Arrays for the combinatorial exploration of cell adhesion

A new method for the fabrication of arrays of self-assembled monolayers (SAMs) of alkane thiols (ATs) on gold to combinatorially assay surfaces for cell adhesion is reported. A fluorous SAM, which is both cytophobic and solvophobic, was used as the background between the array features. The resulting solvophobic background permits the application of an assembly after conjugation strategy for fabrication. SAMs containing mixtures of ATs and peptide-terminated ATs were generated. Multiple cell types demonstrated differential and specific binding to these surfaces. Additionally, pluripotent human embryonic stem cells proliferated on surfaces generated by this method.     

Impedance-matched absorbers for finite-difference parabolic equation algorithms

In this paper, a perfectly matched layer (PML) absorber, recently introduced into the electromagnetic propagation literature by Berenger [J. Comput. Phys. 114, 185-200 (1994)], is adapted for use with both paraxial and wide-angle acoustic parabolic equations (PEs). Our procedure incorporates an imaginary component into the transverse coordinate that mimics the introduction of a fictitious absorber on the edge of the computational grid. Use of such an impedance-matched layer can significantly reduce spurious reflections compared to physical absorbing layer methods and thus allows a smaller number of boundary points to be employed in PE calculations. Numerical results obtained with several higher-order propagator approximations confirm that such impedance-matched absorbers efficiently eliminate reflections.     

Search for direct CP violation in nonleptonic decays of charged Xi and lambda hyperons

A search for direct CP violation in the nonleptonic decays of hyperons has been performed. In comparing the product of the decay parameters, alpha(Xi)alpha(Lambda), in terms of an asymmetry parameter, A(XiLambda), between hyperons and antihyperons in the charged Xi-->Lambdapi and Lambda-->ppi decay sequence, we found no evidence of direct CP violation. The parameter A(XiLambda) was measured to be 0.012+/-0.014.     

Synthesis and Molecular Structure of (C5Me5)2U(OtBu)(SePh): A Mixed-Ligand Alkoxide-Selenide Uranium(IV) Metallocene Complex Resulting from tert-Butoxy-Trimethylsilane Elimination

Abstract  

The title compound (C₅Me₅)₂U(O^tBu)(SePh) (1) was synthesized and characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. This system represents a unique example of an actinide complex with two different group 16 elements coordinated to the metal center and the first mixed-ligand actinide alkoxide-selenide complex. The complex crystallizes in the orthorhombic space group Pbca with unit cell parameters a = 17.830(7) ?, b = 14.973(6) ?, c = 21.254(8) ?, V = 5674(4) ?³, Z = 8, D _calc = 1.727 Mg/m³. The uranium(IV) mixed-ligand alkoxide-selenide complex adopts a pseudo-tetrahedral geometry, with the tert-butoxide and phenylselenide ligands occupying the plane bisecting the metallocene unit. Structural comparisons of the complex (C₅Me₅)₂U(O^tBu)(SePh) (1) are made with related selenide and alkoxide uranium(IV) complexes.     

Zero-field splittings in aromatic triplet states

The zero-field splitting parametersD andE have been calculated for naphthalene using T.B.M. and I. R. M. wave functions, and accurate values of all significant two, three and four centre dipolar interaction integrals. Agreement with experiment is improved in the case ofE, but is less satisfactory forD.     

Asymmetric synthesis of (−)-(S,S)-homaline

The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps from commercially available starting materials using the diastereoselective conjugate addition of the novel lithium amide reagent lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate to install the correct stereochemistry. Subsequent functional group manipulation of the resultant β-amino ester and Sb(OEt)₃-mediated macrolactamisation was followed by homodimerisation to give (−)-(S,S)-homaline in 18% overall yield, representing the first asymmetric, and by far the most efficient synthesis of this natural product reported to date.