XAS and XMCD studies of amorphous FeCo-based ribbons

This paper reports x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies at Fe L_3,2 and Co L_3,2-edges to investigate the electronic structure of (Fe_100 ? xCo_x)₇₈Si₉Nb₃B₉Cu₁ (0 < x < 95) alloys. The influence of controlled Co addition on electronic structural and magnetic properties of (Fe_100 ? xCo_x)₇₈Si₉Nb₃B₉Cu₁ (x = 0, 20, 40, and 60) alloys has been investigated and it has been observed that Co exists as Co²⁺/Co³⁺, while Fe exists as a mixture of Fe⁰ (metallic) and Fe²⁺. The XMCD studies confirm these results and reveal that Co-ions are responsible for the room temperature ferromagnetism (RTFM) in the system, while at Fe L_3,2-edge it shows a diamagnetic behavior.     

Increasing protein stability through control of the nanoscale environment

We have discovered a novel property of single-walled carbon nanotubes (SWNTs)-their ability to stabilize proteins at elevated temperatures and in organic solvents to a greater extent than conventional flat supports. Experimental results and theoretical analysis reveal that the stabilization results from the curvature of SWNTs, which suppresses unfavorable protein-protein lateral interactions. Our results also indicate that the phenomenon is not unique to SWNTs but could be extended to other nanomaterials. The protein-nanotube conjugates represent a new generation of active and stable catalytic materials with potential use in biosensors, diagnostics, and bioactive films and other hybrid materials that integrate biotic and abiotic components.     

Loosely packed hydroxyl-terminated SAMs on gold

We report the preparation of loosely packed hydroxyl-terminated self-assembled monolayers (SAMs) on gold by the adsorption of bis(11,11'-dithioundecyl)perfluoroheptanoate and base-mediated cleavage of the fluorocarbon terminal group. As shown through complementary characterization methods, the partially fluorinated SAM exhibits a structure in which the outer surface contains mostly -CF(3) groups, the fluorocarbon groups are slightly canted on average, and the hydrocarbon chains underneath are in a fluidlike state. Upon cleavage of the fluorocarbon group, the hydroxyl-terminated alkyl chains relax into an increasingly canted, fluidlike state. The resulting monolayer packing exposes both methylene and hydroxyl functionalities, yielding an intermediate surface energy (theta(a)(H(2)O) approximately 68 degrees ). As compared to a densely packed hydroxyl-terminated SAM prepared from bis(11-hydroxyundecyl)disulfide, the cleaved films are thinner because of the greater average chain cant and exhibit a approximately 50% higher capacitance and a factor of 5 lower charge-transfer resistance. The addition of THF to the electrolyte solution as a cosolvent intercalates into the loosely packed SAM to double the charge-transfer resistance and increase the capacitance by approximately 20% but does not affect the capacitance of the densely packed SAM. The loosely packed SAM is also more easily exchanged upon exposure to a solution of n-docosanethiol.     

Three-component diastereoselective cascade synthesis of thiohydantoins

A new three-component cascade reaction for the synthesis of thiohydantoins is reported. The reaction between α-amino esters, nitrostyrenes, and aromatic isothiocyanates is efficiently promoted by organic bases to afford highly substituted thiohydantoins in moderate to good yields and diastereoselectivities.     

Comparison of FM dye lasers in standing-wave and ring configuration

We have compared the operation of a frequency-modulated dye laser (FML) in a standing-wave and ring configuration. As expected, for a given frequency detuning (difference between the drive frequency for the phase modulator and the cavity mode spacing) the enhanced modulation index is twice as large for the standing-wave configuration as for the ring configuration. In addition, we have demonstrated that application of small amounts of phase modulation in the ring configuration leads to improved mode stability. The fine structure of the rf beats for both FM lasers, have been studied and the results suggest that spatial hole burning complicates the detailed structure.     

A heterocyclic analog of leucine-enkephalin

A series of di-, tri-, tetra- and pentapeptide analogs of leucine-enkephalin have been prepared in which the initial tyrosinylglycine fragment has been replaced by the 5,6-dihydro-5,5-dimethyl-2-oxo-3-phenyl-1(2H)-pyrazineacetic acid moiety.