We have examined the influence of osteocalcin, one of the 10 most abundant proteins of the human body, on hydroxyapatite (HAP, Ca10(PO4)6(OH)2) formation. Different functions in biomineralization are attributed to the bone-specific protein osteocalcin because of its Ca2+ binding including HAP binding properties and its capability to inhibit HAP precipitation. To study nucleation and crystal growth, a model system with osteocalcin-controlled dissolution−reprecipitation of brushite (DCPD, CaHPO4·2H2O) to HAP has been investigated. After DCPD crystals were grown from aqueous solution, they were exposed to an osteocalcin-containing buffer solution of pH 7.4. Thin apatite-like crystals with hexagonal symmetry grew on the (010) brushite planes. The apatite (0001) planes were fully covered with osteocalcin molecules. Thus, osteocalcin has been found to regulate HAP formation in two different ways:  (i) it accelerates nucleation, and (ii) it acts as a specific inhibitor of the apatite (0001) plane, supressing crystal growth perpendicular to this plane. A stress-induced growth model was developed illustrating HAP growth along the brushite−HAP interface considering compressions in the protein-covered HAP crystals.

No abstract

Se,NBr,, a planar molecule shaped liked dividers, was formed by the reaction of SeBr, with N(SiMe,), , which reduced the selenium to the trivalent state. Under the same conditions, Se,NCI, was obtained by the reaction of SeCI, with N(SiMe,),, retaining the tetravalent state of selenium. The molecule is formed by two edge-sharing pseudotrigonal bipyramids with selenium as their central atoms. Se,NCI, reacts with PPh,CI to form the Se,NCI, ion by the addition of a CIion to only one of the two selenium atoms, resulting in pseudooctahedral coordination of this atom. Ab initio calculations for all the compounds reported confirm the experimentally determined structures.

Die Kristallstrukturen der Titelverbindungen wurden röntgenographisch ermittelt. SeCl3+SbCl6−: Raumgruppe P21/m, Z = 4, Strukturlösung mit 1795 beobachteten unabhängigen Reflexen, R = 0,022. Gitterkonstanten bei −80°C: a = 940,9; b = 1066,3; c = 1234,9 pm; β = 102,79°. Die Verbindung bildet Ionenpaare mit der Struktur eines flächenverknüpften Doppeloktaeders. SeBr3+GaBr4−: Raumgruppe Pc, Z = 2, Strukturlösung mit 1461 beobachteten unabhängigen Reflexen, R = 0,058, Gitterkonstanten bei −60°C: a = 660,1; b = 655,3; c = 1431,3 pm; α = 101,17°. Die Verbindung kristallisiert im SCl3[AlCl4]‐Strukturtyp. Zwischen den Ionen bestehen zwei relativ kurze Se … BrGa‐Kontakte. PCl4+SeCl5−: Raumgruppe Ima2, Z = 8, Strukturlösung mit 1757 beobachteten unabhängigen Reflexen, R = 0,029. Gitterkonstanten bei −50°C; a = 1651,6; b = 1201,2; c = 1166,4 pm. Die SeCl5− ‐Ionen sind über interionische SeCl … Se‐Kontakte entlang der kristallographischen c‐Achse zu Ketten assoziiert. (PPh4+)2SeCl42− · 2CH3CN: Raumgruppe P21/n, Z = 2, Strukturlösung mit 2578 beobachteten unabhängigen Reflexen, R = 0,050. Gitterkonstanten bei −80°C: a = 1288,5; b = 726,0; c = 2585,8 pm; β = 101,65°. Die Verbindung enthält planar‐quadratische SeCl42−‐Ionen, die nahezu D4h‐Symmetrie erfüllen.

Shielding by four TeCl molecules is observed for the distorted rhombic dodecahedron core of the tellurium nitride Te N (see picture). With the characterization of this structure, the composition of the tellurium nitride discovered 100 years ago has now been determined. As a result of the shielding effect, the explosive character of the nitride is lost.