Lisbel Martínez González

Electronic and chemical properties of mixed-metal oxides: Adsorption and reaction of NO on SrTiO3(100)

The interaction of NO with SrTiO3(100) surfaces was investigated using thermal desorption, photoemission, and first-principles density-functional calculations. The crystals used in the experiments exposed mainly (>80%) the TiO2-terminated face of SrTiO3(100). On the stoichiometric surfaces, the adsorption of NO was completely reversible at submonolayer coverages. Clear peaks for desorption of NO were found at 125 (multilayer state), 160, and 260 K, plus a long tail between 300 and 450 K. Desorption of N2O was detected only near 125 K with the multilayer of NO. DF calculations give adsorption energies of 14 and 6 kcal/mol for NO on the TiO2- and SrO-terminated faces of SrTiO3(100), which are consistent with the peaks at 260 and 160 K seen in thermal desorption. On the TiO2-terminated face of SrTiO3(100), there is substantial hybridization between the orbitals of NO and the oxide bands. This is not seen on the SrO-terminated face, where the large positive charge on the Sr sites leads to weak adsorption bond...

ASPERSIÓN FOLIAR CON BIOBRAS-16 ESTIMULA EL CRECIMIENTO DE PLANTAS JÓVENES DE ARROZ (Oryza sativa L.) SOMETIDAS A TRATAMIENTO CON NaCl

Salinity is one of the most pressing stresses today and brassinosteroids are compounds which, not only stimulate plant growth but also improve plant tolerance to salt stress. In this paper, the effect of foliar spraying with a brassinosteroid analogue (Biobras-16, BB-16) on rice seedlings under this kind of stress was evaluated. For this purpose, rice young plants cv. J-104 were sprayed with BB-16 (0; 0,01; 0,1; 1 μmol L-1), half of them was treated with NaCl (100 mmol L-1) for seven days and later, these plants were transferred to nutrient solution to assess recovery during fourteen days. The growth evaluations (shoot and root length and dry mass) were made at the beginning and the end of saline treatment and seven and fourteen days after the recovery. From the results of this experiment, the best BB-16 concentration was chosen and a second experiment, following the same methodology, was performed and, where, the growth indicators and some biochemical indicators such as malondialdehyde, proline, chlorophylls and the activities of peroxidase and catalase enzymes were determined. Results demonstrated, in general, that the foliar spraying with BB-16 0,1 μmol L-1 increased the length of rice seedlings under saline conditions what appears to be associated with increased antioxidant defenses as well as an increase of the concentration of chlorophylls, chlorophyll a fundamentally.