Speciation of Transition-Metal-Substituted Keggin-Type Silicotungstates Affected by the Co-crystallization Conditions with Proteinase K

Abstract

We report on the synthesis of the tetrasubstituted sandwich-type Keggin silicotungstates as the pure Na salts Na 14 [(A-α-SiW 10 O 37 ) 2 {Co 4 (OH) 2 (H 2 O) 2 }]·37H 2 O ( Na{SiW 10 Co 2 } 2 ) and Na 14 [(A-α-SiW 10 O 37 ) 2 {Ni 4 (OH) 2 (H 2 O) 2 }]·77.5H 2 O ( Na{SiW 10 Ni 2 } 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{SiW 10 Co 2 } 2 and Na{SiW 10 Ni 2 } 2 were studied side by side with the literature-known K 5 Na 3 [A-α-SiW 9 O 34 (OH) 3 {Co 4 (OAc) 3 }]·28.5H 2 O ( {SiW 9 Co 4 } ) 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 H x Na 5– x [SiW 10 Co 2 O 38 ] 3– and H x Na 5– x [SiW 10 Ni 2 O 38 ] 3– ( {SiW 10 M 2 } , M = Co II and Ni II ) followed by partial rearrangement to the monosubstituted compounds ( α-{SiW 11 Co} and α-{SiW 11 Ni} ) after 1 week of aging. The protein crystal structure analysis revealed monos...

Exploiting Interactions between Polyoxometalates and Proteins for Applications in (Bio)chemistry and Medicine

“…X‐ray diffraction has become an indispensable tool in understanding POM‐protein interactions on a near‐atomic level. Co‐crystallization of POMs has been reported with several different proteins, such as human serum albumin (HSA), [34] hen egg white lysozyme (HEWL), [26, 29, 39] and the proteinase K enzyme [40, 41] . To date, more than 70 crystal structures of proteins with POMs have been deposited in the protein data bank (PDB), of which almost 50 % have been deposited in the last 5 years, demonstrating the increasing interest in elucidating POM‐protein interactions.…”

“…Co-crystallization of POMs has been reported with several different proteins, such as human serum albumin (HSA), [34] hen egg white lysozyme (HEWL), [26,29,39] and the proteinase K enzyme. [40,41] To date, more than 70 crystal structures of proteins with POMs have been deposited in the protein data bank (PDB), of which almost 50 % have been deposited in the last 5 years, demonstrating the increasing interest in elucidating POM-protein interactions. This increasing number of crystal structures has provided valuable molecular-level insight into the complex interactions between POMs and proteins.…”