Presence Of Silver Oxide Research Articles

One-Pot Synthesis of 3,4-Dihydrocoumarins via C-H Oxidation/Conjugate Addition/Cyclization Cascade Reaction.

The 3,4-dihydrocoumarin derivatives were obtained from 2-alkyl phenols and oxazolones via C-H oxidation and cyclization cascade in the presence of silver oxide (Ag2O) and p-toluenesulfonic acid as a Brønsted acid catalyst. This approach provides a one-pot strategy to synthesize the multisubstituted 3,4-dihydrocoumarins with moderate to high yields (64-81%) and excellent diastereoselectivity (>20:1).

Synthesis of silver oxide nanoparticles using gomutra mediation and their investigations on anti-oxidant property

Animal and plant waste which are readily available with no cost in the nature can be considered as the mediating materials for the synthesis of many metal/metal oxide nanoparticles. Rice husk, neem plant, cow urine etc., are few among them which can be considered as reducing agents for the synthesis of silica, and silver nanoparticles respectively. In this study, we present a straightforward green synthesis of silver nanoparticles that uses gomutra (Cow urine) as a reducing agent due to the presence of numerous biological components. The method was opted due to its biocompatibility and environment friendly nature. An X-ray diffraction measurement (XRD) was used to identify the phase of the as-synthesized silver oxide nanoparticles, and the face-centered cubic nature of the as-synthesized silver oxide nanoparticles was determined. The presence of silver oxide was shown by Fourier transform infrared spectroscopy (FTIR) on the nanoparticles, with a prominent peak at 520 cm−1. The spherical shape of the silver oxide nanoparticleswith a particle size estimated atabout 18 nm is supported by FESEM examinations, and energy dispersive x-ray analysis (EDAX) supports 37.99% of silver and 36.64% of oxygen in the nanoparticlessynthesised. The biological activities of the silver nanoparticles were investigated in addition to the aforementioned studies for their potential anti-oxidant property. The work also revealed a cost-effective industrial scale production of gomutra-mediated silver nanoparticles for a range of biomedical applications.

Boronic Acid-Catalyzed Regioselective Koenigs-Knorr-Type Glycosylation.

Boronic acid-catalyzed regioselective Koenigs-Knorr-type glycosylation is presented. The reaction of an unprotected or partially protected glycosyl acceptor with a glycosyl halide donor in the presence of silver oxide and a low catalytic amount of imidazole-containing boronic acid was found to proceed smoothly, which enables construction of a 1,2-trans glycosidic linkage with high regioselectivities. This is the first example of the use of a boronic acid catalyst to initiate regioselective glycosylation via the activation of cis-vicinal diols in glycosyl acceptors.

Structure and composition characterization of biocomposites filled with sol–gel bioglasses from the CaO–SiO2–P2O5–Ag2O systems

Lately silver has become extremely important among alloying additives used to produce glassy materials with specific tailored properties. The aim of the study is to characterize bioactive glasses belonging to the CaO–SiO2–P2O5–Ag2O system by SEM and EDX methods, as well as biocomposites based on natural rubber containing those fillers. The focus is on the influence that silver oxide and the mechanism of its effect have upon the properties of glasses and biocomposites. The results show that silver particles serve as crystallization centers for apatite formation in sol–gel glasses what leads to a serious change in the morphology and size of crystals and consequently in glass microstructure. Particles in the form of plates have been identified. This is an indication of silver-stimulated crystalline structure. A relation between the hydroxylapatite plaque and the concentration of silver particles has been found. The influence of silver oxide is expressed in noticeable changes in the adsorption texture properties of the glasses. In the composites, the aggregation of the filler particles has been observed and their size increases in the presence of silver oxide. The hydroxylapatite formed as a stand-alone phase in the sol–gel glass and acting as a filler has the most important role in tailoring the composite characteristics.

Catalytic Atropenantioselective Heteroannulation between Isocyanoacetates and Alkynyl Ketones: Synthesis of Enantioenriched Axially Chiral 3-Arylpyrroles.

We report herein the first examples of catalytic enantioselective synthesis of axially chiral 3-arylpyrroles. Reaction of α-isocyanoacetates with β-aryl-α,β-alkynic ketones in the presence of silver oxide and a phosphine ligand derived from Cinchona alkaloid occurred chemoselectively to afford enantioenriched 3-arylpyrroles in high yields with excellent enantiomeric excesses. The pyrrole ring was constructed de novo in this process.

Catalytic Atropenantioselective Heteroannulation between Isocyanoacetates and Alkynyl Ketones: Synthesis of Enantioenriched Axially Chiral 3‐Arylpyrroles

AbstractWe report herein the first examples of catalytic enantioselective synthesis of axially chiral 3‐arylpyrroles. Reaction of α‐isocyanoacetates with β‐aryl‐α,β‐alkynic ketones in the presence of silver oxide and a phosphine ligand derived from Cinchona alkaloid occurred chemoselectively to afford enantioenriched 3‐arylpyrroles in high yields with excellent enantiomeric excesses. The pyrrole ring was constructed de novo in this process.

Dehydrogenative etherification homocoupling of heterocyclic N-oxides

A novel approach was developed for the dehydrogenative etherification homocoupling of heterocyclic N-oxides in the presence of silver oxide and PyBroP. Various substrates were well tolerated and the desired products were obtained in moderate to good yields. Generally, this reaction features excellent functional group compatibility, broad substrate scope and good regioselectivity.

Influence of oxygen content on the antibacterial effect of Ag-O coatings deposited by magnetron sputtering

Abstract Ag and AgO x thin films were deposited by pulsed DC magnetron sputtering, for medical devices, in order to provide antibacterial properties. During the deposition process, oxygen flow, and, consequently, oxygen fraction, was varied (0–15 sccm) to understand the influence of oxygen species in the physical, chemical and structural properties of thin films. Coatings morphology was observed by scanning electron microscopy (SEM) and their nanostructure and composition were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. XRD and XPS analyses revealed that Ag thin films are composed by metallic Ag, which crystallizes in fcc-Ag phase; whereas AgO x showed a mixture of Ag 2 O and AgO phases for low oxygen fraction that became single AgO with the increase of oxygen fraction in the discharge. Surface wettability and surface tension of the coatings were also determined showing hydrophobic character. Halo inhibition zone tests were performed against Staphylococcus epidermidis , in order to evaluate the antibacterial behavior of coatings, and silver ion release was measured. Only AgO x presented antibacterial behavior, showing that the presence of silver oxide are the main reasons for the antibacterial effect, probably due to the increased production of ROS (Reactive Oxygen Species), making these coatings promising for medical applications.

Functionalization of Silver Nanowires Surface using Ag-C Bonds in a Sequential Reductive Method.

Silver nanowires (Ag-NW) assembled in interdigitated webs have shown an applicative potential as transparent and conducting electrodes. However, upon integration in practical device designs, the presence of silver oxide, which instantaneously forms on the Ag-NW surfaces in ambient conditions, is unwanted. Here, we report on the functionalization of Ag-NWs with 4-nitrophenyl moieties through A-C bonds using a versatile two step reduction process, i.e., ascorbate reduction combined electrografting. We show that 40% of the Ag atop sites were terminated and provide high surface stability toward oxidation for more than 2 months while keeping the same intrinsic conductivity as in bulk silver.

First total synthesis of Boehmenan

The first total synthesis of dilignan Boehmenan has been achieved. A biomimetic oxidative coupling of the ferulic acid methyl ester in the presence of silver oxide is the crucial step in the synthesis sequence, generating the dihydrobenzofuran skeleton. Hydroxyl group was protected with DHP and reducted with LiAlH 4 to afford the intermediate diol. The diol was condensated with the derivative of ferulic acid, then removed the protecting groups, to get Boehmenan. Meanwhile, a study on the ring-opening reaction of the intermediate dihydrobenzofuran neolignan under base conditions was described. The first total synthesis of dilignan Boehmenan was achieved through eight steps from vanillin. Meanwhile, a study on ring-opening reaction of the intermediate dihydrobenzofuran neolignan under base conditions was described.

2,3-Bis(4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)oxirane

The title compound, which has two photoreactive groups in a molecule, was synthesized by the coupling reaction of 3-(4-(bromomethyl)phenyl)-3-(trifluoromethyl)-3H-diazirine in the presence of silver oxide in DMSO.

A Stereocontrolled 1,2‐Addition Reaction of Tetrazoles with Alkyl Propiolates for the Synthesis of Highly Functionalized Enamines

AbstractA stereocontrolled 1,2‐addition reaction of 1‐aryl‐1H‐tetrazoles with alkyl propiolates for the synthesis of highly functionalized enamines was developed. In the presence of silver oxide (Ag2O), the 1,2‐addition reaction generated (Z)‐N‐cyano enamines in good yields with exclusive formation of the Z‐isomers. Meanwhile, the 1,2‐addition reaction generated (E)‐N‐cyano enamines in the presence of Ag2O and potassium carbonate (K2CO3) with high stereoselectivity and yields.

Base-Free Method for Preparation ofO-Sulfonyl Aldoximes Starting from Aldoximes and Sulfonyl Chlorides

A series of O-sulfonyl oxime derivatives have been synthesized by the reaction of oximes with sulfonyl chlorides in the presence of silver oxide and potassium iodide. In the case of aromatic aldoximes and ketoximes, desired products were obtained in 56%~87% yields. But then no desired products were obtained when p-nitrobenzaldoxime, aliphatic aldoximes and α,β-unsaturated aldoximes were employed as substrates in the process. Keywords O-sulfonyl oximes; synthesis; oximes; sulfonyl chlorides; silver oxide

Nucleation promotion of zeolite crystals by in situ formation of silver-based heterogeneous nuclei

The size of zeolite crystals can be controlled by modifying the nucleation frequency by the addition of silver-based promoters. Nanoparticles of silver oxide can be formed in the alkaline solutions used in zeolite synthesis and can act as effective heterogeneous nuclei for the crystallization of zeolites in a wide range of topology and composition (zeolites LSX, X, Y, A, L, and beta). The presence of silver oxide does not affect the normal nucleation mechanism of zeolites from gels and provides a number of additional seeds proportional to the amount of silver oxide precursors introduced in the synthesis systems. The yield of zeolite crystallization is not significantly affected by the presence of the nucleation promoters. The volume of the crystals formed can be decreased by a factor 20 in the appropriate conditions. The effectiveness of the nucleation promotion is not affected by the presence of organic cations but is largely reduced in extremely alkaline media, in which silver oxides are significantly soluble.

A novel method for the preparation of silver/chitosan-O-methoxy polyethylene glycol core shell nanoparticles

Uniformly sized silver/chitosan-O-methoxy polyethylene glycol (chitosan-O-MPEG) core shell nanoparticles with different degree of substitution were synthesized. Thus, N-phthaloyl chitosan is reacted with polyethylene glycol monomethyl ether iodide in the presence of silver oxide by the following steps. At first, amino groups of chitosan are protected by fourfold excess of phthalic anhydride. Then N-phthaloyl chitosan is reacted with an appropriate amount of monomethyl ether iodide in the presence of silver oxide and lastly N-phthaloyl groups are removed to yield silver/chitosan-O-MPEG core shell nanoparticles. Structure of prepared silver/chitosan-O-MPEG core shell nanoparticles have been characterized by UV/Vis spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray diffraction, and scan electron microscopy (SEM-EDX). Experimental results revealed that the prepared silver core particles had the size 18 ± 2 nm. Core shell structure with chitosan-O-MPEG-coating had the size 40 ± 2 nm.

Synthesis of New 9-glycosyl-4,9-dihydropyrano [3,4-b]indole-1(3H)-ones as Antibacterial Agents

A series of new 9-glycosyl-4,9-dihydropyrano[3,4-b]indole-1(3H)-ones 3 was synthesized in moderate to low yields. 4,9-Dihydropyrano[3,4-b]indole-1(3H)-ones (1) were coupled with different acetobromoglycopyranoses 2 in refluxing toluene in the presence of silver oxide to afford one coupling product of the respective N-glycosides. α-L-Arabinopyranosides 3j and 3m were the most active glycosides among the tested compounds against certain Gram positive and Gram negative bacterial strains.

ChemInform Abstract: Facile Synthesis of Substituted Alkynes by Nano‐Palladium Catalyzed Oxidative Cross‐Coupling Reaction of Arylboronic Acids with Terminal Alkynes.

Abstract The oxidative cross-coupling of terminal alkynes with arylboronic acids catalyzed by the porous palladium nanospheres was developed. In the presence of silver oxide, triphenylphosphine and cesium carbonate, the reaction provided the corresponding arylalkynes with good to excellent yields. There were also other obvious advantages such as broad applicability, high selectivity, simple experimental operation as well as the convenient preparation, high efficiency and reusability of catalyst. The possible mechanism of this transition-metal nanoparticles catalyzed oxidative cross-coupling reaction of two nucleophiles was proposed.

ChemInform Abstract: 1,3‐Diynes Synthesis by Homo‐Coupling of Terminal Alkynes Using a Pd(PPh3)4/Ag2O Simple Catalyst System.

AbstractAmine‐ and copper‐free Pd‐catalyzed homocoupling of terminal alkynes proceeds efficiently in the presence of silver oxide, which serves as both promoter and oxidant.

Regioselective Oxidative Coupling Reactions of 3-Substituted Thiophenes with Arylboronic Acids

Under optimized conditions, 3-substituted thiophenes (EWG = COOEt, PO(OEt)(2)) undergo a facile and regioselective oxidative coupling reaction at carbon atom C4. The reactions were performed with various aryl boronic acids as nucleophiles in the presence of silver oxide (2.0 equiv), cesium trifluoroacetate (tfa) (1.0 equiv), benzoquinone (BQ) (0.5 equiv), and catalytic amounts of Pd(tfa)(2) (10 mol %) employing trifluoroacetic acid (TFA) as the solvent.

ChemInform Abstract: Convenient One‐Pot Synthesis of trans‐1,2‐Diaryloxiranes from the Direct Coupling of Benzyl Halides.

trans-1,2-Diaryloxiranes were conveniently prepared in an one-pot reaction by the direct coupling of benzyl halides in the presence of silver oxide and DMSO under mild conditions.