A new deuterated alkylating agent for quantitative proteomics

Weakly basic molecules containing a double bond, such as 2- and 4-vinylpyridine, are able to react and selectively alkylate -SH groups in proteins, thus preventing their re-oxidation to disulphide bridges. In contrast to conventional alkylating agents such as iodoacetamide and non-charged acrylamide derivatives, such molecules achieve 100% alkylation of all -SH residues, even in complex proteins, without reacting with other functional groups. Their use is particularly effective in proteome analysis and more generally for analyzing proteins in which the -SH groups should be blocked. Additionally, the use of vinylpyridines, partially or totally deuterated and thus with a mass difference compared with their non-deuterated counterparts of 4-7 Da, allows studies of induction/repression of protein synthesis (quantitative proteomics).     

Crystal structures of rhodacyclopentane derivatives

Two complexes containing a rhodacyclopentane ring, viz. (acac)Rh(C₆H₈)(py)₂ and (acac)₂Rh₂(C₆H₈)(PPh₃) have been studied by X-ray diffraction. The ring forms through oxidative coupling of two allene molecules giving the structure A with trivalent, octahedrally-coordinated rhodium. In the second complex the unsaturated hydrocarbon part is also π-bonded to another Rh atom, and one acac group acts as a five-electron donor.     

Functionalization and Dissolution of Single-Walled Carbon Nanotubes by Chemical-Physical and Electrochemical Treatments

Single-Walled Carbon Nanotubes (SWCNTs) possess a wealth of exceptional structural, mechanical and electronic properties. These have made them potentially useful for applications in nanotube-reinforced materials, nanoelectronic devices, field emitters, probe tips for SPM, as well as for sensors, biosensors, and actuators. However, manipulation and processing of SWCNTs has been limited by their insolubility in most common solvents, although some dissolution has recently been obtained. Their chemical modification might pave the way to many useful applications, including the preparation of composite materials or the immobilization of biological molecules as enzymes (i.e., for biosensors and electrochemical sensors). Attachment of oxygen-containing functional groups (i.e., carboxy groups, carbonyl groups, hydroxy groups, etc.) on the surface of the carbon nanotubes could be achieved using different pretreatments of the nanostructured material. These involved (a) chemical and physical procedures; and (b) electrochemical functionalization. Different attempts at sidewall modification have been hampered by the presence of significant contaminants as graphitic and amorphous carbon or have required solubilization via chemical reactions on the ends of cut nanotubes. A more accommodating and direct approach to functionalize nanotubes is therefore required. We report here the sidewall functionalization of purified SWCNTs, obtained by different approaches and finally, we can discuss possible applications of functionalized SWCNTs in the sensing area.     

Piperazine quaternary diammonium salts as additives to background electrolytes in capillary zone electrophoresis

The differential behavior of five different quaternary mono- and diammonium salts, among the 18 investigated, in modulating the electroendoosmotic flow (EOF) and analyte separations in capillary zone electrophoresis is evaluated. It is found that quaternary diammonium salts with positive charges separated by more than four carbon atoms, while exhibiting a very strong affinity for chromatographic silica beads, to the point of exhibiting Rf values close to zero, display, on the contrary, a very poor affinity for the silica wall of capillaries. Compounds separated only by a C2 unit (i.e., 1,4-dialkyl-1,4-diazoniabicyclo[2,2,2,]octane, salts 17 and 18) show high Rf values due to strong ion pair association. The unique behavior of quaternary monoammonium salts possessing an iodinated alkyl (butyl or octyl) tail (i.e., 1, 6, and 7) is attributed to their ability to be covalently affixed to the silica wall via alkylation of ionized silanols at alkaline pH values. They thus strongly modulate and typically invert the EOF, even when not present in the background electrolyte. On the contrary, all diammonium salts, devoid of such alkyl tails, are unable to modulate the EOF and to prevent analyte binding to the silica wall, since they are rapidly removed from the wall by the voltage gradient. However, if added in small amount to the background electrolyte, they offer excellent separations of mixtures of very similar organic acids and prevent any interaction with the capillary wall.     

Mass spectrometry of heterocyclic compounds VIII–electron-impact-induced fragmentation of 1,2-diphenyl-pyrazolidine-3,5-dione and some 4-substituted derivatives

The mass spectra of 1,2-diphenyl-pyrazolidine-3,5-dione and twenty-one 4-substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4-position of the heterocycle and/or from the ß-position of the 4-substituent groups, lead to the main primary fragment ions [C₁₂H₁₁N₂]⁺ (m/e 183) as shown by the metastables. The 4,4-d₂ derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4-unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4-derivatives by the loss of 4-substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C₃O₂ and C₃HO₂. Important rearrangements leading to elimination of C₆H₆N and C₆H₇N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron-impact and/or thermal decompostion of some complex compounds containing more than one 1,2-diphenyl-pyrazolidine-3,5-dione system. The [C₆H₅N₂]⁺ (m/e 105) and [C₆H₅]⁺ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4-substituent groups can be excluded.     

A general criterion based on the implicit function theorem to model aggregation and adsorption in colloidal dispersions

This paper, which may interest not only colloid scientists and physical chemists but also applied mathematicians, completes some previous results on aqueous silicon nitride dispersions. Experimental data on adsorption from liquid solution were first obtained by a titration method and then used to derive the number of solid particles from an equilibrium constraint. To discuss the complex mechanisms affecting simultaneous solid particle aggregation and small ion adsorption at the solid/liquid interface, the Dini implicit function theorem (DT) has been applied to the equilibrium condition for a former suspension Gibbs free energy. It was able to relate the average particle number to the ion concentration adsorbed, but not to unequivocally specify their dependence on the liquid phase pH. We attempt here to model aggregation both through bulk and interfacial quantities. The generalized DT-based criterion has first been formulated in all generality, and then adopted according to a wider investigation. The results obtained confirm the original guess, i.e., to regard solid aggregation as dominated by interfacial mechanisms.     

Compatible Lie algebroids and the periodic Toda lattice

We give the set of maps from to the structure of a Poisson manifold endowed with a pair of compatible Lie algebroids. A suitable reduction process, of the Marsden–Ratiu type, yields a smaller manifold with the same geometrical properties as the original manifold. Moreover, is a bi-Hamiltonian manifold and the flows naturally defined on it are the periodic Toda flows.     

Saddle-Node Bifurcations of Cycles in a Relief Valve

We extend the asymptotic perturbation (AP) method to the studyof a linear partial differential equation with nonlinear boundaryconditions. A relief valve under the combined effects of static anddynamic loadings is considered with the following resonances between thenth linear mode and the external periodic excitation: primaryresonance, subharmonic resonance of order one-half or one-third,superharmonic resonance of order-two or order-three and combinationresonance. The AP method uses two different procedures for thesolutions: introducing an asymptotic temporal rescaling and balancing ofthe harmonic terms with a simple iteration. We obtain amplitude andphase modulation equations and determine external force-response andfrequency-response curves. Stability of steady-state motions is alsoinvestigated. Saddle-node bifurcations of cycles are observed and underappropriate conditions the performance of the relief valve may beunsatisfactory due to the presence of jumps and hysteresis effects inthe system response. Global analysis is used in order to exclude theexistence of modulated motion. The validity of the method is highlightedby comparing approximate solutions with results of the numericalintegration.     

Visible and near-infrared absorption spectroscopy by an integrating sphere and optical fibers for quantifying and discriminating the adulteration of extra virgin olive oil from Tuscany

Because of its high price, extra virgin olive oil is frequently targeted for adulteration with lower quality oils. This paper presents an innovative optical technique capable of quantifying and discriminating the adulteration of extra virgin olive oil caused by lower-grade olive oils. An original set-up for diffuse-light absorption spectroscopy in the wide 400–1,700 nm spectral range was experimented. It made use of an integrating sphere containing the oil sample and of optical fibers for illumination and detection; it provided intrinsically scattering-free absorption spectroscopy measurements. This set-up was used to collect spectroscopic fingerprints of authentic extra virgin olive oils from the Italian Tuscany region, adulterated by different concentrations of olive-pomace oil, refined olive oil, deodorized olive oil, and refined olive-pomace oil. Then, a straightforward multivariate processing of spectroscopic data based on principal component analysis and linear discriminant analysis was applied which was successfully capable of predicting the fraction of adulterant in the mixture, and of discriminating its type. The results achieved by means of optical spectroscopy were compared with the analysis of fatty acids, which was carried out by standard gas chromatography.