Interaction Study and Reactivity of ZrIV-Substituted Wells-Dawson Polyoxometalate towards Hydrolysis of Peptide Bonds in Surfactant Solutions

The interaction between the 1:2 Zr-IV:Wells-Dawson complex, K15H[Zr((2)-P2W17O61)(2)] (1), and a range of surfactants was studied in detail with the aim of developing metal-substituted POMs as potential artificial proteases for membrane proteins. The surfactants include the positively charged cetyl(trimethyl)ammonium bromide (CTAB), the negatively charged sodium dodecyl sulfate (SDS), the neutral Triton X-100 (TX-100), and zwitterionic 3-[dodecyl(dimethyl)ammonio]-1-propanesulfonate (Zw3-13) and 3-[dimethyl(3-{[(3,5,7,12)-3,7,12-trihydroxy-24-oxocholan-24-yl]amino}propyl)ammonio]-1-propanesulfonate (CHAPS). A combination of multinuclear H-1, C-13, and (PNMR)-P-31 spectroscopy, H-1 diffusion-ordered NMR spectroscopy ((HDOSY)-H-1), and nuclear Overhauser effect spectroscopy (NOESY) was used to examine the interaction between 1 and each surfactant on the molecular level. Cationic surfactant CTAB caused precipitation of 1 due to strong electrostatic interactions, while the anionic SDS and neutral TX-100 surfactants did not exhibit any interaction at neutral pD. (HDOSY)-H-1 NMR spectroscopy indicated an interaction between 1 and zwitterionic surfactants Zw3-12 and CHAPS, which occurs via the positively charged ammonium group in the surfactant molecule. In the presence of anionic, neutral, and zwitterionic surfactants, 1 preserves its catalytic activity towards the hydrolysis of the peptide bond in the dipeptide glycyl-l-histidine (GH). The fastest hydrolysis was observed at pD7.0 and could be rationalized by taking into account pD-dependent speciation of 1 and coordination properties of GH.