Spectroscopic and Theoretical Studies on Solid 1,2‐Ethylenediamine Dihydrochloride Salt

Abstract

A structural study of [H3N(CH2)2NH3)]2+⋅2Cl−, the smallest element of the homologous series of the α,ω‐diamine dihydrochlorides, was carried out by means of Raman and FTIR spectroscopy coupled to ab initio molecular orbital (MO) calculations. As a primary concern, an adequate molecular model for the representation of these solid amine salts was chosen. Thus, several models, varying in the number and position of the counterions as well as in the number of diamine units, were considered. It was found that the best molecular system (i.e., that yielding the best compromise between accuracy and computational requirements) consists of one ethylenediamine cation surrounded by six chloride ions in an arrangement based on the crystal structure reported in the literature for [H3N(CH2)2NH3)]2+⋅2Cl−. This conclusion will hopefully allow for a better understanding of the conformational preferences, in the solid state, of these biologically relevant linear polyamines.

Polyamines: fundamental characters in chemistry and biology

“…anticancer drugs) as described above. Linear aliphatic amines, specifically, are recognised to have a high conformational freedom (Batista de Carvalho et al 1999; Costa et al 2002Costa et al , 2003Costa et al , 2004Amado et al 2004) and may be designed to display high flexibility and polidenticity, which constitutes an advantage for an effective interaction with biological receptors. In addition, the dual hydrophilic-lipophilic character of the polyamine ligands, comprising cationic amine groups (both primary and secondary) and variable length hydrophobic alkyl linkers, will possibly lead to an enhanced cellular uptake.…”

“…R-HN-HÁÁÁNH 2 -R), which determine the solid-state conformational behaviour of the amines and may give rise to either infinite chain polymeric forms or to dimeric species (e.g. for diaminoethane) (Amado et al 2004).…”

On the correction of calculated vibrational frequencies for the effects of the counterions — α,ω-diamine dihydrochlorides

“…In a previous quantum chemical study performed for the 1,2-ethylenediamine dihydrochloride salt Electronic supplementary material The online version of this article (doi:10.1007/s00894-015-2818-7) contains supplementary material, which is available to authorized users. [26], for instance, the authors verified that accounting for the interactions between the protonated amine groups and the surrounding chloride counterions is essential for an accurate prediction of the corresponding vibrational spectra. The explicit consideration of the counterions is, however, associated to significant computational costs that may render calculations unfeasible.…”

“…Characterization of both free ligands and metal complexes has been performed by vibrational spectroscopy (Raman, Fourier transform infrared (FTIR) and inelastic neutron scattering (INS)) coupled to quantum chemical calculations [24][25][26][27][28][29][30][31][32][33][34].…”

Vibrational spectroscopy studies on linear polyamines

“…The homologous series of the linear α,ω-diamines [H 2 N(CH 2 ) n NH 2 ] (n = 2-10, n = 12) and the tri-and tetramines spermidine and spermine ( Figures 1A-1C) were studied in order to achieve a thorough knowledge of their structural preferences, both for their unprotonated and Nprotonated forms [24][25][26][27][28][29][30][31][32][33]. Several theoretical molecular models were proposed for an accurate representation of these linear polyamines, yielding the best possible agreement with the experimental data (both vibrational spectroscopy results and reported X-ray structures).…”