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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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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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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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