X-ray absorption spectroscopy study of the solvation structure of zinc(II) in dimethyl sulfoxide solution

The influence of ZnII coordination sphere and chemical structure over the reactivity of metallo-β-lactamase model compounds

The first coordination sphere influences the reactivity of metallo-β-lactamase monozinc model complexes.

Insulin fibrillation: The influence and coordination of Zn2

Protein amyloid fibrillation is obtaining much focus because it is connected with amyloid-related human diseases such as Alzheimer's disease, diabetes mellitus type 2, or Parkinson's disease. The influence of metal ions on the fibrillation process and whether it is implemented in the amyloid fibrils has been debated for some years. We have therefore investigated the influence and binding geometry of zinc in fibrillated insulin using extended X-ray absorption fine-structure and X-ray absorption near-edge structure spectroscopy. The results were validated with fibre diffraction, Transmission Electron Microscopy and Thioflavin T fluorescence measurements. It is well-known that Zn²⁺ ions coordinate and stabilize the hexameric forms of insulin. However, this study is the first to show that zinc indeed binds to the insulin fibrils. Furthermore, zinc influences the kinetics and the morphology of the fibrils. It also shows that zinc coordinates to histidine residues in an environment, which is similar to the coordination seen in the insulin R₆ hexamers, where three histidine residues and a chloride ion is coordinating the zinc.

Solvation structure of the halides from x-ray absorption spectroscopy

Three-dimensional models for the aqueous solvation structures of chloride, bromide, and iodide are reported. K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near edge (MXAN) analyses found well-defined single shell solvation spheres for bromide and iodide. However, dissolved chloride proved structurally distinct, with two solvation shells needed to explain its strikingly different X-ray absorption near edge structure (XANES) spectrum. Final solvation models were as follows: iodide, 8 water molecules at 3.60 ± 0.13 Å and bromide, 8 water molecules at 3.40 ± 0.14 Å, while chloride solvation included 7 water molecules at 3.15 ± 0.10 Å, and a second shell of 7 water molecules at 4.14 ± 0.30 Å. Each of the three derived solvation shells is approximately uniformly disposed about the halides, with no global asymmetry. Time-dependent density functional theory calculations simulating the chloride XANES spectra following from alternative solvation spheres revealed surprising sensitivity of the electronic state to 6-, 7-, or 8-coordination, implying a strongly bounded phase space for the correct structure during an MXAN fit. MXAN analysis further showed that the asymmetric solvation predicted from molecular dynamics simulations using halide polarization can play no significant part in bulk solvation. Classical molecular dynamics used to explore chloride solvation found a 7-water solvation shell at 3.12 (-0.04/+0.3) Å, supporting the experimental result. These experiments provide the first fully three-dimensional structures presenting to atomic resolution the aqueous solvation spheres of the larger halide ions.

K-edge XANES investigation of octakis(DMSO)lanthanoid(III) complexes in DMSO solution and solid iodides

The potential of high energy XANES (X-ray absorption near edge structure) as a tool for the structural analysis of lanthanoid-containing systems has been explored. The K-edge XANES spectra of La(3+), Gd(3+), and Lu(3+) ions both in DMSO solution and solid octakis(DMSO)lanthanoid(III) iodides have been analysed. Although the K-edges of lanthanoids cover the energy range of 38 (La) to 65 (Lu) keV, the large widths of the core hole states do not appreciably reduce the potential structural information of the XANES data. We show that, for lanthanoid compounds, accurate structural parameters are obtained from the analysis of K-edge XANES signals if a deconvolution procedure is carried out. We found that in solid octakis(DMSO)lanthanoid(III) iodides the Ln(3+) ions are coordinated by eight DMSO ligands arranged in a quite symmetric fashion. In DMSO solution the Ln(3+) ions retain a regular eight-coordination structure and the coordination number does not change along the series. In contrast to when in water the second coordination shell has been found to provide a negligible contribution to the XANES spectra of Ln(3+) ions in DMSO solution.