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91.
MeHg and inorganic Hg compounds were measured in aqueous media for isotope ratio analysis using aqueous phase derivatization,
followed by purge-and-trap preconcentration. Compound-specific isotope ratio measurements were performed by gas chromatography
interfaced to MC-ICP/MS. Several methods of calculating isotope ratios were evaluated for their precision and accuracy and
compared with conventional continuous flow cold vapor measurements. An apparent fractionation of Hg isotopes was observed
during the GC elution process for all isotope pairs, which necessitated integration of signals prior to the isotope ratio
calculation. A newly developed average peak ratio method yielded the most accurate isotope ratio in relation to values obtained
by a continuous flow technique and the best reproducibility. Compound-specific isotope ratios obtained after GC separation
were statistically not different from ratios measured by continuous flow cold vapor measurements. Typical external uncertainties
were 0.16‰ RSD (n = 8) for the 202Hg/198Hg ratio of MeHg and 0.18‰ RSD for the same ratio in inorganic Hg using the optimized operating conditions. Using a newly
developed reference standard addition method, the isotopic composition of inorganic Hg and MeHg synthesized from this inorganic
Hg was measured in the same run, obtaining a value of δ
202Hg = −1.49 ± 0.47 (2SD; n = 10). For optimum performance a minimum mass of 2 ng per Hg species should be introduced onto the column. 相似文献
92.
Delphine Moraleda 《Tetrahedron letters》2006,47(31):5471-5474
Calculations at the B3LYP/6-311G(d,p) level of the structures of diastereoisomeric pairs of alcohols 1E-12E and 1Z-12Z, resulting from either reduction or methylation of sterically unbiased ketones show that the newly formed C-Nu bond lengths of the major isomers are larger than those of the minor isomers. 相似文献
93.
Chrétien JM Zammattio F Gauthier D Le Grognec E Paris M Quintard JP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(26):6816-6828
The preparation of polymer-supported allyltin reagents was shown to be possible for both unfunctionalized and functionalized allyl units. These reagents were treated with aldehydes in the presence of cerium(III) or indium(III) salts to afford high yields of homoallylic alcohols, practically uncontaminated with organotin residues (less than 5 ppm). Some mechanism aspects are briefly discussed and the potential for regeneration and reuse of these supported reagents is pointed out. 相似文献
94.
Fibronectin (Fn), a high molecular weight glycoprotein, is a central element of extracellular matrix architecture that is involved in several fundamental cell processes. In the context of bone biology, little is known about the influence of the mineral surface on fibronectin supramolecular assembly. We investigate fibronectin morphological properties induced by its adsorption onto a model mineral matrix of hydroxyapatite (HA). Fibronectin adsorption onto HA spontaneously induces its aggregation and fibrillation. In some cases, fibronectin fibrils are even found connected into a dense network that is close to the matrix synthesized by cultured cells. Fibronectin adsorption-induced self-assembly is a time-dependant process that is sensitive to bulk concentration. The N-terminal domain of the protein, known to be implicated in its self-association, does not significantly inhibit the protein self-assembly while increasing ionic strength in the bulk alters both aggregation and fibrillation. The addition of a non-ionic surfactant during adsorption tends to promote aggregation with respect to fibrillation. Ultimately, fibronectin fibrils appear to be partially structured like amyloid fibrils as shown by thioflavine T staining. Taken together, our results suggest that there might be more than one single organization route involved in fibronectin self-assembly onto hydroxyapatite. The underlying mechanisms are discussed with respect to Fn conformation, Fn/surface and Fn/Fn interactions, and a model of fibronectin fibrillogenesis onto hydroxyapatite is proposed. 相似文献
95.
n-Tributylphosphine was found to efficiently catalyze the alpha-P addition of H-phosphonates, H-phosphinates, and H-phosphine oxide pronucleophiles on alkynes bearing phosphane oxide activating moieties. The reaction leads to 2-aryl-1-vinyl-1,1-diphosphane dioxide derivatives in good yields affording a new route to P-C-P backbones. The products of this reaction are easily converted to biologically important 1,1-bis-phosphonates analogues. 相似文献
96.
An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using 205Tl/203Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated (202Hg/198Hg, 202Hg/199Hg, 202Hg/200Hg, and 202Hg/201Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio 202Hg/198Hg expressed as δ values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to −4.00‰. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00‰. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our δ values for the overall method was within ±0.28‰ (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74‰) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5‰. 相似文献
97.
Roux D Muyard F Girard C Colombain M Tillequin F Waterman PG Bévalot F 《Natural product research》2006,20(3):279-283
Phebaclavin I, a novel 3-prenylated coumarin, was isolated from the aerial parts of Phebalium aff. tuberculosum (Rutaceae) together with five known related compounds, Phebaclavin A, B, D, G, H. The structure of phebaclavin I was established by spectroscopic methods. Several other known coumarins were obtained, including trichoclin acetate, a furocoumarin isolated for the first time from a natural source, but previously described from acetylation of trichoclin. 相似文献
98.
Delphine Maury François Couderc Jerzy Czaplicki Jean Christophe Garrigues Véréna Poinsot 《Biomedical chromatography : BMC》2010,24(4):343-346
The monosaccharides GlcNAc (N‐acetylglucosamine) and the home‐made GlcNC16 (N‐palmitoyl‐D‐glucosamine) were labeled with 2‐AB (2‐aminobenzamide) by reductive amination of the sugar. The aldehyde group of the monosaccharide reacts with the amino group of 2‐AB, forming a Schiff base. In the second step, the Schiff base is reduced with sodium cyanoborohydride to yield a stable secondary amine. We describe here a simple and fast procedure. Previous studies reported the same labeling at high concentration (10?1 M) during 30 h with further purification steps. In the present paper all operations were carried out in an Eppendorf tube and the reaction medium was directly analyzed without purification. Using the described protocol, the whole procedure can be accomplished in less than 6 h at 65°C at very low concentration (10?4 M). For both GlcNC16 and GlcNAc, the 2‐AB labeling conditions were optimized and, in addition, new conditions of high‐performance liquid chromatography analysis were developed. These N‐alkylated sugars were analyzed on reversed‐phase HPLC with fluorimetric detection at excitation and emission wavelengths of 340 and 400 nm, respectively. The separation was achieved on a C18 column with a gradient mobile phase composed of water (0.1% formic acid)–methanol (volume varying) in less than 19 min with 12.5 and 18.3 min retention times for GlcNAc and GlcNC16, respectively. Positive‐ion electrospray ionization mass spectrometry (ESI‐MS) analysis enabled their structural determination. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
99.
Vincent Lemaur Jérôme Cornil Delphine Didier Aline Mujawase Sergey Sergeyev 《Helvetica chimica acta》2007,90(11):2087-2095
We report on the synthesis and electronic spectra of the chiral, donor‐acceptor (push‐pull) chromophores (±)‐ 4 and (±)‐ 5 with a 6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine scaffold (Scheme 1 and Fig. 2). The electronic structures of these compounds were investigated at a quantum‐chemical level (Figs. 2 and 3). The chemical reactivity of 6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine ((±)‐ 11 ) towards aromatic electrophilic substitution (Scheme 2 and Table) provided additional information about its electronic structure and confirmed nonnegligible delocalization of the lone pair of the bridge‐head N‐atoms in this heterocyclic system. 相似文献
100.
Mikac N Foucher D Niessen S Fischer JC 《Analytical and bioanalytical chemistry》2002,374(6):1028-1033
In this work we investigated the behaviour of pure HgS during extraction with dilute HCl to establish its extractability in 1 and 6 M HCl at the concentration level close to those occurring in natural sediments and soils. We found that neither cinnabar nor metacinnabar were soluble in 1 M HCl, whereas both were partially extracted by 6 M HCl. Metacinnabar precipitated in the laboratory was most prone to dissolution in 6 M HCl (up to 90%), followed by crystalline (commercial) metacinnabar (up to 70%) and cinnabar (up to 15%). Solubility of HgS in 6 M HCl was found to be dependent on its concentration, and an exponential relationship between quantity of HgS added to 20 mL of 6 M HCl (the range of 0.1-10 mg was used) and the solubility in 6 M HCl was established. For higher concentrations of HgS (10 mg in 20 mL of acid), a similarly low solubility of cinnabar was obtained as found in the literature. A study of dissolution kinetics of HgS in 6 M HCl indicated that it was a fairly slow process. Unexpected oxidation of HgS in water or 1 M HCl was found for extractions performed in Teflon vials previously used for the digestion of residual undissolved HgS by aqua regia. We presumed that the Teflon material could preserve some oxidising gases (presumably Cl(2)) developed during digestion with aqua regia which can then oxidise HgS during extraction with water or 1 M HCl. Regarding the extraction of Hg from natural sediments, we concluded that 6 M HCl could not be used to extract reactive Hg and predict bioavailability of mercury in sediments containing HgS and that experiments with model compounds should not be done at a concentration level several orders of magnitude higher than in natural samples. 相似文献