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Publication Abstract from PubMed

We report on the synthesis of the tetrasubstituted sandwich-type Keggin silicotungstates as the pure Na salts Na14[(A-alpha-SiW10O37)2{Co4(OH)2(H2O)2}].37H2O (Na{SiW10Co2}2) and Na14[(A-alpha-SiW10O37)2{Ni4(OH)2(H2O)2}].77.5H2O (Na{SiW10Ni2}2), which were prepared by applying a new synthesis protocol and characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Proteinase K was applied as a model protein and the polyoxotungstate (POT)-protein interactions of Na{SiW10Co2}2 and Na{SiW10Ni2}2 were studied side by side with the literature-known K5Na3[A-alpha-SiW9O34(OH)3{Co4(OAc)3}].28.5H2O ({SiW9Co4}) featuring the same number of transition metals. Testing the solution behavior of applied POTs under the crystallization conditions (sodium acetate buffer, pH 5.5) by time-dependent UV/vis spectroscopy and electrospray ionization mass spectrometry speciation studies revealed an initial dissociation of the sandwich POTs to the disubstituted Keggin anions HxNa5-x[SiW10Co2O38](3-) and HxNa5-x[SiW10Ni2O38](3-) ({SiW10M2}, M = Co(II) and Ni(II)) followed by partial rearrangement to the monosubstituted compounds (alpha-{SiW11Co} and alpha-{SiW11Ni}) after 1 week of aging. The protein crystal structure analysis revealed monosubstituted alpha-Keggin POTs in two conserved binding positions for all three investigated compounds, with one of these positions featuring a covalent attachment of the POT anion to an aspartate carboxylate. Despite the presence of both mono- and disubstituted anions in a crystallization mixture, proteinase K selectively binds to monosubstituted anions because of their preferred charge density for POT-protein interaction.

Speciation of Transition-Metal-Substituted Keggin-Type Silicotungstates Affected by the Co-crystallization Conditions with Proteinase K.,Breibeck J, Tanuhadi E, Gumerova NI, Giester G, Prado-Roller A, Rompel A Inorg Chem. 2021 Oct 18;60(20):15096-15100. doi: 10.1021/acs.inorgchem.1c02005., Epub 2021 Sep 16. PMID:34529407^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.