Determination of the 8B neutrino spectrum.

We have measured the total energy of the alpha particles following the beta decay of 8B by implanting 8B into a planar silicon surface barrier detector. Calibration was performed using alpha particles following the beta decay of 20Na, similarly implanted. The alpha spectrum is used to infer the 8B neutrino spectrum which is an important input in the interpretation of experiments that detect energetic neutrinos from the Sun. The alpha spectrum reported here is in disagreement with the previous best measurement which used two detectors in coincidence.

The crystal and molecular structure of VH amylose by electron diffraction analysis.

The crystal and molecular structures of VH amylose were determined by a constrained linked-atom least-squares refinement, utilizing intensities measured from electron diffraction patterns and stereochemical restraints. Hexagonal platelet single crystals were grown from dilute aqueous ethanol solution and their electron diffraction diagrams analysed. These data indicated that the amylose chains were crystallized in a hexagonal lattice with a = b = 13.65 A, c (chain axis) = 8.05 A and space group P6(5)22. The best model obtained using the base plane data coupled with a stereochemical refinement yielded R = 0.24 (R'' = 0.25). It corresponded to a system of left-handed 6-fold helices packed on an hexagonal net but with statistically random up/down chain disorder. A column of six water molecules was present within each helical repeat. Additionally, the gap between each pair of adjacent helices was bridged by two water molecules positioned so as to allow hydrogen bonding with chains of either sense. This proposed crystal structure differs somewhat from previous reports which invoked orthorhombic lattices and requires a regularly alternating arrangement of up and down chains to account for the intensity. Suggestions are made to account for these differences.

Solid-state 13C NMR and X-ray diffraction of dermatan sulfate.

Dermatan sulfate in the solid state has been studied by 13C CP/MAS nmr and X-ray diffraction in order to establish the ring conformation of the L-iduronate moiety. The solid state nmr spectrum is similar to the solution spectrum obtained previously, indicating that a ring conformation at least approximating to 1C4 predominates in the solid state. X-ray powder diffraction data from the same sample indicate the presence of the 8-fold helix form previously observed by fiber diffraction, and interpreted in terms of a 4C1 ring form. A likely explanation of the results is that a distorted 1C4 L-iduronate ring conformation, not considered in the initial X-ray analysis, may emerge to provide a satisfactory interpretation of all available physical-chemical data.

Studies on some characteristics of hydrogen production by cell-free extracts of rumen anaerobic bacteria.

Hydrogen production was studied in the following rumen anaerobes: Bacteroides clostridiiformis, Butyrivibrio fibrisolvens, Enbacterium limosum, Fusobacterium necrophorum, Megasphaera elsdenii, Ruminococcus albus, and Ruminococcus flavefaciens. Clostridium pasteurianum and Escherichia coli were included for comparative purposes. Hydrogen production from dithionite, dithionite-reduced methyl viologen, pyruvate, and formate was determined. All species tested produced hydrogen from dithionite-reduce methyl viologen, but only C. pasteurianum, B. clostridiiformis, E. limosum, and M. elsdenii produced hydrogen from dithionite. All species except E. coli produced hydrogen from pyruvate, but activity was low or absent in extracts of E. limosum, F. necrophorum, R. albus, and R. flavefaciens unless methyl viologen was added. Hydrogen was produced from formate only by E. coli, B. clostridiiformis, E. limosum, F. necrophorum, and R. flavefaciens. Extracts were subjected to ultracentrifugation in an effort to determine the solubility of hydrogenase. The hydrogenase of all species except E. coli appeared to be soluble, although variable amounts of hydrogenase activity were detected in the pellet. Treatment of extracts of the rumen microbial species with DEAE-cellulose resulted in loss ofhydrogen production from pyruvate. Activity was restored by the addition of methyl viologen. It is concluded that hydrogen production in these rumen microorganisms is similar to that in the saccharolytic clostridia.

Details of glycosaminoglycan conformations and intermolecular interactions.

Among the mucopolysaccharides, similarities of chemical constitution are manifested in the similar molecular conformations that can be assumed by most of them. The differences, however, result in a preference for particular conformations. Small amounts of one glycosaminoglycan in a mixture can change the conformational preference of the major component. Advances in the techniques of fiber diffraction analysis allow us to visualize the roles of water and ions in some of these structures and to rationalize the strikingly different effects produced by Ca2+ and Na+ in hyaluronate systems, for example.