β-Sheet peptide-assisted polymerization of diacetylene at the air–water interface and thermochromic property

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,

Electrophoretic Deposition Polymerization of Diacetylenes with Tunable Structure

“…The serial multi-chiral diacetylene (DA) monomers 1 possessing 2(5 H )-furanone structure were synthesized via the Glaser reaction [ 29 ] of N -[5-( S )-alkoxy-2(5 H )-furanonyl] amino acid propargyl esters 6 (Scheme S1, Supporting Information), [ 30,31 ] and systematically characterized by 1 H NMR, 13 C NMR, FTIR, UV, MS, and elemental analysis (see their data, especially their spectra and the discussion on the structural characterization of DA monomers 1 in the Supporting Information). DA monomers 1 are constructed from four parts, 2(5 H )-furanone, L -menthol, amino acid, and propargyl bromide, and the former three units may make 1 have multiple chiral centers (Scheme S1, Supporting Information), which can easily bring the novel chiral PDAs with tunable structure.…”

“…The DA monomers 1 were polymerized after their self‐assembly resulted from the hydrogen bonding between amine and carbonyl groups (Scheme ) during the preparation of DA vesicles (see Experimental Section, Supporting Information) . There are many poly­merization methods for the preparation of PDAs, and the common approach is the UV‐induced photo‐polymerization .…”

“…Furthermore, the introduction of chiral structure into PDAs is helpful for the conjugated materials with some new properties, such as helical chirality, nonlinear response, and photo‐modulation. Thus, more and more people are attracted to the intensive research on the preparation of chiral PDAs as a challenge recently . Especially, chiral PDA films can be used as film sensors .…”

“…Thus, more and more people are attracted to the intensive research on the preparation of chiral PDAs as a challenge recently. [9][10][11][12][13][14] Especially, chiral PDA fi lms can be used as fi lm sensors. [ 15 ] Compared with other non-fi lm PDA sensors, they are more sensitive to a variety of environmental perturbations, such as interfacial pressure and specifi c chemical binding.…”

Investigation on the Interactions between Self-Assembled β-Sheet Peptide Nanofibers and Model Cell Membranes

“…At a higher concentration (1.0 μM), the π– A isotherm curves of the binary systems were completely different from those of the sole DPPC membrane ( Figure 7 ). It has been reported that β-sheet peptides themselves form a monolayer at the air–water interface by compression [ 45 , 46 ]. π was already high at the start point of compression, which indicated that a large amount of EG n peptides might be present at the interface.…”