Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 62. Darstellung und NMR-spektroskopische Untersuchung von Komplexen des Tetramethyltitans

Contributions to the Chemistry of Transition Metal Alkyl Compounds. 62. Preparation and NMR-spectroscopic Characterization of Tetramethyltitanium Complexes Complexes of tetramethyltitanium with THF and oxygen, nitrogen and phosphorous containing chelating ligands were synthesized and characterized by low temperature n.m.r. spectroscopy. The obtained complexes show a dynamic behaviour in solutions. The results of semiempirical MO calculations favour octahedral and not a trigonal prismatic configuration of the complexes.     

Quasi-steady state in the Michaelis–Menten system

We discuss the differential equations derived from the Michaelis–Menten model of an enzyme-catalyzed reaction, with no a priori conditions on parameters or initial concentrations. Using an elementary approach, we derive and investigate inequalities and conditions for the validity of the quasi-stationary approximation, confirming results by Segel and Slemrod, and determine new estimates for the pre-steady state period.     

Polymer-induced alignment of DL-alanine nanocrystals to crystalline mesostructures

Crystallization of DL-alanine by cooling of a supersaturated solution in the presence of a chiral double-hydrophilic block copolymer poly(ethylene glycol)-block-poly(ethylene imine)-S-isobutyric acid (PEG4700-PEI1200-S-iBAc) yields crystal superstructures with an astonishing morphology. Although analysis by light microscopy reveals these crystals to be apparently well facetted, electron microscopy shows that they consist of three-dimensionally, well-aligned nanocrystals that are scaffolded to a so-called mesocrystal. This mesocrystal is formed by polymer-mediated structuration, and provides evidence for the importance of mesoscopic events in a typical crystallization process.     

Extremely base-resistant organic phosphazenium cations

A series of peralkylated polyaminophosphazenium cations exhibiting extraordinary base resistance under phase-transfer conditions were efficiently synthesized from readily available starting materials. Their half lives under these conditions exceed those of the most stable conventional organic cations by factors of up to 3000.