Enhanced stability of recombinant keratinocyte growth factor by mutagenesis

Native sequence keratinocyte growth factor (KGF) is fairly unstable, as manifested by the loss of the monomeric native protein accompanied by the accumulation of aggregated species during storage at moderate temperatures. Several different types of analogs were generated and the storage stability of the protein assessed. In the first type of analog one or more of the five cysteinyl residues in KGF were replaced; in the second class the N-terminal residues that included the first disulfide bond were deleted. Both of these types of analogs involved removal of the disulfide bond between cysteines 1 and 15. The third group involved mutating one of the basic amino acids located in a cluster of positive charges (involved in heparin binding) around Arg144 to a neutral or acidic amino acyl residue. Among the cysteine replacement analogs, the double mutation of Cys1 and 15 to Ser resulted in significantly increased stability without compromising the mitogenic activity, while Cys to Ser mutations at other positions were either destabilizing or had no effect. Deletion of the 15, 23 or 27 N-terminal amino acyl residues also increased the stability of the protein. The activity of the analogs was not affected by the deletion of 15 or 23 amino acids, but it was significantly decreased upon removal of the 27 N-terminal amino acyl residues. Much greater stability was achieved by mutation of the basic amino acids, especially Arg144, to Glu or Gln, but this increase in stability was accompanied by large decrease in activity. The analog with the 23 N-terminal amino acyl residues deleted represents one of the best compromises between increased stability and retention of activity.     

Organic–inorganic hybrid materials. II. Preparation and properties of higher silica containing polycarbonate–silica hybrid materials

The sol–gel reaction of a polycarbonate (PC) oligomer having triethoxysilyl groups at both ends of the PC chain (PCS) with a tetraethoxysilane or tetramethoxysilane oligomer provided transparent or semitransparent films of higher silica containing organic–inorganic hybrid materials (HSPC‐HMs). The films were superior to those from PC and from PCS in terms of the morphological homogeneity, heat resistance, and surface hardness. The HSPC‐HM films had minimum oxygen permeability at a PCS/tetraethoxysilane ratio of 3/7. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4273–4279, 2006     

In situ measurement of corrosion of type 316L stainless steel in 553 K pure water via the electrical resistance of a thin wire

A system for the in situ monitoring of corrosion depth via electrical resistance measurements was applied to study the corrosion rate of type 316L stainless steel at 553 K in pure water. Corrosion depth was measured using a 50 μm diameter wire probe mounted axially in the tube. Measurements were in good agreement with literature data for both the hydrogen water chemistry (HWC) condition and the normal water chemistry (NWC) condition. Oxide film analyses by scanning electron microscopy and laser Raman spectroscopy on the wire probe and the tube showed no effects from shape of the test specimens or the application of electric current. Corrosion kinetics was evaluated by fitting equations to the measurements. Data for the HWC condition could be fitted by a two-step logarithmic–parabolic law. A single-step logarithmic law fitted data for the NWC condition. Changes in corrosion rate by the water chemistry changes were readily detected with the technique. Corrosion depth change could be observed for the water chemistry change from the NWC condition to the HWC condition with electrochemical corrosion potential (ECP) of ?0.56 V vs. standard hydrogen electrode, which is lower than the ECP that the phase of iron oxide changes from α-Fe₂O₃ to Fe₃O₄.     

Intergranular stress corrosion cracking initiation model of austenite stainless steels used in BWRs for optimized water chemistry control

A calculation model on intergranular stress corrosion cracking (IGSCC) initiation time of materials used in boiling water reactors (BWRs) has been developed to evaluate effectiveness of water chemistry control for mitigation of the IGSCC. The model was composed of four terms which determine passive film break time: (1) a chemical term based on electrochemical corrosion potential (ECP) and impurity concentration; (2) a mechanical term based on strain rate; (3) a material term based on sensitization; and (4) an irradiation term based on acceleration of corrosion by γ-rays and neutron irradiation. The contribution of the chemical term in the passive film break was calculated based on a deterministic local corrosion model. Then, the local corrosion model was modified by adding mechanical acceleration of the film rupture to treat the IGSCC phenomenon. The model could reproduce the behavioral tendency seen in the slow strain rate tensile test on high carbon contents with sensitization heat treatment (for example, 620°C × 24 h). Under BWR operating conditions, IGSCC initiation time could be extended by a factor of 5 by lowering the electric conductivity from 1.0 to 0.06 μS/cm. If the ECP was reduced below the critical potential by a mitigation method, the IGSCC initiation time was predicted to become sufficiently long for pipings and components.     

Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature – high purity water. In order to specify which constituent element determines the dissolution characteristics of these materials, the anodic polarization curves of pure iron, pure nickel, and pure chromium were also surveyed. The anodic polarization curve of 316L SS was determined to have active, passive, and transpassive states which were the same as type 304 SS (304 SS) showed. But, Alloy 182 had different polarization characteristics especially near the corrosion potential as it had no active state. From comparison results of the polarization characteristics of these materials and their constituent elements, the corrosion characteristics of these materials were concluded to be mainly determined by the corrosion characteristics of chromium.     

Selective catalytic reduction of nitrogen oxides with hydrocarbons over Zn–Al–Ga complex oxides

Selective reduction of NO with hydrocarbons was studied using metal oxide catalysts having a spinel structure. A Zn–Al–Ga complex oxide was found to be very active and selective for the catalytic reduction of NO with both C₃H₆ and CH₄. It was revealed that the role of oxygen at the initial stage of the reaction strongly depends on the reductants; oxygen is mainly used for NO oxidation to NO₂ in the reduction with CH₄, whereas it is used both for NO oxidation to NO₂ and oxidation of C₃H₆ to an active intermediate in the reduction with C₃H₆. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quantification of cell adhesion force with AFM: distribution of vitronectin receptors on a living MC3T3-E1 cell

Distribution of vitronectin (VN) receptors on a living murine osteoblastic cell was successfully measured by atomic force microscopy (AFM). First, the distribution of the integrin beta(5) subunit which constitutes a part of the VN receptor on the cell was confirmed by conventional immunohistochemistry after fixing the cell. To visualize the distribution of the receptor on a living cell by an independent and potentially a more quantitative method, the AFM was used with a microbead attached to the cantilever tip to increase the area of contact and VN was immobilized on the microbead. Force measurements were then performed over a large area of a living murine osteoblastic cell using the microbead covered with VN.     

Development of a two-dimensional dual pendulum thrust stand for Hall thrusters

A two-dimensional dual pendulum thrust stand was developed to measure thrust vectors [axial and horizontal (transverse) direction thrusts] of a Hall thruster. A thruster with a steering mechanism is mounted on the inner pendulum, and thrust is measured from the displacement between inner and outer pendulums, by which a thermal drift effect is canceled out. Two crossover knife-edges support each pendulum arm: one is set on the other at a right angle. They enable the pendulums to swing in two directions. Thrust calibration using a pulley and weight system showed that the measurement errors were less than 0.25 mN (1.4%) in the main thrust direction and 0.09 mN (1.4%) in its transverse direction. The thrust angle of the thrust vector was measured with the stand using the thruster. Consequently, a vector deviation from the main thrust direction of +/-2.3 degrees was measured with the error of +/-0.2 degrees under the typical operating conditions for the thruster.