Comparison of Air-Assisted,Vortex-Assisted and Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for the Determination of BTEX Compounds in Water Samples Prior to GC-FID Analysis

Three new dispersive liquid–liquid microextraction (DLLME) methods, air-assisted (AA-DLLME), vortex-assisted (VA-DLLME) and ultrasound-assisted (UA-DLLME), were compared from the point of view of their analytical application for preconcentration of trace amounts of benzene, toluene, ethylbenzene and xylene isomers (BTEX) in water samples. In all of these methods, no dispersive solvent is required and dispersion of extractant is carried out by air bubbles, vortex and ultrasound for AA-DLLEM, VA-DLLME, and UA-DLLME, respectively. Advantages and disadvantages of these three liquid phase microextraction methods and their capability in dispersion of a similar extractant phase in sample solutions were comprehensively compared. All other extraction parameters, which have an influence on the microextraction, were also investigated and optimized. Under optimized conditions, analytical figures of merit for the three techniques were determined and compared. It was found that the limit of detection of the three methods is almost the same, while AA-DLLME has a wider linear dynamic range and the shortest analysis time. Enrichment factors of 182, 45 and 245 were achieved for AA-DLLEM, VA-DLLME, and UA-DLLME, respectively.     

Mild,four-component synthesis of 6-amino-4-aryl-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles catalyzed by titanium dioxide nano-sized particles

A convenient and efficient solvent-free procedure is described for preparation of 6-amino-4-aryl-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles by four-component reaction of hydrazine hydrate, ethyl acetoacetate, aryl aldehyde, and malononitrile in the presence of a catalytic amount of titanium dioxide nano-sized particles. Short reaction times, high yields under ambient conditions, simple reaction, clean work-up, and reusability of the nano heterogeneous catalyst are the advantages of this method.     

Ab initio study of aerogen-bonds between some heterocyclic compounds of benzene with the noble gas elements (Ne,Ar, and Kr)

Structural Chemistry - Ab initio calculations have been performed to study the complexes between the noble gas elements (Ae = Ne, Ar, Kr) with a series of benzene isoelectronic heterocyclic...     

Novel (4-oxothiazolidine-2-ylidene)benzamide derivatives: synthesis,characterization and crystal structures

Research on Chemical Intermediates - A convenient, one-pot, multicomponent synthesis of new (4-oxothiazolidine-2-ylidene)benzamide derivatives by unsymmetrical thioureas, various amines and methyl...     

Synthesis of phosphonato esters involving heterocyclic biological bases in a highly diastereoselective and chemoselective route

Abstract  

Synthesis of five phosphonato esters has been accomplished via reaction between dimethyl acetylenedicarboxylate and triphenyl phosphite in the presence of biological compounds such as theophylline, 4-hydroxypyrimidine, 2H-3,1-benzoxazine-2,4(1H)-dione, 2-chloroaniline, or 3-nitroaniline at ambient temperature. The configuration of the compounds was determined on the basis of coupling constants emerging from the Karplus equation.     

The impact of protonation and deprotonation of 3-methyl-2'-deoxyadenosine on N-glycosidic bond cleavage

The enzyme-substrate contacts that are believed to be involved in depurination by proton transfer have been modelled by protonation and deprotonation of 3-methyl-2'-deoxyadenosine (3-MDA) using quantum mechanical calculations in the gas-phase and solution media. The change in the charge distribution on the sugar ring and nucleobase that is introduced by the protonation and deprotonation strongly affects the N-glycosidic bond length. The unimolecular cleavage and hydrolysis of the N-glycosidic bond, involving D(N)*A(N) and A(N)D(N) pathways, have been considered at several levels of theory. The trend in the energy barriers is A(N)D(N) > cleavage > D(N)*A(N). All probable proton transfer reactions resulting from enzyme-substrate contacts do not facilitate the N-glycosidic bond cleavage of 3-MDA. The deprotonation of 3-MDA that may result from the interaction between H6 and enzyme do not facilitate bond cleavage. The protonation at N7 induces more positive charge on the sugar ring and further facilitates the depurination relative to the protonation at N1. The changes in the charges calculated on the ribose and nucleobase are in good relationship with the C1'-C2', C1'-O4', and N-glycosidic bond lengths along the cleavage. The change in energy barrier ΔE of glycosidic bond cleavage from the gas-phase to solution media strongly depends on the charge of the species.     

Co(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O as a powerful and reusable catalyst for the synthesis of phenylbenzo[<Emphasis Type="Italic">g</Emphasis>]chromenes

An efficient and easy protocol for the one-pot three-component synthesis of phenylbenzo[g]chromenes was developed. The synthesis was achieved by the reaction of aromatic aldehydes, Meldrum’s acid, and 2-hydroxynaphthalene-1,4-dione in the presence of catalytic amount of Co(NO₃)₂·6H₂O at room temperature. The important advantages of this procedure are short reaction times, high yields, easy work-up, reusable catalyst, and no need to column chromatography.     

Quantum chemical study of the nature of interactions between the boraphosphinine and alumaphosphinine with some of the mono- and divalent cations: cation–π or cation–lone pair?

Structural Chemistry - Quantum chemical study of the nature of interactions between the boraphosphinine (BP) and alumaphosphinine (AlP) with some of the alkali metal cations (Li+, Na+, K+) and...