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Chemistry Seminar

February 21, 2013
Room 203, Smith Hall 11:00 a.m.

Mr. David Saeva

The Impact of Surface Charge and Size on the Pulmonary
Toxicity of Multiwall Carbon Nanotubes

Carbon nanotubes (CNTs) are promising fullerene nanomaterials that exhibit novel properties, such as high mechanical strength and electrical conductivity. However, pristine CNTs remain limited in application due to dispersibility issues, which may be overcome through surface functionalization, as well as continuing debate over their potentially-negative impacts upon the environment and human health. The impact of diameter, as well as surface charge via functionalization, on the pulmonary toxicity of multi-walled CNTs (MWCNT) was assessed in two studies. Results depict an inverse relationship between pulmonary toxicity in vivo and in vitro with MWCNT diameter as indicated by elevated oxidative stress and inflammatory response. Conversely, a binary relationship between surface charge and pulmonary toxicity was observed, with anionic functionalized MWCNTs (f-MWCNTs) depicting toxicity below neutral or pristine MWCNTs and cationic f-MWCNTs depicting greater toxicity. Overall, these results indicate that large-diameter, anionic f-MWCNTs may be a promising option for biological application, warranting further investigation.

Mr. Zachary McAtee

Enhanced Cell Death Imaging Using Multivalent
Zinc(II)-bis(dipicolylamine) Fluorescent Probes

Apoptosis, cell death, is a critical process that helps maintain homeostasis within organisms. Observations of apoptosis allows for a deeper understanding of the regulatory process. Fluorescently doped molecules with specific affinities to dead/dying cells allows for early detection and treatment of biological diseases where normal apoptosis is disrupted. Phosphatidylserine (PS), a positively charged phospholipid, becomes exposed to the surface of the cell membrane early in apoptosis. The exposure of the PS is how macrophages recognize apoptotic cells for destruction. The Zinc(II)-bis-(dipicolylamine) (Zn2BDPA) probe binds to the phosphatidylserine with a medium affinity. When Zn2BDPA is complexed with the highly fluorescent squaraine rotaxane (SR) scaffold multivalency is achieved and the affinity for PS is dramatically increased. The binding affinity of the Zinc probe is directly proportional to the number of Zn2BDPA complexed around the SR. The experiment specifically uses two structurally related probes, bis- Zn2BDPA-SR and tetra-Zn2BDPA-SR. A higher affinity and specificity to the apoptotic cell membrane was observed with the tetra-Zn2BDPA-SR.