Dynamical basis for the Poincaré stresses

We explore the possibility that the Poincaré stresses needed to stabilize a completely electrodynamical electron arise through a phase transition in the vacuum. By extending our previous work on dynamical symmetry breaking in finite quantum electrodynamics we are able to look for extended structures to see whether a composite electron could be stabilized by critically polarizing its own negative energy sea.     

EPR of Pb3+ in ZnO

The influence of doping zinc oxide with lead has been studied by electron paramagnetic resonance technique. Beside the signal nearg=1.956 (electron trapped in an oxygen vacancy) the resonances of Pb³⁺-ions are observed. Due to the strong Fermi-contact-hyperfine interaction of the 6s-electron with the Pb-207-nucleus the Breit-Rabi-diagram is evaluated with the experimentally obtainedA-value. The dependences of the resonances on optical illumination and temperature are investigated.     

Compact and almost compact breathers: a bridge between an anharmonic lattice and its continuum limit

We demonstrate that certain strictly anharmonic one-dimensional FPU lattices with a suitable quartic site potential appended support almost-compact discrete breathers over a macroscopic localized domain that is essentially fixed independently of the sparseness of the lattice. Beyond that domain the discrete breather tails decay at a double-exponential rate in the lattice-cell index, becoming truly compact in the continuum limit. Furthermore, the discrete breather is stable for amplitudes below a sharp threshold that depends on the sparseness of the lattice. For the two-dimensional version of the problem, the continuum limit of a planar hexagonal lattice with a purely quartic interaction potential begets an isotropic multidimensional nonlinear wave equation. When a quartic site potential of the appropriate sign is appended, the continuum equation has a compactly supported radial breather solution.     

CoMFA and docking studies on glycogen phosphorylase a inhibitors as antidiabetic agents

Glycogen phosphorylase (GP(a)) is a specific target for the design of inhibitors and may prevent glycogenolysis under high glucose conditions in type II diabetes. The carboxamides first reported by Hoover D. J. et al. (J. Med. Chem. 1998, 41, 2934-2938) are one of the major classes of GP(a) inhibitors other than glucose derivatives. The recent, X-ray crystallographic analyses (Oikonomakos et al. Biochim. Biophys. Acta 2003, 1647, 325-332) have revealed a distinct mechanism of action for these inhibitors, which bind at a new allosteric site away from the inhibitory and catalytic sites. To elucidate the essential structural and physicochemical requirements responsible for binding to the GP(a) enzyme and to develop predictive models, CoMFA and docking studies have been carried out on a series of indole-2-carboxamide derivates. The CoMFA model developed using pharmacophoric alignments and hydrogen-bonding fields demonstrated high predictive ability against the training (r2 = 0.98, q2 = 0.68) and the test set (r2pred = 0.85). Further the superimposition of PLS coefficient contour maps from CoMFA with the GP(a) active site (PDB: 1lwo) has shown a high level of compatibility.     

Substituted aziridines by lithiation-electrophile trapping of terminal aziridines

[reaction: see text] Regio- and stereoselective deprotonation of N-Bus (Bus = tert-butylsulfonyl)-protected terminal aziridines with lithium 2,2,6,6-tetramethylpiperidide generates a nonstabilized (H-substituted) aziridinyl anion that undergoes in situ or external electrophile trapping under experimentally straightforward conditions to give trans-disubstituted aziridines in good to excellent yields.     

Biosynthesis of the allene (-)-marasin in Marasmius ramealis

[1-14C]-E-dehydromatricaria methyl ester and dimethyl [1-14C]-deca-4,6,8-triyne-1,10-dioate are incorporated into the allene (-)-marasin in Marasmius ramealis without scrambling of the 14C label. This and the levels of the incorporations (0.8% and 4.9% respectively) strongly suggests that the above esters, or close relatives, can be converted directly into (-)-marasin in M. ramealis, and that the diyne-allene moiety in this latter compound arises by the rearrangement, under enzymic control, of an alkyltriyne moiety.     

Asymmetric epoxidation of cis-alkenes mediated by iminium salts: highly enantioselective synthesis of levcromakalim

[reaction: see text] A range of cis-substituted olefins has been epoxidized with a new dihydroisoquinolinium salt catalyst, using tetraphenylphosphonium monoperoxysulfate as the stoichiometric oxidant, giving ee's of up to 97%. The reaction has been used as the key step in an enantioselective synthesis of the antihypertensive agent levcromakalim.     

Sporolides A and B: structurally unprecedented halogenated macrolides from the marine actinomycete Salinispora tropica

[structure: see text] Analysis of the fermentation broth of a strain of the marine actinomycete Salinispora tropica has led to the isolation of two unprecedented macrolides, sporolides A (1) and B (2). The structures and absolute stereochemistries of both metabolites were elucidated using a combination of NMR spectroscopy and X-ray crystallography.     

Shedding light on the structure of a photoinduced transient excimer by time-resolved diffraction

Time-resolved single-crystal diffraction performed with synchrotron radiation shows that the 53(1) micros phosphorescent state, generated in the crystalline phase of trimeric {[3,5-(CF3)(2)Pyrazolate]Cu}(3) molecules by exposure to 355 nm of light at 17 K, is due to the formation of an excimer rather than the shortening of the intramolecular Cu...Cu distances within the trimeric units, or the formation of a continuous chain of interacting molecules. One of the intermolecular Cu...Cu distances contracts by 0.56 Angstroms from 4.018(1) to 3.46(1) Angstroms;, whereas the interplanar spacing of the trimers is reduced by 0.65 Angstroms; from 3.952(1) to 3.33(1) Angstroms. Density-functional theory calculations support the formation of a Cu...Cu bond through the intermetallic transfer of a Cu 3d electron to a molecular orbital with a large 4p contribution on the reacting Cu atoms.