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  • Title: Water evaporation analysis of L-phenylalanine from initial aqueous solutions to powder state by vibrational spectroscopy.
    Author: Olsztynska S, Dupuy N, Vrielynck L, Komorowska M.
    Journal: Appl Spectrosc; 2006 Sep; 60(9):1040-53. PubMed ID: 17002830.
    Abstract:
    The water evaporation from L-phenylalanine (L-phe) aqueous solutions at different initial pH (0-13) was studied by vibrational spectroscopy. Next, the attenuated total reflection-Fourier transform infrared (ATR-FT-IR) spectra of aqueous solutions were compared to those recorded after drying for 72 h at 21 degrees C at appropriate initial pH values. Micro-Raman results collected after the water evaporation process are also presented and interpreted. Between pH = 2.5 and 8.76 a white non-transparent gel was observed, possibly due to the presence of the NaCl salt. The significant differences of the band intensities of L-phe functional groups noticed at pH near pK(a) values indicate the structural changes of L-phe molecules due to dimer formation (hydrogen bonds between the -COOH and -CO(2)(-) groups, and the -NH(3)(+) and -NH(2) groups). The presence of the hydrophobic interactions leads to the aggregation of L-phe molecules, most probably via phe-phe stacking as well as complexes of phe with Na(+) ions, HCl, or H(2)O molecules.
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