| 1. |
- Bramer, Tobias, et al.
(författare)
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Effects of pH and ionic strength on catanionic drug-surfactant mixtures used for prolonged release from gels.
- 2007
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Ingår i: Journal of drug delivery science and technology. - 1773-2247. ; 17:4, s. 285-291
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate the influence of pH and ionic strength on the phase behavior of two different catanionic drug-surfactant mixtures, and to study drug release from gels facilitated by the catanionic aggregates. Simplified phase diagrams were constructed for diphenhydramine or tetracaine mixed with SDS, varying the pH approximately between 6 and 11, and the NaCI concentration from 0.45 to 1.8%. The phases formed were studied visually, rheologically and with cryo-TEM. Some mixtures containing catanionic vesicles and micelles were selected for drug release studies from gels, varying the pH and NaCI concentration here as well. Both catanionic systems investigated proved relatively resilient to changes in the ionic strength. Changes in pH, on the other hand, caused marked effects to the phase behavior in both systems. The influence of pH was particularly strong in the drug-rich part of the tetracaine/SDS system, where increasing the pH causes precipitation. As expected, the drug release in both systems was somewhat affected by changes in both pH and ionic strength, but remained in all cases significantly prolonged as compared to the release of free, non-complexed, drug. These studies show that catanionic mixtures may be used to obtain prolonged drug release from gels, and that the concept also works when the gels are exposed to a pH that is a couple of units above the pKa of the cationic component. Furthermore, the ionic strength has no pronounced effect on the drug release, as long as it is kept within reasonable pharmaceutical levels.
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| 2. |
- Dew, Noel, et al.
(författare)
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Gel formation in systems composed of drug containing catanionic vesicles and oppositely charged hydrophobically modified polymer.
- 2009
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Ingår i: Colloids and Surfaces B. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 70:2, s. 187-197
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to explore if mixtures of drug containing catanionic vesicles and polymers give rise to gel formation, and if so, if drug release from these gels could be prolonged. Catanionic vesicles formed from the drug substances alprenolol or tetracaine, and the oppositely charged surfactant sodium dodecyl sulphate were mixed with polymers. Three polymers with different properties were employed: one bearing hydrophobic modifications, one positively charged and one positively charged polymer bearing hydrophobic modifications. The structure of the vesicles before and after addition of polymer was investigated by using cryo-TEM. Gel formation was confirmed by using rheological measurements. Drug release was studied using a modified USP paddle method. Gels were observed to form only in the case when catanionic vesicles, most likely with a net negative charge, were mixed with positively charged polymer bearing lipophilic modifications. The release of drug substance from these systems, where the vesicles are not trapped within the gel but constitute a founding part of it, could be significantly prolonged. The drug release rate was found to depend on vesicle concentration to a higher extent than on polymer concentration.
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| 3. |
- Gelin, Kristina, et al.
(författare)
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Characterization of water in bacterial cellulose using dielectric spectroscopy and electron microscopy
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:26, s. 7623-7631
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that only 10% of the 99 wt% water present in bacterial cellulose (BC) gels, produced by Acetobacter xylinum, behave like free bulk water; the majority of the water molecules in the gels is more or less tightly bound to the cellulose. The magnitude of the diffusion coefficients of ions transported in the water phase of the BC gels as well as the information contained in freeze fracture transmission electron microscopic images of the gel structures indicates that the bulk-like water is confined in “lakes” rather than forming a continuous phase throughout the gel. Water desorption isotherms suggest that these “lakes” decrease in size with increasing oxygen concentration used during the biosynthesis process of the gels.
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| 4. |
- Awad, Doaa, et al.
(författare)
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Interaction of Na2B12H11SH with dimyristoyl phosphatidylcholine liposomes.
- 2009
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Ingår i: Chemistry and Physics of Lipids. - : Elsevier BV. - 0009-3084 .- 1873-2941. ; 157:2, s. 78-85
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Tidskriftsartikel (refereegranskat)abstract
- Previous investigations have revealed that the boron cluster compound Na2B12H11SH (BSH) is very potent in causing major structural rearrangements of and leakage from phosphatidylcholine liposomes. This somewhat unexpected finding is interesting from a fundamental point of view and may also constitute the basis of future important pharmaceutical/medical applications of BSH. In order to further explore the BSH-lipid interaction, we have studied the effects caused by BSH on dimyristoyl phosphatidylcholine (DMPC) liposomes. Cryo-transmission electron microscopy showed that BSH induces aggregation, membrane rupture and increasing wall thickness of the liposomes. Differential scanning calorimetry revealed a BSH dependent shift of the gel to liquid crystalline phase transition temperature of DMPC. The zeta potential of the liposomes decreases with increasing BSH concentrations, and an apparent dissociation constant of 0.23 mM was found. BSH caused leakage of liposome-encapsulated carboxyfluorescein; leakage was higher at 23 °C (near the phase transition temperature) than at 15 °C and 37 °C. It induced lipid mixing only at very high concentrations.
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| 5. |
- Bastiat, Guillaume, et al.
(författare)
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Development of Non-Phospholipid Liposomes Containing a High Cholesterol Concentration
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:14, s. 7695-7699
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel formulation of non-phospholipid liposomes formed from cholesterol and palmitic acid. Despite the fact that these two lipidic species do not form individually fluid bilayers, we show that once mixed together, fluid bilayers can be obtained and, moreover, these can be extruded using classical extrusion processes to form liposomes. The chem. anal. indicates that these liposomes contain 70 mol % cholesterol, a content that is considerably higher that the satn. limit generally reported for phospholipid bilayers. These cholesterol-rich liposomes, formed with mols. that have low toxicity in vivo, display an improved impermeability relative to that of traditional phospholipid liposomes. In addn., because of the presence of palmitic acid, the stability of the liposomes is pH-dependent, and it is possible to trigger the release of encapsulated materials by pH stimuli.
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| 6. |
- Bezemer, TM, et al.
(författare)
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Plant species and functional group effects on abiotic and microbial soil properties and plant-soil feedback responses in two grasslands
- 2006
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 94:5, s. 893-904
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1 Plant species differ in their capacity to influence soil organic matter, soil nutrient availability and the composition of soil microbial communities. Their influences on soil properties result in net positive or negative feedback effects, which influence plant performance and plant community composition. 2 For two grassland systems, one on a sandy soil in the Netherlands and one on a chalk soil in the United Kingdom, we investigated how individual plant species grown in monocultures changed abiotic and biotic soil conditions. Then, we determined feedback effects of these soils to plants of the same or different species. Feedback effects were analysed at the level of plant species and plant taxonomic groups (grasses vs. forbs). 3 In the sandy soils, plant species differed in their effects on soil chemical properties, in particular potassium levels, but PLFA (phospholipid fatty acid) signatures of the soil microbial community did not differ between plant species. The effects of soil chemical properties were even greater when grasses and forbs were compared, especially because potassium levels were lower in grass monocultures. 4 In the chalk soil, there were no effects of plant species on soil chemical properties, but PLFA profiles differed significantly between soils from different monocultures. PLFA profiles differed between species, rather than between grasses and forbs. 5 In the feedback experiment, all plant species in sandy soils grew less vigorously in soils conditioned by grasses than in soils conditioned by forbs. These effects correlated significantly with soil chemical properties. None of the seven plant species showed significant differences between performance in soil conditioned by the same vs. other plant species. 6 In the chalk soil, Sanguisorba minor and in particular Briza media performed best in soil collected from conspecifics, while Bromus erectus performed best in soil from heterospecifics. There was no distinctive pattern between soils collected from forb and grass monocultures, and plant performance could not be related to soil chemical properties or PLFA signatures. 7 Our study shows that mechanisms of plant-soil feedback can depend on plant species, plant taxonomic (or functional) groups and site-specific differences in abiotic and biotic soil properties. Understanding how plant species can influence their rhizosphere, and how other plant species respond to these changes, will greatly enhance our understanding of the functioning and stability of ecosystems.
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| 7. |
- Boija, Elisabet, et al.
(författare)
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Bilayer disk capillary electrophoresis : a novel method to study drug partitioning into membranes
- 2008
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 29:16, s. 3377-3383
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Tidskriftsartikel (refereegranskat)abstract
- CE in the presence of lipid bilayer disks was introduced as a new approach in membrane partitioning studies. The disks were used as a pseudostationary phase in the partial-filling mode of CE and the partitioning of cationic drugs was determined. The migration times of the analytes increased linearly with the lipid amount in the system. An appropriate algorithm for the calculation of a partition coefficient is presented. In the disk-shaped bilayers, which have excellent stability and shelf life, all of the lipids are readily available for interaction and the disks can be used as realistic cell membrane models.
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| 8. |
- Boija, Elisabet, et al.
(författare)
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Evaluation of bilayer disks as plant cell membrane models in partition studies
- 2007
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Ingår i: Analytical Biochemistry. - : Elsevier BV. - 0003-2697 .- 1096-0309. ; 364:2, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the partitioning of a set of phenolic compounds used as lignin precursor models into lipid bilayer disks and liposomes. The bilayer disks are open bilayer structures stabilized by polyethylene glycol-conjugated lipids. Our results indicate that disks generate more accurate partition data than do liposomes. Furthermore, we show that the partitioning into the membrane phase is reduced slightly if disks composed of 1,2-distearoyl-sn-glycero-3-phosphocholine and cholesterol are exchanged for disks with a lipid composition mimicking that of the root tissue of Zea mays L.
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| 9. |
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| 10. |
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