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Terejanszky P.,Budapest University of Technology and Economics | Makra I.,Budapest University of Technology and Economics | Furjes P.,Research Center for Natural science | Gyurcsanyi R.E.,Budapest University of Technology and Economics
Analytical Chemistry

The feasibility of using quartz nanopipets as simple and cost-effective Coulter counters for calibration-less quantitation and sizing of nanoparticles by resistive pulsing sensing (RPS) was investigated. A refined theory was implemented to calculate the size distribution of nanoparticles based on the amplitude of resistive pulses caused by their translocation through nanopipets of known geometry. The RPS provided diameters of monodisperse latex nanoparticles agreed within the experimental error with those measured by using scanning electron microscopy (SEM), dynamic light scattering (DLS), and nanoparticle tracking analysis (NTA). The nanopipet-based counter, by detecting individual nanoparticles, could resolve with similar resolution as SEM mixtures of monodisperse nanoparticles having partially overlapping size distributions, which could not be discriminated by DLS or NTA. Furthermore, by calculating the hydrodynamic resistance of the nanopipets and consequently the volume flow through the tip enabled for the first time the calibration-less determination of nanoparticle concentrations with nanopipets. The calibration-less methodology is applied to sizing and quantitation of inactivated poliovirus of ∼26 nm diameter, which is the smallest size spherical shape virus ever measured by resistive pulse sensing. © 2014 American Chemical Society. Source

Ysacco C.,Aix - Marseille University | Karoui H.,Aix - Marseille University | Casano G.,Aix - Marseille University | Le Moigne F.,Aix - Marseille University | And 6 more authors.
Applied Magnetic Resonance

We have prepared a series of dinitroxides and we investigated their properties as polarizing agents for solid-state nuclear magnetic resonance/dynamic nuclear polarization applications at 100 K, 9.34 T (263 GHz electron paramagnetic resonance and 400 MHz 1H nuclear magnetic resonance). Our results show that a rigid structure with an orthogonal relative orientation of electron g tensors and the appropriate orientation of the two N - O. bonds are required to obtain maximum polarization enhancements. In addition, with dinitroxides exhibiting a long T 1e, the saturation of the irradiated electron spin packet is favored leading to more efficient dynamic nuclear polarization. © 2012 Springer-Verlag. Source

Karoui H.,Aix - Marseille University | Nsanzumuhire C.,Aix - Marseille University | Le Moigne F.,Aix - Marseille University | Hardy M.,Aix - Marseille University | And 5 more authors.
Chemistry - A European Journal

The 5-diethoxyphosphonyl-5-methyl-1-pyrroline N-oxide superoxide spin adduct (DEPMPO-OOH) is much more persistent (about 15 times) than the 5,5-dimethyl-1-pyrroline N-oxide superoxide spin adduct (DMPO-OOH). The diethoxyphosphonyl group is bulkier than the methyl group and its electron-withdrawing effect is much stronger. These two factors could play a role in explaining the different half-lifetimes of DMPO-OOH and DEPMPO-OOH. The trifluoromethyl and the diethoxyphosphonyl groups show similar electron-withdrawing effects but have different sizes. We have thus synthesized and studied 5-methyl-5-trifluoromethyl-1-pyrroline N-oxide (5-TFDMPO), a new trifluoromethyl analogue of DMPO, to compare its spin-trapping performance with those of DMPO and DEPMPO. 5-TFDMPO was prepared in a five-step sequence by means of the Zn/AcOH reductive cyclization of 5,5,5-trifluoro-4-methyl-4- nitropentanal, and the geometry of the molecule was estimated by using DFT calculations. The spin-trapping properties were investigated both in toluene and in aqueous buffer solutions for oxygen-, sulfur-, and carbon-centered radicals. All the spin adducts exhibit slightly different fluorine hyperfine coupling constants, thereby suggesting a hindered rotation of the trifluoromethyl group, which was confirmed by variable-temperature EPR studies and DFT calculations. In phosphate buffer at pH-7.4, the half-life of 5-TFDMPO-OOH is about three times shorter than for DEPMPO-OOH and five times longer than for DMPO-OOH. Our results suggest that the stabilization of the superoxide adducts comes from a delicate balance between steric, electronic, and hydrogen-bonding effects that involve the β group, the hydroperoxyl moiety, and the nitroxide. New pieces to the puzzle! A new fluorinated 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-based spin trap (5-TFDMPO; see figure) was synthesized and studied by EPR/spin-trapping techniques. The properties of the new spin trap are reported for various radicals. The role of the trifluoromethyl group on the spin-trapping properties of the superoxide radical is discussed on the basis of a comparison with other spin traps. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Trunov M.L.,Uzhgorod National University | Lytvyn P.M.,V Lashkaryov Institute Of Semiconductors Nas Ukraine | Nagy P.M.,Research Center for Natural science | Csik A.,Institute for Nuclear Research | Kokenyesi S.,Debrecen University
Physica Status Solidi (B) Basic Research

Two types of amorphous functional materials, based on light-sensitive inorganic compounds like Se and As20Se80 chalcogenide glass (ChG) were investigated with the aim to establish the influence of plasmonic fields, excited by the recording light in nanocomposite layers made of these compounds and gold nanoparticles on their photomechanical response. Both these basic materials are characterized by pronounced photoplastic effect and used for real-time optical recording of optoelectronic elements (based mainly on surface relief gratings) due to high photofluidity and polarization-dependent mass-transport. We have established that mass-transport processes in these ChG can be enhanced in the presence of localized plasmonic fields generated by light if the condition of surface plasmon resonance (SPR) is fulfilled. The subjects of special interest are the mass-transport processes at nano-scale stimulated in the nano-composite layers either by uniform or periodically distributed optical fields. It was found that irradiation by light in the presence of SPR really enhanced the efficiency of mass-transport and produced surface nanostructurizations. The variation in the topography follows closely and permanently the underlying near field intensity pattern. Nanostructurization of photosensitive amorphous As20Se80 film by surface plasmon near field irradiation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Aresta M.,CIRCC | Dibenedetto A.,CIRCC | Dibenedetto A.,University of Bari | Angelini A.,CIRCC | And 2 more authors.
Topics in Catalysis

Dialkylcarbonates, (RO)2CO, can be prepared from alcohols and CO2. Such reaction is clean (water is the co-product) but thermodynamically disfavored. In principle, the reaction mechanism of formation of carbonates requires the acid-base activation of alcohols. Existing data support that the first step is the formation of the alkoxo group RO- that reacts with CO2 to give the hemicarbonate moiety ROC(O)O-. The latter converts into the relevant carbonate (RO)2CO following different pathways depending on the catalyst used. DFT calculations have been used in a few cases to support the reaction mechanism. Transition states relevant to various mechanistic scenarios have been identified. The results indicated that the relative energies of these transition states depend on the nature of the alkyl group and the molecularity of the reactive step. Organic catalysts, homogeneous-, heterogenized- and heterogeneous-metal systems are discussed in this paper and the known relevant mechanisms compared. Water represents a serious limitation to equilibrium shift to the right and can affect the catalysts. Techniques used to remove water are also discussed. © 2014 Springer Science+Business Media New York. Source

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