1. Metallcarboranes  of F-block Elements
   Our primary research focus over the years have been in the primary areas  of synthetic inorganic chemistry of metal carborane complexes.  Currently, we are interested in the synthesis, characterization and reactivity of  f-block-metalla-carborane complexes with geometry constraining -donor group tethered to the carbon atom of the carborane (figure 1.).    These complexes are expected to exhibit  interesting structural features, enhanced Lewis acidity, and high reactivity especially, as polymerization catalyst.
    The role of the tethered ligand L, can be viewed in two ways.  If L, is a strongly coordinating ligand such as phenol or phenoxide and their  derivatives, it should bind firmly to the oxophilic  f-block elements.  This will provide enhanced stability in catalytic cycles in which the carboranyl ligand has the tendency to dissociate. With a less strongly coordinating ligand such as in pyridine, it may afford a semi labile site that could be displaced by an incoming substrate molecule.  The ligand can easily be fine tuned sterically and electronically to achieve desired chemical reactivity.  By incorporating a bulky aryl or alkyl group on carbon six of the pyridine or phenol, we can control the rate of associative displacement and chain transfer for the generation of longer or shorter polymer chains, and reduce or increase the amount of branching  in Zeigler type polymerization.    We are interested in  how structural changes affect the geometry around the metal,  the reactivity of the complexes as catalysts in C-C bond formation, and the control of stereo and regio- chemistry in olefin  polymerization.        
   
2. Bioglass and hybrid Composites for Bone Repair and Tissue Engineering
   There is a strong need for the development of biomaterials that can physically support bone growth (osteoconductive) and also stimulate new bone growth (osteoinductive).   These biomaterials would be useful in treating delayed fracture unions, bone defects arising from surgical treatment of bone metastases, as well as many other orthopedic conditions.  In addition, they will accelerate the progress of bone tissue engineering.  Various materials have been developed, and tested with bone cells.   One material that has achieved  highest clinical success of any synthetic material is the Bioglass.    The most widely used Bioglass is the 45S5, a four component melt-derived glass of

composition SiO2-P2O5-CaO-Na2O.  However, the poor mechanical strength of the bio-glass monolith has limited its application to particulate fillers for bone and periodontal defects.  In addition, the release of sodium ion in the 45S Bioglass?, a necessary process for bone bonding ability, leads to an increase in pH of the local environment beyond physiological level .   This has a significant impact on the activity of osteogenic cells.  The problem was addressed in our earlier work on bioglass, in which we replaced sodium oxide in the formulation with zinc oxide to alleviate the problem of pH increase, and improve on osteoconductivity .  Zinc ions are known to be very osteoconductive and stimulate osteogenesis. 

We are currently developing hybrid materials where organic polymers are chemically incorporated into bioglass network at the molecular level.   Such materials are expected to combine excellent mechanical properties derived from the organic polymer, with improved bone bonding ability coming from the inorganic bioglass network.    the specific aims of our effort in this area of research are:

1. To synthesize by sol-gel techniques hybrid materials incorporating varying amount of organic polymers with triethoxysilane side-chain groups, and zinc containing bioglass (polymer-CaO-P2O5-SiO2-ZnO).
2. To develop structure-property relationships that describe how the material porosity and local microstructure impact material properties.
3. To determine the effect of compositional variation of the polymer, co-polymer and bioglass combination on the apatite forming ability in stimulated body fluid (SBF) and mechanical properties.
4. To undertake in vitro testing of the materials using human fetal osteoblastic cells, hFOB 1.19 cells incubated at 37oC and comparison to the 45S5 Bioglass.