![]() Advantageously, the N-(2-aminoethyl)-glycine-based peptide backbone is not charged and quite hydrophobic, thereby not limiting the studies to polar solvents and water. 25 Therefore, if a chromophore is used to replace the nucleobase on PNA, it should be possible to direct the formation of duplexes consisting of multiple chromophores. 24 By introducing cyanine dyes into PNA, a series of PNA-FIT probes was successfully constructed and applied to the imaging of specific mRNA molecules. 22, 23 Because of the similarity of the structures, PNA can also form complementary duplexes of high stability with DNA and RNA through base-paring. N-(2-aminoethyl)-glycine-based pseudopeptide backbones have indeed been used very successfully as a substitute for the (deoxy)ribose phosphate backbone in nucleic acids. c) Schematic representation of the self-assembly of the complementary duplex of PNAs and peptide MC oligomers. b) Self-assembly of dipolar MCs into antiparallel stacked dimers. a) Neutral and zwitterionic resonance structures of the merocyanine (MC) chromophore, and the chemical structures of the oligomers investigated in this study. 14- 17 Inspired by research on peptide nucleic acids (PNAs) 18, 19 and research on the folding of peptide backbones driven by donor-acceptor interactions 20, 21 we herein explore the suitability of N-(2-aminoethyl)-glycine-based pseudopeptide backbones for the formation of oligomeric dye duplex structures (Figure 1).Ĭoncept for a peptide backbone-directed self-assembly of peptide MC (PMC) oligomers into duplex structures. 12, 13 In another approach, dyes are embedded within DNA duplex structures by replacing entire nucleotides in the phosphodiester backbone, but here it is challenging to accommodate the dyes within the DNA backbone in a predictable supramolecular arrangement due to the spatial constraints of the DNA duplex. In principle, the sugar phosphate backbone found in DNA can also be utilized for the assembly of other π-scaffolds which, however, limits the research to aqueous environments and π-scaffolds often appended to natural nucleobases. In contrast, the well-ordered double helix structure of DNA demonstrates a base pair guided backbone-directed self-assembly process that enables the formation of DNA double strands of any length. 9- 11 These examples reveal general strategies for the design of dimers and tetramers but also highlight the lack of a general approach towards larger oligomers of defined structure and size. 1, 4 So far, chemists have developed a variety of strategies to construct multichromophore assemblies which include steric shielding, 5, 6 templating, 7, 8 and backbone-directed self-assembly. 2, 3 To explore structural and functional properties, multichromophore systems with well-defined size and structure are needed. 1 This is not only because well-ordered ensembles of multiple chromophores afford unique and desirable photophysical and photochemical properties different from those of the monomers but also because the functional properties of π-conjugated molecular solid-state materials are governed by the electronic coupling between the molecular building blocks. For all aggregate species a moderate aggregation-induced emission enhancement is observed.ĭye assembly has attracted considerable attention in the past two decades. In contrast, upon further extension of the oligomer, the chosen peptide backbone cannot direct the formation of a defined duplex architecture anymore due to intramolecular aggregation between the dyes. Our concentration-, temperature- and solvent-dependent UV/Vis absorption studies show that under the control of dipole–dipole interactions, smaller-sized oligomers consisting of one, two or three dyes self-assemble into defined duplex structures containing two up to six chromophores. Toward this goal a series of peptide merocyanine (PMC) dye oligomers connected to a N-(2-aminoethyl)-glycine backbone were prepared through peptide synthesis. Here we demonstrate the suitability of this backbone for the formation of structurally defined dye stacks. The pseudopeptide backbone provided by N-(2-aminoethyl)-glycine oligomers with attached nucleobases has been widely utilized in peptide nucleic acids (PNAs) as DNA mimics.
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