Triorganostannylation of halo- and dihaloadamantanes and 5-chloro-2-adamantanone in liquid ammonia by the S(RN)1 mechanism. Relative reactivity of nucleophiles and bridgehead halides

The reactions of 1-bromo-, 1-iodo-, 2-bromo-, 1,3-dibromo-, and 1,4-dibromoadamantane with Me(3)Sn(-) ions were studied in liquid ammonia. The photostimulated reaction of 1-haloadamantane (1-XAd, X = Br, I) or 2-BrAd with Me(3)Sn(-) ions gave in a few minutes excellent yields of the substitution products. The 1,3-dibromo- and 1,4-dibromoadamantane with Me(3)Sn(-) ions also reacted very fast under irradiation to give the disubstitution product in good yields. In competition experiments, 1-ClAd is 5.3 times more reactive than 5-chloro-2-adamantanone (9) toward Me(3)Sn(-) ions in liquid ammonia. When the nucleophile is the Ph(2)P(-) ion, 1-ClAd reacts 2.4 times faster than 9. This is the first time that no redox catalysis was observed when the bridgehead compound bears a carbonyl group as a pi acceptor. On the other hand, the nucleophile Me(3)Sn(-) ion was ca. >1000 times more reactive than Ph(3)Sn(-) ions toward 1-adamantyl radicals, in contrast to the behavior of aryl radicals, where both nucleophiles have the same reactivity.     

Outer product analysis of electronic nose and visible spectra: application to the measurement of peach fruit characteristics

Visual aspect and aroma are among the most important features of fruit that determine consumer preferences. Electronic nose and spectroscopic techniques have shown positive results in evaluating some basic analytical parameters of fruit and global features such as the cultivar.In this paper, we illustrate and discuss a study aimed at evaluating the improvement derived by the fusion of visible spectra and electronic nose data. These experiments were performed on a population of yellow peaches belonging to two cultivars. Each sample was measured by visible optical spectroscopy and by electronic nose. In addition, a number of reference parameters were also measured by conventional destructive methodologies.Collected data were analysed individually and then fused together in order to classify the two cultivars and to estimate the reference parameters. Data fusion was performed building the outer product matrix for each measurement. The set of matrices was then successively unfolded and analysed by conventional chemometrics tools.Results were improved using outer products, for instance in classification average percentage errors of 25, 10, and 7 for electronic nose, spectra, and outer product, respectively was achieved. Regression analysis provides the evidence of a substantial orthogonal appearance of the datasets, which offer former hidden information on fruit classification.     

Detection of NAD+-dependent alcohol dehydrogenase activities in YR-1 strain of Mucor circinelloides, a potential bioremediator of petroleum contaminated soils

Different soluble NAD⁺-dependent alcohol dehydrogenase (ADH) isozymes were detected in cell-free homogenates from aerobically grown mycelia of YR-1 strain of Mucor circinelloides isolated from petroleumcontaminated soil samples. Depending on the carbon source present in the growth media, multiple NAD⁺-dependent ADHs were detected when hexadecane or decane was used as the sole carbon source in the culture media. ADH activities from aerobically or anaerobically grown mycelium or yeast cells, respectively, were detected when growth medium with glucose added was the sole carbon source; the enzyme activity exhibited optimum pH for the oxidation of different alcohols (methanol, ethanol, and hexadecanol) similar to that of the corresponding aldehyde (≈7.0). Zymogram analysis conducted with partially purified fractions of extracts from aerobic mycelium or anaerobic yeast cells of the YR-1 strain grown in glucose as the sole carbon source indicated the presence of a single NAD⁺-dependent ADH enzyme in each case, and the activity level was higher in the yeast cells. ADH enzyme from mycelium grown in different carbon sources showed high activity using ethanol as substrate, although higher activity was displayed when the cells were grown in hexadecane as the sole carbon source. Zymogram analysis with these extracts showed that this particular strain of M. circinelloides has four different isozymes with ADH activity and, interestingly, one of them, ADH4, was identified also as phenanthrene-diol-dehydrogenase, an enzyme that possibly participates in the aromatic hydrocarbon biodegradation pathway.     

Enantiomeric separation of chiral peptide nucleic acid monomers by capillary electrophoresis with charged cyclodextrins

Direct chiral separation of chiral peptide nucleic acid (PNA) monomers has been achieved for the first time by capillary electrophoresis (CE) with charged cyclodextrins as chiral selectors added to the electrophoretic buffer. Selectively modified 6-deoxy-6-N-histamino-beta-cyclodextrin and sulfobutyl ether-beta-CD were successfully used as chiral selectors for the enantiomeric separation of chiral monomers based on different aminoethylamino acids bearing thymine or adenine as nucleobases. Chiral separations were obtained at low selector concentrations (1-3 mM) with good enantioselectivity and resolution factors. Separations were optimized as a function of pH in order to exploit the effect of the electrostatic interactions between the oppositely charged selector and selectand. The method has been applied to the analysis of the enantiomeric excess of chiral monomers used for the solid phase synthesis of chiral PNA oligomers. CE chiral analysis showed that a very high enantiomeric purity was generally achieved in the synthesis of all monomers, except for histidine and aspartic acid based monomers in which ca. 10% of the "wrong" enantiomer was always present.     

Evaluation of polymeric flocculants for oily water systems using a photometric dispersion analyzer

During oil production and treatment, oil-in-water (O/W) emulsions are formed. These dispersions require treatment prior to disposal. In order to improve oil/water separation processes through any physical process (decanting, flotation, centrifuging etc), the particle size of the dispersed phase should be increased. This may be obtained by a flocculation process, which consists in the agglomeration of several particles or drops using as flocculating agent hydrophilic high molecular weight macromolecules. Poly (ethylene-b-propylene oxide) and poly (vinyl alcohol) polymers have been evaluated as flocculating agents for oily water systems. Their performance is related to the particle size increase of the dispersed phase. In this work, a photometric dispersion analyzer (PDA) has been used to accomplish the oil drop agglomeration. Synthetic as well as produced water was used. Data are in good agreement with previous tests. Qualitative information related to aggregates or particle size distribution of the oily water systems can be obtained using PDA.     

Fast solid-phase extraction-gas chromatography-mass spectrometry procedure for oil fingerprinting. Application to the Prestige oil spill

A rapid and simple fractionation procedure using solid-phase extraction (SPE) cartridges was developed for an accurate determination of aliphatic and polycyclic aromatic hydrocarbons in petroleum residues and further application in chemical fingerprinting of oil spills by gas chromatography-mass spectrometry (GC-MS). Among the adsorbents evaluated, SiO2/C3-CN exhibited the best selectivity, providing, by elution with n-hexane (4 ml) and n-hexane-CH2Cl2 (1:1) (5 ml), two well-resolved aliphatic and aromatic hydrocarbon fractions, with recoveries of 97 +/- 7.2 and 99.7 +/- 13.9%, respectively. The SPE fractionation procedure was compared with the conventional silica-alumina adsorption chromatography showing similar results but practical advantages in terms of reproducibility, analysis time, solvent reduction and cost. Moreover, is particularly suitable for routine analysis with a high sample throughput. The developed methodology was tested in the characterization of fuel-oil samples collected along the Spanish north-west coast, after the Prestige oil spill accident.     

A new GROMOS force field for hexopyranose-based carbohydrates

A new parameter set (referred to as 45A4) is developed for the explicit-solvent simulation of hexopyranose-based carbohydrates. This set is compatible with the most recent version of the GROMOS force field for proteins, nucleic acids, and lipids, and the SPC water model. The parametrization procedure relies on: (1) reassigning the atomic partial charges based on a fit to the quantum-mechanical electrostatic potential around a trisaccharide; (2) refining the torsional potential parameters associated with the rotations of the hydroxymethyl, hydroxyl, and anomeric alkoxy groups by fitting to corresponding quantum-mechanical profiles for hexopyranosides; (3) adapting the torsional potential parameters determining the ring conformation so as to stabilize the (experimentally predominant) (4)C(1) chair conformation. The other (van der Waals and nontorsional covalent) parameters and the rules for third and excluded neighbors are taken directly from the most recent version of the GROMOS force field (except for one additional exclusion). The new set is general enough to define parameters for any (unbranched) hexopyranose-based mono-, di-, oligo- or polysaccharide. In the present article, this force field is validated for a limited set of monosaccharides (alpha- and beta-D-glucose, alpha- and beta-D-galactose) and disaccharides (trehalose, maltose, and cellobiose) in solution, by comparing the results of simulations to available experimental data. More extensive validation will be the scope of a forthcoming article. (c) 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1400-1412, 2005.     

Effect of gravitational radiation upon electromagnetic waves in a dispersive medium

We show that linearized gravitational radiation produces fluctuations in intensity and position of a distant source if the ray travels in a dispersive medium. The effect, however, depends upon the nongeodesic character of the ray and does not occur in an electrostatic plasma. When the index of refraction n is greater than unity a Cerenkov type resonance produces scintillation proportional to D _O ^3/2 (D _O being the distance of the source) and a dancing proportional to D _O ^1/2 if, instead, n<1 the scintillation behaves like D _O and the dancing does not diverge as D _O . The calculation is performed in detail for a random and isotropic spectrum of gravitational waves W(). This effect allows one to set an upper limit to W() at the frequency at which the fluctuations are observed, but for the rarified interstellar and intergalactic plasmas these limits are not very interesting.