I.Metal Ion-Responsive Functional Polymers with Different Backbone Structures: Flexible/Rigid Hydrocarbon Chain and Ether Linkage II.Metal Ion-Induced Random Coil/Helix Conformation Transition of Functional Oligo-L-Lysine Based Octamers III.Acridinium Salt-Based Fluoride and Acetate Chromofluorescent Probes: Molecular Insights into Anion Selectivity Switching
Date Issued
2011
Date
2011
Author(s)
Lin, Yu-Chen
Abstract
Chapter I describes the development of side-chain functionalized polymers containing metal ion-responsive units with flexible/rigid backbone structures that have potential in developing metal ions sensory materials or self-assembly into hierarchical ordered structures. Poly-norbornene based homopolymer derived from ring-opening metathesis polymerization (ROMP) is regarded as rigid backbones because of the bicyclic constraints of norbornene. Decrease of backbone rigidity can be achieved through the alternating copolymerization of an appropriate cyclic olefin comonomer. A balance of ring strain and steric hindrance of the comonomers plays a key role in constructing alternating backbone structures. Thus, the incorporation of hydrocarbon or ether spacers into copolymers efficiently keeps two metal ion-chelators away from each other to prevent self-quenching of the dye molecules and makes a difference in polymer solubility that copolymers with ether linkage in the backbone chain enhance solubility in organic solvents. The use of 7-membered and 14-membered heterocyclic olefin comonomers results in no and lower levels of alternation behavior suggesting that low ring strain comonomer could not undergo cross-propagation with norbornene monomer.
Chapter II describes that oligo-L-lysine based octamer PGLM8 containing metal ion-chelators in the side chains is of interest because the restricted rotation of peptide bonds provides a rigid backbone structure. PGLM8 adopts a stable helix conformation due to the formation of intramolecular sandwich-type complexes with four equivalents strontium ions through metal-coordination interaction at i, i + 4 spacing. The addition of more than four equivalents strontium ions results in the deformation of helix structure with a concomitant fluorescence enhancement. It is found that the presence of other alkaline earth metal ions such as Ca2+ and Ba2+ also promote the helix formation; other metal ions such as Na+, K+, and Pb2+ cannot induce the conformation transition, indicating that alkaline earth metals are suitable side chain cross-linking agents due to their higher charge density and coordination geometry.
Chapter III describes the development of acridinium salt-based chromofluorescent probes for the detection of anions – fluoride and acetate. Analytes that form covalent bonds with receptors to trigger highly selective reactions and induce changes in fluorescence emission or absorption are being used to design target-specific chromogenic/fluorogenic probes. A nucleophilic attack occurs at the highly electron- deficient C9 position of acridinium salts more readily than at the corresponding position in their pyridinium or quinolinium counterparts. Our strategy is using this reaction feature to develop acridinium-based chromogenic and fluorescent sensors ACD1–ACD4 for effective anion sensing and delineate the sensing mechanisms for F–, AcO– ions, and halides. Both of F– and AcO– ions act as nucleophiles to attack at the C9 position of acridinium moiety inducing pronounced changes in UV-vis absorption and fluorescence emission while halides only exert collision quenching of acridinium. Anion selectivity can be achieved through controlling the steric congestion around the reactive site. As a matter of fact, our designed fluorescent probes successfully differentiate fluoride and acetate and the sensing action of the probes is reversible, which is an important feature for fluorescent probes.
Subjects
Metal Ion-Responsive Functional Polymers
Flexible/Rigid Backbone Structures
Helix Conformation
Fluoride and Acetate Chromofluorescent Probes
Type
thesis
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