Directed Evolution of a Cp*RhIII-Linked Biohybrid Catalyst Based on a Screening Platform with Affinity Purification

Directed evolution of Cp*Rh^III-linked nitrobindin (NB), a biohybrid catalyst, was performed based on an in vitro screening approach. A key aspect of this effort was the establishment of a high-throughput screening (HTS) platform that involves an affinity purification step employing a starch-agarose resin for a maltose binding protein (MBP) tag. The HTS platform enables efficient preparation of the purified MBP-tagged biohybrid catalysts in a 96-well format and eliminates background influence of the host E. coli cells. Three rounds of directed evolution and screening of more than 4000 clones yielded a Cp*Rh^III-linked NB(T98H/L100K/K127E) variant with a 4.9-fold enhanced activity for the cycloaddition of acetophenone oximes with alkynes. It is confirmed that this HTS platform for directed evolution provides an efficient strategy for generating highly active biohybrid catalysts incorporating a synthetic metal cofactor.     

Synthesis of thermoresponsive copolymer/silica-coated magnetite nanoparticle composite and its application for heavy metal ion recovery

To enhance chemical stability and suppress of aggregation of magnetite nanoparticles (MNPs), which are used as a support for thermoresponsive copolymer immobilization, silica coating of the MNPs is applied via the electrooxidation method. Although the resulting silica coated-MNPs also formed aggregates, the size distribution of the aggregate shifted to smaller size range. Because of that, the surface area available for copolymer immobilization increased approximately 6.7 times at maximum as compared with that of the uncoated MNPs. It contributed to the increase of the amount of the immobilized copolymer on the silica-coated MNPs, which is approximately four times larger than that on the uncoated MNPs. Fe₃O₄ dissolution test confirmed enhancement of chemical stability of MNPs. The thermoresponsive copolymer immobilized on the silica-coated MNPs shows the ability to recycle Cu(II) ion from Cu(II) containing solution by changing temperature with significantly shorter time than those in other thermoresponsive adsorbents in gel form.     

Mechanism of Magnetite Seam Formation and its Role for FeO Scale Transformation

The phase transformation behavior of a thermally grown oxide scale of FeO on pure-Fe and an Fe–2wt%Au alloy was investigated. Particular attention was paid to formation of a magnetite seam, which is the Fe₃O₄ layer formed at the FeO/alloy interface at an initial stage of the phase transformation, since it has important effects on the overall phase transformation of FeO scale. A thin Au(Fe) layer was found to develop on the Fe–Au alloy at the FeO/alloy interface after 32 min of oxidation at 750 °C in air. This Au(Fe) layer prevented formation of a magnetite seam and accelerated the FeO eutectoid reaction. The Au(Fe) layer acted as a “chemical diffusion barrier” for inward diffusion of Fe from the FeO to the alloy substrate across the FeO/alloy interface and prevented magnetite seam formation.     

Effect of heating process on the formation of nanoparticles of elastin model polypeptide, (GVGVP)251, by gamma-ray crosslinking

Nanoparticles were prepared by the thermosensitive aggregation of the elastin model polypeptide, (GVGVP)₂₅₁, and gamma-ray crosslinking. Three different heating processes, “slow heating,” “fast heating,” and “heat shock,” were used for the aggregation of the peptide, followed by gamma-ray crosslinking. Only the “heat shock” process successfully yielded stable nanoparticles with diameters of less than ca. 150 nm and a narrow size distribution. Circular dichroism (CD) spectrometry showed that this polypeptide formed a type-II β-turn structure when the temperature was increased to above the cloudy point in the case of the “heat shock” process; suggesting that this structure might contribute to stable nanoparticle formation by gamma-rays. CD spectrometry also suggested that this structure would be affected during the formation of stable crosslinked particles.     

Removal of entrapped iron compounds from isothermally treated catalytic chemical vapor deposition derived multi-walled carbon nanotubes

Compositional changes of the residual iron compounds in isothermally treated catalytic chemical vapor deposition derived multi-walled carbon nanotubes have been monitored using ⁵⁷Fe transmission Mössbauer spectroscopy and X-ray fluorescence. The iron phases entrapped in the as-synthesized carbon nanotubes consist of γ-iron, α-iron, Fe₃C and Fe_1−xS. The Fe_1−xS phase decomposes completely around 1500 °C while the iron carbide phase decomposes in the temperature range of 1500-2400 °C. The obtained apparent activation energy of ca. 76 kcal/mol suggests that the entrapped iron was removed via a diffusion process during thermal treatment.     

Identification of Tumor Antigens in Ovarian Cancers Using Local and Circulating Tumor-Specific Antibodies

Ovarian cancers include several disease subtypes and patients often present with advanced metastatic disease and a poor prognosis. New biomarkers for early diagnosis and targeted therapy are, therefore, urgently required. This study uses antibodies produced locally in tumor-draining lymph nodes (ASC probes) of individual ovarian cancer patients to screen two separate protein microarray platforms and identify cognate tumor antigens. The resulting antigen profiles were unique for each individual cancer patient and were used to generate a 50-antigen custom microarray. Serum from a separate cohort of ovarian cancer patients encompassing four disease subtypes was screened on the custom array and we identified 28.8% of all ovarian cancers, with a higher sensitivity for mucinous (50.0%) and serous (40.0%) subtypes. Combining local and circulating antibodies with high-density protein microarrays can identify novel, patient-specific tumor-associated antigens that may have diagnostic, prognostic or therapeutic uses in ovarian cancer.     

Effect of Mo on corrosion behavior of Ni20Cr–xMo alloys in air with NaCl–KCl–CaCl2 vapor at 570°C

The effect of Mo on the corrosion behavior of Ni20Cr–xMo alloys in an oxidizing chlorine-containing atmosphere using air mixed with the salt-vapor mixture of NaCl–KCl–CaCl₂ at 570°C was investigated. The results revealed that the corrosion performance of the Ni20Cr alloys in the oxidizing chlorine atmosphere was improved by Mo addition of up to 3 wt%. The Mo-free alloy formed a potassium chromate during corrosion as a result of the reaction between the Cr₂O₃ scale and KCl vapor. The chromate formation increased the chlorine potential at the scale surface and induced the breakdown of the protective Cr₂O₃ scale, resulting in internal chromium chloride precipitates and a Cr-depleted zone. In contrast, the presence of Mo resulted in the formation of a NiO scale, which did not react with the salt vapors and, therefore, prevented the formation of chromates. The beneficial effect of Mo on the high-temperature chlorination of Ni–Cr alloys in salt-vapor-containing atmospheres was ascribed to the suppression of chlorine generation due to NiO scale formation.     

Miscibility and pressure‐sensitive adhesive performances of acrylic copolymer and hydrogenated rosin systems

Relationship between the miscibility of pressure‐sensitive adhesives (PSAs) acrylic copolymer/hydrogenated rosin systems and their performance (180° peel strength, probe tack, and holding power), which was measured over a wide range of time and temperature, were investigated. The miscible range of the blend system tended to become smaller as the molecular weight of the tackifier increased. In the case of miscible blend systems, the viscoelastic properties (such as the storage modulus and the loss modulus) shifted toward higher temperature or toward lower frequency and, at the same time, the pressure‐sensitive adhesive performance shifted toward the lower rate side as the T_g of the blend increased. In the case of acrylic copolymer/hydrogenated rosin acid systems, a somewhat unusual trend was observed in the relationship among the phase diagram, T_g, and the pressure‐sensitive adhesive performance. T_g of the blend was higher than that expected from T_gs of the pure components. This trend can be due to the presence of free carboxyl group in the tackifier resin. However, the phase diagram depended on the molecular weight of the tackifier. The pressure‐sensitive adhesive performance depended on the viscoelastic properties of the bulk phase. A few systems where a single T_g could be measured, despite the fact that two phases were observed microscopically, were found. The curve of the probe tack of this system shifted toward a lower rate side as the T_g increases. However, both the curve of the peel strength and the holding power of such system did not shift along the rate axis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 651–663, 1999     

Pore Structure and Thermal Stability of Mesoporous Mullite Fibers Prepared by Crystallization and Selective Leaching of Al2O3-SiO2 Glass Fibers

Porous mullite fibers were prepared by crystallization and selective leaching of Al2O3-SiO2 glass fibers using buffered HF-NH4F(BHF) aqueous solutions. The optimum concentration of BHF solution for selective leaching of the fibers was 0.9 mass% HF and 17.0 mass% NH4F. By firing at 1000–1300°C, the glass fibers changed into composite texture of mullite and glassy phase. Since the pores in the fibers were formed by selective leaching of glassy phase among mullite grains, they were tunable by changing the firing conditions of fibers. Pore size of the samples changed from around 4 nm in the 1100°C fired sample to 16 and 40 nm in the 1200 and 1300°C fired samples, respectively. The highest specific surface area obtained was around 30 m2/g, when the fibers were heat treated at 1200°C for 24 h and leached for 20 h in 0.9 mass% HF-17.0 mass% NH4F solution. From the thermal stability tests of the porous mullite fibers, its specific surface area was found to be maintained up to 1200–1300°C.