No abstract

In oxides, the substitution of non-oxide anions (F(-),S(2-),N(3-) and so on) for oxide introduces many properties, but the least commonly encountered substitution is where the hydride anion (H(-)) replaces oxygen to form an oxyhydride. Only a handful of oxyhydrides have been reported, mainly with electropositive main group elements or as layered cobalt oxides with unusually low oxidation states. Here, we present an oxyhydride of the perhaps most well-known perovskite, BaTiO(3), as an O(2-)/H(-) solid solution with hydride concentrations up to 20% of the anion sites. BaTiO(3-x)H(x) is electronically conducting, and stable in air and water at ambient conditions. Furthermore, the hydride species is exchangeable with hydrogen gas at 400 °C. Such an exchange implies diffusion of hydride, and interesting diffusion mechanisms specific to hydrogen may be at play. Moreover, such a labile anion in an oxide framework should be useful in further expanding the mixed-anion chemistry of the solid state.

Two recently proposed 13 C-13 C recoupling methods under magic angle spinning ͑MAS͒, resonant interference recoupling ͑RIR͒, and 13 C-1 H dipolar-assisted rotational resonance ͑DARR͒, are examined on a common theoretical foundation using the average Hamiltonian theory. In both methods, a rf field is applied on not 13 C but 1 H to recouple the 13 C-1 H dipolar interactions, and spectral overlap necessary to conserve energy for 13 C-13 C polarization transfer is achieved by the 13 C-1 H dipolar line broadening. While DARR employs time-independent 13 C-1 H interactions recoupled by suitable rf irradiation to 1 H spins, RIR uses time-dependent 13 C-1 H interactions modulated appropriately by 1 H rf irradiation. There are two distinct cases where 13 C-1 H line broadening realizes 13 C-13 C spectral overlap. For a pair of a carbonyl or aromatic carbon and an aliphatic carbon, spectral overlap can be achieved between one of the spinning sidebands of the former 13 C resonance and the 13 C-1 H dipolar powder pattern of the latter. On the other hand for a pair of spins with a small chemical shift difference, the two center bands are overlapped with each other due to 13 C-1 H dipolar broadening. For the former, we show that both RIR and DARR occur in the first order, while for the latter, DARR recoupling is appreciable for time-independent 13 C-1 H interactions. We refer to the former DARR as the first-order DARR recoupling and the latter as the second-order DARR. Experimentally, we examined the following 13 C-1 H recoupling methods for DARR: 1 H CW irradiation fulfilling a rotary-resonance condition or a modulatory-resonance condition, and 1 H pulses applied synchronously to MAS. For RIR, the FSLG-m2mm sequence is applied to 1 H. Several one-dimensional DARR and RIR experiments were done for N-acetyl͓1,2-13 C, 15 N͔ DL-valine, and ͓2,3-13 C͔ L-alanine. It was found that the polarization transfer rate for RIR is larger than that for DARR except for fast spinning, while the rate for DARR is less sensitive to the spinning speed. Further, we showed that the efficiency of the second-order DARR recoupling is not significantly less than that of the first-order DARR. Among the 13 C-1 H recoupling methods examined, CW irradiation at the nϭ1 rotary-resonance condition is superior for DARR because it gives a larger 13 C-1 H dipolar broadening, leading to broadband recoupling. We showed that a broadband-recoupling experiment with the first and the second-order DARR by CW irradiation at the nϭ1 rotary-resonance condition is applicable to signal assignment as well as structural determination of a multiply/uniformly 13 C labeled molecule as demonstrated by two-dimensional 13 C-13 C DARR polarization-transfer experiments of uniformly 13 C, 15 N-labeled glycylisoleucine.

Background:The inhibitory mechanism of A␤42 aggregation by flavonoid is fully unknown. Results: The oxidant enhanced the inhibitory activity of (ϩ)-taxifolin against A␤42 aggregation by forming A␤42-taxifolin adducts between the Lys residues and oxidized (ϩ)-taxifolin. Conclusion:The inhibitory activity of catechol-type flavonoids requires autoxidation to form an o-quinone to react with Lys. Significance: These may help design promising inhibitors against A␤42 aggregation for Alzheimer disease therapy.

Aggregation of the 42-residue amyloid beta-protein (Abeta42) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Despite numerous structural studies on Abeta aggregates, the relationship between tertiary structure and toxicity remains unclear. Our proline scanning and solid-state NMR studies suggested that aggregates both of wild-type Abeta42 and of E22K-Abeta42 (one of the mutants related to cerebral amyloid angiopathy) contain two conformers: a major one with a turn at positions 25 and 26, and a minor one with a turn at positions 22 and 23. To identify the toxic conformer, the derivative Abeta42-lactam(22K-23E), in which the side chains at positions 22 and 23 were covalently linked, was synthesized as a minor conformer surrogate, along with Abeta42-lactam(25K-26E) as a major conformer surrogate. The Abeta42-lactam(22K-23E) showed stronger aggregation, neurotoxicity, radical generation, and oligomerization than wild-type Abeta42, whereas in Abeta42-lactam(25K-26E) were weak. The transition from the physiological conformation with a turn at positions 25 and 26 to the toxic conformation with a turn at positions 22 and 23 might be a key event in the pathogenesis of AD.