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Browsing by Author "Valente, A. J. M."

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  • Cyclodextrin-grafted cellulose: physico-chemical characterization
    Publication . Medronho, B.; Andrade, R.; Vivod, V.; Ostlund, A.; Miguel, M. G.; Lindman, B.; Voncina, B.; Valente, A. J. M.
    Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them very attractive in different areas, such as pharmaceutics, biochemistry, food chemistry and textile. In this communication we will report on the physico-chemical characterization of cellulose modified with CDs by means of infra-red spectroscopy (FTIR), cross polarization magic angle spinning solid state nuclear magnetic resonance (CP-MAS NMR), polarized optical microscopy (POM) and thermal gravimetric analysis (TGA). Both CP-MAS NMR and FTIR indicate that CDs are chemically attached to cellulose backbone through the formation of ester bonds. Furthermore, the CD-grafted cellulose was dissolved in a "superphosphoric" acid solution but, despite the increase of hydrophilicity due to the modification, POM revealed that grafted cellulose was less soluble when compared to the unmodified polymer. The formation of a complex CD-cellulose network is suggested. (C) 2012 Elsevier Ltd. All rights reserved.
    2013Journal article Restricted access Show more
  • Inclusion complexes of rosmarinic acid and cyclodextrins: stoichiometry, association constants, and antioxidant potential
    Publication . Medronho, B.; Valente, A. J. M.; Costa, P.; Romano, Anabela
    The interaction between beta-cyclodextrin (beta-CD) and the polyphenol rosmarinic acid (RA) is here reported by H-1 NMR titration experiments. The formation of an aqueous soluble inclusion complex is confirmed and valuable information regarding mode of penetration of guest into beta-CD, stoichiometry, and stability of the complex is obtained. The analysis by the continuous variation method shows the undoubted formation of 1:1 beta-CD/RA complex. Additionally, the estimated apparent association constants reveal the importance of the asymmetry of the RA in the complexation; the incorporation of the catechol moiety closer to the carboxylic group is more favorable (K = 2,028 M-1) than from the other end of the RA molecule (K = 1,184 M-1). Finally, we have also investigated the antioxidant activity and storage stability of the beta-CD/RA complexed system; the presence of beta-CD was found to produce a remarkable enhancement on the antioxidant activity.
    2014Journal article Restricted access Show more