RAMAN SUPPLEMENT


phosphite (TPP). Obtaining information on the molecular organisation in disordered states, from the analysis of the spectrum of collective vibrations, requires subtracting the QES intensity and transformation into Raman susceptibility according to


χ”(ν) spectra are plotted in Figure 2 for the different states of TPP. Raman susceptibility is related to the VDOS,


g(ν) via the light-vibration coupling coefficient C(ν) according to3,4


χ”(ν) reflects the VDOS with a higher resolution than g(ν)1


, rigorously obtained by inelastic


FIGURE 1 Reduced intensity spectra of amorphous states of triphenyl phosphite (TPP); the glassy state (G) at temperature below Tg the melting temperature Tm


, the under cooled state (UL) at temperatures slightly above Tg , and the liquid state at temperature above Tm


associated with the quasi-elastic (QES) intensity, and intermolecular motions. The Raman intensity is usually converted


into reduced intensity, and slightly below


“Disordered states can have physical properties different from


those of ordered stable states such as solubility, which can lead to different bio-availabilities”


important in the low-frequency range1,2


where n(ν) is the bose factor. The reduced intensity is then free of band shape distortion due to thermal population effects that are very


.


Reduced intensity spectra are plotted inFigure 1 at different temperatures in the liquid, under- cooled liquid and glassy states of triphenyl


neutron scattering experiments, as shown for TPP in the inset of Figure 2. The LFRS is very suitable for the detection and the identification of the early stage of crystallisation in an amorphous matrix2,5,6


, and for the discrimination


FIGURE 3 χ”(ν) spectra of under cooled liquid, glacial state (GS) and crystal at the same temperature slightly above Tg


. The arrows localise


the main differences between the glacial state and the under cooled liquid state. They can be easily identified as corresponding to crystalline signatures


of a nanocrystalline state from an amorphous state6,7


, between FIGURE 2 χ”(ν) spectra of amorphous states of TPP compared to the phonon spectrum of the crystal 12


European Pharmaceutical Review Volume 16 | Issue 5 | 2011


the under cooled liquid and an apparently amorphous state (named glacial state, GS)


. TPP has been widely investigated, since


the observation of a first order transformation under atmospheric conditions8


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