Iron(III) hydroxides are abundant in near-surface natural environments and play an important role in geochemical processes and the fate of contaminants. The issue of the structure of the common nanophase material ferrihydrite (ferric hydroxide) is controversial and has been debated in the literature for many years without definitive resolution. At least two types of ferrihydrite, the 2-line and 6-line forms, are conventionally recognized. It has been suggested that these forms possess different structures built up by different mixtures of distinct nanophase components. However, traditional crystallographic methods provide depictions of structure that are most sensitive either to short-range order (X-ray absorption) or long-range periodicity (X-ray diffraction or electron diffraction). We used high-energy X-ray total scattering for pair distribution function analysis to observe both the short- and intermediate-range ordering (exceeding ∼15 Å) of synthetic ferrihydrite with three distinct average domain sizes of 2, 3, and 6 nm. We show that there are no significant differences in the underlying structures of these materials and that the differences in the diffraction patterns can be entirely interpreted by variations in the average size of the coherent scattering domains. The average crystallite sizes inferred from the PDF analysis are in good agreement with direct observation by high-resolution transmission electron microscopy.

In this review article the function of the binding site monomers in the molecular imprinting procedure is discussed. Especially, new developments towards stoichiometric noncovalent interactions are highlighted. In stoichiometric noncovalent interactions template and binding site monomer in an 1:1 molar ratio are nearly completely bound to each other. This is only possible if the association constants are considerably high (Kass > 900 M(-1)). Using this type of interaction in molecular imprinting no excess of binding sites is necessary and binding sites are only located inside the imprinted cavity. Since all cavities can be reloaded these polymers show high capacity (e.g., for preparative application) and are especially suited for the synthesis of catalytically active imprinted polymers. Discussed are binding site interactions based on amidines (and guanidines), multiple hydrogen bonding, charge-transfer interactions, and host-guest inclusion. The systematic investigation of the underlying binding reaction is described in detail. With low-molecular weight model substances the thermodynamics of the association can be conveniently investigated, e.g., by NMR spectroscopy.

The structural behaviour of SnS under high-pressure has been investigated by angular dispersive synchrotron powder diffraction up to 38.5 GPa. A structural phase transition from orthorhombic α-SnS to monoclinic γ-SnS was observed at 18.15 GPa. The fit of a Birch–Murnaghan equation-of-state gave the volume at zero pressure of V0 = 192.6(3) Å3, the bulk modulus at zero pressure of B0 = 36.6(9) GPa and the pressure derivative of the bulk modulus for α-SnS and V0 = 160(1) Å, B0 = 86.0(5) GPa and for γ-SnS. The improper ferro-elastic transition is of first-order and is accompanied by a large volume discontinuity of about 9.1%. The phase transition can be described in terms of a group/subgroup relationship. The doubling of the unit cell indicates a wavevector (1/2,0,1/2) at the U-point in the Brillouin zone.