Hydrogen peroxide decomposition by a non-heme iron(III) catalase mimic: a DFT study

Non-heme iron(III) complexes of 14-membered tetraaza macrocycles have previously been found to catalytically decompose hydrogen peroxide to water and molecular oxygen, like the native enzyme catalase. Here the mechanism of this reaction is theoretically investigated by DFT calculations at the (U)B3LYP/6-31G* level, with focus on the reactivity of the possible spin states of the FeIII complexes. The computations suggest that H2O2 decomposition follows a homolytic route with intermediate formation of an iron(IV) oxo radical cation species (L.+FeIV==O) that resembles Compound I of natural iron porphyrin systems. Along the whole catalytic cycle, no significant energetic differences were found for the reaction proceeding on the doublet (S=1/2) or on the quartet (S=3/2) hypersurface, with the single exception of the rate-determining O--O bond cleavage of the first associated hydrogen peroxide molecule, for which reaction via the doublet state is preferred. The sextet (S=5/2) state of the FeIII complexes appears to be unreactive in catalase-like reactions.     

Convergent perturbation theory for a q–deformed anharmonic oscillator

A q–deformed anharmonic oscillator is defined within the framework of q–deformed quantum mechanics. It is shown that the Rayleigh–Schr?dinger perturbation series for the bounded spectrum converges to exact eigenstates and eigenvalues, for q close to 1. The radius of convergence becomes zero in the undeformed limit. Received: 6 August 1998 / Published online: 16 September 1998     

Stress distribution in a lap joint under tension-shear

This paper deals with the elastostatic load transfer of a tensile load in a model of an adhesive lap joint (tension-shear problem). The adhesive layer is regarded as infinitesimally thin and the displacement and traction vectors in the adherends are assumed to be continuous across the bond. The problem is reduced to a pair of Fredholm integral equations of the second kind which involve the mean angle between the deformed bond line and the tensile load. This angle, in turn, is determined by means of a scheme due to Goland and Reissner. Numerical results for the bond line stresses and the stress intensity factors at the ends of the bonded region are presented.     

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4′-ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, T_i using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as T_i increased, and reached a value of unity, i.e., full conversion at 400°C. At the same T_i, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various T_i. The primary determinant of w for all isomers was T_i, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998     

Perfluoro‐Tagged Benzyloxycarbonyl Protecting Group and Its Application in Fluorous Biphasic Systems

The synthesis of a new perfluoro‐tagged benzyloxycarbonyl protecting group is reported, as well as its application in the parallel protection of amines. Isolation of the protected amines was performed by simple liquid‐liquid extraction between perfluorinated and organic solvents. Deprotection was achieved by standard hydrogenolysis. The novel protecting group was also applied to cyclization protocols leading to quinazoline‐2,4‐diones. These products were isolated by simple extraction procedures     

Di‐ and tri‐organotin derivatives of 3S,4S‐3‐[(R)‐1‐(tert‐butyl‐dimethylsilyloxy)ethyl]‐4‐[(R)‐1‐carboxyethyl]‐2‐azetidinone: synthesis,characterization and in vitro antitumour activity

Di‐n‐butyl‐, triphenyl and tri‐n‐butyltin derivatives of 3 S, 4 S ‐3‐[( R )‐1‐(tert‐butyldimethyl‐­<?tw=103.5%>silyloxy)ethyl‐4‐[( R )‐1‐carboxyethyl]‐2‐azetidi<?tw>‐­none were synthesized and characterized. Their antitumour activity was screened against seven tumoural cell lines of human origin. Copyright © 1999 John Wiley & Sons, Ltd.