Robert F. Pasternack

Solution properties of tetrakis-(4-N-methyl)pyridylporphineiron(III)

Abstract Tetrakis-(4-N-methyl)pyridylporphineiron(III) (FeTMpyP) was synthesized and its aqueous solution properties studied. The visible spectrum of FeTMpyP was found to be dependent on pH and ionic strength. The following equilibria were sufficient to account for the titration data: H 2 O + FeP ( H 2 O ) 5+ ⥂ FeP ( OH )( H 2 O ) 4+ + H + ;p K a1 =4.7±0.2 FeP ( OH )( H 2 O ) 4+ ⥂ FeP (OH) 2 3+ + H + ; p K a2 =6.5±0.3 2 FeP ( OH ) 2 3+ ⥂O−( FePOH ) 2 6+ + H 2 O ; K D ≃9×10 5 M −1 . Magnetic susceptibility measurements and Mossbauer spectroscopy were used to characterize the FeTMpyP species at low and high pH. In the range pH 1–3, monomeric, high-spin, pentacoordinated iron(III) is the primary species. A μ-oxo dimer involving low-spin hexacoordinated iron(III) exists at pH 10–12. The rate of dissociation of the dimer at μ = 0.05 M and t = 25°C was found a two-term rate law: − d [ dimer ] d t =(k 1 +k′ 1 [ H + ])[ dimer ] where k1 = 0.42 sec−1 and K1 = 31 M−1 sec−1. These results are compared with those obtained for the dissociation of dimer of tetraphenylporphinesulfonatoferrate(III), FeTPPS.

The substitution reactions of a water soluble cobalt(III) porphyrin with thiocyanate as a function of pH

Abstract Stability and rate constants as well as activation parameters have been determined for the reactions of cobalt(III)tetra(N-methylpyridyl)porphine with thiocyanate ion as a function of pH. The porphyrin ligand increases the substitution rates at the metal center by several orders of magnitude relative to most other cobalt(III) complexes. The rates of formation and dissociation of the thiocyanate complexes are also dependent on the nature of the axial ligand (water, hydroxide or thiocyanate) trans to the leaving group. A bound thiocyanate ion labilizes the remaining water molecule by a factor greater than 10 4 and also changes the p K a of this group by at least three log units.

AGGREGATION PROPERTIES OF WATER‐SOLUBLE PORPHYRINS

The chemical properties of metalloporphyrins continue to attract considerable interest because of the vital role some of these species play in biological processes. It has been shown that the porphyrin ligand has a profound inhence on the kinetic and thermodynamic properties of ternary complex a much greater influence than do other ligands, such as 2,2’-dipyrid~I,~ which also permit electron delocalization from the metal ion onto the ligand molecule. Furthermore, the formation of porphyrin complexes of the labile metal ions is considerably slower and more complicated than other complexation reactions of these metal In order to gain further insight into the porphyrin properties which account for this atypical behavior, we have undertaken studies of uncomplexed water-soluble porphyrins. The species discussed here are: the tetraethylenediaminederivative of protoporphyrin IX, (TEP IX); tetrapyridylporphine, (TPyP); tetra(-N-methyl-pyridylporphine), (TMPyP); tetracarboxyphenylporphine, (TCPP); and two derivatives of tetraphenylporphinesulfonate, one containing three sulfonates and one containing four (TPPSa) and TPPS4). Of these six porphyrins, the latter five are of the mesosubstituted variety and the last three are negatively charged at the periphery when water-soluble. Both TPyP and TMPyP are positively charged at the periphery in the pH region in which they are water-soluble.

Solution properties of nickel(II) tetra(4-N-methylpyridyl) porphine and the influence of acetone, pyridine and imidazole

Abstract NiTMPyP has been shown to exist in aqueous solution as an equilibrium mixture between diamagnetic, four-coordinate nickel and paramagnetic, six-coordinate nickel complexed by water molecules in the axial positions. The addition of acetone promotes the four-coordinate species while the addition of pyridine or imidazole promotes the formation of six-coordinate species which may contain no, one or two molecules of the nitrogenous base depending on the ligand concentration.

Anticancer activity of metal compounds with superoxide dismutase activity

LARRY W. OBERLEY I, S.W.C. LEUTHAUSER l, ROBERT F. PASTERNACK 2, TERRY D. OBERLEY 3, LOREN SCHUTT J and JOHN R. J. SORENSON 4 JRadiation Research Laboratory, 14 Medical Laboratories, The University of Iowa, Iowa City, Iowa 52242, USA 2Department of Chemistry, Ithaca College, Ithaca, New York 14850, USA, 3Department of Pathology and Immunobiology Research Center, University of Wisconsin, 470 North Charter Street, Madison, Wisconsin 53706, USA, and 4College of Pharmacy, University of Arkansas Medical Sciences Campus, 4301 West Markham Street, Little Rock, Arkansas 72201, USA

Superoxide dismuting activity of an iron porphyrin

Abstract The efficiency of tetrakis-(4-N-methylpyridyl)porphineiron(III) as a superoxide dismuting catalyst has been determined using a pulse radiolysis technique.

Reactions of a water soluble Cobalt Porphyrin with thiocyanate

Abstract Rate and equilibrium constants have been determined for the reactions of Cobalt(III)Tetra(N-methyltetrapyridyl)Porphine with thiocyanate as a function of pH. The porphyrin ligand increases the substitution rates at the Co(III) center by several orders of magnitude relative to many other Co(III) complexes. The rates of formation and dissociation of the thiocyanate complexes are also dependent on the nature of the axial ligand trans to the water molecule being removed.

Substitution reactions of a water-soluble metalloporphyrin with azide and 1,1,3,3-tetramethyl-2-thiourea.

The substitution reactions of tetrakis-(4-N-methylpyridyl)porphinecobalt (III) (CoIIITMpyP) with azide and with 1,1,3,3-tetramethyl-2-thiourea (TMTU) have been studied as a function of pH at 25 degrees and an ionic strength of 0.5 M. The mechanistic pathway proposed for thiocyanate [1] and pyridine [2] is applicable to these ligands as well once allowance is made for two attacking forms of azide, N3- and HN3. A TMTU axial substituent has about the same influence on the rate of further ligand substitution as does SCN- and a much larger influence than does azide. Similar behavior between bound SCN- and bound TMTU is also shown in electron-transfer reactions with Ru(NH3)62+. Whereas both sulfur-containing ligands enhance the rate relative to the diaquo complex, the azide complex undergoes reduction an order of magnitude more slowly than does the diaquo complex.

On the mechanism of the catalase-like activity of cobalt(III)-hematoporphyrin☆

Evidence is presented on the basis of literature data that the disproportionation of H2O2, catalyzed by the Co(III) complex of hematoporphyrin IX (CoIIIHP), proceeds via the following mechanism: CoIIIHP(H2O2 ⇌CoIIIHP(OOH−)+H+ CoIIIHP(OOH−)+H2O2⇌CoIIIHP(OOH−)(H2O2) CoIIIHP(OOH−)(H2O2)→ CoIIIHP+H2O2+OH− + O2 The corresponding equilibrium and rate constants are estimated.

Kinetics of reactions of labile metal ions with bidentate and tridentate ligands

Abstract The temperature-jump technique has been applied to the study of the complexation reactions of nickel(II) and cobalt(II) with the ligands α-alanine, β-alanine, iminodiacetic acid, aspartic acid and iminodipropionic acid and of copper(II) with the latter three ligands. These results, when considered with those in the literature for copper(II) and the alaninates, lead us to conclude that the Sterically Controlled Mechanism which has been shown to apply to the chelate formation of bidentate ligands forming six-membered rings, applies to tridentate ligands as well. The effect is pronounced when the ligand forms chelate rings all of which are greater than five-membered.