We report 57 Fe-NMR studies on the oxygen-deficient iron (Fe)-based oxypnictide superconductor LaFeAsO0.7 (Tc = 28 K) enriched by 57 Fe isotope. In the superconducting state, the spin component of 57 Fe-Knight shift 57 K decreases almost to zero at low temperatures and the nuclear spin-lattice relaxation rate 57 (1/T1) exhibits a T 3 -like dependence without the coherence peak just below Tc, which give firm evidence of the unconventional superconducting state formed by spin-singlet Cooper pairing. All these events below Tc are consistently argued in terms of the extended s±-wave pairing with a sign reversal of the order parameter among Fermi surfaces. In the normal state, we found the remarkable decrease of 1/T1T upon cooling for both the Fe and As sites, which originates from the decrease of low-energy spectral weight of spin fluctuations over whole q space upon cooling below room temperature. Such behavior has never been observed for other strongly correlated superconductors where an antiferromagnetic interaction plays a vital role in mediating the Cooper pairing.

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The cerebrospinal fluid-to-blood efflux transport of estrone-3-sulfate (E 1 S) via the blood-cerebrospinal fluid barrier (BCSFB) may play an important role in regulating E 1 S levels in the brain. Here, we investigated the efflux transport of E 1 S at the BCSFB using conditionally immortalized rat choroid plexus epithelial cells (TR-CSFB) and identified the responsible transporter. The [ 3 H]E 1 S uptake by TR-CSFB cells was composed of saturable and nonsaturable components, and the K m and V max values of the saturable component were determined to be 16.8 Ϯ 5.1 M and 12.3 Ϯ 2.3 pmol/min/mg of protein, respectively. [ 3 H]E 1 S uptake was inhibited by probenecid, cholate, taurocholate, sulfobromophthalein, dehydroepiandrosterone sulfate, triiodothyronine, thyroxin, and digoxin but not by p-aminohippuric acid, ␥-aminobutyric acid, or methotrexate, suggesting the involvement of organic anion transporting polypeptide (oatp) in the uptake. Reverse transcription-polymerase chain reaction analysis revealed that oatp3 was expressed in TR-CSFB cells and isolated rat choroid plexus, although oatp1 was not detected in either. Xenopus laevis oocytes expressing oatp3 exhibited [ 3 H]E 1 S uptake activity with a K m of 8.09 Ϯ 2.83 M and V max of 8.02 Ϯ 0.87 pmol/h/oocyte. Moreover, oatp3 is localized at the brush-border membrane of choroid plexus epithelial cells. These results suggest that oatp3 is involved in the E 1 S efflux transport at the BCSFB.

We report systematic 57 Fe-NMR and 75 As-NMR/NQR studies on an underdoped sample (T c ¼ 20 K), an optimally doped sample (T c ¼ 28 K), and an overdoped sample (T c ¼ 22 K) of oxygen-deficient iron (Fe)-based oxypnictide superconductor LaFeAsO 1Ày . A microscopic phase separation between superconducting domains and magnetic domains is shown to take place in the underdoped sample, indicating a local inhomogeneity in association with the density distribution of oxygen deficiencies. As a result, 1=T 1 T in the normal state of the superconducting domain decreases significantly upon cooling at both the Fe and As sites regardless of the electron-doping level in LaFeAsO 1Ày . On the basis of this result, we claim that 1=T 1 T is not always enhanced by antiferromagnetic fluctuations close to an antiferromagnetic phase in the underdoped superconducting sample. This contrasts with the behavior in hole-doped Ba 0:6 K 0:4 Fe 2 As 2 (T c ¼ 38 K), which exhibits a significant increase in 1=T 1 T upon cooling. We remark that the crucial difference between the normal-state properties of LaFeAsO 1Ày and Ba 0:6 K 0:4 Fe 2 As 2 originates from the fact that the relevant Fermi surface topologies are differently modified depending on whether electrons or holes are doped into the FeAs layers.