Ryohei Kakuchi

Size-specific, colorimetric detection of counteranions by using helical poly(phenylacetylene) conjugated to L-leucine groups through urea acceptors.

A colorimetric detection susceptible to the dimensions of guest counteranions has been demonstrated by using poly(phenylacetylene) with L-leucine and urea functionalities (poly-PA-Leu). Poly-PA-Leu was prepared from N-(4-ethynylphenylcarbamoyl)-L-leucine ethyl ester (PA-Leu) by using [Rh(+){eta(6)-C(6)H(5))B(-)(C(6)H(5))(3)}(2,5-norbornadiene)] as a catalyst. The biased helical conformation of poly-PA-Leu was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of ammonium salts, including tetra-n-butylammonium acetate, tetra-n-butylammonium chloride, and tetra-n-butylammonium bromide anions (CH(3)COO(-), Cl(-), and Br(-)), into the poly-PA-Leu solution intensified the CD responses of poly-PA-Leu, which is indicative of the chiral adjustability of anion recognition by using urea groups. In addition, the combination of poly-PA-Leu with the CH(3)COO(-), Cl(-), and Br(-) anions promoted large redshifts in the absorption spectra, thus providing dramatic color changes from pale yellow to red. Guest dependency in the CD and UV/Vis spectra was clearly correlated with the size of the counteranions. Fundamentally, the addition of tetra-n-butylammonium nitrate, tetra-n-butylammonium hydrogen sulfate, tetra-n-butylammonium perchlorate, tetra-n-butylammonium azide, tetra-n-butylammonium fluoride, and tetra-n-butylammonium iodide anions (NO(3) (-), HSO(4) (-), ClO(4) (-), N(3) (-), F(-), and I(-)) has no effect on either the CD or UV/Vis profiles of poly-PA-Leu. The guest specificity observed in the CD and UV/Vis spectra clearly demonstrated the guest-dimension selectivity of poly-PA-Leu in counteranion recognition.

Control of thermoresponsive property of urea end‐functionalized poly(N‐isopropylacrylamide) based on the hydrogen bond‐assisted self‐assembly in water

The hydrogen bond has been recognized as one of the representative non-covalent interactions for realizing a three-dimensionally organized molecular architecture. In fact, biological macromolecular systems ingeniously construct specific higherorder structures that are stable in an aqueous medium, in which multiple hydrogen bonds are indispensable for stabilizing the structures. Although there are a number of artificial molecular architectures fabricated through hydrogen bonding in organic solvents, the realization of a supramolecular assembly based on hydrogen bonding in water has still remained an interesting issue because the intermolecular hydrogen bonds are easily disrupted in protic and polar solvents, such as water. For the supramolecular assembly based on hydrogen bonding in water, the hydrophobic microenvironment approach that is inspired by a biological system have been developed for protecting the hydrogen bonding capability from disruptive solvation by water molecules, thus making it possible to construct a wellordered self-assembly from synthetic molecules in water [1–3]. For example, Meijer et al. revealed that bifunctional ureidotriazines can self-assemble to form a helical supramolecular polymer in water through cooperative hydrogen bonds that are shielded by the hydrophobic microenvironment [4]. Kimizuka et al. achieved fabrication of a hierarchically self-assembled bilayer membrane in water through complementary hydrogen-bond pairs [5]. Sijbesma et al. further succeeded in the formation of the self-assembly from an amphiphilic triblock copolymer in water, in which urea groups that are placed at the center of a nonpolar segment contribute to the strong intermolecular hydrogen bonding [6]. Despite the definite validity of these approaches, the construction of stable intermolecular hydrogen bonding in water has still been a challenging task because an accurate and strict molecular design is required for the functional groups involved in the intermolecular hydrogen bonding, hydrophilic chains for water-solubility, and a hydrophobic microenvironment for realization of the hydrogen bonding properties. Additionally, only the construction of the self-assembly with a specific structure and morphology Chapter 2 Control of Thermoresponsive Properties of Urea End-Functionalized Poly(N-isopropylacrylamide) Based on the Hydrogen Bond Assisted Self-Assembly in Water