title: The temperature-dependent single-crystal Raman spectroscopy of a model dipeptide: L-Alanyl-L-alanine.
abstract: A single-crystal of peptide L-alanyl-L-alanine (C6H12N2O3) was studied by Raman spectroscopy at low-temperature, and a tentative assignment of the normal modes was given. Evidence of a second order structural phase transition was found through Raman spectroscopy between the temperatures of 80K and 60K. Group theory considerations suggest that the transition leads the sample from the tetragonal to a monoclinic structure. Additionally, our study suggests that the mechanism for the structural phase transition is governed by the occupation of non-equivalent C1 local symmetry sites by the CH3 molecular groups. Analysis based on group theory suggests L-alanyl-L-alanine presents C2 symmetry at low temperatures.
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: J G
authors.initials: JG
authors.lastname: Silva
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: L M
authors.initials: LM
authors.lastname: Arruda
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil; Departamento de Física, Campus Ministro Petrônio Portella, Universidade Federal do Piauí, CEP 64049-550 Teresina, PI, Brazil. Electronic address: gardenia@fisica.ufc.br.
authors.forename: G S
authors.initials: GS
authors.lastname: Pinheiro
authors.affiliation: Departamento de Física, Campus Ministro Petrônio Portella, Universidade Federal do Piauí, CEP 64049-550 Teresina, PI, Brazil.
authors.forename: C L
authors.initials: CL
authors.lastname: Lima
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: F E A
authors.initials: FE
authors.lastname: Melo
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: A P
authors.initials: AP
authors.lastname: Ayala
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: J Mendes
authors.initials: JM
authors.lastname: Filho
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, C.P. 6030, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: P T C
authors.initials: PT
authors.lastname: Freire
mesh_terms: D003080:Cold Temperature; D003460:Crystallization; D004151:Dipeptides / Q000737:chemistry*; D008958:Models, Molecular; D044367:Phase Transition; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D004151:Dipeptides; C002956:alanylalanine
keywords: Infrared spectroscopy; Peptide; Phase transition; Raman spectroscopy