Helical conformation of alkanes in a hydrophobic cavitand     

Trembleau L  Rebek J 《Science (New York, N.Y.)》2003,301(5637):1219-1220

Alkanes adopt extended conformations in solution that minimize steric interactions and maximize surface area. Folding can reduce the amount of hydrophobic surface exposed to solvent, but sterically unfavorable gauche interactions result. However, we found that the alkyl chains of two common surfactants in aqueous solution adopt helical conformations when bound within a synthetic receptor. The receptor recognizes the helical alkane better than the extended conformation, even though 2 to 3 kilocalories per mole of strain is introduced. The proper filling of space and burial of hydrophobic surface drive the molecular recognition between the receptor and the coiled alkane.  相似文献   

Deep Impact observations by OSIRIS onboard the Rosetta spacecraft   总被引：1，自引：0，他引：1  

Keller HU  Jorda L  Küppers M  Gutierrez PJ  Hviid SF  Knollenberg J  Lara LM  Sierks H  Barbieri C  Lamy P  Rickman H  Rodrigo R 《Science (New York, N.Y.)》2005,310(5746):281-283

The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet activity. Dust particles were flowing outward in the coma at >160 meters per second, accelerated by the gas. The slope of the brightness increase showed a dip about 200 seconds after the impact. Dust Afrho values before and long after the impact confirm the slight decrease of cometary activity. The dust-to-water mass ratio was much larger than 1.  相似文献   

Arabidopsis EDS1 connects pathogen effector recognition to cell compartment-specific immune responses     

Heidrich K  Wirthmueller L  Tasset C  Pouzet C  Deslandes L  Parker JE 《Science (New York, N.Y.)》2011,334(6061):1401-1404

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Synthesis and structure determination of the hierarchical meso-microporous zeolite ITQ-43     

Jiang J  Jorda JL  Yu J  Baumes LA  Mugnaioli E  Diaz-Cabanas MJ  Kolb U  Corma A 《Science (New York, N.Y.)》2011,333(6046):1131-1134

The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography.  相似文献   

In vitro digestibility of α-casozepine, a benzodiazepine-like peptide from bovine casein, and biological activity of its main proteolytic fragment     

Cakir-Kiefer C  Le Roux Y  Balandras F  Trabalon M  Dary A  Laurent F  Gaillard JL  Miclo L 《Journal of agricultural and food chemistry》2011,59(9):4464-4472

α-Casozepine is a peptide, corresponding to the sequence 91-100 of the bovine α(s1)-casein, displaying anxiolytic activity in the rat. The α(s1)-casein tryptic hydrolysate containing this peptide decreases stress effects after oral administration in various species including man. Therefore, the stability of this peptide toward gastric and pancreatic proteases has been assessed by using pepsin, chymotrypsin/trypsin, Corolase PP, pepsin followed by chymotrypsin/trypsin or pepsin followed by Corolase PP. α-Casozepine was slowly degraded by chymotrypsin, much more sensitive to pepsin and Corolase PP but not completely destroyed after 4 h kinetics. The bonds in the region 91 to 95 of the α-casozepine were totally resistant to hydrolysis by all studied proteases. Surprisingly, a fragment, corresponding to the sequence 91-97 and found in all the hydrolysis media in significant amount, possessed an anxiolytic activity in three behavioral tests measuring this parameter. This peptide could participate in the in vivo activity of α-casozepine.  相似文献   

Biodegradation of 3-chloro-1,2-propanediol with Saccharomyces cerevisiae     

Bel-Rhlid R  Talmon JP  Fay LB  Juillerat MA 《Journal of agricultural and food chemistry》2004,52(20):6165-6169

A novel enzymatic dehalogenating activity of 3-chloro-1,2-propanediol (3-MCPD) with Saccharomyces cerevisiae (baker's yeast) is reported. All bioconversion assays were carried out under aerobic conditions, at 28 degrees C, and the kinetics were monitored. The biodegradation was performed at different pH values (6.2, 7.0, and 8.2), in the presence and absence of glucose, using racemic 3-MCPD at two different concentrations (7.3 micromol/L and 27 mmol/L). Optimal conversion (68%) of racemic (R,S)-3-MCPD at a concentration of 27 mmol/L was achieved after 48 h of reaction time, at pH 8.2, and in the presence of glucose. At a concentration of 7.3 micromol/L, 73% degradation was observed after 72 h, at pH 8.2 and in the absence of glucose. Under the same experimental conditions, the conversion of pure (S)-3-MCPD (85%) was higher than that of the (R)-enantiomer (60%).  相似文献   

Differential transfer of organic micropollutants through intestinal barrier using Caco-2 cell line     

Cavret S  Feidt C  Laurent F 《Journal of agricultural and food chemistry》2005,53(7):2773-2777

Food seems to be one of the main ways of animal and human contamination with polycyclic aromatic hydrocarbons (PAHs) and dioxins. In vivo studies showed a blood absorption of these xenobiotics after their ingestion. Our work aimed at studying the in vitro transfer of PAHs and dioxins through intestinal barrier. Caco-2 cells were cultivated on permeable filters to measure transepithelial permeability of (14)C labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin, benzo[a]pyrene, pyrene, and phenanthrene, which differed in their physicochemical properties. The results showed that the molecules were able to cross intestinal cell layers. All the molecules were detected associated with cells, even if the dioxin was the less uptaken compound. Phenanthrene appeared in basal media faster, and its level after a 6-h exposure was respectively 1.1, 2, and 7 times higher than pyrene, benzo[a]pyrene, and 2,3,7,8-tetrachlorodibenzo-p-dioxin levels. These findings suggest that intestinal epithelium plays a key role in selective permeability and then in bioavailibility of micropollutants.  相似文献   

Precipitation of cheddar cheese whey lipids by electrochemical acidification     

Shee FL  Angers P  Bazinet L 《Journal of agricultural and food chemistry》2005,53(14):5635-5639

Lipid separation from cheddar cheese whey allows a better valorization of protein fractions. In this study, bipolar membrane electroacidification (BMEA) was used to obtain precipitates with a high level of lipids. Whey samples with normal and low (by way of electrodialysis) mineral salt levels have been treated by a BMEA process and centrifuged. The composition of flocs and precipitation yields were determined. The BMEA process increased lipid precipitation rates by almost 50% in comparison with a centrifugation step only whereas a demineralization step prior to electroacidification had a limited effect on the precipitation level. Precipitates obtained were mainly composed of lipids (probably phospholipids) but also contained proteins. BMEA of cheddar cheese whey would allow the production of a lipid-enriched fraction and of a protein-enriched whey.  相似文献   

Time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy analyses of Bixa orellana seeds     

Felicissimo MP  Bittencourt C  Houssiau L  Pireaux JJ 《Journal of agricultural and food chemistry》2004,52(7):1810-1814

Three different experiments were performed in order to obtain the major carotenoid composition of the natural colorant annatto (E160b) through ToF-SIMS (time-of-flight secondary ion mass spectrometry) and XPS (X-ray photoelectron spectroscopy) analyses. In the first experiment, Bixa orellana seeds aril as well as its interior part were analyzed. The analysis of the seeds aril by ToF-SIMS gives the colorant fingerprint without any sample treatment, showing the presence of bixin and its characteristic fragments. The analysis performed in the interior part of the seeds indicates the presence of Fe. The second set of measurements was conducted on the seeds organic extract right after extraction revealing the same components observed by in situ measurement. A third set of measurements was performed aiming to determine the reason for the organic extract color shift observed after 3 months of exposure to ambient light at room temperature. In this case, it was possible to evidence the degradation of bixin by the loss of xylene molecules through ToF-SIMS and the probable carotenoid oxidation based on the C1s XPS spectrum of the degraded extract.  相似文献   

Incidental capture of marine turtles by the Italian trawl fishery in the north Adriatic Sea     

Paolo Casale  Luc Laurent 《Biological conservation》2004,119(3):287-295

In the north Adriatic Sea on-board observations on midwater and bottom trawlers were carried out during years 1999 and 2000. Results indicate that the north Adriatic Sea, and especially the north-east part, is a very important foraging and overwintering habitat for loggerhead turtles (Caretta caretta). Since the distribution of fishing effort in the area is not known, the total turtle catch by the Italian bottom trawl fleet was conservatively estimated from the lower catch rate observed in the south-west sub-area: 4273 turtle captures/year (95% C.I.=2186-8546). The actual total catch in the whole north Adriatic is likely to be much higher, due both to an unknown Italian trawling effort in the south-west part with multi-gear vessels and to the Italian and Croatian trawling efforts in the north-east part, where catch rate was 15 times greater than in the south-west part. In the south-west sub-area 9.4% of captured turtles were dead and potential mortality (assuming that all comatose turtles would die too) was 43.8%. Hence, trawling in the north Adriatic is likely to represent a serious threat to the populations, and possible conservation measures are discussed.  相似文献