Study of the protonation/deprotonation sequence of two polyamines:: Bis-[(2S)-2-pyrrolidinylmethyl] ethylenediamine and spermidine by 1H and 13C nuclear magnetic resonance

In this paper we describe the study of protonation/deprotonation of two polyamines: bis-[(2S)-2-pyrrolidinylmethyl]ethylenediamine (tetra) and spermidine (Spd). A new synthetic route was established for the synthesis of tetra, which structure was confirmed by IR, elemental analyzes, H-1-NMR, C-13-NMR(Pendant) and 2D-NMR (COSY, C-13-H-1 HETCOR and HMQC) spectra. The protonation/deprotonation sequence studies of tetra and Spd were determined by potentiometric and NMR methods. For the NMR studies, the tetra and Spd samples were dissolved in D2O and the pD adusted with NaOD. The protonation/deprotonation sequences of tetra and Spd were determined by means of the values and the variations of the hydrogen atom and C-13 NMR chemical shifts as a function of hydrogen atom pD. The variation of delta(1)H with pD clearly showed that the first protonation of tetra occurs at the pyrrolidine nitrogen atoms and the second protonation occurs at the ethylenediamine nitrogen atom. The analysis of the C-13-NMR spectra confirmed the results obtained by 'H-NMR, as a greater chemical shift variation was observed for C-6 (5.6 ppm), as compared to C-8 (1.8 ppm). In the study with Spd, the greater chemical shift variation was observed for C-2 (6.75 ppm) and C-5 (4.95 ppm), indicating that the deprotonation occurs first at the secondary nitrogen atoms and the second and third deprotonation steps occur at the primary nitrogen atoms.