Atomic resolution density maps reveal secondary structure dependent differences in electronic distribution

The X-ray crystal structure of the flavoenzyme cholesterol oxidase, SCOA (Streptomyces sp.SA-COO) has been determined to 0.95 A resolution. The large size (55kDa) and the high-resolution diffraction of this protein provides a unique opportunity to observe detailed electronic effects within a protein environment and to obtain a larger sampling for which to analyze these electronic and structural differences. It is well-known through spectroscopic methods that peptide carbonyl groups are polarized in alpha-helices. This electronic characteristic is evident in the sub-Angstrom electron density of SCOA. Our analysis indicates an increased tendency for the electron density of the main chain carbonyl groups within alpha-helices to be polarized toward the oxygen atoms. In contrast, the carbonyl groups in beta-sheet structures tend to exhibit a greater charge density between the carbon and oxygen atoms. Interestingly, the electronic differences observed at the carbonyl groups do not appear to be correlated to the bond distance of the peptide bond or the peptide planarity. This study gives important insight into the electronic effects of alpha-helix dipoles in enzymes and provides experimentally based observations that have not been previously characterized in protein structure.     

The encapsulation of Rh(III) phthalocyanines in zeolites X and Y

The template syntheses of rhodium(III) phthalocyanine complexes within the supercage structures of zeolites X and Y are reported. These ship-in-a-bottle compounds are characterized by elemental analysis, UV-Vis, IR, XRD and X-ray photoelectron spectroscopy. The effect of temperature on the encapsulation process is also discussed.     

Isolating blocks for Morse flows

We present a constructive general procedure to build Morse flows on n-dimensional isolating blocks respecting given dynamical and homological boundary data recorded in abstract Lyapunov semi-graphs. Moreover, we prove a decomposition theorem for handles which, together with a special class of gluings, insures that this construction not only preserves the given ranks of the homology Conley indices, but it is also optimal in the sense that no other Morse flow can preserve this index with fewer singularities.      

The crossing number of c4 × c4

We prove that the crossing number of C₄ × C₄ is 8. © 1995 John Wiley & Sons, Inc.