The Binding Characteristics Of Ionic Liquids And Thionine On Nano-structure Surfaces And Their Interaction With DNA

The binding of functional molecules, such as bioactive dyes, ionic liquids, drug etc. on the nano-sized structure materials, for example, micelles, metal nanoparticles, will greatly improve the surface properties of nano-sized materials, even result in the alteration of structure and functionality of the materials, which is of great importance in the biomedical field. However, to fabricate the functional composite materials on the basis of the binding characteristic of organic molecules on nanomaterials, and to develop their application in life science, it is necessary to solve the following questions. One is the binding mechanism of functional molecules on nano-sized structures, and the other is the application of the binding behavior in life science, such as the separation and purification of biomacromolecules, interaction modes of drug on DNA or proteins, etc.. Therefore, the research presented in this dissertation has been focused on the following aspects.1. The ionic liquid (IL) 1-alkyl-3-methylimidazolium bromide (CnmimBr, n= 4,8, 12), induced micelle to vesicle transition in a dodecyl benzenesulfonate(SDBS) aqueous solution was investigated for the first time by using turbidity, dynamic light scattering(DLS), negative-stained and cryogenic transmission electron microscopy (cryo-TEM),ζ-potential measurements,1H nuclear magnetic resonance (1HNMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), isothermal titration microcalorimetry (ITC), and density functional theory (DFT) calculations. It is found that a minimum IL concentration is required to induce the micelle to vesicle transition, which is accompanied with a remarkable turbidity increase. DLS results clearly show the micelle to vesicle transition process, which was confirmed by the TEM images of vesicles. The spontaneously formed vesicles are multilamellar structures with tunable size, and show superstability with time and temperature. With the increasing chain length of the IL CnmimBr, the onset concentration of micelle to vesicle transition CMVT is significantly decreased from 15 mM for C4mimBr to 1 mM for C12mimBr, suggesting that the ability of inducing the structural transition is enhanced with the chain length of the IL. During the micelle to vesicle transition, only a part of the IL molecules are bounded onto the SDBS aggregates. The formed vesicles is negatively charged, and the surface charge density on the vesicles can be tuned by changing the molar ratio of the IL to SDBS. ITC indicates that the micelle to vesicle transition induced by C4mimBr is endothermic, and the enthalpy change△HMVT is about 3.1 kJ/mol. The 1HNMR and FT-IR spectra indicate that the imidazole ring of C4mim+, including the-CH3 and-CH2 groups linked to the ring, interacts with phenyl ring of SDBS through the strong electrostatic interaction, and the hydrocarbon chain of C4mim+ interacts with that of SDBS through hydrophobic interaction. A moleular mechanism of the micelle to vesicle transition was proposed. At lower concentrations of C4mimBr, the individual C4mimBr molecules bind onto the oppositely charged SDBS molecules in the micelles to form C4mim+-DBS- ion pairs with the-C4H and-C5H groups of imidazole ring pointing to the phenyl ring of SDBS. The electrostatic and hydrophobic forces disrupt SDBS micelles, make the C4mim+-DBS- ion pairs to form aggregates of lower curvature. Following this, the hydrophobic interaction drive the micelle to vesicle transition. Furthermore, the geometry and energy analysis obtained from the DFT calculations confirm the above transition mechanism.2. Binding characteristics of thionine on gold nanoparticles with different sizes have been systematically studied by using UV-vis spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), cyclic voltammetry, Fourier transform infrared spectroscopy and quantum chemical calculations. With the increasing concentration of gold nanoparticles, the absorption peak intensity of H-type dimers of thionine increases continuously, whereas that of monomers of thionine first increases and then decreases. The addition of gold nanoparticles makes the equilibrium between the monomer and H-type dimer forms of thionine move toward the dimer forms. Due to the binding between thionine and gold nanoparticles, the fluorescence quenching of thionine by gold nanoparticles is enhanced with increasing amounts of gold nanoparticles, and the quenching is both static and dynamic. TEM images and DLS measurements show that the addition of thionine results in the formation of gold nanoclusters, and further support the spectral results. Cyclic voltammetric and infrared spectroscopic studies show that the nitrogen atoms of both of the NH2 moieties of thionine strongly bind to the gold nanoparticle surfaces, which is confirmed by the quantum chemical calculations based on the density functional theory (DFT) at the B3LYP level. Furthermore, the adsorption behavior of thionine on gold nanoparticles is also influenced by the particle size. For 15-20 nm and 3-6 nm particles, the numbers of adsorbed thionine molecules per gold nanoparticle are about 7.66×104 and 1.21×103, respectively, and the effect of smaller particles is more significant. Thionine molecules can not only bind to a particle to form a compact monolayer via both of the NH2 moieties, but they can also bind to two particles via their two NH2 moieties, respectively. The unique binding behavior will provide an important method of designing the novel functionalized dye-inorganic nanocomposite materials.3. The binding characteristic and molecular mechanism of the interaction between a typical ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim]Cl), as a green solvent, and DNA were investigated for the first time by conductivity measurements, fluorescence spectroscopy, dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), circular dichroism (CD) spectroscopy,31P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, isothermal titration calorimetry (ITC), and quantum chemical calculations. It is found that the critical aggregation concentration of [bmim]Cl is decreased in the presence of DNA, and the addition of [bmim]Cl induces a continuous fluorescence quenching of the intercalated probe ethidium bromide (EtBr), indicating that the interaction between the ionic liquid and DNA is sufficiently strong to exclude EtBr from DNA. DLS results show that [bmim]Cl can induce a coil to globule transition of DNA at a low IL concentration, which was confirmed by the cryo-TEM images of DNA-IL complexes. With [bmim]Cl added, the resulting globular DNA structures and the extended DNA coils are first compacted, and then grow in their sizes. During the binding process, DNA maintains the B-form, but the base packing and helical structure of DNA are altered to a certain extent. The 31P NMR and IR spectra indicate that the cationic bmim+ interact with the phosphate groups of DNA through electrostatic attraction, and the hydrocarbon chains of bmim+ groups interact with the bases through strong hydrophobic association. ITC results reveal the interaction enthalpy between [bmim]Cl and DNA, and show that the hydrophobic interaction between the hydrocarbon chains of [bmim]Cl and the bases of DNA provides the dominant driving force in the binding. Based on the quantum chemical calculations, it can be inferred that at a low IL concentration, the cationic headgroups of [bmim]Cl would be localized within several A from DNA phosphates, whereas the hydrophobic chains would lay down on the DNA surface. When the IL concentration is above 0.06 mol/L, the cationic headgroups are near DNA phosphates, and the hydrocarbon chains stand on the DNA surface.4. The interaction model between thionine and DNA was investigated by UV-vis and fluorescence spectroscopy. It is found that at low ratios of DNA to thionine, thionine is mostly intercalated into DNA, whereas at high ratios of DNA to thionine the electrostatic interaction play the main role in the interaction between them. Furthermore, with the increasing concentration of 3 nm gold nanoparticles, the hypochromic effect and fluorescence quenching are gradually increased, even disappear at a relatively high concentration of gold nanoparticles. This indicates that the intercalation of thionine into DNA is weakened, and finally, is completely inhibited. Dynamic light scatting and TEM studies indicate that the addition of gold nanoparticles result in the formation of more compacted Th-DNA complexes, in which the thionine molecules are released from DNA due to the electrostatic attraction. During the binding process, the addition of gold nanoparticles make the conformation of DNA transform from B form to A form gradually. Therefore, it is feasible to adjust the interaction model of thionine in DNA by changing the molar ratio of thionine to DNA or by adding gold nanoparticles.