Journal
JOURNAL OF MOLECULAR STRUCTURE
Volume 1074, Issue -, Pages 144-156Publisher
ELSEVIER
DOI: 10.1016/j.molstruc.2014.05.019
Keywords
Cyclamic acid; Cyclamate ion; Vibrational spectra; Molecular structure; Force field; DFT calculations
Categories
Funding
- CIUNT (Consejo de Investigaciones, Universidad Nacional de Tucuman)
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In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HAIR (Horizontal Attenuated Total Reflectance) and Raman spectroscopies. The theoretical structures of cyclamate ion, the zwitterionic and neutral forms of the cyclamic acid and its dimer were optimized in gas and aqueous solution phases by using the hybrid B3LYP/6-31G* method. The solvent effects for the four species in aqueous solutions were simulated by using self-consistent reaction field (SCRF) calculations employing the integral equation formalism variant (IEFPCM) model. The complete assignments of the vibrational spectra of all the forms of cyclamic acid were performed taking into account the factor group analysis with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The existence of the zwitterionic and neutral forms of the cyclamic acid and its dimer in a solution of cyclamate in water is evidenced by characteristic bands in the HAIR and Raman spectra. The dimerization of cyclamate in aqueous solution was previously reported by conductimetric method. The natural population analysis (NPA) and Merz-Kollman (MK) charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) calculations predict for all the species the principal donor and acceptor sites for the H bonds formation in aqueous solution. The SQM force fields for the cyclamate ion, the zwitterionic and neutral species of the cyclamic acid were obtained and their corresponding force constants in both phases were reported. Additionally, the solvation energies for those species were reported. (C) 2014 Elsevier B.V. All rights reserved.
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