| 1. |
- Alves, Luis, et al.
(författare)
-
On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants : Role of the surfactant architecture
- 2018
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 513, s. 489-496
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis The rheological control of suspensions is of key interest in the formulation design. A chemically cross-linked hydrophobically modified poly(acrylic acid) (HMCL-PAA), used as rheology modifier, is pH sensitive and shows swelling behavior above a critical pH due to the ionization of the acrylic acid groups. At low pH, HMCL-PAA suspensions are liquid and turbid. The binding of surfactants to HMCL-PAA, at low pH conditions, can result in significant changes on rheology and transparency of the polymeric suspensions, due to the swelling of the microgel particles. Experiments The influence of surfactants addition on the rheological properties and transparency of HMCL-PAA suspensions was determined. A systematic study was performed using different types of surfactants (ionic, non-ionic and zwitterionic). Findings The gelation efficiency of HMCL-PAA suspensions at low pH is strongly dependent on surfactant architecture: ionic surfactants are found to be much more efficient than non-ionic or zwitterionic surfactants. Ionic surfactants lead to a liquid-to-gel transition accompanied by an increase of transparency of the suspensions. Among the ionic surfactants, anionics show stronger interactions with the polymer. Also the surfactant hydrophobicity is relevant; the more hydrophobic the surfactant, the stronger is the binding to the polymer and thus the larger the particle swelling.
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| 2. |
- Bialik, Erik, et al.
(författare)
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Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution
- 2016
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society. - 1948-7185 .- 1948-7185. ; 7:24, s. 5044-5048
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.
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| 3. |
- Dias, R, et al.
(författare)
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DNA-lipid systems. A physical chemistry study
- 2002
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Ingår i: Brazilian Journal of Medical and Biological Research. - 0100-879X. ; 35:5, s. 509-522
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the interaction of polyelectrolytes with oppositely charged surfactants leads to an associative phase separation; however, the phase behavior of DNA and oppositely charged surfactants is more strongly associative than observed in other systems. A precipitate is formed with very low amounts of surfactant and DNA. DNA compaction is a general phenomenon in the presence of multivalent ions and positively charged surfaces; because of the high charge density there are strong attractive ion correlation effects. Techniques like phase diagram determinations, fluorescence microscopy, and ellipsometry were used to study these systems. The interaction between DNA and catanionic mixtures (i.e., mixtures of cationic and anionic surfactants) was also investigated. We observed that DNA compacts and adsorbs onto the surface of positively charged vesicles, and that the addition of an anionic surfactant can release DNA back into solution from a compact globular complex between DNA and the cationic surfactant. Finally, DNA interactions with polycations, chitosans with different chain lengths, were studied by fluorescence microscopy, in vivo transfection assays and cryogenic transmission electron microscopy. The general conclusion is that a chitosan effective in promoting compaction is also efficient in transfection.
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| 4. |
- Dias, Rita, et al.
(författare)
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Electrophoretic properties of complexes between DNA and the cationic surfactant cetyltrimethylammonium bromide
- 2005
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 26:15, s. 2908-2917
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Tidskriftsartikel (refereegranskat)abstract
- We use agarose gel electrophoresis to characterize how the monovalent catioinic surfactant cetyltrimethylammonium bromide (CTAB) compacts double-stranded DNA, which is detected as a reduction in electrophoretic DNA velocity. The velocity reaches a plateau at a ratio R = 1.8 of CTAB to DNA-phosphate charges, i.e., above the neutralization point, and the complexes retain a net negative charge at least up to R = 200. Condensation experiments on a mixture of two DNA sizes show that the complexes formed contain only one condensed DNA molecule each. These CTAB-DNA globules were further characterized by time-resolved measurements of their velocity inside the gel, which showed that CTAB does not dissociate during the migration but possibly upon entry into the gel. Using the Ogston-model for electrophoresis of spherical particles, the measured in-gel velocity of the globule is quantitatively consistent with CTAB having two opposite effects, reduction of both the electrophoretic charge and DNA coll size. In the case of CTAB the two effects nearly cancel, which can explain why opposite velocity shifts (globule faster than uncomplexed DNA) have been observed with some catioinic condensation agents. Dissociation of the complexes by addition of anionic surfactants was also studied. The DNA release from the globule was complete at a mixing ratio between anionic and cationic surfactants equal to 1, in agreement with equilibrium studies. Circular DNA retained its supercoiling, and this demonstrates a lack of DNA nicking in the compaction-release cycle which is important in DNA transfection and purification applications.
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| 5. |
- Agzenai, Y, et al.
(författare)
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In Situ X-ray Polymerization: From Swollen Lamellae to Polymer-Surfactant Complexes
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:4, s. 1159-1167
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the monomer diallyldimethylammonium chloride (D) on the lamellar liquid crystal formed by the anionic surfactant aerosol OT (AOT) and water is investigated, determining the lamellar spacings by SAXS and the quadrupolar splittings by deuterium NMR, as a function of the D or AOT concentrations. The cationic monomer D induces a destabilization of the AOT lamellar structure such that, at a critical concentration higher than 5 wt %, macroscopic phase separation takes place. When the monomer, which is dissolved in the AOT lamellae, is polymerized in situ by X-ray initiation, a new collapsed lamellar phase appears, corresponding to the complexation of the surfactant with the resulting polymer. A theoretical model is employed to analyze the variation of the interactions between the AOT bilayers and the stability of the lamellar structure.
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| 6. |
- Almgren, Mats, et al.
(författare)
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Dispersed lipid liquid crystalline phases stabilized by a hydrophobically modified cellulose
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:5, s. 2768-2777
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of monoolein (MO) with a commercial hydrophobically modified ethyl hydroxyethyl cellulose ether (HMEHEC) have been investigated with respect to the morphologies of the liquid crystalline nanoparticles. Only very low proportions of HMEHEC are accepted in the cubic and lamellar phases of the monoolein−water system. Due to the broad variation of composition and size of the commercial polymer, no other single-phase regions were found in the quasi-ternary system. Interactions of MO with different fractions of the HMEHEC sample induced the formation of lamellar and reversed hexagonal phases, identified from SAXD, polarization microscopy, and cryogenic TEM examinations. In excess water (more than 90 wt %) coarse dispersions are formed more or less spontaneously, containing particles of cubic phase from a size visible by the naked eye to small particles observed by cryoTEM. At high polymer/MO ratios, vesicles were frequently observed, often oligo-lamellar with inter-lamellar connections. After homogenization of the coarse dispersions in a microfluidizer, the large particles disappeared, apparently replaced by smaller cubic particles, often with vesicular attachments on the surfaces, and by vesicles or vesicular particles with a disordered interior. At the largest polymer contents no proper cubic particles were found directly after homogenization but mainly single-walled defected vesicles with a peculiar edgy appearance. During storage for 2 weeks, the dispersed particles changed toward more well-shaped cubic particles, even in dispersions with the highest polymer contents. In some of the samples with low polymer/MO ratio, dispersed particles of the reversed hexagonal type were found. A few of the homogenized samples were freeze-dried and rehydrated. Particles of essentially the same types, but with a less well-developed cubic character, were found after this treatment.
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| 7. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:1, s. 247-258
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Tidskriftsartikel (refereegranskat)abstract
- The understanding of the state of dissolution of cellulose in a certain solvent is a critical step forward in the development of new efficient solvent systems for cellulose. Nevertheless, obtaining such information is not trivial. Recently, polarization transfer solid-state NMR (PTssNMR) was shown to be a very promising technique regarding an efficient and robust characterization of the solution state of cellulose. In the present study, combining PTssNMR, microscopic techniques and X-ray diffraction, a set of alkaline aqueous systems are investigated. The addition of specific additives, such as urea or thiourea, to aqueous NaOH based systems as well as the use of an amphiphilic organic cation, is found to have pronounced effects on the dissolution efficiency of cellulose. Additionally, the characteristics of the regenerated material are strongly dependent on the dissolution system; typically less crystalline materials, presenting smoother morphologies, are obtained when amphiphilic solvents or additives are used.
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| 8. |
- Alves, Luis, et al.
(författare)
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Dissolution state of cellulose in aqueous systems. 2. Acidic solvents
- 2016
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 151, s. 707-715
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is insoluble in water but can be dissolved in strong acidic or alkaline conditions. How well dissolved cellulose is in solution and how it organizes are key questions often neglected in literature. The typical low pH required for dissolving cellulose in acidic solvents limits the use of typical characterization techniques. In this respect, Polarization Transfer Solid State NMR (PT ssNMR) emerges as a reliable alternative. In this work, combining PT ssNMR, microscopic techniques and X-ray diffraction, a set of different acidic systems (phosphoric acid/water, sulfuric acid/glycerol and zinc chloride/water) is investigated. The studied solvent systems are capable to efficiently dissolve cellulose, although degradation occurs to some extent. PT ssNMR is capable to identify the liquid and solid fractions of cellulose, the degradation products and it is also sensitive to gelation. The materials regenerated from the acidic dopes were found to be highly sensitive to the solvent system and to the presence of amphiphilic additives in solution.
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| 9. |
- Alves, Luis, et al.
(författare)
-
New Insights on the Role of Urea on the Dissolution and Thermally-Induced Gelation of Cellulose in Aqueous Alkali
- 2018
-
Ingår i: GELS. - : MDPI AG. - 2310-2861. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- The gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 degrees C for a system containing 5wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
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| 10. |
- Alves, Luis, et al.
(författare)
-
On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions
- 2015
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 483, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved.
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| 11. |
- Alves, Luis, et al.
(författare)
-
Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM, PTssNMR and DWS
- 2021
-
Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 252
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 °C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.
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| 12. |
- Alves, L., et al.
(författare)
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Unusual extraction and characterization of nanocrystalline cellulose from cellulose derivatives
- 2015
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 210, s. 106-112
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Tidskriftsartikel (refereegranskat)abstract
- Unlike many nanomaterials, nanocrystalline cellulose (CNC) is not synthesized from molecular or atomic components but rather extracted from naturally occurring cellulose. Undoubtedly, the exploitation of CNCs will become a bridge between nanoscience and natural resource products, which could play a major role in reviving the forest industry. In this work, CNC was successfully extracted from unusual sources, hydroxypropyl methylcellulose (HPMC) and carboxymethylcellulose (CMC). The extracted crystallites were purified and further characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and dynamic light scattering (DLS). The average size of the CNCs extracted from HPMC and CMC was found to be less (and with lower zeta potential) than the ones extracted from microcrystalline cellulose (MCC). On the other hand, FTIR and XRD revealed that native HPMC and CMC are unexpectedly highly crystalline and hence can be used as a source for CNCs. © 2014 Elsevier B.V.All rights reserved.
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| 13. |
- Angelescu, Daniel, et al.
(författare)
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Adsorption of Branched-Linear Polyethyleneimine-Ethylene Oxide Conjugate on Hydrophilic Silica Investigated by Ellipsometry and Monte Carlo Simulations
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:16, s. 9961-9971
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica aqueous solution interface have been studied by in situ null ellipsornetry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.
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| 14. |
- Antunes, Filipe, et al.
(författare)
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A rheological investigation of the association between a non-ionic microemulsion and hydrophobically modified PEG. Influence of polymer architecture
- 2003
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 215:1-3, s. 87-100
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Tidskriftsartikel (refereegranskat)abstract
- ydrophobically modified polymers (HM-P) typically behave as thickeners in a wide range of systems. The thickening effect in an aqueous solution of this kind of polymer depends on intermolecular hydrophobic associations and also on chain entanglements if the polymer concentration is significantly above the overlap concentration. In the present investigation a rather short end-capped polymer has been investigated at concentrations that are significantly below the overlap concentration. Despite the rather low polymer concentration, polymer chains were connected into a three-dimensional network by using microemulsion droplets as cross-linking points. The simple structure of the solution simplifies interpretations of results since chain entanglements can be expected to be of low importance and only intermolecular hydrophobic associations have to be considered. In particular the rheological response is in most cases well characterized by one single relaxation time and, then, the solution can be rationalized withi the framework of the Maxwell model. We have found that the length of the polymer chain's hydrophobic end-groups, as well as the temperature, have a large influence on dynamics of the system, while the length of the hydrophilic mid-block has a relatively small significance. On the other hand, the connectivity in the system depends critically on the microemulsion concentration. Thus, a maximum was found in viscosity as a function of volume fraction, interpreted as being due to a decrease in crosslink lifetime. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 15. |
- Antunes, Filipe E., et al.
(författare)
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Polymer-vesicle association
- 2009
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 1873-3727 .- 0001-8686. ; 147-48, s. 18-35
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Forskningsöversikt (refereegranskat)abstract
- Mixed polymer-surfactant systems have been intensively investigated in the last two decades, with the main focus on surfactant micelles as the surfactant aggregate in interaction. The main types of phase behavior, driving forces and structural/rheological effects at stake are now fairly well understood. Polymer-vesicle systems, on the other hand, have received comparatively less attention from a physico-chemical perspective. In this review, our main goal has been to bridge this gap, taking a broad approach to cover a field that is in clear expansion, in view of its multiple implications for colloid and biological sciences and in applied areas. We start by a general background on amphiphile self-assembly and phase separation phenomena in mixed polymer-surfactant solutions. We then address vesicle formation, properties and stability not only in classic lipids, but also in various other surfactant systems, among which catanionic vesicles are highlighted. Traditionally. lipid and surfactant vesicles have been studied separately, with little cross-information and comparison, giving duplication of physico-chemical interpretations. This situation has changed in more recent times. We then proceed to cover more in-depth the work done on different aspects of the associative behavior between vesicles (of different composition and type of stability) and different types of polymers, including polysaccharides. proteins and DNA. Thus. phase behavior features. effects of vesicle structure and stability, and the forces/mechanisms of vesicle-macromolecule interaction are addressed. Such association may generate gels with interesting theological properties and high potential for applications. Finally, special focus is also given to DNA, a high charge polymer. and its interactions with surfactants, and vesicles. in particular, in the context of gene transfection studies. (C) 2008 Elsevier B.V. All rights reserved
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| 16. |
- Antunes, FE, et al.
(författare)
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Ionization by pH and Anionic Surfactant Binding Gives the Same Thickening Effects of Crosslinked Polyacrylic Acid Derivatives
- 2012
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 33:9, s. 1368-1372
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Tidskriftsartikel (refereegranskat)abstract
- Physical properties of aqueous solutions of hydrophobically modified crosslinked polyacrylic acids change quite extensively as the polymer is charged up. A study is carried out concerning the similarities between two polymer ionization processes, that is, by pH increment and anionic surfactant addition. The two processes charge the polymer by distinctly different mechanisms. At sufficiently high pH the carboxylic groups of the polymer are virtually all ionized and the polymer is, therefore, fully charged. The effective repulsion among the charged groups due to the entropy of the counterions promotes an increased stiffness as well as an expansion of the polymer particles. We investigate here how the ionization and swelling will be if, instead of high pH, the polymer is at low pH conditions but associated to ionic surfactants. Surfactants associate to the polymer both in a noncooperative way by the binding of individual surfactant molecules and in a cooperative way as micelles since the polymer promotes surfactant self-assembly. This binding leads to a highly charged polymer-surfactant complex and leads to an osmotic swelling as well. The swelling and the gelation were monitored by rheology and dynamic light scattering, of polymer solutions by varying the pHs and adding ionic surfactants at low pH. The results show that ionization by surfactants and by pH lead to approximately the same gelation degree, as can be seen by similar viscosity values. Both processes result in dramatic viscosity increases, up to 8 orders of magnitude. More hydrophobic surfactants, with longer alkyl chain, are shown to be more efficient as enhancers of swelling and gelation. The network that is formed at high pH or at sufficiently high concentration of surfactant can be weakened or even disrupted if monovalent or divalent salts are added, demonstrating the role of counterion entropy.
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| 17. |
- Antunes, Filipe, et al.
(författare)
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Mechanisms behind the faceting of catanionic vesicles by polycations: Chain crystallization and segregation
- 2007
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Ingår i: The Journal of Physical Chemistry Part B. - 1520-5207. ; 111:1, s. 116-123
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Tidskriftsartikel (refereegranskat)abstract
- Vesicles composed of an anionic and a cationic surfactant, with a net negative charge, associate strongly with a hydrophobically modified polycation (LM200) and with an unmodified polycation with higher charge density (JR400), forming viscoelastic gel-like structures. Calorimetric results show that in these gels, LM200 induces a rise of the chain melting temperature (T-m) of the vesicles, whereas JR400 has the opposite effect. For both polymer-vesicle systems, the shear viscosity exhibits an inflection point at T-m, and for the LM200 system the measured relaxation times are significantly higher below T-m. The neat vesicles and the polycation-bound vesicles have a polygonal-like faceted shape when the surfactant chains in the bilayer are crystallized, as probed by cryo-transmission electron microscopy. Above T-m, the neat and the LM200-bound vesicles regain a spheroidal shape, whereas those in the JR400 system remain with a deformed faceted shape even above T-m. These shape changes are interpreted in terms of different mechanisms for the polymer-vesicle interaction, which seem to be highly dependent on polymer architecture, namely charge density and hydrophobic modification. A crystallization-segregation mechanism is proposed for the LM200-vesicle system, while, for the JR400-vesicle one, charge polarization-lateral segregation effects induced by the polycation in the catanionic bilayer are envisaged.
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| 18. |
- Antunes, Filipe, et al.
(författare)
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Mixed systems of hydrophobically modified polyelectrolytes: Controlling rheology by charge and hydrophobe stoichiometry and interaction strength
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:22, s. 10188-10196
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Tidskriftsartikel (refereegranskat)abstract
- Rheology and phase separation were investigated for aqueous mixtures of two oppositely charged hydrophobically modified polyelectrolytes. The typical phase separation, normally seen for oppositely charged polymer mixtures, is dramatically reduced by the presence of hydrophobic modification, and phase separation is only detected close to the point of charge neutralization. While the two polyelectrolytes separately can give high viscosities and a gel-like behavior, a pronounced maximum in viscosity and storage modulus with the mixing ratio of the polyelectrolytes is observed; the maximum is located between the points of charge and hydrophobe stoichiometry and reflects a combination of hydrophobic and electrostatic association. Lowering the charge density of the anionic polymer leads to a strengthened association at first, but at lower charge densities there is a weakened association due to the onset of phase separation. The strength of the electrostatic interaction was modified by adding salt. Increased ionic strength can lead to phase separation and to increased or decreased viscosity depending on the polyelectrolyte mixing ratio.
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| 19. |
- Antunes, Filipe, et al.
(författare)
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Network formation of catanionic vesicles and oppositely charged polyelectrolytes. Effect of polymer charge density and hydrophobic modification
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:11, s. 4647-4656
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Tidskriftsartikel (refereegranskat)abstract
- In nonequimolar solutions of a cationic and an anionic surfactant, vesicles bearing a net charge can be spontaneously formed and apparently exist as thermodynamically stable aggregates. These vesicles can associate strongly with polymers in solution by means of hydrophobic and/or electrostatic interactions. In the current work, we have investigated the rheological and microstructural properties of mixtures of cationic polyelectrolytes and net anionic sodium dodecyl sulfate/didodecyldimethylammonium bromide vesicles. The polyelectrolytes consist of two cationic cellulose derivatives with different charge densities; the lowest charge density polymer contains also hydrophobic grafts, with the number of charges equal to the number of grafts. For both systems, polymer-vesicle association leads to a major increase in viscosity and to gel-like behavior, but the viscosity effects are more pronounced for the less charged, hydrophobically modified polymer. Evaluation of the frequency dependence of the storage and loss moduli for the two systems shows further differences in behavior: while the more long-lived cross-links occur for the more highly charged hydrophilic polymer, the number of cross-links is higher for the hydrophobically modified polymer. Microstructure studies by cryogenic transmission electron microscopy indicate that the two polymers affect the vesicle stability in different ways. With the hydrophobically modified polymer, the aggregates remain largely in the form of globular vesicles and faceted vesicles (polygon-shaped vesicles with largely planar regions). For the hydrophilic polycation, on the other hand, the surfactant aggregate structure is more extensively modified: first, the vesicles change from a globular to a faceted shape; second, there is opening of the bilayers leading to holey vesicles and ultimately to considerable vesicle disruption leading to planar bilayer, disklike aggregates. The faceted shape is tentatively attributed to a crystallization of the surfactant film in the vesicles. It is inferred that a hydrophobically modified polyion with relatively low charge density can better stabilize vesicles due to formation of molecularly mixed aggregates, while a hydrophilic polyion with relatively high charge density associates so strongly to the surfactant films, due to strong electrostatic interactions, that the vesicles are more perturbed and even disrupted.
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| 20. |
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| 21. |
- Barreleiro, Paula, et al.
(författare)
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Mechanism of formation of DNA-cationic vesicle complexes
- 2003
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 122, s. 191-201
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Tidskriftsartikel (refereegranskat)abstract
- Cationic vesicles and DNA form complexes that are promising gene delivery systems. Despite the increasing number of publications on their morphology and structure, the mechanism leading to their formation is not yet understood due to a lack of kinetic data. In the present study the kinetics of the interaction between DNA and cationic vesicles were followed using stopped-flow turbidity and small-angle neutron scattering techniques. The neutron real-time experiments were performed on a high-flux diffractometer, the D22 at the ILL, using a stopped-flow set-up. Extruded mixed vesicles of dimethyldioctadecylammonium bromide (DODAB) with various amounts of dioleoylphosphatidylethanolamine (DOPE) were investigated at 25degreesC. The results show that the transition from unilamellar vesicles to a multilamellar structure upon DNA addition occurs in three steps. The first step, on the millisecond time scale, is currently not accessible to neutron scattering but was observed by stopped-flow turbidity and fluorescence experiments. The second step, on a time scale of seconds, corresponds to the formation of an intermediate with a locally cylindrical structure. As time progresses this unstable intermediate evolves to a multilamellar structure, on a time scale of minutes. An understanding of the mechanisms behind the DNA cationic vesicle complex formation event will allow the production of more homogeneous, efficient delivery systems in pharmaceutically acceptable forms.
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| 22. |
- Barreleiro, Paula, et al.
(författare)
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The kinetics of DNA-cationic vesicle complex formation
- 2003
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:25, s. 6208-6213
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Tidskriftsartikel (refereegranskat)abstract
- Stopped-flow fluorescence studies were performed to investigate the kinetics of formation of complexes between DNA and cationic vesicles. We followed the kinetics as a function of charge ratio and lipid vesicle composition. Binary mixtures of a saturated cationic lipid, dioctadecyldimethlammonium bromide (DODAB), and a zwitterionic lipid, dioleoylphosphatidylethanolamine (DOPE), were used to prepare small unilamellar vesicles at 25 degreesC. The binding followed first-order reactions and occurred stepwise. The results presented indicate the existence of a three-step mechanism for cationic vesicle "binding" to DNA: first DNA rapidly ads rbs onto the oppositely charged membrane surface (milliseconds), and thereafter, on a longer time scale (seconds), the formed DNA-lipid complex continues to aggregate and grow; a third step is also observed, which seems to be due to rearrangement of the complex with a further change of the DNA conformation. The time constant of each step was determined by the relative amounts of DNA and cationic vesicles and the composition of the lipid bilayer of the vesicles.
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| 23. |
- Berezhnoy, Nikolay V., et al.
(författare)
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Supramolecular Organization in Self-Assembly of Chromatin and Cationic Lipid Bilayers is Controlled by Membrane Charge Density
- 2012
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 13:12, s. 4146-4157
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Tidskriftsartikel (refereegranskat)abstract
- In this work we have investigated the structures of aggregates formed in model systems of dilute aqueous mixtures of "model chromatin" consisting of either recombinant nucleosome core particles (NCPs) or nucleosome arrays consisting of 12 NCPs connected with 30 bp linker DNA, and liposomes made from different mixtures of cationic and zwitterionic lipids, 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The aggregates formed were characterized using different optical microscopy methods and small-angle X-ray scattering (SAXS), and the results are discussed in terms of the competing intermolecular interactions among the components. For a majority of the samples, the presence of lamellar structures could be identified. Ir. samples with high fractions of DOTAP in the liposomes, well-defined lamellar structures very similar to those formed by the corresponding lipid mixtures and DNA alone (i.e., without histone proteins) were observed; in these aggregates, the histones are expelled from the model chromatin. The findings suggest that, with liposomes containing large fractions of cationic lipid, the dominating driving force for aggregation is the increase in translational entropy from the release of counterions, whereas with lower fractions of the cationic lipid, the entropy of mixing of the lipids within the bilayers results in a decreased DNA-lipid attraction.
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| 24. |
- Bergh, Jonas, et al.
(författare)
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Tailored fluorouracil, epirubicin, and cyclophosphamide compared with marrow-supported high-dose chemotherapy as adjuvant treatment for high-risk breast cancer : A randomised trial
- 2000
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 356:9239, s. 1384-1391
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Tidskriftsartikel (refereegranskat)abstract
- Background: Chemotherapy drug distribution varies greatly among individual patients. Therefore, we developed an individualised fluorouracil, epirubicin, cyclophosphamide (FEC) regimen to improve outcomes in patients with high-risk early breast cancer. We then did a randomised trial to compare this individually tailored FEC regimen with conventional adjuvant chemotherapy followed by consolidation with high-dose chemotherapy with stem-cell support. Methods: 525 women younger than 60 years of age with high-risk primary breast cancer were randomised after surgery to receive nine cycles of tailored FEC to haematological equitoxicity with granulocyte colony-stimulating factor (G-CSF) support (n=251), or three cycles of FEC at standard doses followed by high-dose chemotherapy with cyclophosphamide, thiotepa, and carboplatin (CTCb), and peripheral-blood stem-cell or bone-marrow support (n=274). Both groups received locoregional radiation therapy and tamoxifen for 5 years. The primary outcome measure was relapse-free survival, and analysis was by intention to treat. Findings: At a median follow-up of 34.3 months, there were 81 breast-cancer relapses in the tailored FEC group versus 113 in the CTCb group (double triangular method p=0.04). 60 deaths occurred in the tailored FEC group and 82 in the CTCb group (log-rank p=0.12). Patients in the CTCb group experienced more grade 3 or 4 acute toxicity compared with the tailored FEC group (p<0.0001). Two treatment-related deaths (0.7%) occurred in the CTCb group. Six patients in the tailored FEC group developed acute myeloid leukaemia and three developed myelodysplastic syndrome. Interpretation: Tailored FEC with G-CSF support resulted in a significantly improved relapse-free survival and fewer grade 3 and 4 toxicities compared with marrow-supported high-dose chemotherapy with CTCb as adjuvant therapy of women with high-risk primary breast cancer.
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| 25. |
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| 26. |
- Bilalov, Azat, et al.
(författare)
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A cubic DNA-lipid complex
- 2009
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 5:20, s. 3827-3830
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Tidskriftsartikel (refereegranskat)abstract
- DNA-lipid interactions play a significant biological and biotechnological role but remain poorly understood. In investigations of mixed lipid-DNA systems a novel bicontinuous cubic phase, composed of lecithin, water and dodecyltrimethylammonium with DNA as the counterion (DNA-DTA), was identified. The cubic phase is stable only in a narrow composition range and in the temperature range 20-65 degrees C. The samples have a transparent rubber-like morphology, are rigid, optically isotropic and show a shear-induced optical birefringence. The NMR spectrum consists of a broadened singlet. Upon increasing the lecithin content the phase transforms to lamellar phase. The liquid crystal (LC) is determined to be in Ia3d symmetry from investigations by small angle X-ray scattering (SAXS). Model calculations indicate that the cubic phase is normal, i.e. being composed of DNA chains and water incorporated in polar group bilayers separating two hydrophobic domains containing hydrocarbon tails of lipids.
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| 27. |
- Bilalov, Azat, et al.
(författare)
-
Complexation between DNA and surfactants and lipids: phase behavior and molecular organization
- 2012
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:43, s. 11022-11033
-
Forskningsöversikt (refereegranskat)abstract
- The interaction between DNA and various cationic species, e. g. cationic surfactant (CS), has a broad biological and biotechnological significance. In the cell nucleus as well as in transfection formulations, other species, mainly zwitterionic lipids, are also present but their exact role needs elucidation. A closer investigation of the stability of structures formed as well as the molecular arrangements is hampered by the complexity of the systems with respect to the number of components. A powerful way for reducing the number of components is to base studies on the stoichiometric (1 : 1) compound CSDNA, where the simple (sodium) counterions have been ion-exchanged by a cationic amphiphile ion. CSDNA is typically insoluble in water but is able to form liquid crystalline phases in aqueous mixtures with many additives capable of associating with the amphiphilic counterions (alcohols, non-ionic surfactants, lipids, cyclodextrins, etc.). Mixtures of CSDNA with a number of components have been investigated in detail with respect to phase behavior. The phase diagrams demonstrate a rich liquid crystallinity. The organization of DNA and the surfactant-lipid self-assemblies is controlled by different factors for different cases, mainly (i) the lipophilic characteristics of the components, (ii) the [CSDNA]/[amphiphile] ratio and (iii) DNA packing constraints, due to the large persistence length. A summary of phase diagrams is presented together with structural investigations based mainly on small-angle X-ray scattering. The role of DNA rigidity is illustrated in a comparison with analogous systems based on flexible polyanions.
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| 28. |
- Bilalov, Azat, et al.
(författare)
-
DNA-lipid self-assembly: phase behavior and phase structures of a DNA-surfactant complex mixed with lecithin and water
- 2011
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:2, s. 730-742
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Tidskriftsartikel (refereegranskat)abstract
- The co-assembly of DNA and lipids has broad implications, from the structure of the cell nucleus to gene delivery formulations. To progress in the fundamental understanding of DNA-lipid interactions the self-assembly behavior of a cationic surfactant (dodecyltrimethylammonium, DTA) with DNA as a counterion in mixtures of water and lecithin was investigated. The phase diagram was established and the different regions of the phase diagram characterized with respect to the microstructure by H-2 NMR, small-angle X-ray scattering (SAXS), and other techniques. Three liquid crystalline (LC) phases were identified: cubic, lamellar and hexagonal. All LC phases are stable in the temperature range 20-65 degrees C. The cubic phase is stable only in a narrow composition range. Upon increasing the lecithin content the phase transforms to the lamellar phase via an extended biphasic area. Drying of the lamellar phase leads to the formation of hexagonal phase. Adding salt to the ternary mixtures causes a slight increase in the unit cell dimension of the LC phases. Very high ionic strength may lead to DNA release from liquid crystals and the formation of DNA free liquid crystalline phases. In particular we observe a coexistence of two lamellar phases. One contains DNA and one being essentially free of DNA.
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| 29. |
- Bilalov, Azat, et al.
(författare)
-
DNA with amphiphilic counterions: tuning colloidal DNA with cyclodextrin
- 2012
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:18, s. 4988-4994
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Tidskriftsartikel (refereegranskat)abstract
- DNA compaction in vitro can be controlled by lipids. Cyclodextrins can disperse lipids in the form of water soluble inclusion complexes, thus tuning their self-assembly. To progress in the fundamental understanding of double-stranded (ds) DNA-lipid-cyclodextrin interactions, the aqueous phase behavior of a cationic surfactant (dodecyltrimethylammonium, DTA)-dsDNA compound in the presence of cyclodextrin (hydroxypropyl-beta-cyclodextrin, HPbCD, or beta-cyclodextrin, beta CD) was investigated. beta CD has a low water solubility due to the formation of stable crystals. The more hydrophobic HPbCD, on the other hand, is highly water soluble because the bulky HP substitution destabilizes the crystalline state. Both beta CD and HP beta CD form strong inclusion complexes with DTA, with an essentially infinite binding constant, and the DNA self-assembly behavior is controlled by the molar ratio R [DTA]/[CD], in addition to the DNA concentration. DTA-DNA can be solubilized in the isotropic liquid phase of water and HPbCD when R <= 1. This phase is micelle free and from the sharp phase boundary at R 1 it is concluded that HPbCD does not associate with DNA, only with DTA. Increasing the DTA-DNA concentration, keeping R < 1, leads to the formation of a liquid crystal with 2D hexagonally ordered DNA. With a further increase of the DTA-DNA and R > 1.5-2, a second, novel, anisotropic phase is formed that we identify as having a tetragonal lattice. In this phase, the DNA duplexes are still parallel but with a simple square rather than a hexagonal packing. The periodicity in the direction of the DNA duplexes is coupled to the DNA pitch length, 3.3 nm. With beta CD, the phase behavior is less rich because of the poor water solubility of the cyclodextrin. Here, only a very small hexagonal phase region is formed in the center of the ternary phase diagram, with R similar or equal to 1.
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| 30. |
- Bilalov, Azat, et al.
(författare)
-
Mixing oil and water by a DNA-based surfactant
- 2004
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:39, s. 15408-15414
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly behavior of a cationic surfactant (dodecyltrimethylammonium) with DNA as counterion in mixtures of water and decanol was investigated. The phase diagram was established and the different regions of the phase diagram characterized with respect to microstructure by H-2 NMR (D2O), small-angle X-ray scattering (SAXS), and other techniques. The DNA-cationic surfactant aggregate is virtually insoluble in water but shows a high solubility in decanol; in decanol, highly viscous solutions/rubberlike solid material is found. In the presence of both solvents, there is a formation of liquid crystalline phases. Both lamellar and reversed hexagonal phases are found, the former favored by higher water contents, the latter by higher concentrations of decanol. The liquid crystalline phases are in equilibrium, via two-phase and three-phase regions, with the essentially pure components.
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| 31. |
- Bo, A D, et al.
(författare)
-
Ethyl(hydroxyethyl)cellulose-sodium dodecanoate interaction investigated by surface tension and electrical conductivity techniques
- 2005
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 256:2-3, s. 171-180
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of ethyl (hydroxyethyl)cellulose (EHEC) and sodium dodecanoate (SDoD) were investigated using surface tension, conductivity and transmittance measurements. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration (cac) and saturation of the polymer by SDoD (psp) were determined from the plots of surface tension and specific conductivity versus surfactant concentration. The transmittance versus [SDoD] profiles exhibited bands that, in conjunction with conductivity and surface tension data, gave support to the explanation of the behavior of EHEC-SDoD-water solutions. Transmittance bands determined in the presence of EHEC and surfactant are sensitive to the process of surfactant to polymer binding. In this process, a discontinuity point represented by a second broader peak in the transmittance plots was identified, implying a slight inhibition of the breakdown of the network process. This is explained as a kind of intermediate re-structural network of the complexes produced by the formation of regular SDoD micelles. It was demonstrated that the second conductivity breakpoint marks the polymer saturation by surfactant clusters, and the effect of the EHEC concentration on the process of binding can be described by a linear correlation when the psp breakpoint is plotted against the polymer concentration. (c) 2005 Elsevier B.V. All rights reserved.
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| 32. |
- Braem, Alan, et al.
(författare)
-
Influence of DNA adsorption and DNA/cationic surfactant coadsorption on the interaction forces between hydrophobic surfaces
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:15, s. 6407-6413
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Tidskriftsartikel (refereegranskat)abstract
- The forces between hydrophobic surfaces with physisorbed DNA are markedly and irreversibly altered by exposure to DNA/cetyltrimethylammonium bromide (CTAB) mixtures. In this colloidal probe atomic force microscopy study of the interactions between a hydrophobic polystyrene particle and an octadecyl-trimethylethoxysilane-modified mica surface in sodium bromide solutions, we measure distinct changes in colloidal forces depending on the existence and state of an adsorbed layer of DNA or CTAB-DNA complexes. For bare hydrophobic surfaces, a monotonically attractive approach curve and very large adhesion are observed. When DNA is adsorbed at low bulk concentrations, a long-range repulsive force dominates the approach, but on retraction some adhesion persists and DNA bridging is clearly observed. When the DNA solution is replaced with a CTAB-DNA mixture at relative low CTAB concentration, the length scale of the repulsive force decreases, the adhesion due to hydrophobic interactions greatly decreases, and bridging events disappear. Finally, when the surface is rinsed with NaBr solution, the length scale of the repulsive interaction increases modestly, and only a very tiny adhesion remains. These pronounced changes in the force behavior are consistent with CTAB-induced DNA compaction accompanied by increased DNA adsorption, both of which are partially irreversible.
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| 33. |
- Cárdenas, Marité, et al.
(författare)
-
DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:20, s. 8597-8603
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption and formation of DNA and cationic surfactant complexes at the silica-aqueous interface have been studied by ellipsometry. The interaction between the DNA-surfactant complexes at the mica-aqueous interface has been determined by the interferometric surface force apparatus. Adsorption was as expected not observed on negatively charged hydrophilic surfaces for DNA and when DNA-cationic surfactant complexes were negatively charged. However, adsorption was observed when there is an excess of cationic surfactant, just below the point of phase separation. The adsorption process requires hours to reach steady state. The adsorbed layer thickness is large at low surface coverage but becomes more compact and thinner at high coverage. A long-range repulsive force was observed between adsorbed layers of DNA-cationic surfactant complexes, which was suggested to be of both electrostatic and steric origin. The forces were found to be dependent on the equilibration time and the experimental pathway.
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| 34. |
- Cárdenas, Marité, et al.
(författare)
-
DNA and cationic surfactants at solid surfaces
- 2005
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 270-271, s. 33-43
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of DNA at different types of interfaces and how the formed structures DNA at an interface could be affected by cationic surfactant has been studied. Particular attention was paid to how the type of cationic surfactant and DNA (single or double stranded and length) affects the compaction/decompaction of DNA. Adsorption of DNA-cationic surfactant complexes is determined by a delicate balance of DNA-surface, cationic surfactant-surface, and cationic surfactant-DNA interactions. DNA do not adsorb on hydrophilic negatively charged surfaces due to effective electrostatic repulsion between DNA and the surfacs. However, the interaction between DNA cationic surfactant ions leads to a substantial adsorption of the formed DNA-cationic surfactant complex once the charge density of both the DNA macromolecule and the surface is sufficiently decreased. On hydrophobic surfaces, where both DNA and cationic surfactant interact with the surface, the presence of the cationic surfactant leads to a considerable increase in adsorbed amount and a significant layer compaction of DNA. The stability of the mixed adsorbed layer largely depends on the strength of the interactions between DNA and the cationic surfactant, as well as between the surface and the cationic surfactant. DNA interacts with small latex particles in a similar way as to the macroscopic hydrophobic flat surfaces. (c) 2005 Elsevier B.V All rights reserved.
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| 35. |
- Cárdenas, Marité, et al.
(författare)
-
DNA compaction at hydrophobic surfaces induced by a cationic amphiphile
- 2003
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:19, s. 7712-7718
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Tidskriftsartikel (refereegranskat)abstract
- Cetyltrimethylammonium bromide (CTAB) induces partially irreversible compaction of DNA-adsorbed layers on hydrophobic silica. Additionally, there is a synergistic increase in the adsorbed amount when both CTAB and DNA are present as compared to the surface excess concentration of either of the individual components. In this study of the DNA adsorption and DNA-CTAB coadsorption by ellipsometry, emphasis has been placed on the DNA molecular weight as well as its conformation (single and double stranded). The DNA molecular weight and conformation have a large effect on the surfactant-free DNA adsorption behavior but not on he mixed DNA-CTAB adsorption behavior. Comparison between interfacial and bulk complexation has been made where possible. The DNA-CTAB complexes at the interface are neutral despite the large excess of DNA in the bulk. The final structure of the adsorbed layer was found to be dependent on the history of complex formation and DNA size.
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| 36. |
- Cárdenas, Marité, et al.
(författare)
-
DNA compaction by cationic surfactant in solution and at polystyrene particle solution interfaces: a dynamic light scattering study
- 2004
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 6:7, s. 1603-1607
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Tidskriftsartikel (refereegranskat)abstract
- The effect of cationic surfactant on the compaction of DNA both in bulk solution and on polystyrene particles has been studied by dynamic light scattering. DNA undergoes a transition from a semiflexible coil to a more compact globule in aqueous solution as a consequence of cationic surfactant binding. Thus the hydrodynamic radius of DNA decreases from 107 nm to about 50 nm in the presence of cationic surfactant. Such compaction is also observed on DNA coated polystyrene particles. In this case, the hydrodynamic layer thickness of DNA coated particles is reduced from 36 to 5 nm in the presence of cetyltrimethylammonium bromide.
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| 37. |
- Cárdenas, Marité, et al.
(författare)
-
DNA compaction onto hydrophobic surfaces by different cationic surfactants
- 2005
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:14, s. 6495-6502
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Tidskriftsartikel (refereegranskat)abstract
- DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.
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| 38. |
- Cárdenas, Marité, et al.
(författare)
-
Interaction between DNA and charged colloids could be hydrophobically driven
- 2005
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 6:2, s. 832-837
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of DNA with amino-functionalized polystyrene particles has been studied by using a dynamic light scattering (DLS) technique. In 10 mM NaBr solution the particles have a hydrodynamic radius of 76 nm and the DNA macromolecule investigated (double stranded) has a hydrodynamic radius of 107 nm. At very low DNA concentrations, DNA adopts a flat conformation on the particle surface. If the DNA concentration is increased above 0.1 mu g/mL, the thickness of the DNA layer increases, suggesting the presence of large loops and tails. Although the particles contain primary amino groups, they have a negative net charge under the conditions used in this work. Thus, the driving force for DNA adsorption is not of electrostatic origin but rather due to a hydrophobic effect. Addition of cationic surfactant to the DNA-precoated amino functionalized particles induces changes in the adsorbed layer conformation, in agreement with the coadsorption of cationic surfactant.
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| 39. |
- Cárdenas, Marité, et al.
(författare)
-
SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles
- 2005
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:8, s. 3578-3583
-
Tidskriftsartikel (refereegranskat)abstract
- The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was observed at a negative-to-positive charge ratio far below the phase separation region, at a negative-to-positive charge ratio of 18. Additionally, large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addition of a cationic surfactant to the DNA-coated latex particles at a negative-to-positive charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the negative-to-positive charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.
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| 40. |
- Cárdenas, Marité, et al.
(författare)
-
The interaction between DNA and cationic lipid films at the air-water interface
- 2005
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 286:1, s. 166-175
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air-aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the &UPi;-A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded-liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson-Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer. © 2005 Elsevier Inc. All rights reserved.
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| 41. |
- Carlstedt, Jonas, et al.
(författare)
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Condensation and decondensation of DNA by cationic surfactant, spermine, or cationic surfactant–cyclodextrin mixtures : macroscopic phase behavior, aggregate properties, and dissolution mechanisms
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:21, s. 7976-7989
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Tidskriftsartikel (refereegranskat)abstract
- The macroscopic phase behavior and other physicochemical properties of dilute aqueous mixtures of DNA and the cationic surfactant hexadecyltrimethylammounium bromide (CTAB), DNA and the polyamine spermine, or DNA, CTAB, and (2-hydroxypropyl)-β-cyclodextrin (2HPβCD) were investigated. When DNA is mixed with CTAB we found, with increasing surfactant concentration, (1) free DNA coexisting with surfactant unimers, (2) free DNA coexisting with aggregates of condensed DNA and CTAB, (3) a miscibility gap where macroscopic phase separation is observed, and (4) positively overcharged aggregates of condensed DNA and CTAB. The presence of a clear solution beyond the miscibility gap cannot be ascribed to self-screening by the charges from the DNA and/or the surfactant; instead, hydrophobic interactions among the surfactants are instrumental for the observed behavior. It is difficult to judge whether the overcharged mixed aggregates represent an equilibrium situation or not. If the excess surfactant was not initially present, but added to a preformed precipitate, redissolution was, in consistency with previous reports, not observed; thus, kinetic effects have major influence on the behavior. Mixtures of DNA and spermine also displayed a miscibility gap; however, positively overcharged aggregates were not identified, and redissolution with excess spermine can be explained by electrostatics. When 2HPβCD was added to a DNA–CTAB precipitate, redissolution was observed, and when it was added to the overcharged aggregates, the behavior was essentially a reversal of that of the DNA–CTAB system. This is attributed to an effectively quantitative formation of 1:1 2HPβCD–surfactant inclusion complexes, which results in a gradual decrease in the concentration of effectively available surfactant with increasing 2HPβCD concentration.
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| 42. |
- Carlstedt, Jonas, et al.
(författare)
-
Cyclodextrin-Surfactant Coassembly Depends on the Cyclodextrin Ability To Crystallize.
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:5, s. 2387-2394
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Tidskriftsartikel (refereegranskat)abstract
- Full equilibrium phase diagrams are presented for two ternary systems composed of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), water (D(2)O), and a cyclodextrin, either β-cyclodextrin (β-CD) or (2-hydroypropyl)-β-cyclodextrin (2HPβCD). (2)H NMR, SAXS, WAXS, and visual examination were used to determine the phase boundaries and characterize the nature of the phases formed. Additionally, diffusion (1)H NMR was used to investigate parts of the diagrams. The water solubility of 2HPβCD is 80% (w/w), whereas it is only 1.85% (w/w) for β-CD. Solubility increases for both species upon complexation with DTAB; while the increase is minute for 2HPβCD, it is dramatic for β-CD. Both systems displayed an isotropic liquid solution (L(1)) one-phase region, the extension of which differs extensively between the two systems. Additionally, the DTAB:2HPβCD:water system also comprised a normal hexagonal (H(1)) area, which was not found for the DTAB:β-CD:water system. In the DTAB:β-CD:water system, on the other hand, we found cocrystallization of DTAB and β-CD. From this work we conclude that DTAB and CD molecules form 1:1 inclusion complexes with high affinities. Moreover, we observed indications of an association of 2HPβCD to DTAB micelles in the isotropic solution phase, which was not the case for β-CD and DTAB micelles. This is, to our knowledge, the first complete phase diagrams of surfactant-CD mixtures; as a novel feature it includes the observation of cocrystallization at high concentrations.
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| 43. |
- Carlstedt, Jonas, et al.
(författare)
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Release of DNA from surfactant complexes induced by 2-hydroxypropyl-beta-cyclodextrin.
- 2010
-
Ingår i: International Journal of Biological Macromolecules. - : Elsevier BV. - 1879-0003 .- 0141-8130. ; 46:2, s. 153-158
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Tidskriftsartikel (refereegranskat)abstract
- Decompaction of DNA-CTA self-assembled complexes by 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD) was studied and the results were compared with beta-CD. Different degrees of 2-HP substitution (0.6, 0.8 and 1.0, respectively) were used and the decompaction was successful with all degrees of substitution. Fluorescence microscopy, steady state fluorescence spectroscopy, density and sound velocity measurements, thermal melting and circular dichroism were used. Compared to previous work using alpha- and beta-CD, the fluorescence spectroscopy results showed that the 2-HP-substituted CDs more efficiently released DNA into solution. Furthermore, dissociation of macroscopically phase separated DNA-CTA complexes was achieved upon addition of 2-HP-beta-CD and the results gave strong indications on the non-equilibrium nature of the system. The globule-to-coil transition was not found to proceed through a coexistence region, which seems to be a general phenomenon in DNA decompaction using CDs.
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| 44. |
- Carmen Moran, M., et al.
(författare)
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Counter-ion effect on surfactant-DNA gel particles as controlled DNA delivery systems
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:11, s. 3200-3211
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Tidskriftsartikel (refereegranskat)abstract
- The ability to entrap drugs within vehicles and subsequently release them has led to new treatments for a number of diseases. Based on an associative phase separation and interfacial diffusion approach, we developed a way to prepare DNA gel particles without adding any kind of cross-linker or organic solvent. Among the various agents studied, cationic surfactants offered particularly efficient control for encapsulation and DNA release from these DNA gel particles. The driving force for this strong association is the electrostatic interaction between the two components, as induced by the entropic increase due to the release of the respective counter-ions. However, little is known about the influence of the respective counter-ions on this surfactant-DNA interaction. Here we examined the effect of different counter-ions on the formation and properties of the DNA gel particles by mixing DNA (either single-(ssDNA) or double-stranded (dsDNA)) with the single chain surfactant dodecyltrimethylammonium (DTA). In particular, we used as counter-ions of this surfactant the hydrogen sulfate and trifluoromethane sulfonate anions and the two halides, chloride and bromide. Effects on the morphology of the particles obtained, the encapsulation of DNA and its release, as well as the haemocompatibility of these particles are presented, using counter-ion structure and DNA conformation as controlling parameters. Analysis of the data indicates that the degree of counter-ion dissociation from the surfactant micelles and the polar/hydrophobic character of the counter-ion are important parameters in the final properties of the particles. The stronger interaction with amphiphiles for ssDNA than for dsDNA suggests the important role of hydrophobic interactions in DNA.
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| 45. |
- Carmen Moran, M., et al.
(författare)
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DNA gel particles from single and double-tail surfactants: supramolecular assemblies and release characteristics
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:5, s. 2001-2010
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Tidskriftsartikel (refereegranskat)abstract
- Cationic surfactants with one alkyl chain have offered a particularly efficient control of the properties of DNA-based particles. However, most transfection lipids do not form micelles as single-chain surfactants. In this work, the formation of DNA gel particles mixing DNA (either single- (ssDNA) or double-stranded (dsDNA)) with the vesicle-forming double chain surfactant didodecyldimethylammonium bromide (DDAB) is described. For comparative purposes, the formation of DNA gel particles using the single chain surfactant dodecyltrimethylammonium bromide (DTAB) has been investigated. Results on the encapsulation of DNA and its release are strongly dependent on the surfactant structure. DDAB-DNA gel particles have been shown to form ordered multi-vesicular assemblies which resemble the architecture of biological tissues. The characteristic sizes and shapes of the resulting structures strongly depend on the secondary structure of the DNA. Some features about the DNA-vesicle interaction involved in these particles have been deduced from direct optical, fluorescence and electron microscopy observations.
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| 46. |
- Carmen Moran, M., et al.
(författare)
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Novel Biocompatible DNA Gel Particles
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:13, s. 10606-10613
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants with the cationic functionality based on an amino acid structure have been used to prepare novel biocompatible devices for the controlled encapsulation and release of DNA. We report here the formation of DNA gel particles mixing DNA (either single- (ssDNA) or double-stranded (dsDNA)) with two different single-chain amino acid-based surfactants: arginine-N-lauroyl amide dihydrochloride (A LA) and N-alpha-lauroyl-arginine-methyl ester hydrochloride (LAM). The degree of DNA entrapment, the swelling/deswelling behavior, and the DNA release kinetics have been studied as a function of both the number of charges in the polar head of the amino acid-based surfactant and the secondary structure of the nucleic acid. Analysis of the data indicates a stronger interaction of ALA with DNA, compared with LAM, mainly at to the double charge carried by the former surfactant compared to the singly charged headgroup of the latter species. The stronger interaction with amphiphiles for ssDNA compared with dsDNA suggests the important role of hydrophobic interactions in DNA. Data on the microstructure of the complexes obtained from small-angle X-ray scattering (SAXS) of the particles strongly suggests a hexagonal packing. It was found that, the shorter the lattice parameter, the stronger the surfactant-DNA in and the slower the DNA release kinetics. Complexation and neutralization of DNA on the DNA gel particles was confirmed by agarose gel electrophoresis measurements.
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| 47. |
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| 48. |
- Costa, Carolina, et al.
(författare)
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Emulsion Formation and Stabilization by Biomolecules : The Leading Role of Cellulose.
- 2019
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).
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| 49. |
- Costa, Carolina, et al.
(författare)
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Interfacial activity and emulsion stabilization of dissolved cellulose
- 2019
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Ingår i: Journal of Molecular Liquids. - : Elsevier B.V.. - 0167-7322 .- 1873-3166. ; 292
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Tidskriftsartikel (refereegranskat)abstract
- Some aspects of the interfacial behavior of cellulose dissolved in an aqueous solvent were investigated. Cellulose was found to significantly decrease the interfacial tension (IFT) between paraffin oil and 85 wt% phosphoric acid aqueous solutions. This decrease was similar in magnitude to that displayed by non-ionic cellulose derivatives. Cellulose's interfacial activity indicated a significant amphiphilic character and that the interfacial activity of cellulose derivatives is not only related to the derivatization but inherent in the cellulose backbone. This finding suggests that cellulose would have the ability of stabilizing dispersions, like oil-in-water emulsions in a similar way as a large number of cellulose derivatives. In its molecularly dissolved state, cellulose proved to be able to stabilize emulsions of paraffin in the polar solvent on a short-term. However, long-term stability against drop-coalescence was possible to achieve by a slight change in the amphiphilicity of cellulose, effected by a slight increase in pH. These emulsions exhibited excellent stability against coalescence/oiling-off over a period of one year. Ageing of the cellulose solution before emulsification (resulting in molecular weight reduction) was found to favour the creation of smaller droplets.
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| 50. |
- Costa, Carolina, et al.
(författare)
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Lignin enhances cellulose dissolution in cold alkali
- 2021
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 274
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.
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