Bioactive, Ion-Releasing PMMA Bone Cement Filled with Functional Graphenic Materials.

Graphene oxide and functionalized graphenic materials (FGMs) have promise as platforms for imparting programmable bioactivity to poly(methyl methacrylate) (PMMA)-based bone cement. To date, however, graphenic fillers have only been feasible in PMMA cements at extremely low loadings, limiting the bioactive effects. At higher loadings, graphenic fillers decrease cement strength by aggregating and interfering with curing process. Here, these challenges are addressed by combining bioactive FGM fillers with a custom cement formulation. These cements contain an order of magnitude more graphenic filler than previous reports. Even at 1 wt% FGM, these cements have compressive strengths of 78- 88 MPa, flexural strengths of 74-81 MPa, and flexural stiffnesses of 1.8-1.9 GPa, surpassing the ASTM requirements for bone cement and competing with traditional PMMA cement. Further, by utilizing designer FGMs with programmed bioactivity, these cements demonstrate controlled release of osteogenic calcium ions (releasing a total of 5 ± 2 µmol of Ca2+ per gram of cement over 28 d) and stimulate a 290% increase in expression of alkaline phosphatase in human mesenchymal stem cells in vitro. Also, design criteria are described to guide creation of future generations of bone cements that utilize FGMs as platforms to achieve dynamic biological activity.

Acid Mine Drainage Remediation: Aluminum Chelation Using Functional Graphenic Materials.

Acid mine drainage (AMD) is a pervasive source of metal pollution that severely impacts freshwater ecosystems and has a direct impact on human health. Conventional active and passive methods work very well for removing iron in AMD remediation, which is typically the highest metallic impurity. However, conventional passive remediation fails to remove all aluminum, which has severe ecological implications. Removal of aluminum ions using chelation, which traditionally uses small molecules that bind metals tightly for sequestration, holds promise. Yet, chelation strategies are limited because once introduced into surface water, small molecules are difficult to reclaim and often persist in the environment as pollutants. To address this, we have designed six unique scaffolds based on functional graphenic materials (FGMs) to create nonsoluble materials that could be placed at the end of a passive remediation process to remove persistent aluminum. When tested for efficacy, all six FGMs successfully demonstrated a reversible capacity to remove aluminum from acidic water, chelating up to 21 µg of Al/mg of FGM. Furthermore, when they were exposed to E. coli as an approximation for environmental compatibility, viability was unaffected, even at high concentrations, suggesting these FGMs are nontoxic and viable candidates for passive chelation-based remediation.

Masked Radicals: Iron Complexes of Trityl, Benzophenone, and Phenylacetylene.

We report the first Fe─CPh3 complex, and show that the long Fe─C bond can be disrupted by neutral π-acceptor ligands (benzophenone and phenylacetylene) to release the triphenylmethyl radical. The products are formally iron(I) complexes, but X-ray absorption spectroscopy coupled with density functional and multireference ab initio calculations indicates that the best description of all the complexes is iron(II). In the formally iron(I) complexes, this does not imply that the π-acceptor ligand has radical character, because the iron(II) description arises from doubly-occupied frontier molecular orbitals that are shared equitably by the iron and the π-acceptor ligand, and the unpaired electrons lie on the metal. Despite the lack of substantial radical character on the ligands, alkyne and ketone fragments can couple to form a high-spin iron(III) complex with a cyclized metalladihydrofuran core.