Stereochemistry of post-transition metal oxides: revision of the classical lone pair model

The chemistry of post transition metals is dominated by the group oxidation state N and a lower N-2 oxidation state, which is associated with occupation of a metal s(2) lone pair, as found in compounds of Tl(I), Pb(II) and Bi(III). The preference of these cations for non-centrosymmetric coordination environments has previously been rationalised in terms of direct hybridisation of metal s and p valence orbitals, thus lowering the internal electronic energy of the N-2 ion. This explanation in terms of an on-site second-order Jahn-Teller effect remains the contemporary textbook explanation. In this tutorial review, we review recent progress in this area, based on quantum chemical calculations and X-ray spectroscopic measurements. This recent work has led to a revised model, which highlights the important role of covalent interaction with oxygen in mediating lone pair formation for metal oxides. The role of the anion p atomic orbital in chemical bonding is key to explaining why chalcogenides display a weaker preference for structural distortions in comparison to oxides and halides. The underlying chemical interactions are responsible for the unique physicochemical properties of oxides containing lone pairs and, in particular, to their application as photocatalysts (BiVO(4)), ferroelectrics (PbTiO(3)), multi-ferroics (BiFeO(3)) and p-type semiconductors (SnO). The exploration of lone pair systems remains a viable a venue for the design of functional multi-component oxide compounds.     

Total synthesis of microcin B17 via a fragment condensation approach

The total synthesis of the 43 amino acid antibacterial peptide Microcin B17 (MccB17) is described. The natural product was synthesized via a convergent approach from a heterocycle-derived peptide and peptide thioester fragments prepared via Fmoc-strategy solid phase peptide synthesis (SPPS). Final assembly was achieved in an efficient manner using two Ag(I)-assisted peptide ligation reactions to afford MccB17 in excellent overall yield.     

Inhibitors of an essential mycobacterial cell wall lipase (Rv3802c) as tuberculosis drug leads

The first targeted inhibitors of an essential M. tuberculosis cell wall lipase, Rv3802c, are described. Lead compounds exhibited nanomolar inhibition of the enzyme, and encouraging antibacterial activity against M. tuberculosis in vitro, supporting Rv3802c as a novel TB drug target.     

Spatial decay estimates for the Brinkman and Darcy flows in a semi-infinite cylinder

The flow of a fluid through a porous medium is often modeled by the Brinkman or the Darcy system. In this paper we investigate Saint-Venant type decay of solutions for both systems when the medium is confined to a semi-infinite cylinder and appropriate homogeneous initial and boundary values are assumed. Received: February 1, 1997     

Eine neue Darstellung von Normal-Jodl?sung

Ohne Zusammenfassung     

Spreads,flocks, and generalized quadrangles

A spread of PG(3,q), q an odd prime, recently constructed by R. Baker and G. Ebert, when generalized for q an odd prime power is isomorphic to a spread derived by J. A. Thas from a flock of a quadratic cone discovered by J. C. Fisher. The associated generalized quadrangle has an unusual colllneation.     

Configuration space Faddeev calculations

Three nucleon ground state wave functions are displayed graphically in configuration space. Both the Schrödinger functions and the Faddeev amplitudes from which they are constructed are plotted. It is demonstrated that for the case where the two-nucleon interaction contains strong repulsion at short distances, the Faddeev amplitude bears no resemblance to the Schrödinger function, and is not even positive definite. Furthermore, the Faddeev amplitude is a much smoother function of the three independent coordinate variables, and is therefore much easier to calculate. Certain intuitive features of the Schrödinger wave function are seen to be present.     

Unrestricted lower bounds for eigenvalues for classes of elliptic equations and systems of equations with applications to problems in elasticity

Lower bounds for the eigenvalues of some elliptic equations and elliptic systems over bounded regions are obtained. The bounds are universal in that they depend only upon the volume of the region. Specific applications include the clamped plate, the buckling problem for the clamped plate and the equations of linear elasticity. Our results are consequences of extensions of the methods of Li and Yau (Comm. Mat. Phys. 88 (1983) 309–318) who obtained such results for the eigenvalues of the fixed membrane problem.     

The synthesis of l-alkyl-1,4-dihydro-4-quinolone-2-carboxylic acids

A general method tor the preparation of 1,4-dihydro-4-quinolone-2-carboxylic acids, especially those which carry alkyl substituents on the ring N-atom, is described.     

Spin-rotation measurements in π−p → K0Λ

The first measurements of spin-rotation in meson-baryon scattering in the resonance region are presented. These measurements, for the reaction π^?p → K⁰Λ, confirm the main predictions of a previous partial-wave analysis. Comments are made on resonant couplings in the reaction π^?p → K⁰Λ.