Coulomb-potential-dependent decohesion of Magnéli phases.

Transition metal oxide Magnéli phases are traditionally described as crystallographic shear structures. Some of these phases feature a layered crystal structure based on deformed metal-oxygen octahedra. Here, we describe the correlation between structure, decohesion energies and elastic properties of WO(3), ReO(3), MoO(2), VO(2), V(2)O(5) and TiO(2) using ab initio calculations. Decohesion energies and elastic constants C(44) are inversely proportional to the original distance between the cleaved layers and correspond to the screened Coulomb potential. This can be understood based on the electronic structure. The bond strength decreases rapidly as the distance is increased, resulting in weak coupling between the layers, which in turn causes the formation of easily plastically deformable structures.

Ab initio calculations of the structure and mechanical properties of vanadium oxides.

VO, V(2)O(3), VO(2), V(6)O(13), V(4)O(9), V(3)O(7) and V(2)O(5) have been investigated in terms of structure, bulk modulus B and elastic constant C(44) using ab initio calculations. The C(44) values for V(6)O(13), V(4)O(9), V(3)O(7) and V(2)O(5) are significantly lower than those for V(2)O(3) and VO(2). As the V valency is increased from 3 to 5, C(44) decreases by 83%, whereas the bulk modulus decreases by 61%, leading to an increase in the B/C(44) ratio from 1.4 to 3.4. This is consistent with calculated decohesion energies for cleavage in VO(2) and V(2)O(5). When cleaving V(2)O(5), decohesion energies are considerably lower than those of VO(2). This behaviour may be understood based on V valency induced changes in the crystal and electronic structure as well as in the chemical bonding. As the V valency is increased, the bond strength decreases. The phases with a V valency >4 exhibit low C(44) values, large anisotropy and possess weak ionic bonding between the layers. The formation of easily plastically deformable structures is enabled by the screened Coulomb potential. The largest distance and therefore weakest bond strength is observed for V(2)O(5) in the (002) plane.

Ba3Li2V2O7Cl4, a new vanadate with a channel structure.

The tribarium dilithium divanadate tetrachloride Ba(3)Li(2)V(2)O(7)Cl(4) is a new vanadate with a channel structure and the first known vanadate containing both Ba and Li atoms. The structure contains four non-equivalent Ba(2+) sites (two with m and two with 2/m site symmetry), two Li(+) sites, two nonmagnetic V(5+) sites, five O(2-) sites (three with m site symmetry) and four Cl(-) sites (m site symmetry). One type of Li atom lies in LiO(4) tetrahedra (m site symmetry) and shares corners with VO(4) tetrahedra to form eight-tetrahedron Li(3)V(5)O(24) rings and six-tetrahedron Li(2)V(4)O(18) rings; these rings are linked within porous layers parallel to the ab plane and contain Ba(2+) and Cl(-) ions. The other Li atoms are located on inversion centres and form isolated chains of face-sharing LiCl(6) octahedra.

Immobilized DNA aptamers used as potent attractors for porcine endothelial precursor cells.

Because of their insufficient biocompatibility and high thrombogenicity, small diameter artificial vascular prostheses still do not show a satisfactory patency rate. In vitro endothelialization of artificial grafts before implantation has been established experimentally years ago, but, this procedure is extremely time consuming and expensive. This study deals with the coating of graft surfaces with capture molecules (aptamers) for circulating endothelial progenitor cells (EPCs), mimicking a prohoming substrate to fish out EPCs from the bloodstream after implantation and to create an autologous functional endothelium. Using the SELEX technology, aptamers with a high affinity to EPCs were identified, isolated, and grafted onto polymeric discs using a blood compatible star-PEG coating. A porcine in vitro model that demonstrates the specific adhesion of EPCs and their differentiation into vital endothelial-like cells within 10 days in cell culture is presented. We suggest that the rapid adhesion of EPCs to aptamer-coated implants could be useful to promote endothelial wound healing and to prevent increased neointimal hyperplasia. We hypothesize that future in vivo self-endothelialization of blood contacting implants by homing factor mimetic capture molecules for EPCs may bring revolutionary new perspectives towards clinical applications of stem cell and tissue engineering strategies.

Synthesis and structural characterization of BaV4O9.

The new spin (1/2) V(4+) barium oxovanadate BaV(4)O(9) was synthesized and studied by means of single-crystal X-ray diffraction. Its room-temperature structure is monoclinic, space group P2/c. We discuss the temperature evolution of the crystal structure and thermal expansion tensor of the material between 293 and 100 K.