Specific Lon Effects On The Interactions Between Macromolecules

In this dissertation, we investigated the important influence of ion-specificity on the interactions between macromolecules, and the difference of physical properties of the polymer materials, which resulting from the interactions between the macromolecules. The results demonstrated that there was a significant influence of counterion-specificity on the protein adsorption property of polyelectrolyte brushes; and so on, the formation and physical properties of polymeric rotaxanes were also controlled by ion-specificity. The main results are as follows:(1) We studied the protein adsorption on the polyelectrolyte brushes in the presence of different types of counterion by quartz crystal microbalance with dissipation (QCM-D) measurements. The protein adsorption is driven by a decrease of osmotic pressure within the brushes with an increase of entropy via release of counterions. Our study demonstrates that counterion specificity has a significant influence on protein adsorption on the polyelectrolyte brushes. There are two different regimes for the counterion-specific protein adsorption. When the released counterions cannot bind onto the protein surface, the counterion-specific protein adsorption is dominated by the ion-specific counterion condensation within the polyelectrolyte brushes. If the released counterions can bind onto the protein surface, then the counterion-specific protein adsorption is dominated by the ion-specific re-binding of released counterions onto the protein surface.(2) We found that there was a significant effect of sodium salt in mediating supramolecular assemblies between1,2-polypropylene glycol (PPG) and β-cyclodextrin (CD). First, the aggregates precipitated from different sodium salt solutions exhibit different stoichiometric ratios of PPG to β-CD:PPG-(β-CD)7for NaCl and Na2CO3and PPG-(β-CD)8for NaAsO2, both of which are completely different from PPG-(β-CD)5for pure water and from PPG-(β-CD)6for lithium salts. Second, the interaction between PPG chains and sodium salts was studied by three independent experiments (viscosity, surface tension and molar conductivity), the results may partially explain the difference in compositions of the aggregates. We believe that the dehydration of PPG chains is initiated by inorganic ions, and the effect of anions dominates the process; and the presence of cation ions might be involved in a protective role against dehydration for PPG chains. Third, field emission scanning electron microscopy (FE-SEM) and thermogravimetric analyses (TGA) indicate that the supramolecular assemblies prepared, even though having the same composition, have rather different surface features and physical properties.(3) Based on the effect of ion-specificity, the introducing of a third component ferrocene (Fc) resulted in the formation of a ternary aggregate of polyethylene glycol (PEG),β-CD and Fc. The results indicate that the intermolecular aggregation behaviour leads to a striking change in structure and thermal property of the components aggregated. First, the data of X-ray diffraction (XRD), solid-state cross polarization/magic angle spinning (CP/MAS)13C NMR spectra and two-dimensional rotating frame nuclear Overhauser effect spectroscopy (ROESY) give us sufficient information about the formation and structure of the aggregate, Second, the ternary aggregate exhibits a one-step degradation mechanism and has much lower thermal stability than free components and especially the physical mixture of the components, this may not only relate to the structure of the aggregate, but also relate to the triple interaction between the three components in the aggregate, in this situation, Fc plays a role of stabilizer to promote the assemble between PEG and β-CD.