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The Role of Charge Regulation in Weak Polyampholytes
Lunkad, Raju ; Košovan, Peter (advisor) ; de Sousa Dias, Rita (referee) ; Gonzalez, Jose Luis Garces (referee)
A weak polyampholyte is a polymer that consists of both acid and base groups along the chain. In aqueous solutions, these groups dissociate in a certain pH range, leading to a dramatic change in the overall charge of the polyampholyte from positive to negative as the pH increases. The ability of weak ampholytes to switch their charge in response to changes in pH makes them useful in various applications. Despite the considerable research on weak polyampholytes, the understanding of some aspects is still insufficient. To address this, I systematically investigated the charge regulation of weak polyam- pholytes, specifically peptides, both in solution and during their interaction with polyelectrolytes. Furthermore, I also looked at the charge regulation of polyzwitterions. All these studies were carried out using a simple coarse-grained bead-spring model in Langevin dynamics simulations. In addition, I used the constant-pH ensemble to account for the ionization reactions of acid and base groups in the implicit solvent. Through our simulations, we made significant advancements in understanding how charges and the ionization states of acid and base groups in various peptides and polyzwitterions respond to pH changes. By comparing simulation results with the ideal results predicted by the...
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Post-polymerization modification of block copolymers as a tool for preparation of new drug delivery nanosystems
Marková, Pavlína ; Uchman, Mariusz Marcin (advisor) ; Košovan, Peter (referee)
Amphiphilic block copolymers self-assemble into clinically efficacious nanostructures, whose size, stability, and surface chemistry can be easily adjusted for each purpose. This versatility has prompted the vast scope of their biomedical applications, especially in the field of drug delivery. In particular, polyester-based nanoparticles have been used in gene, nucleic acid, therapeutic protein and drug delivery for their in vivo biocompatibility and biodegradability. However, most studies have only focused on amphiphilic copolymers with either short hydrophobic segments, no modification or a single preparation pathway. This diploma thesis focuses on the synthesis of poly(ethylene oxide)-b-poly(caprolactone) copolymers containing propargyl groups using two parallel approaches, namely a copolymerization with a modified monomer and a post-polymerization modification. A subsequent thiol-yne click reaction with 1-thioglycerol yielded copolymers with vicinal diols, which can reversibly bind to benzoxaborole- and boronic acid-derived compounds. Both synthetic pathways were evaluated based on macromolecular characteristics afforded by nuclear magnetic resonance spectroscopy and by size exclusion chromatography. Furthermore, we characterized the self-assembled nanoparticles by static and dynamic light...
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Simulation of electromigration in nanodimensions
Novotný, Tomáš ; Gaš, Bohuslav (advisor) ; Košovan, Peter (referee)
4 Abstract Computer softwares used for the prediction of the electromigration behaviour do not account for the local deviation from the electroneutrality condition, and thus cannot be used in nanodimensions. The aim of this work is to present a new mathematical model which can predict the behaviour of electrolytes in nano-channels. The mathematical model joins together (i) Nernst-Planck continuity equation for charged particles, (ii) the continuity equation for the electric charge, (iii) the Poisson equation and (iv) the G- function, which was appropriately modified from its original formulation. The set of partial differential equations is solved numerically in COMSOL Multiphysics, which is a powerfull tool based on the finite element method. Crucial part of the study of the electromigration in nano-dimensions is a precise description of the electrical double-layer in silica nano-channels. A new concept of a charged surface is presented in this work using the gel layer of silanol to create the electric charge on the wall. The accuracy of the solution of gel-layer concept is verified with another experiment using the Neumann boundary condition. Keywords: Electrical double-layer, electromigration, electroneutrality condition, Poisson equation
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Effect of acid-base equilibria on the association behaviour of polyelectrolytes
Staňo, Roman ; Košovan, Peter (advisor) ; Heyda, Jan (referee)
Title: Effect of acid-base equilibria on the association behaviour of polyelec- trolytes Author: Roman Staňo Department: Department of physical and macromolecular chemistry Supervisor: RNDr. Peter Košovan, Ph.D., Department of physical and macro- molecular chemistry Abstract: Macromolecules bearing charged monomeric units are omnipresent in the nature. Living systems utilize complex mechanisms to regulate the charge on biomacromolecules, hence controlling their structure or activity. Recently, there has been a surge in the preparation of bioinspired macromolecular mate- rials, such as drug delivery systems or self-healing hydrogels, possessing a high degree of responsivity to the external stimuli, such as pH. However, the fundamen- tal understanding of pH-based charge regulation in both natural and synthetic systems seems to be lacking, presumably because of the deficiency of suitable theoretical models and computational methods. Herein, we used coarse-grained simulations to shed light on the underyling physical principles of the relation between the pH, ionization, multivalency and structure of macromolecules. We presented a novel model of complex coacervates, and used it to describe phase equilibria and ion partitioning in such systems. Next, we explored the effects of multivalent ions and charged...
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Intramolecular self-organised structures in amphiphilic (co)polymers
Košovan, Peter
This dissertation presents an overview of our computer simulation studies of the conformational behaviour of amphiphilic polymers. In the studies we showed that the polymers form a variety of self-organised structures at a single molecule level. These include the pearl-necklace structure, spherical and cylindrical intramolecular micelles and bundles. From the simulations we were able to obtain a deeper insight into the behaviour of amphiphilic polymers and conditions under which the above-mentioned structures are formed. Some of the results were compared to experimental or theoretical studies of similar polymers. In some cases the simulations confirmed earlier interpretations which were based on analogy or intuition. In other cases they revealed new phenomena which had not been considered before.
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Effect of acid-base equilibria on the association behaviour of polyelectrolytes
Staňo, Roman ; Košovan, Peter (advisor) ; Heyda, Jan (referee)
Title: Effect of acid-base equilibria on the association behaviour of polyelec- trolytes Author: Roman Staňo Department: Department of physical and macromolecular chemistry Supervisor: RNDr. Peter Košovan, Ph.D., Department of physical and macro- molecular chemistry Abstract: Macromolecules bearing charged monomeric units are omnipresent in the nature. Living systems utilize complex mechanisms to regulate the charge on biomacromolecules, hence controlling their structure or activity. Recently, there has been a surge in the preparation of bioinspired macromolecular mate- rials, such as drug delivery systems or self-healing hydrogels, possessing a high degree of responsivity to the external stimuli, such as pH. However, the fundamen- tal understanding of pH-based charge regulation in both natural and synthetic systems seems to be lacking, presumably because of the deficiency of suitable theoretical models and computational methods. Herein, we used coarse-grained simulations to shed light on the underyling physical principles of the relation between the pH, ionization, multivalency and structure of macromolecules. We presented a novel model of complex coacervates, and used it to describe phase equilibria and ion partitioning in such systems. Next, we explored the effects of multivalent ions and charged...
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Interaction of weak polyelectrolytes with multivaltent ions
Staňo, Roman ; Košovan, Peter (advisor) ; Heyda, Jan (referee)
By means of molecular simulations, we study dissociative behavior of weak polyacids with added mutlivalent salt. Weak polyacids are macromolecules that bear weak acid groups, therefore, their ionization varies with pH. The titration curve of such an acid deviates from the ideal one - its ionization is suppressed because of the strong repulsion between charged groups on the polyacid contour. The presence of salt in solution of a polyacid enhances the ionzation due to the effects of electrostatic screening and counterion condensation. Up to now, the influence of the salt valency on the weak polyacid ionization has not been explored, although it plays an important role in biological processes. In this thesis, we examine weak polyacid solutions with added salt of various cation valencies (+1,+2,+3) at fixed charge ratio of salt cations to po- lymer segments. We show that increasing the salt valency promotes the polyelectrolyte ionization in a manner which is different from the effect of increasing ionic strength. A higher counterion valency leads to a lower value of the critical Manning parameter, initiating strong counterion condensation which results in additional ionization due to ion-ion correlations between the condensed counterions and charged groups of the polyelectrolytes.
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Computational modeling of diffusion in polymer solutions
Kubečka, Jakub ; Košovan, Peter (advisor) ; Šachl, Radek (referee)
We performed coarse-grained molecular dynamics simulations of fully dissociated polyelectrolytes in the presence of monovalent and multivalent counterions and charged oligomers. The dynamics of these systems has been studied to follow internal dynamics of polyelectrolyte and counterions. The dynamics is presented via the mean square displacement which we obtain from the simulation trajectory and, moreover, via curves of Fluorescence Correlation Spectroscopy (FCS) obtained also from the simulation trajectory. FCS is an experimental technique which can be used to study condensation of counterions on polyelectrolytes. Therefore, we analyze the FCS curves and investigate applicability of various analytical models to fit these FCS curves. The aim of this work is a discussion about the fitting of the FCS curves and presentation of our observations for dynamics of counterions during condensation on the polyelectrolyte.
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