Salicylate-functionalized bismuth oxido clusters: Hydrolysis processes and microbiological activity

Hydrolysis of either Bi(HSal4Me)3 (A) or [Bi22O26(HSal4Me)14](B) in dmso gave the 4-methylsalicylate-substituted bismuth oxido cluster [Bi38O45(HSal4Me)24(dmso)14(H2O)2]·4H2O (1·4H2O), which crystallizes in the triclinic space group P with cell parameters of a = 20.7214(5), b = 20.9654(6), c = 22.2128(6) A, α = 100.867(2), β = 114.108(2), γ = 107.895(2)° and V = 7815.1(4) A3. The hydrolysis of A was studied by using 1H DOSY NMR spectroscopy and electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry, both of which showed the formation of several larger species under ambient conditions in the presence of moisture. Furthermore, ESI-FTICR MS analysis of cluster B showed the formation of mainly {Bi23O26} species, which indicates the partial dissociation of cluster B in solution. In addition, the three different bismuth species containing 1 (A), 22 (B) or 38 (1·4H2O) bismuth atoms per molecular formula were tested for their microbiological activity against three strains of Helicobacter pylori (251, 26695 and B128). A minimum inhibitory concentration (MIC) of 6.25 μg mL–1 for the mononuclear bismuth complex A was obtained, whereas the bismuth oxido cluster B showed a lower activity with MIC values in the range 25–50.0 μg mL–1. The activity of 1·4H2O is comparable to commercial remedies based on antimicrobial bismuth subsalicylate (BSS; 12.5 μg mL–1).