Gold Nanoparticles Carrying Diatomic Molecules (O2 and CO) in Aqueous Solution

Gold nanoparticles (AuNPs) prepared by citrate reduction of aurochloric acid (HAuCl₄) were functionalized by tris(4‐sulfonatophenyl)porphinatoiron(III) (Fe^IIIP2) and poly(ethylene glycol) with thiolated arms (PEG‐SH). Fe^IIIP2 on the AuNP surface existed as its μ‐oxo dimer, which was reduced by Na₂S₂O₄ to yield monomeric Fe^IIP2. Fe^IIP2‐bearing AuNPs were further functionalized through inclusion of two sulfonatophenyl groups of Fe^IIP2 by a per‐O‐methylated β‐cyclodextrin dimer with a pyridine linker (Py3CD) to obtain AuNPs capable of carrying diatomic molecules in the body. The resulting AuNPs (hemoCD‐AuNPs) bound O₂ as well as CO in an aqueous solution. Although a noncolloidal 1:1 complex of 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphinatoiron(II) and Py3CD injected into the femoral vein of a rat was rapidly excreted in the urine, no excretion was observed with ferric hemoCD‐AuNPs, which were gradually accumulated in the spleen and liver of a rat. These results suggest that hemoCD‐AuNPs can be used as a carrier of diatomic molecules such as O₂ and CO in vivo.     

Iron(III) Triflimide as a Catalytic Substitute for Gold(I) in Hydroaddition Reactions to Unsaturated Carbon–Carbon Bonds

In this work it is shown that iron(III) and gold(I) triflimide efficiently catalyze the hydroaddition of a wide array of nucleophiles including water, alcohols, thiols, amines, alkynes, and alkenes to multiple C? C bonds. The study of the catalytic activity and selectivity of iron(III), gold(I), and Brønsted triflimides has unveiled that iron(III) triflimide [Fe(NTf₂)₃] is a robust catalyst under heating conditions, whereas gold(I) triflimide, even stabilized by PPh₃, readily decomposes at 80 °C and releases triflimidic acid (HNTf₂) that can catalyze the corresponding reaction, as shown by in situ ¹⁹F, ¹⁵N, and ³¹P NMR spectroscopy. The results presented here demonstrate that each of the two catalyst types has weaknesses and strengths and complement each other. Iron(III) triflimide can act as a substitute of gold(I) triflimide as a catalyst for hydroaddition reactions to unsaturated carbon–carbon bonds.     

Intramolecular Oxidative O‐Demethylation of an Oxoferryl Porphyrin Complexed with a Per‐O‐methylated β‐Cyclodextrin Dimer

The intramolecular oxidation of ROCH₃ to ROCH₂OH, where the latter compound spontaneously decomposed to ROH and HCHO, was observed during the reaction of the supramolecular complex (met‐hemoCD3) with cumene hydroperoxide in aqueous solution. Met‐hemoCD3 is composed of meso‐tetrakis(4‐sulfonatophenyl)porphinatoiron(III) (Fe^IIITPPS) and a per‐O‐methylated β‐cyclodextrin dimer having an ‐OCH₂PyCH₂O‐ linker (Py=pyridine‐3,5‐diyl). The O=Fe^IVTPPS complex was formed by the reaction of met‐hemoCD3 with cumene hydroperoxide, and isolated by gel‐filtration chromatography. Although the isolated O=Fe^IVTPPS complex in the cyclodextrin cage was stable in aqueous solution at 25 °C, it was gradually converted to Fe^IITPPS (t_1/2=7.6 h). This conversion was accompanied by oxidative O‐demethylation of an OCH₃ group in the cyclodextrin dimer. The results indicated that hydrogen abstraction by O=Fe^IVTPPS from ROCH₃ yields HO‐Fe^IIITPPS and ROCH₂^.. This was followed by radical coupling to afford Fe^IITPPS and ROCH₂OH. The hemiacetal (ROCH₂OH) immediately decomposed to ROH and HCHO. This study revealed the ability of oxoferryl porphyrin to induce two‐electron oxidation.     

Ruthenium(III) catalysis in the reaction of hexacyanoferrate(III) and iodide ions in perchloric acid medium

RuCl₃ can further catalyze the reaction between hexacyanoferrate(III) and iodide ions, which is already catalyzed by the hydrogen ions obtained from perchloric acid. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated graphically from the rate when ruthenium(III) and H⁺ ions both catalyze the reaction. Reactions studied separately in the presence as well as in the absence of RuCl₃ under similar conditions were found to follow second order kinetics w.r.t. [I⁻]. While the rate showed direct proportionality w.r.t. [Fe(CN)₆]³⁻ and [RuCl₃]. At low concentrations the reaction shows direct proportionality with respect to [H⁺] which tends to become proportional to the square of hydrogen ion concentrations. External addition of [Fe(CN)₆]⁴⁻ ions retards the reaction velocity while change in ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, extent of the reaction, which takes place without adding ruthenium(III) was calculated and it was in accordance with the values obtained from the separately studied reaction in which only H⁺ ions catalyze the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate-determining step. Arrhenius parameters at four different temperatures were also calculated.      

Electroprecipitation of Ag(II)/Ag(III) tetraphenylsulfonate porphyrin and electrocatalytic behavior of the films

The electrochemical precipitation on glassy carbon and gold electrodes of Ag(II) tetraphenylsulfonate porphyrin (Ag(II)TPPS) from aqueous HClO₄ solutions, is reported. Electrochemical quartz crystal microbalance (EQCM) results indicate the possible formation of an Ag(II)–Ag(III) porphyrin dimer species. This species is oxidized and reduced in two consecutive steps: oxidation at +0.31 and +0.36 V (vs. SCE) and reduction at +0.11 and +0.07 V. The films show catalytic behavior toward O₂ reduction in 10⁻² M HClO₄ at relatively low potentials (E<−0.1 V) but catalyze NO reduction at relatively high-reduction potentials (E<0.4 V). The electrochemical results seem to indicate that the catalytic cycle in the case of NO involves formation of Ag(II)TPPS–Ag(II)TPPS(NO)⁺ and its electroreduction to regenerate Ag(II)TPPS–Ag(III)TPPS and NO-reduction products.     

Well-Defined Ni(0) and Ni(II) Complexes of Bicyclic (Alkyl)(Amino)Carbene (MeBICAAC): Catalytic Activity and Mechanistic Insights in Negishi Cross-Coupling Reaction

Negishi cross-coupling reaction of organozinc compounds as nucleophiles with aryl halides has drawn immense focus for C−C bond formation reactions. In comparison to the well-established library of Pd complexes, the C−C cross-coupling of this particular approach is largely primitive with nickel-complexes. Herein, we describe the syntheses of Ni(II) complexes, [(^MeBICAAC)₂NiX₂] (X=Cl ( 1 ), Br ( 2 ), and I ( 3 )) by employing the bicyclic (alkyl)(amino)carbene (^MeBICAAC) ligand. The reduction of complexes 1 – 3 using KC₈ afforded the two coordinate low valent, Ni(0) complex, [(^MeBICAAC)₂Ni(0)] ( 4 ). Complexes 1 – 4 have been characterized by spectroscopic techniques and their solid-state structures were also confirmed by X-ray crystallography. Furthermore, complexes 1 – 4 have been applied in a direct and convenient method to catalyze the Negishi cross-coupling reaction of various aryl halides with 2,6-difluorophenylzinc bromide or phenylzinc bromide as the coupling partner in the presence of 3 mol % catalyst. Comparatively, among all-pristine complexes, 1 exhibit high catalytic potential to afford value-added C−C coupled products without the use of any additive. The UV-vis studies and HRMS measurements of controlled stochiometric reactions vindicate the involvement of Ni(I)−NI(III) cycle featured with a penta-coordinated Ni(III)-aryl species as the key intermediate for 1 whereas Ni(0)/Ni(II) species are potentially involved in the catalytic cycle of 4 .     

A Myoglobin Functional Model Composed of a Ferrous Porphyrin and a Cyclodextrin Dimer with an Imidazole Linker

A 1:1 inclusion complex (Fe^IIPImCD) of 5,10,15,20‐tetrakis‐ (4‐sulfonatophenyl)porphinatoiron(II) (Fe^IIP) and an O‐methylated β‐cyclodextrin dimer with an imidazole linker (ImCD) was found to bind dioxygen in aqueous solution. The half‐saturation pressure of dioxygen (P_1/2^O2) is 1.7 torr at 25 °C, which is 10 times lower than that for a previous myoglobin functional model (hemoCD) with a pyridine linker. Meanwhile, the half‐life of oxygenated Fe^IIPImCD is 3 h, which is 10 times shorter than that of oxygenated hemoCD. The covering of the iron(II) center by a microscopic environment is essential for preventing autoxidation of oxygenated ferrous porphyrin, which is promoted by nucleophilic attack of H₂O and/or nucleophiles such as inorganic anions. Due to structural requirements, covering of the Fe^II center of Fe^IIPImCD is insufficient compared with the case of hemoCD. As a result, water molecules can penetrate more easily the cleft of the O₂–Fe^IIPImCD complex and act as an autoxidation inducer. This structure also causes poorer selectivity against carbon monoxide (M=1040). In contrast, the dioxygen affinity of Fe^IIPImCD is much higher than that of hemoCD because the imidazole moiety is a stronger electron donor than pyridine.     

Fe3O4 Anisotropic Nanostructures in Hydrogels: Efficient Catalysts for the Rapid Removal of Organic Dyes from Wastewater

Fe₃O₄ anisotropic nanostructures that exhibit excellent catalytic performance are rarely used to catalyze Fenton‐like reactions because of the inevitable drawbacks resulting from traditional preparation methods. In this study, a facile, nontoxic, water‐based approach is developed for directly regulating a series of anisotropic morphologies of Fe₃O₄ nanostructures in a hydrogel matrix. In having the advantages of both the catalytic activity of Fe₃O₄ and the adsorptive capacity of an anionic polymer network, the hybrid nanocomposites have the capability to effect the rapid removal of cationic dyes, such as methylene blue, from water samples. Perhaps more interestingly, hybrid nanocomposites loaded with Fe₃O₄ nanorods exhibit the highest catalytic activity compared to those composed of nanoneedles and nanooctahedra, revealing the important role of nanostructure morphology. By means of scanning electrochemical microscopy, it is revealed that Fe₃O₄ nanorods can efficiently catalyze H₂O₂ decomposition and thus generate more free radicals (^.OH, ^.HO₂) for methylene blue degradation, which might account for their high catalytic activity.     

Electrochemical properties of polyaniline film doped by Ce3+ cation

Electrochemical Synthesis (ES)of polyaniline (PAni) is carried out in the presence in electrolyte (1 M H₂SO₄) of cerium (III) sulfate under potentiostatic and potentiodynamic modes. It is shown that Ce³⁺ cations in electrolyte catalyze ES, i.e. accelerate both ES variants. The obtained polymers were characterized using the scanning electron microscopy (SEM) technique and also on the basis of the calculation of electrochemical characteristics. Relaxation in PAni polymers doped by the Ce³⁺ cation occurs several times faster than in proton-doped PAni. The minimum change in ΔE and E is observed in polymers doped by Ce³⁺ cations during the electrochemical cycling of PAni and PAni-Ce at high rates.     

Efficient epoxidation of electron-deficient alkenes with hydrogen peroxide catalyzed by [γ-PW10O38V2(μ-OH)2]3-

A divanadium‐substituted phosphotungstate, [γ‐PW₁₀O₃₈V₂(μ‐OH)₂]^3? ( I ), showed the highest catalytic activity for the H₂O₂‐based epoxidation of allyl acetate among vanadium and tungsten complexes with a turnover number of 210. In the presence of I , various kinds of electron‐deficient alkenes with acetate, ether, carbonyl, and chloro groups at the allylic positions could chemoselectively be oxidized to the corresponding epoxides in high yields with only an equimolar amount of H₂O₂ with respect to the substrates. Even acrylonitrile and methacrylonitrile could be epoxidized without formation of the corresponding amides. In addition, I could rapidly (≤10 min) catalyze epoxidation of various kinds of terminal, internal, and cyclic alkenes with H₂O₂ under the stoichiometric conditions. The mechanistic, spectroscopic, and kinetic studies showed that the I ‐catalyzed epoxidation consists of the following three steps: 1) The reaction of I with H₂O₂ leads to reversible formation of a hydroperoxo species [γ‐PW₁₀O₃₈V₂(μ‐OH)(μ‐OOH)]^3? ( II ), 2) the successive dehydration of II forms an active oxygen species with a peroxo group [γ‐PW₁₀O₃₈V₂(μ‐η²:η²‐O₂)]^3? ( III ), and 3) III reacts with alkene to form the corresponding epoxide. The kinetic studies showed that the present epoxidation proceeds via III . Catalytic activities of divanadium‐substituted polyoxotungstates for epoxidation with H₂O₂ were dependent on the different kinds of the heteroatoms (i.e., Si or P) in the catalyst and I was more active than [γ‐SiW₁₀O₃₈V₂(μ‐OH)₂]^4?. On the basis of the kinetic, spectroscopic, and computational results, including those of [γ‐SiW₁₀O₃₈V₂(μ‐OH)₂]^4?, the acidity of the hydroperoxo species in II would play an important role in the dehydration reactivity (i.e., k₃). The largest k₃ value of I leads to a significant increase in the catalytic activity of I under the more concentrated conditions.     

Three-dimensional 3d–4f hetero-bimetallic coordination polymers through hydrogen bonds: synthesis,structures and mössbauer spectrum analysis

Four cyano-bridged 3d–4f hetero-bimetallic Ln(III)–Fe(III) assemblies, {[Ln(DMF)₄(H₂O)₃(µ-CN)Fe(CN)₅]· H₂O} _n (Ln?=?Ce (1), Nd (2), Sm (3) and Gd (4); DMF?=?N,N-dimethylformamide), have been synthesized. X-ray crystallographic analysis of both 3 and 4 reveals three-dimensional network structures resulting from hydrogen bonds in the crystals. With respect to the coordination number on Sm(III) atoms, 3 is different from previously reported structures. Structural comparison indicates that the differences in magnetic properties between 3 and 4 do not derive from structural factors. Mössbauer spectra at both 298 and 10?K reveal that the characteristic quadrupole splitting for low-spin Fe(III) ions (S?=?1/2) remains unchanged, indicating that the spin state of Fe(III) ions in 1–4 is not affected by temperature. The magnetic anisotropy derived from the ground states of Ln(III) ions with odd 4f ⁿ electrons (n?=?1, 3, 5 and 7), ²F_5/2,⁴I_9/2, ⁶H_5/2 and ⁸S_7/2 for Ce(III), Nd(III), Sm(III) and Gd(III), respectively, dominates the exchange interaction in the Ln(III)–NC–Fe(III) systems.     

Outer-sphere electron-transfer reactions of co(III)–polymer complexes in relation to its polymer effects

The outer-sphere electron-transfer reactions between [Co(III)(NH₃)₅L] (CIO₄)₃ [L = polyethyleneimine (PEI), L = NH₃(Amm)] or cis-[Co(III)(en)₂L′Cl]Cl₂ [L′ = poly-N-vinyl-2-methylimidazole(PVI), poly-4-vinylpyridine (PVP), N-ethylimidazole (NEI), pyridine (Py)] and various Fe(II) were studied. In the reaction with Fe(II)-(phen)₃²⁺, the reactivity of Co(III)–PEI was smaller than that of Co(III)–Amm due to the larger electrostatic repulsion. On the other hand, the reactivity of Co(III)–PEI was larger by a factor of 80 in the reaction with Fe(II)(H₂O)₆²⁺. From the results of rapid-scanning spectroscopy, the higher reactivity of Co(III)–PEI is caused by the coordination of free ethyleneimine residues in the Co(III)–PEI to Fe(II)–ion. Further more, the hydrophobic interaction between heteroaromatic polymer ligands and Fe(II)-(phen)₃²⁺ brought about the higher reactivities of Co(III)–PVI and Co(III)–PVP. Three interactions caused by the essential properties of polymers are discussed in relation to conformational changes.     

Oxidation of Ascorbate by Ni(III) Complexes with Tetraaza-macrocyclic Ligands in Neutral Aqueous Solutions. A Pulse-Radiolysis Study

Abstract

The mechanisms and kinetics of oxidation of ascorbate, AH^?, by Ni(III)Lⁱ _aq and by LⁱNi(III) (HPO₄)₂ ^? complexes (L¹ = meso-(5,12)-7,7,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; L² = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) in neutral aqueous solutions have been investigated.

The oxidation of ascorbate by the LⁱNi(III) (HPO₄)₂ ^? and Ni(III)L¹ _aq proceeds via two consecutive reactions well separated in time. The products of the first reaction are the A^.? radical anion and the corresponding Ni(II) complex. The oxidations by the LⁱNi(III)(HPO₄)₂ ^? complexes proceed via the outer sphere mechanism, whereas the detailed mechanism of reaction of Ni(III)L¹ _aq cannot be determined. The rate of reaction decreases with the increase in the concentration of phosphate, thus indicating that LⁱNi(III)(HPO₄)(H₂O)⁺ and LⁱNi(III)OH²⁺ are stronger oxidizing agents than LⁱNi(III)(HPO₄)^? ₂.

The oxidation of ascorbate by Ni(III)L² _aq proceeds via three consecutive reactions which are well separated in time. Thus the results clearly point out that this process occurs via the inner sphere mechanism. The first transient observed is tentatively identified as L²(H₂O)Ni(II)(A^.?)²⁺, i.e., an unexpected complex of the ascorbate anion radical. Also in this process the last transient observed is the A^.? anion radical. The stabilization of the ascorbyl radical in a transient complex might be of biological significance.     

Speciation of the Vanadium(III) Complexes with 1,10-Phenanthroline, 2,2′-Bipyridine,and 8-Hydroxyquinoline

The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline (8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm⁻³ KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows the formation of [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes. In the vanadium(III)–bipy system the [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]⁺, [V(OH)₂L], [VL₂]⁺ and [VL₃] were detected.     

Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

Interaction of Dialkyl (α-Carbomethoxy-β,β,β-Trifluoro-Ethyl) and Dialkyl-S-Carboethoxychloromethylthiol Phosphates with Mammalian Esterases. Role of Esterases in Toxicity Mechanisms

Abstract

The interaction of insecticides (RO)₂P (0)OCH (CF₃) COOCK₃ (I) and (RO)₂P(0)SCH(X)COOC₂H₅ (X=Cl(II), Br(III); R=Me, Et, Pr, i-Pr, Bu, i-Bu, Am, Hex) with acetylcnolinesterase (ACnE), butyrylcholinesterase (BChE) and carboxylesterase (CE) was studied in connection with their role in organo-phosphate toxicity mechsnisms. Toxicity of I–III to mice was determined. I–III were not hydrolysed by CE and irreversibly inhibited all the enzymes, II, IIi had a greater inhibitory potency compared to I: lgk^II _AChE = 2–4 (I), 6 (II, III); lgk^II _BChE = 3–6 (I), 5–8 (II, III); lgk^II _CE = 3–7 (I), more than 8 (II, III). With multiple regression analysis the dependence of antienzymatic activity on hydrophobicity and steric properties of alkyl substituents was investigated. The contribution of the hydrophobic interactions to dChE and CE (enzymes-“sites of loss”) inhibition was the same and more significant than that to AChE (target enzyme) inhibition. Steric effects are more important in AChE inhibition. The dependences lg(I/LD₅₀) = f(ΓΠ) for I–III were in great extent determined by binding with nonspecific esterases that rises with increasing hydrophobicity. These results indicate that nonspecific esterases CE and BChE play a buffer role in toxic action of I and especially II and III.     

Iridium(III) catalyzed oxidation of iodide ions in aqueous acidic medium

Oxidation of iodide ions by K₃Fe(CN)₆, catalyzed by hydrogen ions obtained from hydrochloric acid was found to be further catalyzed by iridium(III) chloride. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated from the rate when iridium(III) and H⁺ions both, catalyze the reaction. Reactions studied separately in the presence as well as in the absence of IrCl₃ under similar conditions were found to follow second order kinetics with respect to [I⁻]. While the rate showed direct proportionality with respect to [K₃Fe(CN)₆] and [IrCl₃]. At low concentrations the reaction shows direct proportionality with respect to [H⁺] which tends to become proportional to the square of hydrogen ions at higher concentrations. Strong retarding affect of externally added hexacyanoferrate(II) ions was observed in the beginning but further addition affects the rate to a little extent. Changes in [Cl⁻] and also ionic strength of the medium have no effect on the rate. With the help of the intercept of catalyst graph, the extent of the reaction, which takes place without adding iridium(III), was calculated and was found to be in accordance with the values obtained from the separately studied reactions in which only H⁺ ions catalyze the reaction. It is proposed that iridium forms a complex, which slowly disproportionates into the rate-determining step. Thermodynamic parameters at four different temperatures were calculated.     

Hydrazinium Oxalatometallates of Rare Earths(III)

Oxalates of La(III), Ce(III), Pr(III), Nd(III) and Sm(III) with the hydrazinium cation with the general formulae (N₂H₅)₄Ln₂(C₂O₄)₅7H₂O (Ln=La³⁺, Ce³⁺, Pr³⁺) and N₂H₅Ln(C₂O₄)₂·3.5H₂O (Ln=Nd³⁺, Sm³⁺) were synthesized. The thermal decompositions of these compounds take place in three stages: thermal dehydration at 65–100°C, exothermic decomposition of the N₂H₄ at 230–260°C, and oxidation of the oxalate ion.This revised version was published online in November 2005 with corrections to the Cover Date.     

New biocatalysts mimicking oxidative hemoproteins: Hemoabzymes

Catalytic antibodies with a metalloporphyrin cofactor or “hemoabzymes”, used as models for hemoproteins like peroxidases and cytochrome P450s, represent a promising route to catalysts tailored for selective oxidation reactions.The first strategy has been to produce anti-porphyrin antibodies, raised against various N-substituted- and meso-carboxyaryl-porphyrins, which led to monoclonal antibodies exhibiting, in the presence of the corresponding iron-porphyrin cofactor, a significant peroxidase activity. We ourselves obtained an artificial hemoprotein by associating a monoclonal antibody, 13G10, and its iron(III)-α,α,α,β-meso-tetrakis(ortho-carboxyphenyl)porphyrin (Fe(ToCPP)) hapten, which exhibited a significant peroxidase activity. Biological studies suggested that in this antibody, a carboxylic acid side chain of the protein participated in the catalysis, but no amino acid residue acting as an axial ligand of the iron was detected. Therefore, to provide the iron atom with an axial ligand, we raised antibodies against microperoxidase 8, a heme octapeptide containing a histidine bound to the iron atom.This strategy was successful, as an antibody–microperoxidase 8 complex (3A3–MP8) led to the best k_cat/K_m ever reported for antibody–porphyrin complexes. The ability of the 3A3–MP8 complex to catalyze the selective oxidation of substrates was studied and it was found able to catalyze the regioselective nitration of aromatics by NO₂⁻/H₂O₂ as well as the stereoselective oxidation of sulfides like thioanisole by H₂O₂.Other strategies based on antibodies have to be developed to obtain more efficient biomimetic systems for cytochrome P450s. A first one could involve the modification of anti-substrate antibodies by covalent linkage of an iron(III)-porphyrin close to the binding site of the substrate, to obtain an artificial hemoprotein able to catalyze its regioselective oxidation.     

A comparative DFT study of oxygen reduction reaction on mononuclear and binuclear cobalt and iron phthalocyanines

The oxygen reduction reaction (ORR) catalyzed by mononuclear and planar binuclear cobalt (CoPc) and iron phthalocyanine (FePc) catalysts is investigated in detail by density functional theory (DFT) methods. The calculation results indicate that the ORR activity of Fe-based Pcs is much higher than that of Co-based Pcs, which is due to the fact that the former could catalyze 4e^- ORRs, while the latter could catalyze only 2e^- ORRs from O₂ to H₂O₂. The original high activities of Fe-based Pcs could be attributed to their high energy level of the highest occupied molecular orbital (HOMO), which could lead to the stronger adsorption energy between catalysts and ORR species. Nevertheless, the HOMO of Co-based Pcs is the ring orbital, not the 3d Co orbital, thereby inhibiting the electron transfer from metal to adsorbates. Furthermore, compared with mononuclear FePc, the planar binuclear FePc has more stable structure in acidic medium and more suitable adsorption energy of ORR species, making it a promising non-precious electrocatalyst for ORR.