Palladium‐Catalyzed C−H Iodination of Arenes by Means of Sulfinyl Directing Groups

C?H iodination of aromatic compounds has been accomplished with the aid of sulfinyl directing groups under palladium catalysis. The reaction proceeds selectively at the peri‐position of polycyclic aryl sulfoxides or at the ortho‐position of phenyl sulfoxides. The iodination products can be further converted via iterative catalytic cross‐coupling at the expense of the C?I and C?S bonds. Computational studies suggest that peri‐C?H palladation would proceed via a non‐directed pathway, wherein neither of the sulfur nor oxygen atom of the sulfinyl group coordinates to the palladium before and at the transition state.     

Crystal growth of Co ferrite on fine acicular γ-Fe2O3 particles

Highly coercive magnetic powder was obtained by growing cobalt ferrite on the surface of γ-Fe₂O₃ particles in highly alkaline suspensions containing cobalt and ferrous ions in a Co/Fe molar ratio = $\text{1}\text{2}$. The mechanism of the growth and the structure of cobalt ferrite on γ-Fe₂O₃ were studied by X-ray diffraction and electron diffraction techniques. Results show that crystals of cobalt ferrite CoFe₂O₄ with a spinel type crystal structure of lattice constant 8.415 Å grew epitaxially on γ-Fe₂O₃. The acicular direction of the epitaxially grown Co-γ-Fe₂O₃ as well as γ-Fe₂O₃ was in the [$\text{1}$01] direction. It was found that from the lattice constant value and the half width of X-ray diffraction peaks, the lattice constant epitaxially grown Co γ-Fe₂O₃ may be attributed to two kinds of crystals, viz., seed γ-Fe₂O₃ ($\text{a = 8.35 ～ 8.37}\text{A}\text{?}$) which was partly reduced to Fe₃O₄, and surface layer CoFe₂O₄ ($\text{a = 8.415}\text{A}\text{?}$). The crystal growth in the interface between the seed crystals and the growth layer was affected by the crystal structure of the seed crystals. The lattice constant of CoFe₂O₄ which was located in the vicinity of the interface was almost equal to that of the seed crystals.     

2,2′-Bipyridyl formation from 2-arylpyridines through bimetallic diyttrium intermediate

An alkylyttrium complex supported by an N,N′-bis(2,6-diisopropylphenyl)ethylenediamido ligand, (ArNCH₂CH₂NAr)Y(CH₂SiMe₃)(THF)₂ (1, Ar = 2,6-ⁱPr₂C₆H₃), activated an ortho-phenyl C–H bond of 2-phenylpyridine (2a) to form a (2-pyridylphenyl)yttrium complex (3a) containing a five-membered metallacycle. Subsequently, a unique C(sp²)–C(sp²) coupling of 2-phenylpyridine proceeded through a bimetallic yttrium intermediate, derived from an intramolecular shift of the yttrium center to an ortho-position of the pyridine ring in 3a, to yield a bimetallic yttrium complex (4a) bridged by two-electron reduced 6,6′-diphenyl-2,2′-bipyridyl. Aryl substituents at the ortho-position of the pyridine ring were key in order to destabilize the μ,κ²-(C,N)-pyridyldiyttrium intermediate prior to the C(sp²)–C(sp²) bond formation.     

Communication: The reason why +c ZnO surface is less stable than -c ZnO surface: first-principles calculation

It has been experimentally shown that an O(-c)-polar ZnO surface is more stable than a Zn(+c)-polar surface in H(2) ambient. We applied first-principles calculations to investigating the polarity dependence on the stability at the electronic level. The calculations revealed that the -c surface terminated with H atom was stable maintaining a wurtzite structure, whereas the +c surface was unstable due to the change of coordination numbers of Zn at the topmost surface from four (wurtzite) to six (rock salt). This causes the generation of O(2) molecules, resulting in instability at the +c surface.     

Crystal structure and molecular conformation of E-64, a cysteine protease inhibitor

In order to elucidate the conformational characteristics of cysteine protease inhibitors contributing to their inhibitory activities, the conformation of E-64 (N-[N-(L-3-trans-carboxyoxiran-2-carbonyl)-L-leucyl]-agmatine), a potent inhibitor of papain, was determined by X-ray crystal structure analysis. The molecules were packed in the crystal through electrostatic forces and hydrogen bonding between the oppositely charged terminal groups and between the amide groups. Two crystallographically independent E-64 molecules both took a flattened and slightly curved structure, which is similar to that of loxistatin, a related cysteine protease inhibitor. Based on the present results, a possible inhibitory mechanism of E-64 is proposed, with reference to the binding mode observed in the crystal structure of papain-substrate analogue complex.     

Fabrication and hard X-ray photoemission analysis of photocathodes with sharp solar-blind sensitivity using AlGaN films grown on Si substrates

Photocathode devices operating in reflection-mode, where the photoemission is detected on the same side as the light irradiation, were developed for the detection of deep ultraviolet light by using p-Al_xGa_1−xN films grown on Si(1 1 1) substrates. The external quantum efficiencies were as high as 20-15% at 200 nm and 280 nm, while the value was as low as 10⁻²% at 310 nm. The on-off ratio was more than four orders of magnitude, which represents high solar-blind sensitivity. The escape probability of Al_xGa_1−xN photocathode was decreased with increase of AlN mole fraction. The effective barrier potential against the photoelectron emission near the surface was reduced due to the upward shift of conduction band of Al_xGa_1−xN. The photoemission from the Al_xGa_1−xN films terminated with Cs-O adatoms will be discussed in terms of band diagrams that were evaluated by hard X-ray photoelectron spectroscopy.     

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF₂ by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF₂ has a tendency to grow along an orientation close to 1 1 0. Degradation in optical transmittance was evaluated by irradiating the crystal to γ-rays up to a dose of 10⁵ rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.