Dissociative electron transfer to haloacetonitriles. An example of the dependency of in-cage ion-radical interactions upon the leaving group

The reductive cleavage of the haloacetonitriles (Cl, Br, I) in DMF provides additional examples of the formation of a fragment cluster upon dissociative electron transfer, which is able to survive in this polar solvent thanks to the electron-withdrawing character of the cyano group. The remarkable sensitivity of the activation energy to small changes of the interaction energies allows, with help of the "sticky" dissociative electron-transfer model, the precise determination of interaction energies down to a few millielectronvolts from the cyclic voltammetric data. The interaction energy rapidly decreases from Cl to Br and to I, correlated with the increase of the halide radius. These observations add to the previously gathered evidence to confirm the existence of such interactions and to highlight their electrostatic character. This is further corroborated by the quantum chemical computation of the potential energy profiles, which exhibit a long-distance energy minimum. This revisiting of the notion of sigma-ion radicals and of their status in a polar medium makes them appear as an electrostatic radical-ion pair rather than covalently bound molecules. Their stability is a function of the Lewis acid-base properties of both the radical and the leaving ion and is strongly influenced by the nature of the solvent.     

EPR study of the hemoglobin rotational correlation time and microviscosity during the polymerization of hemoglobin S

The microviscosity and the protein rotational correlation time are analyzed in samples of hemoglobin A and hemoglobin S with the intracellular concentration at 36°C and during spontaneous deoxygenation. With this purpose, we use glutathione and carbonmonoxy hemoglobin labeled with 4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) as probes and 4-maleimido TEMPO bound to the hemoglobin (A and S) as a spin label. The saturation transfer electron paramagnetic resonance experiment showed a sigmoidal behavior, and an increase (about twice) of the hemoglobin rotational correlation time and microviscosity during the polymerization process of hemoglobin S. The delay time determined by this method coincides with that obtained in proton magnetic resonance experiments. These results help to explain the temporal behavior of the proton relaxation times obtained in samples of hemoglobin A and S under the same experimental conditions.     

The effects of membrane metallization in capacitive microfabricated ultrasonic transducers

The mechanical effects of the metal layer on the membranes of capacitive micromachined ultrasonic transducers (CMUTs) are analyzed in this paper by means of finite element simulations. The influence of electrode size and thickness on the electrostatic behavior of the single CMUT cell, including diaphragm displacement, cell capacitance, and collapse voltage, is explored. The effect on device sensitivity is investigated through the transformation factor of the cell, that is computed by FEM and compared with the parallel plate model prediction. It is found that for a non-negligible electrode thickness, as in the majority of fabricated devices, both the static and dynamic performance of the cell can be affected in a significant way. Thus, the effects of membrane metallization must be taken into account in CMUT design and optimization.     

Excess electron transfer in G-quadruplex

The excess electron transfer in a G-quadruplex is successfully probed by using the reaction of hydrated electrons with quadruplex complex of pentamers and the 8-bromoguanine moieties as the detection system.     

A characterization of the family of lines external to a hyperbolic quadric of PG (3, q)

In this paper we characterize the family of external lines to a hyperbolic quadric of PG (3, q).     

Optical characterization of the polymer embedded alloyed bimetallic nanoparticles

A theoretical approach for the calculation of the bimetallic nanoparticles absorption spectra has been developed as an extension of the Mie theory in which nanoparticle dielectric function is found by the weighted linear combination of the dielectric functions for particles made of the corresponding pure metals. In the frame work of the theoretical model an expression for the resonance light absorption frequency were derived taking into account the interband transitions in the dielectric functions. We propose a simple method for the on-line monitoring of the bimetallic nanoparticles composition based on the measurement of the absorption peak position. Elaborated theoretical approach was used to investigate the polymer embedded Ag/Au nanoparticles which were prepared by reducing gold and silver salts (HAuCl4 and AgNO3, respectively) by ethylene glycol in presence of poly(vinyl pyrrolidone) (PVP) at room temperature. Calculated absorption spectra for the Ag/Au nanoscopic systems showed good agreement with the experimental data. Temporal evolution of the Ag/Au nanoparticles has also been investigated by this approach.     

Reversed-phase HPLC behaviour of metal complexes with 4-(2-pyridylazo) resorcinol. A detailed study in the light of solvophobic theory

Summary The chromatographic behaviour of Cu(II), Fe(II), Ni(II) and Co(II) complexes with 4-(2-pyridylazo)resorcinol was studied. The experimental results were very sensitive even to less obvious operational parameters like the kind of the cation (sodium or ammonium) of the phosphate salt used as buffer. The puzzling pattern of the data obtained was interpreted in terms of the equations formulated by Horvath's ‘olvophobic” theory which correlates the capacity factors of the solutes with the surface tension of the mobile phase. A satisfactory rationalization of the data was obtained together with qualitative information on the stoichiometry and charge state of metal complexes. Useful suggestions about the direction to address the experimental work in order to obtain the best results was also obtained.     

A simplex-optimized chromatographic separation of fourteen cosmetic preservatives: analysis of commercial products

An ion-interaction high-performance liquid chromatography (HPLC)-diode-array detection method is developed and optimized for the separation of typical antimicrobial agents used in cosmetics and hygiene products. The most used preservatives contain different molecular structures, different functionalities, and are characterized by different chemical properties. Organic acids, alkyl esters of benzoic acids, alkyl p-hydroxy benzoic acids (parabens), phenol derivatives, and carbanilides represent the most used preservatives, and are often present in multicomponent mixtures. In order to develop a multicomponent method to be used in quality control analysis, the ion-interaction reagent reversed-phase HPLC technique seems to be particularly suitable, because it allows for the simultaneous separation of acidic, basic, and neutral species. The experimental conditions of the method are developed by OVAT (one variable at a time) treatment and further optimized by a multivariate approach based on a Simplex algorithm that works on a desirability function targeted to maximize the resolution in a multicomponent mixture. The new method proposed that is able to simultaneously separate fourteen preservatives is applied in the analysis of commercial products.     

Resistivity and magnetoresistivity of amorphous rare-earth alloys

The resistivity and magnetoresistivity of amorphous rare-earth alloys are studied starting from the general approach of Van Peski-Tinbergen and Dekker. The random axial crystal-field and the magnetic correlations between the rare-earth ions are consistently taken into account. The characteristic features of the available experimental data are explained both of the case of random ferromagnetic and antiferromagnetic order.     

Reversed-phase liquid chromatographic separation of phenolic compounds with a new derivatizing reaction

Summary A reversed-phase HPLC method for resolution of phenoic compounds is presented. A new derivatization reaction has been developed employing diazotized 4-amino-benzonitrile, which reacts also with parasubstituted phenols. The products of the reaction can be extracted in n-butanol, allowing preconcentration and clean-up steps; the extracts are very stable and show strong absorption in the visible, where many interferences are avoided. The possibility of resolution of complex mixtures is discussed with reference to the use of reversed-phase columns using octadecyl- and phenyl bonded silica.