Nia Dorsey
A professor at Georgia Southern is studying the comparison of photolysis capabilities between protonated and unprotonated tetraphenyl porphyrin solutions. Jim LoBue is a physical chemistry professor at Georgia southern. He earned his Bachelor of Arts degree from Carleton College in 1978 and his Ph.D. from Wesleyan University in 1986. His graduate work involved the study of van der Waals molecules using microwave spectroscopy in a molecular beam under the direction of Dr. Stewart Novick.
Dr. LoBue is involved in two very different projects in this area of research. His students at Georgia Southern investigate the photochemical properties of tetra-substituted porphyrins. These molecules have properties that make them candidates for a type of cancer therapy called photodynamic therapy. This work involves using various spectrometers available in the Chemistry Department, principally the ISS-K2 Phase Modulated Spectrofluorometer.
In Lobues laboratory, they have many molecules that are derived from something called Porphyrin. They use molecules with a core unit that looks like a structure similar to the outer of a spider web. “It is a chemical formula, showing you the pattern that the atoms choose to connect.” Chemists have a shorthand because they don’t have to draw everything out. After all, they have so much detail that you cant see everything. So what they do is draw different line segments in the web that represent chemical bonds and wherever there is a vertex. There are spaces with no symbols representing an element; you are to imagine a carbon put there. A basic ring would have 20 carbons around it. In the center, there would be nitrogen atoms. And another grouping of atoms which again is a shorthand.
They have a whole series of “webs” that are different based on what the PH is. So they have between 25 and 30 other molecules that are different based on a choice of whatever you wanted to put on the outer segments. The molecule is noticeably very symmetrical. The center is called a Porphyrin unit, and it appears a lot in biochemistry. The hemoglobin molecule has four units and what they are supposed to have in the middle is an iron atom, and the iron atom carries oxygen. So the hemoglobin when fully oxygenated as four oxygen molecules in every hemoglobin molecule. In your lungs, the hemoglobin grabs these very favorably oxygen molecules and carries them into the bloodstream wherever your tissues need them, which is all over your body.
A student of his, Megan Dempsy, aided in explaining his research, “Photodynamic cancer therapy (PDT) is an effective way to treat external cancers. Due to their ring structure and double bond character, porphyrin molecules work well as photosensitizers in PDT. Tetraphenyl porphyrins have four phenyl groups attached to the central ring.”
Dempsey introduced me to the methods they used to reach results. Stock samples of porphyrin solutions were created and diluted to 5μM. 180μM DPA was added to the answers to make them 2.5μM Porphyrin and 90μM DPA. The solutions attempted titration with varying levels of HCl. The level was determined with previous research done in porphyrin titration. Microliter aliquots of HCl were added to the diluted Porphyrin, and DPA solutions and UV-Visible light spectra were taken. Unprotonated solutions undergo photolysis with 514nm laser light, but protonated solutions undergo photolysis with 635nm laser light. UV-Vis spectra were taken every 15 minutes for 90 minutes total. The spectra were analyzed in excel for DPA depletion.
This study found that it was inconclusive if the protonated Porphyrin worked as well as the unprotonated Porphyrin in photodynamic cancer therapy (PDT). The work towards a usable porphyrin is essential because the laser light for protonated porphyrins is longer. This longer laser light can penetrate tissues more deeply and make PDT more effective for the patient.