Nuclear magnetic resonance study of strongly correlated superconductors

This paper introduces nuclear magnetic resonance works in the strongly correlated super-conductors: heavy-Fermion, high-T _C superconductors and Sr₂RuO₄. The analyses strongly support the spin-fluctuation-mediated superconductivity model in a high-T _C superconductor.     

57Fe and57Co Mössbauer studies of highT c Y-Ba-Cu oxides

The⁵⁷Co emission Mössbauer spectra from YBa₂Cu₃O_6.92 (1-2-307) and YBa₂Cu₃O_6.00 (1-2-306) have been measured and compared with the⁵⁷Fe absorption spectra from YBa₂Cu_2.95Fe_0.05O_7?δ in order to clarify decisively the site assignments for the⁵⁷Fe quadrupole-split doublets in these compounds. Mössbauer spectra obtained from both specimens consist of four components whose hyperfine interaction parameters well agree with each other. It is shown that the Co and Fe atoms mainly substitute at Cu1 chain sites in 1-2-307, but in 1-2-306 the Co atoms occupy randomly the Cu2 plane sites and indicate magnetically-split sextet which converts to a paramagnetic doublet of S-state Fe³⁺ in 1-2-307 by a post-annealing in O₂ gas.     

NMR in highly correlated superconductors

Results of our systematic NMR study in highT _c cuprates are reviewed. The antiferromagnetic spin fluctuations (AFSF) decrease in the order of La_1.85Sr_0.15CuO₄. YBa₂Cu₃O₇ and Tl₂Ba₂CuO_6+y . 1/T ₁ of⁶³Cu in the CuO₂ plane in the normal state follows essentially a Curie-Weiss law at high temperature andT ₁ T = const. law at low temperature. The temperature dependence of 1/T ₁ and the Knight shift together with their impurity effect in the superconducting state strongly suggest d-wave pairing implying the AFSF to be responsible for the occurrence of superconductivity. From the NQR frequency measurement the density of Cu 3d and O 2p holes decreases and increases, respectively, in the order of La, Y and Tl compounds, which is consistent with the change of AFSF. The relation betweenT _c andv _Q, and their pressure dependence suggest that there exists and optimum value of the ratio of Cu 3d and O 2p hole density to give a maximum inT _c.     

NMR study of the self-induced vortex in (Ce1−xGdx)Ru2

NMR measurement of ¹⁵⁷Gd has been performed in zero external field in (Ce_1?xGd_x)Ru₂ for x = 0.100and 0.119 at low temperature down to 25 mK. Zero field NMR is observed with large enhancements both of H₁ and the intensity of the signal that are characteristic in ferromagnet. T₁T increases rapidly with decreasing temperature, which is attributed to the appearance of the superconducting energy gap whose magnitude is estimated to be 0.066kT_Cforx = 0.100. The NMR intensity in the superconducting state decreases not so drastically as expected in the perfect Meissner state. These results are qualitatively the same as reported previously for x ≥ 0.105 and T ≥ 60 mK. The results suggest that the system is in the state of self-induced vortices predicted theoretically.     

Remarkable diastereomeric rearrangement of an alpha-acyloxy beta-ketosulfide to an alpha-acyloxy thioester: a novel approach to the synthesis of optically active (2S,3S) beta-amino alpha-hydroxy acids

[reaction: see text] A novel and efficient synthetic method is described for (2S,3S)-3-amino-2-hydroxy-4-phenyl butyric acid derivatives, which are useful intermediates of enzyme inhibitors. This involves a Pummerer rearrangement of a beta-ketosulfoxide derived from l-phenylalanine followed by highly stereoselective acyl migration. From these studies, it appears that nitrogen-protecting groups exert a substantial influence over stereoselectivity. The mechanism of the rearrangement is discussed. beta-Amino alpha-hydroxy carboxylic acids are important pharmaceutical intermediates, and this method may provide a versatile synthesis from various amino acids in a few steps.     

Antenna Performance of a Directly Dug Corrugated Feedhorn for the 150-GHz Band

We have developed a 150 GHz band corrugated feed horn. These corrugated feed horns have been established by a new machining method, which involves digging corrugations through a metal material. We were able to realize E plane and H plane symmetry, low side lobe level, and low cross-polarization level. Measured co-polarization beam patterns above − 35 dB were consistent with the simulated patterns within a designed frequency range. The peak levels of cross-polarization beam patterns were less than − 30 dB. And, the performances were uniform in several horns. In the present paper, we describe the corrugated horn produced by this methods.     

Preparation of pH-sensitive liposomes retaining SOD mimic and their anticancer effect

We prepared an anticancer drug based on a pH-sensitive liposome retaining Fe-porphyrin as an SOD mimic. The liposomes contained cationic/anionic lipid combinations and were composed of Fe-porphyrin, 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine, dimethylditetradecylammonium bromide, sodium oleate, and Tween-80. The Fe-porphyrin was released from the liposome at low pH, and the cytotoxicity for cancer cells by the liposome depended on the acidic environments of the endosomes in the cells. Furthermore, although the liposome exhibited an excellent anticancer effect on a gastric cancer cell line, the SOD activity of Fe-porphyrin was shown to have a significant influence on the cytotoxicity toward cancer cells. These findings suggest that the pH-sensitive liposome retaining the Fe-porphyrin as an SOD mimic promises to be a novel anticancer drug for endosomal escape.