Frank E. Sowrey

Structural trends in copper(II) bis(thiosemicarbazone) radiopharmaceuticals

Redox-related changes in biological properties of copper bis(thiosemicarbazone) radiopharmaceuticals are induced by backbone alkylation. To determine whether these changes are mediated by changes in core structural parameters, eight X-ray structures of variously alkylated complexes were determined. The complexes include the hypoxia tracer diacetylbis(4-methyl-3-thiosemicarbazonato)copper(II) (CuATSM). The structures of the nickel analogue NiATSM and the corresponding free ligand ATSMH2 were also included. Distortions from planarity were slight and only present when there were significant intermolecular interactions (mainly pairs of N–H–N and N–H–S hydrogen bonds). These give rise to cross-linked flat or helical ribbons of complexes. Alkylation at the terminal nitrogen atoms interrupts hydrogen bonding, allowing complexes to become planar, but does not otherwise affect the coordination sphere. Alkylation at the backbone carbon atoms increases the backbone C–C bond length, allowing the metal to fit better into the ligand cavity with shorter Cu–S bonds.

Systematic empirical analysis of calcium–oxygen coordination environment by calcium K-edge XANES

The X-ray absorption near edge structure (XANES) at the calcium K-edge is rich in information, but complex and difficult to interpret fully. We present here a systematic study of a range of calcium/oxygen containing compounds and minerals and show that the XANES may be used to obtain qualitative information on the calcium coordination environment.

The structure of a bioactive calcia:silica sol-gel glass

Sol-gel derived calcium silicate glasses may be useful for the regeneration of damaged bone. The mechanism of bioactivity is as yet only partially understood but has been strongly linked to calcium dissolution from the glass matrix. In addition to the usual laboratory-based characterisation methods, we have used neutron diffraction with isotopic substitution to gain new insights into the nature of the atomic-scale calcium environment in bioactive sol-gel glasses, and have also used high energy X-ray total diffraction to probe the nature of the processes initiated when bioactive glass is immersed in vitro in simulated body fluid. The data obtained point to a complex calcium environment in which calcium is loosely bound within the glass network and may therefore be regarded as facile. Complex multi-stage dissolution and mineral growth phases were observed as a function of reaction time between 1 min and 30 days, leading eventually, via octacalcium phosphate, to the formation of a disordered hydroxyapatite (HA) layer on the glass surface. This methodology provides insight into the structure of key sites in these materials and key stages involved in their reactions, and thereby more generally into the behaviour of bone-regenerative materials that may facilitate improvements in tissue engineering applications.

The effect of substitution of a thioether donor by a phosphine donor in thiacrown complexes of iron

Abstract Electrospray mass spectrometry and thermogravimetric analysis reveals that bis(1-phenyl-1-phospha-4,7-dithiacyclononane)iron(II) is more susceptible to ethene loss than bis(1,4,7-trithiacyclononane)iron(II). This is in accord with X-ray crystallographic studies, which show that the C–S bonds are longer in the former complex suggesting an increased population of the C–S σ* π-acceptor orbitals.

The Atomic-Scale Interaction of Bioactive Glasses with Simulated Body Fluid

The formation of a carbonate-containing hydroxyapatite, HCAp, layer on bioactive calcium silicate sol-gel glass of the formula (CaO)0.3(SiO2)0.7 has been studied in-vitro in Simulated Body Fluid (SBF). Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR) measurements have been performed with results showing the formation of a significantly amorphous HCAp layer after less than 5 hours in solution.