Determination Of Association Constants And FRET In Hydrazide-based Molecular Duplex Strands

Construction of models from abiotic building blocks to mimic biomolecules and enhance our understanding on them,is a hot topic in supramolecular chemistry.Fluorophores were introduced into our previously reported DNA mimics—— hydrazide-based molecular duplex strands in the thesis.On the one hand,the molecular duplexes were endowed with fluorescence;on the other hand,we wished to determine the association constants for the duplexes via fluorescence method and study fluorescence resonance energy transfer(FRET)in the duplexes.Though various NMR methods are powerful tools for hydrogen bonding mediated self-assembly,the limited sensitivity precludes their applications in dilution solution.While FL methods are good complements due to their high sensitivity and low detection limit.Due to its easy formation of excimer band that is well separated from its monomer emission band,we attached pyrene fluorophore into hydrazide-based oligomers to determine the association constants for the duplexes.The pyrene fluorophores were drawed together to induce intense excimer emission band due to formation of the duplexes.The dimerization constants were obtained by nonlinear fitting the excimer intensity at varied concentrations.What's more,excimer-monomer transition was observed when a non-fluorescent oligomer with complementary hydrogen bonding sites was added to the pyrene labelled oligomers via supramolecular substitution.Based on this phenomenon,the association constants for heterodimers were also determined.The association constants increased substantially with increase of inter-strand hydrogen bonds.When oligomer with pyrene and perylene fluorophores were mixed,high efficient FRET from pyrene to perylene was observed due to proximity of the two type of fluorophores via similar supramolecular substitution reaction.Mixing concentrations,temperature,polarity of the solvents,and non-fluorescent oligomers,could affect the efficiency of FRET substantially.We found that the stronger the association,the less affected.In summary,the association constants for hydrazide-based hydrogen bonding mediated molecular duplexes were successfully determined in the current thesis.In addition,the FRET in the duplexes was explored.These findings deeply enhanced our understanding on the self-assembly behavior of hydrazide-based duplexes and would in turn guide further design and application.