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11.
Fabris F De Lucchi O Nardini I Crisma M Mazzanti A Mason SA Lemée-Cailleau MH Scaramuzzo FA Zonta C 《Organic & biomolecular chemistry》2012,10(12):2464-2469
(+)-syn-Benzotriborneol forms stable complexes with one molecule of water. This is due to the ability of the host to form three hydrogen bonds with water, to act simultaneously as a hydrogen-bond acceptor and donor, and to a perfect geometrical match between the pair. We report experimental (X-ray and neutron diffraction, VT NMR, DSC, TGA) and stereochemical studies carried out to elucidate and quantify the molecular and thermodynamic aspects of this supramolecular complex. 相似文献
12.
Marie-Hélène Bossel 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1988,39(5):733-742
Résumé Soit
1 la première valeur propre d'une membrane élastiquement liée inhomogène ou sur une surface. On caractérise
1 comme Maximum, avec une méthode inspirée par celle des longueurs extrémales de Beurling et Ahlfors [1]. Cette caractérisation permet une nouvelle extension du théorème isopérimétrique de Rayleigh-Faber-Krahn ([10], p. 191 ou [4], p. 104).
Cette recherche a été soutenue par le Fonds national suisse de la recherche scientifique. 相似文献
Summary Let 1 be the first eigenvalue of an elastically supported membrane, either inhomogeneous or on a surface. 1 is caracterized as a Maximum by a method close to the extremal length of Beurling and Ahlfors [1]. This caracterization allows a new extension of Rayleigh-Faber-Krahn's isoperimetric theorem ([10], p. 191 or [4], p. 104).
Cette recherche a été soutenue par le Fonds national suisse de la recherche scientifique. 相似文献
13.
Schröder G Kozelka J Sabat M Fouchet MH Beyerle-Pfnür R Lippert B 《Inorganic chemistry》1996,35(6):1647-1652
A model compound of the second most abundant DNA adduct of the antitumor agent cisplatin has been synthesized and structurally and spectroscopically characterized and its conformational behavior examined: cis-[(NH(3))(2)Pt(9-MeA-N7)(9-EtGH-N7)](NO(3))(2).2H(2)O (9-MeA = 9-methyladenine; 9-EtGH = 9-ethylguanine) crystallizes in the monoclinic system, space group P2(1)/n (No. 14) with a = 7.931(2), b = 11.035(3), c = 26.757(6) ?, beta = 94.94(2) degrees, and Z = 4. The two purine bases adopt a head-to-head orientation, with NH(2) of 9-MeA and CO of 9-EtGH being at the same side of the Pt coordination plane. A theoretical conformational analysis of the complex cis-[(NH(3))(2)Pt(Ade)(Gua)](2+) (Ade = adenine; Gua = guanine) based on molecular mechanics calculations of the nonbonded energy has revealed four minimum-energy zones similar to those derived previously for cis-[(NH(3))(2)Pt(Gua)(2)](2+) (Kozelka; et al. Eur. J. Biochem. 1992, 205, 895). This conformational analysis has allowed, together with the calculation of chemical shifts due to ring effects, the attribution of the two conformers observed for cis-[(NH(3))(2)Pt{d(ApG)}](+) by Dijt et al. (Eur. J. Biochem. 1989, 179, 344) to the two head-to-head conformational zones. The orientation of the two nucleobases in the crystal structure of cis-[(NH(3))(2)Pt(9-MeA)(9-EtGH)](2+) corresponds, according to our analysis, roughly to that preferentially assumed by the minor rotamer of cis-[(NH(3))(2)Pt{d(ApG)}](+). 相似文献
14.
Perro A Reculusa S Pereira F Delville MH Mingotaud C Duguet E Bourgeat-Lami E Ravaine S 《Chemical communications (Cambridge, England)》2005,(44):5542-5543
Janus silica nanoparticles, regioselectively functionalized by two different chemical groups, were synthesized through a multistep procedure based on the use of a polystyrene nodule as a protecting mask. 相似文献
15.
Headspace solid-phase microextraction combined with gas chromatography-ion trap tandem mass spectrometry (HS-SPME-GC-ITMS-MS) method has been developed and studied for the simultaneous determination of 15 organochlorine pesticides (OCPs) and 20 polychlorinated biphenyls (PCBs) in aqueous samples. To perform the HS-SPME polydimethylsiloxane (PDMS) (7, 30 and 100 microm film thickness) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) fibers were initially compared on the basis of their absorption capacities for the selected compounds, and PDMS 100 microm film thickness was selected to accomplish the rests of essays. The influence of various parameters on OCPs and PCBs extraction efficiency by HS-SPME was thoroughly studied using GC-electron capture detector (ECD). Parameters such as collision induced dissociation (CID) resonant excitation amplitude and RF storage level were optimized to increase specificity and sensibility for ITMS-MS analysis. The performance of proposed HS-SPME-GC-ITMS-MS methodology with respect to linearity, reproducibility and limit of detection (LOD) was evaluated by water spiked with target compounds. The linear range of most compounds was found to be between 0.01 and 1 ng mL(-1) and the limits of detection were between 0.4 and 26 pg mL(-1). The reproducibility of the method (n = 6), expressed as relative standard deviation (RSD), was between 5 and 21%. Finally, developed procedure was applied to determine selected OCPs and PCBs in river water samples in concentration below 0.1 ng mL(-1) can be easily carried out with ultra-selectivity and precision. 相似文献
16.
Guyon F Gaillard L Salagoïty MH Médina B 《Analytical and bioanalytical chemistry》2011,401(5):1555-1562
High-performance liquid chromatography linked to isotope ratio mass spectrometry (HPLC-co-IRMS) via a Liquiface? interface has been used to simultaneously determine 13C isotope ratios of glucose (G), fructose (F), glycerol (Gly) and ethanol (Eth) in sweet and semi-sweet wines. The data has
been used the study of wine authenticity. For this purpose, 20 authentic wines from various French production areas and various
vintages have been analyzed after dilution in pure water from 20 to 200 times according to sugar content. If the 13C isotope ratios vary according to the production area and the vintage, it appears that internal ratios of 13C isotope ratios (
R13\textC {R_{{{}^{{13}}{\text{C}}}}} ) of the four compounds studied can be considered as a constant. Thus, ratios of isotope ratios are found to be 1.00 ± 0.04
and 1.02 ± 0.08 for
R13\textC\textG/F {R_{{{}^{{13}}{{\text{C}}_{{{\text{G/F}}}}}}}} and
R13\textC\textGly/Eth {R_{{{}^{{13}}{{\text{C}}_{{{\text{Gly/Eth}}}}}}}} , respectively. Moreover,
R13\textC\textEth/Sugar {R_{{{}^{{13}}{{\text{C}}_{{{\text{Eth/Sugar}}}}}}}} is found to be 1.15 ± 0.10 and 1.16 ± 0.08 for
R13\textC\textGly/Sugar {R_{{{}^{{13}}{{\text{C}}_{{{\text{Gly/Sugar}}}}}}}} . Additions of glucose, fructose and glycerol to a reference wine show a variation of the
R13\textC {R_{{{}^{{13}}{\text{C}}}}} value for a single product addition as low as 2.5 g/L−1. Eighteen commercial wines and 17 concentrated musts have been analyzed. Three wine samples are suspicious as the
R13\textC {R_{{{}^{{13}}{\text{C}}}}} values are out of range indicating a sweetening treatment. Moreover, concentrated must analysis shows that 13C isotope ratio can be also used directly to determine the authenticity of the matrix. 相似文献
17.
Marie-Hélène Dévier Patrick Mazellier Sélim Aït-Aïssa Hélène Budzinski 《Comptes Rendus Chimie》2011,14(7-8):766-779
Toxic effects evidenced in the environment are most often caused by mixtures of known and unknown pollutants. One of the key challenges in environmental chemistry and ecotoxicology is to characterize and identify those toxicants in relation with the effect. However, many of the current bottlenecks in the assessment of organic contaminants in our environment are related to the difficulty of evaluating various chemical classes and biological effects within complex mixtures and more precisely to link both approaches. To tackle these analytical challenges, the bioanalytical concept has emerged during the last decade. In this article, we describe through some outstanding examples the current limitations in the chemical-driven approach such as problems encountered for a correct evaluation of water quality when the continuous introduction of new chemicals has to be taken into account in monitoring for correct evaluation of this quality and could led to tremendous analytical costs or some of the integrated bioanalytical approaches as promising powerful tools to improve environmental risk assessment by taking into account the link presence/effect. 相似文献
18.
19.
El Amri C Baron MH Maurel MC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(11):2645-2654
Studies on the interactions of biological macromolecules with mineral surfaces are crucial for the detecting biomarkers. But before this can be done for real samples like rocks or sediments, rational methods based on mineral models plus known amounts of nucleic acids must be developed. The methods must be very sensitive, as the amount of bound macromolecule may be very small. Surface-enhanced Raman spectroscopy (SERS) is perfect for detecting picomolar amounts of nucleic acid materials. In this study, the models used were adenine and GAAA hairpin for nucleic acids materials and a clay (montmorillonite) plus colloidal silver (used for SERS detection) for mineral supports. We have shown that OH(-) anions compete with adenine and the adenyl residues in the GAAA loop for adsorption onto nano-sized silver particles in basic medium. The GAAA adenyl moieties are less well adsorbed onto either clay or silver than is adenine. Also, the transfer of either adenine or the RNA hairpin from the clay to the silver aggregates is pH-dependent. Contact between adenine and the montmorillonite also seems to disperse adenine aggregates. The clay could also increase the flexibility of the RNA hairpin so that it is released from the clay at pH 10, and the affinity of its adenyl moieties for the metallic substrate is enhanced. 相似文献
20.
Annette Marchand Marie-Therese Forel Monique Biviere-Baudet Marie-Hélène Soulard 《Journal of organometallic chemistry》1978,156(2):341-358
The normal modes of (CH3)3MN(CH3)2 (M= Si, Ge or Sn) compounds are discussed using infrared and Raman spectra analysis. A valence force field model has been utilized to calculate the frequencies and potentiel energy distribution for each molecule in different structural hypotheses.Experimental results and calculated values are in good agreement when the dihedral angle ψ between the two MNC planes decreases from silicon (144°) to germanium (130°) to tin (120°).The differences in the molecular geometries may be related to the basicity and to the Pπ → dπ interactions of these compounds. 相似文献