| 1. |
- Evertsson, H., et al.
(författare)
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NMR self diffusion measurements of the monooleoylglycerol/poly ethylene glycol/water L-3 phase
- 2002
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 26:02-jan, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- The monooleoylglycerol (GMO)/poly ethylene oxide (PEG)/water sponge (L-3) phase has been investigated by pulsed-gradient spin-echo NMR self-diffusion. The data allow the L-3 phase to be modeled as a bicontinuous system with respect to the lipid and water domains. It is proposed by using the interconnected rod model that the solvent PEG mainly distributes to the water domain, but has a higher weight fraction partition to the lipid head groups of the local GMO bilayer than water. The data is put in relation to earlier self-diffusion measurements on the binary GMO/water cubic phase, as well as earlier conductivity and X-ray diffraction measurements on the very same L-3 phase.
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| 2. |
- Jeong, Sang Won, et al.
(författare)
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Encapsulation and Diffusion of Water-Soluble Dendrimers in a Bicontinuous Cubic Phase
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:4, s. 1073-6
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Tidskriftsartikel (refereegranskat)abstract
- Bicontinuous cubic (QII) phases composed of hydrated lipids are a unique mesoporous organic material. The diameter of the water channels in the range of 5-10 nm could be used as a reservoir for macromolecular therapeutic agents. Here, we describe the synthesis of water-soluble poly(amidoamine) (PAMAM) dendrimer derivatives labeled with fluorine and their diffusion in the water channels of a QII phase. A QII phase with Ia3d symmetry was prepared by hydration of a 9:1 molar mixture of polymerizable monoacylglycerol and the corresponding 1,2-diacylglycerol. The dendrimers having fluorine were synthesized by Michael reaction of PAMAM dendrimers with a mixture of ethyl 4,4,4-trifluorocrotonate and methyl acrylate. The hydrated diameter of the fluorinated dendrimer of generation 2.5 (G2.5AFH) is 32.6 Å as measured by 19F NMR. The diffusion coefficient of G2.5AFH at 25 C in the water channels of the QII phase, determined by pulsed field gradient 19F NMR spectroscopy, is 1 × 10-12 m2/s, which is compared to the free diffusion coefficient of the dendrimer in water (1.42 × 10-10 m2/s). These data indicate that small globular proteins or similar molecules can diffuse rapidly enough in stabilized QII phases to be technically useful.
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| 3. |
- Lindblom, Göran, et al.
(författare)
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Regulation of Lipid Composition in Acholeplasma laidlawii and Escherichia coli Membranes: NMR Studies of Lipid Lateral Diffusion at Different Growth Temperatures
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:38, s. 11512-5
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Tidskriftsartikel (refereegranskat)abstract
- Lipid lateral diffusion coefficients have been directly determined by pulsed field gradient NMR spectroscopy on macroscopically aligned, fully hydrated lamellar phases containing dimyristoylphosphatidylcholine and total lipid extracts from Acholeplasma laidlawii and Escherichia coli. The temperature dependence of the diffusion coefficient was of the Arrhenius type in the temperature interval studied. The sharp increase in the diffusion coefficient at the growth temperature of E. coli obtained by FRAP measurements, using a fluorescent probe molecule (Jin, A. J., Edidin, M., Nossal, R., and Gershfeld, N. L. (1999) Biochemistry 38, 13275-13278), was not observed. Thus, we conclude that the lipid structural properties (i.e., those affecting the lipid phase behavior), rather than the lipid dynamics, are involved in the adjustment of the membrane lipid composition. Further support for this conclusion is given by the finding that lipid extracts from A. laidlawii grown at different temperatures have about the same diffusion coefficients. Finally, the lipid lateral diffusion in bilayers of phospholipids was found to be much faster than that in bilayers of mainly glucolipids, which can be understood in terms of a free volume theory for the diffusion process.
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| 4. |
- Orädd, Greger, et al.
(författare)
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Lateral Diffusion of Cholesterol and Dimyristoylphosphatidylcholine in a Lipid Bilayer Measured by Pulsed Field Gradient NMR Spectroscopy
- 2002
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Ingår i: Biophys Journal. ; 83:5, s. 2702-4
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Tidskriftsartikel (refereegranskat)abstract
- The pulsed field gradient NMR method for measuring self-diffusion has been used for a direct determination of the lateral diffusion coefficient of cholesterol, fluorine labeled at the 6-position, for an oriented lamellar liquid-crystalline phase of dimyristoylphosphatidylcholine (DMPC)/cholesterol/water. It is found that the diffusion coefficients of DMPC and cholesterol are equal over a large temperature interval. The apparent energy of activation for the diffusion process (58 kJ/mol) is about the same as for a lamellar phase of DMPC/water, whereas the phospholipid lateral diffusion coefficient is approximately four times smaller in the presence of cholesterol.
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| 5. |
- Rilfors, Leif, et al.
(författare)
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Regulation of lipid composition in biological membranes-biophysical studies of lipids and lipid synthesizing enzymes
- 2002
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Ingår i: Colloids and Surfaces B: Biointerfaces. - 0927-7765. ; 26:1, s. 112-24
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Tidskriftsartikel (refereegranskat)abstract
- The study of the role played by membrane lipids, functional lipidomics, has become increasingly important in membrane biology. The physico-chemical properties of the lipids in biological membranes are subject to some fundamental requirements. In general, the acyl chains shall be in a liquid-like state to keep the membrane proteins active, and the lipids must form a bilayer structure in order for the membrane to be an insulating barrier. However, a potential ability of the lipids to form nonbilayer structures seems to be a prequisite for several membrane-associated cell processes. Therefore, organisms exposed to changes in the environmental conditions, such as temperature and uptake of fatty acids, adjust their membrane lipid composition. Examples of prokaryotic organisms that have been studied in this respect are the cell wall-less bacterium Acholeplasma laidlawii, the Gram-negative bacterium Escherichia coli, and the Gram-positive bacteria Bacillus megaterium and Clostridium butyricum, and among eukaroytic organisms are found fungi, higher plants, and poikilothermic animals. By synthesizing a proper combination of acyl chain and polar head group structures, the organisms modify the phase transition temperatures of the membrane lipids so that they are maintained in a lamellar liquid crystalline phase, and the formation of a lamellar gel phase as well as reserved nonlamellar phases is avoided. It has been shown that A. laidlawii and E. coli maintain a balance between lamellar-formed and nonlamellar-forming lipids. A growing body of evidence shows that nonlamellar-forming membrane lipids play essential roles in many aspects of membrance functioning. Short-lived nonbilayer structures are probably formed in the processes of fusion and fission of lipid bilayers, and long-lived bilayer structures with a small radius of curvature occur in several types of biological membranes (e.g. smooth endoplasmic reticulum, inner mitochondrial membrane, and prolamellar bodies). The activity of membrane-associated proteins can be modulated by adding detergents or nonlamellar-forming lipids to bilayers. Some examples are the regeneration of denatured bacteriorphodopsin, and the activities of protein kinase C, some phospholipases, and some key lipid synthases involved in the lipid metabolism of eukaryotic cells, A. laidlawii, and E. coli. The physico-chemical properties of the lipid matrix can be a direct feed-back signal on the activity of the lipid synthases. Finally, nonlamellar-forming lipids are essential for a proper cell division, and an efficient translocation of proteins across the plasma membrane, of E. coli cells.
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| 6. |
- Wästerby, Pär, et al.
(författare)
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Anisotropic Water Diffusion in Macroscopically Oriented Lipid Bilayers Studied by Pulsed Magnetic Field Gradient NMR
- 2002
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Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807. ; 157:1, s. 156-9
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Tidskriftsartikel (refereegranskat)abstract
- The anisotropy, D///D, of water diffusion in fully hydrated bilayers of dimyristoylphosphatidylcholine at 29°C has been measured by pulsed magnetic field gradient (pfg) NMR. By using NMR imaging hardware to produce magnetic field gradients in an arbitrary direction with respect to a stack of macroscopically aligned lipid bilayers, translational diffusion of water was measured as a function of the angle between the direction of the magnetic field gradient and the normal of the lipid membrane. The observed diffusion coefficient is found to depend strongly on this angle. The anisotropy cannot be accurately determined due to the very small value of D, but a lower limit of about 70 can be estimated from the observed diffusion coefficients. The results are discussed in terms of the relatively low permeability of water across the lipid bilayer, instrumental limitations, and/or possible defects in the lamellae.
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