Book Description

Metal ions can interact with both natural and synthetic macromolecules to produce changes in their structure and conformation. This thesis addresses structure-property relationships in several classes of macromolecular materials which fit this description. In Chapter II, the gelation mechanism of 50/50 w/w mixtures of guanosine (G) and 2',3',5'-tri-O-acetylguanosine (TAcG) in aqueous 0.354 M KCl is investigated using static light scattering (SLS), polarized and depolarized dynamic light scattering (VV and VH DLS), small-angle neutron and X-ray scattering (SANS and SAXS), and viscometry. The results indicate sol and microgel phases coexist up to the macroscopic gel point. An unusual transient contribution to the gel modulus is attributed to fibrillar species trapped within the gel network. In Chapter III, a class of stimuli-responsive metallo-supramolecular gels self-assembled in good/poor solvent mixtures from metal ions and a ditopic macromonomer consisting of oligoethylene glycol end-capped with a 2,6-bis(1'-methylbenzimidazolyl)-4-pyridine ligand (MeBIP) is studied by SAXS and differential scanning calorimetry (DSC). An evolution from turbid to transparent gels with increase of good solvent content is shown to be due to the formation of a solvent-swollen lamellar structure. In Chapter IV, with the goal of developing redox-active assembly of supramolecular polymers in solution, we describe structural studies using viscosity, SAXS, SLS and DLS of the supramolecular polymers formed via binding of Cu(II) and Cu(I) ions to a ditopic macromonomer consisting of polytetrahydrofuran end-capped with MeBIP ligands. The results demonstrate differences in the molecular weight of the metallo-supramolecular polymers formed at fixed stoichiometry via Cu(II)-MeBIP versus Cu(I)-MeBIP binding. Chapter V describes structural characterization by SAXS of a cruciform base-paired ribonucleic acid (RNA) complex, which catalyzes an RNA splicing reaction. Comparison of the radii of gyration (Rg) of mutant complexes versus the wild type indicates a preference for one of four possible magnesium ion-driven folded conformers. Energy minimized atomistic structures are generated for the wild type and mutant complexes. Since the juxtaposition of catalytically-active groups in the selected conformer differs from that found in the native activated spliceosome, the results suggest a chaperoning role for spliceosomal proteins in ensuring the correct tertiary stacking of the base-paired helices.