Synthesis and photoinduced electron transfer processes of rotaxanes bearing [60]fullerene and zinc porphyrin: effects of interlocked structure and length of axle with porphyrins

Three rotaxanes, with axles with two zinc porphyrins (ZnPs) at both ends penetrating into a necklace pending a C60 moiety, were synthesized with varying interlocked structures and axle lengths. The intra-rotaxane photoinduced electron transfer processes between the spatially positioned C60 and ZnP in rotaxanes were investigated. Charge-separated (CS) states (ZnP*+, C60*-)rotaxane are formed via the excited singlet state of ZnP (1ZnP*) to the C60 moiety in solvents such as benzonitrile, THF, and toluene. The rate constants and quantum yields of charge separation via 1ZnP decrease with axle length, but they are insensitive to solvent polarity. When the axle becomes long, charge separation takes place via the excited triplet state of ZnP (3ZnP*). The lifetime of the CS state increases with axle length from 180 to 650 ns at room temperature. The small activation energies of charge recombination were evaluated by temperature dependence of electron-transfer rate constants, probably reflecting through-space electron transfer in the rotaxane structures.     

Anionic copolymerizations of acrylonitrile with β-propiolactone

Anionic copolymerizations of acrylonitrile (monomer 1) with β-propiolactone (monomer 2) and the structures of the resulting copolymers were studied. The copolymerization with sodium cyanide in N,N-dimethylformamide gave copolymers of the structure I containing acid anhydride linkage in the molecular chains, with the monomer reactivity ratios, r₁ = 1.20, r₂ = 0.00. The copolymerization with potassium hydroxide gave either copolymers of the structure II (r₁ = 0.00, r₂ = 3.64 at 30°C; r₁ = 0.00, r₂ = 5.00 at 40°C) in N,N-dimethylformamide or only β-propiolactone homopolymer in toluene.      

Cloning, sequencing, and functional analysis of the biosynthetic gene cluster of macrolactam antibiotic vicenistatin in Streptomyces halstedii

Vicenistatin, an antitumor antibiotic isolated from Streptomyces halstedii, is a unique 20-membered macrocyclic lactam with a novel aminosugar vicenisamine. The vicenistatin biosynthetic gene cluster (vin) spanning approximately 64 kbp was cloned and sequenced. The cluster contains putative genes for the aglycon biosynthesis including four modular polyketide synthases (PKSs), glutamate mutase, acyl CoA-ligase, and AMP-ligase. Also found in the cluster are genes of NDP-hexose 4,6-dehydratase and aminotransferase for vicenisamine biosynthesis. For the functional confirmation of the cluster, a putative glycosyltransferase gene product, VinC, was heterologously expressed, and the vicenisamine transfer reaction to the aglycon was chemically proved. A unique feature of the vicenistatin PKS is that the loading module contains only an acyl carrier protein domain, in contrast to other known PKS-loading modules containing certain activation domains. Activation of the starter acyl group by separate polypeptides is postulated as well.     

Preparation and analytical properties of a chelating resin containing phenylalanine groups

A polystyrene-based macroreticular resin containing phenylalanine groups has been prepared and its analytical properties have been investigated and compared with Dowex A-1. The phenylalanine resin shows high selectivity for mercury(II) and copper(II) in the pH region 2-3. The sorption behaviour of copper has been examined in detail, with the intention of using the resin analytically. The important characteristics of the resin are fast equilibration, high selectivity and small volume change between its hydrogen form and metal forms. These enable it to be applied for the rapid concentration of trace amounts of copper in the presence of large amounts of diverse metals. It may be used for the determination of copper in sea-water and the separation of copper/cobalt and copper/nickel.     

Chelate and intramolecular ion-pair formation: A guiding concept for structure/selectivity relationships in the liquid-liquid extraction of alkali and alkaline earth metal ions by anionic crown ether derivatives

Crown ether dyes with pendent anionic side-arms were synthesized for extractionspectrophotometry of alkali and alkaline earth metal ions. Dramatic changes in metal selectivity were obtained simply by changing the nature of the anionic side-arm on the same crown ether skeleton. A structure/metal selectivity relationship is discussed in detail in terms of “chelate” and “intramolecular ion-pair” formation. Small metal cations (high charge density) are preferred in the extraction by a crown ether reagent with a charge-localized anionic side-arm through the formation of a “chelate”. Large metal cations (low charge density) are preferred in the extraction by reagents with a charge-delocalized anionic side-arm through the formation of an “intramolecular ion-pair”. Steric restrictions imposed by the side-arm on the metal ion approaching the crown ether are also important factor in controlling the selectivity of these reagents.     

Reactivities of Stable Rotamers: XLIV. Ring-Opening Reactions of 1-(9-Fluorenyl)-2-(2-methyl-2-oxiranyl)naphthalene Rotamers With Acids and the Structure of Oxiranes

X-ray crystallography of the ap-form of the 1-(9-fluorenyl)-2-(2-methyl-2-oxiranyl)naphthalene has revealed that the carbon atom of the oxirane which is connected to the naphthyl group in this compound is almost planar. The specific structural features of the epoxy ring in this compound are caused by sterical effects and by the presence of a -system in the immediate vicinity of the oxirane ring. Certain differences have been found also in reactivity of rotational isomers of 2-X-substituted 1-[1-(9-fluorenyl)-2-naphthyl]ethyl cations (X = O, S, Se). At X = O arose more deprotonation product from the -position of the oxygen than in reactions of sulfur and selenium-containing analogs. Reactions of epoxides with zinc chloride almost exclusively gave the corresponding aldehydes.     

REDUCTION OF BIS(BROMO(MESITYL)-{2,4,6-TRIS[BIS(TRIMETHYLSILYL)METHYL]- PHENYL}SILYL)BUTADIYNE WITH POTASSIUM GRAPHITE: UNEXPECTED FORMATION OF 2-ALLENYL-1-BENZOSILOLE

The reductive debromination of an very crowded bis(bromodiaryl- silyl)butadiyne 2 was performed with potassium graphite to give the corresponding 2-allenyl-1-benzosilole 3 was isolated as a main product.