Red Fluorescence from Organic Microdots: Leveraging Foldamer-Linked Azobenzene for Enhanced Stability and Intensity in Bioimaging Applications.

Azobenzene, while relevant, has faced constraints in biological system applications due to its suboptimal quantum yield and short-wavelength emission. This study presents a pioneering strategy for fabricating organic microdots by coupling foldamer-linked azobenzene, resulting in robust fluorescence intensity and stability, especially in aggregated states, thereby showing promise for bioimaging applications. Comprehensive experimental and computational examinations elucidate the mechanisms underpinning enhanced photostability and fluorescence efficacy. In vitro and in vivo evaluations disclose that the external layer of cis-azo-foldamer microdots performs a self-sacrificial function during photo-bleaching. Consequently, these red-fluorescent microdots demonstrate extraordinary structural and photochemical stabilities over extended periods. The conjugation of a ß-peptide foldamer to the azobenzene chromophore through a glycine linker instigates a blue-shifted and amplified π*-n transition. Molecular dynamics simulations reveal that the aggregated state of cis-azo-foldamers fortifies the stability of cis isomers, thereby augmenting fluorescence efficiency. This investigation furnishes crucial insights into conceptualizing novel, biologically inspired materials, promising stable and enduring imaging applications, and carries implications for diverse arenas such as medical diagnostics, drug delivery, and sensing technologies.

Programmed hierarchical radial association of anisotropic foldamer assemblies.

Herein, we report the first example of a programmed radial assembly of anisotropic microparticles derived from a helical foldamer with a C-terminal cysteine residue. Surface-exposed thiols played a crucial role in facilitating the interparticle hydrogen bonding to form higher-order structures in an aqueous solution.

Directing Foldamer Self-Assembly with a Cyclopropanoyl Cap.

The rational design of self-assembling organic materials is extremely challenging due to the difficulty in precisely predicting solid-state architectures from first principles, especially if synthons are conformationally flexible. A tractable model system to study self-assembly was constructed by appending cyclopropanoyl caps to the N termini of helical α/ß-peptide foldamers, designed to form both N-H⋅⋅⋅O and Cα -H⋅⋅⋅O hydrogen bonds, which then rapidly self-assembled to form foldectures (foldamer architectures). Through a combined analytical and computational investigation, cyclopropanoyl capping was observed to markedly enhance self-assembly in recalcitrant substrates and direct the formation of a single intermolecular N-H⋅⋅⋅O/Cα -H⋅⋅⋅O bonding motif in single crystals, regardless of peptide sequence or foldamer conformation. In contrast to previous studies, foldamer constituents of single crystals and foldectures assumed different secondary structures and different molecular packing modes, despite a conserved N-H⋅⋅⋅O/Cα -H⋅⋅⋅O bonding motif. DFT calculations validated the experimental results by showing that the N-H⋅⋅⋅O/Cα -H⋅⋅⋅O interaction created by the cap was sufficiently attractive to influence self-assembly. This versatile strategy to harness secondary noncovalent interactions in the rational design of self-assembling organic materials will allow for the exploration of new substrates and speed up the development of novel applications within this increasingly important class of materials.

Connecting two proteins using a fusion alpha helix stabilized by a chemical cross linker.

Building a sophisticated protein nano-assembly requires a method for linking protein components in a predictable and stable structure. Most of the cross linkers available have flexible spacers. Because of this, the linked hybrids have significant structural flexibility and the relative structure between their two components is largely unpredictable. Here we describe a method of connecting two proteins via a 'fusion α helix' formed by joining two pre-existing helices into a single extended helix. Because simple ligation of two helices does not guarantee the formation of a continuous helix, we used EY-CBS, a synthetic cross linker that has been shown to react selectively with cysteines in α-helices, to stabilize the connecting helix. Formation and stabilization of the fusion helix was confirmed by determining the crystal structures of the fusion proteins with and without bound EY-CBS. Our method should be widely applicable for linking protein building blocks to generate predictable structures.

A Hollow Foldecture with Truncated Trigonal Bipyramid Shape from the Self-Assembly of an 11-Helical Foldamer.

The creation of self-assembling microscale architectures that possess new and useful physical properties remains a significant challenge. Herein we report that an 11-helical foldamer self-assembles in a controlled manner to form a series of 3D foldectures with unusual three-fold symmetrical shapes that are distinct from those generated from 12-helical foldamers. The foldamer packing motif was revealed by powder X-ray diffraction technique, and provides an important link between the molecular-level symmetry and the microscale morphologies. The utility of foldectures with hollow interiors as robust and well-defined supramolecular hosts was demonstrated for inorganic, organic, and even protein guests. This work will pave the way for the design of functional foldectures with greater 3D shape diversity and for the development of biocompatible delivery vehicles and containment vessels.

Self-assembled peptide architecture with a tooth shape: folding into shape.

Molecular self-assembly is the spontaneous association of molecules into structured aggregates by which nature builds complex functional systems. While numerous examples have focused on 2D self-assembly to understand the underlying mechanism and mimic this process to create artificial nano- and microstructures, limited progress has been made toward 3D self-assembly on the molecular level. Here we show that a helical ß-peptide foldamer, an artificial protein fragment, with well-defined secondary structure self-assembles to form an unprecedented 3D molecular architecture with a molar tooth shape in a controlled manner in aqueous solution. Powder X-ray diffraction analysis, combined with global optimization and Rietveld refinement, allowed us to propose its molecular arrangement. We found that four individual left-handed helical monomers constitute a right-handed superhelix in a unit cell of the assembly, similar to that found in the supercoiled structure of collagen.

Synthesis and properties of a polyhedral oligomeric silsesquioxane-based new light-emitting nanoparticle.

A polyhedral oligomeric silsesquioxane (POSS)-based electroluminescent nanoparticle, POSS-NPA, which contains anthracenenaphthyl chromophores on each of its eight arms, was easily prepared via the hydrosilylation reaction between octakis(dimethylsiloxy)silsesquioxane and allyl-functionalized 9-naphthalene-2-yl-10-phenyl anthracene chromophores. POSS-NPA was completely soluble in common organic solvents such as chloroform, THF, toluene, p-xylene, and chlorobenzene, and showed good film-forming properties on a quartz plate or an indium tin oxide (ITO) plate, i.e., it has good solution processing properties. The UV-visible absorption and the photoluminescence (PL) emission maxima of POSS-NPA in chlorobenzene solution were found to be 378 nm and 433 nm while those of POSS-NPA in the solid state were 379 and 464 nm, respectively. An electroluminescent (EL) device with the configuration of ITO/PEDOT:PSS/POSS-NPA (50 nm)/BAIq (40 nm)/LiF (1 nm)/Al (120 nm) was also fabricated and the blue light emission was successfully obtained.

Synthesis of a new polymeric host material for efficient organic electro-phosphorescent devices.

We have synthesized a new polymeric host material for phosphorescent dyes, which can be used in phosphorescent light-emitting layers. An alternating copolymer, composed of N-alkylcarbazole and tetramethylbenzene units was synthesized through the Suzuki coupling reaction. We fabricated electro-phosphorescent devices using the synthesized polymeric host doped with solution-processible green and red phosphorescent dyes. Light-emitting devices have an ITO/PEDOT/polymer + dopant/Balq3/Alq3/LiF/Al configuration. The device containing one of two studied green dopants (designated as green 1) in the polymeric host showed the best performance, with a maximum luminous efficiency of 29 cd/A. A thin film of this polymeric was successfully patterned by laser-induced thermal imaging (LITI), and an electro-phosphorescent device was fabricated using the patterned film. This patterned device showed performance characteristics similar to those of a spin-coated device.