Structural and vibrational investigation on species derived from the cyclamic acid in aqueous solution by using HATR and Raman spectroscopies and SCRF calculations

• Published in: Journal of molecular structure 2014-09, Vol.1074, p.144-156
• Main Authors: Brizuela, Alicia B., Raschi, Ana B., Castillo, María V., Davies, Lilian, Romano, Elida, Brandán, Silvia A.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Bonding; Cyclamate ion; Cyclamic acid; DFT calculations; Dimers; Force field; Mathematical models; Molecular structure; Phases; Raman spectroscopy; Sodium; Vibrational spectra
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2014.05.019

•Solutions of cyclamate in water were characterized by HATR and Raman spectroscopies.•The vibrational spectra were assigned taking into account the factor group analysis.•The solvent effects for the four species were simulated using the IEFPCM model.•The principal donor and acceptor sites in solution were predicted by calculations.•The SQM force fields were obtained and the force constants were reported. In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HATR (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 HATR 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.