Browsing by Subject "Monomers"

Now showing 1 - 4 of 4

Open Access
Catalytic self-threading: a new route for the synthesis of polyrotaxanes
(American Chemical Society, 2004) Tuncel, D.; Steinke, J. H. G.
Main chain and branched polyrotaxanes have been synthesized in which polymerization and rotaxane formation occur simultaneously, due to the presence of the catalytically active self-threading macrocycle cucurbit[6]uril. Using monomers that contain stopper groups to prevent the catalytic macrocycle from noncatalytic threading, it was possible to prepare polyrotaxanes in high yields with molecular weights up to 39000. These polyrotaxanes are structurally perfect in the sense that exactly two macrocyles are threaded onto each structural repeat unit. Investigations into the polymerization mechanism have demonstrated that the catalyst cucurbit[6]uril is highly sensitive toward the structure of the monomers employed and a poorly designed monomer may result in complete inactivity. Features of the mechanism are discussed in some detail.
Open Access
Enhanced interactions of amino acids and nucleic acid bases with bare black phosphorene monolayer mediated by coadsorbed species
(American Chemical Society, 2019) Kadıoğlu, Y.; Görkan, T.; Üzengi-Aktürk, O.; Aktürk, E.; Çıracı, Salim
In this paper, we characterize amino acids and nucleic acid bases (nucleobases), such as glutamine, histidine, tyrosine, adenine, guanine, cytosine, and thymine, and examine their interaction with bare, as well as with gold cluster and Ti adatom covered, black phosphorene (α-P) monolayers using density functional theory. The binding of these amino acids and nucleobases to the bare α-P monolayer is realized generally through weak van der Waals interaction and comprises only a small amount of charge exchange. Accordingly, the electronic energy structures of adsorbates and underlying substrate are not affected significantly. However, the electronic structure of bare α-P is significantly affected upon adsorption of a gold cluster and a single Ti adatom; depending on the size of the adsorbate and the symmetry of their coverage, the energy band gap can be tuned and permanent magnetic moments can be attained. Additionally, the adsorption of amino acids or nucleobases to these adsorbates on an α-P monolayer results in enhanced binding and hence makes their sustainable fixation on α-P monolayer possible. In particular, a semiconducting Au decorated α-P monolayer undergoes a metal–insulator transition upon the adsorption of tyrosine. This and similar effects favor the α-P monolayer in biosensor applications. In contrast to the situation with adsorbates, the binding of amino acid is not enhanced when it adsorb to patterned vacancy or divacancy sites of the α-P monolayer. Our study shows that the absorbance of the bare α-P monolayer can be enhanced by coating with amino acid and nucleobases. The absorbance spectrum can be further modified by the adsorption of these molecules to gold atoms on the α-P monolayer.
Open Access
Novel molecular building blocks based on the boradiazaindacene chromophore: applications in fluorescent metallosupramolecular coordination polymers
(2009) Bozdemir, Ö. A.; Büyükcakir, O.; Akkaya, E. U.
We designed and synthesized novel boradiazaindacene (Bodipy) derivatives that are appropriately functionalized for metal-ion-mediated supramolecular polymerization. Thus, ligands for 2-terpyridyl-, 2,6-terpyridyl-, and bipyridyl-functionalized Bodipy dyes were synthesized through Sonogashira couplings. These fluorescent building blocks are responsive to metal ions in a stoichiometry-dependent manner. Octahedral coordinating metal ions such as Zn II result in polymerization at a stoichiometry corresponding to two terpyridyl ligands to one Zn II ion. However, at increased metal ion concentrations, the dynamic equilibria are re-established in such a way that the monomeric metal complex dominates. The position of equilibria can easily be monitored by 1H NMR and fluorescence spectroscopies. As expected, although open-shell Fe II ions form similar complex structures, these cations quench the fluorescence emission of all four functionalized Bodipy ligands. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
Open Access
Synthesis of polybenzoxazine/clay nanocomposites by in situ thermal ring-opening polymerization using intercalated monomer
(2011) Demir, K.D.; Tasdelen, M.A.; Uyar, T.; Kawaguchi, A.W.; Sudo, A.; Endo, T.; Yagci, Y.
A new class of polybenzoxazine/montmorillonite (PBz/MMT) nanocomposites has been prepared by the in situ polymerization of the typical fluid benzoxazine monomer, 3-pentyl-5-ol-3,4-dihydro-1,3-benzoxazine, with intercalated benzoxazine MMT clay. A pyridine-substituted benzoxazine was first synthesized and quaternized by 11-bromo-1-undecanol and then used for ion exchange reaction with sodium ions in MMT to obtain intercalated benzoxazine clay. Finally, this organomodified clay was dispersed in the fluid benzoxazine monomers at different loading degrees to conduct the in situ thermal ring-opening polymerization. Polymerization through the interlayer galleries of the clay led to the PBz/MMT nanocomposite formation. The morphologies of the nanocomposites were investigated by both X-ray diffraction and transmission electron microscopic techniques, which suggested the partially exfoliated/intercalated structures in the PBz matrix. Results of thermogravimetric analysis confirmed that the thermal stability and char yield of PBz nanocomposites increased with the increase of clay content. © 2011 Wiley Periodicals, Inc.