High-pressure studies on l,l-dileucine crystals by Raman spectroscopy and synchrotron X-ray diffraction combined with DFT calculations

C B Silva; J G da Silva Filho; G S Pinheiro; A M R Teixeira; F F de Sousa; P T C Freire

doi:10.1016/j.saa.2019.117899

High-pressure studies on l,l-dileucine crystals by Raman spectroscopy and synchrotron X-ray diffraction combined with DFT calculations

Spectrochim Acta A Mol Biomol Spectrosc. 2020 Mar 15:229:117899. doi: 10.1016/j.saa.2019.117899. Epub 2019 Dec 5.

Authors

C B Silva¹, J G da Silva Filho², G S Pinheiro³, A M R Teixeira⁴, F F de Sousa⁵, P T C Freire⁶

Affiliations

¹ Departamento de Física, Universidade Federal do Ceará, C.P. 6030, Campus do Pici, 60.455-760 Fortaleza, CE, Brazil. Electronic address: [email protected].
² Instituto de Centro de Ciências Sociais, Saúde e Tecnologia, Universidade Federal do Maranhão, Imperatriz, MA 65900-410, Brazil.
³ Departamento de Física, Universidade Federal do Piaui, campus Ministro Petrônio Portella, 64.049-550, Teresina, PI, Brazil.
⁴ Departamento de Física, Universidade Regional do Cariri, 63.010-970 Juazeiro do Norte, CE, Brazil.
⁵ Instituto de Ciências Exatas e Naturais, Universidade Federal do Pará, 66.075-110 Belém, PA, Brazil.
⁶ Departamento de Física, Universidade Federal do Ceará, C.P. 6030, Campus do Pici, 60.455-760 Fortaleza, CE, Brazil.

PMID: 31839580
DOI: 10.1016/j.saa.2019.117899

Abstract

The vibrational properties of the dipeptide l-leucyl-l-leucine hydrate were investigated through Raman and infrared spectroscopy. With the aid of first principle calculations using the density functional theory, the assignment of the vibrational modes from the material was furnished. In addition, the behavior of the crystal under high pressure was investigated using Raman spectroscopy (~8 GPa) and synchrotron X-ray diffraction (~26 GPa). The results show significant changes in both the X-ray diffractogram and the Raman spectra, suggesting that l-leucyl-l-leucine hydrate undergoes a phase transition between 2.3 and 2.9 GPa. Finally, for pressures above 16 GPa the broadening of X-ray peaks suggests a disorder in the crystal lattice induced by high-pressure effects.

Keywords: DFT calculations; Dipeptide crystals; High pressure; Phase transitions; Raman spectroscopy; X-ray diffraction.

MeSH terms

Crystallography, X-Ray
Dipeptides / chemistry*
Models, Molecular*
Spectrum Analysis, Raman

Substances

Dipeptides
leucylleucine