Determination of ammonia based on the electro-oxidation of hydroquinone in dimethylformamide or in the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The results detail a novel methodology for the electrochemical determination of ammonia based on its interaction with hydroquinone in DMF. It has been shown that ammonia reversibly removes protons from the hydroquinone molecules, thus facilitating the oxidative process with the emergence of a new wave at less positive potentials. The analytical utility of the proposed methodology has been examined with a linear range from 10 to 95 ppm and corresponding limit-of-detection of 4.2 ppm achievable. Finally, the response of hydroquinone in the presence of ammonia has been examined in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide, [EMIM][N(Tf)(2)]. Analogous voltammetric waveshapes to that observed in DMF were obtained, thereby confirming the viability of the method in either DMF or [EMIM][N(Tf)(2)] as solvent. (C) 2003 Elsevier B.V. All rights reserved.

Chondrogenic Differentiation Alters the Immunosuppressive Property of Bone Marrow-Derived Mesenchymal Stem Cells, and the Effect is Partially due to the Upregulated Expression of B7 Molecules

To investigate the immunosuppressive properties of mesenchymal stem cells (MSCs), in the present study we examined the immunogenicity of undifferentiated and tri-lineage (chondrocytes, osteoblasts and adipocytes) differentiated rat bone marrow-derived MSCs under xenogeneic conditions. After chondrogenic-differentiation, rat bone marrow-derived MSCs stimulated human peripheral blood monocyte-derived DCs (hDCs), leading to 8- and 4-fold higher lymphocyte proliferation and cytotoxicity than that of undifferentiated MSCs. The Chondrogenic-differentiated MSCs were chemotactic to hDCs in Dunn chamber chemotaxis system and were rosetted by hDCs inrosette assays. Flow cytometry analysis revealed that chondrogenic-differentiated MSCs had promoted hDCs maturation causing higher CD83 expression in hDCs, whereas undifferentiated MSCs, osteogenic-and adipogenic-differentiated MSCs showed inhibitory effect on hDCs maturation. The co-stimulatory molecules B7 were up-regulated only in the chondrogenic-differentiated MSCs. After blocking B7 molecules with specific monoclonal antibodies in the chondrogenic-differentiated MSCs, CD83 expression of co-cultured hDCs was greatly reduced. In conclusion, chondrogenic differentiation may increase the immunogenicity of MSCs, leading to stimulation of DCs. The up-regulated expression of B7 molecules on the chondrogenic differentiated MSCs may be partially responsible for this event.

Cold collisions of electrons with molecules

Results are presented of high-resolution scattering experiments involving electron collisions with CO2 and CS2, between a few meV and 200 meV impact energy. Virtual state scattering is shown to dominate the low-energy behaviour for both species. The most striking features of the scattering spectrum for CS2 are, however, giant resonances with cross sections greater by more than an order of magnitude than those generally encountered in low-energy scattering. A strong feature centred at 15 meV is attributed to the involvement of CS2- and is interpreted to be a consequence of the virtual state effect.

Experimental observation of dissociative electron attachment to S2O and S2O2 with a new spectrometer for unstable molecules

A new spectrometer, electron radical interaction chamber, has been developed to study dissociative electron attachment to unstable molecules such as free radicals. It includes a trochoidal electron monochromator and a time-of-flight mass spectrometer. Radicals are generated with a microwave discharge at 2.45 GHz. Preliminary data are presented for radicals formed when a mixture of helium and sulphur dioxide was passed through the microwave discharge. Several new resonances are observed with the discharge on. Resonances at 0 eV (S-), 0.8, 1.2, 3.0 eV (SO-) and 3.7 eV (SO- and S2O-) are assigned to the radical S2O2 and a resonance at 1.6 eV (S-) is assigned to S2O. No new resonances have been assigned to SO, which was also generated in the microwave discharge.

Dissociative ionization of molecules in intense laser fields

Accurate and efficient grid based techniques for the solution of the time-dependent Schrodinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H-2(+) with fixed internuclear separation, H-2(+) with vibrating nuclei and H-2 with fixed internuclear separation and illustrative results presented.