Photodynamic Therapy (PDT) has emerged as an alternative to conventional treatments for dermatologically and endoscopically accessible cancers. Typically, 1O2 is the cause of the cellular damage, which limits the applicability of these drugs in combating hypoxic cancers. Novel types of metal complexes as PDT agents, independent of the generation of 1O2, are desirable targets. The potential use of [cis-Rh2(�-O2CCH3)2(CH3CN)6][BF4]2 as PDT agent was discovered by our collaborator Turro upon irradiation under visible light (400-700 nm) for 30 minutes. Under these conditions LC50 values for Hs-27 human skin cells decreased from 410�9 to 12�2 �M. The activity is attributed to the exchange of two of the equatorial CH3CN ligands with H2O under irradiation, generating the photo-activated [cis-Rh2(�-O2CCH3)2(CH3CN)2(H2O)4][BF4]2 species which can bind to double strand DNA. The compound [cis-Rh2(DTolF)2(CH3CN)6][BF4]2 has been probed by us as well, but the strong trans-effect exhibited by the DTolF- ligand renders the equatorial CH3CN ligand labile in the dark, ruling it out as a PDT agent candidate. Subsequently, F-form was used because of the strong s electron withdrawing ability of F atoms. Monitoring of [cis-Rh2(F-form)2(CH3CN)6][BF4]2 by 1H-NMR spectroscopy revealed exchange of the CH3CN ligand with bulk CD3CN solvent in the dark albeit at a slower rate. Another strategy being adopted is tuning of the electronic properties of the mono-dentate ligands released in the photoexcited state. Since formamidinate ligands render the dirhodium metal core electron rich, much better p acceptor co-ligands could lead to stronger M-L bonds interaction. In this vein, isocyanide is being considered. The methyl isocyanide derivative was prepared and 1H NMR spectra revealed the stability of the compound in the dark. These results as well as the TDDFT calculations that help in the assignment of the electronic transitions in the electronic absorption spectra and information about HOMO and LUMO levels will be presented.

Investigation of [cis-Rh2(µ-L-L)2(L')6[BF4]2 “partial paddlewheel” compounds as photodynamic therapy agents

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.