From p- to n-Type Mixed Conduction in Isoindigo-Based Polymers through Molecular Design.

Organic mixed ionic and electronic conductors are of significant interest for bioelectronic applications. Here, three different isoindigoid building blocks are used to obtain polymeric mixed conductors with vastly different structural and electronic properties which can be further fine-tuned through the choice of comonomer unit. This work shows how careful design of the isoindigoid scaffold can afford highly planar polymer structures with high degrees of electronic delocalization, while subtle structural modifications can control the dominant charge carrier (hole or electron) when probed in organic electrochemical transistors. A combination of experimental and computational techniques is employed to probe electrochemical, structural, and mixed ionic and electronic properties of the polymer series which in turn allows the derivation of important structure-property relations for this promising class of materials in the context of organic bioelectronics. Ultimately, these findings are used to outline robust molecular-design strategies for isoindigo-based mixed conductors that can support efficient p-type, n-type, and ambipolar transistor operation in an aqueous environment.

Analyte-Driven Disassembly and Turn-On Fluorescent Sensing in Competitive Biological Media.

Many indicator displacement assays can detect biological analytes in water, but these often have reduced performance in the presence of an unavoidable component: NaCl. We report here a new self-assembled sensor, DimerDye, that uses a novel photochemical guest-sensing mechanism and that is intrinsically tolerant of cosolutes. We synthetically integrated a dye into a calixarene macrocycle, forming two new merocyanine calixarenes (MCx-1 and MCx-2). Both compounds self-assemble into nonemissive dimers in water. The addition of good guests like trimethyllysine induces a turn-on fluorescence response of MCx-1 due to simultaneous dimer dissociation and formation of an emissive host-guest complex. DimerDyes remain functional in solutions containing the various salts, metal ions, and cofactors that are needed for enzymatic reactions. MCx-1 provides a real-time, turn-on fluorescence signal in response to the lysine methyltransferase reaction of PRDM9.

Efficient synthesis of benzocyclotrimer analogues by Negishi cross-coupling and intramolecular nucleophilic substitution.

We report a new and efficient synthetic strategy that allows access to flexible and functionalized benzocyclotrimers under mild conditions and in few steps. The Negishi cross-coupling reaction was used for the C-C bond formation, whereas intramolecular O-alkylations provided the oxepane rings.

Synthesis and conformational analysis of cyclic homooligomers from pyranoid ε-sugar amino acids.

New pyranoid ε-sugar amino acids were designed as building blocks, in which the carboxylic acid and the amine groups were placed in positions C2 and C3 with respect to the tetrahydropyran oxygen atom. By using standard solution-phase coupling procedures, cyclic homooligomers containing pyranoid ε-sugar amino acids were synthesized. Conformation analysis was performed by using NMR spectroscopic experiments, FTIR spectroscopic studies, X-ray analysis, and a theoretical conformation search. These studies reveal that the presence of a methoxy group in the position C4 of the pyran ring produces an important structural change in the cyclodipeptides. When the methoxy groups are present, the structure collapses through interresidue hydrogen bonds between the oxygen atoms of the pyran ring and the amide protons. However, when the cyclodipeptide lacks the methoxy groups, a U-shape structure is adopted, in which there is a hydrophilic concave face with four oxygen atoms and two amide protons directed toward the center of the cavity. Additionally, we found important evidence of the key role played by weak electrostatic interactions, such as the five-membered hydrogen-bonded pseudocycles (C5) between the amide protons and the ether oxygen atoms, in the conformation equilibrium of the macrocycles and in the cyclization step of the cyclic tetrapeptides.