Syntheses and photochemical applications of dithiane and dithiepine-based molecular systems.

摘要

The goal of this thesis was to synthesize dithiane-based photolabile molecular objects and to study the photochemistry of methyldithiepines.; Functionalized dithianes were synthesized and used as photocleavable linkages to prepare various photolabile compounds including phospholipid- and glycolipid-like compounds, calixarene containing guest-host systems and carbohydrate bearing photocleavable chiral building blocks. As shown by this research, the dithiane-carbonyl adduct photochemistry can be successfully adopted to assemble a diverse set of organic molecules and macromolecules, which undergo photoinduced disassembly in the presence of electron-transfer sensitizers. In addition, several self-sensitized photolabile lipids were synthesized and employed to prepare photosensitive liposomes in formulation with POPC/DSPC and cholesterol. These liposomes unloaded their content upon irradiation due to the severing of the hydrophilic head group of the light sensitive lipids. An assay based on PFG NMR to monitor the release of small organic molecules was developed to measure quantitatively the photo-triggered change of the membrane permeability. The results support the use of TMSNa and fluorine containing compounds as probes to achieve high sensitivity.; The study of the photochemistry of methyldithiepines included the photooxidation of methyldithiepines with electron-donating groups to carboxaldehydes in oxygenated CCl₄ and, the photoinduced 1,3-proton shift of methyldithiepines with electron-withdrawing groups in deoxygenated solvents. Respective mechanisms were proposed for these two reactions. For the photooxidation reaction, after the initial electron transfer between the excited substrate and solvent CCl ₄, there was no peroxide formation which would otherwise have resulted in S-directed oxidation. The mechanism for the photoinduced 1,3-proton shift included protonation of the ethylenic moiety in the excited methydithiepine followed by the ground-state deprotonation of the methyl group. The first reaction provided a simple synthetic method, while the structure isomerization in the second reaction effectively disrupted the conjugation between the donor and the acceptor moieties, offering a potential way of modulating hyperpolarizabilities.