A novel crystallization-induced diastereomeric transformation based on a reversible carbon-sulfur bond formation. Application to the synthesis of a gamma-secretase inhibitor

This paper describes a remarkably efficient process for the preparation of gamma-secretase inhibitor 1. The target is synthesized in only five steps with an overall yield of 58%. The key operation is a highly selective and practical, crystallization-driven transformation for the conversion of a mixture of tertiary benzylic alcohols into the desired sulfide diastereomer with 94:6 dr. This unprecedented process is based upon a reversible carbon-sulfur bond formation under acidic conditions.     

Magnetic phase diagram of layered cobalt dioxide LixCoO2

The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.     

Weakly integrally closed domains:minimum polynomials of matrices

Must the coefficients of the minimum polynomial of a matrix over a domain lie in that domain? This question leads to the notion of a weakly integrally closed domain, over which the answer is ’yes’ for 3-by-3 matrices. It is shown that certain subalgebras of k[t] are weakly integrally closed, as are rings consisting of quadratic algebraic numbers.     

Stereospecific intramolecular C-H amination of 1-aza-2-azoniaallene salts

We report that 1-aza-2-azoniaallene salts, generated from α-chloroazo compounds by treatment with halophilic Lewis acids, participate in intramolecular C-H amination reactions to provide pyrazoline products in good to excellent yield. This intramolecular amination occurs readily at both benzylic and tertiary aliphatic positions and proceeds at an enantioenriched chiral center without loss of enantiomeric excess. A competition reaction shows that insertion occurs more readily at an electron-rich benzylic position than an electron-deficient one. These observations are consistent with the 1-aza-2-azoniaallene intermediate reacting as a nitrenium-like ion by a concerted insertion mechanism.     

Dynamics of Heavy Carriers in the Ferromagnetic Superconductor UGe<Subscript>2</Subscript>

Superconductivity and ferromagnetism in a number of uranium-based materials come from the same f-electrons with a relatively large effective mass, suggesting the presence of a band of heavy quasiparticles, whose nature is still a mystery. Here, UGe₂ dynamics in both ferromagnetic and paramagnetic phases is studied employing high-field μ⁺SR spectroscopy. The spectra exhibit a doublet structure characteristic to formation of subnanometer-sized magnetic polarons. This model is thoroughly explored here and correlated with the unconventional physics of UGe₂. The heavy-fermion behavior is ascribed to magnetic polarons; when coherent they form a narrow band, thus reconciling heavy carriers with superconductivity and itinerant ferromagnetism.     

Building Teacher‐Scientist Partnerships: Teaching About Energy Through Inquiry

This study evaluated the effectiveness of teacher‐scientist partnerships for increasing the use. of inquiry in precollege classrooms. It assessed the influence of the Teaching About Energy Through Inquiry Institutes for middle and high school teachers and energy scientists on participants' attitudes about science and science education, use of inquiry instructional techniques, and student attitudes about their classroom environments. Participant surveys, institute and classroom observations, lesson plans, and interviews indicated increased appreciation for inquiry, greater confidence in teaching using inquiry, and greater use of inquiry in the classroom. Student surveys and classroom observations pointed to higher levels of student satisfaction and less friction among classmates during inquiry‐based investigations implemented after the institutes. Moreover, scientist partners reported increased familiarity with principles of science education and best teaching practice, which are essential skills and knowledge for disseminating results of scientific research to nonscientific audiences, as well as their own students. These results suggest that collaborations between teachers and research scientists can positively affect the environment for learning science in precollege and college classes. Successful collaborations are most likely to occur when equal status for teachers and scientists in the partnership is stressed and partners have the opportunity to explore inquiry‐based curricula together.     

Evidence of two dimensionality in quasi-one-dimensional cobalt oxides

The quasi-one-dimensional (Q1D) cobalt oxides A(N + 2)Co(n + 1)O(3n + 3) (A = Ca, Sr, and Ba, n = 1 - infinity) were investigated by muon-spin spectroscopy under applied pressures of up to 1.1 GPa. The relationship between the onset Néel temperature T(on)(N) and the interchain distance (d(ic)), which increases monotonically with n, is well fitted by the formula T(N)/T(N,0) = (1 - d(ic)/d(ic,o)(beta), here for T(on)(N) approximately 100 K for Ca(3)Co(2)O(6) (n = 1) and approximately 15 for BaCoCoO(3) (n = infinity at ambient P. The T(on)(N) - d(ic) curve also predicts a large dependence of Y(N) for the compounds with n > or = 5, i.e., in the vicinity of , while the compounds show only a very small effect. Indeed, our high-pressure mu(+) results show that of BaCoO(3) is enhanced by with a slope of 2.2 K(Gpa), whereas no detectable changes by P for both Ca(3)Co(2)O(6) and Sr(4)Co(3)O(9) (n = 2). This clearly confirms the role of the 2D-antiferromagnetic interaction on T(on)(N) in the Q1D cobalt oxides.     

Muonium quantum diffusion and spin dynamics in solid xenon

We present measurements of the transverse (T ₂ ^–1 ) and longitudinal (T ₁ ^–1 ) spin relaxation rates of muonium (Mu) atoms in solid natural xenon (n-Xe) as well as pure¹³⁶Xe (which has no nuclear moments). The temperature dependences ofT ₂ ^–1 andT ₁ ^–1 in natural Xe belowT 115 K demonstrate the quantum character of Mu diffusion governed by one-phonon interactions. Taking into account both the polaron effect (PE) and the effect of fluctuational preparation of the barrier (FPB) makes it possible to consistently describe Mu diffusion in Xe. Mu spin relaxation in¹³⁶Xe at high temperatures is not due to nuclear hyperfine (NHF) interactions.     

Noncollinear magnetic hyperfine fields in the Ag spacers of Fe/Ag multilayers

Nearly perpendicular magnetic hyperfine fields have been observed for the first time in the Ag "spacers" of Fe/Ag multilayers using low temperature nuclear orientation of (110)Ag(m) at 6 mK. At the same time, vibrating sample magnetometry measurements at temperatures down to 4 K have shown the magnetic anisotropy of the Fe to be in plane. The direction of the Ag hyperfine field is thus noncollinear (nearly orthogonal) to the Fe anisotropy. These results are compared with full potential linearized augmented plane wave calculations using the wien97 code.     

Direct observation of orbital magnetism in cubic solids

We present x-ray magnetic circular dichroism determinations of the orbital/spin magnetic moment ratios of dilute 3d-series impurities in Au (and Cu) host matrices. This is the first direct measurement of considerable orbital moments in cubic symmetry for a localized impurity in a bulk metal host. It is shown that the unquenching of orbital magnetism depends on a delicate balance of hybridization effects between the local impurity with the host and the filling of the 3d states of the impurity. The results are accompanied by ab initio calculations that support our experimental findings.