Ytterbium-sensitized thulium-doped fiber laser with a single-mode output operating at 1900-nm region

A single-mode laser is demonstrated using a newly developed double-clad thulium-ytterbium-doped fiber (TYDF) in a linear cavity formed by two fiber Bragg gratings (FBGs). The YTF used is drawn from a D-shape preform fabricated using the modified chemical vapor deposition and solution doping technique. The laser is operated at 1 901.6 nm via the transition of thulium ions from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The efficiencies of the laser are 0.71% and 0.75% at 927- and 905-nm multimode pumping, respectively. The thresholds of the launched pump power for 927- and 905-nm pumping are 1 314 and 1 458 mW, respectively. A 7-mW output is obtained at a 905-nm pump power of 2 400 mW.     

A novel synthesis of beta-lactam fused cyclic enediynes by intramolecular Kinugasa reaction

A general synthetic route to beta-lactam-fused enediynes by intramolecular Kinugasa reaction has been successfully developed. The method has widened the scope of Kinugasa reaction in the synthesis of sensitive systems like the one described in this communication.     

Stable Tin (n = 2-15) clusters and their geometries: DFT calculations

We present a detailed structural analysis for small Tin (n = 2-15) clusters based on ab initio quantum mechanical calculations of their binding energies, frontier orbital gaps, and second energy derivatives. Local density approximation calculations revealed that while the smaller clusters (n < or = 8) prefer hexagonal atomic arrays with bulklike crystal symmetry, the bigger clusters prefer pentagonal atomic arrays. From the stability criteria of the magic number clusters we could identify three magic number clusters Ti7, Ti13, and Ti15. While the most stable configuration of Ti7 is a decahedral bipyramid induced by tetrahedral atomic arrays, the most stable configuration of Ti13 is an icosahedron. The other stable cluster Ti15 takes a closed-shell icosahedron-like configuration with both pentagonal and hexagonal symmetries. The stability of the Tin clusters strongly depends on their geometries and charge states. The HOMO-LUMO gap of the Tin clusters approaches its bulk value for n > 8. While there is not much difference between the HOMO and LUMO isosurface charge distributions for the Ti7 and Ti13 clusters in their most stable configurations, they are very different in the case of Ti15. Such a distinct charge distribution in Ti15 indicates its singular chemical selectivity over the other two magic number clusters.     

Kinetic preference for interaction of cisplatin with the G-C-rich wobble basepair region in both tRNAAla and MhAla

The anticancer active complex cisplatin interacts preferentially with the common, G-C rich, wobble base pair region of both tRNA(Ala) and Mh(Ala) in a reaction that at pH 6.3 is rate limited by the acid hydrolysis of the metal complex.     

Electrical bistability in electrostatic assemblies of CdSe nanoparticles

We report electrical bistability in electrostatic assembly of CdSe nanoparticles. We obtained thin films of the nanoparticles via layer-by-layer electrostatic assembly technique, which provided a nanoscale control to tune the thickness. Devices based on such thin films exhibit electrical bistability along with memory phenomenon. The bistability is due to charge confinement in the nanoparticles. Conduction mechanism changes from an injection-dominated to a bulk one during switching from a low- to a high-conducting state. Additionally, results from impedance spectroscopy show that the dielectric constant of the material increases during the transition. Both random-access and read-only memory applications are observed in these systems.     

Resonance Raman spectroscopic investigation of structural changes of CO‐heme in soluble guanylate cyclase generated by effectors and substrate

The influence of the effectors YC‐1 and BAY on the CO‐heme structure of bovine lung soluble guanylate cyclase (sGC) was investigated with resonance Raman spectroscopy. The effectors produced a five‐coordinate (5c) CO‐heme in addition to the His‐bound six‐coordinate (6c) CO‐heme, and both their Soret maxima were determined by simulation. On the basis of the absorption intensity, the amount of the 5c species was not dominant, in contrast to the high activity. The heme structural features common to the 5c and 6c CO‐hemes generated by effectors are that the vinyl and propionate side chains are more coplanar to the pyrrole rings. The out‐of‐plane Raman bands were observed only for the 5c species, for which the saddling and propeller distortions of heme were deduced to be large. The Fe CO stretching bands of the 5c species at 522 cm⁻¹ and of the 6c species at 488 cm⁻¹ were most enhanced upon excitation at 407 and 422 nm, respectively, which is consistent with the simulated spectra. Unexpectedly, the ¹³C¹⁸O isotope sensitivity appeared in low wavenumber porphyrin modes. From these observations, we propose that the high catalytic activity of sGC‐CO in the presence of effectors is a result of the concerted effects of protein conformational changes triggered by certain local interactions between the heme side chains and effectors/substrate in the heme pocket, which partly induce the cleavage of the Fe Hisβ 105 bond. Copyright © 2010 John Wiley & Sons, Ltd.     

Magnetic aftereffect in Co-P trilayer films

This paper reports on the results of experimental investigations of the magnetic properties of a trilayer system that consists of high-coercive polycrystalline and low-coercive amorphous magnetic Co-P layers and a nonmagnetic amorphous Ni-P interlayer. It has been established that the coercive force and the bias field of the hysteresis loop of the low-coercive layer undergo anomalous changes in the range of small thicknesses of the hard magnetic layer. In the same range of thicknesses, a magnetic aftereffect is found to manifest itself, which is unusual for this type of magnetic structures. The observed features are associated primarily with the kinetics of formation of a crystal structure of the high-coercive layer.     

Complexes of metal ions with phosphorus or arsenic containing ligands. III. Complexes of Mercury (II) halides with 1,2-ethylenebisdiphenylphosphine and 1,4-butylenebisdiphenylphosphine

Mercury(II) halides react with 1,2-ethylenebisdiphenylphosphine (DPE) and 1,4-butylenebisdiphenylphosphine (DPB) to give two types of complexes having the general formulae, [(diphos)HgX₂] and [(diphos)(HgX₂)₂]. The former seems to possess chain structure, while the latter has probably a bridged structure. In both the cases mercury(II) acquires sp³ tetrahedral configuration.