Tris(porphyrinyl-oxinato)Ga Complexes as a Photosynthetic Antenna Miniature

Two oxinylporphyrins, 5-(8-hydroxy-5-quinolinyl)-10,15,20-( p -tolyl)- porphyrin ( 1 ) and 5,15-bis(8-hydroxy-5-quinolinyl)-10,20-bis( n -heptyl)-porphyrin ( 2 ), were prepared and coordinated with Ga(III) to afford tris(oxinato) complex 3 and poly(oxinato) complex 4 , respectively. The structure of 3 was analyzed by variable temperature NMR study with referring to tris(8-hydroxy-5-quinolinyl)Ga(III) complex 5 to be in a meridional form. Oxinato ligands of 3 and 5 were exchanged with one another, with keeping the meridional structure. UV-Vis and fluorescence spectra of tris(oxinato)complex 3 and poly(oxinato)complex 4 were compared with each monomeric compound 1 and 2 . The absorption spectra showed only a slight broadening of the Soret band, suggesting trivial electronic and excitonic interactions. The fluorescence intensity was increased significantly compared with each monomeric compound 1 and 2 . At the same time, efficient excitation energy transfer among three porphyrins has been observed.     

Chemoselective Oxidation of Secondary Hydroxy Functions Catalyzed by [PMo12O40]3-[C5H5N+(CH2)15 CH3]3

Abstract

The epoxidation of allylic alcohols with H₂O₂ catalyzed by a new Mo-species, [PMo₁₂O₄₀]^3?[C₅H₅N⁺(CH₂)₁₅CH₃]₃ (MPCP), prepared from 12-molybdatophosphoric acid (H₃PMo₁₂O₄₀) and cetylpyridinium chloride [C₅H₅N⁺(CH₂)₁₅CH₃ · Cl^?], has recently rep0rted.) The high regioselectivity for the epoxidation by this MPCP-H₂O₂ system was comparable to that of Sharpless method using t-BuOOH as oxidant.     

A highly selective cobalt-catalyzed carbonylative cyclization of internal alkynes with carbon monoxide and organic thiols

Despite the fact that many transition-metal-catalyzed reactions of organosulfur compounds with internal alkynes are ineffective, cobalt carbonyl (Co₂(CO)₈) is an excellent catalyst for carbonylative cyclization of internal alkynes with carbon monoxide. When Co₂(CO)₈-catalyzed reactions of internal alkynes with organic thiols are conducted in acetonitrile under 4 MPa pressure of carbon monoxide, thiolative lactonization of internal alkynes successfully takes place with incorporation of two molecules of CO. This carbonylation provides a useful tool to prepare the corresponding α,β-unsaturated γ-thio-γ-lactones (butenolide derivatives) in good yields. In the cases of unsymmetrical alkynes, such as 2-octyne and 6-methyl-2-heptyne, the thiolative lactonization proceeds with moderate regioselectivity to give the butenolide derivatives on which the carbonyl group preferentially bonds to the less hindered acetylenic carbon. Mechanistic pathways about the present thiolative lactonization are also discussed.     

Liquid crystals of some new tolane derivatives containing a 1,2-ethylene linkage

Abstract

Three types of nematogenic compound, 4-[2-(trans-4-alkylcyclohexyl)ethyl]-4′-alkyltolanes, 2-fluoro-4-[2-(trans-4-alkylcyclohexyl)ethyl]-4′-alkyltolanes and 4-[2-(trans-4-alkylcyclohexyl)ethyl]-4′-halogenotolanes, have been synthesized and their transition temperatures and enthalpies determined. Their bulk viscosity and birefringence have been estimated from those of mixtures with other liquid-crystalline compounds. These compounds have been found to be excellent materials for twisted nematic displays, because of their wide nematic temperature range, high birefringence (Δn = 0·26), and low viscosity (η = 21 cP at 20°C). Several related compounds having other central linkages, namely -CH₂O-, a single bond or -COO-, in place of the 1,2-ethylene group, have also been studied.     

Synthesis of Methyl (Methyl D-and L-Idopyranosid)Uronates from myo-Inositol

Abstract

Methyl (methyl α-D-(9a), α-(9b), β-D-(10a), and β-L-(10b) idopyranosid)uronates were synthesized from myo-inositol. Baeyer-Villiger oxidation of the optically resolved inosose derivatives (3a and 3b) proceeded regioselectively to afford 4a and 4b in high yields, respectively. Ring-opening of the 7-membered hemiacetal-lactones (4a and 4b) with acid and subsequent deprotection gave the title compounds.     

Studies on the Thioglycosides of N-Acetyl-Neuraminic Acid 8: Synthesis of S-(α-Sialyl)-(2→ 6)-β-Hexopyranosyl and -(2→ 6')-β-Lactosyl Ceramides Containing β-Thioglycosidically Linked Ceramide

ABSTRACT

Coupling of the sodium salt of S-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-galacto-2-nonulopyranosylonate)-(2→'6)-2,3,4-tri-O-acetyl-1,6-dithio-β-D-glucopyranose (5), -β-D-galactopyranose (8), or S-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→'6)-O-(2,3,4-tri-O-acetyl-6-thio-β-D-galactopyranosyl)-(1→'4)-2,3,6-tri-O-acetyl-1-thio-β-D-glucopyranose (12), which were prepared from the corresponding 1-hydroxy compounds, 1, 2, and 9, via 1-chlorination, displacement with thioacetyl group, and S-deacetylation, with (2S,3R,4E)-2-azido-3-O-benzoyl-1-O-(p-toluenesulfonyl)-4-octadecene-1,3-diol (13), gave the corresponding β-thioglycosides 14, 18 and 22, respectively in good yields. The β-thioglycosides obtained were converted, via selective reduction of the azide group, condensation with octadecanoic acid, and removal of the protecting groups, into the title compounds.     

Vanadium-catalyzed green oxidation of benzylic alcohols in water under air atmosphere

The oxidation of alcohols using catalytic amounts of metal complexes is highly attractive from the viewpoint of green chemistry principles. However, examples of metal complex-catalyzed oxidations of alcohols with O₂ using water as the solvent are still rare, and precious metals, high-pressure O₂ or air, and a stoichiometric amount of base are often required. In this study, it was found that an oxovanadium-4,4′-t-Bubpy (4,4′-di-tert-butyl-2,2′-bipyridyl) complex exhibited high catalytic activity in the oxidation of benzhydrols under an atmosphere of O₂ in water as the sole solvent. Interestingly, this catalytic oxidation method could be applied to the gram-scale aerobic oxidation of alcohols in water under the atmosphere.     

Effects of post-deposition annealing on chemical composition of SiNx film in SiO2/SiNx/SiO2/Si stacked structure

To systematically evaluate the quality of SiN_x films in multi-stacked structures, we investigated the effects of post-deposition annealing (PDA) on the film properties of SiN_x within the SiO₂/SiN_x/SiO₂/Si stacked structure by performing X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier transform infrared (FT-IR) spectroscopy, and scanning transmission electron microscope–electron energy loss spectroscopy (STEM-EELS) analyses. The XPS results showed that PDA induces the oxidation of the SiN_x layer. In particular, new finding is that Si-rich SiN_x in the SiN_x layer is preferentially oxidized by PDA even in multi-stacked structure. The XRR results showed that the SiN_x layer becomes thinner, whereas the interface layer between the SiN_x layer and Si becomes thicker. It is concluded by STEM-EELS and XPS that this interface layer is SiON layer. The density of N–H and Si–H bonding within the stacked structure strongly depends on the PDA temperature. Our study helps elucidate the properties of SiN_x films in stacked structures from various perspectives.     

Formation and stability of cellulose–copper–NaOH crystalline complex

We investigated the crystal structure of alkali-celluloses, Na-cellulose IIA and II(Cu), formerly known as Na-cellulose IIB, by synchrotron X-ray diffraction. Na-cellulose IIA, formed from cellulose I by high-concentration NaOH treatment, has a fiber repeat of 15 Å and a threefold-like helical conformation. Na-cellulose II(Cu), prepared by treating cellulose I with copper-saturated alkali solution, also has a fiber repeat of 15 Å with threefold helical symmetry. Incorporation of Cu(II) ions into cellulose was confirmed by multiwavelength anomalous diffraction. Monitoring by X-ray diffraction revealed that the formation of this complex from cellulose I is remarkably slow, probably because of the involvement of copper ion. The stability of alkali-cellulose II(Cu) was tested to estimate the influence of the presence of copper in the crystal. Na-cellulose II(Cu) characteristically dissolved in aqueous ammonia solution, indicating strong coordination of copper ion to cellulose.     

Intense Red-Blue Luminescence Based on Superfine Control of Metal–Metal Interactions for Self-Assembled Platinum(II) Complexes

A series of assembled Pt^II complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups, [Pt(CN)₂(R-impy)] (R-impyH⁺=1-alkyl-3-(2-pyridyl)-1H-imidazolium, R=Me ( Pt-Me ), Et ( Pt-Et ), ⁱPr ( Pt- ⁱ Pr ), and ^tBu ( Pt- ^t Bu )). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield of 0.51–0.81 in the solid state at room temperature, originating from the triplet metal-metal-to-ligand charge transfer (³MMLCT) state. Their emission colors cover the entire visible region from red for Pt-Me to blue for Pt- ^t Bu . Importantly, Pt- ^t Bu is the first example that exhibits blue ³MMLCT emission. The ³MMLCT emission was proved and characterized based on the temperature dependences of the crystal structures and emission properties. The wide-range color tuning of luminescence using the ³MMLCT emission presents a new strategy of superfine control of the emission color.