- Micellar Dynamics and Organization. A Multifield 13C NMR Spin-Lattice Relaxation and /1H/13C Nuclear Overhauser Effect Study
-
An extensive 13C spin-relaxation study is presented for four micellar systems.These are dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, potassium palmitate, and sodium p-octylbenzenesulfonate.The spin relaxation data are analyzed with a relaxation model that takes into account the complexity of molecular motions in surfactant systems.The results show that the internal motions in the micelles are quite fast, occurring on a time scale of 10-11 s, which is similar to that found for liquid hydrocarbons of comparable chain lengths.The motional restrictions imposed by the aggregate-water interface resemble those found in other types of surfactant aggregates.A correlation time associated with the motions of the whole aggregate is extracted.The value of this correlation time implies that, apart from the rotational tumbling and monomer diffusion, the micelles undergo additional motions.
- Walderhaug, Harald,Soederman, Olle,Stilbs, Peter
-
-
Read Online
- The salts of fatty acids as precursors for preparation of silver nanoparticles in organic solvents
-
The silver salts of fatty acids were studied as precursors for the preparation of colloidal dispersions of silver nanoparticles and UHMWPE (ultra-high-molecular-weight polyethylene) composite with silver nanoparticles, as well as the composition, the spectra and SEM (scanning electron microscopy) results.
- Glushko,Anisimova,Blokhina
-
p. 1759 - 1764
(2016/10/24)
-
- Photolysis of phenacyl esters in a two-phase system
-
Phenacyl esters are useful photoremovable protecting groups for carboxylic acids in organic synthesis and biochemistry. In this work, simple one-pot arrangements of the phenacyl and 2,5-dimethylphenacyl ester photolysis are proposed. The reactions were performed in both the benzene/water two-phase system and in water. Cetyltrimethylammonium bromide was found to increase substantially the efficiency of the deprotection as well as the purity of the products by lowering the interfacial tension between the phases. Utilizing water as a medium significantly reduced the necessity to use environmentally malign organic solvents. The overall yields varied from 72 to 98% depending on the reaction conditions.
- Ruzicka, Radovan,Zabadal, Miroslav,Klan, Petr
-
p. 2581 - 2590
(2007/10/03)
-
- Salt effects on solvolysis reactions of p-nitrophenyl alkanoates catalyzed by 4-(dialkylamino)pyridine-functionalized polymer in buffered water and aqueous methanol solutions
-
Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of p-nitrophenyl alkanoates 2 (n = 2-16) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 in aqueous Tris buffer solution at pH 8.0 and 30°C. Macromolecule 1 was found to exhibit clear substrate preference for 2 (n = 6) in 0.05 M aqueous Tris buffer solution, as contrasted with the corresponding reaction in 0.05 M aqueous phosphate or borate buffer solutions where the substrate selectivity is absent. The formation of a reactive catalyst substrate complex, 1·2, appears to be promoted by the presence of tris(hydroxymethyl)methylammonium ion, an efficient salting-in agent, from the Tris buffer system. The salting-in effect on formation of 1·2 complex is presumed responsible for the substrate specificity. The salting-out effects of sodium chloride on the solvolysis of 2 catalyzed by 1 were also investigated in 1:1 (v/v) methanol-water solution at pH 8.0 and 30°C. The rate of 1-catalyzed solvolysis of 2 (n = 10-16) was found to vary inversely with NaCl concentration (0-1.0 M). The magnitude of the salting-out effects is dependent on the alkyl chain length in 2 and the concentrations of 1 and NaCl. At 7.5 x 10-5 unit mol L-1 1 and 0-1.0 M NaCl the order of reactivity for 2 (n = 10-16) was n = 10 > 12 > 14 > 16. However, at 5.0 x 10-6 unit mol L-1 1, a revised reactivity order, 2, n = 14 > 12 > 16, was obtained at [NaCl] 0.15 M. A significant decrease in the substrate preference for 1-catalyzed solvolysis of 2 (n = 10-16) was observed at higher NaCl concentrations. We suggest that the reduced catalytic efficiency and selectivity expressed by 1 in the presence of sodium chloride should be attributed to changes in the morphology and composition of aggregates containing 1 and 2 in aqueous methanol solution that lead to decreased dependence of aggregate formation on the hydrophobicity of the substrate.
- Wang, Guang-Jia,Ye, Donghao,Fife, Wilmer K.
-
p. 12536 - 12540
(2007/10/03)
-
- Einfluss verschiedener Vorbehandlungen auf die Strukturbildung und thermischen Umwandlungserscheinungen ausgewaehlter Natrium-Seifen
-
Das thermische Phasenverhalten und die strukturellen Abwandlungen ausgewaehlter Na-Seifen (Na-Kaprylat, Na-Palmitat und Na-Stearat) wurden mit den Methoden der Differential-Scanning-Kalorimetrie, Roentgen- und Elektronenbeugung untersucht.Der Einfluss verschiedener Vorbehandlungen auf die Struktur und thermischen Umwandlungserscheinungen stand im Mittelpunkt des Interesses.Folgende Ergebnisse sind hervorzuheben: 1.Verschiedene Vorbehandlungen (Probenpraeparationen) beeinflussen die Restwassermengen in den Na-Seifen.Zur Herstellung wasserfreier Produkte muss fest gebundenes Wasser (ca. 1/2 mol) unter drastischen Bedingungen entfernt werden. 2.Die Umwandlungstemperaturen und -enthalpien unterschiedlicher Formen obiger Na-Seifen werden angegeben und mit dem Wassergehalt in Beziehung gesetzt. 3.Mit Ausnahme des Kristalls laesst sich der feste Zustand verschieden vorbehandelter Seifen strukturell nicht einheitlich deuten.Die Grenzen bekannter Modellvorstellungen werden diskutiert. 4.Der Kristallzustand laesst sich nur durch Loesungsmittelkristallisation erreichen.Im Kristall sind die Molekuele (NaC18) in einem Gitter der Abmessungen a=9,19 Angstroem und b=8,05 Angstroem gepackt.Die trikline Subzelle TII als Anordnung der aliphatischen Ketten wurde durch Elektronenbeugung an Mikroeinkristallen gesichert.Als Ueberstrukturelemente koennen duenne lamellare Fasern angenommen werden.Eine periodische Anordnung derartiger Fasern ist nachgewiesen worden. 5.Aus den Roentgenbeugungsaufnahmen folgt, dass das Aufschmelzen der Ketten fuer das NaC8, NaC16 und NaC18 einheitlich bei etwa 118 deg C satttfindet und mit einer thermischen Kontraktion und einem Wechsel in der Ueberstruktur verbunden ist.Das Roentgenbeugungsverhalten beim Aufheizen verschiedener Zustaende der Seifen ist jeweils unterschiedlich und konnte nicht in allen Faellen strukturell gedeutet werden.Die Hochtemperaturphasen liessen sich nur beim wasserfreien NaC18 mit dem Modell zentrierter Baenderstrukturen in Uebereinstimmung bringen.
- Foerster, G.,Brezesinski, G.,Gerlach, E.,Maedicke, A.,Doerfler, H.-D.
-
p. 1009 - 1031
(2007/10/02)
-
- Dibenzo?b,e!?1,4!diazepines
-
A compound represented by the formula STR1 wherein R is H, loweralkyl, hydroxyloweralkyl or STR2 where R2 is an alkyl group of 1 to 15 carbon atoms; and R1 is H or STR3 where R2 is an alkyl group of 1 to 15 carbon atoms. These compounds are useful as antischizophrenics.
- -
-
-
