Synthesis, characterization and antibacterial properties of two POM-based supramolecular compounds with the natural active ingredient: (THB)3(H5PMo12O40) and (THB)3(H3PW12O40)

Two supramolecular compounds of Keggin POMs supporting the natural active ingredient, (THB)(3)(H5PMo12O40) (1) and (THB)(3)(H3PW12O40) (2) (THB = tetrahydroberberine), have been synthesized and characterized by X-ray single-crystal diffraction, elemental analyses, IR, XRPD and TGA. A crystallization screening of a series of pH value and stoichiometric ratio combinations was performed in order to investigate the synthetic conditions of two compounds. Compound 1 was synthesized at pH = 1.5 and has a 3:7 stoichiometric ratio, in which THB molecules exist two configurations and link to polyanion via 14 H-bonds. Compound 2 was obtained at a relatively high pH (pH = 2.0) and has the same stoichiometric ratio as 1, in which THB molecules exist only one configuration and link to polyanion via 8 H-bonds. The discrepancies of pH values, and volumes and oxygen basicities of polyanions could significantly affect the number of H-bonds between POMs and THBs, and then the number of H-bonds may affect configurations of THB molecules. This result implicitly indicates that it is providing a new thought and method for chiral resolution of (+/-)-tetrahydroberberine. Additionally, two title compounds show advantages in terms of antibacterial properties against Staphylococcus aureus and Escherichia coli in comparison to their corresponding parent compounds. (C) 2016 Elsevier B.V. All rights reserved.