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Molecular Motions in Amorphous Ibuprofen As Studied by Broadband Dielectric Spectroscopy

Brás, Ana R ; Noronha, João P ; Antunes, Alexandra M. M ; Cardoso, Maria M ; Schönhals, Andreas ; Affouard, Frédéric ; Dionísio, Madalena ; Correia, Natália T

The journal of physical chemistry. B, 2008-09, Vol.112 (35), p.11087-11099 [Periódico revisado por pares]

United States: American Chemical Society

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  • Título:
    Molecular Motions in Amorphous Ibuprofen As Studied by Broadband Dielectric Spectroscopy
  • Autor: Brás, Ana R ; Noronha, João P ; Antunes, Alexandra M. M ; Cardoso, Maria M ; Schönhals, Andreas ; Affouard, Frédéric ; Dionísio, Madalena ; Correia, Natália T
  • Assuntos: B: Statistical Mechanics, Thermodynamics, Medium Effects ; Calorimetry, Differential Scanning ; Chromatography, High Pressure Liquid ; Electric Conductivity ; Hydrogen Bonding ; Ibuprofen - chemistry ; Models, Molecular ; Motion ; Spectrometry, Mass, Electrospray Ionization ; Spectrophotometry, Infrared ; Spectrum Analysis - methods ; Temperature
  • É parte de: The journal of physical chemistry. B, 2008-09, Vol.112 (35), p.11087-11099
  • Notas: istex:5A1A3B1A5FB719CB119E4668D52BA1DF0401FBAE
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  • Descrição: The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as α, β, γ, and D, were detected and characterized, and a complete relaxation map was given for the first time. The γ-process has activation energy E a = 31 kJ·mol−1, typical for local mobility. The weak β-relaxation, observed in the glassy state as well as in the supercooled state was identified as the genuine Johari−Goldstein process. The temperature dependence of the relaxation time of the α-process (dynamic glass transition) does not obey a single VFTH law. Instead two VFTH regimes are observed separated by a crossover temperature, T B = 265 K. From the low temperature VFTH regime, a T g diel (τ =100 s) = 226 K was estimated, and a fragility or steepness index m = 93, was calculated showing that ibuprofen is a fragile glass former. The D-process has a Debye-like relaxation function but the temperature dependence of relaxation time also follows the VFTH behavior, with a Vogel temperature and a pre-exponential factor which seem to indicate that its dynamics is governed by the α-process. It has similar features as the Debye-type process observed in a variety of associating liquids, related to hydrogen bonding dynamics. The strong tendency of ibuprofen to form hydrogen bonded aggregates such as dimers and trimers either cyclic or linear which seems to control in particular the molecular mobility of ibuprofen was confirmed by IR spectroscopy, electrospray ionization mass spectrometry, and MD simulations.
  • Editor: United States: American Chemical Society
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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