Selenonicotinamide, 2,2'-diselenobis[3-amidopyridine] (NictSeSeNict) exhibits glutathione-peroxidase (GPx)-like activity, catalyzing the reduction of hydrogen peroxide (H2O2) by glutathione (GSH). Estimated reactivity parameters for the reaction of selenium species, according to the Dalziel kinetic model, towards GSH (ϕGSH) and H2O2 (ϕH2O2), indicated that the rate constant for the reaction of NictSeSeNict with GSH is higher as compared to that with H2O2, indicating that the activity is initiated by reduction. (77)Se NMR spectroscopy, HPLC analysis, mass spectrometry (MS) and absorption spectroscopy were employed to understand the nature of selenium intermediates responsible for the activity. The (77)Se NMR resonance at 525 ppm due to NictSeSeNict disappeared in the presence of GSH with the initial appearance of signals at δ 364 and 600 ppm, assigned to selone (NictC=Se) and selenenyl sulfide (NictSeSG), respectively. Reaction of H2O2 with NictSeSeNict produced a mixture of selenenic acid (NictSeOH) and seleninic acid (NictSeO2H) with (77)Se NMR resonances appearing at 1069 and 1165 ppm, respectively. Addition of three equivalents of GSH to this mixture produced a characteristic (77)Se NMR signal of NictSeSG. HPLC analysis of the product formed by the reaction of NictSeSeNict with GSH confirmed the formation of NictC=Se absorbing at 375 nm. Stopped-flow kinetic studies with global analysis revealed a bimolecular rate constant of 4.8 ± 0.5 × 10(3) M(-1) s(-1) and 1.7 ± 0.6 × 10(2) M(-1) s(-1) for the formation of NictC=Se produced in two consecutive reactions of NictSeSeNict and NictSeSG with GSH, respectively. Similarly the rate constant for the reaction of NictC=Se with H2O2 was estimated to be 18 ± 1.8 M(-1) s(-1). These studies clearly indicated that the GPx activity of NictSeSeNict is initiated by reduction to form NictSeSG and a stable selone, which is responsible for its efficient GPx activity.

Selenoethers attached to functional groups through propyl chain viz., bis(3-carboxypropyl)selenide (SeBA), bis(3-hydroxypropyl)selenide (SePOH) and bis(3-aminopropyl)selenide dihydrochloride (SePAm), have been examined for their ability to inhibit peroxyl radical mediated DNA damage, peroxyl radical scavenging ability and glutathione peroxidase (GPx) like activity. The DNA damage was monitored by gel electrophoresis, bimolecular rate constants for scavenging of model peroxyl radical were determined by pulse radiolysis and the GPx activity was followed by their ability to reduce hydrogen peroxide in the presence of glutathione utilizing NADPH decay and HPLC analysis. Among these compounds, SeBA showed maximum DNA protecting activity and it was also the most efficient in scavenging peroxyl radicals with the highest GPx mimicking activity. Quantum chemical calculations confirmed that SeBA with the highest energy level of HOMO (highest occupied molecular orbital) is the easiest to undergo oxidation and therefore exhibits better radical scavenging, GPx mimicking and DNA protecting activity than SePOH or SePAm.

SynopsisExperimental data, which includes catalyst lifetimes, thermal analyses, fractionation by urea complexation, x-ray diffraction, and 13C-NMR spectroscopy, are presented to confirm the successful synthesis of ABA propylene-ethylene block copolymers. A dry catalyst system of DEAC-TiC13(AA) and a gas-phase polymerization technique was used to prepare the copolymers. PRP-and ERE-type copolymers (P-isotactic polypropylene, E-polyethylene, and R-random propylene-ethylene copolymer block) were prepared. Some preliminary physical property data are given which indicate that PRP-type copolymers can behave as elastomeric fibers. The stress-strain behavior also indicates block copolymer formation. EXPERIMENTALThe preparation of the active dry catalyst from Et2AlCl and TiC13(AA) and the technique for sequential addition of propylene and ethylene has already been d e~c r i b e d .~?~ Experimental conditions for the various copolymers are summarized in Table 1. The random B blocks were synthesized by admitting both monomers simultaneously, in various ratios, to the reaction vessel. The end A

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The ligand N’,N’‐bis(6‐chloropyridin‐3‐yl)pyridine‐2,6‐dicarboxamide (1) in their di‐deprotonated forms have been used to synthesize two new iron (III) 2 and 3 metal complexes. The iron(III) is surrounded by two tridentate ligands for complex 2, and one tridentate ligand for complex 3. Both complexes have been characterized by NMR, UV‐Visible, IR spectroscopy and elemental analysis. The solid‐state structure of 2 was determined by X‐ray diffraction analysis. Both iron complexes were further studied for ethylene polymerization in the presence of co‐catalyst methylaluminoxane (MAO) under various reaction conditions. It was found that the pincer containing complex 3 exhibited good activities for ethylene polymerization at 80 °C, while the bis‐ligated iron complex 2 did not show activity for ethylene polymerization.

SynopsisABA triblock copolymers of propylene and ethylene, where the central block is a random copolymer of ethylene and propylene and the A blocks are either isotactic polypropylene or polyethylene, are described. Structural changes induced by stretching at room and elevated temperatures are reported. WAXS was used to monitor these changes. The results indicate that block copolymers were synthesized and that different combinations of mechanical properties may be obtained by varying the type and length of the A blocks and adjusting the monomer ratio in the random B block.