Viscosity of aqueous solutions of univalent electrolytes from 5 to 95°C

Viscosity measurements of a series of univalent electrolytes in water have been performed with an automatic dual viscometer system, covering the temperature range of 5 to 95°C. Results are discussed in terms of Jones-DoleB andD coefficients. TheB coefficients of the salts are divided into their ionic contributions according toB(K⁺)=B(Cl^–) at all temperatures. On a simple model intrinsic and structural contributions inB are calculated for the different ions. The structural term depends exponentially on the temperature in a unique manner, independent of the ion (except for Li⁺).     

Isomorphism within the hexagonal columnar mesophase of molecular and macromolecular self- and co-assembled columns containing tapered groups

Abstract

The phase behaviour of binary mixtures of self-assembled tapering molecules based on monoesters of oligooxyethylene glycol and 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid, their corresponding polymethacrylates, and of 4′-methyl (benzo-15-crown-5)-3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate within their hexagonal columnar mesophase (Φ_h) is described. The binary blends between molecular tapers co-assemble into a single supramolecular column resulting in isomorphism within their Φ_h mesophase over the entire range of composition. The binary blends between polymethacrylates containing tapered side groups co-assemble into a single Φ_h phase only when the columns of the parent polymers are of similar diameters. This results in binary mixtures which are isomorphic within the Φ_h mesophase over the entire composition range. When the diameters of the columns formed by the parent polymers are dissimilar, isomorphic mixtures are obtained only over a narrow range of composition. Binary mixtures between molecular tapers and macromolecular systems containing tapered side groups co-assemble into a single column to the extent that intercalation of the molecular taper, within the column formed by the macromolecular system containing tapered side groups, is permissible. In all systems increased intracolumnar interactions can be induced by complexation of CF₃SO₃Li by the oligooxyethylenic receptors leading to isomorphism in otherwise non-isomorphic mixtures. Ternary mixtures between molecular tapers with non-specific oligooxyethylenic receptors and specific crown ether receptors and CF₃SO₃ Na as the third component are non-isomorphic within their Φ_h phase due to preferential complexation of the alkali metal cation by the column of the crown ether containing the molecular taper. This results in two columns of dissimilar diameters, which are isomorphic in the Φ_h phase only within a limited range of composition.     

Increased melanogenesis is a risk factor for oxidative DNA damage--study on cultured melanocytes and atypical nevus cells

Melanin synthesis is an oxygen-dependent process that acts as a potential source of reactive oxygen species (ROS) inside pigment-forming cells. The synthesis of the lighter variant of melanin, pheomelanin, consumes cysteine and this may limit the capacity of the cellular antioxidative defense. We show that tyrosine-induced melanogenesis in cultured normal human melanocytes (NHM) is accompanied by increased production of ROS and decreased concentration of intracellular glutathione. Clinical atypical (dysplastic) nevi (DN) regularly contain more melanin than do normal melanocytes (MC). We also show that in these cultured DN cells three out of four exhibit elevated synthesis of pheomelanin and this is accompanied by their early senescence. By using various redox-sensitive molecular probes, we demonstrate that cultured DN cells produce significantly more ROS than do normal MC from the same donor. Our experiments employing single-cell gel electrophoresis (comet assay) usually reveal higher fragmentation of DNA in DN cells than in normal MC. Even if in some cases the normal alkaline comet assay shows no differences in DNA fragmentation between DN cells and normal MC, the use of the comet assay with formamidopyrimidine DNA glycosylase can disclose that the DNA of the cultured DN cells harbor more oxidative damage than the DNA of normal MC from the same person.     

Direct photothermal techniques for rapid quantification of total anthocyanin content in sour cherry cultivars

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration (TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP and HPLC obviate the need for the extraction of analyte. The outcome of the study leads to the conclusion that PAS and OW are both suitable for quick screening of TAC in sour cherries. The correlation between the two methods and SP is linear with R² = 0.9887 for PAS and R² = 0.9918 for OW, respectively. Both methods are capable of the rapid determination of TAC in sour cherries without a need for a laborious sample pretreatment.     

Multiplicity One for Representations Corresponding to Spherical Distribution Vectors of Class ρ

In this paper one considers a unimodular second countable locally compact group G and the homogeneous space X:=H\G, where H is a closed unimodular subgroup of G. Over X complex vector bundles are considered such that H acts on the fibers by a unitary representation with closed image. The natural action of G on the space of square integrable sections is unitary and possesses an integral decomposition in so-called spherical distributions of class . The uniqueness of this decomposition can be characterized by a number of equivalent properties. Uniqueness is shown to hold for a class of semidirect products. In the case that H is compact, the multiplicity free decomposition is shown to be equivalent with the commutativity of a suitable convolution algebra. As an example, one takes for X a symmetric k-variety , with k a locally compact field of characteristic not equal to two, and for a character of _k, whose square is trivial. Here is a reductive algebraic group defined over k and is the fixed point group of an involution of defined over k. It is shown then that the natural representation of G_k on the Hilbert space is multiplicity free if is anisotropic. Next a criterion is derived that leads to multiplicity one also in the noncompact situation. Finally, in the non-Archimedean case, a general procedure is given that might lead to showing that a pair is a generalized Gelfand pair. Here and are suitable algebraic groups defined over k.Mathematics Subject Classifications (2000) 20G15, 20G20, 22E15, 22E46.Aloysius G. Helminck: Partially supported by N.S.F. Grant DMS-9977392.     

Analytical separation and detection methods for flavonoids

Flavonoids receive considerable attention in the literature, specifically because of their biological and physiological importance. This review focuses on separation and detection methods for flavonoids and their application to plants, food, drinks and biological fluids. The topics that will be discussed are sample treatment, column liquid chromatography (LC), but also methods such as gas chromatography (GC), capillary electrophoresis (CE) and thin-layer chromatography (TLC), various detection methods and structural characterization. Because of the increasing interest in structure elucidation of flavonoids, special attention will be devoted to the use of tandem-mass spectrometric (MS/MS) techniques for the characterization of several important sub-classes, and to the potential of combined diode-array UV (DAD UV), tandem-MS and nuclear magnetic resonance (NMR) detection for unambiguous identification. Emphasis will be on recent developments and trends.