67Zn solid-state NMR spectroscopy of ([Tp But,Me]Zn(OH2))[HOB(C6F5)3]. the importance of the anion [HOB(C6F5)3]-.
One of the paradigms of Zn2+ metallobiochemistry is that coordination of water to Zn2+ provides a mechanism of activation that involves lowering the pKa by approximately 7 pH units. This idea has become central to the development of mechanisms of action for zinc metalloproteins. However, the direct measurement of the pKa of water bound to Zn2+ in a metalloprotein has yet to be accomplished. Developing models for Zn2+-OH2 species has been a significant challenge, but we have utilized solid-state 67Zn NMR spectroscopy as a means to characterize one of the few examples of water bound to mononuclear tetrahedral Zn2+: ([Tp(But,Me)]Zn(OH2))[HOB(C6F5)3]. The measured quadrupole coupling (Cq) constant is 4.3 MHz with an asymmetry parameter of etaq of 0.6. Likewise, due to the small value of Cq, anisotropic shielding also contributed to the observed 67Zn NMR lineshape. As expected, the computed values of the magnetic resonance parameters depend critically on the nature of the anion. The predicted value of Cq for ([Tp(But,Me)]Zn(OH2))[HOB(C6F5)3] is -4.88 MHz. We discuss the results of these calculations in terms of the nature of the anion, the local electrostatics, and its subsequent hydrogen bonding to [Tp(But,Me)]Zn(OH2)+.
Lipton
Andrew S
AS
Biological Sciences Division, Pacific Northwest National Laboratories, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Morlok
Melissa M
MM
Parkin
Gerard
G
Ellis
Paul D
PD
D000838:Anions / Q000737:chemistry*; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*; D015033:Zinc Isotopes
D000838:Anions; D009942:Organometallic Compounds; D015033:Zinc Isotopes; D015032:Zinc