Fine tuning the reactivity of corrole-based catalytic antioxidants

In order to determine the electronic factors that may affect the catalytic antioxidant activity of water-soluble metallocorroles a series of 10-aryl-5,15-pyridinium manganese(III) corroles was prepared. These complexes were examined regarding the effect of the C(10) substituent on the Mn(IV)/Mn(III) redox potentials, catalytic rate constants for decomposition of HOONO, prevention of tyrosine nitration, and superoxide dismutase activity. This structure-activity relationship investigation provides new insight regarding the mechanism by which manganese(III) corroles act as catalytic antioxidants. It also discloses the superiority of the C(10)-anysil-substituted complex in all examined aspects.     

A chromophore-supported structural and functional model of dinuclear copper enzymes,for facilitating mechanism of action studies

Type III dicopper centres are the heart of the reactive sites of enzymes that catalyze the oxidation of catechols. Numerous synthetic model complexes have been prepared to uncover the fundamental chemistry involved in these processes, but progress is still lagging much behind that for heme enzymes. One reason is that the latter gain very much from the informative spectroscopic features of their porphyrin-based metal-chelating ligand. We now introduce sapphyrin-chelated dicopper complexes and show that they may be isolated in different oxidation states and coordination geometries, with distinctive colors and electronic spectra due to the heme-like ligands. The dicopper(i) complex 1-Cu2 was characterized by ¹H and ¹⁹F NMR spectroscopy of the metal-chelating sapphyrin, the oxygenated dicopper(ii) complex 1-Cu2O2 by EPR, and crystallographic data was obtained for the tetracopper(ii)-bis-sapphyrin complex [1-Cu2O2]2. This uncovered a non-heme [Cu₄(OH)₄]⁴⁻ cluster, held together with the aid of two sapphyrin ligands, with structural features reminiscent of those of catechol oxidase. Biomimetic activity was demonstrated by the 1-Cu2O2 catalyzed aerobic oxidation of catechol to quinone; the sapphyrin ligand aided very much in gaining information about reactive intermediates and the rate-limiting step of the reaction.

Di-copper chelation by sapphyrin facilitates reaction mechanism investigations and characterization of reactive intermediates regarding biomimetic catechol oxidation.     

Influence of load torque on stability of rotor driven by flexible shaft

The influence of the load torque on the stability of a symmetric rotor, driven by a flexible shaft, is studied. Both linear and angular displacements of the rotor are considered. The analysis—which is approximate, and with the deflection, the damping and the load torque assumed to be small—shows that the main destabilizing effect of the load torque is due to the transverse moments acting while the rotor is inclined. The reaction pattern at the ends of the shaft, determined by means of the Kirchhoff equations, indicates that the semitangential mode of loading (conservative) is operative.     

How acidic are corroles and why?

The pH-dependent absorption and emission spectra of the water-soluble 2,17-disulphonato-5,10,15-tris(pentafluorophenyl)corrole revealed that its inner-core nitrogen atoms can be both protonated and deprotonated, with acidity constants of 2.5 and 5.2, respectively. An analysis of the structural features of free-base corroles suggests that the quite limited pH range at which corroles remain neutral is reminiscent of the instability of mono-protonated porphyrins.     

Iron(III) and iron(IV) corroles: synthesis,spectroscopy, structures,and no indications for corrole radicals

A delicate control of reaction conditions allows the isolation of several distinctively different iron complexes of tris(pentafluorophenyl)- and tris(2,6-dichlorophenyl)corrole. As long as coordinating ligands are present, the iron(III) complexes are stable in solution. Otherwise they are aerobically oxidized to either mononuclear chloroiron(IV) or dinuclear (mu-oxo)iron(IV) complexes, in acidic and basic solutions, respectively (the latter holds only for tris(pentafluorophenyl)corrole). When treated with NaNO(2), the mononuclear chloroiron(IV) corroles are efficiently converted into diamagnetic iron nitrosyl complexes. The low- and intermediate-spin iron(III), iron nitrosyl, and chloroiron(IV) corroles were fully characterized by a combination of spectroscopic methods and X-ray crystallography. There was no indication for an open-shell corrole in any of the complexes.     

Glucose oxidase–magnetite nanoparticle bioconjugate for glucose sensing

Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of magnetite (Fe₃O₄) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase to the amino-modified nanoparticle surface. Functionalization of the magnetic nanoparticle surface with amino groups greatly increased the amount and activity of the immobilized enzyme compared with immobilization procedures involving physical adsorption. The enzymatic activity of the glucose oxidase-coated magnetic nanoparticles was investigated by monitoring oxygen consumption during the enzymatic oxidation of glucose using a ruthenium phenanthroline fluorescent complex for oxygen sensing. The glucose oxidase-coated magnetite nanoparticles could function as nanometric glucose sensors in glucose solutions of concentrations up to 20 mmol L^–1. Immobilization of glucose oxidase on the nanoparticles also increased the stability of the enzyme. When stored at 4°C the nanoparticle suspensions maintained their bioactivity for up to 3 months.     

Organometallic synthons: The wittig reaction of tricarbonyl [(3,4,5,6-η)-1,3,5-cycloheptatriene-1-carboxaldehyde] iron

The utility of the Wittig reaction in synthesis of organometallic compounds is exemplified by its application to the preparation of a series of tetraene—Fe(CO)₃ complexes from aldehyde 9 and a variety of triphenylphosphoranes. Reaction of 9 with triphenylmethylene phosphorane afforded unexpectedly a $\text{1}\text{1}$ isomeric mixture of 8-methylheptafulveneiron tricarbonyl (12), probably via a (1,9) hydrogen shift of intermediate 11. Triphenylbenzylidene phosphorane condensed with 9 to give the cis and trans isomers of cycloheptatrienyl—styrene complex 14. The triphenylphosphoranes of carbomethoxymethylene, carboethoxymethylene and cyanomethylene react with 9 yielding the appropriate trans condensation products exclusively. Tetracyanoethylene (TCNE) and N-phenyltriazolinedione (NPTD) readily react periselectively with the unrearranged Wittig reaction products at the free diene moiety, affording the corresponding 4+2 cycloadducts. Heptafulvene complex 12, upon reaction with TCNE, gave the 8+2 cycloadduct 26.     

Proficiency testing as tool for ISO 17025 implementation in National Public Health Laboratory: a mean for improving efficiency

Public Health Laboratories (PHL) as part of Public Health Services are involved in law enforcement and ensuring food and water quality. The laboratories had to go through an organizational and monetary change imposed by the growing and changing needs of the state of Israel. The laboratories had to become more modern and to implement new and more sophisticated testing methods. Another requirement was to perform a steadily increasing number of tests and to be more flexible towards customers’ demands. Yet, the budget was not changed accordingly, as the Public Service to which the laboratories belong to do not respond to changing needs. Management realization was that the accreditation process could be used as a tool to achieve organizational and cultural change. Understanding and transformation were required throughout the organization, including management. Proficiency testing is performed for all testing methods in all areas even for non-accredited tests such as clinical tests. Proficiency testing was used as a tool for organizational culture change. It is a great index with game elements, that gives employees and managers the possibility for comparison, fixing problems and corrective action. The demands of ISO 17025 made it necessary to change peoples’ attitudes and views on both professional and communication levels. Laboratory quality consists now on the four main principles, described in the 5M&E model which is typical to small organizations and which ensures a constantly improving system: ”Policy statement”, ”Machine”, ”Material”, ”Measurement”, ”Method”, ”Manpower”, and ”Environment” targeted to achieve ”Quality upgrade”. Slowly we succeeded in providing better and more reliable services and have increased our income on what would hopefully become our way to financial independence. We hope this process would provide the Ministry of Health with a better chance to public health using the same financial sources. Received: 25 October 2000 Accepted: 12 December 2000     

Polymerization of 4‐methylpentene and vinylcyclohexane by amine bis(phenolate) titanium and zirconium complexes

The polymerization of the substituted olefins 4‐methylpentene and vinylcyclohexane by dibenzyl titanium and zirconium complexes of three amine bis(phenolate) ligands is reported. The ligands featured a dimethylamino side‐arm donor and either electron‐withdrawing (Cl and Br) or methyl phenolate substituents. After activation with B(C₆F₅)₃, the zirconium catalysts exhibited a higher activity than the titanium catalysts toward these bulky olefins. Very high weight‐average molecular weight poly(4‐methylpentene) was obtained with the zirconium catalysts. The zirconium catalysts were employed in 1‐hexene polymerization, and their activity was found to be the highest ever reported for catalysts of the amine bis(phenolate) family. The catalysts featuring methyl phenolate substituents showed a higher activity toward these substituted olefins than the electron‐poor catalysts; this trend was opposite to their activity toward 1‐hexene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1136–1146, 2006     

Optical fiber based radial polarizer

In this paper we present a new type of optical fiber aiming to radially polarize the electrical field. This special device is composed of a tapered fiber having a classical core while on top of its external surface, radially oriented nanorods are disposed. The tails of the propagated wave are interacting with those radially oriented nanorods. This interaction performs the polarization of the propagated mode into a radial polarization.