Bis(2‐, 3‐, 4‐carboxyethylpyridinium) hexafluorosilicates as potential caries prophylactic agents

Abstract

Interaction of 2‐, 3‐, 4‐carboxyethylpyridines (L1, L2, L3) with fluorosilicic acid results in the corresponding bis(pyridinium) hexafluorosilicates I–III, characterized by elemental analysis, IR, 1H, 19F nuclear magnetic resonance (NMR), and mass spectrometry, solubility data, and X‐ray crystallography. Crystallographic data: Fdd2, Z=8, a = 28.610(2) Å, b = 18.8378(14) Å, c = 7.3236(5) Å (I); P‐1, Z=1, a = 6.2712(4) Å, b = 7.1706(5) Å, c = 10.9721(7) Å, α = 102.514(6)°, β=97.037(5)°, γ=93.640(6)° (II); P21/c, Z=2, a = 10.0345(6) Å, b = 9.8734(5) Å, c = 9.4704(6) Å, β = 94.347(6)° (III). The dominant intermolecular contacts from the Hirshfeld surface analysis are H…F/F…H, H…H, and H…O/O…H with percentages of 33.3%–34.5%, 26.4%–30.0%, and 16.0%–21.8%. The infrared spectra for I–III exhibit stretching vibrations ν(N+H) at 3300–3050 cm–1; stretching and deformation vibrations ν(SiF) and δ(SiF2) for [SiF6]2– anions are registered near 740 cm–1 and in the range of 480–440 cm–1. In the 19F NMR spectra of aqueous solutions of I–III, strong singlet signals of the [SiF6]2– anion were registered at δ(F) = −133.35 ppm (I), –131.43 ppm (II), –129.02 ppm (III) with two satellites due to the spin‐spin interaction 29Si–19F (J(29Si–19F) = 107.5 Hz (II), 107.6Hz (III)). I–III reveal high solubility in water and dimethyl sulfoxide and very poor solubility in methanol and ethanol. All compounds demonstrate noticeable anticaries activity and absence of hepatotoxic effects, and bis(3‐carboxyethylpyridinium) hexafluorosilicate II displays the highest caries‐preventive efficacy, which significantly exceeds values for the reference preparations, NaF and (NH4)2[SiF6].