Oxo-Replaced Polyoxometalates: There Is More than Oxygen

The presence of oxo-ligands is one of the main required characteristics for polyoxometalates (POMs), although some oxygen ions in a metallic environment can be replaced by other nonmetals, while maintaining the POM structure. The replacement of oxo-ligands offers a valuable approach to tune the charge distribution and connected properties like reducibility and hydrolytic stability of POMs for the development of tailored compounds. By assessing the reported catalytic and biological applications and connecting them to POM structures, the present review provides a guideline for synthetic approaches and aims to stimulate further applications where the oxo-replaced compounds are superior to their oxo-analogues. Oxo-replacement in POMs deserves more attention as a valuable tool to form chemically activated precursors for the synthesis of novel structures or to upgrade established structures with extraordinary properties for challenging applications

The crystallization additive hexatungstotellurate promotes the crystallization of the HSP70 nucleotide binding domain into two different crystal forms

<div><p>The use of the tellurium-centered Anderson−Evans polyoxotungstate [TeW₆O₂₄]⁶⁻ (TEW) as a crystallization additive has been described. Here, we present the use of TEW as an additive in the crystallization screening of the nucleotide binding domain (NBD) of HSP70. Crystallization screening of the HSP70 NBD in the absence of TEW using a standard commercial screen resulted in a single crystal form. An identical crystallization screen of the HSP70 NBD in the presence of TEW resulted in both the “TEW free” crystal form and an additional crystal form with a different crystal packing. TEW binding was observed in both crystal forms, either as a well-defined molecule or in overlapping alternate positions suggesting translational disorder. The structures were solved by both molecular replacement and single wavelength anomalous diffraction (SAD) using the anomalous signal of a single bound molecule of TEW. This study adds one more example of TEW binding to a protein and influencing its crystallization behavior.</p></div

Data collection and refinement statistics.

<p>Data collection and refinement statistics.</p

TEW bound to HSP70 at a crystal contact (crystal form 2, site 1).

<p>HSP70 is colored cyan, the symmetry related HSP70 is colored grey. The two alternate positions are shown with oxygen atoms colored red or yellow. 2Fo-Fc electron density (contoured at 2 σ) is shown for the TEW molecule.</p

Chemical structure of TEW.

<p>Chemical structure of TEW.</p

Surface potential of crystal form 2, site 1 calculated using APBS.

<p>Surface potential of crystal form 2, site 1 calculated using APBS.</p

Surface potential of crystal form 1 calculated using APBS.

<p>Surface potential of crystal form 1 calculated using APBS.</p

Thermal unfolding (DSF) curves of HSP70 alone and in the presence of ligands.

<p>HSP70 (Tm = 45.23±0.13 K) and combined with ligands TEW (Tm = 44.84 ± 0.33 K), ADP (Tm = 54.48 ± 0.34 K) or ATP (Tm = 53.3 ± 0.24 K). Lines represent the mean of quadruplicate fluorescence intensity measurements; error bars have been omitted for clarity.</p

Surface potential of crystal form 2, site 2 calculated using APBS.

<p>Surface potential of crystal form 2, site 2 calculated using APBS.</p

TEW bound to HSP70 at a crystal contact (crystal form 2, site 2).

<p>HSP70 is shown in cyan, the symmetry related HSP70 and its bound ADP are shown in grey. The two alternate positions of TEW are shown with the oxygen atoms colored in red (position A) or yellow (position B). 2Fo-Fc electron density (contoured at 1.5 σ) is shown for the TEW molecule.</p