I-Kinetic And Mechanistic Investigations Of Amino Acid Substrates Reactivities With Ferryl Species

ABSTRACT I-KINETIC AND MECHANISTIC INVESTIGATIONS OF AMINO ACID SUBSTRATES REACTIVITIES WITH FERRYL SPECIES II-SYNTHESIS AND CHARACTERIZATION OF DERIVATIVES OF THE BN-TPEN LIGAND AND THEIR METAL COMPLEXES by AHMED IBRAHIM YOUSSEF ABOUELATTA MAY 2011 Advisor: Dr. Jeremy Jacob Kodanko Major: Chemistry (Organic) Degree: Doctor of philosophy The reactivity of tryptophan, methionine, aspartic acid, glutamic acid, histidine and hydrochloride salt of lysine amino acid substrates with the N4Py ferryl species was studied by UV-vis spectroscopy and product characterization. Based on kinetic isotope effect studies and product analysis, an ET-PT mechanism was proposed for the reaction of tryptophan substrate with N4Py ferryl and an oxygen-atom transfer mechanism was proposed for the reaction of methionine substrate with N4Py ferryl species. The reactivity of the five significantly reactive amino acid substrates (Cys, Tyr, Trp, Met and Gly) amino acid substrates was investigated with Me-N4Py, Bn-TPEN and TMC ferryl species and compared to their reactivity with N4Py ferryl species. This study indicated that the Bn-TPEN ferryl species was the most reactive with these five substrates followed by N4Py and Me-N4Py which were more reactive than TMC ferryl species. The different relative rate constants obtained for the substrates with different ferryl species and the slow reactivity of methionine substrate with Me-N4Py ferryl with respect to N4Py ferryl suggested that steric factor is involved in controlling these reactions. Studies towards the modification of the structure of the Bn-TPEN ligand were achieved and three new Bn-TPEN derivatives were synthesized and characterized. In addition, the synthesis and characterization of the racemic and enantioenriched Zn(II) and Fe(II) complexes and the enantioenriched Co(III) metal complexes of the Bn-CDPy3 was performed. These metal complexes were characterized with X-ray crystallography, circular dichroism, UV-vis, IR, 1-D and 2-D NMR spectroscopy in addition to elemental analysis and mass spectrometry. Based on these experiments, the three Bn-CDPy3 metal complexes were found to favor one isomer (C) over the other four possible isomers. The reason of the stability of isomer C over isomers A, B, D and E was attributed to a combination of steric and electronic effects