Incubation of the apoB2 subunit of Escherichia coli ribonucleotide reductase with Fe2+ and O2 produces native B2, which contains the tyrosyl radical-dinuclear iron cluster cofactor required for nucleotide reduction. The chemical mechanism of this reconstitution reaction was investigated by stopped-flow absorption spectroscopy and by rapid freeze-quench EPR (electron paramagnetic resonance) spectroscopy. Two novel intermediates have been detected in the reaction. The first exhibits a broad absorption band centered at 565 nanometers. Based on known model chemistry, this intermediate is proposed to be a mu-peroxodiferric complex. The second intermediate exhibits a broad absorption band centered at 360 nanometers and a sharp, isotropic EPR signal with g = 2.00. When the reaction is carried out with 57Fe2+, this EPR signal is broadened, demonstrating that the intermediate is an iron-coupled radical. Variation of the ratio of Fe2+ to B2 in the reaction and comparison of the rates of formation and decay of the intermediates to the rate of formation of the tyrosyl radical (.Y122) suggest that both intermediates can generate .Y122. This conclusion is supported by the fact that both intermediates exhibit an increased lifetime in a mutant B2 subunit (B2-Y122F) lacking the oxidizable Y122. Based on these kinetic and spectroscopic data, a mechanism for the reaction is proposed. Unlike reactions catalyzed by heme-iron peroxidases, oxygenases, and model complexes, the reconstitution reaction appears not to involve high-valent iron intermediates.

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A novel method for the production of homogeneous samples of hollow carbon nanospheres is reported from cellulose, an inexpensive and renewable precursor. The nanospheres are of diameter 50 nm, graphitic wall thickness 5-10 nm, and can easily be produced in several hundred milligram batches. The nanospheres are derived from the laser pyrolysis of a nickel chloride templated cellulose char via open Ni-core shells.

Ab initio calculations (UB3LYP/6-31G(d)// UHF/6-31G(d)) and transition state theory on the title polymerization provide relative kinetic information which show the following:  that the hexyl group adequately represents the polymer chain, that theory predicts experimental reactivity ratios with reasonable accuracy, that the penultimate unit effect is small for this copolymerization, that inverted addition to give vicinal diacetoxy units should increase dramatically with polymerization temperature, and that the most favorable short chain branching reaction gives butyl braches as well as 1-acetoxybutyl branches, provided that inverted addition reactions place the acetoxy group six and four carbon atoms from the radical site, respectively. For primary radicals, the absolute values of the computed Arrhenius A factors are believed to be reliable, but the activation enthalpies are about 2 kcal/mol too low, based on a set of calibration reactions used to test the quality of our theoretical methods.

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