Nanofibers and Lyotropic Liquid Crystals from a Class of Self-Assembling β-Peptides

Ca2+ and Ag+ orient low-molecular weight amphiphile self-assembly into "nano-fishnet" fibrillar hydrogels with unusual β-sheet-like raft domains

Low-molecular weight gelators (LMWGs) are small molecules (M_w < ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water when triggered by an external stimulus. A great majority of SAFiN gels involve an entangled network of self-assembled fibers, in analogy to a polymer in a good solvent. In some rare cases, a combination of attractive van der Waals and repulsive electrostatic forces drives the formation of bundles with a suprafibrillar hexagonal order. In this work, an unexpected micelle-to-fiber transition is triggered by Ca²⁺ or Ag⁺ ions added to a micellar solution of a novel glycolipid surfactant, whereas salt-induced fibrillation is not common for surfactants. The resulting SAFiN, which forms a hydrogel above 0.5 wt%, has a "nano-fishnet" structure, characterized by a fibrous network of both entangled fibers and β-sheet-like rafts, generally observed for silk fibroin, actin hydrogels or mineral imogolite nanotubes, but not known for SAFiNs. The β-sheet-like raft domains are characterized by a combination of cryo-TEM and SAXS and seem to contribute to the stability of glycolipid gels. Furthermore, glycolipid is obtained by fermentation from natural resources (glucose, rapeseed oil), thus showing that naturally engineered compounds can have unprecedented properties, when compared to the wide range of chemically derived amphiphiles.

Directing the Self-Assembly of Aromatic Foldamer Helices using Acridine Appendages and Metal Coordination

Folded molecules provide complex interaction interfaces amenable to sophisticated self-assembly motifs. Because of their high conformational stability, aromatic foldamers constitute suitable candidates for the rational elaboration of self-assembled architectures. Several multiturn helical aromatic oligoamides have been synthesized that possess arrays of acridine appendages pointing in one or two directions. The acridine units were shown to direct self-assembly in the solid state via aromatic stacking leading to recurrent helix-helix association patterns under the form of discrete dimers or extended arrays. In the presence of Pd(II), metal coordination of the acridine units overwhelms other forces and generates new metal-mediated multihelical self-assemblies, including macrocycles. These observations demonstrate simple access to different types of foldamer-containing architectures, ranging from discrete objects to 1D and, by extension, 2D and 3D arrays.

Cells and material-based strategies for regenerative endodontics

<p class = "Abstract" style = "margin: 0 cm; line-height: 32px; font-size: 12 pt; font-family: "Times New Roman", serif; color: rgb(0, 0, 0); "><span lang = "EN-US">The carious process leads to inflammation of pulp tissue. Current care options include root canal treatment or apexification. These procedures, however, result in the loss of tooth vitality, sensitivity, and healing. Pulp capping and dental pulp regeneration are continually evolving techniques to regenerate pulp tissue, avoiding necrosis and loss of vitality. Many studies have successfully employed stem/progenitor cell populations, revascularization approaches, scaffolds or material-based strategies for pulp regeneration. Here we outline advantages and disadvantages of different methods and techniques which are currently being used in the field of regenerative endodontics. We also summarize recent findings on efficacious peptide-based materials which target the dental niche.<o:p></o:p></span></p>

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Pulp infection necessitates removal of necrotic, inflamed and infected tissue.

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Materials used clinically are inert (such as gutta percha, mineral trioxide aggregate).

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Recent developments in materials (angiogenic hydrogels, stem cell composites) have tuneable bioactivity.

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Dental pulp regeneration may now be possible through the use of bioactive systems, that guide regeneration.

Advances in hybrid peptide-based self-assembly systems and their applications

Self-assembly of peptides demonstrates a great potential for designing highly ordered, finely tailored supramolecular arrangements enriched with high specificity, improved efficacy and biological activity. Along with natural peptides, hybrid peptide systems composed of natural and chemically diverse unnatural amino acids have been used in various fields, including drug delivery, wound healing, potent inhibition of diseases, and prevention of biomaterial related diseases to name a few. In this review, we provide a brief outline of various methods that have been utilized for obtaining fascinating structures that create an avenue to reproduce a range of functions resulting from these folds. An overview of different self-assembled structures as well as their applications will also be provided. We believe that this review is very relevant to the current scenario and will cover conformations of hybrid peptides and resulting self-assemblies from the late 20^th century through 2022. This review aims to be a comprehensive and reliable account of the hybrid peptide-based self-assembly owing to its enormous influence in understanding and mimicking biological processes.

Enzymatic Noncovalent Synthesis for Targeting Subcellular Organelles

Enzymatic noncovalent synthesis (ENS) exploits enzymatic reactions to produce spatially organized higher-order supramolecular assemblies that modulate cellular processes. While ENS is a general mechanism to create higher-order assemblies of proteins for diverse cellular functions, the exploration of ENS of other bioactive molecules, such as peptides or small organic molecules, is rather limited. Since ENS generates non-diffusive supramolecular assemblies locally, it provides a unique approach to targeting subcellular organelles. In this Review, we highlight the recent progress of the application of ENS of peptide assemblies for targeting subcellular organelles. After a brief introduction of the concept of ENS, we introduce the case of generating artificial filaments by ENS in cell cytosol, then discuss the use of ENS for targeting endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes, and finally we describe the targeting of nucleus by ENS. We hope to illustrate the promise of ENS, as a localized molecular process in an open system, for understanding diseases, controlling cell behaviors, and developing new therapeutics.

Structures of synthetic helical filaments and tubes based on peptide and peptido-mimetic polymers

Synthetic peptide and peptido-mimetic filaments and tubes represent a diverse class of nanomaterials with a broad range of potential applications, such as drug delivery, vaccine development, synthetic catalyst design, encapsulation, and energy transduction. The structures of these filaments comprise supramolecular polymers based on helical arrangements of subunits that can be derived from self-assembly of monomers based on diverse structural motifs. In recent years, structural analyses of these materials at near-atomic resolution (NAR) have yielded critical insights into the relationship between sequence, local conformation, and higher-order structure and morphology. This structural information offers the opportunity for development of new tools to facilitate the predictable and reproduciblede novodesign of synthetic helical filaments. However, these studies have also revealed several significant impediments to the latter process – most notably, the common occurrence of structural polymorphism due to the lability of helical symmetry in structural space. This article summarizes the current state of knowledge on the structures of designed peptide and peptido-mimetic filamentous assemblies, with a focus on structures that have been solved to NAR for which reliable atomic models are available.

Discrete Stacked Dimers of Aromatic Oligoamide Helices

Tight binding was observed between the C‐terminal cross section of aromatic oligoamide helices in aqueous solution, leading to the formation of discrete head‐to‐head dimers in slow exchange on the NMR timescale with the corresponding monomers. The nature and structure of the dimers was evidenced by 2D NOESY and DOSY spectroscopy, mass spectrometry and X‐ray crystallography. The binding interface involves a large hydrophobic aromatic surface and hydrogen bonding. Dimerization requires that helices have the same handedness and the presence of a C‐terminal carboxy function. The protonation state of the carboxy group plays a crucial role, resulting in pH dependence of the association. Dimerization is also influenced by neighboring side chains and can be programmed to selectively produce heteromeric aggregates.

Hierarchical Nanomaterials Assembled from Peptoids and Other Sequence-Defined Synthetic Polymers

In nature, the self-assembly of sequence-specific biopolymers into hierarchical structures plays an essential role in the construction of functional biomaterials. To develop synthetic materials that can mimic and surpass the function of these natural counterparts, various sequence-defined bio- and biomimetic polymers have been developed and exploited as building blocks for hierarchical self-assembly. This review summarizes the recent advances in the molecular self-assembly of hierarchical nanomaterials based on peptoids (or poly-N-substituted glycines) and other sequence-defined synthetic polymers. Modern techniques to monitor the assembly mechanisms and characterize the physicochemical properties of these self-assembly systems are highlighted. In addition, discussions about their potential applications in biomedical sciences and renewable energy are also included. This review aims to highlight essential features of sequence-defined synthetic polymers (e.g., high stability and protein-like high-information content) and how these unique features enable the construction of robust biomimetic functional materials with high programmability and predictability, with an emphasis on peptoids and their self-assembled nanomaterials.

Peptide foldamer-based self-assembled nanostructures containing cyclic beta-amino acids

Peptide soft materials belong to an emerging branch of materials sciences due to their growing importance as responsive materials in diagnostics, therapeutics, and biomedical applications. The diversity provided by easily modifiable peptide sequences can be further increased by introducing nonnatural amino acids such as cyclic β-amino acids, leading to the formation of foldamers. Moreover, it is possible to combine peptide chains with other polymers, aromatic compounds, etc. to create hybrids with completely new properties and applications. In this review, we focus on the cis/trans enantiomers of three cyclic β-amino acids: 2-aminocyclobutane-1-carboxylic acid (ACBC), 2-aminocyclopentane-1-carboxylic acid (ACPC) and 2-aminocyclohexane-1-carboxylic acid (ACHC). The peptides discussed here either contain exclusively β-amino acids or are α,β-peptides, and they undergo self-assembly by forming different interactions that lead to the creation of well-defined nanostructures.

Amino Acid and Peptide-Based Liquid Crystals: An Overview

The role of amino acids and peptides has found remarkable usage in both living systems and nonliving materials, which have enabled its utility by virtue of crafting molecular architectures through covalent bonds and non-covalent interactions. In material chemistry, the role of peptides in Liquid Crystals (LCs) is profound, especially in the rapid construction of supramolecular hierarchical networks. The importance of LCs for a variety of societal needs leads to the synthesis of innumerable LCs by conventional mesogenic strategy and nonconventional molecular design principles. For example, electronic appliances, including flat panel TV displays, electronic notebooks, digital cameras, domestic devices, use LCs as an integral component for such applications. In addition, LCs are useful in biological systems, including stem cell research, sensors for bacteria, virus, and proteins. These accomplishments are possible mostly due to the non-conventional molecular design principles for crafting LCs using smaller molecular motifs. The usage of amino acids and peptides in LCs facilitates many intrinsic characteristics, including side-chain diversity, chirality, directionality, reversibility, electro-optical, columnar axis, stimuli-responsive complex molecular architectures. The next essential criteria for any LCs design for useful applications are room temperature LC (RT-LC); therefore, the quest for such LCs system remains highly significant. Evidently, there are around half a million liquid crystalline molecules; only a handful of RTLCs has been found, as there is no simple, precise strategy or molecular design principles to obtain RT-LC systems. The smaller molecular motifs of amino acids and linear peptides as a structural part of mesogenic molecules led to many LC phases with properties, including lyotropic, thermotropic, and its applications in different realms. Therefore, this review serves as a compilation of Small Peptide-based LCs (SPLCs) exhibiting lyotropic and thermotropic phases with applications in the recent advancements.

The Diverse World of Foldamers: Endless Possibilities of Self-Assembly

Different classes of foldamers, which are synthetic oligomers that adopt well-defined conformations in solution, have been the subject of extensive studies devoted to the elucidation of the forces driving their secondary structures and their potential as bioactive molecules. Regardless of the backbone type (peptidic or abiotic), the most important features of foldamers are the high stability, easy predictability and tunability of their folding, as well as the possibility to endow them with enhanced biological functions, with respect to their natural counterparts, by the correct choice of monomers. Foldamers have also recently started playing a starring role in the self-assembly of higher-order structures. In this review, selected articles will be analyzed to show the striking number of self-assemblies obtained for foldamers with different backbones, which will be analyzed in order of increasing complexity. Starting from the simplest self-associations in solution (e.g., dimers of β-strands or helices, bundles, interpenetrating double and multiple helices), the formation of monolayers, vesicles, fibers, and eventually nanostructured solid tridimensional morphologies will be subsequently described. The experimental techniques used in the structural investigation, and in the determination of the driving forces and mechanisms underlying the self-assemblies, will be systematically reported. Where applicable, examples of biomimetic self-assembled foldamers and their interactions with biological components will be described.

Soft-Matter Nanotubes: A Platform for Diverse Functions and Applications

Self-assembled organic nanotubes made of single or multiple molecular components can be classified into soft-matter nanotubes (SMNTs) by contrast with hard-matter nanotubes, such as carbon and other inorganic nanotubes. To date, diverse self-assembly processes and elaborate template procedures using rationally designed organic molecules have produced suitable tubular architectures with definite dimensions, structural complexity, and hierarchy for expected functions and applications. Herein, we comprehensively discuss every functions and possible applications of a wide range of SMNTs as bulk materials or single components. This Review highlights valuable contributions mainly in the past decade. Fifteen different families of SMNTs are discussed from the viewpoints of chemical, physical, biological, and medical applications, as well as action fields (e.g., interior, wall, exterior, whole structure, and ensemble of nanotubes). Chemical applications of the SMNTs are associated with encapsulating materials and sensors. SMNTs also behave, while sometimes undergoing morphological transformation, as a catalyst, template, liquid crystal, hydro-/organogel, superhydrophobic surface, and micron size engine. Physical functions pertain to ferro-/piezoelectricity and energy migration/storage, leading to the applications to electrodes or supercapacitors, and mechanical reinforcement. Biological functions involve artificial chaperone, transmembrane transport, nanochannels, and channel reactors. Finally, medical functions range over drug delivery, nonviral gene transfer vector, and virus trap.

Novel Materials From the Supramolecular Self-Assembly of Short Helical β3-Peptide Foldamers

Self-assembly is the spontaneous organization of small components into higher-order structures facilitated by the collective balance of non-covalent interactions. Peptide-based self-assembly systems exploit the ability of peptides to adopt distinct secondary structures and have been used to produce a range of well-defined nanostructures, such as nanotubes, nanofibres, nanoribbons, nanospheres, nanotapes, and nanorods. While most of these systems involve self-assembly of α-peptides, more recently β-peptides have also been reported to undergo supramolecular self-assembly, and have been used to produce materials-such as hydrogels-that are tailored for applications in tissue engineering, cell culture and drug delivery. This review provides an overview of self-assembled peptide nanostructures obtained via the supramolecular self-assembly of short β-peptide foldamers with a specific focus on N-acetyl-β3-peptides and their applications as bio- and nanomaterials.

Developing Biopolymer Mesocrystals by Crystallization of Secondary Structures

Particle-based mesocrystals have been known for over 10 years; however, examples of biopolymer mesocrystals are rather scarce. The synthesis of particle precursors of biopolymers, the identification of particle-mediated crystallization processes, and thus the synthesis of mesocrystals of biopolymers are challenging. Here, we summarize the existing examples of biopolymer crystallization based on self-assembly of the secondary structures, which could induce the formation of biopolymer mesocrystals. As basic building units, simple secondary structures such as β-sheets or α-helixes could provide a useful tool for the design of biopolymer mesocrystals.

Fabrication of cationic nanostructures from short self-assembling amphiphilic mixed α/β-pentapeptide: Potential candidates for drug delivery, gene delivery, and antimicrobial applications

The present article describes designing and fabrication of nanostructures from a mixed α/β-pentapeptide, Lys-βAla-βAla-Lys-βAla, which majorly contains non-natural β-alanine residues in the backbone with two α-lysine residues at 1- and 4-positions. The amphiphilic pentapeptide showed the ability to self-assemble into cationic nanovesicles in an aqueous solution. The average size of peptide nanostructures was found to be ~270 nm with a very high cationic charge of ~+40 mV. TEM micrographs revealed the average size of the same nanostructures ~80 nm bearing vesicular morphology. CD and FTIR spectroscopic studies on self-assembled pentapeptide hinted at random coil conformation which was also correlated with conformational search program using Hyper Chem 8.0. The pentapeptide nanostructures were then tested for encapsulation of hydrophobic model drug moieties, L-Dopa, and curcumin. Transfection efficiency of the generated cationic nanostructures was evaluated on HEK293 cells and compared the results with those obtained in the presence of chloroquine. The cytotoxicity assay performed using MTT depicted ~75-80% cell viability. The obtained nanostructures also gave positive results against both Gram-negative and Gram-positive bacterial strains. Altogether the results advocate the promising potential of the pentapeptide foldamer, H-Lys-βAla-βAla-Lys-βAla-OEt, for drug and gene delivery applications along with the antimicrobial activity.

Foldectures: 3D Molecular Architectures from Self-Assembly of Peptide Foldamers

The wide range of fascinating supramolecular architectures found in nature, from DNA double helices to giant protein shells, inspires researchers to mimic the diverse shapes and functions of natural systems. Thus, a variety of artificial molecular platforms have been developed by assembling DNA-, peptide-, and protein-based building blocks for medicinal and biological applications. There has also been a significant interest in the research of non-natural oligomers (i.e., foldamers) that fold into well-defined secondary structures analogous to those found in proteins, because the assemblies of foldamers are expected not only to form biomimetic supramolecular architectures that resemble those of nature but also to display unique functions and unprecedented topologies at the same time due to their different folding propensities from those of natural building blocks. Foldamer-based supramolecular architectures have been reported in the form of nanofibers, nanochannels, nanosheets, and finite three-dimensional (3D) shapes. We have developed a new class of crystalline peptidic materials termed "foldectures" (a compound of foldamer and architecture) with unprecedented topological complexity derived from the rapid and nonequilibrium aqueous phase self-assembly of foldamers. In this Account, we discuss the morphological features, molecular packing structures, physical properties, and potential applications of foldectures. Foldectures exhibit well-defined, microscale, homogeneous, and finite structures with unique morphologies such as windmill, tooth, and trigonal bipyramid shapes. The symmetry elements of the morphologies vary with the foldamer building blocks and are retained upon surfactant-assisted shape evolution. Structural characterization by powder X-ray diffraction (PXRD) revealed the molecular packing structures, suggesting how the foldamer building blocks assembled in the 3D structure. The analysis by PXRD showed that intermolecular hydrogen bonding connects foldamers in head-to-tail fashion, while hydrophobic attraction plays a role in arranging foldamers in parallel, antiparallel, or cholesteric phase-like manners. Each packing structure from the foldamer building blocks possesses distinct symmetry elements that are directly expressed in the 3D morphologies. Because of their well-ordered molecular packing structures, foldectures exhibit facet-dependent surface characteristics and anisotropic magnetic susceptibility. The facet-dependent surface property was harnessed to synthesize anisotropic metal nanoparticle-foldecture composites, and the anisotropic magnetic susceptibility enables foldectures to undergo real-time alignment and rotating motion in response to an external magnetic field. By means of their unusual shapes and properties, foldectures have been demonstrated to mimic the functionality of natural systems such as magnetosomes or carboxysomes. Further development of foldectures using higher-order building units, complicated packing motifs, and functional moieties could provide a novel biocompatible platform rivaling 3D biological architectures in natural systems.

Unique Functional Materials Derived from β-Amino Acid Oligomers

The unique structures formed by β-amino acid oligomers, or β-peptide foldamers, have been studied for almost two decades, which has led to the discovery of several distinctive structures and bioactive molecules. Recently, this area of research has expanded from conventional peptide drug design to the formation of assemblies and nanomaterials by peptide self-assembly. The unique structures formed by β-peptides give rise to a set of new materials with altered properties that differ from conventional peptide-based materials; such new materials may be useful in several bio- and nanomaterial applications.

Supramolecular Self-Assembly into Biofunctional Soft Nanotubes: From Bilayers to Monolayers

The inner and outer surfaces of bilayer-based lipid nanotubes can be hardly modified selectively by a favorite functional group. Monolayer-based nanotubes display a definitive difference in their inner and outer functionalities if bipolar wedge-shaped amphiphiles, so-called bolaamphiphiles, as a constituent of the monolayer membrane pack in a parallel fashion with a head-to-tail interface. To exclusively form unsymmetrical monolayer lipid membranes, we focus herein on the rational molecular design of bolaamphiphiles and a variety of self-assembly processes into tubular architectures. We first describe the importance of polymorph and polytype control and then discuss diverse methodologies utilizing a polymer template, multiple hydrogen bonds, binary and ternary coassembly, and two-step self-assembly. Novel biologically important functions of the obtained soft nanotubes, brought about only by completely unsymmetrical inner and outer surfaces, are discussed in terms of protein refolding, drug nanocarriers, lectin detection, a chiral inducer for achiral polymers, the tailored fabrication of polydopamine, and spontaneous nematic alignment.

Hexagonal Lyotropic Liquid Crystal from Simple "Abiotic" Foldamers

The motivation of foldamer chemistry is to identify novel building blocks that have the potential to imitate natural species. Peptides and peptide mimetics can form stable helical conformations and further self-assemble into diverse aggregates in water, where it is difficult to isolate a single helix. In contrast, most "abiotic" foldamers may fold into helical structures in solution, but are difficult to assemble into tertiary ones. It remains a challenge to obtain "abiotic" species similar to peptides. In this paper, a novel foldamer scaffold, in which p-phenyleneethynylene units are linked by chiral carbon atoms, was designed and prepared. In very dilute solutions, these oligomers were random coils. The hexamer and octamers could form a hexagonal lyotropic liquid crystal (LC) in CH2Cl2 when the concentrations reached the critical values. The microscopic observations indicated that they could assemble into the nanofibers in the LC. Interestingly, after some LC phases were diluted at room temperature, the nanofibers could be preserved. The good stabilities of the assemblies are possibly attributed to a more compact backbone and more rigid side chains.

Magnetotactic molecular architectures from self-assembly of β-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 β-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.

Spontaneous nematic alignment of a lipid nanotube in aqueous solutions

The dispersibility and liquid crystal formation of a self-assembled lipid nanotube (LNT) was investigated in a variety of aqueous solutions. As the lipid component, we chose a bipolar lipid with glucose and tetraglycine headgroups, which self-assembled into an LNT with a small outer diameter of 16 to 17 nm and a high axial ratio of more than 310. The LNT gave a stable colloidal dispersion in its dilute solutions and showed spontaneous liquid crystal (LC) alignment at relatively low concentrations and in a pH region including neutral pH. The LNT samples with shorter length distributions were prepared by sonication, and the relationship between the LNT axial ratio and the minimum LC formation concentration was examined. The robustness of the LNT made the liquid crystal stable in mixed solvents of water/ethanol, water/acetone, and water/tetrahydrofuran (1:1 by volume) and at a temperature of up to 90 °C in water. The observed colloidal behavior of the LNT was compared to those of similar 1D nanostructures such as a phospholipid tubule.

Amino acid sequence in constitutionally isomeric tetrapeptide amphiphiles dictates architecture of one-dimensional nanostructures

The switching of two adjacent amino acids can lead to differences in how proteins fold thus affecting their function. This effect has not been extensively explored in synthetic peptides in the context of supramolecular self-assembly. Toward this end, we report here the use of isomeric peptide amphiphiles as molecular building blocks to create one-dimensional (1D) nanostructures. We show that four peptide amphiphile isomers, with identical composition but a different sequence of their four amino acids, can form drastically different types of 1D nanostructures under the same conditions. We found that molecules with a peptide sequence of alternating hydrophobic and hydrophilic amino acids such as VEVE and EVEV self-assemble into flat nanostructures that can be either helical or twisted. On the other hand, nonalternating isomers such as VVEE and EEVV result in the formation of cylindrical nanofibers. Furthermore, we also found that when the glutamic acid is adjacent to the alkyl tail the supramolecular assemblies appear to be internally flexible compared to those with valine as the first amino acid. These results clearly demonstrate the significance of peptide side chain interactions in determining the architectures of supramolecular assemblies.

Exploiting aromatic interactions for β-peptide foldamer helix stabilization: a significant design element

Tetrameric H10/12 helix stabilization was achieved by the application of aromatic side-chains in β-peptide oligomers by intramolecular backbone-side chain CH-π interactions. Because of the enlarged hydrophobic surface of the oligomers, a further aim was the investigation of the self-assembly in a polar medium for the β-peptide H10/12 helices. NMR, ECD, and molecular modeling results indicated that the oligomers formed by cis-[1S,2S]- or cis-[1R,2R]-1-amino-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid (ATENAC) and cis-[1R,2S]- or cis-[1S,2R]-2-aminocyclohex-3-enecarboxylic acid (ACHEC) residues promote stable H10/12 helix formation with an alternating backbone configuration even at the tetrameric chain length. These results support the view that aromatic side-chains can be applied for helical structure stabilization. Importantly, this is the first observation of a stable H10/12 helix with tetrameric chain-length. The hydrophobically driven self-assembly was achieved for the helix-forming oligomers, seen as vesicles in transmission electron microscopy images. The self-association phenomenon, which supports the helical secondary structure of these oligomers, depends on the hydrophobic surface area, because a higher number of aromatic side-chains yielded larger vesicles. These results serve as an essential element for the design of helices relating to the H10/12 helix. Moreover, they open up a novel area for bioactive foldamer construction, while the hydrophobic area gained through the aromatic side-chains may yield important receptor-ligand interaction surfaces, which can provide amplified binding strength.

Cytocompatibility of novel extracellular matrix protein analogs of biodegradable polyester polymers derived from α-hydroxy amino acids

One of the challenges in regenerative medicine is the development of novel biodegradable materials to build scaffolds that will support multiple cell types for tissue engineering. Here we describe the preparation, characterization, and cytocompatibility of homo- and hetero-polyesters of α-hydroxy amino acid derivatives with or without lactic acid conjugation. The polymers were prepared by a direct condensation method and characterized using gel permeation chromatography, (1)H-nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, optical activity, and solubility. The surface charge of the polymers was evaluated using zeta potential measurements. The polymers were coated onto glass cover slips followed by characterization using nano-surface profiler, thin film reflectometry, and atomic force microscopy (AFM). Their interaction with endothelial and neuronal cells was assessed using adhesion, proliferation, and differentiation assays. Of the characterized polymers, Poly-HOVal-LA, but not Poly-(D)HOPhe, significantly augmented nerve growth factor (NGF)-induced neuronal differentiation of the PC12 pheochromcytoma cells. In contrast, Poly-HOLeu increased by 20% the adhesion of endothelial cells, but did not affect PC12 cell differentiation. NGF-induced Erk1/2 phosphorylation in PC12 cells grown on the different polymers was similar to the effect observed for cells cultured on collagen type I. While no significant association could be established between charge and the differentiative/proliferative properties of the polymers, AFM analysis indicated augmentation of NGF-induced neuronal differentiation on smooth polymer surfaces. We conclude that overall selective cytocompatibility and bioactivity might render α-hydroxy amino acid polymers useful as extracellular matrix-mimicking materials for tissue engineering.

Self-association of an enantiopure β-pentapeptide in nematic liquid crystals

Herein, we report for the first time that nematic liquid-crystalline environments drive the reversible self-aggregation of an enantiopure β-pentapeptide into oligomers with a well-defined structure. The peptide contains four (1S,2S)-2-aminocyclopentane carboxylic acid (ACPC) residues and the paramagnetic β-amino acid (3R,4R)-4-amino-1-oxyl-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid (POAC). The structure of the oligomers was investigated by electron paramagnetic resonance (EPR) spectroscopy, which allowed us to obtain the intermonomer distance distribution in the aggregates as a function of peptide concentration in two nematic liquid crystals, E7 and ZLI-4792. The aggregates were modeled on the basis of the EPR data, and their orientation and order in the nematic phase were studied by the surface tensor method.

Hierarchical ordering of amyloid fibrils on the mica surface

The aggregation of amyloid peptides into ordered fibrils is closely associated with many neurodegenerative diseases. The surfaces of cell membranes and biomolecules are believed to play important roles in modulation of peptide aggregation under physiological conditions. Experimental studies of fibrillogenesis at the molecular level in vivo, however, are inherently challenging, and the molecular mechanisms of how surface affects the structure and ordering of amyloid fibrils still remain elusive. Herein we have investigated the aggregation behavior of insulin peptides within water films adsorbed on the mica surface. AFM measurements revealed that the structure and orientation of fibrils were significantly affected by the mica lattice and the peptide concentration. At low peptide concentration (~0.05 mg mL(-1)), there appeared a single layer of short and well oriented fibrils with a mean height of 1.6 nm. With an increase of concentration to a range of 0.2-2.0 mg mL(-1), a different type of fibrils with a mean height of 3.8 nm was present. Interestingly, when the concentration was above 2.0 mg mL(-1), the thicker fibrils exhibited two-dimensional liquid-crystal-like ordering probably caused by the combination of entropic and electrostatic forces. These results could help us gain better insight into the effects of the substrate on amyloid fibrillation.

Dimerization of helical β-peptides in solution

Molecular simulations are used to examine the aggregation behavior of several β-peptides in explicit water. The particular peptides considered here adopt a helical, rodlike conformation in aqueous solution. Four distinct molecular sequences are considered. Earlier experimental studies have revealed the formation of ordered and disordered aggregates for such molecules, depending on sequence. The simulations reported here, which are conducted by resorting to metadynamics techniques, lead to free energy surfaces for dimerization of the peptides in water as a function of separation and relative orientation. Such surfaces are used to identify the molecular origins for the behaviors observed in the experiments.

Bio-inspired supramolecular self-assembly towards soft nanomaterials

Supramolecular self-assembly has proven to be a reliable approach towards versatile nanomaterials based on multiple weak intermolecular forces. In this review, the development of bio-inspired supramolecular self-assembly into soft materials and their applications are summarized. Molecular systems used in bio-inspired "bottom-up self-assembly" involve small organic molecules, peptides or proteins, nucleic acids, and viruses. Self-assembled soft nanomaterials have been exploited in various applications such as inorganic nanomaterial synthesis, drug or gene delivery, tissue engineering, and so on.