Fluorometric analysis of uranium(VI) by means of extraction and flying spot scanner

Summary A fluorometric method for the determination of ng amounts of uranium has been developed. Instead of using the conventional solid fluorescent photometry with pellets, the uranium fluorescence in a spot of the trioctylphosphine oxide-benzene extract on a TLC plate is continuously monitored by means of a flying spot scanner. The proposed method may be usefully applied to small amounts of inorganic and biological samples, because it excludes the pellet preparation and is therefore able to analyze more samples per unit of time than the conventional method. The interferences by coexisting elements as encountered in the conventional method are eliminated by preceding extraction.     

Sequential injection chemiluminescence immunoassay for anionic surfactants using magnetic microbeads immobilized with an antibody

A rapid and sensitive immunoassay for the determination of linear alkylbenzene sulfonates (LAS) is described. The method involves a sequential injection analysis (SIA) system equipped with a chemiluminescence detector and a neodymium magnet. Magnetic beads, to which an anti-LAS monoclonal antibody was immobilized, were used as a solid support in an immunoassay. The introduction, trapping and release of the magnetic beads in the flow cell were controlled by means of a neodymium magnet and adjusting the flow of the carrier solution. The immunoassay was based on an indirect competitive immunoreaction of an anti-LAS monoclonal antibody on the magnetic beads and the LAS sample and horseradish peroxidase (HRP)-labeled LAS, and was based on the subsequent chemiluminscence reaction of HRP with hydrogen peroxide and p-iodophenol, in a luminol solution. The anti-LAS antibody was immobilized on the beads by coupling the antibody with the magnetic beads after activation of a carboxylate moiety on the surface of magnetic beads that had been coated with a polylactic acid film. The antibody immobilized magnetic beads were introduced, and trapped in the flow cell equipped with the neodymium magnet, an LAS solution containing HRP-labeled LAS at constant concentration and the luminol solution were sequentially introduced into the flow cell based on an SIA programmed sequence. Chemiluminescence emission was monitored by means of a photon counting unit located at the upper side of the flow cell by collecting the emitted light with a lens. A typical sigmoid calibration curve was obtained, when the logarithm of the concentration of LAS was plotted against the chemiluminescence intensity using various concentrations of standard LAS samples (0-500 ppb) under optimum conditions. The time required for analysis is less than 15 min.     

Use of marker ion and cationic surfactant plastic membrane electrode for potentiometric titration of cationic polyelectrolytes

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to stearyltrimethylammonium (STA) ion is applied to the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by potentiometric titration, using a potassium poly (vinyl sulfate) (PVSK) solution as a titrant. The end-point of the titration is detected as the potential change of the plasticized PVC membrane electrode caused by decrease in the concentration of STA ion added to the sample solution as a marker ion due to the ion association reaction between the STA ion and PVSK. The effects of the concentration of STA ion, coexisting electrolytes in the sample solution and pH of the sample on the degree of the potential change at the end-point were examined. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2×10⁻⁵ to 4×10⁻⁴ N for Cat-floc, glycol chitosan, and methylglycol chitosan.     

Efficient incorporation of a copper hydroxypyridone base pair in DNA

Recently, we reported the first artificial nucleoside for alternative DNA base pairing through metal complexation (J. Org. Chem. 1999, 64, 5002-5003). In this regard, we report here the synthesis of a hydroxypyridone-bearing nucleoside and the incorporation of a neutral Cu(2+)-mediated base pair of hydroxypyridone nucleobases (H-Cu-H) in a DNA duplex. When the hydroxypyridone bases are incorporated into the middle of a 15 nucleotide duplex, the duplex displays high thermal stabilization in the presence of equimolar Cu(2+) ions in comparison with a duplex containing an A-T pair in place of the H-H pair. Monitoring temperature dependence of UV-absorption changes verified that a Cu(2+)-mediated base pair is stoichiometrically formed inside the duplex and dissociates upon thermal denaturation at elevated temperature. In addition, EPR and CD studies suggested that the radical site of a Cu(2+) center is formed within the right-handed double-strand structure of the oligonucleotide. The present strategy could be developed for controlled and periodic spacing of neutral metallobase pairs along the helix axis of DNA.     

Quantitative taste evaluation of total enteral nutrients

The purpose of this study was to evaluate quantitatively the taste of the various total enteral nutrients marketed in Japan using human gustatory sensation tests and an artificial taste sensor. In the human gustatory sensation test, four basic taste intensities (sweetness, saltiness, sourness, and bitterness), as well as 15 kinds of palatability scales, were evaluated according to the semantic differential (SD) method. Among 15 palatability items, the item; difficult to drink/easy to drink, was adopted as an overall palatability since it shows the highest factor loading by factor analysis. The overall palatability was found to be highly positively correlated with sweetness and sourness, but negatively correlated with bitterness and saltiness. Addition of a flavour to the amino acid-based enteral nutrient AminolebanEN significantly improved its palatability. This effect is presumably due to sour components of the flavour, such as citric acid, which reduce the bitterness intensity of branched-chain amino acids in the product. The sweetness and sourness intensities predicted by the taste sensor showed a high correlation with the results obtained in the human gustatory sensation tests. The taste sensor was able to predict the overall palatability of the total enteral nutrients with high accuracy. The products could be classified into three groups (peptide-based, amino-acid-based, and protein-based) by principal component analysis using sensor output of 8 channels. The products could be also classified into four groups; peptide-based, amino-acid-based, and protein-based and flavor addition group by principal component analysis using sensor output of channels 1, 3, 4 and 7, which are specific to basic tastes. The taste sensor could therefore be useful in predicting the taste or palatability of total enteral nutrients, and could contribute to attempts to improve compliance for such products and for enteral nutrients.     

Weak interactions at the photoexcited states of partially oriented aromatic chromophores in man-made bilayer membranes

Monoalkyl and dialkyl quarternary ammonium salt-type cationic surfactants containing a phenoxy group as aromatic chromophores at different positions of alkyl chains were synthesized. Monoalkyl-type surfactants formed micelles in aqueous solutions. The bilayer structure similar to that found in phospholipid liposomes was obtained in the aqueous dispersions of dialkyl-type surfactants. The phenoxy groups were partially oriented and aligned in these molecular assemblies. The interactions of aligned phenoxy groups in micelles or bilayers resulted in luminescence with lower energy than that of the monomer fluorescence or in a radiationless deactivation of excited states. Such interactions could be effectively prevented in bilayer structures composed of surfactant molecules containing a “spacer chain” between aligned chromophores. Evidence was obtained supporting energy migrations between aligned chromophores that were separated by a dodecyl chain in the bilayer structure.     

Contrast effect of hydrogen bonding on the acceptor and donor OH groups of intramolecularly hydrogen-bonded OH pairs in diols

We studied the influence of hydrogen bonding on the fundamental and overtone bands of the OH-stretching vibration of each OH group in the intramolecularly hydrogen-bonded OH(I)::OH(II) pair in 1,2-, 1,3- and 1,4-diols. The hydrogen bonding between the two OH groups significantly increases in strength from the five-membered ring of a 1,2-diol to the seven-membered ring of a 1,4-diol. Although the hydrogen bonding does not affect the vibrational property of the OH(II) (or acceptor), it significantly influences the OH(I) (or donor). As the hydrogen bonding becomes stronger from a 1,2- to a 1,4-diol, the fundamental band of the OH-stretching shifts downwards by from about 50 to 140 cm(-1), and the overtone band markedly decreases in intensity, although the effect on the intensity and bandwidth of the fundamental band varies among 1,2-, 1,3- and 1,4-diols. The quantum-mechanically calculated normal frequencies of the acceptor and donor OH groups in the hydrogen-bonded ring are in good agreement with the observed frequencies. The calculated interatomic distance between the O of an acceptor OH and the H of a donor OH is the shortest for a 1,4-diol, which is consistent with the largest frequency shift caused by the hydrogen bonding.     

Topology of tectosilicate frameworks

The concept of coordination networks is introduced for classifying and deriving possible frameworks of tectosilicates, in which the nth coordination network is defined as a set of all points from topological distance 0 to n and all their connection lines. In the second network, it is possible to derive 26 different structures by connection of the points with 3 degrees of freedom; 39 different structures of tectosilicates examined were found to be distributed on the simple coordination networks. The results are compared with those of the secondary building unit criterion proposed by Meier and Breck.     

Separation of polar compounds using carbon columns

The objective of this review with 122 references is to provide structure and retention mechanisms of porous graphitic carbon by chromatographic analysis and computational chemical analysis of retention mechanisms. Synthesis methods of porous graphitic carbon are described. Applications for use as matrix for dynamic coating on porous graphitic carbon and direct separation of polar compounds on porous graphitic carbon demonstrated that the physical and chemical stability of graphitic carbons performed in both chromatography and extraction, especially for polar compounds, those are difficult on both silica-based and organic polymer-based packing materials. The disadvantage is difficult desorption of non-polar compounds adsorbed on the surface. The development of 3.5-microm particles improves the separation power of graphitic carbon columns with the high theoretical plate number.     

Electroreductive intramolecular coupling of 1-indolealkanones

The electroreduction of 1-indolealkanones in isopropanol gave five-, six-, and seven-membered trans-cyclized products stereospecifically. On the other hand, the electroreduction of 3-methoxycarbonyl-1-indolealkanones afforded mixtures of two diastereomers of the corresponding trans- and cis-cyclized products. The DFT calculations for the radical anions support that the reductive couplings of 1-indolealkanones and 3-methoxycarbonyl-1-indolealkanones proceed through different reaction mechanisms.