Tunable atomic line molecular (TALM) spectrometer

A highly specific technique for real time monitoring of simple and complex molecules is described. This technique depends on using the Zeeman effect to tune an atomic emission line to coincide with a sharp molecular absorption feature and has been named TALMS (Tunable Atomic Line Molecular Spectroscopy). Results are presented on the determination of di-atomic (NO), tri-atomic (NO₂, SO₂), tetra-atomic (H₂CO) and more complex molecules. An explanation is offered for the ability of this technique to determine complex molecules, which suggests that the method should be highly specific. It is concluded that work in this area will lead to instrumentation that will be valuable for process control or environmental monitoring.     

Design and synthesis of DNA-tethered ruthenium complexes that self-assemble into linear arrays

Ruthenium(II) bis(terpyridine) complexes have been prepared with two triethylene glycol linkers to which DNA sequences have been attached; hybridization at various complex ratios results in linear arrays of varying lengths.     

Carbon nanostructures grown with electron and ion beam methods

We present a comparative study where carbon nanostructures were prepared by electron and ion beam methods. Thin films of 10×10 μm² area were prepared and analysed by Raman analysis, nanoindentation, energy dispersive X-ray analysis (EDX) and atomic force microscopy (AFM). The material formed is not soft and graphitic, but of intermediate hardness (6–13 GPa) and with Raman spectral features similar to those of hydrogenated amorphous carbon, although it contains a significant Ga content (up to 25 at. %). This study was used to form sharp AFM supertip structures which were used to image sintered ceramic samples and films of aligned carbon nanotubes. Compared to traditional Si tips, this gave an improved rendering of the sample’s aspect ratio although the resolution is limited by the diameter of the C supertips. PACS 81.05.Uw; 81.07.-b; 78.30.-j     

Chemical tuning of positive and negative magnetoresistances, and superconductivity in 1222-type ruthenocuprates

A remarkable variety of conducting states has been found in RuSr2(R2-xCex)Cu2O10-delta ruthenocuprates by tuning the properties of the magnetic CuO2 and RuO2 layers through small changes in the chemistry of the (R,Ce)2O2-delta slab. Both the R3+ cation size and the charge transfer determined by the R/Ce ratio and the oxygen deficiency delta are important controlling parameters that tune ground-state properties from positive magnetoresistive to negative magnetoresistive to superconducting.     

Frequency-coded quantum key distribution

We report an intrinsically stable quantum key distribution scheme based on genuine frequency-coded quantum states. The qubits are efficiently processed without fiber interferometers by fully exploiting the nonlinear interaction occurring in electro-optic phase modulators. The system requires only integrated off-the-shelf devices and could be used with a true single-photon source. Preliminary experiments have been performed with weak laser pulses and have demonstrated the feasibility of this new setup.     

Formation and stability of a Janus-Wedge type of DNA triplex

A new type of DNA targeting with the formation of a Janus-Wedge (J-W) triple helix is described. The "wedge" residue (W) attached to a PNA backbone is designed to insert itself into double-stranded DNA and base pair with both Watson-Crick faces. To study the stability of such an assembly, we have examined the formation of the J-W triplex with dC8 - T8 target sequence. The use of this target sequence permits the study of this new helix form without competing Watson-Crick interactions between the two target residues. Studies indicate that the W strand binds to both target strands, with defined polarity and a stability (-15.2 kcal/mol) that is roughly the sum of the two independent duplex interactions.     

Ramanujan-Slater type identities related to the moduli 18 and 24

We present several new families of Rogers-Ramanujan type identities related to the moduli 18 and 24. A few of the identities were found by either Ramanujan, Slater, or Dyson, but most are believed to be new. For one of these families, we discuss possible connections with Lie algebras. We also present two families of related false theta function identities.     

Preparation of stereodefined homoallylic amines from the reductive cross-coupling of allylic alcohols with imines

Regio-, diastereo-, and enantioselective coupling reactions between imines and allylic alcohols have been developed. These coupling reactions deliver complex homoallylic amine products through a convergent C-C bond forming process that does not proceed through intermediate allylic organometallic reagents. In general, convergent coupling, by exposure of an allylic alkoxide to a preformed Ti-imine complex, occurs with allylic transposition in a predictable and stereocontrolled manner. While simple diastereoselection in these reactions is high, delivering anti-products with ≥20:1 selectivity, the organometallic transformation described is compatible with a diverse range of functionality and substrates (including aliphatic and aromatic imines, allylic silanes, trisubstituted alkenes, vinyl- and aryl halides, trifluoromethyl groups, thioethers, and aromatic heterocycles). Alkene geometry of the products is a complex function of the allylic alcohol structure and is consistent with a mechanistic proposal based on syn-carbometalation followed by syn-elimination by way of a boat-like transition state geometry. Single asymmetric coupling reactions provide a means to translate the stereochemical information of the allylic alcohol to the homoallylic amine or to control diastereoselection in the coupling reactions of achiral allylic alcohols with chiral imines. Double asymmetric coupling reactions are also described that afford a unique means to control stereoselection in these complex convergent coupling processes. Finally, empirical models are proposed that are consistent with the observed stereochemical course of these coupling reactions en route to chiral homoallylic amines possessing di- or trisubstituted alkenes and anti- or syn- relative stereochemistry at the allylic and homoallylic positions.