Reaction mechanism for target-like products from197Au target bombarded with12C ions of energies above 100 MeV/u

Target-like products, that is,^191–200Au,^185–200Pt, and^183–195Ir, from¹⁹⁷Au target bombarded with¹²C ions at the energies of 180, 230, and 400 MeV/u were measured by using off-line gamma-ray spectrometry combined with chemical separation procedures. Spallation systematics by Rudstam reproduces well the measured cross sections for formation of platinum and iridium isotopes. It was found that the cross sections of gold nuclides increase with increase of the incident energy in the range studied and they are enhanced if compared with the reported proton-induced reaction of gold at a similar incident energy. It is suggested that the electromagnetic dissociation process plays a role for production of such gold nuclides.     

Anion recognition by 1,3-disiloxane-1,1,3,3-tetraols in organic solvents

Anion recognition by 1,3-disiloxane-1,1,3,3-tetraols has been elucidated by ¹H NMR titrations and ESI-MS in organic solvents. The association constants of the receptors for halide anions are larger than those of silanediol and 1,3-disiloxane-1,3-diol due to the cooperative hydrogen bonds by four silanol hydroxy groups of 1,3-disiloxane-1,1,3,3-tetraols.     

Surface analysis of nitride layers formed on Fe‐based alloys through plasma nitride process

Nitriding phenomena that occur on the surfaces of pure Fe and Fe? Cr alloy (16 wt% Cr) samples were investigated. An Ar + N₂ mixture‐gas glow‐discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar⁺ ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasma‐nitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N₂⁺) and nitrogen molecule from the glow‐discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle‐resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N_x‐Fe_y‐O, NO⁺, and NO₂^?. In the Fe? Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoinduced processes of newly synthesized bisferrocene- and bisfullerene-substituted tetrads with a triphenylamine central block

Photoinduced electron transfer processes of two newly synthesized tetrads with a triphenylamine (TPA) as central building block, to which bisfullerenes (C₆₀) and bisferrocenes (Fc) are covalently connected, have been studied. One of them has a TPA linked with one C₆₀ moiety and two ferrocene moieties C₆₀-TPA-(Fc)₂ and another tetrad has a TPA linked with two C₆₀ moieties and one ferrocene unit (C₆₀)₂-TPA-Fc. The photophysical properties of (C₆₀)_m-TPA-(Fc)_n have been investigated by applying the picosecond time-resolved fluorescence and nanosecond transient absorption techniques in both polar and nonpolar solvents. The charge separation process via the excited singlet state of the C₆₀ moiety of the C₆₀-TPA-(Fc)₂ is more efficient than that of the (C₆₀)₂-TPA-Fc. It is found that the ratio of Fc-donor to C₆₀-acceptor affects charge separation efficiency via the excited singlet state of the C₆₀ moiety.     

Cyclopropanation of electron-deficient alkenes with activated dibromomethylene compounds mediated by lithium iodide or tetrabutylammonium salts

Reactions of electron-deficient alkenes with dibromomethylene compounds activated by cyano and ester groups were promoted by LiI or tetrabutylammonium bromide to afford the corresponding cyclopropanes in high yields.     

Total Synthesis of (−)‐FR182877 through Tandem IMDA–IMHDA Reactions and Stereoselective Transition‐Metal‐Mediated Transformations

Intelligent design : The total synthesis of the cytotoxic (?)‐FR182877 relies on 1) tandem Diels–Alder reactions to close rings A–D (see scheme), 2) a palladium‐mediated 7‐exo‐trig reaction, and 3) an iridium‐mediated isomerization followed by epimerization and stereoselective reduction.

     

Experimental probe for hyperconjugative resonance contribution in stabilizing the singlet state of 2,2-dialkoxy-1,3-diyls: Regioselective 1,2-oxygen migration

A detailed study of the regioselectivity of 1,2-oxygen migration was conducted using the unsymmetrically substituted singlet 2,2-dialkoxy-1,3-diarylcyclopentane-1,3-diyls 5. The alkoxy group selectively migrates to the electron-donating p-methoxyphenyl-substituted carbon. The regioselective migration of oxygen clearly indicates a hyperconjugative resonance structure, that is, zwitterionic characteristics, in singlet 2,2-dialkoxy-1,3-diyls. This represents the first attempt to experimentally probe the contribution of hyperconjugation to stabilizing the singlet state.     

Molecular recognition of viologen by zinc porphyrinic receptors with diarylurea sidearms. Toward construction of a supramolecular electron transfer system

A series of zinc porphyrinic receptors for a viologen substrate (hexyl viologen, HV²⁺) were synthesized, in which varying numbers of diarylurea moieties, from one to four, were appended at the porphyrin's meso positions. The increase in the number of the diarylurea moiety led to the increase in stability of the receptor-HV²⁺ complex, showing that the convergent dipoles set up on the porphyrin platform played an essential role in the complexation. In this system, formation of the stable electron donor-acceptor complex resulted in the effective electron transfer from the singlet excited state of the zinc porphyrin to HV²⁺.     

Chemical reaction-inspired crystal growth of a coordination polymer toward morphology design and control

This paper reports a novel crystal growth system of a coordination framework {[Cu3(CN)3{hat-(CN)3(OEt)3}]}n (1) (hat-(CN)3(OEt)3 = 2,6,10-tricyano-3,7,11-triethoxy-1,4,5,8,9,12-hexaazatriphenylene). The coordination polymer is crystallized through the reaction of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (hat-(CN)6), ethanol, and copper(I) complex, involving the breaking and forming of covalent bonds. The crystal morphologies obtained in the present system contain dumbbells, cogwheels, and superlattices. Moreover, in the growth perpendicular to the c-axis, periodic ramification at regular interval is observed, affording superlattice morphologies. Observation of the growth of dumbbell crystals shows that the growth rates parallel and perpendicular to the crystallographic c-axis are quite different: the former shows a drastic change with the reaction duration, while the latter is almost constant. These results are reproduced as a simple reaction-diffusion system, indicating that chemical reactions on crystal surfaces play an important role in determining the macroscopic crystal morphologies.