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991.
Queiroz MJ Abreu AS Ferreira PM Oliveira MM Dubest R Aubard J Samat A 《Organic letters》2005,7(22):4811-4814
[structure: see text] A new photochromic thieno-2H-chromene alpha-amino acid derivative was prepared by C-N palladium-catalyzed cross-coupling of a bromothieno-2H-chromene with the aminated aromatic side chain of the methyl ester of a N,N-diprotected amino acid. Its good photochromic properties demonstrated by flash photolysis and continuous irradiation indicate a possible application in ophthalmic lenses. It may also be inserted into peptides to give photoinduced reversible structural changes. 相似文献
992.
Robin Zuluaga Jean-Luc Putaux Adriana Restrepo Iñaki Mondragon Piedad Gañán 《Cellulose (London, England)》2007,14(6):585-592
Cellulose microfibrils have been prepared from banana rachis using a combination of chemical and mechanical treatments. The
morphology and structure of the samples were characterized using transmission electron microscopy, atomic force microscopy,
and X-ray diffraction. Fourier-transformed infrared spectroscopy (FTIR) was used to characterize the chemical modifications
of the samples after each treatment. Suspensions of bundled or individualized 5-nm-wide microfibrils were obtained after homogenization
(PH) whereas an organosolv (PO) treatment resulted in shorter aggregates of parallel cellulose microcrystallites. The sharper
rings in the X-ray diffraction pattern of the PO-treated sample suggest a higher crystallinity due to a more efficient removal
of hemicelluloses and dissolution of amorphous zones by the acid treatment. Both microfibrils and microcrystals prepared by
both methods can be used as reinforcing filler in nanocomposite materials. 相似文献
993.
Standardising quality of measurements at both the national and international level results in a unity in measurement that
may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference
materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting
for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of
both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national
adoption of international standards, as well as harmonisation between different international documents are currently relevant,
and Ukrainian experience may be useful to others in this field.
Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel. 相似文献
994.
A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO2 powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a
highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO2 powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO2 formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles
were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical
simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive
droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics
of CeO2 formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO2 were found. 相似文献
995.
R. A. Alieva S. Z. Gamidov F. M. Chyragov A. A Azizov 《Journal of Analytical Chemistry》2005,60(12):1114-1117
A method is developed for cadmium and zinc preconcentration on a minicolumn packed with a new chelating polymer sorbent. The effects of the test solution pH and volume, the sample matrix composition, the eluent volume, and the sample and eluent flow rates are studied. Zinc and cadmium in the eluate are determined by flame atomic absorption spectrometry. Under optimal conditions, the determined ion recovery is more than 95%. The detection limits (3σ, n = 20) are found to be 15.0 (Cd) and 17.2 (Zn) ng/mL. The developed method is employed for cadmium and zinc determination in samples of seawater and water obtained after oil pumping. 相似文献
996.
An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational
characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200
samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic
conditions. 相似文献
997.
Jean F. M. Oth 《Colloid and polymer science》1960,168(1):49-56
Résumé Nous avons mesuré, en fonction de la température, le degré de gonflement dans l'eau de fibres de collagène amorphes qui ont
été tannées différemment, ceci dans le but de pouvoir déterminer, pour chaque degré de tannage (pontage chimique) la chaleur
de mélange du collagène amorphe sec avec l'eau de gonflement.
En utilisant la théorie relative au gonflement des réseaux polymériques amorphes dans un excès de diluant, on a pu montrer
que le paramètre thermodynamiqueχ
1 caractéristique du système collagène-eau (paramètre deFlory-Huggins) varie avec la composition du réseau gonflé. Par contre, le paramètre ?enthalpique? correspondantϰ
1=−
=−0,34 est indépendant de cette composition.
La chaleur de mélangeΔH
mél/V
0 d'un cm3 de collagène amorphe sec avec l'eau de gonflement peut être calculée pour les différents degrées de tannage. Elle a le signe
deϰ
1, i. e. elle est négative et est donnée par:ΔH
mél/V
0=RT gK1(1−v2
éq).
Sa valeur absolue est donc d'autant moins importante que le degré de tannage des fibres est poussé; v2
éq augmente en effet avec la concentration en liens intermoléculaires introduits dans les échantillons.
La variation d'enthalpie accompagnant la transformation d'une fibre de collagène cristalline sèche en fibre amorphe gonflée
(enthalpie de rétraction dans l'eau) diminuée de la chaleur de mélange correspondant au gonflement de la fibre amorphe sèche
dans l'eau donne la chaleur de fusion du collagène sec. Cette quantité est égale à:ΔH/V
0=28±1,5 cal./cm3 et est indépendante du degré de tannage comme on doit s'y attendre.
Travail effectué au Laboratoire de Chimie-Physique de l'Université de Liège, Liège (Belgique). 相似文献
Summary We have measured the temperature dependence of the swelling of amorphous collagen fibres of different degrees of tanning in an excess of water. This was done for the purpose of determining the heat of mixing of amorphous dry collagen with the equilibrium swelling water for each degree of tanning (chemical crosslinking). Using the theory of swelling of polymeric networks in an excess of diluent we were able to show that the parameterχ 1 of the system collagen-water (Flory-Huggins parameter) is a function of the composition of the swollen network. On the other hand, the energy parameterϰ 1=− =−0,34 is found to be concentration independent. The heat of mixingΔH mél/V 0 of 1 cm3 of dry amorphous collagen with the equilibrium swelling water can be calculated for the different degrees of tanning. It has the same sign asϰ 1, i. e. is negative, and is given byΔH mél/V 0=RTϰ 1 (1−v2 éq). Its absolute value decreases therefore with increasing degrees of tanning, sincev 2 éq increases with the density of the cross-links in the sample. The change in heat content on transforming 1 cm3 of dry crystalline collagen fibre into amorphous swollen fibre (heat of shrinking in water), decreased by the heat of swelling of the dry amorphous fibre in water, gives the heat of fusion of dry collagen. This latter equalsΔH/V 0=28±1.5 cal/cm3 and is, as expected, independent of the degree of tanning.
Zusammenfassung Um die Mischungsw?rme des amorphen trockenen Kollagens mit dem Quellungswasser zu bestimmen, wurde die Temperaturabh?ngigkeit des Quellungsgrades von verschieden stark gegerbten amorphen Kollagenfasern gemessen. Auf Grund der Theorie der Quellung von amorphen polymeren Netzwerken in einem überschu? von Quellungsmittel konnte gezeigt werden, da? der thermodynamische (Flory- Huggins) Parameterχ 1 für das System Kollagen-Wasser vom Quellungsgrad des Netzwerkes abh?ngt. Hingegen ist der Enthalpieparameterϰ 1=− =−0,34 davon unabh?ngig. Die Mischungsw?rmeΔH mél/V0 eines cm3 trockenen amorphen Kollagens mit dem Quellungswasser kann für verschiedene Gerbungsgrade (Vernetzungsgrade) berechnet werden. Sie hat das gleiche Vorzeichen wieϰ 1 d. h. ist negativ, und gehorcht der Gleichung:ΔH mél/V 0=RTϰ 1 (1−v2 éq). Der Betrag der Mischungsw?rme ist um so kleiner, je h?her der Gerbungsgrad der Faser ist; in der Tat w?chstv 2 éq mit der Konzentration der Vernetzungspunkte an. Wenn von der Enthalpie?nderung, welche mit dem übergang von einer trockenen kristallinen Faser zu einer gequollenen amorphen verbunden ist, (Schrumfungsenthalpie im Wasser), die oben definierte QuellungsenthalpieΔH mél/V 0 abgezogen wird, so bleibt die Schmelzw?rme des trockenen Kollagens übrig. Diese Schmelzw?rme betr?gt:ΔH/V 0=28±1,5 cal./cm3 und ist, wie zu erwarten, vom Vernetzungsgrad (Gerbungsgrad) des Fadens unabh?ngig.
Travail effectué au Laboratoire de Chimie-Physique de l'Université de Liège, Liège (Belgique). 相似文献
998.
In the course of investigations on equestrian supplemental products for the presence of doping substances, two products were found to contain forbidden substances. As reported earlier a plant extract (Mexican cactus extract) named “Energy 5” contained the anabolic androgenic steroids (AAS) stanozolol, 17β-hydroxy-17α-methyl-5α-androstane-3β-ol (3β,5α-THMT) as well as mestanolone not declared on the label. In the present study, a product called “Super Kalm Paste” was tested. Analysis by gas chromatography - mass spectrometry (GC-MS) revealed that the preparation contained the class I anti-arrhythmics quinine (trade names KinidinTM, Durules) and cinchonine. The samples were prepared according to a sample preparation procedure established for anabolic steroids in nutritional supplements for humans. The sample treatment comprised the extraction and purification of the analytes as well as the chemical conversion with N-methyl-N-trimethylsilyl-trifluoracetamide (MSTFA) to yield the trimethylsilyl (TMS)-derivatives. To verify whether the administration of such products could lead to positive doping tests, a pilot excretion study on “Energy 5” was conducted with two geldings, and urine samples were collected. Gas chromatography - high resolution mass spectrometry (GC-HRMS) after solid phase extraction and mixed derivatisation has demonstrated the presence of the stanozolol metabolite 16β-hydroxy-stanozolol in urine samples after “Energy 5” application. 相似文献
999.
Furuta P Brooks J Thompson ME Fréchet JM 《Journal of the American Chemical Society》2003,125(43):13165-13172
The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device. 相似文献
1000.
Chemical investigation of the dichloromethane extract of the Red Sea marine sponge Lamellodysidea herbacea led to the isolation of seven new polychlorinated derivatives 3-6 and 8-10 in addition to the known dysidamide 1, dysidamide B 2 and dysidamide C 7. Their structures were established by extensive NMR spectroscopic data. The absolute configuration of compound 9 was determined by X-ray crystallographic diffraction analysis. Dysidamide 1 exhibited neurotoxic effects towards both mesencephalic and cortical murine neurones at 0.8 μg/ml. 相似文献