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- Bryskhe, Karin, et al.
(författare)
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Formation of internally nanostructured triblock copolymer particles
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:19, s. 8597-8600
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Tidskriftsartikel (refereegranskat)abstract
- Particles with an internal structure have been found in dilute water solutions of a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), which has short hydrophilic PEO endblocks compared to the central hydrophobic PPO block (EO5PO68EO5, L121). The properties of the block copolymer particles (i.e., their structure, size, and time stability) have been investigated using cryogenic transmission electron microscopy (cryo-TEM) in combination with dynamic light scattering (DLS) and turbidity measurements. The particles were formed in dilute solutions by quenching the temperature to temperatures where the reversed hexagonal phase is in equilibrium with a solution of unaggregated L121 copolymers (L-1). From the DLS measurements, a mean hydrodynamic radius of 158 mn was extracted. The time-scan turbidity measurements were found to be unchanged for about 46 h. At higher copolymer concentrations, a reversed hexagonal phase (H-2) exists in the L121/water system. SAXS was used to investigate the internal structure of the dispersed L121-based particles containing 15 wt % L121. It was found that the internal structure transforms from H2 to an inverse micellar system (L-2) as the temperature increases from 37 to 70 degrees C.
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| 2. |
- Bryskhe, Karin, et al.
(författare)
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Lipid-Block Copolymer-Immiscibility
- 2001
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 3, s. 1303-1309
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the binary system of a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), EO5PO68EO5, in water. The ternary system with the same polymer, water and soybean phosphatidylcholine (lecithin) has also been studied. Small-angle X-ray scattering (SAXS), 2H NMR and differential scanning calorimetry (DSC) were used to characterize these systems. The phase diagram of the binary system is presented together with the characteristic parameters in the lamellar and hexagonal phases. In the ternary system, it was found that the lecithin and the block copolymer are essentially immiscible, forming separate phases. In a differential scanning calorimetry experiment it was found that the presence of the block copolymer did not affect the melting temperature of dipalmitoyl phosphatidyl choline. Again indicating immiscibility. The alkane hexadecane is a bad solvent for polypropylene oxide at room temperature. We conclude that it is the difference in hydrophobicity (or polarity) of the hydrophobic parts of the lecithin (lipid) and the block copolymer that explains their immiscibility
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| 3. |
- Bryskhe, Karin, et al.
(författare)
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Spontaneous vesicle formation in a block copolymer system
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:28, s. 9710-9719
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the formation of vesicles in the binary system of a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) with the average composition EO5PO68EO5 in water. Vesicles are formed when a solution of unimers is heated into a two-phase region where, at equilibrium, a concentrated lamellar phase coexists with a dilute solution of unimers. The vesicles were characterized by cryo-TEM, static and dynamic light scattering, and NMR experiments. The average vesicle radius is approximately 60 nm, with an exponential size distribution, and the concentration of vesicles depends strongly on the temperature. The vesicles remain stationary on the time scale of hours. A striking observation is that, on this time scale, both the vesicle size distribution and the concentration of vesicles are reversible with respect to temperature cycles. However, on the time scale of weeks a sedimentation is observed in the solutions.
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| 7. |
- Accardo, Antonella, et al.
(författare)
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High-relaxivity supramolecular aggregates containing peptides and Gd complexes as contrast agents in MRI
- 2007
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Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 1432-1327 .- 0949-8257. ; 12:2, s. 267-276
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Tidskriftsartikel (refereegranskat)abstract
- Mixed supramolecular aggregates, obtained by assembling together two amphiphilic monomers (C18H37)2NCO(CH2)2CO(AdOO)5-G-CCK8 (AdOO is 8-amino-3,6-dioxaoctanoic acid, CCK8 is C-terminal octapeptide of cholecystokinin) and (C18H37)2NCO(CH2)2COLys(DTPAGlu)CONH2 (DTPAGlu is N,N-bis[2-[bis(carboxyethyl)amino]ethyl]-l-glutamic acid), are characterized for their structural parameters by dynamic light scattering and for their relaxometric properties, in the absence and in the presence of 0.9 wt% NaCl. Two different aggregates (micelles and bilayer structures) are present in the absence of NaCl, while only bilayer structures are observed at physiological ionic strength. The presence of NaCl increases the ionic strength, promoting a decrease in the repulsions between the polar heads and among the aggregates in solution, thus supporting the formation of large-curvature aggregates such as bilayer structures like vesicles. In these conditions the closed, vesicular shape and the large size (hydrodynamic radius of about 300 Å) of the aggregates allow a high number of paramagnetic gadolinium complexes and bioactive peptides to be accommodated on the inner and external surfaces . The presence of the salt causes a variation in the structural arrangement of the molecules and a partial rigidification of the assembled Gd(III) complexes on the surface vesicles, reducing their internal motions and giving an approximately 15% higher relaxivity value (r 1p = 21.0 and 18.6 Mm−1 s−1 in the presence and in the absence of NaCl, respectively). The vesicles obtained, for the high relaxivity of each gadolidium complex and for the presence of a surface-exposed bioactive peptide, are very promising candidates as target-selective MRI contrast agents.
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| 10. |
- Ainalem, Marie-Louise, et al.
(författare)
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Dynamic light scattering and fluorescence study of the interaction between double-stranded DNA and poly(amido amine) dendrimers
- 2007
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 8:5, s. 1557-1563
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a cationic poly(amido amine) (PAMAM) dendrimer of generation 4 and double-stranded salmon sperm DNA in 10 mM NaBr solution has been investigated using dynamic light scattering (DLS) and steady-state fluorescence spectroscopy. The structural parameters of the formed aggregates as well as the complex formation process were studied in dilute solutions. When DNA is mixed with PAMAM dendrimers, it undergoes a transition from a semiflexible coil to a more compact conformation due to the electrostatic interaction present between the cationic dendrimer and the anionic polyelectrolyte. The DLS results reveal that one salmon sperm DNA molecule forms a discrete aggregate in dilute solution with several PAMAM dendrimers with a mean apparent hydrodynamic radius of 50 nm. These discrete complexes coexist with free DNA at low molar ratios of dendrimer to DNA, which shows that cooperativity is present in the complex formation. The formation of the complexes was confirmed by agarose gel electrophoresis measurements. DNA in the complexes was also found to be significantly more protected against DNase catalyzed digestion compared to free DNA. The number of dendrimers per DNA chain in the complexes was found to be approximately 35 as determined by steady-state fluorescence spectroscopy.
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