Current Organic Chemistry - Volume 16, Issue 14, 2012

The discovery and implementation of new materials in sample preparation have a significant impact on the development of new analytical methods and often on the instrumentation used in chemical analysis. In recent years, nanostructured materials of different chemical composition, such as nanoparticles, nanowires or nanotubes have received increasing attention. Their introduction in almost every stage of chemical analysis has constituted a significant milestone in modern analytical chemistry. Carbon nanotubes (CNTs) are allotropes of carbon that can be obtained as a single-walled (SWCNTs), or multi-walled (MWCNTs) material with a cylindrical nanostructure. Since their discovery in 1991, they have attracted great attention, because of their unique properties, which make them potentially useful in a wide range of scientific fields, from electronics to medicinal chemistry. In analytical chemistry, CNTs can be used as chromatographic solid phase material, and can therefore be directly involved in any step of chemical analysis. More specifically, due to the porous graphite structure of CNTs, they can be used as sorbents in sample preparation techniques, such as Solid Phase Extraction or Solid Phase Microextraction, for the cleaning up and the pre-concentration of a great variety of analytes in different matrices. Many applications can be found in literature regarding the analysis of phenolic compounds, pesticides, pharmaceuticals, inorganic ions, organometallic compounds, etc. in food, in environmental samples, or in biofluids with the use of CNTs. The objective of this review is to summarize the applications of carbon nanotubes in sample preparation over the past decade.

Native glycosidic bonds in carbohydrates, are sensitive to the presence of enzymes. Thus, design of small molecule mimics (glycomimetics) is an active area of research. This review will focus on the development of a new class of glycomimetics: anomeric and N-glycosyl sulfonamides. These novel compounds have been demonstrated to be enzyme inhibitors or antiproliferative agents.

Due to its particular properties the use of ionic liquids in organic transformations is maturing. Immobilized ionic liquids, supported in different substrates or used as functional support, have found important applications in the last decade. In this review, a critical overview of the applications of immobilized ionic liquids in organic transformations as catalysts or to carry reagents or nanoparticles will be presented. Special relevance will be attributed to green procedure, use of nontoxic solvents and recover and reuse of materials. Metal catalysts, organocatalysts, asymmetric aldol reactions, functional group transformations, oxidations, reductions, biooligomer synthesis like oligosaccharide and peptide synthesis will be some of the transformations to be considered.

Theoretical computations were performed on the 1,3-dipolar cycloaddition reactions of pyridinium-3-olates and pyrazinium-3- olates with methyl methacrylate employing density functional theory at the B3LYP/6-31G(d) level in the gas phase and in THF. The two possible regioisomeric pathways, forming 6-esters and 7-esters, along with the two stereoisomeric channels, endo and exo, have been considered. Thermodynamic and kinetic parameters calculated at room temperature have been analyzed while the regioselectivity has been interpreted using reactivity indices. The presence of the methyl group on the dipolarophile compared to methyl acrylate, increases the activation energy but decreases the reaction enthalpy in THF. The rate constants of these reactions have been determined using conventional transition state theory. The thermodynamic and kinetic preferences for the reactions of these pyridinium-3-olates and pyrazinium- 3-olates with methyl methacrylate, in the gas phase and THF, decrease in the order 6-exo > 7-exo > 6-endo > 7-endo. On comparing the reactions of pyridinium-3-olates and pyrazinium-3-olates with methyl acrylate, a different order is observed although the 6-exo cycloadduct remains the major product.

By facile condensation of aromatic amines 4-aminobenzoic acid, 2-amino-4, 6-dimethylpyrimidine, 3-aminopyridine, 4- bromobenzenamine and 4-methylbenzenamine with glyoxal and formaldehyde, catalyzed by acid or base under one or two step reaction sequence, five novel (±) trans-4,5-dihydroxy-1,3-diarylimidazolidines (DHDAIs) were prepared and characterized by X-ray single crystal analysis, NMR, IR and elemental analysis.