title: Water evaporation analysis of L-phenylalanine from initial aqueous solutions to powder state by vibrational spectroscopy.
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.
authors.affiliation: Department of Biomedical Engineering and Instrumentation, Wroclaw University of Technology, Smoluchowskiego 19, 50-370 Wroclaw, Poland. sylwia.olsztynska@pwr.wroc.pl
authors.forename: S
authors.initials: S
authors.lastname: Olsztynska
authors.forename: N
authors.initials: N
authors.lastname: Dupuy
authors.forename: L
authors.initials: L
authors.lastname: Vrielynck
authors.forename: M
authors.initials: M
authors.lastname: Komorowska
mesh_terms: D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D010649:Phenylalanine / Q000032:analysis*; D012031:Refractometry; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D014835:Volatilization; D014867:Water / Q000737:chemistry*
chemical_list: D012996:Solutions; D014867:Water; D012965:Sodium Chloride; D010649:Phenylalanine