations of AgNPs (25, 50, 75 and 100 mg/mL) showed antibacterial activity against Acinetobacter calcoaceticus and Bacillus cereus. Finally, AgNPs from leaf extracts of P. glandulosa may be used as an agent of biocontrol of microorganism of importance medical. However, further studies will be needed to fully understand the antimicrobial activity of silver nanoparticles obtain from P. glandulosa.     

The Syntheses of new Camphorsulfonylated Ligands Derived from 2-Amino-2'-Hydroxy-1,1'-Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

A series of new camphorsulfonylated ligands derived from chiral 2‐amino‐2′‐hydroxy‐1,1′‐binaphthyl (NOBIN) and (+)‐camphorsulfonic acid were synthesized by a short and simple synthetic sequence, and their enantioselective catalytic activities were assessed in the nucleophilic addition reaction of dialkylzinc reagents to aldehydes in the presence of titanium tetraisopropoxide. The most efficient ligand, N‐hydroxycamphorsulfonylated (S)‐NOBIN, gave (S)‐addition products with good yields and up to 87% of ee value. The ¹H nuclear magnetic resonance (NMR) and ¹³C NMR results of the titanium titration experiments on this ligand indicate that the most likely catalytic reactive species involved in this catalytic asymmetric addition is a bimetallic titanium complex. A possible catalytic reaction mechanism is proposed. Chirality 24:825–832, 2012. © 2012 Wiley Periodicals, Inc.     

NHC-containing chiral bidentate ligands: synthesis and evaluation in enantioselective copper-catalyzed conjugate addition

New chiral phosphine-, thiolate-, mesylate-, and tosylate-containing N-heterocyclic carbene ligands have been synthesized in fair to excellent yield. These bidentate ligands have been evaluated in enantioselective copper-catalyzed conjugate addition to both cyclic and acyclic enones and displayed good catalytic activities and poor to good enantiomeric excesses (up to 80%).     

G‐quadruplex DNA‐based asymmetric catalysis of michael addition: Effects of sonication,ligands, and co‐solvents

There is an escalating interest of using double stranded DNA molecules as a chiral scaffold to construct metal‐biomacromolecule hybrid catalysts for asymmetric synthesis. Several recent studies also evaluated the use of G‐quadruplex DNA‐based catalysts for asymmetric Diels‐Alder and Friedel‐Crafts reactions. However, there is still a lack of understanding of how different oligonucleotides, salts (such as NaCl and KCl), metal ligands and co‐solvents affect the catalytic performance of quadruplex DNA‐based hybrid catalysts. In this study, we aim to systematically evaluate these key factors in asymmetric Michael addition reactions, and to examine the conformational and molecular changes of DNA by circular dichroism (CD) spectroscopy and gel electrophoresis. We achieved up to 95% yield and 50% enantiomeric excess (ee) when the reaction of 2‐acylimidazole 1a and dimethylmalonate was catalyzed by 5′‐G₃(TTAG₃)₃?3′ (G4DNA1) in 20 mM MOPS (pH 6.5) containing 50 mM KCl and 40 µM [Cu(dmbipy)(NO₃)₂], and G4DNA1 was pre‐sonicated in ice bath for 10 min prior to the reaction. G‐quadruplex‐based hybrid catalysts provide a new tool for asymmetric catalysis, but future mechanistic studies should be sought to further improve the catalytic efficiency. The current work presents a systematic study of asymmetric Michael addition catalyzed by G‐quadruplex catalysts constructed via non‐covalent complexing, and an intriguing finding of the effect of pre‐sonication on catalytic efficiency. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:891–898, 2016     

The synthesis of chitosan-based silver nanoparticles and their antibacterial activity

Chitosan-based silver nanoparticles were synthesized by reducing silver nitrate salts with nontoxic and biodegradable chitosan. The silver nanoparticles thus obtained showed highly potent antibacterial activity toward both Gram-positive and Gram-negative bacteria, comparable with the highly active precursor silver salts. Silver-impregnated chitosan films were formed from the starting materials composed of silver nitrate and chitosan via thermal treatment. Compared with pure chitosan films, chitosan films with silver showed both fast and long-lasting antibacterial effectiveness against Escherichia coli. The silver antibacterial materials prepared in our present system are promising candidates for a wide range of biomedical and general applications.     

Borane‐mediated asymmetric reduction of acetophenone by enantiopure aminonaphthols and aminoalcohols as catalytic source

Practical, cheap, and stereoselective synthetic methods were applied to the preparation of novel 1‐(aminoalkyl)naphthol and γ‐aminoalcohol tridentate ligands. The ligands obtained were conveniently applied with good results as catalytic sources in the borane‐mediated enantioselective reduction of acetophenone with borane dimethylsulfide. Conformational analysis through molecular modeling allows the rationalization of observed stereochemical outcomes. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

Influence of gold and silver nanoparticles on the germination and growth of Mimusops laurifolia seeds in the South-Western regions in Saudi Arabia

In the Saudi Arabia, the tree of Mimusops laurifolia is suffering from a severe slow growth, in addition to their weakness of natural regeneration, and lack of artificial regeneration to improve their renewal growing. This tree is suffering from extinction because of the misuse of them. The aim of this study is to investigate the effect of gold (Au) particles and silver (Ag) nanoparticles to speed the germination and growth of Mimusops laurifolia trees. This study shows the importance of nanotechnology to contribute the topic of scientific researches and to enrich the scientific libraries of new and affective techniques in the field of physics and botany. We have tried to study the effect of gold and silver nanoparticles on the seeds of Mimusops laurifolia. After the treatments by these granules’ nanoparticles on germination, the result was completely negative and there was no germination and in all the transactions the germination rate were zero, even after the usage of Sulphuric acid to seeds to soften the test of the seed. This study concludes by following-up the leaf growth of seedlings of Mimusops laurifolia after the treatments of gold and silver nanoparticles, it was noted as positive impact of silver nanoparticles, and there was obvious increase in both number and size of the leaves compared with the seedlings, which has transmitted by gold nanoparticles and with the control seedling.     

3-substituted BINOL Schiff bases and their reductive products for catalytic asymmetric addition of diethylzinc to aldehydes

Three new chiral 3-substituted BINOL Schiff bases and their reductive 3-arylaminomethyl BINOL products have been synthesized and used for the asymmetric addition reaction of diethylzinc to aldehydes in the presence of titanium tetraisopropoxide. The reaction provided optically active secondary alcohols in high yield (86-100%) and good enantioselectivity (up to 92% ee).