title: Raman spectroscopic evidence of low temperature stability of D,L-glycolic and L-(+)-lactic acid crystals.
abstract: Raman and infrared spectra of polycrystalline D,L-glycolic and L-(+) lactic acid are presented and assigned both by an ab initio calculation of normal modes of free conformers and by self-consistent-charge density-functional-theory computational program DFTB+. Temperature dependent Raman spectra from 295 K to 10 K reveal great stability of crystal lattices, since no soft modes and no band splittings that could be attributed to changes of the number of molecules per unit cell were observed. A semiempirical calculation with GULP program was used to estimate the strength of hydrogen bonds in crystals: in glycolic acid they have energies of -0.337 eV/mol, -0.329 eV/mol, -0.262 eV/mol and -0.242 eV/mol, while in lactic acid two hydrogen bonds have energies of -0.283 eV/mol and -0.202 eV/mol.
authors.affiliation: Ruđer Bošković Institute, Bijenička cesta 54, 10002 Zagreb, POB 180, Croatia. Electronic address: mohacek@irb.hr.
authors.forename: Vlasta
authors.initials: V
authors.lastname: Mohaček-Grošev
authors.affiliation: Stupnička 14, 10000 Zagreb, Croatia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Šoštarić
authors.affiliation: Ruđer Bošković Institute, Bijenička cesta 54, 10002 Zagreb, POB 180, Croatia.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Maksimović
mesh_terms: D003080:Cold Temperature; D003460:Crystallization; D006016:Glycolates / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry*; D008958:Models, Molecular; D013059:Spectrum Analysis, Raman
chemical_list: D006016:Glycolates; C031149:glycolic acid; D019344:Lactic Acid
keywords: Biodegradable material; Glycolic acid; Lactic acid; Normal modes; Phonons; Temperature stability