Phase transformation in the C form of myristic-acid crystals and DFT calculations

J R S Miranda; A J R de Castro; J G da Silva Filho; P T C Freire; G S Pinheiro; S G C Moreira; G D Saraiva; F F de Sousa

doi:10.1016/j.saa.2018.09.065

Phase transformation in the C form of myristic-acid crystals and DFT calculations

Spectrochim Acta A Mol Biomol Spectrosc. 2019 Feb 5:208:97-108. doi: 10.1016/j.saa.2018.09.065. Epub 2018 Oct 5.

Authors

J R S Miranda¹, A J R de Castro², J G da Silva Filho³, P T C Freire³, G S Pinheiro⁴, S G C Moreira¹, G D Saraiva⁵, F F de Sousa⁶

Affiliations

¹ Instituto de Ciências Exatas e Naturais, Universidade Federal do Pará, CEP 66075-110 Belém, PA, Brazil.
² Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil; Campus Quixadá, Universidade Federal do Ceará, CEP 63902-580 Quixadá, CE, Brazil.
³ Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil.
⁴ Departamento de Física, Campus Ministro Petrônio Portella, Universidade Federal do Piauí, CEP 64049-550 Teresina, PI, Brazil.
⁵ Faculdade Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará, CEP 63900-000 Quixadá, CE, Brazil. Electronic address: gilberto.saraiva@uece.br.
⁶ Instituto de Ciências Exatas e Naturais, Universidade Federal do Pará, CEP 66075-110 Belém, PA, Brazil. Electronic address: ffs@ufpa.br.

PMID: 30296674
DOI: 10.1016/j.saa.2018.09.065

Abstract

In this study, the vibrational frequencies of myristic acid (CH₃(CH₂)₁₂COOH) were obtained using density functional theory calculations, and the results were compared with experimental Raman and infrared data. Additionally, Raman spectra of crystalline myristic acid were recorded in the 300-20 K range. Raman spectroscopy gives important insights into the effect of low temperatures on its monoclinic phase. X-ray diffraction was performed from 298 to 133 K to provide additional information about the cryogenic behavior of the crystals. These undergo a phase transformation, which was confirmed by differential scanning calorimetry through an enthalpy anomaly observed at low temperatures. Raman spectra and X-ray diffraction refinement of the cell parameters in combination with differential scanning calorimetry at low temperatures revealed slight modifications, confirming a conformational change in the myristic acid molecules involving rearrangement of dimers within the unit cell.

Keywords: DFT calculations; Myristic-acid crystals; Phase transformation; Raman scattering; X-ray powder diffraction.