Over the past three decades, researchers have investigated the existence of possible relationships between crystal nucleation kinetics and the atomic-scale structure of silicate glasses. The main driving force for this quest was the fact that while the vast majority of glass-forming substances only undergo surface (heterogeneous) nucleation when sufficiently heated, a few systems also show the thermodynamically less favourable case of internal (homogeneous) nucleation on laboratory time/length scales. For such glass systems, various macroscopic properties, such as densities, configurational entropies and frozen-in birefringence, have suggested that the structure in the glassy state shows a closer resemblance to the structure of the phase formed upon crystallisation than in the case of glass systems only undergoing heterogeneous nucleation. However, the specific structural features and their length scales have remained uncertain. In this article, we review and discuss the research investigating relationships between the occurrence of internal nucleation and structural parameters related to various different length scales. The latter include (1) short-range order, concerning both network modifier cation-oxygen distances and coordination numbers as well as network former Q n distributions, (2) intermediate range order describing network former connectivities, network former/network modifier correlations, and network modifier distance distributions, and (3) medium range order as reflected by silicate tetrahedral ring-size statistics. Inspection of this data for several stoichiometric oxide glasses and their respective isochemical crystals suggests a positive correlation between homogeneous nucleation ability and structural similarity at the level of short- and intermediate-range order of the network modifier cations. In contrast, no correlation can be found with regard to any structural parameters describing the local structures of the network former species (Q n distributions). Based on the limited set of data available, we develop concrete recommendations for future experiments to test this hypothesis.

Retroviral vectors designed to transduce hemopoietic stem cells have to be optimised with respect to basic requirements for gene transfer and expression, (i) The cis-regulatory elements of the genomic vector RNA interacting with retroviral proteins supplied from packaging cells must allow for optimal packaging, reverse transcription and integration into the genome of the target cell, (ii) The cis-regulatory elements of the integrated ’proviral’ vector DNA interacting with the cellular transcriptional machinery must guarantee efficient and long-lasting gene expression in the target cell and its progeny.

Insights into details of the biomechanism by which porphobilinogen (1) cyclotetramerizes to uroporphyrinogen III (2) as well as promising synthetic applications are provided by investigation of this reaction in vitro. The cyclotetramerization of newly prepared norporphobilinogen (5) proved to be extemely specific due to strong conformation control. Advantage was taken of this finding by preparing a N,N,N,N-tetramethyl-porphyrinogen (13a) for the first time. Protected derivatives of the linear tetramer of porphobilinogen (20c) which is regarded as an intermediate of the cyclotetramerization were gained by total synthesis and their transformations investigated.