Conformational investigation of amino acid derivatives and corresponding intramolecular interactions through NMR and IR spectroscopies and theoretical calculations

Author(s)

Carolyne Brustolin Braga

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2016-11-28

Examining board members

Roberto Rittner Neto; Luiz Alberto Colnago; Jarbas Magalhães Resende; Miguel Angel San Miguel Barrera; Anita Jocelyne Marsaioli

• Advisor: Roberto Rittner Neto

Abstract

This work entitled: "CONFORMATIONAL INVESTIGATION OF AMINO ACID DERIVATIVES AND CORRESPONDING INTRAMOLECULAR INTERACTIONS THROUGH NMR AND IR SPECTROSCOPIES AND THEORETICAL CALCULATIONS" aimed to evaluate the conformational preferences and the corresponding intramolecular interactions of esterified and N-acetylated derivatives of the amino acids L-proline, L-aspartic acid, L-cysteine and L-histidine in isolated phase and with inclusion of the solvent effect. To this end, we employed NMR and IR spectroscopies, supported by theoretical calculations of electronic structure. The energetically favorable conformers in isolated phase, their energies and structural properties were determined at different DFT (Density Functional Theory) functionals and with the ab initio MP2 method, together with the aug-cc-pVTZ basis set, available in the Gaussian 09 program package. Furthermore, the implicit solvent model IEF-PCM was used to simulate the effect of several solvents on the conformational isomerism of the studied compounds. A joint analysis of frequency calculations of the carbonyl groups stretching vibrations and IR experimental data, both in solvent of different polarities, was carried out to determine the number of conformers and their corresponding populations in solution. The comparison between the experimental 3JHH coupling constants and the theoretically predicted ones for each conformer allowed to estimate the most stable conformers of each compound in less and more polar solvents. Finally, the Natural Bond Orbitals (NBO), the Quantum Theory of Atoms in Molecules (QTAIM) and the Non Covalent Interactions (NCI) analyses were applied to assess the intramolecular interactions (steric, hiperconjugation and/or hydrogen bonding) that govern the observed conformational preferences. The analysis of all these data provided a complete description of the conformational behaviour of these compounds both in isolated phase and in different solvents. Therefore, to explore the conformational behaviour of amino acid derivatives and to map the most significant interactions that are present in these systems is essential for a better understanding of more complex molecules of biological importance (AU)

• FAPESP's process: 12/18567-4 - Conformational investigation of amino acid derivatives and corresponding intramolecular interactions through NMR and IR spectroscopies and theoretical calculations
• Grantee: Carolyne Brustolin Braga
• Support Opportunities: Scholarships in Brazil - Doctorate