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Author: Hamidreza Shojaei-Mahib
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Interaction of charged macromolecules among themselves and with charged interfaces in salty aqueous medium is a common phenomenon prevalent in biology and synthetic systems. We have addressed several inter-related issues in this general context. First we present a theory of adsorption of polyelectrolytes on the interior and exterior surfaces of a charged spherical vesicle. We derive the critical adsorption condition and the density profile of the polymer in terms of various characteristics of the polymer, vesicle, and the solution, such as the length and charge density of polymer, the radius and charge of the vesicle, the salt concentration of the solution, and the dielectric constant of the solvent. We have used the Wentzel-Kramers-Brillouin (WKB) method to solve the equation for the probability distribution function of the chain. For the polyelectrolyte inside the vesicle, the competition between the loss of conformational entropy and the attractive electrostatic energy between the vesicle and the polyelectrolyte, results in two different encapsulated states. By considering the adsorption from outside, we calculate the entropic and the energetic contributions to the free energy for the polymer being adsorbed in the interior and exterior states and the free energy penalty for the polyelectrolyte being expelled from the vesicle. The kinetics of the polyelectrolyte complexation have been studied using the Smoluchowski equation. We derive the mean distance between two oppositely charged polyelectrolytes and the reaction rate for the complexation in terms of the salt concentration and polyelectrolyte characteristics. We also calculate the half-time for the complexation process at different salt concentrations and initial distances.\\ For a vesicle, we have derived the free energy landscape of translocation through the pore by accounting for the energy penalty of bending and stretching the vesicle from due to deformation by pore. Using the Fokker-Planck formalism, we have calculated the average translocation time corresponding to the various free energy landscapes representing different parameter sets. We also discuss the dependencies of the average translocation time on the strength of the external force, vesicle size, bending and stretching moduli of the vesicle, and the radius and length of the pore. Finally, we formulate a theory of the effects of long-range interactions on surface tension and spontaneous curvature of proteinaceous shells based on the general Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. we have derived the renormalized spontaneous curvature as a function of capsid's inner and outer charge density and solution properties.
Author: Hamidreza Shojaei-Mahib
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Interaction of charged macromolecules among themselves and with charged interfaces in salty aqueous medium is a common phenomenon prevalent in biology and synthetic systems. We have addressed several inter-related issues in this general context. First we present a theory of adsorption of polyelectrolytes on the interior and exterior surfaces of a charged spherical vesicle. We derive the critical adsorption condition and the density profile of the polymer in terms of various characteristics of the polymer, vesicle, and the solution, such as the length and charge density of polymer, the radius and charge of the vesicle, the salt concentration of the solution, and the dielectric constant of the solvent. We have used the Wentzel-Kramers-Brillouin (WKB) method to solve the equation for the probability distribution function of the chain. For the polyelectrolyte inside the vesicle, the competition between the loss of conformational entropy and the attractive electrostatic energy between the vesicle and the polyelectrolyte, results in two different encapsulated states. By considering the adsorption from outside, we calculate the entropic and the energetic contributions to the free energy for the polymer being adsorbed in the interior and exterior states and the free energy penalty for the polyelectrolyte being expelled from the vesicle. The kinetics of the polyelectrolyte complexation have been studied using the Smoluchowski equation. We derive the mean distance between two oppositely charged polyelectrolytes and the reaction rate for the complexation in terms of the salt concentration and polyelectrolyte characteristics. We also calculate the half-time for the complexation process at different salt concentrations and initial distances.\\ For a vesicle, we have derived the free energy landscape of translocation through the pore by accounting for the energy penalty of bending and stretching the vesicle from due to deformation by pore. Using the Fokker-Planck formalism, we have calculated the average translocation time corresponding to the various free energy landscapes representing different parameter sets. We also discuss the dependencies of the average translocation time on the strength of the external force, vesicle size, bending and stretching moduli of the vesicle, and the radius and length of the pore. Finally, we formulate a theory of the effects of long-range interactions on surface tension and spontaneous curvature of proteinaceous shells based on the general Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. we have derived the renormalized spontaneous curvature as a function of capsid's inner and outer charge density and solution properties.
Author: Per Johan Råsmark
Publisher:
ISBN: 9789155460839
Category :
Languages : en
Pages : 71
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Book Description
Author: Caleb Edward Gallops
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Polyelectrolyte complexes formed from nucleic acids and synthetic polycations have been studied for their use in non-viral gene delivery. Polyethylenimine (PEI) is a highly-studied polycationic vector with a high transfection efficiency that has been linked with its pH-responsiveness. In this series of studies, we examine the structural characteristics of PEI in atomistic detail and investigate the formation of polyelectrolyte complexes/aggregates using coarse-grained molecular dynamics.Atomistic molecular dynamics simulations of a linear 40mer PEI chain were performed for 9 protonation states and various NaCl concentrations to examine how the structure of PEI depends on pH and salt concentration. PEI continuously expands as it transitions from being unprotonated to fully protonated; however, we observe that two different regimes underlie this expansion. Sparsely protonated chains behave as weakly charged polyelectrolytes whose expansion is associated with the reduction of intrachain hydrophobic interactions. In contrast, the expansion of densely protonated chains with increased protonation involves increasing chain stiffness and breaking intrachain hydrogen bonds. The weakly-to-highly charged transition occurred at ~40% protonation, suggesting it may occur in endosomal conditions. These results provide a microscopic picture of changes in PEI structure during the gene delivery process.Coarse-grained molecular dynamics simulations are performed to examine the impact of chain length and polyanion stiffness on polyplex formation and aggregation. Polyplexes containing single polyanion chain fall into three structural regimes depending on polyanion stiffness: flexible polyanions form collapsed complexes, semiflexible polyanions form various morphologies including toroids and hairpins, and stiff polyanions form rod-like structures. Polyplex size generally decreases as polycation length increases. Aggregation (i.e., formation of complexes containing multiple polyanions) is observed in some simulations containing multiple polyanions and an excess of short polycations. Aggregation is observed to only occur for semiflexible and stiff polyanions and is promoted by shorter polycation lengths. Simulations of short, stiff polyanions condensed by long polycations are used as a model for siRNA gene delivery complexes. These simulations show multiple polyanions are spaced out along the polycation with polyanion-polyanion interactions, usually limited to overlapping chain ends. These structures differ from aggregates of longer polyanions in which the polyanions are packed together in parallel, forming bundles..
Author: Kehua Lin
Publisher:
ISBN:
Category : Materials science
Languages : en
Pages : 94
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Book Description
Polyelectrolyte and microgel were used as a model to investigate the structure and dynamics of complex liquid. In chapter 2, a coacervate system that is associated with net neutral polybetaine and cationic P2VP was applied in this research work as an environment for polyelectrolyte whose confirmation is characterized by fluorescence correlation spectroscopy. Surprisingly, the chain confirmation of the positive charged polyelectrolyte, P2VP, behaves oppositely compared to that in dilute solution. With the increased pH, the chain remains swollen upon coacervation or even slightly more expanded while the chain would collapse due to the low charge density at high pH. Schematic illustration of f-P2VP and the phase behavior is further investigated. In chapter 3 and 4, the spatial confinement of the microgel system suspension at near supercool region and supercool region under different confinement wall was investigated under confocal microscope and the dynamics was further extracted by image analysis. We found the softer wall can weaken the confinement effect and result in a higher mobility, even for the hard microgel suspension. The onsite height of confinement effect is increase with decreased stiffness of the wall. The mobile cluster which treated as dynamics structure and the pair correlation function under different surface confinement was further investigated. The size of mobile cluster decreased and a more disorder structure is observed when stiffness of the confinement wall reduced.
Author: Visakh P. M.
Publisher: Springer
ISBN: 3319016806
Category : Technology & Engineering
Languages : en
Pages : 388
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Book Description
This book offers a valuable reference source to graduate and post graduate students, engineering students, research scholars polymer engineers from industry. The book provides the reader with current developments of theoretical models describing the thermodynamics polyelectrolytes as well as experimental findings. A particular emphasis is put on the rheological description of polyelectrolyte solutions and hydrogels.
Author: Michael A. Leaf
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Decades of progress have yielded a tremendous variety of organic electronics, with great strides in the development of photovoltaics, thermoelectrics and other flexible devices. Ubiquitous in these research areas are films of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT: PSS), a complex of oppositely-charged polyelectrolytes initially suspended in water before film formation. This material has high electronic conductivity and good water processability. Pristine film conductivity is somewhat low, but is dramatically enhanced through simple treatments like ionic liquid addition or shear. Can this enhancement be understood so that further optimization might render PEDOT: PSS commercially viable? PEDOT: PSS is a complicated material, with electrostatic complexation between PEDOT and oppositely-charged PSS, dissociated counterions and an inherent insolubility of PEDOT in water. These characteristics among others muddle the already challenging task of understanding the film formation process. In this doctoral thesis work, the goal is to build on our fundamental understanding of PEDOT: PSS and conducting polyelectrolyte complexes in general. The structural aspects of PEDOT: PSS dispersions are studied upon the addition of four conductivity enhancers: EMIM BF4, NaCl, DMSO and EG. PEDOT: PSS collects into many-chain charged micro-gels that are hundreds of nanometers in scale. An observed sensitivity to ionic strength underscores the dominance of electrostatic forces in PEDOT: PSS solutions. Micro-gels can macroscopically percolate or phase segregate, much like associating polymers. PEDOT: PSS conduction predominatly occurs electronically in films and ionically in solutions. When the four enhancers are introduced, no correlation is found between changes to film conductivity and changes to solution phenomenology. This apparent lack of correlation strengthens the widely-held belief that conductivity enhancement is closely linked to PEDOT ordering. Langevin dynamics simulations show that PEDOT clusters into stacked domains at high polymer concentration and ionic strength, and this clustering can be explained as an interplay between hydrophobic and electrostatic drivers. A new theory of polyelectrolyte complex phase separation is proposed, and it relies on induced dipoles formed from the association of oppositely-charged backbones. It predicts the phase behavior for model systems, but does not apply directly to PEDOT: PSS. Nevertheless, it gives insight into the role of dipoles for complex coacervation.
Author: Sarkyt E. Kudaibergenov
Publisher: Springer Science & Business Media
ISBN: 9780306467813
Category : Science
Languages : en
Pages : 232
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Book Description
This book comprehensively reviews the synthesis, characterization and application aspects of linear and crosslinked synthetic polyampholytes - simple model of biopolymers - starting from the 1950's. The synthetic strategy of "annealed", "quenched" and "zwitterionic" polyampholytes, the properties of polyampholytes in solutions and in gel state are considered. The complexation ability of polyampholytes with respect to transition metal ions, ionic surfactants, dyes and organic probes polyelectrolytes, proteins and colloid particles is discussed. Stimuli-sensitive behavior of various amphoteric gel and membrane systems demonstrating rhythmically phenomenon similar to that of heart beat, deformation, oscillation or self-oscillation phenomena stimulated by temperature, pH and electric field are illustrated. Catalytic properties of synthetic polyampholytes simulating the function of enzymes are also considered.
Author: Junzhe Lou
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Rational design of hydrogels and charged polymers is important for understanding the underlying principles that govern complex mechanical and phase behaviors of biomacromolecular systems. Mimicking and capturing such behaviors in synthetic polymer systems are highly desired for many biomedical and technical applications. Biological tissues exhibit complex dynamic mechanical properties. To capture and control dynamics in synthetic hydrogel scaffolds, I developed a hyaluronic acid (HA)-based dynamic hydrogel system crosslinked by dynamic covalent hydrazone bonds. The HA hydrogels and collagen I generated an interpenetrating network, which exhibited both well-controlled mechanical tunability and fibrillarity, thus providing an adaptable platform to study the cell-matrix interactions. A biocompatible catalyst that accelerates the exchange of hydrazones was then incorporated into the HA-hydrazone hydrogel to modulate the dynamics of crosslinks without affecting network structures. This approach was used to develop injectable hydrogels for cell delivery with high injectability and stability enabled by temporal catalyst controlled hydrogel dynamics. The catalyst control of network dynamics also enabled quantitative and unambiguous correlation between the network parameters and mechanical properties of dynamic polymer networks. In the second part, I investigated the fundamental study on liquid-like polyelectrolyte complexes (PECs) formed by oppositely charged polyelectrolytes. PECs are important in biological systems for membraneless compartments, however the understanding of the mechanism and structure-property relationship is limited. I developed a series of well-defined polymers with tunable structural parameters to modulate the microenvironment of PECs and clearly revealed the importance of local polarity and polyelectrolyte composition on PECs.
Author: Kevin Wayne Mattison
Publisher:
ISBN:
Category : Polyelectrolytes
Languages : en
Pages : 168
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Book Description
Author: John J. Kasianowicz
Publisher: Springer Science & Business Media
ISBN: 9781402006975
Category : Science
Languages : en
Pages : 46
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Book Description
Polymers are essential to biology because they can have enough stable degrees of freedom to store the molecular code of heredity and to express the sequences needed to manufacture new molecules. Through these they perform or control virtually every function in life. Although some biopolymers are created and spend their entire career in the relatively large free space inside cells or organelles, many biopolymers must migrate through a narrow passageway to get to their targeted destination. This suggests the questions: How does confining a polymer affect its behavior and function? What does that tell us about the interactions between the monomers that comprise the polymer and the molecules that confine it? Can we design and build devices that mimic the functions of these nanoscale systems? The NATO Advanced Research Workshop brought together for four days in Bikal, Hungary over forty experts in experimental and theoretical biophysics, molecular biology, biophysical chemistry, and biochemistry interested in these questions. Their papers collected in this book provide insight on biological processes involving confinement and form a basis for new biotechnological applications using polymers. In his paper Edmund DiMarzio asks: What is so special about polymers? Why are polymers so prevalent in living things? The chemist says the reason is that a protein made of N amino acids can have any of 20 different kinds at each position along the chain, resulting in 20 N different polymers, and that the complexity of life lies in this variety.
