No abstract

No abstract

A peptide-diacetylene hybrid (PDH), in which 5,7-dodecadiynedioic acid was conjugated to the amphiphilic penta-peptide Leu-Lys-Leu-Lys-Leu, which can form b-sheets on both ends of the diacetylene moiety, was prepared through solid-phase peptide synthesis using fluorenylmethoxycarbonyl chemistry. Spreading experiments and spectroscopic observations showed that the PDH formed a stable Langmuir monolayer, primarily in the parallel b-sheet conformation at the air-water interface. When the PDH monolayer was exposed to ultraviolet radiation and a single-layer Langmuir-Blodgett (LB) film of the treated monolayer was deposited on a CaF 2 plate, the polymerization proceeded successfully and provided highly p-conjugated, blue-colored polydiacetylenes with absorption maxima at 653 and 640 nm, respectively. The polymerized PDH LB film displayed almost completely reversible thermochromism between blue and red (less conjugated) states upon heating and cooling. Polymer Journal (2012) 44, 195-199; doi:10.1038/pj.2011.105; published online 9 November 2011Keywords: b-Sheet; diacetylene; peptide; surface monolayer; thermochromism; topochemical polymerization INTRODUCTION Polydiacetylenes are conjugated polymeric materials with unique optical properties. The efficient polymerization of diacetylene yielding highly conjugated backbones requires the positioning of atoms in a crystalline lattice, and there is little displacement before and after polymerization; such a reaction is known as a topochemical reaction. 1-3 When properly aligned, diacetylene groups undergo ultraviolet (UV)-induced photopolymerization to form an ene-yne alternating polymer backbone, resulting in organized structures. In aqueous environments, these materials often appear blue or red, with the blue color indicating greater order in the conjugated p-system. 4 As the conjugated p-system becomes less ordered, the observed color shifts from blue to red. This unique chromatic property has made polydiacetylenes applicable to colorimetric biosensors. [5][6][7][8][9][10][11] We describe herein the thermoreversible color change of polydiacetylene prepared through b-sheet peptide-templated polymerization at the air-water interface. b-Sheet peptides are promising candidates for such a template or scaffold because they are often present in natural fibers as a structural element. Langmuir monolayers of b-sheet peptides were, for example, reported to function as templates and serve as nuclei for the formation of inorganic nanocrystallites at the air-water interface. 12 Recently, numerous research groups have demonstrated that amphiphilic peptides self-assemble into b-sheet nanofiber architectures, 13-20 the surface of which has potential as a novel nanotemplate. [21][22][23] Several groups 24-27 have separately used b-sheet peptide nanofibers as templates to organize diacetylenes or dienes and promote their topochemical polymerization. In this study,