Density Functional Theory and UPLC/MS/ESI⁺ studies of the zwitterionic surfactant-Na⁺ pair formation

The formation in solution of supramolecular complexes type zwitterion-cation have been shown. The industrial grade zwitterion surfactants cocamidopropyl hydroxysultaine and cocamidopropyl betaine with sodium ion were studied. A combined experimental and theoretical point of view was performed, through the use of Ultra-Performance Liquid Chromatography/Mass Spectrometry/ElectroSpray Ionization with positive mode (UPLC/MS/ESI+) analytic technique and Density Functional Theory (DFT) theoretical approach. Then, the supramolecular complex zwitterion-cation-anion triplets are shown to be viable. Mass/Charge (m/z) relationships have been determined through MS/ESI using positive mode as an ionization source, obtaining five and four molecular species for industrial grade sultaine and betaine chemical products, respectively. Also, molecular zwitterion-NaCl complexes were theoretically studied in three different dielectric constants corresponding to water, methanol, and acetone solvents. It was found that acetone, the lower dielectric constant solvent studied, shows the higher interaction energy. In both vacuum neutral, zwitterion-NaCl, and vacuum positive, zwitterion-Na⁺, molecular complexes the interaction of the cocamidopropyl hydroxysultaine pairs is less strong than cocamidopropyl betaine ones.