Preliminary molecular replacement results for a crystalline gene 4 protein-deoxyoligonucleotide complex.

Complexes of the gene 5 protein from bacteriophage fd with a variety of oligodeoxynucleotides, ranging in length from two to eight and comprised of several different sequences, have been formed and crystallized for X-ray diffraction analysis. The crystallographic parameters of four different unit cells, all of which are based on hexagonal packing arrangements, indicate that the fundamental unit of the complex is composed of six gene 5 protein dimers. We believe this aggregate has 622 point group symmetry and is a ring formed by end-to-end closure of a linear array of six dimers. From our results we have proposed a double-helix model for the gene 5 protein-DNA complex in which the protein forms a spindle or core around which the DNA is spooled. Currently 5.0-A X-ray diffraction data from one of the crystalline complexes is being analyzed by molecular replacement techniques to obtain a direct image of the protein-nucleic acid complex.     

Röntgenstrukturuntersuchungen über elastisches Gewebe unter besonderer Berücksichtigung der Dehnung und Entquellung

Ohne Zusammenfassung Herrn Prof. Dr. H. Vo?, von dem ich die Anregung zu dieser Arbeit erhielt, sowie Herrn Prof. Dr. E. Schiebold danke ich ganz besonders für ihr st?ndiges f?rderndes Interesse und die wertvollen Hinweise bei meinen Untersuchungen. Die R?ntgenaufnahmen wurden in der physikalisch-chemischen und R?ntgen-Abteilung des Mineralogischen Instituts angefertigt, für die Erlaubnis hierzu sei dem Institutsdirektor Prof. Dr. K. H. Scheumann auch an dieser Stelle bestens gedankt. Ebenfalls danke ich Herrn Dr. W. Hofmann und Herrn Dr. F. Halle für die Beratung bei der Anfertigung und Ausdeutung der Diagramme.     

Channeling of Auroral Kilometric Radiation During Geomagnetic Disturbances

JETP Letters - The electromagnetic fields measured on the ERG satellite are presented and their comparative analysis with measurements on the WIND satellite is carried out. The possibility of...     

Deformation der Mikrofibrillen von Baumwoll-und Bakterien-Cellulose

Ohne Zusammenfassung     

Polarization effects on the surface chemistry of PbTiO3-supported Pt films

To demonstrate a new paradigm of dynamical control of surface structure and reactivity, we perform density functional theory calculations of the adsorption of several molecules and atoms to the surface of ultrathin Pt(100) films supported on ferroelectric PbTiO3. We show that reorienting the polarization direction of the substrate can dramatically change the chemisorption energies of CO, O, C, and N and alter the reaction pathways for dissociation of CO, O2, N2, and NO. We discuss the structural and electronic effects of a polarized substrate on the metal surface, and we suggest potential applications in tunable catalysis.     

The cellulose microfibril as an imperfect array of elementary fibrils.

Cellulose microfibrils are viewed as imperfect array of elementary fibrils. We have investigated the possible defects in Valonia cellulose microfibrils, which are such that the microfibrils can be broken into elementary fibrils by deformation, but are not sufficient to allow for a small angle maximum corresponding to the elementary fibril dimension. The microfibril has been constructed by convolution of th elementary fibril with a two dimensional point lattice. Defects have been incorporated in the microfibril, first by introduction of gaps between the elementary fibrils. These regular gaps were then replaced by a statistical distribution of the elementary fibrils about the lattice points, modeled by Hosemann distortions of the first type. The cylindrically averaged transforms of such structures show that significant distortions can be incorporated within the microfibril without producing large scale changes in the equatorial intensity distribution. Larger distortions are necessary before a small angle maximum corresponding to the 35 A elementary fibril is predicted, by which stage the wide angle x-ray pattern is unacceptable.     

Coumarins and phenolic carboxylic acids from Astragalus onobrychis

Pyatigorsk Pharmaceutical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 6, p. 719, November–December, 1992.     

X-ray structure determination of isotactic poly(2-vinylpyridine)

The structure of isotactic poly(2-vinylpyridine) has been determined from x-ray fiber data utilizing rigid-body least-squares refinement techniques. The polymer exists as a threefold helix with three chains passing through a hexagonal unit cell having the dimensions a = b = 15.49 Å and c = 6.56 Å (fiber axis) and space group P3₁ or P3₂. The asymmetric unit consists of three monomeric units (one in each chain), resulting in three crystallographically independent chains in the unit cell. The results show that two of the chains are interlocked through pyridine ring interactions whereas the third chain is less restricted. A statistical structure is proposed in which any two chains in the unit cell can be interlocked, provided they have the same sense. Such a situation permits a completely statistical structure in which half the chains in any crystallite are oriented upward and the other half downward.     

Evolution of the structure and thermodynamic stability of the BaTiO3(001) surface

We report a series of new surface reconstructions on BaTiO3(001) as a function of environmental conditions, determined via scanning tunneling microscopy and low energy electron diffraction. Using density functional theory calculations and thermodynamic modeling, we construct a surface phase diagram and determine the atomic structures of the thermodynamically stable phases. Excellent agreement is found between the predicted phase diagram and experiment. The results enable prediction of surface structures and properties under the entire range of accessible environmental conditions.