Dopant Control of Solution-Processed CuI:S for Highly Conductive p-Type Transparent Electrode.

Copper iodide (CuI) has garnered considerable attention as a promising alternative to p-type transparent conducting oxides owing to its low cation vacancy formation energy, shallow acceptor level, and readily modifiable conductivity via doping. Although sulfur (S) doping through liquid iodination has exhibited high efficacy in enhancing the conductivity with record high figure of merit (FOM) of 630 00 MΩ-1, solution-processed S-doped CuI (CuI:S) for low-cost large area fabrication has yet to be explored. Here, a highly conducting CuI:S thin-film for p-type transparent conducting electrode (TCE) is reported using low temperature solution-processing with thiourea derivatives. The optimization of thiourea dopant is determined through a comprehensive acid-base study, considering the effects of steric hindrance. The modification of active groups of thioureas facilitated a varying carrier concentration range of 9 × 1018-2.52 × 1020 cm-3 and conductivities of 4.4-390.7 S cm-1. Consequently, N-ethylthiourea-doped CuI:S exhibited a FOM value of 7 600 MΩ-1, which is the highest value among solution-processed p-type TCEs to date. Moreover, the formulation of CuI:S solution for highly conductive p-type TCEs can be extended to CuI:S inks, facilitating high-throughput solution-processes such as inkjet printing and spray coating.

Crystalline Metal-Peptide Networks: Structures, Applications, and Future Outlook.

Metal-peptide networks (MPNs), which are assembled from short peptides and metal ions, are considered one of the most fascinating metal-organic coordinated architectures because of their unique and complicated structures. Although MPNs have considerable potential for development into versatile materials, they have not been developed for practical applications because of several underlying limitations, such as designability, stability, and modifiability. In this review, we summarise several important milestones in the development of crystalline MPNs and thoroughly analyse their structural features, such as peptide sequence designs, coordination geometries, cross-linking types, and network topologies. In addition, potential applications such as gas adsorption, guest encapsulation, and chiral recognition are introduced. We believe that this review is a useful survey that can provide insights into the development of new MPNs with more sophisticated structures and novel functions.

Designed Amyloid Fibers with Emergent Melanosomal Functions.

Short peptides designed to self-associate into amyloid fibers with metal ion-binding ability have been used to catalyze various types of chemical reactions. This manuscript demonstrates that one of these short-peptide fibers coordinated with CuII can exhibit melanosomal functions. The coordinated CuII and the amyloid structure itself are differentially functional in accelerating oxidative self-association of dopamine into melanin-like species and in regulating their material properties (e.g., water dispersion, morphology, and the density of unpaired electrons). The results have implications for the role of functional amyloids in melanin biosynthesis and for designing peptide-based supramolecular structures with various emergent functions.

Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch.

Photoswitching organic molecules that undergo light-driven structural transformations are key components to construct adaptive molecular systems, and they are utilized in a wide variety of applications. In most studies employing photoswitches, several important photophysical properties such as maximum wavelengths of absorption and emission, molar attenuation coefficient, fluorescence lifetime, and photoisomerization quantum yield are carefully determined to investigate their electronic states and transition processes. However, measurement of the photoisomerization quantum yield, the efficiency of photoisomerization with respect to the absorbed photons, in a typical laboratory setting is often complicated and prone to error because it requires the implementation of rigorous spectroscopic measurements and calculations based on an appropriate integration method. This article introduces a set of procedures to measure the photoisomerization quantum yield of a bistable photoswitch using a photochromic hydrazone. We anticipate that this article will be a useful guide for the investigation of bistable photoswitches that are being increasingly developed.

Synthesis of gold nano-mushrooms via solvent-controlled galvanic replacement to enhance phototherapeutic efficiency.

In advanced galvanic replacement, variable factors such as the combination of two elements where actual redox reaction and post-synthetic structural transformation take place. Research on manufacturing distinctive nanostructures has mainly focused on the shape of the sacrificial nanotemplate, the presence or absence of additives, and the reaction temperature. Here, we have attempted to confirm the dependency on the solvent, which was considered to simply serve as a medium for a homogeneous chemical reaction to proceed by aiding the dispersion of the nanotemplate and reactants. Thus, we obtained mushroom-like Au nanoplates (mAuNPs) by comprehensive galvanic replacement reaction between solvents, additives, and adsorbents. The mAuNPs with a porous Au nanoplate head and a hollow nanotube tail structure were formed via an optimization process in a 50 v/v% solvent comprising water and ethylene glycol. As a result of confirming the galvanic replacement in co-solvent conditions, in which various types of water miscible solvents were introduced, it was revealed that the most critical factors for regulating the surface polymeric environment of the nanoplate were the relative polarity index of the co-solvent and the hydrogen bonding type. These depend on the molecular structure of the solvent. The manufactured mAuNPs exhibited excellent absorbance in the near-infrared region, and efficient photothermal (PT) conversion-mediated heat dissipation under local laser irradiation. These results confirm the viability of the gene-thermo dual-modal combinatorial cancer therapy based on the surface loading of oligonucleotides and peptides, and the PT therapeutic approach in vitro and in vivo.

Hydrazone Photoswitches for Structural Modulation of Short Peptides.

Molecules that undergo light-driven structural transformations constitute the core components in photoswitchable molecular systems and materials. Among various families of photoswitches, photochromic hydrazones have recently emerged as a novel class of photoswitches with superb properties, such as high photochemical conversion, spectral tunability, thermal stability, and fatigue resistance. Hydrazone photoswitches have been adopted in various adaptive materials at different length scales, however, their utilization for modulating biomolecules still has not been explored. Herein, we present new hydrazone switches that can photomodulate the structures of short peptides. Systematic investigation on a set of hydrazone derivatives revealed that installation of the amide group does not significantly alter the photoswitching behaviors. Importantly, a hydrazone switch comprising an upper phenyl ring and a lower quinolinyl ring was effective for structural control of peptides. We anticipate that this work, as a new milestone in the research of hydrazone switches, will open a new avenue for structural and functional control of biomolecules.

Conformational Adaptation of ß-Peptide Foldamers for the Formation of Metal-Peptide Frameworks.

Metal-coordinated frameworks derived from small peptidic ligands have received much attention thanks to peptides' vast structural and functional diversity. Various peptides with partial conformational preferences have been used to build metal-peptide frameworks, however, the use of conformationally constrained ß-peptide foldamers has not been explored yet. Herein we report the first metal-coordination-mediated assembly of ß-peptide foldamers with 12-helical folding propensity. The coordination of Ag+ to the terminal pyridyl moieties afforded a set of metal-peptide frameworks with unique entangled topologies. Interestingly, formation of the network structures was accompanied by notable conformational distortions of the foldamer ligands. As the first demonstration of new metal-peptide frameworks built from modular ß-peptide foldamers, we anticipate that this work will be an important benchmark for further structural evolution and mechanistic investigation.

Synthetic Foldamers: Rational Design of Advanced Structures with Diverse Applications.

Fruitful Foldamers: Guest Editors Ivan Huc, Sunbum Kwon, and Hee-Seung Lee discuss the development of the field and introduce this Special Collection on the Synthesis, Properties, and Applications of Foldamers. This collection features top-quality multidisciplinary research and review articles that cover design, self-assembly, guest recognition, catalytic activity, and optical and biological properties of foldamers.

Graphene Oxide Derivatives and Their Nanohybrid Structures for Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Analysis of Small Molecules.

Matrix-assisted laser desorption/ionization (MALDI) has been considered as one of the most powerful analytical tools for mass spectrometry (MS) analysis of large molecular weight compounds such as proteins, nucleic acids, and synthetic polymers thanks to its high sensitivity, high resolution, and compatibility with high-throughput analysis. Despite these advantages, MALDI cannot be applied to MS analysis of small molecular weight compounds (<500 Da) because of the matrix interference in low mass region. Therefore, numerous efforts have been devoted to solving this issue by using metal, semiconductor, and carbon nanomaterials for MALDI time-of-flight MS (MALDI-TOF-MS) analysis instead of organic matrices. Among those nanomaterials, graphene oxide (GO) is of particular interest considering its unique and highly tunable chemical structures composed of the segregated sp2 carbon domains surrounded by sp3 carbon matrix. Chemical modification of GO can precisely tune its physicochemical properties, and it can be readily incorporated with other functional nanomaterials. In this review, the advances of GO derivatives and their nanohybrid structures as alternatives to organic matrices are summarized to demonstrate their potential and practical aspect for MALDI-TOF-MS analysis of small molecules.

Ribosomal Incorporation of Aromatic Oligoamides as Peptide Sidechain Appendages.

Derivatives of 4-aminomethyl-l-phenylalanine with aromatic oligoamide foldamers as sidechain appendages were successfully charged on tRNA by means of flexizymes. Their subsequent incorporation both at the C-terminus of, and within, peptide sequences by the ribosome, was demonstrated. These results expand the registry of chemical structures tolerated by the ribosome to sidechains significantly larger and more structurally defined than previously demonstrated.

Multifaceted Influences of Melanin-Like Particles on Amyloid-beta Aggregation.

The properties of eumelanin-like particles (EMPs) and pheomelanin-like particles (PMPs) in regulating the process of amyloid formation of amyloid-beta 42 (Aß42) were examined. EMPs and PMPs are effective both in interfering with amyloid aggregation of Aß42 and in remodeling matured Αß42 fibers. The results suggest that some (but not all) molecular species consisting of melanin-like particles (MPs) are responsible for their inhibiting property toward amyloid formation, and the influence is likely manifested by long-range interactions. Incubating preformed Aß42 fibers with catechols or MPs leads to the formation of mesh-like, interconnected Aß42 fibers encapsulated with melanin-like material. MPs are kinetically more effective than catechol monomers in this process, and a detailed investigation reveals that 4,5-dihydroxyindole, a major intermediate in the formation of melanin-like species, and its derivatives are mainly responsible for remodeling amyloid fibers.

Optimizing aromatic oligoamide foldamer side-chains for ribosomal translation initiation.

The tolerance of ribosomal peptide translation for helical aromatic oligoamide foldamers appended as initiators has been investigated. Small cationic foldamer side-chains were shown to expand the range of foldamer-peptide hybrids that can be produced by the ribosome to more rigid sequences.

Spontaneous Nanobelt Formation by Self-Assembly of ß-Benzyl GABA.

We present the formation of a nanobelt by self-assembly of ß-benzyl GABA (γ-aminobutyric acid). This simple γ-amino acid building block self-assembled to form a well-defined nanobelt in chloroform. The nanobelt showed distinct optical properties due to π-π interactions. This new-generation self-assembled single amino acid may serve as a template for functional nanomaterials.

Self-Assembly of a ß-Peptide Foldamer: The Role of the Surfactant in Three-Dimensional Shape Selection.

The effect of a small ionic surfactant, cetyltrimethylammonium bromide (CTAB), on the self-assembly of a ß-peptide has been systematically studied by using scanning electron microscopy, X-ray diffraction, selected area electron diffraction, and molecular dynamics (MD) simulations. The latter study suggested that the formation of asymmetric microcrystals may be due to the preferential adsorption of CTAB on {011} and (001) crystal faces. This work provides a plausible rationale for the characteristic 3D morphogenesis of foldectures and elucidates the interaction between the surfactant and organic building block molecules.

Publisher Correction: Ribosomal synthesis and folding of peptide-helical aromatic foldamer hybrids.

In the version of this Article originally published, in Fig.1f there was an erroneous 'Gly-Gly' label placed above the foldamer-peptide structure. Furthermore, in Fig. 2a, the expected target structures from substrates 9 and 10 were inadvertently swapped. These errors have been corrected in the online versions.

Ribosomal synthesis and folding of peptide-helical aromatic foldamer hybrids.

Translation, the mRNA-templated synthesis of peptides by the ribosome, can be manipulated to incorporate variants of the 20 cognate amino acids. Such approaches for expanding the range of chemical entities that can be produced by the ribosome may accelerate the discovery of molecules that can perform functions for which poorly folded, short peptidic sequences are ill suited. Here, we show that the ribosome tolerates some artificial helical aromatic oligomers, so-called foldamers. Using a flexible tRNA-acylation ribozyme-flexizyme-foldamers were attached to tRNA, and the resulting acylated tRNAs were delivered to the ribosome to initiate the synthesis of non-cyclic and cyclic foldamer-peptide hybrid molecules. Passing through the ribosome exit tunnel requires the foldamers to unfold. Yet foldamers encode sufficient folding information to influence the peptide structure once translation is completed. We also show that in cyclic hybrids, the foldamer portion can fold into a helix and force the peptide segment to adopt a constrained and stretched conformation.

Magnetotactic molecular architectures from self-assembly of ß-peptide foldamers.

The design of stimuli-responsive self-assembled molecular systems capable of undergoing mechanical work is one of the most important challenges in synthetic chemistry and materials science. Here we report that foldectures, that is, self-assembled molecular architectures of ß-peptide foldamers, uniformly align with respect to an applied static magnetic field, and also show instantaneous orientational motion in a dynamic magnetic field. This response is explained by the amplified anisotropy of the diamagnetic susceptibilities as a result of the well-ordered molecular packing of the foldectures. In addition, the motions of foldectures at the microscale can be translated into magnetotactic behaviour at the macroscopic scale in a way reminiscent to that of magnetosomes in magnetotactic bacteria. This study will provide significant inspiration for designing the next generation of biocompatible peptide-based molecular machines with applications in biological systems.

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.

Foldecture as a core material with anisotropic surface characteristics.

The synthesis of microscale, polyhedrally shaped, soft materials with anisotropic surface functionality by a bottom-up approach remains a significant challenge. Herein we report a microscale molecular architecture (foldecture) with facet-dependent surface characteristics that can potentially serve as a well-defined catalytic template. Rhombic rod shaped foldectures with six facets were obtained by the aqueous self-assembly of helical ß-peptide foldamers with a C-terminal carboxylic acid. An analysis of the molecular packing by X-ray diffraction revealed that carboxylic acid groups were exposed exclusively on the two (001) rhombic facets due to antiparallel packing of the helical peptides. A surface energy calculation by molecular dynamics simulation was performed to provide a plausible explanation for the development of anisotropy during foldecture formation. The expected facet-selective surface properties of the foldecture were experimentally confirmed by selective deposition of metal nanoparticles on the (001) facets, leading to a new class of sequentially constructed, heterogeneous "foldecture core" materials.

Microtubes with rectangular cross-section by self-assembly of a short ß-peptide foldamer.

In nature, complex and well-defined structures are constructed by the self-assembly of biomolecules. It has been shown that ß-peptide foldamers can mimic natural peptides and self-assemble into three-dimensional molecular architectures thanks to their rigid and predictable helical conformation in solution. Using shorter foldamers, which can be prepared more easily than longer ones, to form such architectures is highly desirable, but shorter foldamers have been overlooked due to the seemingly inferior number of intramolecular hydrogen bonds to stabilize a folded state in solution. Here we report that a ß-peptide tetramer, although it lacks full helical propensity in solution, does self-assemble to form well-defined microtubes with rectangular cross-section by evaporation-induced self-assembly.