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851.
852.
Petrie RJ Bailey T Gorman CB Genzer J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9893-9896
In this Letter, we report on the motion of water droplets on surfaces decorated with molecular gradients comprising semifluorinated (SF) organosilanes. SF molecular gradients deposited on flat silica substrates facilitate faster motion of water droplets relative to the specimens covered with an analogous hydrocarbon gradient. Further increase in the drop speed is achieved by advancing it along porous substrates coated with the SF wettability gradients. The results of our experiments are in quantitative agreement with a simple scaling theory that describes the faster liquid motion in terms of reduced friction at the liquid/substrate interface. 相似文献
853.
The sensitivity of an enzyme to its environment has provoked much interest both for its immediate relevance to biochemistry and for the use of enzymes in chemical synthesis. The intercellular or extracellular environment in which an enzyme naturally operates is crowded with macromolecular, small-molecule, and ionic solutes and hence is markedly different from the dilute aqueous buffer solutions commonly cited for comparisons of biochemical processes. We report the results of a kinetic study into the effects of such a crowded solution on the rate of an enzyme-mediated process-the trypsin-catalyzed hydrolysis of a nonnatural substrate ester. The catalytic rate constant decreases linearly with solvent polarity, but substrate binding is independent of the concentration of added crowding agent up to 395 g/L. 相似文献
854.
Reaction of substituted 1-methyl(benzyl)pyridinium salts ( 1 ) with liquid ammonia/potassium permanganate leads to introduction of the imino group at the carbon adjacent to the nitrogen. The regiospecificity of the reaction strongly depends on substituent X: at C-6 for X = H, CONH2, C6H5 and at C-2 for X = CH3. 3-Aminocarbonyl-1-t-butylpyridinium iodide ( 5 ) on treatment with liquid ammonia/potassium permanganate exclusively gives the 4-imino compound 8 ; 1H nmr spectroscopy shows that 5 in liquid ammonia gives a mixture of the σ-adducts 4-amino-1,4-dihydro- and 6-amino-1,6-dihydro-3-pyridinecarbonamide ( 6 and 7 ). Surprisingly, an oxodemethylation reaction is observed on treatment of 3-aminocarbonyl-1,6-dimethylpyridinium iodide ( 13 ) with liquid ammonia/potassium permanganate, 1,6-dihydro-1-methyl-6-oxo-3-pyridinecarboxamide ( 14 ) being obtained. This compound can easily be converted by phosphorus oxychloride into the alkaloid nudiflorine ( 15 ). 相似文献
855.
Sieber A Boskovic C Bircher R Waldmann O Ochsenbein ST Chaboussant G Güdel HU Kirchner N van Slageren J Wernsdorfer W Neels A Stoeckli-Evans H Janssen S Juranyi F Mutka H 《Inorganic chemistry》2005,44(12):4315-4325
A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1. 相似文献
856.
Soncini A Domene C Engelberts JJ Fowler PW Rassat A van Lenthe JH Havenith RW Jenneskens LW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(4):1257-1266
Why are some (4n+2)π systems aromatic, and some not? The ipsocentric approach to the calculation of the current density induced in a molecule by an external magnetic field predicts a four‐electron diatropic (aromatic) ring current for (4n+2)π carbocycles and a two‐electron paratropic (antiaromatic) current for (4n)π carbocycles. With the inclusion of an electronegativity parameter, an ipsocentric frontier‐orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen‐localised currents in alternating azabora‐heterocycles, which rationalises the differences in (magnetic) aromaticity between these isoelectronic π‐conjugated systems. Ab initio valence‐bond calculations confirm the localisation predicted by the naïve model, and coupled‐Hartree–Fock calculations give current‐density maps that exhibit the predicted delocalised‐to‐localised/carbocycle–heterocycle transition. 相似文献
857.
The electrode kinetic parameters of the In(III)/In(I) couple in acidic 4M bromide solution have been determined by means of the rotating disc electrode technique.
Die elektrochemisch-kinetischen Parameter des In(III)/In(I)-Redoxsystems in Bromidlösung (Kurze Mitteilung)
Zusammenfassung Die elektrochemisch-kinetischen Parameter am In(III)/In(I)-Redoxsystem wurden in saurer 4-M-Bromidlösung mittels der rotierenden Scheibenelektrode bestimmt.相似文献
858.
The formal potentials of the Hg2+/Hg 2 2+ , Hg 2 2+ /Hg and Hg2+/Hg redox couples and the apparent equilibrium constants of the reaction Hg2+ + Hg ∝ Hg 2 2+ in conc. aqueous solutions of Mg(ClO4)2 and Ca(ClO4)2 have been determined from emf measurements performed using cells with liquid junction. Based on these data, the hydration numbers of the Hg2+ and Hg 2 2+ ions were estimated. 相似文献
859.
Avelina Ong-Lee Leo Sylvester Jan W. F. Wasley 《Journal of heterocyclic chemistry》1983,20(6):1565-1569
1,3,4,14b-Tetrahydro-2H,10H-pyrazino[1,2-α]pyrrolo[2,1-c] [1,4]benzodiazepines (1a-e) were synthesized to investigate their potential CNS activity. The key step in the synthesis was the formation of the 10,11-dihydro-5H-pyrrolo[2,1-c][1,4]benzodiazepine (13) by reduction and concomitant cyclization of the nitroketone (11). Biological evaluation of 1a-e revealed interesting properties for 1b (CGS 7525A) [2]. 相似文献
860.
Zusammenfassung Die dünnschichtchromatographische Trennung von Flechtenextrakten zur Unterstützung der Taxonomie wurde in Bezug auf die Trennleistung
und auf die Reproduzierbarkeit optimiert. Dabei wurden besonders gute Trennleistungen erhalten mit dem Flie?mittelgemisch
Benzol:Dioxa:Eisessig=90∶25∶4 bei Verwendung von Kieselgel, dessen Aktivit?t durch eine Umgebung mit relativer Feuchte von
70% festgelegt wurde, und mit Methylenchlorid als Eluiermittel bei Verwendung von mit Oxals?ure impr?gniertem Kieselgel und
antiparallelem Aktivit?tsgradienten. Eine hohe Reproduzierbarkeit der Trennungen wurde erreicht durch Verwendung der Vario-KS-Kammer
nach Geiss, die die Einstellung einer definierten Schichtaktivit?t bzw. eines definierten Aktivit?tsgradienten und eine reproduzierbare
Vorbedampfung der Schicht mit Flie?mittel erm?glicht. Es konnte gezeigt werden, da? durch unterschiedliche chromatographische
Trennungen der gleichen Extrakte und durch die Verwendung verschiedener Anf?rbereagenzien die Identifizierung und damit die
Aussagekraft für taxonomische Probleme steigt.
Standardisation of the thin-layer chromatographic separation of lichen acids for the chemotaxonomy of lichens
Summary The thin-layer chromatography of lichen extracts for taxonomic studies has been optimized in relation to separation and to reproducibility. Especially good separations were found with benzene:dioxane:acetic acid (90∶25∶4) developer and silica gel thin-layer plates, whose activity was fixed by an ambient moisture content of 70%, and with methylene chloride developer and silica gel plates impregnated with oxalic acid and antiparallel activity gradient. High reproducibility of separation was obtained using the Geiss Vario-KS tank, which allows the activity of the plates or the activity gradient to be adjusted and which also allows reproducible exposure of plates to the vapour of developing solvents. By different chromatographic separations of the same extracts and by using different colour reactions the accuracy of identification for taxonomic studies has been improved.
相似文献