Supramolecular chirality of charged water-soluble porphyrins on polyglutamate

Date of Award

2013

Degree Name

M.S. in Chemistry

Department

Department of Chemistry

Advisor/Chair

Advisor: Angela Mammana

Abstract

The aggregation of three charged water soluble porphyrins, meso-Tetra(4-sulfonatophenyl)porphine (TPPS), meso-trans-di(N-methyl-4-pyridyl)diphenyl porphine (trans DmPyDPP) and meso-cis-di(N-methyl-4-pyridyl)diphenyl porphine (cis DmPyDPP) on Poly-L-Glutamate (poly-L-Glu) and Poly-D-Glutamate (poly-D-Glu) was studied. Then, the self-assembling supramolecular structures of two pairs of oppositely charged porphyrins were investigated in the presence of the chiral templates. These pairs include TPPS and trans DmPyDPP as well as TPPS and cis DmPyDPP. The structures were characterized using UV-Vis and circular dichroism spectroscopies. The presence of a chiral template during the aggregation of TPPS and trans DmPyDPP or TPPS and cis DmPyDPP should induce chirality on the hetero-aggregate, making it detectable by circular dichroism spectroscopy. The induced chirality of these supramolecular structures was found to depend upon the order of addition, the pH of the solution, the ionic strength and the chirality of the chiral template. The TPPS was able to aggregate with the templates in two different forms- the wrapping type" and the "pending type". The trans DmPyDPP was found to aggregate with both the random coil structures of poly-L-Glu and poly-D-Glu at pH 7 and the a-helix structure of the templates at lower pHs. The cis DmPyDPP was also able to aggregate with the random coil poly-L-Glu at pH 7.0; however, the porphryin did not aggregate with the a-helix structure of the poly-L-Glu or with either structure of the poly-D-Glu. In a system with both TPPS and trans DmPyDPP, the positively charged porphyrin is able to bridge two adjacent finger-like TPPS J-aggregates due to the position of the positive charges on opposite sides of the molecule when TPPS was added first. This geometry allows the trans DmPyDPP to reorganize dynamically as the polymer changes conformation due to a change in pH. This makes trans DmPyDPP a promising candidate for a biosensor for random coil structures. The order of addition greatly affects the structure of the aggregates forming a "pending type" aggregate when TPPS is added first and a "wrapping type" aggregate when trans DmPyDPP is added first. When cis DmPyDPP is used as the positively charged porphyrin instead of trans DmPyDPP, it is unsuitable for bridging the finger-like TPPS J-aggregates formed when TPPS is added first. It may pull TPPS out of the J-aggregate, disrupting the aggregate structure. It is also possible that the cis DmPyDPP is able to partially intercalate in the J-aggregate structure. The "pending type" aggregate is seen when TPPS is added first just as with the trans DmPyDPP system; however, the complexity of the system when cis DmPyDPP is added first requires further investigation before the formation of a "wrapping type" aggregate can be confirmed or denied."

Keywords

Porphyrins Structure, Porphyrins Synthesis, Chirality, Chemistry; chirality; supramolecular; porphyrin; polyglutamate; aggregation; TPPS

Rights Statement

Copyright © 2013, author

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