NASA Scientific and Technical Aerospace Reports

Thiamin pyrophosphate (TPP)-dependent enzymes are a divergent family of TPP and metal ion binding proteins that
perform a wide range of functions with the common decarboxylation steps of a -(O=)C-C(OH)- fragment of alpha-ketoacids
and alpha- hydroxyaldehydes. To determine how structure and catalytic action are conserved in the context of large sequence
differences existing within this family of enzymes, we have carried out an analysis of TPP-dependent enzymes of known
structures. The common structure of TPP-dependent enzymes is formed at the interface of four alpha/beta domains from at
least two subunits, which provide for two metal and TPP-binding sites. Residues around these catalytic sites are conserved
for functional purpose, while those further away from TPP are conserved for structural reasons. Together they provide a
network of contacts required for flip-flop catalytic action within TPP-dependent enzymes. Thus our analysis defines a
TPP-action motif that is proposed for annotating TPP-dependent enzymes for advancing functional proteomics.
Author
Phosphates; Enzymes; Catalysis; Thiamine
20040121120 NASA Marshall Space Flight Center, Huntsville, AL, USA
Thermally Stable Heterocyclic Imines as New Potential Nonlinear Optical Materials
Nesterov, Volodymyr V.; Antipin, Mikhail Y.; Nesterov, Vladimir N.; Moore, Craig E.; Cardelino, Beatriz H.; Timofeeva,
Tatiana V.; Journal of Physical Chemistry B; 2004; Volume 108, pp. 8531-8539; In English; Original contains black and white
illustrations; Copyright; Avail: Other Sources; Abstract Only
In the course of a search for new thermostable acentric nonlinear optical crystalline materials, several heterocyclic imine
derivatives were designed, with the general structure D-pi-A(D’). Introduction of a donor amino group (D’) into the acceptor
moiety was expected to bring H-bonds into their crystal structures, and so to elevate their melting points and assist in an
acentric molecular packing. Six heterocycle-containing compounds of this type were prepared, single crystals were grown for
five of them, and these crystals were characterized by X-ray analysis. A significant melting temperature elevation was found
for all of the synthesized compounds. Three of the compounds were also found to crystallize in acentric space groups. One
of the acentric compounds is built as a three-dimensional H-bonded molecular network. In the other two compounds, with very
similar molecular structure, the molecules form one-dimensional H-bonded head-to-head associates (chains). These chains are
parallel in two different crystallographic directions and form very unusual interpenetrating chain patterns in an acentric crystal.
Two of the compounds crystallized with centrosymmetric molecular packing.
Author
Heterocyclic Compounds; Imines; Nonlinearity; Optical Materials; Thermal Stability; Crystallinity
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METALS AND METALLIC MATERIALS
Includes physical, chemical, and mechanical properties of metals and metallic materials; and metallurgy.
20040111151 Lawrence Livermore National Lab., Livermore, CA
In-Situ Observations of Phase Transformations in the HAZ of 2205 Duplex Stainless Steel Weldments
Palmer, T. A.; Elmer, J. W.; Wong, J.; Aug. 2001; In English
Report No.(s): DE2004-15005319; UCRL-JC-142147; No Copyright; Avail: National Technical Information Service (NTIS)
Ferrite ((delta))/austenite ((gamma)) transformations in the heat affected zone (HAZ) of a gas tungsten arc (GTA) weld
in 2205 duplex stainless steel are observed in real-time using spatially resolved X-ray diffraction (SRXRD) with high intensity
synchrotron radiation. A map showing the locations of the(delta) and(gamma) phases with respect to the calculated weld pool
dimensions has been constructed from a series of SRXRD scans. Regions of liquid, completely transformed(gamma), a
combination of partially transformed(gamma) with untransformed(delta), and untransformed(delta)+(gamma) are identified.
Analysis of each SRXRD pattern provides a semi-quantitative definition of both the(delta)/(gamma) phase balance and the
extent of annealing which are mapped for the first time with respect to the calculated weld pool size and shape. A combination
of these analyses provides a unique real-time description of the progression of phase transformations in the HAZ. Using these
real-time observations, important kinetic information about the transformations occurring in duplex stainless steels during
heating and cooling cycles typical of welding can be determined.
NTIS
Phase Transformations; Welded Joints; Heat Affected Zone; Stainless Steels
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