Ferritins are ubiquitous iron storage and detoxification proteins distributed throughout the plant and animal kingdoms. Mammalian ferritins oxidize and accumulate iron as a ferrihydrite mineral within a shell-like protein cavity. Iron deposition utilizes both O(2) and H(2)O(2) as oxidants for Fe(2+) where oxidation can occur either at protein ferroxidase centers or directly on the surface of the growing mineral core. The present study was undertaken to determine whether the nature of the mineral core formed depends on the protein ferroxidase center versus mineral surface mechanism and on H(2)O(2) versus O(2) as the oxidant. The data reveal that similar cores are produced in all instances, suggesting that the structure of the core is thermodynamically, not kinetically controlled. Cores averaging 500 Fe/protein shell and diameter approximately 2.6 nm were prepared and exhibited superparamagnetic blocking temperatures of 19 and 22 K for the H(2)O(2) and O(2) oxidized samples, respectively. The observed blocking temperatures are consistent with the unexpectedly large effective anisotropy constant K(eff)=312 kJ/m(3) recently reported for ferrihydrite nanoparticles formed in reverse micelles [E.L. Duarte, R. Itri, E. Lima Jr., M.S. Batista, T.S. Berquó and G.F. Goya, Large Magnetic Anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles, Nanotechnology 17 (2006) 5549-5555.]. All ferritin samples exhibited two magnetic phases present in nearly equal amounts and ascribed to iron spins at the surface and in the interior of the nanoparticle. At 4.2 K, the surface spins exhibit hyperfine fields, H(hf), of 436 and 445 kOe for the H(2)O(2) and O(2) samples, respectively. As expected, the spins in the interior of the core exhibit larger H(hf) values, i.e. 478 and 486 kOe for the H(2)O(2) and O(2) samples, respectively. The slightly smaller hyperfine field distribution DH(hf) for both surface (78 kOe vs. 92 kOe) and interior spins (45 kOe vs. 54 kOe) of the O(2) sample compared to the H(2)O(2) samples implies that the former is somewhat more crystalline.

Aside from carbon, germanium is the only element forming non-polar compounds with hydrogen that are stable under ordinary conditions. The silicanes, while more stable than the germanes toward thermal decomposition, are much more

Measurements of the heat of adsorption of hydrogen on active and heat-treated copper catalysts have been made.The active preparations show maxima in the curves of heat of adsorption plotted against amount adsorbed.With partially de-activated catalysts the maximum occurs when smaller amounts of gas are adsorbed. Further de-activation eliminates such maxima.These results are in harmony with a theory of the catalytic surface with variable elementary spaces, upon the most active of which adsorption is accompanied by an endothermic activation process.

We present comparative Mössbauer investigations of nanosized FeOOH and FeOOD biomineral phases nucleated within the 7-nm diameter cavity of horse-spleen apoferritin in order to assess deuterium isotopic effects on nanoscale, bioinorganic lattice structures with extended hydrogen bond networks. Differences in magnetic anisotropy energy, packing density and degree of crystallinity in the resulting iron oxo-hydroxide nanophases obtained via D 2 O (heavy water) vs. H 2 O (light water) solution chemistry are noted. These observations point to the possibility of stabilizing new thermodynamic states in the solid-state by utilizing isotope effects, with important implications for new synthetic pathways to novel nano materials.

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