We have identified cobalt-base superalloys showing a high-temperature strength greater than those of conventional nickel-base superalloys. The cobalt-base alloys are strengthened by a ternary compound with the L1(2) structure, gamma' Co3(Al,W), which precipitates in the disordered gamma face-centered cubic cobalt matrix with high coherency and with high melting points. We also identified a ternary compound, gamma' Ir3(Al,W), with the L1(2) structure, which suggests that the Co-Ir-Al-W-base systems with gamma+gamma' (Co,Ir)3(Al,W) structures offer great promise as candidates for next-generation high-temperature materials.

Five amino acid residues responsible for extreme stability have been identified in cytochrome c 552 (HT c 552 ) from a thermophilic bacterium, Hydrogenobacter thermophilus. The five residues, which are spatially distributed in three regions of HT c 552 , were replaced with the corresponding residues in the homologous but less stable cytochrome c 551 (PA c 551 ) from Pseudomonas aeruginosa. The quintuple HT c 552 variant (A7F/M13V/Y34F/Y43E/ I78V) showed the same stability against guanidine hydrochloride denaturation as that of PA c 551 , suggesting that the five residues in HT c 552 necessarily and sufficiently contribute to the overall stability. In the three HT c 552 variants carrying mutations in each of the three regions, the Y34F/Y43E mutations resulted in the greatest destabilization, by ؊13.3 kJ mol , respectively). The results of guanidine hydrochloride denaturation were consistent with those of thermal denaturation for the same variants. The present study established a method for reciprocal mutation analysis. The effects of side-chain contacts were experimentally evaluated by swapping the residues between the two homologous proteins that differ in stability. A comparative study of the two proteins was a useful tool for assessing the amino acid contribution to the overall stability.Proteins from thermophilic bacteria usually exhibit enhanced stability against temperature or denaturants compared with the homologues from mesophiles (1, 2). Sequence comparison and rationally designed mutations of thermophilic and mesophilic proteins provide several lines of information on protein stability. In particular, investigation of the relationship between three-dimensional structure and thermodynamic parameters on protein unfolding provides detailed information on factors contributing to the stability.A thermophilic hydrogen-oxidizing Gram-negative bacterium, Hydrogenobacter thermophilus, which grows optimally at 72°C, produces a periplasmic Class I cytochrome c 552 (HT c 552 ) 1 (3). This bacterial cytochrome c has greatly contributed to the understanding of protein stability through pairwise comparison with homologous cytochrome c 551 (PA c 551 ) from a mesophilic bacterium, Pseudomonas aeruginosa, which grows at 37°C (4). These two proteins exhibit 56% sequence identity and have almost the same backbone conformations, but HT c 552 is much more stable than PA c 551 (5-9).On precise structural comparison between HT c 552 and PA c 551 , we predicted that five amino acid residues spatially located in three regions were responsible for the higher stability of HT c 552 (6). These residues were then introduced at the corresponding positions in PA c 551 (7-9). The single mutation Val-78 to Ile (V78I) and two double mutations Phe-7 to Ala/ Val-13 to Met (F7A/V13M) and Phe-34 to Tyr/Glu-43 to Tyr (F34Y/E43Y) in the corresponding three regions of PA c 551 resulted in enhanced protein stability in an additive manner. Although the five residues were proved to be effective for stability, e.g. the denaturation temperature was e...

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The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9×107ergcm−3 at 5K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107ergcm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c∕a due to the thermal expansion.