Metachromins L-Q, new sesquiterpenoid quinones with an amino acid residue from sponge Spongia sp.

Six new sesquiterpenoid quinones with an amino acid residue, metachromins L-Q (1-6), have been isolated from an Okinawan marine sponge Spongia sp. The structures and stereochemistry of 1-6 were elucidated on the basis of the spectroscopic data and chemical correlations. Metachromins L (1) and M (2) showed modest cytotoxicity.     

Transcendence of certain infinite products

We prove the transcendence results for the infinite product , where Ek(x), Fk(x) are polynomials, α is an algebraic number, and r?2 is an integer. As applications, we give necessary and sufficient conditions for transcendence of and , where Fn and Ln are Fibonacci numbers and Lucas numbers respectively, and {ak}_k?0 is a sequence of algebraic numbers with log‖ak‖=o(rk).     

Metachromins R--T, new sesquiterpenoids from marine sponge Spongia sp

Three new sesquiterpenoids, metachromins R--T (1--3), have been isolated from an Okinawan marine sponge Spongia sp. The structures and stereochemistry of 1--3 were elucidated on the basis of the spectroscopic data. Metachromins S (2) and T (3) showed modest cytotoxicity.     

Liquid-liquid equilibria of polyrotaxane and poly(vinyl alcohol)

Liquid–liquid equillibria (LLE) of the tertiary system of hydroxypropylated polyrotaxane (HPPR)–poly(vinyl alcohol) (PVA)–solvent have been investigated by focusing on the internal structures of HPPR–PVA blend gels. The phase diagrams of the HPPR–PVA aqueous systems displayed two liquid phases at a high concentration and molecular weight of PVA. This result was consistent with the prediction of the Flory–Huggins lattice model. On the contrary, the HPPR–PVA–DMSO system exhibited only a single phase. The HPPR–PVA blend gels crosslinked in dimethylsulfoxide (DMSO) were highly transparent over a wide concentration range, while the gels prepared in water were opaque at high polymer concentrations. Spherical domains were observed in the opaque gels by laser scanning confocal microscopy, and the sizes of the domains were significantly dependent on the amount of cross-linking reagent utilized. These results indicated that the transparency of the HPPR–PVA blend gels was strongly affected by the competition between the liquid–liquid two-phase separation and the crosslinking HPPR and PVA polymers during the preparation of the blend gels.     

Highly Enantioselective Asymmetric Autocatalysis of Pyrimidin‐5‐yl Alkanol Induced by Chiral 1,3‐Disubstituted Hydrocarbon Allenes

1,3‐Disubstituted chiral allenes without any heteroatoms act as chiral initiators in the addition of (i‐Pr)₂Zn to pyrimidine‐5‐carbaldehyde to afford, in combination with the subsequent asymmetric autocatalysis, chiral pyrimidin‐5‐yl alkanols with up to 98% ee. The absolute configuration of the pyrimidin‐5‐yl alkanol formed depend on that of the chiral allene.     

rac‐ and meso‐3,3′‐Bis(3,5‐di­methyl­phenyl)‐3H,3′H‐2,2′‐biindenyl­idene‐1,1′(2H,2′H)‐dione

In the rac isomer of the title compound, C₃₄H₂₈O₂, the two C—Ph_{di­methyl­phenyl} bond axes make an angle of 58.7 (1)°. There is no short contact between the two 3,5‐di­methyl­phenyl rings, although the dihedral angle between them is 4.93 (7)°. The meso isomer has a center of symmetry at the middle of the C=C bond, and the two C—Ph_{di­methyl­phenyl} bond axes are antiparallel to one another.     

Substitution‐Pattern‐ and Counteranion‐Depending Ion‐Pairing Assemblies Based on Electron‐Deficient Porphyrin–AuIII Complexes

Porphyrin–Au^III complexes, which were partially or totally modified with C₆F₅ at the meso positions, were synthesized. The highly electron‐withdrawing substituents induced electron‐deficient states and Lewis acid properties. Single‐crystal X‐ray analysis of the ion pairs revealed ion‐pairing assemblies with characteristics dependent on the number and substitution pattern of the C₆F₅ units and the geometries of the anions.     

Small-angle neutron scattering study of dynamically polarized polyethylenes

We carried out a small-angle neutron scattering (SANS) study of dynamically polarized polyethylene (PE) samples doped with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The transmission of the PE with almost fully polarized neutrons (98.5%) increased with increasing the proton polarization, P. The incoherent scattering cross section decreased with increasing P. The effect of P on the polarized neutrons’ transmission and the incoherent scattering cross section agreed well with the theory. The q-dependence of the coherent scattering, which reflects a two-phase structure of PE composed of crystalline and amorphous domains, was kept unchanged by the proton polarization, but the intensity increased by a factor of 3 and 6 for P=+23% and −23%, respectively. The results mean that the contrast between the two phases was successfully enhanced by a dynamic nuclear polarization (DNP) technique. However, the enhancement is only 1/13–1/16 of the enhancement calculated by assuming a homogeneous polarization through the PE sample. The discrepancy suggests that P in amorphous domains (25%) should be higher than that in crystalline domains (22%) by 3%, which in turn may suggest the partial depolarization of proton spins on the way of the spin diffusion from amorphous domains, where TEMPO radicals localize, to crystalline domains.     

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.