Catalytic ammoxidation of propylene was studied using Fe2O3–MoO3/SiO2 catalysts, which have been prepared following a special method. Interaction of ammonia with the catalysts was studied by means of IR spectroscopy and gravimetrically using a McBain balance. Introduction of iron into MoO3/SiO2 catalysts modifies acidic as well as redox properties.
We report on interpolyelectrolyte complexes (IPECs) formed by micelles of ionic amphiphilic diblock copolymers with polyisobutylene (PIB) and poly(sodium methacrylate) (PMANa) blocks interacting with quaternized poly(4-vinylpyridine) (P4VPQ). The interpolyelectrolyte complexation was followed by turbidimetry and small angle neutron scattering (SANS). The data obtained by means of a combination of SANS, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) provide evidence on the core-shell-corona structure of the complex species with the shell assembled from fragments of electrostatically bound PMANa and quaternized P4VPQ fragments, original PIBx-b-PMAAy micelles apparently playing a lyophilizing part. The complex formation is followed by potentiometric titration as well. This process is initially kinetically controlled. In the second step larger aggregates rearrange in favor of smaller complexes with core-shell-corona structure, which are thermodynamically more stable. An increase in ionic strength of the solution results in dissociation of the complex species as proven by SANS and analytical ultracentrifugation (AUC). This process begins at the certain threshold ionic strength and proceeds via a salt-induced gradual release of chains of the cationic polyectrolyte from the complex species. 相似文献
A suitable substitute : All integrin receptors bind their ligands, which contain an aspartate residue, in the metal‐ion‐ dependent adhesion site (MIDAS). So far all attempts to replace the carboxyl group of aspartate with other, pharmacologically favorable isosteric groups have failed. Now it has been shown that a hydroxamic acid group can replace the carboxyl group; the resulting ligand retains its high binding activity. The picture shows one such ligand in the binding site of αvβ3.
The binding of the carboxyl group of an aspartate residue in the metal‐ion‐dependent adhesion site (MIDAS) is a key feature in the binding of ligands to integrins. This finding was demonstrated by the binding of the cyclic pentapeptide cyclo(RGDfNMeV) (Cilengitid) to the integrin αvβ3 (see picture). In their Communication on p. 4436 ff, H. Kessler and co‐workers show that the carboxyl group previously considered essential for binding can be replaced by a hydroxamic acid unit.
