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11.
Effect of the addition of a nonionic surfactant on the complex poly(asparagine)--cationic surfactant
Roscigno P D'Auria G Falcigno L D'Errico G Paduano L 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8123-8130
Poly(asparagine) (pAsn) at 0.1wt % in the presence of dodecyltrimethylammonium bromide (DTAB) and pentaoxyethylene octyl ether (C(8)E(5)) at 1:1 molar ratio leads to the formation of mixed DTAB/C(8)E(5) micelle-like aggregates onto the polypeptide as a total surfactant critical association concentration (cac) is reached, as revealed by surface tension measurements and NMR chemical shifts. Two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) capable of revealing spatial relationships among proximal protons has been performed on the pAsn-DTAB-C(8)E(5)-water system to study structural details of the surfactant-polypeptide aggregates. NOESY cross-peaks at sample temperature of 298.15 K indicate that the polypeptide interacts with the DTAB/C(8)E(5) micelle-like aggregates. The NOE intermolecular effects also show direct interactions between surfactant and polypeptide in the pAsn-DTAB-water system, whereas no interaction has been revealed in the pAsn-C(8)E(5)-water system. Furthermore, the experimental evidence suggest that the DTAB-polypeptide complex is mainly driven by the polar attraction between the two molecules. 相似文献
12.
Luigi Ambrosone Lucia Costantino Gerardino D'errico Vincenzo Vitagliano 《Journal of colloid and interface science》1997,190(2):286
The densities and viscosities of binary aqueous mixtures of poly(ethylenoxide)hexanols [C6H13(OCH2CH2)mOH, C6Em] (m= 3, 4, and 5) have been studied in the micellar composition range. For the same surfactants the self-diffusion coefficients in mixtures with heavy water have been determined by the spin-echo pulsed field gradient method. The volumetric data are interpreted by means of the phase separation model, and values of the CMC, volume change, and standard free energy change of micellization are obtained. From the viscosity data the hydration numbers of the surfactant hydrophilic head in the micellar state are computed; they are in agreement with those obtained from HDO self-diffusion data. The surfactant self-diffusion data are used to calculate the apparent micelle radius and the aggregation number. The micellization parameters obtained for the different surfactants are compared and discussed. 相似文献
13.
Gian Luigi Bendazzoli 《Theoretical chemistry accounts》2007,118(1):135-142
We present and discuss a variational single-product approximation to the van der Waals dispersion interaction leading to a
simple formula for C
6 that seems capable to give more than 99% of the ‘exact’ value. The formula is derived from Hylleraas’ variational principle
in the tensor product space of the interacting molecules and therefore enjoys bounding properties. The formula has been tested
by computing the C
6 dispersion constants of H–H, and, at Full CI level, of the following systems: He–He, He–Li, Li–Li, LiH–LiH, HF–HF. Connections
with the London formula are discussed.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
14.
Pier Luigi Luisi 《Angewandte Chemie (International ed. in English)》1985,24(6):439-450
Reverse micelles are spheroidal aggregates formed by certain surfactants in apolar media. In contrast to normal micelles in water, the polar head groups of the surfactant molecules are directed towards the interior of the aggregate and form a polar core which can solubilize water (the “water pool”); the lipophilic chains are exposed to the solvent. The water of the water pool exhibits properties that (depending on the mole ratio of water to surfactant) differ from those of bulk water. Surprisingly, these reverse micelles are able to solubilize in hydrocarbon solvents hydrophilic molecules, e.g., enzymes and even plasmids, that are much larger than the original water-pool diameter. These biopolymer-containing reverse micelles can be viewed as novel microreactors, whose physical properties can be controlled through the water content. Remarkable is the ability of enzyme-containing micelles to react with water-insoluble, hydrocarbon-soluble substrates, as in the example of lipoxygenase with linoleic acid. 相似文献
15.
Luigi Stradella 《Reaction Kinetics and Catalysis Letters》1996,58(2):261-268
Some photocatalytic reactions on a Ru film, where carbon monoxide participates as a reactant have been studied by means of mass spectrometry. Under UV irradiation carbon monoxide is oxidized to carbon dioxide if treated with oxygen. It is transformed to methanol in the presence of hydrogen, and in mixture with water gives hydrocarbon species. 相似文献
16.
Coppola L Gianferri R Oliviero C Ranieri GA 《Journal of colloid and interface science》2003,264(2):554-557
We report on the first rheological study of the structural relaxations in a nematic liquid crystalline phase. Linear dynamic and transient shear experiments were applied to a polydomain nematic phase of the CTAB/water system: a liquid crystalline mixture composed of 28 wt% CTAB at 35 degrees C. The decay of the shear modulus, G(t), was analyzed using the CONTIN inverse Laplace transform to obtain a distribution of relaxation times which were compared with ones from the usual fitting procedure based on a generalized Maxwell model. The behavior of the nematic lyotropic structure of the CTAB/water system is characterized by the presence of both slow and fast relaxation times. These were interpreted as being due to a progressive loss of the lyotropic domain orientation and to the breaking/reforming process of the cylindrical aggregates, respectively. 相似文献
17.
Complexes [MX2(1)] (M = Ni, Pd and Pt; X=Cl and NCS; 1 = 2,11-bis(dialkyl-[or diaryl]phosphinomethyl)benzo[c]phenanthrene; alkyl = cyclohexyl t-butyl; aryl = m-tolyl, p-anisyl and m-CF3 C6H4) have been synthesized. An NMR. study of the t-butyl complexes provides evidence for a “fan-like” motion of the benzo[c]phenanthrene moiety over the plane of the complex. 相似文献
18.
Mondello L Shellie R Casilli A Quinto Tranchida P Marriott P Dugo G 《Journal of separation science》2004,27(9):699-702
A 5 m x 50 microm capillary column with 0.05 microm stationary phase film thickness, with a calculated efficiency of almost 20,000 plates per metre (under optimum conditions), was used for very fasthigh resolution GC analysis of lime essential oil. The total analysis time of this volatile essential oil was less than 90 s. Fast GC is shown to be appropriate for essential oil quality assurance analysis, and quantitative results of key components are comparable with those obtained by using conventional GC analysis. The fast GC analysis is approximately 33 times faster than the conventional GC method. 相似文献
19.
Fabbrizzi L Foti F Licchelli M Maccarini PM Sacchi D Zema M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(21):4965-4972
A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamide group. In the corresponding nickel(II) complex, binding of the pendant arm to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the NiII center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH- ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the NiII center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chain is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change. 相似文献
20.
Gallo P Nasi A Vinci F Guadagnuolo G Brambilla G Fiori M Serpe L 《Rapid communications in mass spectrometry : RCM》2005,19(4):574-579
In this work we present a method for confirmatory analysis of chloramphenicol (CAP) in bovine and buffalo raw milk. CAP is extracted in acetonitrile and purified by affinity chromatography on an alpha-1-acid glycoprotein (AAG) column, then is identified and determined by ion-trap liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) analysis in the negative ion mode. CAP was identified at the minimum required performance limit (MRPL) of 0.30 ppb, by monitoring the [M-H]- ion and at least two product ions, meeting the qualitative and quantitative criteria set by the European Commission in Decision 2002/657/EC for confirmation of prohibited veterinary drugs. The trueness and within-day and between-day repeatability data are also reported. Moreover, the loading capacity of affinity columns towards CAP was tested. This method, based on the molecular recognition between drug and AAG during the purification step to improve sample cleanup, represents a quantitative and repeatable procedure for confirmatory analysis, and fits the requirements for the routine official control of CAP residues in raw milk. 相似文献