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Influence of ionic strength on the properties of ionic amphiphilic pairs
Filipová, Lenka ; Smilek, Jiří (referee) ; Mravec, Filip (advisor)
The Bachelor thesis studies catanionic vesicle systems consisting of ion pair amphiphile (IPA) and their properties in the presence of ionic strength. Ion pair amphiphile was prepared from single-chained surfactants: cationic surfactant HTMAB (hexadecyltrimethylammonium bromide) and anionic surfactant SDS (sodium lauryl sulfate). Cationic double-chained surfactant DDAC (dimethyldioctadecylammonium chloride) was added in order to stabilize the vesicle system and make it positively charged. Cholesterol was also added to further stabilize the vesicle system. The system is considered to be relatively stable when consisting of 90 % IPA and 10 % DDAC with 43 mol.% cholesterol in a membrane. The stability of the system can be disrupted by external factors such as ionic strength. The Ionic strength was induced by NaCl solutions of varying concentrations (0.0, 0.5, 1.0, 2.0, 50.0, 100.0, 150.0 and 300.0 mM). The change of properties of a vesicle system, which was induced by ionic strength, was analyzed by electrophoretic and dynamic light scattering, fluorescence anisotropy, and generalized polarization. –potential was obtained by electrophoretic light scattering analysis which determines the stability of the system. Dynamic light scattering measurement resulted in the determination of the size of vesicles. The fluidity of vesicles’ membranes was examined by fluorescence anisotropy with DPH (1,6-diphenyl-1,3,5-hexatriene) as a probe. The hydration shell of vesicles was observed by generalized polarization with Laurdan (2-(dimethylamino)-6-dodecanoylnaphthalene) as a probe. As a result, it was found out that low ionic strength (0.5 to 2.0 mM) causes a decrease in the size of vesicles and high ionic strength (50.0 to 300.0 mM) causes vesicles to grow in size. –potential showed a consistent trend for the whole concentration series – its value rapidly decreasing with increasing ionic strength. The samples with the concentrations of salt 50.0 to 300.0 mM were considered unstable according to the –potential data. Fluorescence anisotropy decreases with increasing temperature and increasing ionic strength. The value of generalized polarization decreases with increasing temperature; hence there is more solvation of a vesicle membrane. The highest value of generalized polarization was measured when the concentration of sodium chloride was relatively high (from 50.0 to 300.0 mM), as a result of which the membrane was less hydrated and therefore, more organized.
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Influence of ionic strength on the properties of ionic amphiphilic pairs
Filipová, Lenka ; Smilek, Jiří (referee) ; Mravec, Filip (advisor)
The Bachelor thesis studies catanionic vesicle systems consisting of ion pair amphiphile (IPA) and their properties in the presence of ionic strength. Ion pair amphiphile was prepared from single-chained surfactants: cationic surfactant HTMAB (hexadecyltrimethylammonium bromide) and anionic surfactant SDS (sodium lauryl sulfate). Cationic double-chained surfactant DDAC (dimethyldioctadecylammonium chloride) was added in order to stabilize the vesicle system and make it positively charged. Cholesterol was also added to further stabilize the vesicle system. The system is considered to be relatively stable when consisting of 90 % IPA and 10 % DDAC with 43 mol.% cholesterol in a membrane. The stability of the system can be disrupted by external factors such as ionic strength. The Ionic strength was induced by NaCl solutions of varying concentrations (0.0, 0.5, 1.0, 2.0, 50.0, 100.0, 150.0 and 300.0 mM). The change of properties of a vesicle system, which was induced by ionic strength, was analyzed by electrophoretic and dynamic light scattering, fluorescence anisotropy, and generalized polarization. –potential was obtained by electrophoretic light scattering analysis which determines the stability of the system. Dynamic light scattering measurement resulted in the determination of the size of vesicles. The fluidity of vesicles’ membranes was examined by fluorescence anisotropy with DPH (1,6-diphenyl-1,3,5-hexatriene) as a probe. The hydration shell of vesicles was observed by generalized polarization with Laurdan (2-(dimethylamino)-6-dodecanoylnaphthalene) as a probe. As a result, it was found out that low ionic strength (0.5 to 2.0 mM) causes a decrease in the size of vesicles and high ionic strength (50.0 to 300.0 mM) causes vesicles to grow in size. –potential showed a consistent trend for the whole concentration series – its value rapidly decreasing with increasing ionic strength. The samples with the concentrations of salt 50.0 to 300.0 mM were considered unstable according to the –potential data. Fluorescence anisotropy decreases with increasing temperature and increasing ionic strength. The value of generalized polarization decreases with increasing temperature; hence there is more solvation of a vesicle membrane. The highest value of generalized polarization was measured when the concentration of sodium chloride was relatively high (from 50.0 to 300.0 mM), as a result of which the membrane was less hydrated and therefore, more organized.
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Solvent effects on ion pairing and photoionization in water
Pluhařová, Eva ; Jungwirth, Pavel (advisor) ; Nachtigall, Petr (referee) ; Laage, Damien (referee)
Title: Solvent effects on ion pairing and photoionization in water Author: Mgr. et Ing. Eva Pluhařová Department: Physical and Macromoleculer Chemistry Advisor: Prof. Pavel Jungwirth, DSc., IOCB AS CR, v.v.i. Advisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: Various methods of theoretical chemistry, namely classical molecular dynamics simulations with empirical force fields, ab initio molecular dynamics, enhanced sampling methods, and ab initio calculations were used to provide new insight into ion pairing and photoionization in aqueous solutions. Systems mod- eling aqueous solutions of decreasing size were investigated by computational methods of increasing level of sophistication. In a classical molecular dynamics study of concentrated lithium salt solutions, the electronic continuum correction to account for polarization provided qualita- tive improvement over the conventional non-polarizable force fields and enabled molecular interpretation of neutron scattering measurements. The same model- ing approach was also successful in predicting the affinity of halide ions to the solution/oil interface. By combining ab initio molecular dynamics and potential of mean force cal- culations, we designed a reliable computational protocol for calculating the free energy profile for an ion pair...
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Molecular modelling in drug development
Kolář, Michal ; Hobza, Pavel (advisor) ; Vondrášek, Jiří (referee) ; Clark, Tim (referee)
Molecular modelling has become a well-established tool for studying biological mole- cules, moreover with the prospect of being useful for drug development. The thesis summarises research on the methodological advances in the treatment of molecular flexibility and intermolecular interactions. Altogether, seven original publications are accompanied by a text which aims to provide a general introduction to the topic as well as to emphasise some consequences of the computer-aided drug design. The molecular flexibility is tackled by a study of a drug-DNA interaction and also by an investigation of small drug molecules in the context of implicit solvent models. The approaches which neglect the conformational freedom are probed and compared with experiment in order to suggest later, how to cope with such a freedom if in- evitable. The noncovalent interactions involving halogen atoms and their importance for drug development are briefly introduced. Finally, a model for a faithful description of halogen bonds in the framework of molecular mechanics is developed and its per- formance and limits are tested by a comparison with benchmark ab initio calculations and experimental data. 1
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