Publications (162) View all
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Chapter: Micelles and liquid crystals in aqueous diglycerol monodecanoate systems
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ABSTRACT: The ternary phase diagram of diglycerol monodecanoate-glycerol monodecanoate-water was studied with conventional methods. Aggregate structure in water-rich samples was examined by means of cryo-TEM (cryo-transmission electron microscopy). The phase properties of these commercially available lipids was compared with high-purity fractions of diglycerol monodecanoate and diglycerol didecanoate. The monoester of diglycerol was found to form elongated micelles with water which with increase of temperature or addition of diester condensed to a liquid phase that could coexist with water. Further addition of diglycerol didecanoate or glycerol monodecanoate transforms this liquid phase to a highly swollen (>97% water) lamellar liquid crystalline phase. The phase behavior is viewed in relation to the behavior of common non-ionic surfactants and discussed with respect to aggregate structures observed by cryo-TEM.10/2008: pages 99-104; -
Chapter: Kinetics of surfactant-induced leakage and growth of unilamellar vesicles
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ABSTRACT: The leakage process induced by the addition of nonionic surfactants to small unilamellar lecithin vesicles has been studied. The leakage rate depends strongly on the concentration of the surfactant — to the power 3.4 for C12E8 (octaethylene glycol n-dodecyl monoether) and the power 5 for Triton X-100. This suggests that the process requires the cooperation of several surfactant molecules. The leakage can occur either through a hole or channel created by the surfactants, or by a shuttle mechanism. While the data does not exclude the shuttle mechanism, the fact that different surfactants closely show the same behavior stands against it. the assumption that a hole is formed in the vesicle wall has to be reconciled with the observation that the addition of surfactant does little to enhance the equilibration rate of a labelled lecithin probe between the outer and inner membrane halves. It is argued that a relatively long-lived hole with a high surface coverge of surfactant molecules could explain the observations. 73- at higher additions of surfactant the vesicles grow into much larger but still unilamellar vesicles, with a relatively sharp size distribution and temperature-independent average final size (600±10 Å at a lipid/surfactant ratio of 1:1, at this and higher surfactant concentrations the structures are mainly open “vesicles”). This transition is very fast, completed within a few minutes at 25°C, and only a few seconds at 37°C. At still higher temperatures the final stage of the process proceeds slower; the equilibration of labelled lecithin is fast in this region.02/2008: pages 190-197; -
Article: ENERGY TRANSFER FROM MICELLAR SODIUM PHENYLUNDECANOATE TO SOLUBILIZED NAPHTHALENE
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ABSTRACT: Abstract— Excitation energy transfer from the phenyl groups of surface active phenylundecanoate ions to naphthalene molecules has been studied under conditions such that the naphthalene molecules have been solubilized by micelles of phenylundecanoate. From measurements of the naphthalene fluorescence intensity in solutions of varying surfactant concentration the critical micelle concentration has been determined as 0·0091 M. The product of the micellar aggregation number and the efficiency of energy transfer has been obtained as 75 from measurements of both the sensitized naphthalene fluorescence and the quenching of the phenylgroup fluorescence. In the evaluation of the experimental data it has been assumed that the partition of naphthalene between the micelles and the aqueous phase may be treated as a distribution equilibrium, and that the solubilized naphthalene molecules are partitioned among the micelles according to a Poisson distribution. With this model, the naphthalene fluorescence intensities may be accounted for over the whole range of surfactant concentrations.At high naphthalene concentrations, emission from naphthalene excimers has been observed. The possibility of self-quenching via excimer formation is considered.The experimental results point to a quantum efficiency near unity for the transfer of excitation energy from the phenyl groups of the surfactant ions that form a micelle to a single solubilized naphthalene molecule. The high efficiency suggests that the naphthalene molecule and the phenyl groups are present inside the micelles.Photochemistry and Photobiology 01/2008; 15(3):297 - 309. · 2.41 Impact Factor -
Article: INTERFACIAL ELECTRON TRANSFER INVOLVING RADICAL IONS OF CAROTENE AND DIPHENYLHEXATRIENE IN MICELLES AND VESICLES
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ABSTRACT: Abstract— The radical cations and anions of diphenylhexatriene have been produced and characterized in homogenous and micellar solutions by pulse radiolysis and laser flash photolysis techniques. Both types of radical ions were formed in cyclohexane on pulse radiolysis. The radical cation was formed in dichloroethane on pulse radiolysis, and by two photon photoionization in ethanol, dichloroethane, and various micelles. Both radical ions have intense (? 105M-1 cm-1) absorption peaks at600–650nm. The cation peak occurs at slightly shorter wavelengths than that of the anion.In micelles and vesicles the radical anion of carotene was formed by electron transfer from ea– on pulse radiolysis. The radical cation was formed on pulse radiolysis of micellar solutions containing Br-2 as counterion, presumably by electron transfer to Br2-. The spectra agree with those of the radical cation and anion of carotene that have previously been obtained in homogenous solutions (Dawe and Land, 1975).Electron transfer in micelles and vesicles from the radical anion of biphenyl to carotene and diphenylhexatriene, and from the radical anions of these to inorganic acceptors has been studied.Photochemistry and Photobiology 01/2008; 31(4):329 - 335. · 2.41 Impact Factor -
Chapter: Fluorescence quenching in the C12E6-water system: Diffusion-control in three to zero dimensions
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ABSTRACT: The quenching of fluorescence from pyrene by hexylbenzophenone in the nonionic surfactant C12E6 has been examined, both with the surfactant in neat form and with water added to produce lamellar, cubic, and hexagonal liquid crystalline phases, and the isotropic micellar solution. The efficiency of the quenching decreases in this order, due to that less quenchers are available within a certain distance from the excited state when the dimensionality is decreased. The decay curves were analysed using the appropriate models for diffusion-controlled quenching in three to one dimensions, and for quenching without exchange in small micelles. The values obtained for the mutual diffusion-coefficient of the probe-quencher pair vary between 3.5 and 6.5 × 10−11 m2 s−1 in a nonsystematic way.12/2007: pages 9-12;
