Anisotropic solutions of methylol cellulose

Methylol cellulose solutions in dimethylsulfoxide exhibit a viscosity maximum at 18% w/v followed by a minimum at 20%, as is characteristic of lyotropic liquid crystals. The biphasic solutions exhibit areas of clear and cloudy appearance. The latter are birefringent. The highly anisotropic solutions are uniformly briefringent and in the 25–33% w/v concentration region they are brightly colored. The optical rotations of the mesomorphic phases are high, indicating a cholesteric structure. The sign of the optical rotation depends on the solution concentration and at high concentrations (25+% w/v) varies with the area of the solution viewed.     

Octaethylporphyrin and expanded porphyrin complexes containing coordinated BF2 groups

In contrast to octaethylporphyrin, which forms a very labile bis-BF(2) complex, treatment of the hexa- and octapyrrolic expanded porphyrins amethyrin and [32]octaphyrin with BF(3).Et(2) under standard reaction and work-up conditions gives rise to stable, non-labile mono- and bis-BF(2) complexes; these were readily characterised by, inter alia, X-ray diffraction analyses.     

Effects of Light Energy and Reducing Agents on C60‐Mediated Photosensitizing Reactions

Many biomolecules contain photoactive reducing agents, such as reduced nicotinamide adenine dinucleotide (NADH) and 6‐thioguanine (6‐TG) incorporated into DNA through drug metabolism. These reducing agents may produce reactive oxygen species under UVA irradiation or act as electron donors in various media. The interactions of C₆₀ fullerenes with biological reductants and light energy, especially via the Type‐I electron‐transfer mechanism, are not fully understood although these factors are often involved in toxicity assessments. The two reductants employed in this work were NADH for aqueous solutions and 6‐TG for organic solvents. Using steady‐state photolysis and electrochemical techniques, we showed that under visible light irradiation, the presence of reducing agents enhanced C₆₀‐mediated Type‐I reactions that generate superoxide anion (O₂^.?) at the expense of singlet oxygen (¹O₂) production. The quantum yield of O₂^.? production upon visible light irradiation of C₆₀ is estimated below 0.2 in dipolar aprotic media, indicating that the majority of triplet C₆₀ deactivate via Type‐II pathway. Upon UVA irradiation, however, both C₆₀ and NADH undergo photochemical reactions to produce O₂^.?, which could lead to a possible synergistic toxicity effects. C₆₀ photosensitization via Type‐I pathway is not observed in the absence of reducing agents.     

Boron complexes of porphyrins and related polypyrrole ligands: unexpected chemistry for both boron and the porphyrin

The coordination of boron to a range of polypyrrole-containing ligands is explored in this feature article. The boron dipyrromethenes are well-known as laser dyes and fluorescent labels in biology. Subphthalocyanine and subporphyrin macrocycles containing only three pyrrole rings can exist only when templated by a central boron atom. Boron complexes of expanded porphyrins (six or eight pyrroles) can complex boron in dipyrromethene (but not bipyrrole) sites. The primary focus of the article is on boron porphyrin and corrole complexes, where the tight fit of two boron atoms within the very constrained coordination site gives rise to unexpected chemistry at both boron and the porphyrin ligand. These unusual features are described and reasons for their occurrence postulated.     

Reactivity studies of a corrole germanium hydride complex with aldehydes, olefins and alkyl halides

The tris(pentafluorophenyl) corrole germanium hydride complex (TPFC)Ge-H was prepared by the reduction of (TPFC)Ge-OCH(3) with NaBH(4). The reactivity of (TPFC)Ge-H with series of aldehydes, olefins and alkyl halides to produce α-hydroxy alkyl and alkyl complexes was studied.     

The canted ferrimagnetic structure of Nd5Ge4 by neutron diffraction

The chemical and magnetic structures of the intermetallic compound Nd₅Ge₄ were determined from neutron diffraction powder data. In contrast to the isomorphous heavy rare-earth compounds, Nd₅Ge₄ orders with a canted ferrimagnetic arrangement below T_c = 52 K. The ordered Nd moments are 2.6, 3.1 and 2.4 μ_B for the three sites respectively. The magnetic space group is Pnm'a' and the plane of easy magnetization (010).     

The structure of delphinifoline,a diterpenoid alkaloid from aconitum delphinifolium

The structure of delphinifoline, a minor alkaloid of $\text{Aconitum}$$\text{delphinifolium}$ DC, was established by spectroscopic methods, and X-ray crystallography.     

Einkristalluntersuchungen am Zeolithgermanat Tl3HGe7O16·4H2O

Ohne ZusammenfassungMit 1 Abbildung     

Mediating stochastic switching of single molecules using chemical functionality

We have studied oligo(phenylene-ethynylene)s inserted into amide-containing alkanethiol self-assembled monolayers using scanning tunneling microscopy to demonstrate switching based on chemical functionality of the environment of the inserted molecules. The molecules show stability in two conductance states: an ON and an OFF state. We demonstrate bias-dependent switching due to hydrogen bonding between the inserted oligo(phenylene-ethynylene) and the matrix molecules. In addition, the inserted molecules exhibit fewer switching events than previously reported for alkanethiol matrixes, which we attribute to the rigidity of the hydrogen-bonded matrix.