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We report 11 B and 195 Pt NMR measurements in non-centrosymmetric superconductor Li2Pt3B. We find that the spin susceptibility measured by the Knight shift remains unchanged across the superconducting transition temperature Tc. With decreasing temperature (T ) below Tc, the spinlattice relaxation rate 1/T1 decreases with no coherence peak and is in proportion to T 3 . These results indicate that the Cooper pair is in the spin-triplet state and that there exist line nodes in the superconducting gap function. They are in sharp contrast with those in the isostructural Li2Pd3B which is a spin-singlet, s-wave superconductor, and are ascribed to the enhanced spin-orbit coupling due to the lack of spatial inversion symmetry. Our finding points to a new paradigm where exotic superconductivity arises in the absence of strong electron-electron correlations.PACS numbers: 74.25. Bt, 74.25.Jb, 74.70.Dd In most superconducting materials, there is an inversion center in the crystal which guarantees the parity conservation. In conventional superconductors, such as Al, where the Cooper pair is formed by the attractive force produced by lattice vibration, the orbital wave function (OWF) of the Cooper pairs is in the s-wave form. Since an electron must obey the Fermi statistics, the two spins of such Cooper pair must be in the singlet state. This is also true in most strongly correlated electron systems such as high transition-temperature (T c ) copperoxides [1], cobalt oxide Na x CoO 2 ·1.3H 2 O [2] and many heavy-fermion compounds [3], where the OWF is also symmetric although it has nodes (zeroes). In contrast, if the OWF is asymmetric about the origin with nodes, e.g., a p-wave function, the Cooper pair must be in the spin-triplet state. However, when a superconductor lacks a crystal inversion center, the above-described rule (parity conservation) is violated due to the asymmetric spin-orbit coupling (SOC), and the pairing symmetry becomes nontrivial [8,9,10,11].In this Letter, we present NMR (nuclear magnetic resonance) evidence that increasing the strength of the SOC drastically changes the electron pairing symmetry in non-centrosymmetric superconductors Li 2 Pt(Pd) 3 B. The perovskite-like cubic compounds Li 2 Pd 3 B and Li 2 Pt 3 B are superconducting at T c ∼ 7 K and ∼2.7 K, respectively [12,13]. The inversion symmetry breaking effect is much larger compared to known compounds such as CePt 3 Si (Ref. [14]); all the elements, including the heavy element Pt(Pd), are located in non-centrosymmetric positions, while in CePt 3 Si the main effect comes from non-centrosymmetric Si which is a much lighter element. Also, in CePt 3 Si or UIr (Ref. [15]), the correlated felectrons play a major role in determining the superconducting properties [16,17]; note that the 4f 0 analog of the former compound, LaPt 3 Si, is a conventional superconductor [18]. However, there are no electron correlations in Li 2 Pd 3 B [19,20], which turns out to be also true in Li 2 Pt 3 B (see below). Li 2 Pd 3 B is a spin singlet, s-wave superconductor as...

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The design, synthesis, and biological activity of benzimidazole-7-carboxylic acids bearing 5-oxo-1,2,4-oxadiazole, 5-oxo-1,2,4-thiadiazole, 5-thioxo-1,2,4-oxadiazole, and 2-oxo-1,2,3,5-oxathiadiazole rings are described. These compounds were efficiently prepared from the key intermediates, the amidoximes 4. The synthesized compounds were evaluated for in vitro and in vivo angiotensin II (AII) receptor antagonistic activities. Most were found to have high affinity for the AT1 receptor (IC50 value, 10(-6)-10(-7)M) and to inhibit the AII-induced pressor response (more than 50% inhibition at 1 mg/kg po). The 5-oxo-1,2,4-oxadiazole, 5-oxo-1,2,4-thiadiazole, and 5-thioxo-1,2,4-oxadiazole derivatives showed stronger inhibitory effects than the corresponding tetrazole derivatives, while their binding affinities were weaker. This might be ascribed to their improved bioavailability by increased lipophilicity. The 5-oxo-1,2,4-oxadiazole derivative 2 (TAK-536) and 5-oxo-1,2,4-thiadiazole derivative 8f showed efficient oral bioavailability without prodrug formation. This study showed that the 5-oxo-1,2,4-oxadiazole ring and its thio analog, the 5-oxo-1,2,4-thiadiazole ring, could be lipophilic bioisosteres for the tetrazole ring in nonpeptide AII receptor antagonists.

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