Poly(β-Amino acids). V. Synthesis and conformation of oligomeric α-isobutyl-L-aspartate

α-Isobutyl-L -aspartate oligomers, Z-(α-i-Bu-Asp)_2n–OEt (n = 1–5), where Z = benzyloxycarbonyl and OEt = ethyl ester, were prepared stepwise, and their conformation in solution was investigated by optical rotation, circular dichroism (CD), and NMR spectroscopy. The oligomers up to hexamer existed only in a disordered form. An ordered structure began to appear at octamer and decamer in chloroform and 2,2,2-trifluoroethanol. The ordered structure was more favorable for N-unprotected oligomers, H-(α-i-Bu-Asp)_2n–OEt, in comparison with the corresponding Z-(α-i-Bu-Asp)_2n–OEt. The effects of oligomer concentration and temperature on the structure were slightly observed. The most likely ordered structure was a β form caused by intramolecular association.     

Simple synthesis of 6-alkyl-5H-benzo[a]phenoxazin-5-ones

6-Alkyl-5H-benzo[a]phenoxazin-5-ones were prepared by the reaction of 5H-benzo[a]phenoxazin-5-one with carboxylic acid in the presence of silver ion and peroxydisulfate.

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Eine einfache Synthese von 6-Alkyl-5H-benzo[a]phenoxazin-5-onen (Kurze Mitteilung)

Zusammenfassung 6-Alkyl-5H-benzo[a]phenoxazin-5-one wurden mittels Reaktion von 5H-Benzo[a]phenoxazin-5-onen mit Carbonsäuren in Gegenwart von Silberionen und Peroxydisulfat dargestellt.

     

Effects of substituents on the anionic copolymerization of ring-substituted cinnamonitriles

trans-Cinnamonitrile (M₁) was copolymerized with several of its ring-substituted derivatives (M₂) in toluene at 25°C, calcium zinc tetraethyl being used as catalyst. The ring substituents investigated include H, p-CH₃O, m-CH₃O, p-CH₃, m-CH₃, p-Cl, and m-Cl. It was found that the values of log (1/r₁) are linearly correlated with Hammett's σ constants with the reaction constant σ ρ 0.7. The effects of coordination between monomer and catalyst sites upon the Hammett relation are discussed.     

Synthesis of poly-L-naphthylalanine and its secondary structure

Polypeptides derived from L -naphthylalanine and γ-benzyl L -glutamate were prepared. Conformational properties in solution were investigated by circular dichroism (CD) and infrared spectra on the soluble copolymers, and the copolymers were assumed to take the right-handed α-helical conformation. By the addition of trifluoroacetic acid, a transition of side-chain arrangement is induced simultaneously with the conformational transition of the peptide backbone for the copolymer with the highest content of L -naphthylalanine residues. Fluorescence spectra of the copolymers show no excimer emission, which is evidence for the rigid orientation of the side-chain naphthyl groups. The infrared spectrum and x-ray diagram of poly-L -naphthylalanine do not rule out the helical conformation in the solid state.     

Synthesis of polyphthalamides by ring-opening polyaddition reaction of N,N′-disubstituted bisphthalisoimides with diamines

The ring-opening polyaddition reaction of N,N′-disubstituted bisphthalisoimides with various diamines in amide-type solvents at room temperature afforded polyphthalamides having inherent viscosity of up to 0.26 in excellent yields. Some of the polymers thus obtained are a new class of ordered alternating copolyphthalamides. These polyamides were soluble in polar aprotic solvents, as well as in acidic solvents. They showed relatively low melt temperature in the range of 120–220°C and further low level of thermal stability.     

A ground-state-dominated magnetic field effect on the luminescence of stable organic radicals

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host αH-PyBTM molecular crystals. The magnetic field (0–14 T), temperature (4.2–20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions.

We investigated the mechanism of the magnetic field effect (MFE) on the emission of a luminescent radical doped into host crystals. It was revealed that the spin sublevel population of radical dimers in the ground states is the key that governs the MFE.     

Bulk synthesis of single-crystalline magnesium oxide nanotubes

Crystalline tubular magnesium oxide nanostructures were obtained through carbon-thermal evaporation of a MgO powder. Gallium oxide was added into the mixture of MgO and carbon. The reduction of gallium oxide by carbon resulted in gallium vapor at high temperatures. Condensed gallium droplets catalyzed the anisotropic growth of tubular MgO nanostructures in situ. The products were characterized by X-ray powder diffraction technique, scanning electron microscopy, and high-resolution microscopy. All the analyses indicated that the prepared tubular MgO nanostructures are, in fact, single crystals.     

Errata

A novel palladium compound, (Ph₃P)Pd(Cl)(CH₂SCH₃), was prepared in which the CH₃SCH₂ group acts as a chelate ligand; the stereochemically non-rigid property of (Ph₃P)Pd(CH₂SCH₃)[S₂CN(CH₃)₂] was also discussed in terms of the ligating effect of sulfur in this group.     

Asymmetric halogenation and hydrohalogenation of styrene in crystalline cyclodextrin complexes

Asymmetric halogenation and hydrohalogenation of styrene in microcrystalline cyclodextrin complexes were studied in the gas-solid state, and compared with the homogenous reactions in aqueous or dimethyl sulfoxide solutions. The gas-solid brominations in the - and -cyclodextrin complexes produced predominantly (–)-1,2-dibromo-l-phenylethane. The chiral induction for the reaction of the -cyclodextrin complex rose to 9 times that of the -cyclodextrin complex. Brominations in the homogenous solutions containing the - or -cyclodextrin complexes gave no dibromide but racemic bromohydrin. In the gas-solid chlorination, the -cyclodextrin complex gave (–)-dichloride,S-(+)-2-chloro-l-phenylethanol (14% ee) and (+)-1,2,2-trichloro-l-phenylethane, and the -cyclodextrin complex produced (+)-dichloride,S-(+)-chlorohydrin (8% ee) and (+)-trichloride. The chiral induction of the gas-solid halogenation using the solid cyclodextrin complexes is attributed to the ability to hold rigidly a chiral conformation of the crystalline state. However, the gas-solid hydrohalogenation all gave racemic products.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.