Metallisch leitende Polymere — Jagdgründe für Solitonen?

Polyacetylene is presented as the prototype of a metallic conducting polymer. The concepts of one-dimensional metal physics are illustrated and special attention is drawn to a structural defect called “soliton”. Electrical, magnetic, and optical experiments connected with solitons are discussed. The authors' opinion is expressed that present experimental results do not yet furnish strong evidence for the existence of solitons in polyacetylene, but that the soliton idea is a fruitful stimulus for further investigations and novel applications.     

Evaluating the economic benefits of pesticide usage

In regulating the use of a pesticide, one critical element taken into consideration by the U.S. Environmental Protection Agency is the magnitude of the benefits provided by the pesticide. A number of alternative, and legitimate, definitions of pesticide benefits are discussed and their implications for the regulatory process identified. Recommendations for improving the regulatory process are proposed.     

Symmetriestrukturen der Physik

The fundamental concepts underlying the application of symmetry to physics are discussed. The exposition employs objects from the geometry of two and three dimensions instead of the algebraic formalism.     

Adult-onset GM2 gangliosidosis diagnosed in a fetus

Amniocentesis and subsequent tests are reported on a fetus conceived of a rare mating type: its mother has an intermediate level of β hexosaminidase A (HEX A), characteristic of carriers of Tay-Sachs disease (TSD), while the father suffers from an adult-onset GM₂ ganglio-sidosis (AOG) with severe HEX A deficiency. Activity of HEX A in the cultured fetal cells was very low when measured by the heat-inactivation method, thus showing the typical biochemical phenotype of TSD fetuses. However, upon separation of HEX isozymes by ion exchange chromatography, residual HEX A (17 per cent of total HEX) was demonstrated. Also in contrast to TSD fetuses, this fetus' fibroblasts were able to synthesize the precursor of a chains of HEX, and ultrastructural examination of its brain revealed few atypical lamellar bodies, unlike those found in TSD fetuses of the same gestational age. It is therefore concluded that the fetus was not affected with TSD, but rather with AOG.     

Peptidchemie heute

Peptide chemistry has reached a plateau on which more work is devoted to the improvement of known basic principles than to the development of really new methods. As a consequence, routine syntheses of peptides concentrate on few protecting groups and coupling procedures only. The recent progress in purification of peptides by liquid chromatography helped to promote this trend. Meanwhile, recombinant technology permits the synthesis of proteins and possibly of some lower peptides, too. It cannot compete, however, with chemical solid-phase synthesis of a newly discovered peptide with up to about 40 amino acids in speed but may take over the synthesis for large-scale production. Peptides containing modified or non-natural structures, which are often superior to the natural compounds as drugs, will remain subject of chemical synthesis, too. Present research focuses on the role of peptide and protein factors in the immune response and on structure and biological activities of neuropeptides.