The alpha zein, the maize storage prolamin, is a mixture of several homologous polypeptides that shows two bands in SDS-PAGE, called Z19 and Z22. The conformation studies carried out by several authors in this mixture are conflicting. To elucidate these inconsistencies, we analyzed the conformation of the Z19 fraction, extracted from BR451 maize variety by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and small-angle X-ray scattering. The infrared results show that Z19 has 46% of alpha helix and 22% of beta sheet. The fast N-H to N-D exchange measured by (1)H NMR spectroscopy showed that Z19 is not a compact structure. The scattering measurements indicated an extended structure with 12 by 130 A. With these data, we have modeled the Z19 structure as a hairpin, composed of helical, sheet, turns, and secondary structures, folded back on itself.

Structural characterisations using the SAXS technique in a number of nanoheterogeneous materials and liquid solutions are reviewed. The studied systems are protein (lysozyme)/water solutions, colloidal ZnO particles/water sols, nanoporous NiO-based xerogels, hybrid organic-inorganic siloxane-PEG and PPG nanocomposites and PbTe semiconductor nanocrystals embedded in a glass matrix. These investigations also focus on the transformations of time-varying structures and on structural changes related to variations in temperature and composition. The reviewed investigations aim at explaining the unusual and often interesting properties of nanostructured materials and solutions. Most of the reported studies were carried out using the SAXS beamline at the National Synchrotron Light Laboratory (LNLS), Campinas, Brazil

Many silicate and borate glass systems exhibit sub-liquidus immiscibility. The fine-scale microstructure of phase separated systems has been studied mainly by electron microscopy and small angle X-ray scattering. The classical theories of homogeneous nucleation, spinodal decomposition and coarsening, and more recent statistical theories of segregation are outlined. These theories are compared with experimental data for the kinetics of amorphous phase separation. In the early stages of separation, for compositions and temperatures in the region between the binodal and spinodal and in particular close to the binodal, the results are consistent with a homogeneous nucleation process. The classical theory of spinodal decomposition only agrees qualitatively with experimental data for the central region of the miscibility gap. The kinetics of coarsening are in general agreement with theory. Recent predictions from computer simulation studies on model alloys appear to be valid for glass systems. Experimental studies of the influence of amorphous phase separation on crystallization of glasses are also reviewed. In certain circumstances there is clear evidence that amorphous phase separation enhances the rates of crystal nucleation and growth.

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