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31.
H. Hoffmann G. Platz H. Rehage W. Schorr 《Advances in colloid and interface science》1982,17(1):275-298
The influence of excess NaCl on the properties of viscoelastic detergent solutions of Cetypyridiniumsalicylate (CPySal) has been studied by static and dynamic light scattering, electric birefringence and rheological measurements. It is obeserved that the rodlike micelles of length L which are present in these solutions and which are responsible for their elastic properties grow in length with the increase of the NaCl concentration. As long as the rods are shorter than their mean distance, their length can be determined from the rheological and electric birefringence measurements. For very small shear fields these solutions behave as Newtonian fluids. The viscosity of the solution increases strongly when the rods begin to overlap. Solutions with overlapping rods are elastic. It is postulated from the results that the cmcII (the critical concentration above which rods are present) and the length L of the rods are partially determined by the intermicellar interaction energy. It is furthermore postulated that this intermicellar interaction energy has an influence on the polydispersity of the rods and seems to make the rods relatively monodisperse. 相似文献
32.
P. Hoffmann V. K. Karandashev T. Sinner H. M. Ortner 《Analytical and bioanalytical chemistry》1997,357(8):1142-1148
Data are reported for a first measurement campaign for a great number of cations (the range of concentrations for main components
is given in ng/mL: Na:<70–880; Mg: 12–160; Al:<7–120; K: 200–1600; NH4
+: 2500–9000; Ca: 300–2500; Fe:<140–1200; Zn: 20–320) and anions (HCOO-: 100–1800; CH3COO-: 400–14500; C2O2-
4: <100–460; NO-
2: <20–55; NO-
3: 660–9900; SO2-
3:<100–1150; SO4
2-: 450–19700; Cl-: 170–3200) in rain and snow samples of the Chernogolovka region 80 km northeast of the centre of Moscow. These data serve
as a first assessment of the situation of the atmosphere in this region. For the determination of fluoride, formate, acetate,
nitrite, bromide, nitrate, sulfite, and sulfate by IC, a relevant development of the method was carried out. For some metallic
cations, a critical quality control was achieved by parallel measurements with ICP-MS, TXRF, and IC. Furthermore, time resolved
measurements were performed for a rain event. Filtration experiments were undertaken to differentiate between the presence
of a series of elements and species in liquid or solid state in the collected aqueous samples.
Received: 25 July 1996 / Revised: 26 September 1996 / Accepted: 13 October 1996 相似文献
33.
The basic obstacles for the general use of laser-ablation(LA)-ICP-MS in analytical laboratories are connected with its reproducibility and calibration. A mathematical relation deduced from the correlation function of the analytical signals allows the estimation of the number of craters needed for representative analyses. The procedure was applied to different samples such as manganese crusts and soils. The ion intensities of the major elements in the manganese crusts and nodules were used as internal standards, improving relative standard deviations by factors between 2 and 3. Selected samples of wood and manganese crusts were analyzed by LA-ICP-MS and the results compared with those obtained by solution ICP-MS. The agreement of the values is within the 95% confidence limits. Powdered reference materials and, in the case of wood analysis, cellulose doped with standard solutions were used for the calibration. 相似文献
34.
We examined the influence of semipolar additives on the phase behavior of mixed zwitterionic surfactant/consurfactant systems. It is shown that in these systems with increasing concentration esters like hexylacetate (HA) and ketones like hexylmethylketone (HMK) can behave both like consurfactants and like hydrocarbons. In solutions of 200 mM tetradecyldimethylamineoxide (TDMAO)/cosurfactant the additives cause first a phase transformation from the micellar L(1) phase to a lamellar L(alpha) phase. Upon further increasing concentration, the L(alpha) phase is transformed into a microemulsion. The L(alpha) phase consists of densely packed multilamellar vesicles. The vesicles are shown by electron microscopy. The multilamellar character of the vesicles is also reflected in the conductivity of the phase. It is up to 10 times lower than the conductivity of the L(1) phase. In some systems the vesicles are transformed on rest into a multidomain stacked L(alpha) phase. It is furthermore demonstrated that the two-phase L(1)/L(alpha) region in these systems is very narrow. In situations where enough HA is added to be close to the boundary of the L(1) phase, it is shown that very small amounts of cosurfactant can transform the L(1) phase into the L(alpha) phase. In extreme situations 1 mM cosurfactant is sufficient for transforming the L(1) phase with 200 mM TDMAO into the L(alpha) phase. In the investigated systems the L(alpha) phase is a highly viscoelastic fluid in which the storage modulus is 1 order of magnitude larger than the loss modulus. Besides the conventional way to prepare samples by adding all ingredients and stirring the solution intensively, all investigated systems were additionally prepared without applying any shear forces. In a surfactant/cosurfactant solution the additive was brought into the sample by diffusion. The phase behavior of both types of samples showed fundamental differences in some cases, which give insight into the influence of shear forces on these systems. Copyright 2001 Academic Press. 相似文献
35.
H. Hoffmann 《Fresenius' Journal of Analytical Chemistry》1966,223(5):376
Ohne Zusammenfassung 相似文献
36.
Gräbner D Matsuo T Hoinkis E Thunig C Hoffmann H 《Journal of colloid and interface science》2001,236(1):1-13
A new anionic surfactant (M-LAMS) that is capable of forming intermolecular hydrogen bonds was investigated. Inverse solubilities of Na and Ca salts were found. Critical micelle concentration and aggregation behavior were determined by surface tension, light scattering, electric birefringence, and SANS measurements. It is found that the Na salt forms globular micelles while the Ca salt forms rodlike micelles. The phase behavior of the micellar solutions with increasing cosurfactant concentration was also studied. It is observed that 100 mM Na-LAMS solutions in the presence of 100 mM CaCl(2) undergo several phase transformations with increasing n-hexanol concentration. We found not only the expected micellar L(1) phase and a lamellar phase at concentrations quite low for this kind of system, but also a novel phase: At a cosurfactant/surfactant ratio x(C) of 1.2 a white precipitate is formed at the bottom of the sample. With increasing ratio x(C) the precipitate dissolves into a liquid crystalline L(alpha) phase that at x(C)=3.2 is transformed into an L(3) or sponge phase. Investigation by FF-TEM, light microscopy, and SANS shows that the precipitate consists of agglomerated polydisperse multilamellar vesicles. The vesicles consist of densely packed bilayers that contain little water. The bilayer thickness is about 20 ? and independent of its composition whereas the interlamellar distance is strikingly linked to concentrations of cosurfactant (surfactant/cosurfactant ratio) and electrolyte. With increasing cosurfactant content, the bilayers become less rigid and resulting thermal undulations force the membranes apart and weaken their interactions until a common L(alpha) phase is formed. This transition is an example of a bonding-nonbonding transition of membranes. Copyright 2001 Academic Press. 相似文献
37.
Petit C Bernardes-Génisson V Hoffmann P Souchard JP Labidalle S 《Chemical & pharmaceutical bulletin》2000,48(11):1634-1638
Five novel S-nitrosothiol compounds (6-10) derived from L-cysteine were generated in solution and their decomposition rate was followed by UV spectroscopy. In acetonitrile, compounds 9 and 10 were the most stable of this series with a half-life of 24 h. The final organic decomposition products of the five S-nitrosothiols were also analysed. Derivatives 8, 9, and 10, possessing a phenolic hydroxyl group, afforded an unexpected decomposition pathway, with nitration of aromatic ring occurring in non-aqueous media. A mechanism involving a phenoxy radical seems to be implicated. 相似文献
38.
A series of enantiomerically pure 8-oxabicyclo[3.2.1]oct-6-en-3-ones functionalized in the unsaturated two-carbon bridge has been prepared by the title reaction. Carbocation reactivity has been fined-tuned at -95 degrees C and adjusted to diene nucleophilicity. Conventional electrophilic substitution of 3-silylated and 3-stannylated furan is suppressed in favor of the rapid 4 + 3 cycloaddition mode. In the case of cycloadduct 13A, stereoselectivity (17:1) is perfectly matched to regioselectivity (17:1). High stereoselection as well as unprecedented regioselection and chemoselection is attributed to the low-temperature cycloaddition protocol and the design of chiral auxiliary and tether. 相似文献
39.
The bonding environment of boron is usually thought about in terms of localized 2c-2e/3c-2e bonding (as in diborane) or completely delocalized polyhedral bonding (as in B(12)H(12)(2)(-)). Recently, a number of boron compounds having a rhomboidal B(4) framework have been synthesized; these show an amazing variation in their skeletal electron count, one that cannot be interpreted in familiar ways. In this report, we systematically explore the origin of the range of electron counts in these compounds. We find that four skeletal MOs are primarily responsible for keeping the B(4) skeleton together. As a subunit in a macropolyhedral environment, termed rhombo-B(4), such an arrangement of B atoms deviates from Wade's rule by three electron pairs (if treated as a distorted arachno system derived from B(6)H(6)(2)(-)). Aided by this analysis, we examine the nature of bonding in Na(3)B(20), where the rhombo-B(4) unit forms linear chains fusing closo-B(7) units. Theory suggests that this structure requires one more electron per formula unit for optimal bonding. Finally, we study the nature of bonding in beta-SiB(3), where silicon atoms also adopt the rhomboid framework. 相似文献
40.
Martin Sukopp Luciana Marinelli Markus Heller Trixi Brandl SimonL. Goodman ReinhardW. Hoffmann Horst Kessler 《Helvetica chimica acta》2002,85(12):4442-4452
The (3R,5S,6E,8S,10R)‐11‐amino‐3,5,8,10‐tetramethylundec‐6‐enoic acid (ATUA; 1 ), which was designed as a βII′‐turn mimic according to the concepts of allylic strain and 2,4‐dimethylpentane units, was incorporated into a cyclic RGD peptide. The three‐dimensional structure of cyclo(‐RGD‐ATUA‐) (=cyclo(‐Arg‐Gly‐Asp‐ATUA‐)) 4 in H2O was determined by NMR techniques, distance geometry calculations and molecular‐dynamics simulations. The RGD sequence of 4 shows high conformational flexibility but some preference for an extended conformation. The structural features of the RGD sequence of 4 were compared with the RGD moiety of cyclo(‐RGDfV‐) (=cyclo(‐Arg‐Gly‐Asp‐D ‐Phe‐Val‐)). In contrast to cyclo(‐RGDfV‐), which is a highly active αvβ3 antagonist and selective against αIIbβ3, cyclo(‐RGD‐ATUA‐) shows a lower activity and selectivity. The structure of the ATUA residue in the cyclic peptide resembles a βII′‐turn‐like conformation. Its middle part, adjacent to the C?C bond, strongly prefers the designed and desired structure. 相似文献