Fluorescent 3-methylene-2,3-dihydrochalcogenophenes incorporated in a rigid dibenzobarrelene skeleton

The fluorescent 3-methylene-2,3-dihydroselenophene derivative (Φ(F) = 0.86 in CH(2)Cl(2)) incorporated in a dibenzobarrelene skeleton was synthesized by the reaction of a four-membered selenaplatinacycle with dimethyl acetylenedicarboxylate (DMAD) or reaction of bis(dibenzobarrelenyl) diselenide with DMAD in the presence of Pd(PPh(3))(4) and PPh(3). A fluorescent sulfur homologue (Φ(F) = 1.0 in CH(2)Cl(2)) was also synthesized by the reaction of bis(dibenzobarrelenyl) disulfide with DMAD in the presence of Pd(PPh(3))(4). Selected chemical transformations of these diesters were also investigated.     

Stabilization of organic field-effect transistors by tert-butyl groups in dibenzotetrathiafulvalene derivatives

For a material for organic thin-film transistors, not only high mobility but also low threshold voltage and long-term stability are important requirements. In order to realize these properties, materials with relatively large oxidation potentials, namely weak donors, have been designed as p-channel organic semiconductors. Here we propose a different strategy; transistor properties of dibenzotetrathiafulvalene (DBTTF) are significantly improved by the introduction of tert-butyl groups. Although this chemical modification does not much change the ionization potential, small threshold voltage and stability over several months are attained together with the improved mobility, probably due to some kind of passivation effect of the bulky tert-butyl groups. In contrast, the systematic fluorine substitution rapidly diminishes the transistor performance. There are two kinds of herringbone structures with much different dihedral angles of about 50° and 130°, and the tert-butyl compound falls into the former category.     

Molecular origin for helical winding of fibrils formed by perfluorinated gelators

A chiral low-molecular weight gelator, N,N'-diperfluoroheptanoyl-1,2(R,R)- or -1,2(S,S)-diaminocyclohexane, was prepared to form a gel of acetonitrile. The conformation of the gelator in fibrils was determined by vibrational circular dichroism spectra, providing a molecular model for self-assembly in a helical fibril.     

Model companions of theories of graphs

We study model companions of theories extending the graph axioms. First we prove general results concerning the existence of the model companion. Then, by applying these results to the case of graphs, we give a series of companionable and non‐companionable examples.     

Asymptotic expansion for forward-backward SDEs with jumps

This work provides a semi-analytic approximation method for decoupled forward-backward SDEs (FBSDEs) with jumps. In particular, we construct an asymptotic expansion method for FBSDEs driven by the random Poisson measures with σ-finite compensators as well as the standard Brownian motions around the small-variance limit of the forward SDE. We provide a semi-analytic solution technique as well as its error estimate for which we only need to solve essentially a system of linear ODEs. In the case of a finite jump measure with a bounded intensity, the method can also handle state-dependent and hence non-Poissonian jumps, which are quite relevant for many practical applications.     

Synthetic Studies on Sialoglycoconjugates 23: Total Synthesis of Sialyl-α(2↠6)-Lactotetraosylceramide and Sialyl-α(2↠6)-Neolactotetraosylceramide

ABSTRACT

The first total syntheses of sialyl-α(2→6)-lactotetraosylceramide (29, IV⁶NeuAcLc₄Cer) and sialyl-α(2→6)-neolatotetraosylceramide (33, IV⁶NeuAcnLc₄Cer) are described. Methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio-ß-D-galactopyranoside (11), the key glycosyl donor was prepared, via glycosylation of 2-(trimethylsilyl)ethyl 3-O-benzyl-ß-D-galactopyranoside (2) with the methyl α-thioglycoside 3 of N-acetylneuraminic acid, benzoylation, replacement of the 2-(trimethylsilyl)ethyl group by acetyl, and introduction of the methylthio group with (methylthio)trimethylsilane. Each coupling of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-ß-D-glucopyranosyl)-(1→3′)-per-O-benzyl-ß-lactoside (12) or 2-(trimethylsilyl)ethyl O-(2-acetamido-3-O-acetyl-6-O-benzyl-2-deozy-ß-D-glucopyranosyl)-(1→3′)-per-O-benzyl-ß-D-lactoside (14) prepared from 12 by O-acetylation and reductive opening of the benzylidene acetal, with 11 gave the pentasaccharides 16 and 20 in good yields. Compounds 16 and 20 were converted into the corresponding α-trichloroacetimidates 19 and 24 which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (25), gave the ß-glycosides 26 and 30, respectively. Finally, 26 and 30 were transformed, via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into 29 and 33, respectively.     

Synthetic Studies on Sialoglycoconjugates 27: Synthesis of Sialyl-α(2→6)-Lewis X

ABSTRACT

Synthesis of a positional isomer of sialyl Lewis X with regard to the substitution of the terminal galactose residue of the pentasaccharide by N-acetylneuraminic acid is described. Dimethyl(methylthio)sulfonium triflate-promoted coupling of 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)-O-(2-acetamido-6-O-benzyl-2-deoxy-ß-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-ß-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-ß-D-glucopyranoside (1) with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio-ß-D-galactopyranoside (2) gave the desired hexasaccharide 3. Compound 3 was converted into the α-trichloro-acetimidate 6, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloro-acetonitrile, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (7), gave the ß-glycoside 8. Finally, 8 was transformed, via selective reduction of the azide group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 11 in good yield.     

Synthesis of Sialyl Lewis X Ganglioside Analogs Containing A Variable Length Spacer Between the Sugar and Lipophilic Moieties 1

Abstract

Five sialyl Lew is X ganglioside analogs containing 4-(2-tetradecylhexadecanoylamino)benzyl group in place of ceramide and a variety of lengths of ethylene glycol chains as the spacer, have been synthesized. Glycosidation of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-glacto-2-nonulopyranosylonate)-(2→3)-O-(4-O-acetyl-2,6-di-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-acetylα-L-fucopyranosyl)-(1→3)]-2,4-di-O-benzoyl-α-D-glucopyranosyl trichloroacetimidate (13) with oligo ethyleneglycol monobenzyl ether derivatives 9, 10, 11 and 12, prepared from the corresponding oligo ethyleneglycols by 4-nitrobenzylation, reduction and N-acylation with 2-tetradecylhexadecanoic acid, using boron trifluoride etherate gave the corresponding glycolipid derivatives 14, 15, 16 and 17. A similar glycosidation of 13 with 4-nitrobenzyl alcohol gave the 4-nitrobenzyl glycoside 18, which was converted via reduction of nitro group and N-acylation into the corresponding glycolipid derivative 19. Compounds 14-17 and 19 were transformed into the title compounds by O-deacylation and hydrolysis of methyl ester group in good yields.

     

Molecular Design Rule of Phthalocyanine Dyes for Highly Efficient Near‐IR Performance in Dye‐Sensitized Solar Cells

A series of zinc–phthalocyanine sensitizers ( PcS16 – 18 ) with different adsorption sites have been designed and synthesized in order to investigate the dependence of adsorption‐site structures on the solar‐cell performances in zinc–phthalocyanine based dye‐sensitized solar cells. The change of adsorption site affected the electron injection efficiency from the photoexcited dye into the nanocrystalline TiO₂ semiconductor, as monitored by picosecond time‐resolved fluorescence spectroscopy. The zinc–phthalocyanine sensitizer PcS18 , possessing one carboxylic acid directly attached to the ZnPc ring and six 2,6‐diisopropylphenoxy units, showed a record power conversion efficiency value of 5.9 % when used as a light‐harvesting dye on a TiO₂ electrode under one simulated solar condition.     

Radiation-Induced Copolymerization of Thiophene with Maleic Anhydride

Radiation-induced copolymerization of thiophene with maleic anhydride has been studied. On the copolymerization in chloroform solution, the effects of dose rate, polymerization temperature, and, monomer composition and concentration on the yield and molecular weight of the copolymer were determined. The copolymerization proceeds via a radical mechanism with bimolecular termination of propagating polymer radicals, and the apparent activation energy is 5.3 kcal/mole. By NMR spectroscopy of copolymer, it was also found that these monomers copolymerize alternately to give a copolymer having structure I. In this copolymerization, the higher initial rates were obtained at an equimolar composition of monomers and by using solvents containing chlorine, such as CC1₄, CHC1₃, and C₆H₅C1.