Neuroglobin is a recently discovered member of the globin superfamily. Combined electron paramagnetic resonance and optical measurements show that, in Escherichia coli cell cultures with low O 2 concentration overexpressing wild-type mouse recombinant neuroglobin, the heme protein is mainly in a hexacoordinated deoxy ferrous form (F8His-Fe 2؉ -E7His), whereby for a small fraction of the protein the endogenous protein ligand is replaced by NO. Analogous studies for mutated neuroglobin (mutation of E7-His to Leu, Val, or Gln) reveal the predominant presence of the nitrosyl ferrous form. After sonication of the cells wild-type neuroglobin oxidizes rapidly to the hexacoordinated ferric form, whereas NO ligation initially protects the mutants from oxidation. Flash photolysis studies of wild-type neuroglobin and its E7 mutants show high recombination rates (k on ) and low dissociation rates (k off ) for NO, indicating a high intrinsic affinity for this ligand similar to that of other hemoglobins. Since the rate-limiting step in ligand combination with the deoxy-hexacoordinated wild-type form involves the dissociation of the protein ligand, NO binding is slower than for the related mutants. Structural and kinetic characteristics of neuroglobin and its mutants are analyzed. NO production in rapidly growing E. coli cell cultures is discussed.

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The formation and crystallization of disordered nanosized ZnO resulting from the thermal decomposition of nanocrystalline hydrozincite [Zn5(CO3)2(OH)6] has been observed and investigated during pulse annealing experiments up to 625 °C in air or vacuum by electron paramagnetic resonance of trace amounts of substitutional Mn2+ impurity ions, in correlation with X-ray diffraction and transmission electron microscopy measurements. The mesoporous structure of the disordered ZnO, which initially forms in air and vacuum at 225 and 175 °C, respectively, further transforms into nanocrystalline ZnO of increasing particle size and improved lattice quality at higher annealing temperatures. The crystallization process, which does not affect the concentration of the substitutional impurity ions, as well as the simultaneous presence of both disordered and crystalline phases, should be considered in further applications of the resulting nanosized ZnO.

The correlation of the lattice disorder with the nanocrystal average size, in ZnO nanocrystals synthesized by several different methods, has been quantitatively monitored by line shape analysis of the multifrequency electron paramagnetic resonance (EPR) spectra of low concentrations of substitutional Mn2+ probing ions. The observed correlation between the line broadening parameter of the spectrum and the average ZnO nanocrystals size, independent of the synthesis procedure of the ZnO nanocrystals, demonstrates the dominance of the size related strain/disorder. On the basis of this result, a new method for determining the average ZnO nanocrystal size from the quantitative analysis of the EPR spectra of the Mn2+ probes was derived. The nanocrystallization of the disordered ZnO formed by the thermal decomposition of hydrozincite was monitored using this procedure. The observed ZnO nanocrystallite growth kinetics at lower temperatures was described by a structural relaxation mechanism consisting of the local ordering by rearrangements of the atoms in the interfaces/grain boundaries, with a growth activation energy of ∼23 kJ/mol. When the nanostructured ZnO was more than 75% crystallized, another growth mechanism of the nanocrystals was found to occur, driven by the reduction of the total grain boundary energy.

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