High-efficiency deflection of high-energy protons through axial channeling in a bent crystal

Beam deflection due to axial channeling in a silicon crystal bent along the 111 axis was observed with 400 GeV/c protons at the CERN Super Proton Synchrotron. The condition for doughnut scattering of protons by the atomic strings of the crystal was attained. Such a condition allowed one to observe a beam deflection of 50 murad with about 30% efficiency. The contribution of hyperchanneled states of protons to the observed beam deflection was less than 2% according to simulation results.     

Exchange-induced phase separation in Ni–Cu films

Magneto-structural properties of films of diluted ferromagnetic alloys Ni_xCu_1−x in the concentration range 0.7<x<1.0$0.7<x<1.0$ are studied experimentally. Films deposited by magnetron sputtering show partial phase separation, as evidenced by structural analysis and ferromagnetic resonance measurements. The phase diagram of the Ni_xCu_1−x bulk system is obtained using numerical theoretical analysis of the electronic structure, taking into account the interatomic exchange interactions. The results confirm the experimentally found partial phase separation, explain it as magnetic in origin, and indicate an additional metastable region connected with the ferromagnetic transition in the system.     

1,2,5-Oxadiazolo[3,4-g]indoles via annelation of 6,7-dihydrobenzo[c][1,2,5]oxadiazol-4(5H)-one oxime with acetylene

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Synthesis,structure, and magnetic properties of a Yb<Superscript>III</Superscript> complex with the iminopyridine radical-anionic ligand

The reaction of equimolar amounts of ytterbocene (C₅Me₄H)₂Yb(THF)₂ and iminopyridine 2,6-Prⁱ₂C₆H₃N=CH(C₅H₄N) accompanied by the one-electron oxidation of the ytterbium ion produced the unique lanthanide complex (C₅Me₄H)₂Yb^III[2,6-Prⁱ₂-C₆H₃NCH(C₅H₄N)]–? with the iminopyridine radical-anionic ligand. The structure of the complex in the crystalline state was established by X-ray diffraction and its magnetic properties were studied in the temperature range of 1.8—300 K.     

Light‐Harvesting Three‐Chromophore Systems Based on Biphenyl‐Bridged Periodic Mesoporous Organosilica

Three‐chromophore systems with light‐harvesting behavior were prepared, which are based on periodic mesoporous organosilica (PMO) with crystal‐like ordered structure. The organic bridges of biphenyl‐PMO in the pore walls act as donors and two types of dye are incorporated in the one‐dimensional channels. Consecutive two‐step‐Förster resonance energy transfer is observed from the biphenyl moieties to mediators (diethyl‐aminocoumarin or aminoacridone), followed by energy transfer from mediators to acceptors (dibenzothiacarbocyanine, indodicarbocyanine, sulforhodamine G). High energy‐transfer efficiencies ranging from 70 to 80 % are obtained for two‐step‐FRET, indicating that the mesochannel structure with one‐dimensional ordering provides spatial arrangement of chromophore pairs for an efficient direct energy transfer. The emission wavelength can be tuned by a choice of acceptor dye: 477 nm (diethylaminocoumarin), 519 nm (aminoacridone), 567 nm (sulforhodamine G), 630 nm (dibenzothiacarbocyanine), and 692 nm (indodicarbocyanine).     

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis,Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y^III dialkyl complexes supported by tridentate N^?,N,N monoanionic methylthiazole– or benzothiazole–amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole‐containing system through an unprecedented metal‐to‐ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N^?,N,N^?,S^? ligand as the result of metal‐to‐ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring‐opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph₃C⁺[B(C₆F₅)₄]^?, were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.     

Bis(guanidinate) alkoxide complexes of lanthanides: synthesis, structures and use in immortal and stereoselective ring-opening polymerization of cyclic esters

A series of new bis(guanidinate) alkoxide Group 3 metal complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex [Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex [(Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions.     

Steroids of the spirostan and furostan series from plants of the genus Allium. XXVI. Structure of anzurogenin and anzuroside from the collective fruits of Allium suvorovii and Allium stipitatum

A new steroid glycoside of the spirostan series, anzuroside, has been isolated from the collective fruits of the cocultivatedAllium suvorovii Rgl. andA. stipitatum Rgl. (family Liliaceae, local name “anzur”). Enzymatic cleavage of the glycoside has given the previously undescribed steroid sapogenin anzurogenic C, which has the structure of (24S, 25S)-2α,3β,5,24-tetrahydroxy-5β-spirostan-6-one. Anzuroside is the 24-O-β-D-glucopyranoside of anzurogenin C. Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 505–510, July–August, 1989.     

Polypropylene track membranes as a promising material for targets with polarized protons

Polypropylene track membranes made by irradiation of polypropylene films with a beam of high-energy heavy ions followed by chemical etching of latent ion tracks are proposed for being used as a polarized target material. To give membranes paramagnetic properties needed for allowing dynamic polarization of nuclei, the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl was introduced in the samples by the thermal diffusion technique. Using the electron paramagnetic resonance method, we obtained information on paramagnetic centers in the polymer matrix of the membranes and determined the nitroxyl radical concentration and rotational mobility of the spin probe in them.