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Nitrógeno en el cultivo del gladiolo 2 1 Niveles de nitrógeno y su fraccionamiento en el cultivo del gladiolo para suelos Ferralíticos RojosMaría Isabel Hernández Díaz (1) , Virginia Marrero González (1) , Mayra González Hurtado (2) , Julia Mirta Salgado Pulido (1) Términos para indexación: Gladiolo, floricultura, nutrición mineral. Nitrogen levels and their fractioning in gladiolus cultivation for Ferralitic Red soilsAbstract -The objective of this study was to evaluate growing nitrogen levels and application time of the nitrogen fertilizer in gladiolus cultivation. The experiment was carried out at No differences between nitrogen doses and fertilizer application time in quality variables of spikes and corms were observed. Nevertheless, with the variant 70 kg ha -1 of N, one half applied in plantation and the other half applied 60 days later, a higher spike percentage of commercial categories and a lesser number of stems of inferior quality were obtained. As for the plantation nutritional state, there is a positive relation between the applied nitrogen levels and the foliar content of this element.

In this paper is reported the “in vitro” release kinetic studies of antiepileptic drugs released from an inorganic, titanium oxide (TiO2) porous matrix. In order to determine the drug release mechanism, the experimental values were fitted to different mathematical models: zero-order, firs-order, Higuchi, Hixson-Crowel and Peppas. TiO2 was prepared by the sol-gel method adding valproic acid (VPA) or phenytoine (DHP) during the titanium n-butoxide hydrolysis step. The drug-TiO2 systems were observed by scanning electron microscopy. The “in vitro” release experiments were performed at laboratory scale following the United States Pharmacopeia (USP) standards. The obtained materials have a morphology of nanoparticle agglomerates. The particles have different sizes with some roughness and spherical shape. Peppas model suggests for both systems, that the release mechanism is controlled by two parallel processes. The first one is by diffusion of the drug through the matrix and the second is related to a gradient of constant diffusion by ingress of the solvent in the matrix.

Size and external and internal morphologies of nanoparticles and microparticles are very important on the design of drug devices for controlled release. Random enteric copolymers such as poly (methacrylic acid-coethyl acrylate) and poly (methacrylic acid-co-methyl methacrylate) were used to produce nanoparticles, which contain a model drug and could be employed as drug carriers for proteins. The solvent effect on re-dispersion of such nanoparticles was studied by Scanning Electron Microscopy (SEM) and revealed not only differences in size, but also several shapes, depending on the chemical nature of the polymer matrix and the non-solvent used. Acrylate containing copolymers in acidic aqueous dispersions lead to spheroidal particles. However for the copolymer containing methyl methacrylate, spheroidal particles collapsed in a "grenade" type morphology and besides some cubic structures are also formed.Dynamic Light Scattering (DLS) studies of the re-dispersed nanoparticles showed the strong tendency to form agglomerates not only in acidic water but also in hexane and the presence of bimodal size distributions.