Immuno-based sample preparation for trace analysis

Immuno-based sample preparation techniques are based upon molecular recognition. Thanks to the high affinity and high selectivity of the antigen–antibody interaction, they have been shown to be a unique tool in the sampling area. Immuno-based sample preparation methods include the widely encountered immunoaffinity extraction sorbents, so-called immunosorbents, as well as membrane-based or ultrafiltration techniques. This review describes the new developments and applications that have occurred in recent years with emphasis on (i) the antigen–antibody interactions, (ii) and their importance for the properties and use of immunosorbents, (iii) multiresidue extractions, (iv) the on-line coupling to chromatographic or electrophoretic separations, and (v) the high potential for improving MS detection. The recent use of artificial antibodies for sample pretreatment, so-called molecularly imprinted polymers, is also described.     

"Lego" chemistry for the straightforward synthesis of dendrimers

A new straightforward method of synthesis of dendrimers, using two branched monomers (CA(2) and DB(2)), is described. Each generation is obtained in a single quantitative step, with only N(2) or H(2)O as byproducts; generation 4 is obtained in only four steps. The end groups are alternatively phosphines and hydrazines; their versatile reactivity is illustrated by the reaction of generation 4 with a branched CD(5) monomer, which increases the number of end groups in a single step from 48 to 250.     

Antibody catalysis based on functional mimicry

Approaches aiming at eliciting antibodies (Abs) that catalyze specific chemical transformations are numerous. Most of the developed methods are based on the chemical steps of the reaction catalyzed rather than on the structure of known enzyme active sites. The authors have developed an approach that rests on the mimicry properties of the idiotypic network of immune regulation. Recent results, together with the existence of natural catalytic Abs in autoimmune diseases, indicate the need to better understand the regulation properties of immune response, in order to improve the efficiency of tailor-made catalytic Abs.     

Action of α-cyclodextrin on phospholipid assemblies

Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly. Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface: the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact at least a part of the multilamellar assembly.     

Assessment of 4-(dimethylamino)pyridine as a capping agent for gold nanoparticles

Gold nanoparticles stabilized with 4-(dimethylamino)pyridine (DMAP) were prepared by ligand exchange and phase transfer (toluene/water) of functionalized gold nanoparticles. DMAP-protected gold nanoparticles are water-soluble, positively charged, and fairly monodisperse (6.2 +/- 0.9 nm). To understand the scope of this interesting system, the details of the binding of DMAP to gold nanoparticles were investigated. The adsorption of DMAP onto gold surfaces was studied by electrochemistry and surface plasmon resonance. It is concluded that of the three most likely binding modes, the one involving the pyridine nitrogen binding to the gold surface, as suggested previously (Gittins, D. I.; Caruso, F. Angew. Chem., Int. Ed. 2001, 40, 3001), is consistent with experimental data. Other 4-substituted pyridines were also assessed as capping agents. The solubility in toluene and basicity of the incoming ligand, as well as the ability to form charged nanoparticles, determine whether ligand exchange and subsequent phase transfer of the nanoparticles occur. The solubility and stability of the DMAP-protected gold nanoparticles were studied as a function of pH using UV-visible spectroscopy and transmission electron microscopy (TEM). These nanoparticles are soluble and stable over a wide pH range (5.0-12.8). It was found that excess DMAP is necessary for both the preparation and the stability of the DMAP-protected gold nanoparticles.     

Copper-assisted oxidation of catechols into quinone derivatives

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.

An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper.     

Metastable fragment ions from carbinolamine ethers

The secondary decomposition of fragment ions produced by electron impact of carbinolamine ethers was studied by mass analysed ion kinetic energy spectrometry. A new case was observed of ions of the same structure leading to the same fragments through different mechanisms competing in the metastable time frame and accompanied by a different partitioning of the excess energy (internal vs translational). The role of a fractional positive charge localized at saturated centres in the reactivity of these gaseous organic ions is discussed.     

New access to 1,3-diketones from aldehydes

A simple and efficient methodology to introduce an 1,3-diketone motif from various aldehyde precursors in three steps with good overall yields is described using β-ketosulphone 7 as masked equivalent of acetone.