THE SYNthesis, CHARACTERIZATION, AND ELECTROCHEMICAL STUDY OF TRIS(PYRAZOLYL)-TYPE IRON(II) COMPLEXES, IRON(II) SULFUR- AND SELENIUM-CONTAINING COMPLEXES, AND TRIS(PYRAZOLYL)-TYPE RUTHENIUM(II) COMPLEXES
Date of Award
Master of Science (MS)
Brumaghim, Julia L
Pennington , William T
Smith , Rhett C
Highly reactive radical species such as hydroxyl radical cause oxidative stress, resulting in chronic or degenerative diseases. In the biological Fenton reaction, iron(II) generates hydroxyl radical, OH, but only within a specific electrochemical potential window (-324 mV to 640 mV). Selenium and sulfur compounds have been extensively studied for their antioxidant properties, and they may exert their effects by binding iron(II) and shifting its electrochemical potential out of this window. This work has investigated the synthesis and electrochemical characterization of iron(II) chalcogenate complexes and iron(II) chalcogenone complexes. Cyclic voltammetry (CV) of [Fe(EPh)4][(PPh4)2] (E = S, Se) complexes shows Fe2+/3+ redox potentials of -723 mV (E = S) and -1010 mV (E = Se) vs. NHE. These electrochemical results suggest that selenium coordination stabilizes iron(II) relative to sulfur coordination and may inhibit iron redox cycling.
Because of synthetic difficulties with iron(II) complexes, ruthenium(II) was substituted for iron(II) due to its inert reaction kinetics and diamagnetism, allowing the use of NMR spectroscopy for characterization. Tris(pyrazolyl)methane ruthenium(II) complexes of the formula [TpmRRu(NCCH3)3]2+ (R = Me, Ph) and the previously-reported tris(pyrazolyl)borate ruthenium(II) complexes [TpRRu(NCCH3)3]+ (R = H, Me, Ph) have been synthesized using a new synthetic pathway that reduces the number of required steps on average by 80% and average reaction times by over 95%. Tris(pyrazolyl) (Tp) ligands are used to mimic adenine and guanine coordination to ruthenium(II), known sites of metal localization. CV studies of [TpRu(NCCH3)3][BF4] (Tp = tris(pyrazolyl)borate) and [Tp*Ru(NCCH3)3][OTf] (Tp* = tris(3,5-dimethylpyrazolyl)borate) determined Ru2+/3+ redox potentials of 489 mV and 498 mV, respectively, vs. NHE compared to the Ru2+/3+ redox potential for [Ru(NCCH3)6][(BF4)2] of 517 mV. Thus, coordination of Tp-type ligands substantially affects the redox chemistry of ruthenium as well as iron.
Underwood, Christopher, "THE SYNthesis, CHARACTERIZATION, AND ELECTROCHEMICAL STUDY OF TRIS(PYRAZOLYL)-TYPE IRON(II) COMPLEXES, IRON(II) SULFUR- AND SELENIUM-CONTAINING COMPLEXES, AND TRIS(PYRAZOLYL)-TYPE RUTHENIUM(II) COMPLEXES" (2010). All Theses. 1006.