Article,
Conformational change in the C form of palmitic acid investigated by Raman spectroscopy and X-ray diffraction
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, (2016)
DOI: 10.1016/j.saa.2016.02.035
Abstract
Fatty acids are substances found in most living beings in nature. Here
we report the effect of the low temperature in the vibrational and
structural properties of the C form of palmitic acid, a fatty acid with
16 carbon atoms. The Raman spectra were obtained in the temperature
interval from 300 to 18 K in the spectral range between 30 and 3100
cm(-1). The assignment of the duly observed bands was done based on the
density functional theory. On cooling, the main changes observed in the
lattice mode region of the Raman spectra were interpreted as a
conformational modification undergone by the palmitic acid molecules in
the unit cell. The X-ray diffraction measurements were obtained from 290
to 80 K showing a slight modification in the lattice parameters at about
210 K. Differential scanning calorimetry (DSC) measurements were
recorded between 150 and 300 K and no enthalpic anomaly in the DSC
thermogram was observed. These techniques provided strong evidence of
the conformational change in the molecules of palmitic acid at low
temperatures. (C) 2016 Elsevier B.V. All rights reserved.
