Design of Microspheres from Blue Agave Fructans for Drug Delivery to the Colon. Part 1. Esterification of Agave Fructans artículo Académico uri icon


  • Fructans, oligosaccharides composed of fructose as the repeat unit, were isolated from agave Tequilana Weber, Var. Azul, the plant from which the Mexican spirit tequila is made. Agave fructans were characterized with regard to their molecular weight distribution and degree of polymerization (DP) by size exclusion chromatography (SEC) and HPLC. It was found that agave fructans had a DP of 22 by HPLC and Mn 3103 g · mol−1 (DP20) and Mw 3905 g · mol−1 (DP24) determined by SEC. Esterification of agave fructans was carried out in order to prepare microspheres for drug delivery to the colon. Full acetylation of fructans was achieved after 3.5 h as monitored by the relative intensity ratio of the IR bands at 1740 cm−1/1020 cm−1 (C=O stretching and C—O stretching vibration of the polysaccharide backbone). Agave fructans were also derivatized with succinic and acetic anhydrides. The acetyl/succinyl degree of substitution (DS) in the fructans could be controlled by the amount of the anhydride loaded in the reaction mixture. For instance, a 1:1 acetic:succinic load ratio resulted in an acetyl DS of 1.6 and a succinyl DS of 1.4 which made a fully substituted fructan molecule. Microspheres were prepared from esterified fructans by the coacervation method and examined by scanning electron microscopy. Microspheres in the range of 1–20 m were formed from fully acetylated fructan. Preliminary results showed that the integrity of microspheres loaded with ibuprofen seemed to depend on the acetyl/succinyl content. Higher succinyl content produced cracks on the microsphere surface up to the point where the microspheres were unable to maintain the shell structure and collapsed.
  • The controversy about a Cambrian "explosion" of morphological disparity (followed by decimation), cladogenesis and fossilization is of central importance for the history of life. This paper revisits the controversy (with emphasis in onychophorans, which include emblematic organisms such as Hallucigenia), presents new data about the Chengjiang (Cambrian of China) faunal community and compares it and the Burgess Shale (Cambrian of Canada) with an ecologically similar but modern tropical marine site where onychophorans are absent, and with a modern neotropical terrestrial onychophoran community. Biovolume was estimated from material collected in Costa Rica and morphometric measurements were made on enlarged images of fossils. Cambrian tropical mudflats were characterized by the adaptive radiation of two contrasting groups: the vagile arthropods and the sessile poriferans. Arthropods were later replaced as the dominant benthic taxon by polychaetes. Vagility and the exoskeleton may explain the success of arthropods from the Cambrian to the modern marine and terrestrial communities, both in population and biovolume. Food ecological displacement was apparent in the B. Shale, but not in Chengjiang or the terrestrial community. When only hard parts were preserved, marine and terrestrial fossil deposits of tropical origin are even less representative than deposits produced by temperate taxa, Chengjiang being an exception. Nutrient limitations might explain why deposit feeding is less important in terrestrial onychophoran communities, where carnivory, scavenging and omnivory (associated with high motility and life over the substrate) became more important. Fossil morphometry supports the interpretation of "lobopod animals" as onychophorans, whose abundance in Chengjiang was equal to their abundance in modern communities. The extinction of marine onychophorans may reflect domination of the infaunal habitat by polychaetes. We conclude that (1) a mature ecological community structure was generalized during the Cambrian, and even biodiversity and equitability indices were surprisingly close to modern values; (2) the morphological diversity and geographic distribution of onychophorans indicate a significant pre-Cambrian evolutionary history which does not support the "explosion" hypothesis; (3) disparity among phyla was not as important as the explosion-decimation model predicts, but in the case of onychophorans, disparity within the phylum was greater than it is today and its reduction may have been associated with migration into the sediment when large predators evolved.

fecha de publicación

  • 2007
  • 2000