Jan Hanss

Bromine K-edge EXAFS studies of bromide binding to bromoperoxidase from Ascophyllum nodosum

Bromine K‐edge EXAFS studies have been carried out for bromide/peroxidase samples in Tris buffer at pH 8. The results are compared with those of aqueous (Tris‐buffered) bromide and vanadium model compounds containing Br‐V, Br‐C(aliphatic) and Br‐C(aromatic) bonds. It is found that bromide does not coordinate to the vanadium centre. Rather, bromine binds covalently to carbon. A possible candidate is active site serine.

Water and bromide in the active center of vanadate-dependent haloperoxidases.

Two aqua-oxovanadium complexes, viz. [A-VO(H2O)(sal-L-Leu)] (1) and [VO(H2O)2(5-Br-sal-Gly)] x H2O(2 x H2O), containing the water ligands in cis- and trans-positions to the oxo group at V-OH2 distances ranging from 2.008 to 2.228 A, have been structurally characterized in order to model the apical electron density feature found in the structures of fungal and algal vanadate-dependent peroxidases. Br K-edge XAS of bromide-treated bromoperoxidase from Ascophyllum nodosum and model compounds (including 2 x H2O) has been used to show that the substrate bromide does not bind to active site vanadium but to a light atom, possibly carbon, in its vicinity.

CuN6 Jahn–Teller centers in coordination frameworks comprising fully condensed Kuratowski-type secondary building units: phase transitions and magneto-structural correlations

The metal-organic framework [Cu(ta)(2)] (Hta = 1H-1,2,3-triazole), containing Jahn-Teller active Cu(II) ions and 1,2,3-triazolate ligands, is prepared under solvothermal reaction conditions. The compound shows a reversible phase transition from the tetragonal crystal system (α-[Cu(ta)(2)]: space group I4(1)/amd (no. 141), a = 11.8447(7) Å, c = 18.9782(13) Å, V = 2662.6(3) Å(3)) to the cubic crystal system (β-[Cu(ta)(2)]: space group Fd3m (no. 227), a = 17.4416(15) Å, V = 5305.9(8) Å(3)) within the temperature range of 120-160 °C. Both [Cu(ta)(2)] polymorphs have identical bonding topologies that might be described as fully condensed Kuratowski-type pentanuclear secondary building units of local T(d) point group symmetry in which four Cu(II) ions occupy the vertices of an imaginary tetrahedron. α-[Cu(ta)(2)], as opposed to the high-temperature β-phase, shows a strong tetragonal Jahn-Teller distortion of CuN(6) coordination octahedra. The compounds are characterized by elemental and thermogravimetric analyses, single crystal and powder X-ray diffraction, FTIR-, UV-vis and fluorescence spectroscopy. Magnetic susceptibility investigations reveal two different Cu(II) sites at a ratio of 1 : 2, in agreement with the solid state structure of [Cu(ta)(2)]. At low temperatures the formation of antiferromagnetically coupled Cu(II) dimers is observed, leading to a spin frustration of roughly 1/3 of all magnetically active Cu(II) sites.

Two Ti-doped distrontium ruthenium tetraoxides: Sr2Ru0.93Ti0.07O4 and Sr2Ru0.81Ti0.19O4.

Crystals of titanium-doped distrontium ruthenium tetraoxide, Sr(2)Ru(1-x)Ti(x)O(4), with x = 0.07 and 0.19, were grown by floating-zone melting, and their structures were solved using single-crystal X-ray diffraction. Increasing Ti content leads to a distinctive systematic variation of cell parameters and interatomic distances with respect to the undoped material.

An organometallic chimie douce approach to new RexW1−xO3 phases

Re(x)W(1-x)O3.H2O and Re(x)W(1-x)O3 phases are prepared by a new organometallic chimie douce concept employing the organometallic precursor methyltrioxorhenium.