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, ¹ H, ¹⁹ F 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 ¹⁹ F 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 ²⁹ Si-¹⁹ F (J(²⁹ Si-¹⁹ F) = 107.5 Hz (II), 107.6 Hz (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 ].

Keywords: biological activity; crystal structure; hydrogen bonds; pyridinium hexafluorosilicates; solubility.