Structural Properties Of Ribose-protected Thioguanosine And Preparation Of Organosilsesquioxane (RSiO_1.5)n Crystals From Swollen Polymer

This dissertation includes two aspects of research work. One is about the structural properties of ribose-protected thioguanosin (TG) and hydrogen bonding behaviors of 2'-deoxy-3',5'-O-Diacetyluridine. The other is dealth with a new approach to polysilsesquioxane (CH₃SiO_1.5)₈ crystals from swollen PHEMA, and the reaction mechanism was explored in this section.First of all, a systematic study was performed focusing on the structural properties of ribose-protected thioguanosin (TG). To investigate the supramolecular interactions of thioguanine base of thioguanosine with metal salts, we introduced protective groups on ribose skeleton to produce ribose-protected thioguanosine (TG). From the results concerning the interactions of ribose-protected thioguanosine (TG) with alkali metal and alkali earth metal salts in solution, it is observed that ribose-protected thioguanosine (TG) shows high cesium cation selectivity. Meanwhile, different counterions have different effects on this cesium cation recognition, and the most distinct effect occurs with F- ion. These selective interactions are characterized by UV, FL, ¹H NMR(1D, 2D), ¹³³Cs NMR, ¹³C NMR, ¹⁹F NMR, MALDI-TOF-MS, ESI-MS and IR. It is suggested that the crucial factor of the distinct interactions between TG and these metal salts is the nature of the metal salts rather than their solubility.Disulfide bonded TG dimer can be obtained from the methylene chloride solution of ribose-protected thioguanosine (TG) in moderate yield under natural light environment. The COSY and NOESY spectra showed that TG and disulfide bonded TG dimer are of the same conformation. This process is irreversible. At the excitation wavelengths of 330 nm and 345 nm, disulfide bonded TG dimer revealed strong emission bands near 400 nm, while the emission intensity near 400 nm corresponding to TG is very weak. The quenching mechanism corresponding to TG is probably based on photoinduced electron transfer (PIET).N—H…O intermolecular hydrogen bonds link the independent molecules in single crystal of 2'-Deoxy-3',5'-di-O-acetyluridine , which may be effective in the stabilization of the structure . Dipole-Dipole and van der Waals interactions are also effective in the molecular packing. There is no base-base(Ï€-Ï€)stacking .We have developed a novel, efficient approach to the preparation of discrete, mor- phological polysilsesquioxane (CH₃SiO_1.5)₈ crystals from CH₃Si(OCH₂CH₃)₃ trapped in swollen polymer systems ( such as PHEMA) in 23% yield under certain acidic or alkaline condition. It is noteworthy that swelling-based methods are being explored for preparing other organosilsesquioxane (RSiO_1.5)n crystals. i.e. (C₂H₅SiO_1.5)_n, (C₆H₅SiO_1.5)_n.