Lumichrome complexation by cyclodextrins: influence of pharmaceutical excipients.

Department of Pharmaceutics, School of Pharmacy, University of Oslo, P O Box 1068 Blindern, 0316 Oslo, Norway.
Pharmazie (Impact Factor: 0.96). 12/2010; 65(12):871-6. DOI: 10.1691/ph.2010.0680
Source: PubMed

ABSTRACT Complexation of the model drug lumichrome by 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD), the most widely used cyclodextrin derivative in pharmaceutical preparations, was investigated in this study. The influence of frequently used pharmaceutical excipients, i.e. alcohols (ethanol, glycerol, propylene glycol), buffers (phosphate, citrate) and tonicity modulators (NaCl, MgCl2) was evaluated by phase solubility, absorption and fluorescence emission spectra and fluorescence lifetime studies. Further, complex formation constants and fluorescence quantum yields were calculated. The formation of a 1:1 complex was indicated by phase solubility studies. The shape of the absorption and emission spectra for lumichrome was nearly independent of dissolution medium. The intensity of the absorption peak was slightly decreasing by the addition of HPbetaCD, which indicates formation of an inclusion complex of lumichrome in the ground state. The intensity of the fluorescence emission peak (i.e. fluorescence quantum yield) was also steadily decreasing by the increase in HPbetaCD concentration. Monoexponential fluorescence decay was obtained in the absence of cyclodextrin. In the presence of cyclodextrin, bi-exponential decays were observed in all aqueous vehicles with the exception of plain water or samples containing salts. The longest decay time corresponds to the lifetime of free (uncomplexed) lumichrome, while the shortest decay time was attributed to the excited state of the complexed alloxazine form of lumichrome. The selected excipients influence the complexation constant and the lumichrome excited state deactivation pathways to various extents.

1 Bookmark
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Riboflavin (RF), also known as vitamin B2, belongs to the class of water-soluble vitamins and is widely present in a variety of food products. It is sensitive to light and high temperature, and therefore, needs a consideration of these factors for its stability in food products and pharmaceutical preparations. A number of other factors have also been identified that affect the stability of RF. These factors include radiation source, its intensity and wavelength, pH, presence of oxygen, buffer concentration and ionic strength, solvent polarity and viscosity, and use of stabilizers and complexing agents. A detailed review of the literature in this field has been made and all those factors that affect the photo, thermal and chemical degradation of RF have been discussed. RF undergoes degradation through several mechanisms and an understanding of the mode of photo- and thermal degradation of RF may help in the stabilization of the vitamin. A general scheme for the photodegradation of RF is presented.
    Beilstein Journal of Organic Chemistry 08/2014; 10:1999-2012. · 2.80 Impact Factor