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- Dias, Rita, et al.
(författare)
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DNA and surfactants in bulk and at interfaces
- 2004
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 250:1-3, s. 115-131
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Tidskriftsartikel (refereegranskat)abstract
- Recent investigations of the DNA interactions with cationic surfactants and catanionic Mixtures are reviewed. Several techniques have been used such as fluorescence microscopy, dynamic light scattering, electron microscopy, and Monte Carlo simulations. The conformational behaviour of large DNA molecules in the presence of cationic surfactant was followed by fluorescence microscopy and also by dynamic light scattering. These techniques were in good agreement and it was possible to observe a discrete transition from extended coils to collapsed globules and their coexistence for intermediate amphiphile concentrations. The dependence on the surfactant alkyl chain was also monitored by fluorescence microscopy and, as expected, lower concentrations of the more hydrophobic surfactant were required to induce DNA compaction, although an excess of positive charges was still required. Monte Carlo simulations on the compaction of a medium size polyanion with shorter polycations were performed. The polyanion chain suffers a sudden collapse as a function of the concentration of condensing agent, and of the number of charges on the polycation molecules. C Further increase in the concentration increases the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small-degree of intrachain segregation, which can explain the excess of positive charges necessary to compact DNA. Dissociation of the DNA-cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length: lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA. were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants. like vesicles, from the phase behaviour of the mixed surfactant systems. Studies on the interactions between DNA and catanionic mixtures were also performed. It was observed that DNA does not interact with negatively charged vesicles, even though they carry positive amphiphiles; however, in the presence of positively charged vesicles, DNA molecules compact and adsorb on their surface. Finally Monte Carlo simulations were performed on the adsorption of a polyelectrolyte on catanionic surfaces. It was observed that the mobile charges in the surface react to the presence of the polyelectrolyte enabling a strong degree of adsorption even though the membrane was globally neutral. Our observations indicate that the adsorption behaviour of the polyelectrolyte is influenced by the response given by the membrane to its presence and that the number of adsorbed beads increases drastically with the increase of flexibility of the polymer. Calculations involving polymers with three different intrinsic stiffnesses showed that the variation is non-monotonic. It was observed also that a smaller polyanion typically adsorbs more completely than the larger one, which indicates that the polarisation of the membrane becomes less facilitated as the degree of disruption increases. (C) 2004 Elsevier B.V. All rights reserved.
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- Dias, Rita, et al.
(författare)
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DNA-Surfactant interactions, compaction, condensation, decompaction and phase separation
- 2004
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Ingår i: Journal of the Chinese Chemical Society. - 2192-6549. ; 51:3, s. 447-469
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Forskningsöversikt (refereegranskat)abstract
- Recent investigations-of the interaction between DNA and alkyltrimethyl ammonium bromides of various chain lengths are reviewed. Several techniques have been used such as phase map determinations, fluorescence microscopy, and electron microscopy. Dissociation of the DNA-surfactant complexes, by the addition of anionic surfactant, has received special attention. Precipitation maps for DNA-cationic surfactant' systems were evaluated by turbidimetry for different salt concentrations, temperatures and surfactant chain lengths. Single-stranded DNA molecules precipitate at lower surfactant concentrations than double-helix ones. It was also observed that these systems precipitate for very low concentrations of both DNA and surfactant, and that the extension of the two-phase region increases for longer chain surfactants; these observations correlate well with fluorescence microscopy results, monitoring the system at a single molecule level. Dissociation of the DNA-cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems. The compaction of a medium size polyanion with shorter polycations was furthermore studied by means of Monte Carlo simulations. The polyanion chain suffers a sudden collapse as a function of the condensing agent concentration and of the number of charges on the molecules. Further increase of the concentration gives an increase of the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small-degree of intrachain segregation. However, complete charge neutralization was not a prerequisite to achieve compacted forms.
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- Dias, Rita, et al.
(författare)
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Modeling of DNA compaction by polycations
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:15, s. 8150-8157
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study polycations as efficient compacting agents of a medium size polyanion by means of Monte Carlo simulations. The systems are characterized in terms of a conformational analysis in which shape, overall dimensions, structure factors, radial distribution functions, and the degree of accumulation of the compaction agent near the polyanion are taken into consideration. Results show that the degree of compaction depends on the size of the positive chais and their number. The role of electrostatic interactions is paramount in the compaction process, and an increase in the number of molecules of the compacting agent or in the number of charges of each molecule leads to collapse, which may be followed by some unfolding in situations of overcharging. Compaction is associated with polycations promoting bridging between different sites in the polyanion. When the total charge of the polycations is significantly lower than that of the polyanion, interaction produces only a small degree of intrachain segregation in the latter, allowing for significant translational motion of the compacting agent along the longer chain. However, complete charge neutralization is not mandatory to achieve compact forms. (C) 2003 American Institute of Physics.
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- Kim, Sung-Phil, et al.
(författare)
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Divide-and-conquer approach for brain machine interfaces: nonlinear mixture of competitive linear models.
- 2003
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Ingår i: Neural networks : the official journal of the International Neural Network Society. - 0893-6080. ; 16:5-6, s. 865-71
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a divide-and-conquer strategy for designing brain machine interfaces. A nonlinear combination of competitively trained local linear models (experts) is used to identify the mapping from neuronal activity in cortical areas associated with arm movement to the hand position of a primate. The proposed architecture and the training algorithm are described in detail and numerical performance comparisons with alternative linear and nonlinear modeling approaches, including time-delay neural networks and recursive multilayer perceptrons, are presented. This new strategy allows training the local linear models using normalized LMS and using a relatively smaller nonlinear network to efficiently combine the predictions of the linear experts. This leads to savings in computational requirements, while the performance is still similar to a large fully nonlinear network.
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- Miguel, Maria, et al.
(författare)
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DNA-cationic amphiphile interactions
- 2003
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Ingår i: Colloids and Surfaces a-Physicochemical and Engineering Aspects. ; 228:1-3, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- DNA shows strong interactions with cationic cosolutes and these have both biological and technological significance. We outline our research on various mixed system of DNA and cationic amphiphiles including the interaction of DNA with simple cationic surfactants as well as the interaction with catanionic mixtures and positively charged catanionic vesicles. An overview from phase behavior to microstructure will be presented. We will also address DNA compaction and decompaction phenomena in different systems. Finally, simulations on DNA confinement and interaction with cationic polyions are considered. (C) 2003 Published by Elsevier B.V.
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| 10. |
- Eskilsson, K, et al.
(författare)
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DNA-surfactant complexes at solid surfaces
- 2001
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 17, s. 1666-1669
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report on the adsorption of complexes between DNA of different molecular weight and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), on hydrophobized and hydrophilic negatively charged silica surfaces as measured by ellipsometry. We will demonstrate how the adsorption is affected by the state of the DNA-surfactant complexes formed in bulk solution. High molecular weight DNA molecules, which condense (transform from coil to globule state) on addition of small amounts of cationic surfactants, do not adsorb on hydrophilic silica prior to phase separation. However, DNA-surfactant complexes formed from low molecular weight DNA were found to adsorb. For these complexes surfactants interact with DNA, without condensation of the DNA. Adsorbed DNA-surfactant complexes can easily be removed from the hydrophilic silica surface when replacing the bulk DNA-surfactant solution with pure salt solution. At the hydrophobic surface the DNA adsorbs without addition of cationic surfactant. However, with addition of a very low amount of surfactant, a rapid increase in adsorbed amount and a simultaneous decrease in adsorbed layer thickness are observed. This compaction of the adsorbed layer is to some extent reversible when replacing the bulk DNA-surfactant solution with pure salt solution.
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| 12. |
- Kyle, RA, et al.
(författare)
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Criteria for the classification of monoclonal gammopathies, multiple myeloma and related disorders: a report of the International Myeloma Working Group
- 2003
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Ingår i: British Journal of Haematology. - : Wiley. - 0007-1048. ; 121:5, s. 749-757
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Tidskriftsartikel (refereegranskat)abstract
- The monoclonal gammopathies are a group of disorders associated with monoclonal proliferation of plasma cells. The characterization of specific entities is an area of difficulty in clinical practice. The International Myeloma Working Group has reviewed the criteria for diagnosis and classification with the aim of producing simple, easily used definitions based on routinely available investigations. In monoclonal gammopathy of undetermined significance (MGUS) or monoclonal gammopathy, unattributed/unassociated (MG[u]), the monoclonal protein is < 30 g/l and the bone marrow clonal cells < 10% with no evidence of multiple myeloma, other B-cell proliferative disorders or amyloidosis. In asymptomatic (smouldering) myeloma the M-protein is greater than or equal to 30 g/l and/or bone marrow clonal cells greater than or equal to 10% but no related organ or tissue impairment (ROTI)(end-organ damage), which is typically manifested by increased calcium, renal insufficiency, anaemia, or bone lesions (CRAB) attributed to the plasma cell proliferative process. Symptomatic myeloma requires evidence of ROTI. Non-secretory myeloma is characterized by the absence of an M-protein in the serum and urine, bone marrow plasmacytosis and ROTI. Solitary plasmacytoma of bone, extramedullary plasmacytoma and multiple solitary plasmacytomas (+/- recurrent) are also defined as distinct entities. The use of these criteria will facilitate comparison of therapeutic trial data. Evaluation of currently available prognostic factors may allow better definition of prognosis in multiple myeloma.
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| 13. |
- Lindman, Björn, et al.
(författare)
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DNA-lipid systems. An amphiphile self-assembly and polymer-surfactant perspective
- 2002
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Ingår i: Lipid and Polymer-Lipid Systems. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0340-255X .- 1437-8027. - 9783540430018 ; 120, s. 52-63
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Konferensbidrag (refereegranskat)abstract
- The interaction between DNA and oppositely charged surfactants has been investigated by several techniques, like fluorescence microscopy, electron microscopy, phase diagram determination, and ellipsometry. The phase behaviour is more strongly associative than that in previously studied systems. A precipitate is formed for 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. 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 anionic surfactant can release free DNA back into solution from a compact globular complex between DNA and cationic surfactant. Finally, we investigated DNA interactions with polycations, chitosans with different chain lengths, by fluorescence microscopy, in vivo transfections 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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| 15. |
- van Schayck, Onno C P, et al.
(författare)
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Early detection of chronic obstructive pulmonary disease (COPD) : the role of spirometry as a diagnostic tool in primary care
- 2003
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Ingår i: Primary Care Respiratory Journal. - 1471-4418 .- 1475-1534. ; 12:3, s. 90-93
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Tidskriftsartikel (refereegranskat)abstract
- Chronic obstructive pulmonary disease (COPD) is common and often undiagnosed in its early stages, especially in smokers, who are also most at risk. Patients can develop severe or very severe disease before they consult a physician. It is therefore important to identify patients at-risk of COPD and check their lung function regularly since early stage disease is often asymptomatic or mistaken for asthma. Primary care physicians are often the first health care providers to encounter patients with COPD in the early stages, and their role in early detection and treatment process is pivotal.Spirometry is a cheap, simple and reliable method for the early detection and monitoring of COPD patients, and for establishing a differential diagnosis. Spirometry gives immediate results and communicating the results to smokers has been shown to motivate them to quit. Early diagnosis and appropriate therapy can positively influence disease course, slowing progression, relieving symptoms and reducing the incidence of acute 'flares', or exacerbations.
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