title: Vibrational and structural study of onopordopicrin based on the FTIR spectrum and DFT calculations.
abstract: In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G(∗) basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay's scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential (μ), electronegativity (χ), global hardness (η), global softness (S) and global electrophilicity index (ω) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings.
authors.affiliation: INQUINOA-CONICET, Instituto de Química Orgánica, Facultad de Bioquímica Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000 S.M. de Tucumán, Tucumán, Argentina.
authors.forename: Fernando E
authors.initials: FE
authors.lastname: Chain
authors.affiliation: Cátedra de Química General, Instituto de Química Inorgánica, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000 San Miguel de Tucumán, Tucumán, Argentina.
authors.forename: Elida
authors.initials: E
authors.lastname: Romano
authors.affiliation: Instituto de Química, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile.
authors.forename: Patricio
authors.initials: P
authors.lastname: Leyton
authors.affiliation: Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andrés Bello (UNAB), Quillota 910, Viña del Mar, Chile.
authors.forename: Carolina
authors.initials: C
authors.lastname: Paipa
authors.affiliation: INQUINOA-CONICET, Instituto de Química Orgánica, Facultad de Bioquímica Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000 S.M. de Tucumán, Tucumán, Argentina.
authors.forename: César A N
authors.initials: CA
authors.lastname: Catalán
authors.affiliation: Cátedra de Química Orgánica, Dpto. Cs. Básicas, Facultad de Agronomía y Zootecnia, Universidad Nacional de Tucumán, Av. Néstor Kirchner, 4000 San Miguel de Tucumán, Tucumán, Argentina.
authors.forename: Mario
authors.initials: M
authors.lastname: Fortuna
authors.affiliation: Cátedra de Química General, Instituto de Química Inorgánica, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000 San Miguel de Tucumán, Tucumán, Argentina. Electronic address: sbrandan@fbqf.unt.edu.ar.
authors.forename: Silvia Antonia
authors.initials: SA
authors.lastname: Brandán
mesh_terms: D007783:Lactones / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012717:Sesquiterpenes / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D055672:Static Electricity; D014732:Vibration
chemical_list: D007783:Lactones; D012717:Sesquiterpenes; C075494:onopordopicrin; C012849:cnicin
keywords: DFT calculations; Force field; Molecular structure; Onopordopicrin; Vibrational spectra