Atif Mahammed

Synthesis and Characterization of Germanium, Tin, Phosphorus, Iron, and Rhodium Complexes of Tris(pentafluorophenyl)corrole, and the Utilization of the Iron and Rhodium Corroles as Cyclopropanation Catalysts

The germanium(IV), tin(IV). and phosphorus(v) complexes of tris(pentafluorophenyl)corrole were prepared and investigated by electrochemistry for elucidation of the electrochemical HOMO-LUMO gap of the corrole and the spectroscopic characteristics of the corrole pi radical cation. This information was found to be highly valuable for assigning the oxidation states in the various iron corroles that were prepared. Two iron corroles and the rhodium(I) complex of an N-substituted corrole were fully characterized by X-ray crystallography and all the transition metal corroles were examined as cyclopropanation catalysts. All iron (except the NO-ligated) and rhodium corroles are excellent catalysts for cyclopropanation of styrene, with the latter displaying superior selectivities. An investigation of the effect of the oxidation state of the metal and its ligands leads to the conclusion that for iron corroles the catalytically active form is iron(III), while all accesible oxidation states of rhodium are active.

High-Valent Manganese Corroles and the First Perhalogenated Metallocorrole Catalyst

On pyrrole! The pyrrole-based corrole ligands can offer an alternative to porphyrin systems. The manganese corroles 1-4 are readily synthesized, undergo metal- not ligand-based redox chemistry, and 4 in particular shows impressive catalytic activity in the oxygenation of styrene with iodosylbenzene.

Structural, Electrochemical, and Photophysical Properties of Gallium(III) 5,10,15-Tris(pentafluorophenyl)corrole

High quantum yields are found for the prototype metallocorrole 1, which is readily prepared from GaCl_3 and tris(pentafluorophenyl)corrole. The crystallographic and electronic structures of 1 are reported as well as the simple generation of its π-cation radical complex by chemical oxidation and the characteristic spectroscopic features of this ion.

Tumor detection and elimination by a targeted gallium corrole

Sulfonated gallium(III) corroles are intensely fluorescent macrocyclic compounds that spontaneously assemble with carrier proteins to undergo cell entry. We report in vivo imaging and therapeutic efficacy of a tumor-targeted corrole noncovalently assembled with a heregulin-modified protein directed at the human epidermal growth factor receptor (HER). Systemic delivery of this protein-corrole complex results in tumor accumulation, which can be visualized in vivo owing to intensely red corrole fluorescence. Targeted delivery in vivo leads to tumor cell death while normal tissue is spared. These findings contrast with the effects of doxorubicin, which can elicit cardiac damage during therapy and required direct intratumoral injection to yield similar levels of tumor shrinkage compared with the systemically delivered corrole. The targeted complex ablated tumors at >5 times a lower dose than untargeted systemic doxorubicin, and the corrole did not damage heart tissue. Complexes remained intact in serum and the carrier protein elicited no detectable immunogenicity. The sulfonated gallium(III) corrole functions both for tumor detection and intervention with safety and targeting advantages over standard chemotherapeutic agents.

Cobalt Corrole Catalyst for Efficient Hydrogen Evolution Reaction from H2O under Ambient Conditions: Reactivity, Spectroscopy, and Density Functional Theory Calculations

The feasibility of a hydrogen-based economy relies very much on the availability of catalysts for the hydrogen evolution reaction (HER) that are not based on Pt or other noble elements. Significant breakthroughs have been achieved with certain first row transition metal complexes in terms of low overpotentials and large turnover rates, but the majority of reported work utilized purified and deoxygenated solvents (most commonly mixtures of organic solvents/acids). Realizing that the design of earth abundant metal catalysts that operate under truly ambient conditions remains an unresolved challenge, we have now developed an electronically tuned Co(III) corrole that can catalyze the HER from aqueous sulfuric acid at as low as -0.3 V vs NHE, with a turnover frequency of 600 s(-1) and ≫10(7) catalytic turnovers. Under aerobic conditions, using H2O from naturally available sources without any pretreatment, the same complex catalyzes the reduction of H(+) with a Faradaic Yield (FY) of 52%. Density functional theory (DFT) calculations indicate that the electron density on a putative hydride species is delocalized off from the H atom into the macrocycle. This makes the protonation of a [Co(III)-H](-) species the rate determining step (rds) for the HER consistent with the experimental data.

Specific Delivery of Corroles to Cells via Noncovalent Conjugates with Viral Proteins

PurposeCorroles are amphiphilic macrocycles that can bind and transport metal ions, and thus may be toxic to cells. We predicted that anionic corroles would poorly enter cells due to the negatively charged cell membrane, but could be ideal tumor-targeted drugs if appropriate carriers enabled delivery into tumor cells. In this work, we test the hypothesis that recombinant cell penetrating proteins of the adenovirus (Ad) capsid form noncovalent conjugates with corroles to facilitate target-specific delivery and cell death.MethodsCorroles mixed with recombinant proteins were tested for conjugate assembly, cell penetration, stability, targeted binding, and cell killing in vitro.ResultsSulfonated corroles entered cells only with carrier proteins, and formed stable complexes with recombinant Ad capsid proteins. ErbB receptor-targeted conjugates were cytotoxic to ErbB2-positive but not ErbB2-negative breast cancer cells, whereas molar equivalents of free corrole had no effect on these cells.ConclusionsSulfonated corroles are cytotoxic to ErbB2-positive breast cancer cells when delivered by a targeted cell penetrating protein. The relatively low dose required to accomplish this compared to untargeted compounds suggests that corroles may lend themselves to targeted therapy. Importantly, the amphiphilicity of corroles enables a unique approach to bioconjugate formation whereby the carrier and drug form a stable complex by noncovalent assembly.

Synthesis and structural characterization of a novel covalently-bound corrole dimer.

The (triphenylphosphine)cobalt(III) complex (2) of 5,10,15-tris(pentafluorophenyl)corrole (1) is shown to be an valuable precursor to complexes that have not been fully characterized previously. In contrast to other cobalt corroles, aromatic amines can be substituted for the triphenylphosphine in 2 to form six-coordinate bis(amine)cobalt(III) complexes. This is demonstrated by spectroscopic methods and by X-ray crystallography of the bis-pyridine complex 4, the first of its kind. While 2 and 4 and even their one-electron oxidized complexes are stable, a spontaneous dimerization of the corrole takes place in the absence of strongly bound ligands. The bis-cobalt complex of the novel corrole dimer 6 was fully characterized by spectroscopic methods and X-ray crystallography.

Four-Electron Oxygen Reduction by Brominated Cobalt Corrole

The carbon-supported cobalt(III) complex of β-pyrrole-brominated 5,10,15-tris(pentafluorophenyl)corrole [Co(tpfc)Br(8)/C] is introduced as a nonplatinum alternative for electrocatalytic oxygen reduction in aqueous solutions. Through systematic work, the basic kinetic parameters of this reaction were studied, using rotating ring disk electrode electrochemical methods in the pH range of 0-11. Pronounced catalytic activity was detected in acid solutions along with shifts of the Co(II)/Co(III) and O(2) redox couples to more positive values (onset of 0.56 V at pH 0). A series of independent measurements have been used to prove that the dominant mechanism for oxygen reduction by Co(tpfc)Br(8)/C catalysis is the direct four-electron pathway to water.

Metallocorroles as cytoprotective agents against oxidative and nitrative stress in cellular models of neurodegeneration

J. Neurochem. (2010) 113, 363–373.

Neuroprotection against superoxide anion radical by metallocorroles in cellular and murine models of optic neuropathy

J. Neurochem. (2010) 114, 488–498.