Opal-like Multicolor Appearance of Self-Assembled Photonic Array

Multiple Actions of H2S-Releasing Peptides in Human β-Amyloid Expressing C. elegans

Alzheimer's disease (AD) is a debilitating progressive neurodegenerative disorder characterized by the loss of cognitive function. A major challenge in treating this ailment fully is its multifactorial nature, as it is associated with effects like deposition of Aβ plaques, oxidative distress, inflammation of neuronal cells, and low levels of the neurotransmitter acetylcholine (ACh). In the present work, we demonstrate the design, synthesis, and biological activity of peptide conjugates by coupling a H₂S-releasing moiety to the peptides known for their Aβ antiaggregating properties. These conjugates release H₂S in a slow and sustained manner, due to the formation of self-assembled structures and delivered a significant amount of H₂S within Caenorhabditis elegans. These conjugates are shown to target multiple factors responsible for the progression of AD: notably, we observed reduction in oxidative distress, inhibition of Aβ aggregation, and significantly increased ACh levels in the C. elegans model expressing human Aβ.

Microfabrication of peptide self-assemblies: inspired by nature towards applications

Peptide self-assemblies show intriguing and tunable physicochemical properties, and thus have been attracting increasing interest over the last two decades. However, the micro/nano-scale dimensions of the self-assemblies severely restrict their extensive applications. Inspired by nature, to genuinely realize the practical utilization of the bio-organic super-architectures, it is beneficial to further organize the peptide self-assemblies to integrate the properties of the individual supermolecules and fabricate higher-level organizations for smart functional devices. Therefore, cumulative studies have been reported on peptide microfabrication giving rise to diverse properties. This review summarizes the recent development of the microfabrication of peptide self-assemblies, discussing each methodology along with the diverse properties and practical applications of the engineered peptide large-scale, highly-ordered organizations. Finally, the current limitations of the state-of-the-art microfabrication strategies are critically assessed and alternative solutions are suggested.

A colored hydrophobic peptide film based on self-assembled two-fold topology

Structural colors are abundant in nature and bear advantages over pigment-based colors, such as higher durability, brilliance and often physical hydrophobicity, thus underlying their vast potential for technological applications. Recently, biomimetics of complex natural topologies resulting in such effects has been extensively studied, requiring advanced processing and fabrication techniques. Yet, artificial topologies combining structural coloration and hydrophobicity have not been reported. Herein, we present the bottom-up fabrication of short self-assembling peptides as surface covering films, resulting in an easily achievable multilevel morphology of primary structures in a foam-like enclosure, producing structural colors and hydrophobicity. We demonstrate simple techniques allowing controlled coloration of different surfaces while maintaining an >100° water contact angle (WCA). The new artificial topology is much simpler than the natural counterparts and is not limited to a specific peptide, thus allowing the design of modular materials with unparalleled multifunctionalities and potential for further tuning and modifications.

Diphenylalanine-Derivative Peptide Assemblies with Increased Aromaticity Exhibit Metal-like Rigidity and High Piezoelectricity

Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties. Among self-assembled peptide structures, FF nanotubes display notable stiffness and piezoelectric parameters (Young's modulus = 19-27 GPa, strain coefficient d33 = 18 pC/N). Yet, inorganic alternatives remain the major materials of choice for many applications due to higher stiffness and piezoelectricity. Here, aiming to broaden the applications of the FF motif in materials chemistry, we designed three phenyl-rich dipeptides based on the β,β-diphenyl-Ala-OH (Dip) unit: Dip-Dip, cyclo-Dip-Dip, and tert-butyloxycarbonyl (Boc)-Dip-Dip. The doubled number of aromatic groups per unit, compared to FF, produced a dense aromatic zipper network with a dramatically improved Young's modulus of ∼70 GPa, which is comparable to aluminum. The piezoelectric strain coefficient d33 of ∼73 pC/N of such assembly exceeds that of poled polyvinylidene-fluoride (PVDF) polymers and compares well to that of lead zirconium titanate (PZT) thin films and ribbons. The rationally designed π-π assemblies show a voltage coefficient of 2-3 Vm/N, an order of magnitude higher than PVDF, improved thermal stability up to 360 °C (∼60 °C higher than FF), and useful photoluminescence with wide-range excitation-dependent emission in the visible region. Our data demonstrate that aromatic groups improve the rigidity and piezoelectricity of organic self-assembled materials for numerous applications.

Phenylalanine dimer assembly structure as the basic building block of an amyloid like photoluminescent nanofibril network

A phenylalanine dimer assembly (Phe-DA) is reported as a basic constituent of a light emitting β-amyloid type nanofibril network. The size and composition of the Phe-DA structure were characterized using various theoretical and experimental techniques. Further, the mechanism involved in the phenylalanine self-assembly process from Phe-DA to the nanofibril network was studied using optical spectroscopy and small angle X-ray scattering (SAXS). The discovery of Phe-DA and its unique optical properties may pave the way for design and development of novel theranostics against metabolite based pathalogical disorders. Further, the role of the Phe-DA structure as the elementary unit in the formation of a long range assembly structure may provide vital understanding for the development of functional materials using simple organic molecules.

Core-shell silica-rhodamine B nanosphere for synthetic opals: from fluorescence spectral redistribution to sensing

Photonic crystals are a unique tool to modify the photoluminescence of light-emitting materials. A variety of optical effects have been demonstrated by infiltrating opaline structures with photoactive media. On the other hand, the fabrication of such structures includes complex infiltration steps, that often affect the opal lattice and decrease the efficiency of light emission control. In this work, silica nanospheres were directly functionalized with rhodamine B to create an emitting shell around the dielectric core. Simple tuning of the microsphere preparation conditions allows selecting the appropriate sphere diameter and polydispersity index approaching 5%. These characteristics allow facile self-assembling of the nanospheres into three-dimensional photonic crystals whose peculiar density of photonic states at the band-gap edges induces spectral redistribution of the rhodamine B photoluminescence. The possibility to employ the new stable structure as sensor is also investigated. As a proof of principle, we report the variation of light emission obtained by exposure of the opal to vapor of chlorobenzene.

Microfluidics for real-time direct monitoring of self- and co-assembly biomolecular processes

Molecular self-assembly is a major approach for the fabrication of functional supramolecular nanomaterials. This dynamic, straightforward, bottom-up procedure may result in the formation of various architectures at the nano-scale, with remarkable physical and chemical characteristics. Biological and bio-inspired building blocks are especially attractive due to their intrinsic tendency to assemble into well-organized structures, as well as their inherent biocompatibility. To further expand the morphological diversity, co-assembly methods have been developed, allowing to produce alternative unique architectures, enhanced properties, and improved structural control. However, in many cases, mechanistic understanding of the self- and co-assembly processes is still lacking. Microfluidic techniques offer a set of exclusive tools for real-time monitoring of biomolecular self-organization, which is crucial for the study of such dynamic processes. Assembled nuclei, confined by micron-scale pillars, could be subjected to controlled environments aiming to assess the effect of different conditions on the assembly process. Other microfluidics setups can produce droplets at a rate of over 100 s^-1, with volumes as small as several picoliters. Under these conditions, each droplet can serve as an individual pico/nano-reactor allowing nucleation and assembly. These processes can be monitored, analyzed and imaged, by various techniques including simple bright-field microscopy. Elucidating the mechanism of such molecular events may serve as a conceptual stepping-stone for the rational control of the resulting physicochemical properties.

Phe-Phe Di-Peptide Nanostructure Self-Assembling Modulated by Luminescent Additives

In this work, supramolecular l-l-diphenylalanine (Phe-Phe) nanostructures were self-assembled in solvents of distinct polarity and in the presence of luminescent additives of distinct conjugation length that physically adhere to the nanostructures to provide growth environments of distinct properties. When the additive is poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], an electron donor polymer, and solvent is tetrahydrofuran (THF), Phe-Phe vesicle-like structures are obtained, whereas in water and in the presence of a similar additive in structure, poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene], nanotubes are formed. In contrast, when 9-vinyl-carbazole, an electron acceptor additive is used, nanotubes are formed even when THF is the solvent. The same structures are obtained when the additive is the macromolecule poly(vinyl carbazole). The morphologies of these self-assembled structures were observed by scanning electron microscopy, and their photophysical behavior was determined by steady-state fluorescence spectroscopy and time-resolved fluorescence spectroscopy. These data analyzed altogether inform about the formation mechanisms of such structures and about the influence that distinct interactions exert on self-assembling and charge-transfer processes through formation of complexes between the luminescent additives and the Phe-Phe nano- and microstructures.

Applications of self-assembling ultrashort peptides in bionanotechnology

Peptides are intriguing building blocks for a variety of applications in bionanotechnology. Peptides can self-assemble into well-ordered nanostructures. Among the various nanomorphology forms, peptide nanofibers and nanotubes are relevant in biomedical applications. In this review, their applications as tissue engineering scaffolds, drug delivery vehicles, three-dimensional printing bioinks and bioimaging nanoprobes will be illustrated. This review article describes di-, tri-, tetra-peptides because they are cost-effective, simple to prepare, and amenable to production on a large scale.

Ultrashort peptide applications in bionanotechnology.