Piezobirefringence in GaP and InP

We report measurements of piezobirefringence in GaP and InP in the region below the direct gap. For GaP this includes the region above the indirect gap where the sample is opaque. The experimental data are compared with theoretical calculations of the contributions to the piezobirefringence arising from the E₀, E₁ and E₂ transitions.     

Resonant two magnon Raman scattering in α-Fe2O3

Strong resonant enhancement of two-magnon Raman scattering was observed in antiferromagnetic α-Fe₂O₃ for laser frequencies near the intrinsic absorption edge. One magnon scattering, although allowed by symmetry, was not observed. The laser frequency dependence of the resonance enhancement could be well presented by the square of the magnitude of the first derivative of the electric susceptibility. Based on these facts, we conclude that the scattering arises from an exchange mechanism in the excited state.     

Iterative organometallic addition to chiral hydroxylated cyclic nitrones: highly stereoselective syntheses of alpha,alpha'- and alpha,alpha-substituted hydroxypyrrolidines

[reaction: see text]. Iteration of organometallic addition to chiral hydroxylated pyrroline N-oxides through an addition-oxidation-addition synthetic sequence allowed highly stereoselective double alkylation of pyrrolidine at C-2 or at C-2 and C-5 depending on the regioselectivity of the oxidation step. Application of this methodology has been exemplified by the synthesis of the all-substituted pyrrolidine alkaloid (-)-codonopsinine and of proline-type amino acid precursors possessing a quaternary stereogenic center, whose configuration can be controlled.     

Leishmanicidal activity of passifloricin A and derivatives

Several natural and hemisyntetic passifloricins were assayed against Leishmania panamensis amastigotes. High leishmanicidal activity as well as toxicity was observed. The structure of a new compound is also reported.     

Bismuth nitrate-catalyzed novel synthesis of pyrrole-substituted indolinones

Synthesis of indole derivatives bound to pyrroles is a challenge. In this letter, an expeditious synthesis of these types of molecules starting from isatins and 4-hydroxy proline via a bismuth nitrate-catalyzed reaction is described.     

Dependence of the indirect energy gap of silicon on hydrostatic pressure

A diamond anvil optical cell is employed to measure the pressure dependence of the fundamental indirect Γ-X transition of crystalline Si. The result is

$\text{E (eV) = (1.110 ± 0.002) ? (1.41 ± 0.06) × 10}{}^{\mathrm{?3}}\text{P}$

where the pressure P is in kbar. Between 115 and 126 a transformation takes place to a phase opaque to electromagnetic radiation of wavelength between 0.3 and 2.0 μm. We believe this is the same phase transition reported by Minomura and Drickamer. A pseudopotential calculation assuming a relatively soft core is carried out and its results are in rather good agreement with experiment.