VO²⁺–hydroxyapatite complexes as models for vanadyl coordination to phosphate in bone

Abstract

We describe a 1D and 2D ESEEM investigation of VO2+ adsorbed on hydroxyapatite (HA) at different concentrations and compare with VO2+-triphosphate (TPH) complexes studied previously in detail, in an effort to provide more insight into the structure of VO2+coordination in bone. Structures of this interaction are important because of the role of bone in the long-term storage of administered vanadium, and the likely role of bone in the steady-state release of vanadium leading to the chronic insulin-enhancing anti-diabetic effects of vanadyl complexes. Three similar sets of cross-peaks from phosphorus nuclei observed in the 31P HYSCORE spectra of VO2+-HA, VO2+-TPH, and VO2+-bone suggest a common tridentate binding motif for triphosphate moieties to the vanadyl ion. The similarities between the systems present the possibility that in vivo vanadyl coordination in bone is relatively uniform. Experiments with HA samples containing different amounts of adsorbed VO2+ demonstrate additional peculiarities of the ion-adsorbent interaction which can be expected in vivo. HYSCORE spectra of HA samples show varying relative intensities of 31P lines from phosphate ligands and 1H lines, especially lines from protons of coordinated water molecules. This result suggests that the number of equatorial phosphate ligands in HA could be different depending on the water content of the sample and the VO2+ concentration; complexes of different structure probably contribute to the spectra of VO2+-HA. Similar behavior can be also expected in vivo during VO2+ accumulation in bones.

The structural basis of action of vanadyl (VO2+) chelates in cells

“…They have suggested that the vanadyl (VO 2+ ) ion is coordinated in a tridentate, structural motif by a triphosphate group providing both equatorial and axial oxygen-donor atoms [105, 106]. Figure 16 illustrates the coordination environment of VO 2+ incorporated into the hydroxyapatite matrix of mineralized bone tissue compatible with the results of ESEEM studies [105, 106]. Examples of phosphate groups axially coordinated to VO 2+ have not been previously observed.…”

“…Of considerable interest is that Dikanov and coworkers have analyzed the superhyperfine couplings of 1 H and 31 P nuclei in the vicinity of VO 2+ sites measured by application of ESEEM spectroscopy. They have suggested that the vanadyl (VO 2+ ) ion is coordinated in a tridentate, structural motif by a triphosphate group providing both equatorial and axial oxygen-donor atoms [105, 106]. Figure 16 illustrates the coordination environment of VO 2+ incorporated into the hydroxyapatite matrix of mineralized bone tissue compatible with the results of ESEEM studies [105, 106].…”

Chromium Environment within Cr-Doped Silico-Aluminophosphate Molecular Sieves from Spin Density Studies

“…Such a dispersion of isotropic hyperfine coupling constants, i.e., "a-strain," has been observed previously in both solid-state 16,39 and molecular systems. 40,41 It results from structural fluctuations of the ligand environment around the paramagnetic metal center, which, in our case, can be associated with different locations of Cr 5+ in the lattice, where it experiences slightly different coordination geometries as indicated by DFT calculations (vide infra). The isotropic hyperfine couplings can thus be explained in terms of spin density transfer to 27 Al ions in the second coordination sphere through directly coordinated oxygens and are particularly sensitive to structural variations, the values depending markedly on the M−O−Al bond angle and distance.…”

Identification of LiPF6Decomposition Products in Li‐Ion Batteries with Endogenous Vanadyl Sensors Using Pulse Electron Paramagnetic Resonance and Density Functional Theory

“…[29] Unfortunately, references for the comparison of experimental and calculated 31 P hyperfine values for vanadyl ions are scarce. [39,40] Analyzing the experimental HYSCORE spectrum, relative amplitudes cannot be used to estimate the ratio of 31 P, 19 F, and 1 H because the system is overparameterized. First, the amplitudes for specific nuclei and specific hyperfine characteristics are nontrivial.…”