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51.
Capillary electrochromatography (CEC) was used to separate alkyl phenol ethoxylates (APEs) as model diblock copolymers, with monolithic polymers as stationary phases. The order of elution indicate that the two polymer blocks follow distinct chromatographic modes: size-exclusion for the poly(oxyethylene) group and adsorption interaction for the alkyl part. Therefore, our experimental results were compared to the theory describing liquid exclusion-adsorption chromatography (LEAC). They were found in perfect agreement with the theory, which turned to be verified for the first time over the full range of polymer lengths. 相似文献
52.
Stuart D. R.?GallowayEmail author Elizabeth M.?Broad 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1391-1410
Summary. Oral L-carnitine supplementation is frequently reported to have beneficial effects on exercise capacity in clinical populations and has been considered as a potential ergogenic aid for endurance athletes. However, this latter view is largely unsubstantiated possibly due to many experimental studies being poorly controlled or difficult to compare. The potential for oral L-carnitine supplementation to influence skeletal muscle carnitine content has been questioned and there are several key factors identified that may explain variations between study outcomes. Recent more well controlled research suggests some potential for L-carnitine to act as a key regulator of cellular stress, possibly through an impact on the integration of carbohydrate and lipid metabolism, and this work should be followed up in future by well controlled studies in both athlete and clinical subject groups. 相似文献
53.
The N,N-diisopropylaminomethyl aluminium compound [tBu2AlCH2NiPr2 x LiCl]2(1) and the gallium compounds Li[tBu2Ga(CH2NiPr2)2](2) and [tBu2GaCH2N(H)iPr2]Cl x tBu3Ga (3) were prepared by transmetallation of N,N-diisopropylaminomethyllithium LiCH2NiPr2 with di-tert-butylaluminium or -gallium chloride, and characterised by elemental analyses, multinuclear NMR spectroscopy (1H, 13C, 27Al, 7Li) and IR spectroscopy. The crystal structures have been determined by single crystal X-ray diffraction. Compound aggregates as a centrosymmetric dimer, with two Al-C-N units connected by a frame of two LiCl molecules [Al-Cl 2.367(1), Cl-Li 2.339(4) and 2.374(4), Li-N 1.977(4)A]. Compound 2 is a lithium organogallate with two weak LiN bonds [1.965(7) and 1.937(7)A]. Compound 3 contains two different moieties: tBu3Ga and a [tBu2GaCH2N(H)iPr2]+ cation, which are bridged by a Cl- anion [Ga-Cl 2.445(1) and 2.579(1), HCl 2.362(3)A]. 相似文献
54.
Florian Bentivegna Michael Canva Alain Brun Frédéric Chaput Jean-Pierre Boilot 《Journal of Sol-Gel Science and Technology》1997,9(1):33-39
We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment. 相似文献
55.
Fr. Schremmer O. Hromatka E. Deutsch C. Csoklich 《Monatshefte für Chemie / Chemical Monthly》1956,87(1):87-99
Zusammenfassung Bei den vorliegenden Untersuchungen wurde Hirudin, die blutgerinnunghemmende Wirksubstanz von Hirudo medicinalis L., dadurch gewonnen, daß man Blutegel physiologische Kochsalzlösung, mit oder ohne Zusatz von roten Blutkörperchen, saugen ließ und den Darminhalt künstlich entnahm. Außer dem Darminhalt enthält auch die Futterrestlösung Hirudin, wodurch bewiesen wurde, daß der Egel diesen Wirkstoff auch in die Bißwunde abgibt. Das angereicherte Rohhirudin wurde auf seine gerinnunghemmende Wirkung mit Kaninchenblut und Pferdeblut getestet und seine Antithrombinwirkung, Wirkung auf die Rekalzifikationszeit, Prothrombinzeit und Thrombingerinnungszeit von Oxalatplasma untersucht. Die Untersuchungen zeigen, daß die II. Phase der Blutgerinnung beeinflußt wird. Der Temperatureinfluß (100°, 70° und 37°) auf Lösungen der Wirksubstanz wurde untersucht, ebenso die Wirkung angereicherter Rohprodukte auf das lebende Kaninchen. Bei wiederholter Injektion trat kein anaphylaktischer Schock auf.Die Reinigung des angereicherten Rohproduktes durch Papierelektrophorese wird beschrieben.Herrn Prof. Dr.A. Wacek zum 60. Geburtstag mit den besten Wünschen gewidmet (O. H.). 相似文献
56.
During electrolysis of molten KF-2HF, strongly adherent fluorine bubbles are generated at the surface of carbon anode. The current was passing even if the horizontal anode was fully covered with gas film. The formation and growth of gas bubbles were studied by transient electrochemical techniques. It was observed that the fluorine bubbles do not have the spherical cap shape predicted by the classical theory. The curvature radius of the interface profile is not constant, the edge of the bubble being flat with a contact angle close to zero. The results are interpreted in the frame of a model which takes into account the predominant role of the interfacial properties. 相似文献
57.
Wei Q Nieuwenhuyzen M Meunier F Hardacre C James SL 《Dalton transactions (Cambridge, England : 2003)》2004,(12):1807-1811
The metal-organic framework [Co(INA)(2)]x0.5EtOH (INA = isonicotinate, NC(5)H(4)-4-CO(2)(-)), was synthesised under solvothermal conditions. Its X-ray crystal structure shows channels containing ethanol guests which are hydrogen-bonded to carboxylate oxygens of the framework. The pyridyl rings of the framework alternate between 'open' and 'closed' positions along the channels resulting in large variation in the channel cross-sectional area from ca. 1.4 by 2.3 A at the narrowest point to 4.9 by 5.3 A at the widest. Despite the very small windows, the ethanol guests (of van der Waals diameter ca. 4.2-6.1 A) may be reversibly desorbed and sorbed into the structure quantitatively, as shown by in situ variable-temperture IR spectroscopy and XRPD. The single-crystal structure of the desolvated form [Co(INA)(2)] shows that there is no change in the overall connectivity on desolvation, but the rotational positions of the pyridine rings are altered. This suggests that pyridyl rotation may occur to allow guests to pass in and out. When the synthesis was conducted in 1-propanol solvent [Co(INA)(2)]x0.5Pr(n)OHxH(2)O, was obtained, and a single-crystal X-ray structure revealed the same overall connectivity as in but with pyridine rings disordered over closed and open positions. There was no evidence of included guests from X-ray crystallography, suggesting that they are also highly disordered. Variable-temperature XRPD performed on bulk samples showed peaks which were unsymmetrical and exhibited shoulders, suggesting that for each pattern obtained the material actually consisted of several closely-related phases. The movements of the peaks during desolvation showed the presence of intermediate phases before the final desolvated product was formed. The peak positions of the intermediate phases matched more closely with the calculated pattern for than with or, suggesting that they may have disordered structures similar to. The results also suggest that the intermediate phase represents an initial increase in volume before a larger decrease in volume occurs to give the final desolvated material. 相似文献
58.
J. Szonert B. Bieniak M. Głódź M. Piechota 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(3):177-180
We report measurements of lifetimes of the Rb(n
2
F)(n=6, 7, 8) states performed in a vapour cell. TheF-states were excited in a two-step sequence of an electric-dipole transition followed by an electric-quadrupole transition. Single photon counting was used for detection. The results are: (62
F)=171(4), (72
F)=262(15), (82
F)=387(12) (in ns). These lifetimes, have been compared with theoretical values given by different authors. An estimate of the cross sections for quenching due to collisions with ground-state Rb atoms is also given.This work was supported by the Polish Committee for Scientific Research under grant No. 2 2341 92 03 相似文献
59.
Gabelica V Galic N Rosu F Houssier C De Pauw E 《Journal of mass spectrometry : JMS》2003,38(5):491-501
A method for determining the equilibrium association constant of a complexation reaction A + B left harpoon over right harpoon AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A-B solutions at different concentrations C(0). The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant K(a) and a factor R, defined by I(AB)/I(A) = R x [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexes with alpha,omega-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes. 相似文献
60.
Frédéric Lefebvre Pascale Dupont Aline Auroux 《Reaction Kinetics and Catalysis Letters》1995,55(1):3-9
H3PW12O40/activated carbon catalysts have been studied by microcalorimetry and by the dehydration of methanol to dimethyl ether. It has been shown that the acidity of the polyacid is greatly reduced upon grafting on activated carbon. The decrease is so high that, at low polyanion loadings, the catalysts are relatively inactive in the dehydration of methanol to dimethyl ether. 相似文献