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  • Title: Molecular mobility in liquid and glassy states of telmisartan (TEL) studied by broadband dielectric spectroscopy.
    Author: Adrjanowicz K, Wojnarowska Z, Wlodarczyk P, Kaminski K, Paluch M, Mazgalski J.
    Journal: Eur J Pharm Sci; 2009 Nov 05; 38(4):395-404. PubMed ID: 19766186.
    Abstract:
    The molecular relaxation in liquid and glassy states of Telmisartan (TEL) has been studied by Broadband Dielectric Spectroscopy (BDS) covering wide temperature and frequency range. Multiple relaxation processes were observed. Besides the primary alpha-relaxation, two secondary relaxations beta and gamma (labelled in order of decreasing time scale) have been reported. Well-separated beta-process observed above and below glass transition temperature T(g), has activation energy E(beta)=81.8 kJ/mol and was identified as intermolecular Johari-Goldstein (JG) process. The gamma-relaxation visible in dielectric loss spectra at very low temperatures is most likely non-JG relaxation. The temperature dependence of the relaxation times of alpha-process, measured over 11 orders of magnitude, cannot be described by a single Vogel-Fulcher-Tamman-Hesse (VFTH) equation. At temperature T(B)=475.8K the change in relaxation dynamics occurred, consequently a new set of VFTH parameters was required. From low temperature VFTH fits the glass transition temperature T(g) was estimated as T(g)=400.3 K and fragility index m=87 was calculated. Of particular interest was the time scale of molecular motion below the glass transition temperature. Our observation clearly indicates that the alpha-relaxation times at room temperature most probably would exceed 3 years and amorphous TEL should maintain physically and chemically stable over prolonged storage time.
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