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ABSTRACT: Nine dendronized poly(amide-triazole)s 2-Gm Gn (m=1-3, n=1-3), were prepared by the 1:1 copolymerization between AA-type dendritic diazides 4-Gm (m=1-3) and BB-type dendritic diacetylenes 5-Gn (n=1-3) under the copper(I)-mediated click coupling conditions. The degree of polymerization value of the polymers was found to range from 15-50, and decreased with increasing size of the dendron, suggesting steric hindrance had a retardation role on the copolymerization efficiency. Based on FT-IR and (1)H NMR studies, it was found that significantly strong, interchain hydrogen bonding between the amide units was present in the solution state after copolymerization, whereas the monomers 4-Gm and 5-Gn were devoid of any intermolecular hydrogen-bonding interaction. Hence a positive allosteric hydrogen-bonding effect was observed after polymerization, and could be rationalized by the zip effect. The strength of the interchain association in polymers 2-Gm Gn was found to decrease with increasing size of the dendron (i.e., 2-G1 G1>2-G1 G2>2-G2 G1≈2-G2 G2>2-G1 G3≈2-G3 G1>2-G2 G3≈2-G3 G2>2-G3 G3). Among the nine polymers, only 2-G1 G2 and 2-G2 G1 were good organogelators for aromatic solvents, while the 2-G2 G2 polymer, bearing the closest structural resemblance to the previously reported organogelator 1-G2 prepared from the polymerization of AB-type monomers, was devoid of gelating power. Careful analysis of structures of the present polymer series 2-Gm Gn and the previously reported series 1-Gn suggested that the polymer backbone symmetry played a subtle role in controlling their self-assembling and gelating properties.
Chemistry 06/2011; 17(30):8395-403. · 5.93 Impact Factor
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ABSTRACT: Two series of aliphatic hydrocarbon-based G1-G3 dendritic 2-ureido-4-pyrimidinones (UPy) (S-Gn)₂ and (L-Gn)₂, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p-aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self-assembling behavior and tautomeric preference of the dendritic UPy derivatives were examined by ¹H NMR spectroscopy. The dimerization constants (K(dim*)) of the DDAA tautomers were unchanged at 10⁷ M⁻¹ in CDCl₃ at both 25 and 50°C, which were comparable to those of UPy compounds bearing other nonpolar substituents. Furthermore, the lower limits on the K'(dim*) of the DADA tautomeric forms of the (S-Gn)₂ and (L-Gn)₂ series were determined to be 10⁶ and 10⁵ M⁻¹ in CDCl₃, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the (L-Gn)₂ dimers are more stable than those of (S-Gn)₂ in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond-mediated self-assembling process.
Chemistry - An Asian Journal 10/2010; 5(10):2249-57. · 4.50 Impact Factor
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ABSTRACT: This Feature Article gives a summary on the conformational and supramolecular properties of a special type of click molecules, namely, main chain and cyclic oligo- and polytriazoles. The triazole ring is an interesting structural motif since it is a hydrogen bond donor and acceptor, a large molecular dipole and also a metal ligand. It can interact with a wide variety of functionalities, e.g. hydrogen bonding partners (e.g. amides or anions), molecular dipoles, and metal ions to generate many fascinating conformational features such as pseudo rod-like, U-turn, helical, double helical structures, beta-strands and beta-sheets. Oligo- and polytriazoles can also exhibit interesting supramolecular attributes such as host-guest complexation, self assembly, chemosensing and gelating properties. It is believed that many new and unique conformational and supramolecular properties can be created by incorporating the correct type of functional group partners into the oligo- and polytriazole backbone. This type of research can also advance our understanding on functional properties of such triazole-rich compounds.
Chemical Communications 05/2010; 46(20):3437-53. · 6.17 Impact Factor
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Angewandte Chemie International Edition 01/2008; 47(36):6912-6. · 13.45 Impact Factor
