| 1. |
- 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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| 2. |
- Angelescu, Daniel G., et al.
(författare)
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Branched-linear polyion complexes at variable charge densities
- 2015
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:35
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Tidskriftsartikel (refereegranskat)abstract
- Structural behavior of complexes formed by a charged and branched copolymer and an oppositely charged and linear polyion was examined by Monte Carlo simulations employing a coarse-grained bead-spring model. The fractional bead charge and the branching density were systematically varied; the former between 0e and 1e and the latter such that both the comb-polymer and the bottle-brush limits were included. The number of beads of the main chain of the branched copolymer and of the linear polyion was always kept constant and equal, and a single side-chain length was used. Our analysis involved characterization of the complex as well as investigation of size, shape, and flexibility of the charged moieties. An interplay between Coulomb interaction and side-chain repulsion governed the structure of the polyion complex. At strong Coulomb interaction, the complexes underwent a gradual transition from a globular structure at low branching density to an extended one at high branching density. As the electrostatic coupling was decreased, the transition was smoothened and shifted to lower branching density, and, eventually, a behavior similar to that found for neutral branched polymer was observed. Structural analogies and dissimilarities with uncharged branched polymers in poor solutions are discussed.
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| 3. |
- Angelescu, Daniel G., et al.
(författare)
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Branched-linear polyion complexes investigated by Monte Carlo simulations
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 10:32, s. 6047-6058
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Tidskriftsartikel (refereegranskat)abstract
- Complexes formed by one charged and branched copolymer with an oppositely charged and linear polyion have been investigated by Monte Carlo simulations. A coarse-grained description has been used, in which the main chain of the branched polyion and the linear polyion possess the same absolute charge and charge density. The spatial extension and other structural properties, such as bond-angle orientational correlation function, asphericity, and scaling analysis of formed complexes, at varying branching density and side-chain length of the branched polyion, have been explored. In particular, the balance between cohesive Coulomb attraction and side-chain repulsions resulted in two main structures of a polyion complex. These structures are (i) a globular polyion core surrounded by side chains appearing at low branching density and (ii) an extended polyion core with side chains still being expelled at high branching density. The globule-to-extended transition occurred at a crossover branching density being practically independent of the side chain length.
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| 4. |
- Angelescu, Daniel G., et al.
(författare)
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Monte Carlo Simulations of Multigraft Homopolymers in Good Solvent
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:1, s. 415-426
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Tidskriftsartikel (refereegranskat)abstract
- Multigraft polymers comprise a subclass of branched polymers where more than one side chain is attached to each node (branching point) of the main chain. We have investigated structural properties of single multigraft polymers under good solvent conditions by Monte Carlo simulations, employing a flexible bead-spring model. Beside the grafting density, denoting the linear density of grafted side chains, we have introduced the concept of branching density, denoting the linear density of nodes. At high branching density, both the branching density and the branching multiplicity controlled the structure of the side chains, whereas at lower branching density only the branching multiplicity influenced the side-chain structure. The spatial extension of the main chain and side chains as a function of side-chain length and grafting density was analyzed using scaling formalism. The dependence of the main-chain extension on side-chain length, branching density, and branching multiplicity could be collapsed on a universal curve upon relevant rescaling. Multigraft polymers with equal number of side-chain beads but unequal numbers and lengths of side chains displayed unconventional bending properties. Few and long side chains gave rise to a still relative low locally stiffness but considerable long-range rigidity, whereas more numerous and shorter side chains lead to a higher local stiffness but to a smaller long-range rigidity.
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| 5. |
- Angelescu, Daniel George, et al.
(författare)
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Viruses as supramolecular self-assemblies: modelling of capsid formation and genome packaging
- 2008
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 4:10, s. 1981-1990
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Forskningsöversikt (refereegranskat)abstract
- Viruses are considered the simplest form of live. A virus is basically composed of genomic material surrounded by a protecting capsid. Today, full molecular details of many viruses are known, and several subclasses can be discerned. In this review, we present recent advances made over the past few years obtained from theoretical considerations and model simulations to improve our understanding on two vital aspects of the physics of viruses: viz. viral capsid self-assembly and viral genome packaging. Many processes, such as the self-assembly pathway, genome packing, and ultimately the infection mechanism, differ between viruses containing double-stranded polynucleotides on one hand and single-stranded polynucleotides on the other hand. We believe that these differences to a large degree originate from the different genome flexibilities.
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| 6. |
- Angelescu, Daniel, et al.
(författare)
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Modelling of icosahedral viruses
- 2008
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294. ; 13:6, s. 389-394
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Forskningsöversikt (refereegranskat)abstract
- Theoretical and simulation investigations of viruses attaining icosahedral shape based on molecular models have recently become an exciting and rapidly growing research area. We discuss recent studies addressing the packing of the genome inside the capsid, thermodynamics, and the self-assembly of capsids. Special attention is given to the different packing of double-stranded and single-stranded polynucleotides in the viral capsid and its consequences. (C) 2007 Elsevier Ltd. All rights reserved.
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| 7. |
- Angelescu, Daniel, et al.
(författare)
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Monte Carlo simulation of the mean force between two like-charged macroions with simple 1 : 3 salt added
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:23, s. 9661-9668
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Tidskriftsartikel (refereegranskat)abstract
- The mean force and the potential of the mean force between two like- harged macroions with monovalent counterions and added simple 1:3 salt described within the primitive model and confined in a cylindrical cell have been investigated by Monte Carlo simulations. Without additional salt, a strongly repulsive mean force was obtained at all macroion separations, consistent with a stable solution of macroions. At a trivalent counterion-to-macroion charge ratio of 0.4, the mean force became attractive at short separations but still possessed a substantial repulsion at longer separations. However, at a stoichiometric amount of trivalent counterions, no long-range repulsion remained and the attraction became substantial (approximate to5kT attraction at a short separation). In excess of salt, the magnitude of the attractive mean force was reduced. The attractive component of the mean force originates from spatial correlations between counterions residing near different macroions and is not captured by mean-field theories such as the Poisson-Boltzmann equation or any of its simplific tions. The observed sequence of mean forces is consistent with recent experimental observations on an aqueous solution of sodium dodecyl sulfate micelles as Al(NO3)(3) was added.
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| 8. |
- Angelescu, Daniel, et al.
(författare)
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Monte Carlo simulations of flexible polyelectrolytes inside viral capsids with dodecahedral charge distribution
- 2007
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 75:5
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Tidskriftsartikel (refereegranskat)abstract
- Structural properties of encapsidated flexible polyelectrolytes in viral capsids with dodecahedral charge distribution have been investigated by Monte Carlo simulations using a coarse-grained model. Several capsid charge distributions ranging from a homogeneous surface charge distribution (lambda=0) to a complete dodecahedral distribution (lambda=1) at constant total capsid charge and fixed radial location of the capsid charges have been considered. The radial and lateral organizations of the polyelectrolyte have been examined as a function of the polyelectrolyte length and capsid charge distribution. With short polyelectrolytes a single polyelectrolyte layer was formed at the inner capsid surface, whereas at increasing polyelectrolyte length also a uniform polyelectrolyte density inside the surface layer was established. At low lambda, the polyelectrolyte layer was laterally isotropic, but at lambda >= 0.05 a dodecahedral structure started to appear. At lambda=1, the polyelectrolyte followed essentially a path along the edges of a dodecahedron. With sufficiently long chains, all edges were decorated with polyelectrolyte, facilitated by loop formation. For an undercharged capsid, the capsid counterions inside the capsid also adopted a dodecahedral distribution.
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| 9. |
- Angelescu, Daniel, et al.
(författare)
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Monte Carlo simulations of polyelectrolytes inside viral capsids
- 2006
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 73:4
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Tidskriftsartikel (refereegranskat)abstract
- Structural features of polyelectrolytes as single-stranded RNA or double-stranded DNA confined inside viral capsids and the thermodynamics of the encapsidation of the polyelectrolyte into the viral capsid have been examined for various polyelectrolyte lengths by using a coarse-grained model solved by Monte Carlo simulations. The capsid was modeled as a spherical shell with embedded charges and the genome as a linear jointed chain of oppositely charged beads, and their sizes corresponded to those of a scaled-down T=3 virus. Counterions were explicitly included, but no salt was added. The encapisdated chain was found to be predominantly located at the inner capsid surface, in a disordered manner for flexible chains and in a spool-like structure for stiff chains. The distribution of the small ions was strongly dependent on the polyelectrolyte-capsid charge ratio. The encapsidation enthalpy was negative and its magnitude decreased with increasing polyelectrolyte length, whereas the encapsidation entropy displayed a maximum when the capsid and polyelectrolyte had equal absolute charge. The encapsidation process remained thermodynamically favorable for genome charges ca. 3.5 times the capsid charge. The chain stiffness had only a relatively weak effect on the thermodynamics of the encapsidation.
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| 10. |
- Angelescu, Daniel, et al.
(författare)
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Packaging of a flexible polyelectrolyte inside a viral capsid: Effect of salt concentration and salt valence
- 2007
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 111:29, s. 8477-8485
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Tidskriftsartikel (refereegranskat)abstract
- The effect of salt on the location and structure of a flexible polyelectrolyte confined inside a viral capsid and the Donnan equilibrium of the salt across the capsid have been examined using a coarse-grained model solved by Monte Carlo simulations. The polyelectrolyte was represented by a linear jointed chain of charged beads, and the capsid was represented by a spherical shell with embedded charges. At low salt concentration, the polyelectrolyte was strongly adsorbed onto the inner capsid surface, whereas at high salt concentration it was located preferentially in the central part of the capsid. Under the condition of equal Debye screening length, the electrostatic screening increased as the valence of the polyelectrolyte counterion was increased. The distribution of the small cations and anions was unequal across the capsid. An excess of polyelectrolyte counterions occurred inside the capsid, and the excess increased with the salt concentration. A simplified representation of the small ions through the use of the screened Coulomb potential provided only a qualitatively correct picture; the electrostatic screening originating from the small ions was exaggerated.
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