Spectroscopic and structural investigation on intermediates species structurally associated to the tricyclic bisguanidine compound and to the toxic agent, saxitoxin

• Five species derived from saxitoxin were studied using the IR, NMR and UV spectra.
• The studies suggest the connection between the cyclic cationic and saxitoxin species.
• Some descriptors could explain the Nav blocking activities of these species.
• The complete vibrational assignments for all the species are reported.
• The experimental spectra are in agreement with the corresponding experimental ones.

In the present work, we have studied the structural, topological and spectroscopic properties of five cyclic and of open chain species derived from tricyclic bisguanidine compound in gas and aqueous phases combining the DFT calculations with the experimental infrared and 1H NMR, 13C NMR and UV–visible spectra. These species are members of the saxitoxin family and they were recently synthesized by Tsuchiya et al. (Chemistry. A European Journal, 21 (2015) 7835–7840). Here, the self consistent reaction force (SCRF) calculations were employed in aqueous medium to study the solvation energies by using the polarized continuum (PCM) and solvation (SM) models. All the calculations were performed with the 6-31G* and 6-311++G** basis sets. The atomic charges, electrostatic potentials, bond order, stabilization energy, topological properties suggest the structural connection between the cyclic cationic and saxitoxin species while the electrophilicity and nucleophilicity indexes could be one of the explanations for the Nav blocking activities of these species. The complete vibrational assignments for all the species are reported. The predicted spectra present a reasonable concordance with the corresponding experimental ones.

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