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Determination of pKa of humic acids by means of UV/VIS spectrometry
Kratochvílová, Romana ; Maršálek,, Roman (referee) ; Klučáková, Martina (advisor)
The behaviour of humic acids in aqueous solutions is closely connected to the content of acid functional groups and their dissociation abilities. The titration methods are the most often used for the research of acid-base characteristics of humic acids, their results should lead to the determination of the content of functional groups and their pKa. However the determined values depend on many factors including the titration speed. The spectrophotometric determination of dissociation constant was used in this diploma thesis. Reliability of this method was confirmed in bachelor thesis where is mentioned that spectrophotometric determination of pKa corresponds with realistic dissociation behaviour of humic acids in the water much more better than values obtained from titration methods. The principle of newly used spectrophotometry method is the preparation of humic acids solutions in three different media with different pH values. Acid groups of humic acids are practically completely dissociated in intensely basic environment and the measured absorbance is caused by anion of „humate“. On the contrary their dissociation in acid environment is suppressed so much that we measure the absorbance of non-dissociated molecules of humic acids. Deionized water was used like neutral solvent. Water was replaced by acetic buffer in this thesis because of water’s properties which have significant influence on solutions' pH. Buffer was used for diluting or for solubilisation and in these both cases more stable pH values were occurred. The aim of this diploma thesis is investigate UV/VIS spectra of various solutions of humic acids with different values of pH and determinate mean value of pKa of humic acids which could be used like comparison of dissociation behaviours for vary samples. Values of acid dissociation constant were determined from measured dates and compared with values obtained by titration method. The UV/VIS spectra gained in combination with the results of pH measuring and the conductivity next showed the differences in the behaviour of differently prepared samples of humic acids.
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New methods of protonated aminoacids preparation and their interactions with polyelectrolytes
Trojan, Martin ; Sedlařík,, Vladimír (referee) ; Chytil, Martin (advisor)
This Master thesis investigates the interaction between the polysaccharide sodium hyaluronate (HA) and some amphiphilic molecules. It is known that the presence of the carboxylic group on HA and the aminogroup on the amphiphiles leads to electrostatic interaction between these two compounds. This supposal offers the possibility to physically modify HA and use it as a new type of a carrier of bioactive compounds, for example medicals. However, successful carrier of bioactive compound has to resist a certain value of ionic strength. The high-molecular weights HA (1.75MDa) and amphiphile lysine were chosen for the study of the influence of ionic strength on the system HA – amphiphile. Our results show that system HA – amphiphile system is suppressed even by low concentrate solution of electrolyte. Therefore the system was reinforced by protonation of the aminoacid. The results show, that the interactions were reinforced, nevertheless negative influence of chlorine anions had to be eliminated by lyophilization. The solutions with strengthened system HA – amphiphile were used for the research of ionic strength influence. The amphiphiles lysine, 6 - aminocaproic acid and arginine were selected for this study. The interactions were investigated by means of reometry and conductometry.
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Solubility and dissociation of humic acids
Kratochvílová, Romana ; Jaroslav,, Záhora (referee) ; Klučáková, Martina (advisor)
The behaviour of humic acids in aqueous solutions is closely connected to the content of acid functional groups and their dissociation abilities. The titration methods are the most often used for the research of acid-basic characteristics of humic acids, their results should lead to the determination of the content of functional groups and their pKa. However the determined values depend on many factors including the titration speed. The aim of this bachelor’s thesis is to verify the possibility of UV/VIS spectrophotometry´s use as alternative method for the determination of pKa of humic acids and to compare the gained results with so far used method according to Henderson-Hasselbach. The principle of newly used spectrophotometry method is the preparation of humic acids solutions in three different media with different pH values. Acid groups of humic acids are practically completely dissociated in intensely basic environment and the measured absorbance is caused by anion of „humate“. On the contrary their dissociation in acid environment is suppressed so much that we measure the absorbance of non-dissociated molecules of humic acids. It was found out that after the modification it was possible to use the spectrophotometry method for the determination of pKa of these substances, while the use of method was verified within the three different samples of humic acids. The optimal ratio humic acids – water and the extent of wavelength for measuring UV/VIS spectra were determined. It was proved that the values of pKa determinated by these methods better describe the real dissociation behaviour of humic acids in water than traditional Henderson-Hasselbach method. The UV/VIS spectra gained in combination with the results of pH measuring and the conductivity next showed the differences in the behaviour of differently prepared samples of humic acids.
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Influence of pH and ionic strength on barrier abilities of humic substances
Přítulová, Marie ; Kratochvílová, Romana (referee) ; Klučáková, Martina (advisor)
The main aim of this bachelor thesis is the study of humic acids and their barrier properties. The reactivity of humic acids was studied by simple laboratory diffusion techniques in plastic diffusion cells. This thesis is mainly focused on the through-diffusion processes in hydrogel media. Hydrogel media were based on the thermoreversible polysaccharide (agarose) with or without addition of humic acids. The rate of reactivity of humic acids was compared by the interactions with organic cationic dye – methylene blue. The influence of ionic strength and pH was tested as well.
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The study of the association behavior of the amphiphilic copolymers in solutions containing low molar compounds by means of computer simulations.
Šindelka, Karel ; Limpouchová, Zuzana (advisor) ; Slavíček, Petr (referee) ; Vondrášek, Jiří (referee)
Title: The study of the association behaviour of the amphiphilic copolymers in solutions containing low molar compounds by means of computer simulations. Author: Mgr. Karel Šindelka Department: Faculty of Science, Charles University Supervisor: Doc. Ing. Zuzana Limpouchová, Csc. Abstract This doctoral thesis focuses on the study of electrostatic self- and co-assembly in complex polymer solutions containing polyelectrolyte (PE) block copolymers together with surfactants, neutral homopolymers, or oppositely charged PEs using the dissipative particle dynamics (DPD). It was shown that the electro- static self-assembly depends not only on the cooperative interactions of oppo- sitely charged PE chains, but also on the amphiphilicity of PE species or on the polymer block compatibility, among other properties. PEs with incompatible blocks create well-defined core-shell structures, while large ill-defined crew-cut aggregates form from PEs with compatible blocks In non-stoichiometric mixtures of PEs with incompatible blocks, co-assembled nanoparticles are smaller than in stoichiometric mixtures and are charged. The destabilization of larger aggregates depends on how the PE charge surplus is introduced: the effect is strongest when the density of the surplus PE charge on the PE chains is increased and weakest when the...
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Novel conjugated polymers of the metallo-supramolecular and polyelectrolyte class
Hladysh, Sviatoslav ; Vohlídal, Jiří (advisor) ; Strachota, Adam (referee) ; Jindřich, Jindřich (referee)
This thesis targets the development of conjugated polymers with improved process ability from solutions. Two types of ionic polymers are addressed: (i) conjugated metallo-supramolecular polymers (MSPs) composed of conjugated heteroaromatic unimers (building blocks) linked to chains by various metal ions giving charged main chains, and (ii) polythiophene polyelectrolytes containing ionic pendants. Processing advantages of conjugated polyelectrolytes consist in the possibility of their processing from solutions in green solvents such as alcohols or even water. The advantages of MSPs consist in the thermodynamic control of the degree of polymerization (length) of their chains in solutions by the choice of solvent and temperature. As a result, MSPs reversibly provide systems of low viscosity that can be processed from solutions more easily than high-molar-mass polymers giving highly viscous solutions. Synthesis of appropriately designed unimer(s) is the key step of preparation of an MSP. Within this thesis, a series of novel unimers composed of linear oligothiophene type (mono-, bi-, ter- a thieno-thiophene- diyl) central blocks capped with 2,6-bis(oxazoline-2-yl)pyridine (pybox) or 2,6-bis(imidazole-2-...
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Counterion condensation on a polyelectrolyte: A fluorescence quenching study
Riedlová, Kamila ; Štěpánek, Miroslav (advisor) ; Humpolíčková, Jana (referee)
In this thesis, we studied the counterion condensation on the polyelectrolyte chain by means of the fluorescence quenching technique, using poly(methacrylic acid) (PMAA) labelled by the naphthyl group either at the end or in the middle of the chain and cesium ions as counterions which act as the fluorescence quencher. Both polymer samples were characterized by dynamic light scattering. The interaction of Cs+ ions with the polyelectrolyte was studied in solvents differing in the dielectric permittivity, using mixtures of water with 1,4-dioxane. The results confirm that fluorescence quenching is enhanced by the counterion condensation and that this process is more pronounced in the case of the naphthyl moiety localized in the middle of the PMAA chain.
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Linear semiflexible polyelectrolytes in solutions
Bačová, Petra ; Limpouchová, Zuzana (advisor) ; Lísal, Martin (referee)
Title: Linear semiflexible polyelectrolytes in solutions Author: Petra Bačová Department: Faculty of Science, Charles University in Prague Supervisor: Doc. Ing. Zuzana Limpouchová, CSc. Supervisor's e-mail address: zl@vivien.natur.cuni.cz Consultant: Mgr. Peter Košovan, PhD. Abstract: In this thesis I used the Molecular dynamics simulations for study of charged polymers (polyelectrolytes) and their behaviour in solutions. Wide range of polyelectrolytes are se- miflexible and in contrast to neutral polymers it is possible to influence their stiffness by changing the properties of solution as for example ionic strength. The chain flexibility may be characterized by the persistence length. Thesis explains how to express the persistence length from orientational correlation function which shows the double exponential decay. Two contributions to chain stiffness are discussed and the interest is concentrated around electrostatic persistence length which seems to be scale dependent. An effect of added salt on the chain conformation is studied. Salt is treated implicitly within the Debye-Hückel approximation. The results are confronted with OSF theory and the conclusions of vari- ational calculations of Maghi and Netz. The presented thesis describes the conformational behaviour of polyelectrolytes in salty solutions,...
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The study of the association behavior of the amphiphilic copolymers in solutions containing low molar compounds by means of computer simulations.
Šindelka, Karel
Title: The study of the association behaviour of the amphiphilic copolymers in solutions containing low molar compounds by means of computer simulations. Author: Mgr. Karel Šindelka Department: Faculty of Science, Charles University Supervisor: Doc. Ing. Zuzana Limpouchová, Csc. Abstract This doctoral thesis focuses on the study of electrostatic self- and co-assembly in complex polymer solutions containing polyelectrolyte (PE) block copolymers together with surfactants, neutral homopolymers, or oppositely charged PEs using the dissipative particle dynamics (DPD). It was shown that the electro- static self-assembly depends not only on the cooperative interactions of oppo- sitely charged PE chains, but also on the amphiphilicity of PE species or on the polymer block compatibility, among other properties. PEs with incompatible blocks create well-defined core-shell structures, while large ill-defined crew-cut aggregates form from PEs with compatible blocks In non-stoichiometric mixtures of PEs with incompatible blocks, co-assembled nanoparticles are smaller than in stoichiometric mixtures and are charged. The destabilization of larger aggregates depends on how the PE charge surplus is introduced: the effect is strongest when the density of the surplus PE charge on the PE chains is increased and weakest when the...
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