Efficient aldehyde olefination reactions catalyzed by an iron porphyrin complex in an ionic liquid

The commercially available complex Fe(TPP)Cl is an active and highly (E)-selective catalyst for the olefination of a variety of aldehydes in the presence of PPh₃ and diazoacetate in the ionic liquid (bmim)(PF₆). Dependent on the reactivity of the applied aldehyde, the reaction can be carried out at a reaction temperature of 50-80 °C. After 0.5-24 h quantitative olefin yields are reached with a broad variety of different aldehydes. Due to the application of an ionic liquid as reaction medium the products can be easily removed from the catalyst by a simple extraction and the catalyst is conveniently reusable without significant activity loss. Spectroscopic investigations indicate that the reaction mechanism includes the quantitative formation of a phosphorus ylide, which then reacts further in a Wittig reaction under formation of an olefin.     

Aggregation-induced folding of a de novo designed polypeptide immobilized on gold nanoparticles

This communication reports the first steps in the construction of a novel, nanoparticle-based hybrid material for biomimetic and biosensor applications. Gold nanoparticles were modified with synthetic polypeptides to enable control of the particle aggregation state in a switchable manner, and particle aggregation was, in turn, found to induce folding of the immobilized peptides.     

An example of an iron (III) porphyrin with spin mixed ground state

The paper reports synthesis and physical characterisation of a new iron(III) porphyrin which shows unusual features of quantum mechanically mixed ground state in its magnetic properties. Magnetic susceptibility (300−3·6 K) and M?ssbauer spectroscopy (300−77 K) studies of the compound are described and discussed with reference to some bacterial ferricytochromeC' exhibiting similar spin-mixed ground state.     

Integration of electrochemical generator and detector of nitric oxide with the aid of the iron porphyrin

An electrochemical cell of generating nitric oxide (NO) was constructed in order to realize the catalytic reaction of nitrite by iron porphyrin [Y. Chi, J. Chen, K. Aoki, Inorg. Chem. 43 (2004) 8437]. The cell was composed of the generator of the iron porphyrin-including Nafion^®-coated electrode, the ion-exchange membrane, and the electrochemical detector of NO. The reduction of iron porphyrin in the presence of nitrite at the generator coordinates nitrite to form the NO-included complex, of which oxidation releases NO. The water-dissolved NO diffused to the detector through the membrane to block nitrite. It was detected by voltammetry with the aid of the oxidative catalytic reaction of iron porphyrin.     

Horseradish peroxidase (HRP) catalyzed oxidative coupling reactions using aqueous hydrogen peroxide: an environmentally benign procedure for the synthesis of azine pigments

The horseradish peroxidase (HRP) catalyzed oxidative coupling of 2-hydrazono-4-thiazolines with α-naphthol using aqueous hdrogen peroxide. These transformations allow an environmentally benign synthesis of p-naphthoquinone-thiazol-2-on-azines under mild conditions.     

Synthesis and characterization of the azido-bound five-coordinate high-spin iron(II) “picket fence” porphyrin complex

An Fe(II)-azido five-coordinate picket fence porphyrin complex with the formula [Na(2,2,2-crypt)][Fe^II(TpivPP)(N₃)] · 3C₆H₅Cl (TpivPP = α,α,α,α-tetrakis(o-pivalamidophenyl)porphinato, known as a picket fence porphyrin, and 2,2,2-crypt is the cryptand-222) has been synthesized and characterized. The synthesis utilizes cryptand-222 to solubilize sodium azide in the preparation procedure. The UV–Vis and IR spectroscopic data are consistent with an azido ferrous porphyrinate. The X-ray structural analysis and the Mössbauer results indicate that the ion complex [Fe^II(TpivPP)(N₃)]⁻ is high-spin and has the (d_xy)²(d_xz)¹(d_yz)¹(d_z2)¹(d_x2-y2)¹$({\text{d}}_{\mathit{xy}}{)}^2({\text{d}}_{\mathit{xz}}{)}^1({\text{d}}_{\mathit{yz}}{)}^1({\text{d}}_{z^2}{)}^1({\text{d}}_{x^2-y^2}{)}^1$ ground state electronic configuration.     

Electrocatalytic activity of a new nanostructured polymeric tetraruthenated porphyrin film for nitrite detection

The preparation of the monomer and thin films of a new polymeric tetraruthenated porphyrin material and their characterization by spectroscopic and electrochemical techniques, are described. This material is one of the most active electrocatalyst for the oxidation of nitrite ions to nitrate, exhibiting a heterogeneous cross-exchange rate constant (k_f=(6.2±0.1×10⁴) M^-1 s^-1) 30 times higher than that previously described for the electrostatic assembled porphyrin films. The polymeric films were obtained by electropolymerization of the corresponding molecular films, previously prepared by dip-coating. This strategy leads to an increase in the efficiency of the reticulation process while minimizing the amount of monomer necessary for the preparation of the modified electrodes. The conductivity of the thin films close to the E_1/2 of the Ru(III/II) redox pair is very good, decreasing rapidly as the applied potential departs from it, as expected for a redox polymer. The conductivity decreases when the surface concentration becomes higher than 1.2×10^-8 mol cm⁻² also, reflecting a higher impedance for electrolyte diffusion inside the polymeric material. The high electrocatalytic activity associated with the high conductivity make this new nanostructured material suitable for sensor applications.     

Superoxide dismutase activity of a novel macromolecular manganese porphyrin

The discovery of a novel superoxide dismutase (SOD) mimic which demonstrates SOD activity, chemical stability in H₂O₂ solution and long half‐life in circulation is reported. The SOD mimic consists of a manganese porphyrin (MnP) with SOD activity and a polymer (poly (styrene‐co‐maleic anhydride); SMA) with biological characteristics. The SOD activity of SMA‐MnP at pH = 8.1 measured using the stopped‐flow kinetic analysis technique to monitor the decay of superoxide directly was 1.1 (± 0.1) × 10⁶ M‐1 sec‐1. It is postulated that the reduction by O₂^·− of the oxidized SMA‐Mn(III) is slow, while the oxidation of the reduced SMA‐Mn(II) by O₂^·− is very fast. The retention times of SMA‐MnP in the circulation of rabbits were determined. In vivo, SMA‐MnP that binds to the warfarin site on albumin showed an enhanced half‐life in the circulation. Additionally, in vitro SMA‐MnP indicated an excellent stability to H₂O₂. Copyright © 1999 John Wiley & Sons, Ltd.     

Unusual peroxidase activity of a myoglobin mutant with two distal histidines

By retaining the native distal His64 in sperm whale myoglobin(Mb),a second distal histidine was engineered in Mb by mutating Leu29 to His29.The resultant mutant of L29H Mb exhibits an unusual enhanced peroxidase activity with a positive cooperativity in comparison to that of wild type Mb.The new enzyme with two cooperative distal histidines has not been found in native peroxidase, which emphasizes a creation of the rational protein design.     

The synthesis and catalytic activity of poly(bis(imino)pyridyl) iron(II) metallodendrimer

The first and second generation carbosilane dendrimers with silicon hydride terminated were synthesized, and then reacted with bis(imino)pyridyl containing allyl [4-CH₂CHCH₂-2,6-ⁱPr₂C₆H₃NCMe(C₅H₃N)MeCN(2,6-ⁱPr₂C₆H₃)], in the presence of H₂PtCl₆ as a hydrosilylation catalyst, to afford the first and second generation carbosilane supported ligands. Complexation reactions with FeCl₂ · 4H₂O give rise to iron-containing carbosilane dendrimers with FeCl₂ moieties bound on the periphery. The metallodendrimers were used as catalyst precursors, activated with modified methylaluminoxane, for the polymerization of ethylene. In the case of low Al/Fe molar ratio, the metallodendrimers display much higher catalytic activity towards ethylene polymerization and produce much higher molecule weight polyethylenes than the corresponding single-nuclear complex under the same conditions.     

Advanced approaches for the characterization of a de novo designed antiparallel coiled coil peptide

We report here an advanced approach for the characterization of the folding pattern of a de novo designed antiparallel coiled coil peptide by high-resolution methods. Incorporation of two fluorescence labels at the C- and N-terminus of the peptide chain as well as modification of two hydrophobic core positions by Phe/[15N,13C]Leu enable the study of the folding characteristics and of distinct amino acid side chain interactions by fluorescence resonance energy transfer (FRET) and NMR spectroscopy. Results of both experiments reveal the antiparallel alignment of the helices and thus prove the design concept. This finding is also supported by molecular dynamics simulations. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in combination with NMR experiments was used for verification of the oligomerization equilibria of the coiled coil peptide.     

Multi-wall carbon nanotube-supported manganese(III) porphyrin: An efficient and reusable catalyst for the oxidation of alkenes with H2O2 under ultrasonic irradiation

A manganese complex of meso-tetrakis(p-hydroxyphenyl)porphyrin immobilized onto functionalized multi-wall carbon nanotubes has been synthesized and characterized. The catalytic activity of this heterogeneous catalyst was investigated in the oxidation of various olefins with hydrogen peroxide under ultrasonic irradiation. The role of the stoichiometric amounts of acetic anhydride/or acetic acid as an activator that introduces in situ peracetic acid is discussed. This heterogeneous catalyst was highly reusable in the oxidation reactions and reused several times without significant loss of its catalytic activity.     

第二配位层的氧化还原活性二茂铁促使铁卟啉在氧存在下发生质子还原

采用洁净、可持续的替代能源以解决化石燃料的过度消耗及因其燃烧而导致的日益加剧的全球变暖问题已经成为当务之急.其中,如何实现在大气含氧条件下的析氢反应成为需要攻克的重大挑战.氧还原在热力学上比质子还原更容易进行,并且氧气部分还原时通常产生活性氧物种,致使催化剂失活.因此,需要开发在氧气存在情况下能够有效还原质子的催化剂.本文设计了一种四苯基铁卟啉分子,该分子通过三氮唑将四个二茂铁连接在苯基邻位,并证明该催化剂能够在有氧气的情况下高效还原质子,产生氢气.作为铁卟啉类化合物催化质子还原的活性物种,Fe(0)发生质子还原比发生O2还原的动力学速率快得多,从而为氧气存在下的选择性质子还原奠定了基础.     

The observation of a picosecond transient in the relaxation of an iron porphyrin

Iron(III)tetraphenylporphyrin chloride, excited at 353 nm, showed significant bleaching and new absorption at 445 and 55 550 nm, which relaxed in 50 ps. Ground-state recovery occurs in ?100 fs; the bottleneck is populated with 3% efficiency. The photoproduct spectrum resembles a porphyrin ππ^* triplet, and provides evidence for intersystem crossing in an iron heme.     

Self-assembly of iron TCPP (meso-tetra(4-carboxyphenyl)porphyrin) into a chiral 2D coordination polymer

Synthetic metalloporphyrin complexes are often used as analogues of natural systems, and they can be used for the preparation of high-dimensional coordination polymers. In this work, a new chiral Fe-TCPP (TCPP is meso-tetra-(4-carboxyphenyl)porphyrin) coordination compound has been synthesized and structurally characterized. The compound is 2D via coordination bonds, and it exhibits strong hydrogen bonds that connect the planar arrays forming the 3D framework. The oxidation of the original Fe^II ions to Fe^III accounts for the formation of this array, in which the topological analysis reveals a very high connectivity based on a simple extension fashion of the structure. DFT calculations have been also carried out to study the stabilization of the Fe^III-compound. This is the third example of a 2D coordination compound based on TCPP in which the dimensionality refers just to coordination bonds, and no other ligands are present in the structure.     

Electrochemical Studies of a New Iron Porphyrin Entrapped in a Propylpyridiniumsilsesquioxane Polymer Immobilized on a SiO2/Al2O3 Surface

In this work, a new porphyrin, the 5,10,15,20‐tetrakis‐(2,6‐difluoro‐3‐sulfonatophenyl) porphyrinato iron(III) chloride (denoted as FeTsP) was immobilized on SiO₂/Al₂O₃ (SiAl) coated with n‐propylpyridiniumsilsesquioxane polymer (SiPy⁺Cl^?). The FeTsP was adsorbed on SiAl/SiPyCl by an ion exchange reaction, obtaining a modified solid, SiAl/SiPy/FeTsP, where the porphyrin complex was strongly adhered. Cyclic voltammograms of the SiAl/SiPy/FeTsP carbon paste electrode showed an irreversible response, with an oxidation peak at E_pa=0.40 V and nondefined reduction peak at E_pc=0.15 V (vs. SCE). These peaks were not observed for the nonmetallated porphyrin, indicating that they probably correspond to the Fe(III)/Fe(II) process. Studies made in solutions having different pH, (between pH 2 and 9) using the modified electrode showed that the peak potentials and the current density were not affect by pH changes, indicating that the iron porphyrin is very stable and strongly entrapped in the matrix. The modified electrode presented the property to electrocatalyze the eletrooxidation of hydrazine at 0.41 V (vs. SCE), at pH 7. The potentiality of the SiAl/SiPy/FeTsP electrode as a sensor for hydrazine was evaluated by the using the chronoamperometric technique. A linear response was obtained in the concentration range between 5×10^?5 and 6×10^?4 mol L^?1 of hydrazine.     

In silico locating the immune-reactive segments of Lepidium draba peroxidase and designing a less immune-reactive enzyme derivative

Peroxidases have broad applications in industry, environmental as well as pharmaceutical and diagnosis. Recently applicability of peroxidases in cancer therapy was mentioned. In the present study, a horseradish peroxidase homologue from Lepidium draba was subjected to in silico analyzes aiming at identifying and locating immune-reactive regions. A derivative sequence with decreased immunogenicity and increased stability also suggested. The tertiary structure of the enzyme was predicted. The functional and structural importance of residues was annotated as well as the conservatory status of each residue. The immune-dominant regions of protein were predicted with various software. N-terminal 4 residues, NFSHTGL (186–192), PRNGN (210–214), PLVRAYADGTQKFFN (261–275), and last 4 residues in C-terminal were predicted to be the consensus immunogenic segments of L. draba peroxidase. The modifications were applied to wild type sequence in order to mitigate its immune-reactiveness. The modifications were based on predicted energetic status of residues and naturally occurred amino acids in each position of the enzyme sequence, extracted from alignment file of 150 homologous peroxidases. The new enzyme derivative is predicted to be less immune-reactive and more stable. Thus the sequence is better suited to therapeutic applications.