Abstract
Porphyrins are macrocycles found in many natural compounds. The changes in energy between the protonated (dication) and free base porphyrins were determined using molecular modeling. The data obtained was then compared to experimental enthalpy values. The porphyrins analyzed were octaethylporphyrin, octaethyltetraphenylporphyrin, tetraphenylporphyrin, and tetra-[2]-pentylporphyrin. Molecular mechanics was employed to optimize each porphyrin, and semi-empirical calculation methods RM1 and PM3 were subsequently utilized to test the conformational energies of the protonated and deprotonated porphyrins. The semi-empirical PM3 method was best for analysis of energy changes among the porphyrins; although the obtained values did not exactly match experimental values, the trends of energy differences between the tested porphyrin and base porphyrin when protonated and deprotonated did show correlation with the experimental enthalpy values. The greatest energy change from deprotonated to dicationic with respect to the free-base porphyrin was in the dodecasubstituted porphyrins.
Faculty Sponsors
Dr. Maria Ballester
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-4-2014 1:00 PM
End Date
4-4-2014 5:30 PM
Predicting Porphyrin Basicity Using Semi-Empirical Methods
Alvin Sherman Library
Porphyrins are macrocycles found in many natural compounds. The changes in energy between the protonated (dication) and free base porphyrins were determined using molecular modeling. The data obtained was then compared to experimental enthalpy values. The porphyrins analyzed were octaethylporphyrin, octaethyltetraphenylporphyrin, tetraphenylporphyrin, and tetra-[2]-pentylporphyrin. Molecular mechanics was employed to optimize each porphyrin, and semi-empirical calculation methods RM1 and PM3 were subsequently utilized to test the conformational energies of the protonated and deprotonated porphyrins. The semi-empirical PM3 method was best for analysis of energy changes among the porphyrins; although the obtained values did not exactly match experimental values, the trends of energy differences between the tested porphyrin and base porphyrin when protonated and deprotonated did show correlation with the experimental enthalpy values. The greatest energy change from deprotonated to dicationic with respect to the free-base porphyrin was in the dodecasubstituted porphyrins.
