| 1. |
- Drescher, Simon, et al.
(författare)
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General Synthesis and Aggregation Behaviour of a Series of Single-Chain 1,ω-Bis(phosphocholines)
- 2007
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 13:18, s. 5300-5307
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and physicochem. characterization of a series of polymethylene-1,w-bis(phosphocholines) with even-numbered chain lengths between 22 and 32 carbon atoms is described. Two new synthetic strategies for the prepn. of long-chain 1,wo-diols as hydrocarbon building blocks are presented. The temp.-dependent self-assembly of the single-chain bolaamphiphiles was investigated by cryo transmission electron microscopy (cryo-TEM), differential scanning calorimetry (DSC), and Fourier transform IR spectroscopy (FTIR).
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| 2. |
- Meister, Anette, et al.
(författare)
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Formation of square lamellae by self-assembly of long-chain bolaphospholipids in water
- 2010
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:6, s. 1317-1324
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly process of the symmetric single-chain polymethylene-1,omega-bis(phosphocholine) (PC-C34-PC) with a chain length of 34 carbon atoms and two polar phosphocholine headgroups when put into water is exclusively driven by hydrophobic interactions of the long alkyl chains. This process leads to the formation of a dense network of helical nanofibers and the formation of a hydrogel (Meister et al. J. Phys. Chem. B, 2008, 112, 4506). In contrast, the single-chain bolalipids tetra-and hexatriacontane-1,omega-diyl-bis[2-(dimethylammonio)ethylphosphate] (Me2PE-Cn-Me2PE, n = 34, 36) and the partly deuterated analogue Me2PE-C11-(CD2)12-C11-Me2PE (dMe(2)PE-C34-Me2PE) form a different type of stable aggregate. In a first step, the self-assembly of these long-chain bolalipids in water at room temperature leads to the formation of a dense network of nanofibers which eventually form a hydrogel. Within one day, the nanofibers transform into square lamellae that grow up to an edge length of about 100 nm. Nanofibers are linked to one or two (opposite) corners of the squares leading to the appearance of a kite-like structure. After one week, all fibers have been transformed into square lamellae which are apparently stacked and form a gel cake. Within several weeks, a more compact cake is formed by syneresis, i.e. the expulsion of water.
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| 3. |
- Meister, Anette, et al.
(författare)
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Mixing behaviour of a symmetrical single-chain bolaamphiphile with phospholipids
- 2007
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 3:8, s. 1025-1031
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Tidskriftsartikel (refereegranskat)abstract
- The mixing behavior of the sym. long-chain bolaamphiphile dotriacontane-1,1'-diyl-bis-[2-(trimethylammonio)ethylphosphate] (PC-C32-PC) with conventional phospholipids (DPPC, DMPC, and POPC) was investigated by differential scanning calorimetry and transmission electron microscopy. PC-C32-PC by itself forms nanofibers at room temp., which convert to micellar aggregates at higher temps. The length of the bolaamphiphile corresponds roughly to the thickness of a lipid bilayer. However, a significant insertion of the bolaamphiphile into the phospholipid bilayer vesicles was not obsd. in any of the mixed systems. This is apparently due to packing problems caused by the larger space requirement of the phosphocholine headgroups of PC-C32-PC compared to the small cross-sectional area of the alkyl chain. Obviously, the insertion of these bolaamphiphiles into membrane structures with parallel oriented mols. leads to large void vols. because of this packing problem, so that the bolaamphiphiles prefer to self-assemble into fibers, where the chains can get in closer contact. On the other hand, up to a certain molar ratio, double-chain phospholipids can easily be inserted into the hydrophobic pockets of the bolaamphiphile fibers, where they stabilize the fiber structure.
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| 4. |
- Meister, Annette, et al.
(författare)
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Temperature-dependent self-assembly and mixing behavior of symmetrical single-chain bolaamphiphiles
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:12, s. 6238-46
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Tidskriftsartikel (refereegranskat)abstract
- The temp.-dependent self-assembly and the mixing behavior of sym. single-chain bolaamphiphiles with different polymethylene chain lengths and different headgroup structures were investigated in water by differential scanning calorimetry (DSC), cryo transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS). The even-numbered polymethylene-1,w-bis(phosphocholines) (PC-Cn-PC) are known to form nanofibers composed of stretched mols. with an all-trans alkyl chain conformation (Drescher, S.; Meister, A.; Blume, A.; Karlsson, G.; Almgren, M.; Dobner, B. Chem.-Eur. J.2007, 13, 5300-5307). The odd-numbered analogs were synthesized to study a possible even-odd effect of these bolaamphiphiles during their aggregation in water. In addn. to these bolaamphiphiles with phosphocholine headgroups, a new series of polymethylene-1,w-bis(phosphodimethylethanolamines) (Me2PE-Cn-Me2PE) with smaller headgroup sizes was synthesized. These bolaamphiphiles show an addnl. fiber-fiber transition when the alkyl chain length exceeds 26 carbon atoms. The mixing behavior of both types of bolaamphiphiles indicates that differences in the alkyl chain length up to six carbon atoms are tolerated within the fiber structure. The mixing of two Me2PE-Cn-Me2PE or PC-Cn-PC type bolaamphiphiles with different alkyl chain lengths offers the possibility to adjust the temp., where the crosslinking of the fibers is disrupted and where the fibers break apart. As a consequence, temp. switchable hydrogels are obtained that can be fine-tuned for drug delivery applications. The comparison with dotriacontane-1,32-diyl-bis[2-(methylammonio)-ethylphosphate] (MePE-C32-MePE), a new bolaamphiphile with even smaller phosphomonomethylammonio headgroups, illustrates the importance of the headgroup size for the aggregation behavior. This bolaamphiphile self-assembles exclusively into lamellar structures, and this aggregate type persists in mixts. with the fiber forming Me2PE-C32-Me2PE.
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| 5. |
- Reuter, Marcel, et al.
(författare)
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Poly-L-lysines and poly-L-arginines induce leakage of negatively charged phospholipid vesicles and translocate through the lipid bilayer upon electrostatic binding to the membrane
- 2009
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Ingår i: Biophysical Chemistry. - : Elsevier BV. - 0301-4622 .- 1873-4200. ; 144:1-2, s. 27-37
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Tidskriftsartikel (refereegranskat)abstract
- Poly-lysines (PLL) and poly-arginines (PLA) of different polymer chain lengths interact strongly with neg. charged phospholipid vesicles mainly due to their different elec. charges. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and their mixts. (1/1 mol/mol) with the resp. phosphatidylcholines of equiv. chain length were chosen as model membrane systems that form at room temp. either the fluid Lalpha or the gel phase Lbeta lipid bilayer membranes, resp. Leakage expts. revealed that the fluid POPG membranes are more perturbed compared to the gel phase DPPG membranes upon peptide binding. Furthermore, it was found that pure PG membranes are more prone to release the vesicle contents as a result of pore formation than the lipid mixts. POPG/POPC and DPPG/DPPC. For the longer polymers (>= 44 amino acids) maximal dye-release was obsd. when the molar ratio of the concns. of amino acid residues to charged lipid mols. reached a value of R P = 0.5, i.e. when the outer membrane layer was theor. entirely covered by the polymer. At ratios lower or higher than 0.5 leakage dropped significantly. Furthermore, PLL and PLA insertions and/or translocations through lipid membranes were analyzed by using FITC-labeled polymers by monitoring their fluorescence intensity upon membrane binding. Short PLL mols. and PLA mols. of all lengths seemed to translocate through both fluid and gel phase lipid bilayers. Comparison of the PLL and PLA fluorescence assay results showed that PLA interacts stronger with phospholipid membranes compared to PLL. Isothermal titrn. calorimetry (ITC) measurements were performed to give further insight into these mechanisms and to support the findings obtained by fluorescence assays. Cryo-transmission electron microscopy (cryo-TEM) was used to visualize changes in the vesicles' morphol. after addn. of the polypeptides.
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| 6. |
- Scholtysek, Peggy, et al.
(författare)
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A T-Shaped Amphiphilic Molecule Forms Closed Vesicles in Water and Bicelles in Mixtures with a Membrane Lipid
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:16, s. 4871-4878
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Tidskriftsartikel (refereegranskat)abstract
- The T-shaped amphiphilic molecule A6/6 forms a columnar hexagonal liquid-crystalline phase between the crystalline and the isotropic liquid when studied in bulk (Chen et al., 2005). Because of the hydrophilic and flexible oligo(oxyethylene) side chain terminated by a 1-acylamino-1-deoxy-d-sorbitol moiety attached to a rigid terphenyl core with terminal hexyloxy alkyl chains, it was expected that also formation of lyotropic phases could be possible. We therefore studied the behavior of A6/6 in water and also in mixtures with bilayer-forming phospholipids, such as dipalmitoyl-phosphatidylcholine (DPPC), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and solid-state nuclear magnetic resonance (ssNMR). DSC showed for the pure A6/6 suspended in water a phase transition at ca. 23 °C. TEM and cryo-TEM showed vesicular as well as layered structures for pure A6/6 in water below and above this phase transition. By atomic force microscopy (AFM), the thickness of the layer was found to be 5?6 nm. This leads to a model for a bilayer formed by A6/6 with the laterally attached polar side chains shielding the hydrophobic layer built up by the terphenyl core with the terminal alkyl chains of the molecules. For DPPC:A6/6 mixtures (10:1), the DSC curves indicated a stabilization of the lamellar gel phase of DPPC. Negative staining TEM and cryo-TEM images showed planar bilayers with hexagonal morphology and diameters between 50 and 200 nm. The hydrodynamic radius of these aggregates in water, investigated by dynamic light scattering (DLS) as a function of time and temperature, did not change indicating a very stable aggregate structure. The findings lead to the proposition of a new bicellar structure formed by A6/6 with DPPC. In this model, the bilayer edges are covered by the T-shaped amphiphilic molecules preventing very effectively the aggregation to larger structures.
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