NQPI Seminar | Visible Light Coordination of a Rh(III)-BODIPY Complex to Guanine, Oct. 20

The Nanoscale and Quantum Phenomena Institute (NQPI) 's Seminar Forum series features Eli Skelton discussing "Visible Light Coodination of a Rh(III)-BODIPY Complex to Guanine" Oct. 20 at 4:10 p.m. in Walter 245.

Skelton is a graduate student in Chemistry & Biochemistry at Ohio University.

Abstract : Cancers treated by chemotherapy use reagents such as cisplatin. Cisplatin is a Pt(II) metal complex that terminates cancer cells after undergoing thermal hydrolysis in a solution that activates covalent binding to DNA. Cisplatin is nonselective in differentiating healthy cells from cancer cells and targets them indiscriminately causing unwanted side effects such as ototoxicity and nephrotoxicity. Photodynamic therapy uses photochemical properties of chemical reagents to selectively target cancer cells using visible light. Most photodynamic therapeutics are oxygen-dependent and cannot effectively treat tumors in hypoxic environments. This research aims to take on this challenge by using Rh(III) polypyridyl complexes’ photochemical properties. When irradiated with UV light, cis- [Rh ^III (NN) ₂ Cl ₂ ] ⁺ complexes (where NN is a bidentate polypyridyl ligand) can photodissociate chloride and then covalently bind to DNA, but UV light damages tissue. To make these Rh(III)complexes more visible light active, a BODIPY fluorophore is coupled to the Rh(III) metal center. BODIPY is an emissive fluorophore that absorbs visible light strongly and can undergo excited-state electron transfer. This complex is designed so that the highest molecular orbital (HOMO) is localized around the BODIPY and the lowest molecular orbital (LUMO) is localized around the Rh(III) metal center. The coupling of BODIPY to Rh(III) greatly expanded the electronic absorbance into the visible region with an absorption maximum at 529 nm which as been assigned as the BODIPY π→π*.  Irradiation using 532 nm light (green light), it is observed that the BODIPY π→π* transition at 529 nm decreases. Using spectroelectrochemistry, a similar decrease is observed upon BODIPY oxidation, which supports photo-oxidation of BODIPY upon irradiation with visible light. In addition, photobinding of the Rh(III)-BODIPY complex was observed by mass spectrometry after chloride dissociation with visible light. Calculated thermochemistry values of the Rh complex reaction in methanol, acetonitrile, water, and guanine were determined using DFT calculations. All enthalpic reactions and Gibbs free energies were identified as endothermic and nonspontaneous, respectively. This observation supports the chloride dissociation using 532 nm light. This Rh(III)-BODIPY complex expands the class of visible light-activated Rh(III) photo-cisplatin analogs that may have potential photodynamic therapeutic activity for the treatment of cancers in hypoxic conditions.