Group 5 imido complexes derived from diamido-pyridine ligands.

Reaction of the vanadium(V) imide [V(NAr)Cl(3)(THF)] (Ar = 2,6-C(6)H(3)(i)()Pr(2)) with the diamino-pyridine derivative MeC(2-C(5)H(4)N)(CH(2)NHSiMe(2)(t)()Bu)(2) (abbreviated as H(2)N'(2)N(py)) gave modest yields of the vanadium(IV) species [V(NAr)(H(3)N'N' 'N(py))Cl(2)] (1 where H(3)N'N' 'N(py) = MeC(2- C(5)H(4)N)(CH(2)NH(2))(CH(2)NHSiMe(2)(t)()Bu) in which the original H(2)N'(2)N(py) has effectively lost SiMe(2)(t)()Bu (as ClSiMe(2)(t)()Bu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl(3)(py)(2)] (M = Nb or Ta, R = (t)()Bu or Ar) and the dilithium salt Li(2)[N(2)N(py)] (where H(2)N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NHSiMe(3))(2)), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N(2)N(py))(py)] (M = Nb, R = (t)()Bu 2; M = Ta, R = (t)()Bu 3 or Ar 4). The compounds 2-4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N(2)N(py))]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(N(t)()Bu)Cl(N(2)N(py))] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported.

Resorbable bioceramics based on stabilized calcium phosphates. Part II: evaluation of biological response.

Synthetic materials capable of being remodelled in vivo by the same processes responsible for natural bone turnover have long been sought for use as an artificial bone substitute. These materials must ideally combine osteoinductive capacity with the ability to withstand random dissolution at normal physiological pH, while being resorbed by natural cell-mediated processes. Resorbable calcium phosphate based coatings and bulk ceramics have been developed which promote the uniform deposition of new mineralized bone matrix thus enabling rapid integration with the surrounding host bone tissue in vivo. Furthermore, a critical result of this study is the determination that the silicon-stabilized calcium phosphate ceramics are essentially insoluble in biological media but are resorbed when acted upon by osteoclasts. In vitro biological testing and preliminary in vivo testing show that the important features of this new biomaterial are a characteristic calcium phosphate phase composition and a unique microporous morphology.

Resorbable bioceramics based on stabilized calcium phosphates. Part I: rational design, sample preparation and material characterization.

It has long been the goal of biomaterials research in the field of orthopedics to develop synthetic structures exhibiting comprehensive bioactivity. In particular, an ideal bone-biomaterial would support the activity of osteoblasts in the development of new bone, while simultaneously being resorbed by osteoclasts as part of the lifelong orderly process of bone remodelling. Such resorbable calcium phosphate-based thin films and bulk ceramics have now been created by the high-temperature processing of a fine precipitate, formed from a colloidal sol and stabilized using an additive such as silicon. The materials have two characteristic features: a phase composition which is a mixture of calcium hydroxyapatite and a silicon stabilized tricalcium phosphate, and a microporous morphology based on inter-connected particles (0.2-1 microm in diameter). X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and light scattering experiments indicate that the characteristic phase composition arises during sintering through substitution reactions where silicon enters the calcium phosphate lattice under conditions of high chemical reactivity. The crystallographic features are linked through the glaserite form of the apatite structure.

Atopic disease in ulcerative colitis and Crohn's disease.

Three hundred patients with ulcerative colitis, 200 with Crohn's disease and matched control subjects completed questionnaires about atopic disease. They were asked whether they had ever suffered from asthma, hay fever, allergic rhinitis or eczema; in ulcerative colitis all of these features occurred with twice the frequency, but in Crohn's disease only eczema was more common than in controls.