Study of the Self-Assembly of Positively Charged Porphyrins as a Function of pH and Time
Gabrielle Nicole Snyder
This study focused mainly on the self-assembly of a cationic porphyrin, meso-trans-di(N-methyl-4-pyridyl)diphenyl porphine (trans-DmPyDPP), in various conditions of pH. We explored both the effect of the change of pH of the solution and the effect of time. We observed that the aggregate formed was dependent not only on the pH but also on the mode used to reach that pH: increasing or decreasing pH affected the stability of these aggregates and their formation. With the introduction of Poly-L-Glutamic Acid to a solution containing trans-DmPyDPP, we observed a bisignate circular dichroism signal (exciton couplet) centered at 443 nm that corresponds to the Soret band of the porphyrin. The highest signals were observed at pH around the pKa of the porphyrin, which was found to be around 3.5. The sign of the porphyrin exciton couplet was correlated to the pH dependent secondary structure of the polymer. As indicated in literature, we observed an alpha helix structure at acidic pH (below pH 3) and a random coil structure at neutral or basic pH. We performed a series of pH titrations, involving small additions of base or acid to raise or lower by small increments the pH of various solutions of the trans-DmPyDPP with and without the polymer. In addition, monitoring the various aggregates with time showed an instability of the aggregate formed at relatively acidic pH with or without the presence of the polymer, and even a strong aggregate with a strong signal did not maintain over time. In order to improve the stability of the aggregate, an anionic porphyrin, Copper meso-Tetra(4-sulfonatophenyl)porphine (CuTPPS), was prepared and used to create ternary complexes composed of poly-L-Glu, trans-DmPyDPP and CuTPPS. Initial results showed an improvement of the stability of the aggregate.
Independent Research - Undergraduate
Primary Advisor's Department
Stander Symposium project
"Study of the Self-Assembly of Positively Charged Porphyrins as a Function of pH and Time" (2017). Stander Symposium Projects. 1042.