Insights into Antiradical Behavior: Crystal Structures and DFT Analysis of 2-Formylpyridine N4-Allylthiosemicarbazone Salts

Abstract

In this paper, six new salts of 2-formylpyridine N⁴-allylthiosemicarbazone ([H₂L]X⸱nH₂O, where X is NO₃^- (1), NH₂SO₃^- (2), Cl^- (3), Cl₃CCOO^- (4), Cl₂CHCOO^- (5), ClCH₂COO^- (6); n = 0 (1, 3, 5, 6), 1 (2, 4)) were synthesized and physico-chemically characterized by elemental analysis, molar conductivity measurements, FT-IR studies, ¹H and ¹³C NMR. The crystal structures of compounds 1-5 were determined by single-crystal X-ray diffraction. Analysis of crystal data shows that the structures of these compounds consist of protonated thiosemicarbazone H₂L⁺, anions of acid residue and water molecules in 2 and 4. These compounds manifest antiradical activity toward ABTS^•+ cation radicals that exceeds the activity of non-protonated thiosemicarbazone HL and trolox, that is used in medicine. The most active one is compound [H₂L]Cl (3) with IC₅₀ value 9.9 μmol/L. Density Functional Theory calculations showed that the electronic structure of cation H₂L⁺ is more favorable for electron acceptation if compared with HL.