Perfluoropentacene: high-performance p-n junctions and complementary circuits with pentacene

We report the synthesis and characterization of perfluoropentacene as an n-type semiconductor for organic field-effect transistors (OFETs). Perfluoropentacene is a planar and crystalline material that adopts a herringbone structure as observed for pentacene. OFETs with perfluoropentacene were constructed using top-contact geometry, and an electron mobility of 0.11 cm2 V-1 s-1 was observed. Bipolar OFETs with perfluoropentacene and pentacene function at both negative and positive gate voltages. The improved p-n junctions are probably due to the similar d-spacings of both acenes. Complementary inverter circuits were fabricated, and the transfer characteristics exhibit a sharp inversion of the output signal with a high-voltage gain.     

Structure-affinity relationships of C-terminal cyclic analogue of neuropeptide Y for the Y1-receptor

We previously reported that a cyclic octapeptide amide, c[D-Cys29, Cys-34]NPY Ac-29-36 (YM-42454) showed a high affinity for Y1-receptors in SK-N-MC cells (Ki=0.047,microM) but not for Y2-receptors in the porcine hippocampus membranes (Ki>10microM). To explore the critical residues of this unique cyclic peptide for Y1-binding activity, the structure-affinity relationships were investigated by means of amino acid replacement. The results indicated that the hydrophobic side-chains of Leu30 and Ile31, the guanidinium groups of Arg33 and Arg33, and the C-terminal amide are critical for the binding affinity of YM-42454 to the Y1-receptor. On the other hand, Thr32 in YM-42454 might not be critical for the Y1-binding affinity. 1H-NMR studies for YM-42454 and its derivatives have suggested that the critical residues are involved in the direct interaction with a Y1-receptor rather than in maintaining the bioactive conformation.     

Efficient and beta-Stereoselective Synthesis of 4(5)-(beta-D-Ribofuranosyl)- and 4(5)-(2-Deoxyribofuranosyl)imidazoles(1)

A synthetic route to 4(5)-(beta-D-ribofuranosyl)imidazole (1), starting from 2,3,5-tri-O-benzyl-D-ribose (5), was developed via a Mitsunobu cyclization. Reaction of 5 with the lithium salt of bis-protected imidazole afforded the corresponding 5-ribosylimidazole 7RS. Hydrolysis of 7RS gave a 1:1 mixture of diol isomers 8R and 8S having an unsubstituted imidazole. Mitsunobu cyclization of the mixture 8RS using N,N,N',N'-tetramethylazodicarboxamide and Bu(3)P exclusively afforded benzylated beta-ribofuranosyl imidazole 9beta in 92% yield, accompanied by alpha-anomer 9alpha, in a ratio of 26.3:1. The configuration of 9beta was established by X-ray crystallography of ethoxycarbonyl derivative 10beta. Reductive debenzylation of 9beta over Pd/C was carried out, and the synthesis of 1 was attained from starting 5 in four steps and 87% overall yield. This synthetic methodology was extended to the synthesis of 4(5)-(2-deoxy-beta-D-ribofuranosyl)imidazole (2). Mitsunobu cyclization of a 1:1 mixture of the corresponding diol isomers 14RS produced 15beta and 15alpha in a ratio of 5.4:1. The synthesis of 2 was attained in a 59% overall yield from the starting 3,5-di-O-benzyl-2-deoxy-D-ribose (12). beta-Stereoselective glycosylation in the key step is discussed and explained by intramolecular hydrogen bonding between an NH in the imidazole and the oxygen functional group in the sugar moiety.     

Helical versus Planar Conformation of Homooligopeptides Prepared from Diethylglycine (=2-Amino-2-ethylbutanoic Acid)

Homooligopeptides containing α,α-diethylgycine (=2-amino-2-ethylbutanoic acid), were synthesized by conventional solution methods. An ethyl or methyl ester was used as protecting group at the C-terminus and a trifluoroacetyl group as protecting group at the N-terminus of the peptides. The conformations of such tri-, penta-, and hexapeptides in the solid state were studied using X-ray crystallographic analysis, and were shown to be a bent planar C5-conformation in the case of tripeptide 8a , and a 3₁₀-helical structure in the case of pentapeptide 10 and hexapeptide 11 . IR and ¹H-NMR spectra revealed that the dominant conformation of hexapeptide 11 in CDCl₃ solution was not the 3₁₀-helical structure shown in the solid state, but a fully planar C5 structure.     

Synthesis,Structure, and Redox Properties of [{(η5-C5H5)Co(S2C6H4)}2Mo(CO)2], a Novel Metalladithiolene Cluster

Metal–metal bond formation by a cobaltadithiolene complex was observed for the first time in the reaction of [Co(η⁵-C₅H₅)(S₂C₆H₄)] with [Mo(CO)₃(py)₃] and BF₃ to give the Co-Mo-Co cluster 1 . Cyclic voltammetry reveals that 1 undergoes two one-electron reduction steps at the Co centers, which is indicative of transmission of the Co−Co electronic interaction through the Mo center.     

Synthesis of polymers in aqueous solutions: Esterification reaction of poly(methacrylic acid) with alkyl halides using DBU in aqueous solutions

A convenient esterification reaction of poly(methacrylic acid) (PMAA) with certain alkyl halides was performed using 1,8-diazabicyclo-[5.4.0]-7-undecene (DBU) as a base in aqueous solution or in water. The esterification reaction of PMAA with propargyl bromide (PB) proceeded very smoothly and quantitatively at 30°C to give corresponding poly(propargyl methacrylate), although the rate of the reaction decreased with increasing water. The reaction of PMAA with benzyl bromide, o-nitrobenzyl bromide, and p-nitrobenzyl bromide gave corresponding poly(methacrylic ester) using DBU under suitable reaction conditions in water. The esterification reactions of PMAA with PB were carried out using certain organic bases such as triethylamine, 4(N,N-dimethylamino)pyridine and pyridine. Inorganic bases such as sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide were also tried under the same conditions as with DBU. However, the degrees of estrification with all these bases was much lower than that with DBU. © 1996 John Wiley & Sons, Inc.     

On the ideal class groups of the maximal real subfields of number fields with all roots of unity

In this paper, for a totally real number field k we show the ideal class group of k(∪_n>0μ_n)⁺ is trivial. We also study the p-component of the ideal class group of the cyclotomic Z_p-extension. Received January 15, 1998 / final version received July 31, 1998     

Chirally autocatalytic reaction performed in highly supersaturated conditions

Spontaneous chiral asymmetry generation, which is the preferential production of one enantiomer in a non‐chiral environment by chiral autocatalysis, could be observed in a preparation of a octahedral cobalt complex, cis‐[CoBr(NH₃)(en)₂]Br₂. A concentration fluctuation in a far‐from‐equilibrium chemical system will grow if the rate of local autocatalytic production of a compound in a small volume overcomes its loss due to diffusion. In a chirally autocatalytic system, this phenomenon could produce a large variation in the enantiomeric excess. In a reaction that produces the cobalt complex, the reaction rate was found to increase in the highly supersaturated solution of the product. In supersaturated solutions, before crystals of the solute have nucleated, embryos, which are the clusters of the solute, are formed. Ternary water‐solubility isotherm of each enantiomer of the cobalt complex suggests that each embryo consists of one exclusive enantiomer. Each chiral cluster, which could be regarded as polymeric material, thus formed in a highly supersaturated solution, may act as catalyst for the production of the same enantiomer. Life is a far‐from‐equilibrium self‐organized polymeric system in which chiral symmetry is broken. This reaction system is thus a model for the generation and amplification of chiral asymmetry in polymeric materials; it provides some insight in to the mechanisms that might have produced the observed biomolecular homochirality.     

Reaction of 2-aminobenzamide analogs and 2-aminothiophenol with ethyl 3-ethoxymethylene-2,4-dioxovalerate. Synthesis of pyrrolo[1,2-α]quinazoline and pyrrolo[1,2-a]benzothiazoline derivatives

The reaction of ethyl 3-ethoymethylene-2,4-dioxovalerate (EMDV) ( 1 ) with 2-aminobenzamide ( 2 ), 2-aminobenzthioamide ( 3 ), 2-aminobenzmethylamide ( 4 ) and 3-amino-2-methyl- or phenylpyrazole-4-carbox-amides ( 6 and 7 ) produced ethyl 3-aminomethylene-2,4-dioxovalerates ( 10, 15, 16, 18 and 19 ), which led to pyrrolo[1,2-a]quinazoline-1,5-diones ( 11, 22 and 23 ) and pyrrolo[1,2-a]pyrazolo[4,3-e]pyrimidine-1,5-diones ( 24 and 25 ) under the acidic condition, respectively. Analogously, 2-aminothiophenol reacted with 1 to give 21 , which was subsequently derived to pyrrolo[1,2-a]benzothiazolin-l-one ( 26 ) under the neutral condition. Furthermore, we prepared the heterocyclic steroidal molecules ( 41, 43, 45, 47, 49 and 51 ) by condensation of 11 and 26 with hydrazine, methylhydrazine and phenylhydrazine.     

超临界 CO2 辅助制备 TiO2 外负载火山岩复合体及其光催化降解亚甲基蓝性能

 以钛酸丁酯为前驱体, 封堵的火山岩为载体, 通过超临界 CO₂ 辅助制备了 TiO₂ 外负载火山岩复合体, 并将其用于光催化降解亚甲基蓝反应, 考察了溶液 pH 值及催化剂浓度对反应性能的影响. 结果表明, TiO₂ 外负载火山岩复合体的光催化性能优于纯 TiO₂ 和 TiO₂ 体负载火山岩复合体. 这是由于外负载复合体对亚甲基蓝的高吸附性、小晶粒尺寸的 TiO₂ 颗粒以及吸附和光催化降解间的协同效应. 亚甲基蓝浓度为 1.5 mg/L, 溶液 pH 为 8, 催化剂浓度为 6.8 mg/L 时, 外负载 TiO₂ 火山岩复合体上亚甲基蓝降解速率最高, 且使用后的催化剂仍具有高的光催化活性.