The Smallest Polyoxotungstate Retained by TRIS-Stabilization

Abstract

A polycondensation reaction of the orthotungstate anion WO 4 2– , buffered at pH 7.5 in a TRIS-HCl (0.15 M) solution, results in the first example of a discrete polyoxotungstate anion, with just two W ions stabilized with TRIS ligands. It was isolated and characterized as Na 2 [W VI 2 O 6 (C 4 O 3 NH 10 ) 2 ]·6H 2 O by single-crystal and powder X-ray diffraction, FT-IR spectroscopy, thermogravimetrical analysis (TGA), and elemental analysis in solid state and by electro-spray ionization mass spectrometry (ESI-MS), 13 C, and 183 W NMR, as well as Raman spectroscopy in solution. This synthesis demonstrates the crucial and new role of the added tris-alkoxy ligand in the development of a new hybrid TRIS-isopolytungstate with the lowest known nuclearity (so far) and the terminal oxygens substituted with two nitrogen atoms arising from amines of the TRIS ligands.

Regioselective protein oxidative cleavage enabled by enzyme-like recognition of an inorganic metal oxo cluster ligand

“…Given that ZrK competes with Cu II WD for the same binding sites 32 , 71 , the decrease observed strongly suggest that the binding of Cu II WD to HEWL is crucial for the reaction. Additionally, the oxidative cleavage reaction was conducted in presence of a high concentration of the Tris buffer solution (100 mM tris-HCl pH 7.5), as the Tris buffer has been previously reported to act as a shield around POMs 81 . The amount of cleavage observed by SDS-PAGE was negligible (Supplementary Fig.…”

Tris-decorated multi-iron polyoxotungstates

“…17 The Tris anchoring mode in 1 and 2 is also extremely unusual for POMs as the vast majority of known triol-functionalized polyanions comprise a triol ligand bound in a symmetrical way via all three -CH 2 OH groups [7][8][9][10][11][12] or via one or two -CH 2 OH groups and a terminal -NH 3 + functionality. 13 Solutions of NT-1 and NT-2 in 1 M Tris buffer ( pH 8.0) strongly absorb UV-light with the maximum at 219 nm, which is followed by a distinct absorption shoulder at around 260-270 nm and a broad not well-defined shoulder at 350 nm. The absorption of visible light for NT-1 solution is characterized by a well-pronounced shoulder at 490 nm, while for NT-2 such a shoulder is absent and one can distinguish only very weak absorption without any well-defined characteristics (see Fig.…”

“…12 Another example is a smaller [W VI 2 O 6 (Tris) 2 ] 2− POT, where Tris ligands condense directly to W VI centers, which exhibits a unique connection mode via one –CH 2 OH and the –NH 2 group acting in this POT as a primary amine. 13…”

“…The Tris anchoring mode in 1 and 2 is also extremely unusual for POMs as the vast majority of known triol-functionalized polyanions comprise a triol ligand bound in a symmetrical way via all three –CH 2 OH groups 7–12 or via one or two –CH 2 OH groups and a terminal –NH 3 + functionality. 13…”