Dipeptide-induced chirality organization

This review describes an outline of dipeptide-induced chirality organization by using molecular scaffolds. A variety of ferrocene-dipeptide conjugates as bioorganometallics are designed to induce chirality-organized structures of peptides. The ferrocene serves as a reliable organometallic scaffold with a central reverse-turn unit for the construction of protein secondary structures via intramolecular hydrogen bondings, wherein the attached dipeptide strands are constrained within the appropriate dimensions. Another interesting feature of ferrocene-dipeptide conjugates is their strong tendency to self-assemble through contribution of available hydrogen bonding sites for helical architectures in solid states. Symmetrical introduction of two dipeptide chains into a urea molecular scaffold is performed to induce the formation of the chiral hydrogen-bonded duplex, wherein each hydrogen-bonded duplex is connected by continuous intermolecular hydrogen bonds to form a double helix-like arrangement.     

Medicinal Flowers. XXXI. Acylated oleanane-type triterpene saponins, Sasanquasaponins I-V, with antiallergic activity from the flower buds of Camellia sasanqua

The methanolic extract and its 1-butanol-soluble fraction from the flower buds of Camellia sasanqua THUNB. were found to show inhibitory activities on the release of β-hexosaminidase from rat basophile leukemia (RBL-2H3) cells. From the 1-butanol-soluble fraction, five new acylated oleanane-type triterpene saponins, sasanquasaponins I-V, were isolated together with a known saponin and their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The principal saponin constituents, sasanquasaponins I-III, with an acyl group at the 22-position of the aglycon part showed the inhibitory effects on the release of β-hexosaminidase and some structure-activity relationships were reported.     

Design and characterization of ferrocene-peptide-oligoaniline conjugates

Ferrocene-peptide-oligoaniline conjugates were designed by the introduction of two ferrocene-peptide conjugates into a π-conjugated phenylenediamine spacer to demonstrate the luminescent switching by changing the redox states of the π-conjugated phenylenediamine moiety, wherein the self-aggregation of the π-conjugated moiety was achieved in a higher concentration to induce the chirality organization with a red shift of the maximum emission wavelength.     

Redox-switchable π-conjugated systems bearing terminal ruthenium(II) complexes

p-Phenylenediamine bearing terminal bipyridyl moieties was synthesized by palladium-catalyzed amination. The corresponding ruthenium(II) complex was formed and characterized, providing a redox-switchable photoinduced electron-transfer system.     

Polyaniline‐Induced CH Arylation of Arenes with Arenediazonium Salts

A reduced form of polyaniline has been shown to induce direct arylation of an arenediazonium salt with an arene (Gomberg–Bachmann reaction) to give the cross‐coupling product in moderate to good yields under mild conditions. Various arenediazonium salts and arenes, including heteroarenes such as furans, thiophenes, and pyrroles, are employed for the reaction. The most favorable combination of substrates is an electron‐poor arenediazonium salt with an electron‐rich heteroarene. Investigation of the mechanism by reactions with radical scavengers and experiments on kinetic isotope effects indicated the occurrence of a radical chain reaction initiated by one‐electron reduction of an arenediazonium salt by the polyaniline. Only 1 mol % (based on aniline tetramer) of the polyaniline is required for the cross‐coupling reaction to occur. This reaction proceeds under metal‐free conditions and with no need for photonic activation.     

Self-assembling properties of (arylimido)vanadium(V) compounds

(Imido)vanadium(V) complexes have attracted much attention because of their potential applications as catalysts. Compared with oxo ligands, imido ligands can possess a substituent on the imido nitrogen so that the steric and electronic characters of the metal center are considered to be controlled by the properties of the nitrogen substituent. In such a sense, the design of the imido ligands is envisioned to be one of the key factors in the development of efficient catalysts. Furthermore, architectural control of transition metal-directed assembly to create organized nanostructures is of importance for advanced materials. This review highlights self-assembling properties of (arylimido)vanadium(V) compounds.     

Synthesis of oxosumanenes through benzylic oxidation

Oxosumanenes were synthesized through benzylic oxidation. The electronic and redox properties were revealed to exhibit the expanded π-conjugation compared to sumanene. Single-crystal X-ray analysis of monooxosumanene showed columnar π-stacking in a concave-convex fashion. Stereoselective trimethylation of the trioxo derivative was performed via 1,2-addition to the carbonyl groups.     

Maximal Regular Subsemibands of Singn

We describe maximal regular subsemibands of the singular transformation semigroup Sing_n on the set X_n = {1, 2, . . . n} and obtain their complete classification We show that Sing_n has n(n + 1)/2 maximal regular subsemibands, and formulate the cardinal number of such subsemigroups.