Cerium(IV) triflate-catalyzed domino annulation approaches to the synthesis of highly substituted piperidines

A simple, diastereoselective, inexpensive, and efficient route for the synthesis of highly functionalized piperidines by the condensation of β-keto-esters, aromatic aldehydes and anilines using cerium(IV) triflate as a catalyst is described. In most cases, the piperidine precipitates out of the solution.     

Synthesis,metal ion complexation and first use of a thia-aza substituted macrocyclic diamide as a novel sensing material for preparation of selective and sensitive poly(vinyl chloride)-membrane potentiometric sensors for Ag+ ion

A novel thia-aza substituted macrocyclic diamide 7,10,13-triaza-1-thia-4,16-dioxa-20,24-dimethyl-2,3;17,18-dibenzo-cyclooctadecane-6,14-dione (L) was synthesized and stability of its complexes with several alkaline earth, transition and heavy metal ions were studied conductometrically in methanol solution. The resulting 1:1 Ag⁺–L complex found to be the most stable one among all cation complexes studied. The optimized structures of the ligand and its Ag⁺ complex were also investigated. Based on the preliminary results thus obtained, L was used as an excellent sensing material to prepare polymeric membrane (PME) and coated graphite (CGE) silver-selective electrodes. The electrodes revealed a Nernstian behavior over wide Ag⁺ ion concentration ranges (i.e., 2.0 × 10^?6–1.0 × 10^?2 M for PME and 5.0 × 10^?7–1.0 × 10^?2 M for CGE). The potentiometric responses were independent of pH of the test solution in the range 2.9–6.8. The electrodes possessed advantages of low resistance, relatively fast response time, long lifetimes and, especially, good selectivity relative to a wide variety of other cations. The electrodes were used, as indicator electrodes, in the potentiometric titration of silver ion and in the determination of Ag⁺ ion in waste water, photographic emulsion, radiographic and photographic films and dental amalgams.     

Synthesis of New Dibenzosulfide Macrocyclic Diamides

Some new dibenzosulfide macrocyclic diamides (6–12) are synthesized. The macrocyclization process is performed by reaction of the dimethyl ester (5) and diacid chloride (4) with appropriate diamines by two methods. Also the results of two methods are discussed and compared.     

Silica-supported cobalt(II) tetrasulfophthalocyanine catalyzed aerobic oxidation of thiols to disulfides under neutral conditions

A very simple and mild reaction is described for the aerobic oxidative coupling of thiols to disulfides by silica-supported cobalt(II) tetrasulfophthalocyanine as the catalyst in non-aqueous media under neutral conditions at room temperature. The catalyst can be reused for the oxidative coupling of several thiols without any significant loss of catalytic activity. Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti University, P.O. Box 19396, 4716 Tehran, Iran.     

Nonequilibrium versus equilibrium molecular dynamics for calculating the thermal conductivity of nanofluids

Journal of Thermal Analysis and Calorimetry - Both equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively) methods have been used to predict the thermal conductivity of...     

Preparation of ceramic γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> nanofiltration membranes for desalination

As one of the most recently developed membrane separation processes, nanofiltration (NF) has found a number of industrial applications. Ceramic NF membranes are also regarded as the appropriate choice in many applications, due to their higher chemical and physical stability. In this study, the rejection of the chloride ion is investigated using bi-layered γ-Al₂O₃-TiO₂ NF membranes based on α-alumina supports. Compression is used in preparation of the supports and sol-gel dip-coating for the top-layer formation. SEM micrographs, XRD, and nitrogen adsorption/desorption isotherms are used for membrane characterisation. The results show that the calcination temperature (600°C) results in different crystal structures including the brookite phase of TiO₂, the γ phase of Al₂O₃, and a combined phase of aluminium-titanium oxides. The average pore size of the membrane was identified as 1.6 nm using an adsorption/desorption isotherm. The rejection was also studied for the chloride ion, using a cross-flow filtration module. Filtration tests were carried out under different pressures, pH values, and salt concentrations; these showed a smoother behaviour particularly around the isoelectric points (IEPs) due to the dual-layer structure, with the best rejection at pH of approximately 5.     

Pentafluorophenylammonium triflate as a mild and new organocatalyst for acylation of alcohols, phenols, and amines under solvent-free condition

A simple, inexpensive, environmentally friendly and efficient route for the acylation of a number of alcohols, phenols and amines using pentafluorophenylammonium triflate (PFPAT) as a catalyst is described. PFPAT organocatalyst is air-stable, cost-effective, easy to handle, and easily removed from the reaction mixtures.     

一个简单、环境友好的硅胶固载硫酸催化Biginelli反应体系(英文)

A protocol for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones and-thiones was developed by means of a three-component condensation of an aldehyde,a β-dicarbonyl compound,and urea or thiourea in acetic acid catalyzed by silica-bonded S-sulfonic acid.Compared to the classical Biginelli reaction conditions,this new protocol has the advantages of consistently excellent yields and short reaction times.After the reaction,the catalyst could be recovered easily and reused with little change in its activity.     

Raman Spectroscopy of Natural Bone and Synthetic Apatites

Abstract

Raman spectroscopy of natural bones and hydroxyapatites is described. In addition, how Raman spectroscopy has proved crucial in providing baseline data for the modification of synthetic apatite powders that are routinely used now as bone replacement materials is explained. It is important to understand the chemical structural properties of natural bone. Bone consists of two primary components: an inorganic or mineral phase, which is mainly a carbonated form of a nanoscale crystalline calcium phosphate, closely resembling hydroxyapatite, and an organic phase, which is composed largely of type I collagen fibers. Other constituents of bone tissue include water and organic molecules such as glycosaminoglycans, glycoproteins, lipids, and peptides. Ions such as sodium, magnesium, fluoride, and citrate are also present, as well as hydrogenophosphate. Hence, the mineral phase in bone may be characterized essentially as nonstoichiometric substituted apatite. Such a distinction is important in the development of synthetic calcium phosphates for application as skeletal implants. An understanding of bone function and its interfacial relationship to an implant clearly depends on the associated structure and composition. Therefore, it is essential to fully understand the chemical composition of bone, and Raman spectroscopy is an excellent technique for such an analysis.