Molecular fibers and wires in solid-state and solution self-assemblies of cyclodextrin [2]rotaxanes

Cyclodextrin [2]rotaxanes have been prepared by coupling dimethylanilines with dicarboxylic acids using DMT-MM, in aqueous solutions of alpha-cyclodextrin, and the example illustrated shows unusual fluorescence emission and other spectroscopic behavior characteristic of the formation of molecular wires in solution, similar to the fibers observed in the solid state.     

Total synthesis of solandelactones A, B, E, and F exploiting a tandem Petasis-Claisen lactonization strategy

Solandelactones A, B, E, and F were synthesized using Nozaki-Hiyama-Kishi coupling of iododiene 13 with aldehydes 14 and 99 obtained by oxidation of alcohols 92 and 94. Key steps in the synthesis of 92 and 94 were (i) a Nagao asymmetric acetate aldol reaction of aldehyde 77 with thionothiazolidine 78 to set in place an alcohol that becomes the (7 S) lactone center of solandelactones, (ii) a Simmons-Smith cyclopropanation of 80 directed by this alcohol, and (iii) Petasis methylenation of cyclic carbonate 90 in tandem with a Claisen rearrangement that generates the octenalactone portion of solandelactones. Synthesis of solandelactones A, B, E, and F confirmed their gross structure and absolute configuration at C7, 8, 10, and 14 but showed that alcohol configuration at C11 must be reversed in pairs, A/B and E/F, from the previous assignment made to these hydroid metabolites. Thus, solandelactones A and B are correctly represented by 2 and 1, respectively, whereas solandelactones E and F are 6 and 5. A biogenesis of solandelactones is proposed for these C 22 oxylipins that parallels a hypothesis put forward previously to explain the origin of C 20 cyclopropane-containing algal products.     

Binding geometry and photophysical properties of DNA-threading binuclear ruthenium complexes

The DNA binding conformation and the photophysical properties of the semiflexible binuclear ruthenium complex [micro-bidppz(phen)4Ru2]4+ (2) were studied with optical spectroscopy and compared to the rigid, planar homologue in syn conformation [micro-dtpf(phen)4Ru2]4+ (3) and the parent "light-switch" complex [Ru(phen)2dppz]2+ (1). Comparison of calculated and observed absorption bands of the bridging ligand, bidppz, confirm earlier suggestions that 2 is significantly nonplanar, both free in solution and when intercalated into poly(dAdT)2, but the conclusion that the intercalated conformation is an anti rotamer is not substantiated by comparison of linear and circular dichroism spectra of 2 and 3. The behavior of the emission quantum yield as a function of temperature is similar for the two binuclear complexes 2 and 3 in different protic solvents, and a quantitative analysis suggests that, in solution, the solvent is more strongly hydrogen bonded to the excited state of 2 than to 1. However, the observation that for 2 the radiative rate constant increases to a value similar to 1 upon intercalation into DNA suggests that the difference between 1 and 2 in accepting hydrogen bonds is less pronounced when intercalated.     

Measurement of the eta-meson mass using psi(2S) --> etaJ/psi

We measure the mass of the eta meson using psi(2S) --> etaJ/psi events acquired with the CLEO-c detector operating at the CESR e(+)e(-) collider. Using the four decay modes eta --> gamma gamma, 3pi(0), pi(+)pi(-)pi(0), and pi(+)pi(-)gamma, we find M(eta) = 547.785 +/- 0.017 +/- 0.057 MeV, in which the first uncertainty is statistical and the second systematic. This result has an uncertainty comparable to the two most precise previous measurements and is consistent with that of NA48, but is inconsistent at the level of 6.5 sigma with the much smaller mass obtained by GEM.     

Synthesis and characterization of doped lithium aluminate nanocrystalline particles by sol‐gel method

Nanocrystalline particles of Co²⁺doped lithium aluminate (Co²⁺:LAO) and Ni²⁺‐doped lithium aluminate (Ni²⁺:LAO) were synthesized by sol–gel method. The crystalline nature and particle size of the samples were characterized by X‐ray diffraction analysis (XRD). The morphology and the presence Co²⁺ and Ni²⁺ in the synthesized samples were analyzed by scanning electron microscope (SEM) and energy dispersive X‐ray analysis (EDAX). The presences of functional groups in the samples were analyzed using FT‐IR analysis. The optical absorbance of the synthesized samples were observed using UV absorption spectral analysis. The frequency dependent dielectric behaviour of the synthesized nano materials was analyzed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Topological winding and unwinding in metastable Bose-Einstein condensates

Topological winding and unwinding in a quasi-one-dimensional metastable Bose-Einstein condensate are shown to be manipulated by changing the strength of interaction or the frequency of rotation. Exact diagonalization analysis reveals that quasidegenerate states emerge spontaneously near the transition point, allowing a smooth crossover between topologically distinct states. On a mean-field level, the transition is accompanied by formation of gray solitons, or density notches, which serve as an experimental signature of this phenomenon.     

Measurement of the absolute branching fraction of Ds+ --> tau+ nutau decay

Using a sample of tagged D(s)(+) decays collected near the D(s)(*+/-)D(s)(-/+) peak production energy in e(+)e(-) collisions with the CLEO-c detector, we study the leptonic decay D(s)(+)-->tau(+)nu(tau) via the decay channel tau(+)-->e(+)nu(e)nu(tau). We measure B(D(s)(+)-->tau(+)nu(tau))=(6.17+/-0.71+/-0.34)%, where the first error is statistical and the second systematic. Combining this result with our measurements of D(s)(+)-->mu(+)nu(mu) and D(s)(+)-->tau(+)nu(tau) (via tau(+)-->pi(+)nu(tau)), we determine f(D(s))=(274+/-10+/-5) MeV.     

The Phase Diagram of the Quantum Curie-Weiss Model

This paper studies a generalization of the Curie-Weiss model (the Ising model on a complete graph) to quantum mechanics. Using a natural probabilistic representation of this model, we give a complete picture of the phase diagram of the model in the parameters of inverse temperature and transverse field strength. Further analysis computes the critical exponent for the vanishing of the order parameter in the approach to the critical curve and gives useful stability properties for a variational problem associated with the representation.     

Inversion of magnetoresistance in organic semiconductors

We report that organic semiconductors such as alpha-sexithiophene (alpha-6T) have magnetoresistance (MR) with unexpected sign changes; depending on applied voltage, temperature, and layer thickness, the resistance may either increase or decrease upon application of a small magnetic field (<100 mT). We propose that MR and the inversion of MR are due to the role of hyperfine interaction in a magnetic field, as illustrated by the recombination-limited regime.