Controlling the Diameters of Nanotubes Self-Assembled from Designed Peptide Bolaphiles

Preparation, design, identification and application of self-assembly peptides from seafood: A review

Hydrogels formed by self-assembling peptides with low toxicity and high biocompatibility have been widely used in food and biomedical fields. Seafood contains rich protein resources and is also one of the important sources of natural bioactive peptides. The self-assembled peptides in seafood have good functional activity and are very beneficial to human health. In this review, the sequence of seafood self-assembly peptide was introduced, and the preparation, screening, identification and characterization. The rule of self-assembled peptides was elucidated from amino acid sequence composition, amino acid properties (hydrophilic, hydrophobic and electric), secondary structure, interaction and peptide properties (hydrophilic and hydrophobic). It was introduced that the application of hydrogels formed by self-assembled peptides, which lays a theoretical foundation for the development of seafood self-assembled peptides in functional foods and the application of biological materials.

Controlled Assembly and Disassembly of Higher-Order Peptide Nanotubes

The controlled peptide self-assembly and disassembly are not only implicated in many cellular processes but also possess huge application potential in a wide range of biotechnology and biomedicine. β-sheet peptide assemblies possess high kinetic stability, so it is usually hard to disassemble them rapidly. Here, we reported that both the self-assembly and disassembly of a designed short β-sheet peptide IIIGGHK could be well harnessed through the variations of concentration, pH, and mechanical stirring. Microscopic imaging, neutron scattering, and infrared spectroscopy were used to track the assembly and disassembly processes upon these stimuli, especially the interconversion between thin, left-handed protofibrils and higher-order nanotubes with superstructural right-handedness. The underlying rationale for these controlled disassembly processes mainly lies in the fact that the specific His-His interactions between protofibrils were responsive to these stimuli. By taking advantage of the peptide self-assembly and disassembly, the encapsulation of the hydrophobic drug curcumin and its rapid release upon stimuli were achieved. Additionally, the peptide hydrogels facilitated the differentiation of neural cells while maintaining low cell cytotoxicity. We believe that such dynamic and reversible structural transformation in this work provides a distinctive paradigm for controlling the peptide self-assembly and disassembly, thus laying a foundation for practical applications of peptide assemblies.

Controlling 1D Nanostructures and Handedness by Polar Residue Chirality of Amphiphilic Peptides

Peptide assemblies are promising nanomaterials, with their properties and technological applications being highly hinged on their supramolecular architectures. Here, how changing the chirality of the terminal charged residues of an amphiphilic hexapeptide sequence Ac-I4 K2 -NH2 gives rise to distinct nanostructures and supramolecular handedness is reported. Microscopic imaging and neutron scattering measurements show thin nanofibrils, thick nanofibrils, and wide nanotubes self-assembled from four stereoisomers. Spectroscopic and solid-state nuclear magnetic resonance (NMR) analyses reveal that these isomeric peptides adopt similar anti-parallel β-sheet secondary structures. Further theoretical calculations demonstrate that the chiral alterations of the two C-terminal lysine residues cause the formation of diverse single β-strand conformations, and the final self-assembled nanostructures and handedness are determined by the twisting direction and degree of single β-strands. This work not only lays a useful foundation for the fabrication of diverse peptide nanostructures by manipulating the chirality of specific residues but also provides a framework for predicting the supramolecular structures and handedness of peptide assemblies from single molecule conformations.

Protein Nanotubes as Advanced Material Platforms and Delivery Systems

Protein nanotubes (PNTs) as state-of-the-art nanocarriers are promising for various potential applications both in the food and pharmaceutical industries. Derived from edible starting sources like α-lactalbumin, lysozyme, and ovalbumin, PNTs bear properties of biocompatibility and biodegradability. Their large specific surface area and hydrophobic core facilitate chemical modification and loading of bioactive substances, respectively. Moreover, their enhanced permeability and penetration ability across biological barriers such as intestinal mucus, extracellular matrix, and thrombus clot, make it promising platforms for health-related applications. Most importantly, their simple preparation processes enable large-scale production, supporting applications in the biomedical and nanotechnological fields. Understanding the self-assembly principles is crucial for controlling their morphology, size, and shape, and thus provides the ground to a multitude of applications. Here, the current state-of-the-art of PNTs including their building materials, physicochemical properties, and self-assembly mechanisms are comprehensively reviewed. The advantages and limitations, as well as challenges and prospects for their successful applications in biomaterial and pharmaceutical sectors are then discussed and highlighted. Potential cytotoxicity of PNTs and the need of regulations as critical factors for enabling in vivo applications are also highlighted. In the end, a brief summary and future prospects for PNTs as advanced platforms and delivery systems are included.

Organic chiral nano- and microfilaments: types, formation, and template applications

Organic chiral nanofilaments are part of an important class of nanoscale chiral materials that has recently been receiving significant attention largely due to their potential use in applications such as optics, photonics, metameterials, and potentially a range of medical as well as sensing applications. This review will focus on key examples of the formation of such nano- and micro-filaments based on carbon nanofibers, polymers, synthetic oligo- and polypeptides, self-assembled organic molecules, and one prominent class of liquid crystals. The most critical aspects discussed here are the underlying driving forces for chiral filament formation, potentially answering why specific sizes and shapes are formed, what molecular design strategies are working equally well or rather differently among these materials classes, and what uses and applications are driving research in this fascinating field of materials science.

Neutron reflection and scattering in characterising peptide assemblies

Self-assemblies of de novo designed short peptides at interface and in bulk solution provide potential platforms for developing applications in many medical and technological areas. However, characterising how bioinspired supramolecular nanostructures evolve with dynamic self-assembling processes and respond to different stimuli remains challenging. Neutron scattering technologies including small angle neutron scattering (SANS) and neutron reflection (NR) can be advantageous and complementary to other state-of-the-art techniques in tracing structural changes under different conditions. With more neutron sources now available, SANS and NR are becoming increasingly popular in studying self-assembling processes of diverse peptide and protein systems, but the difficulty in experimental manipulation and data analysis can deter beginners. This review will introduce the basic theory, general experimental setup and data analysis of SANS and NR, followed by provision of their applications in characterising interfacial and solution self-assemblies of representative peptides and proteins. SANS and NR are remarkably effective in determining the morphological features self-assembled short peptides, especially size and shape transitions as a result of either sequence changes or in response to environmental stimuli, demonstrating the unique capability of NR and SANS in unravelling the interactive processes. These examples highlight the potential of NR and SANS in supporting the development of novel short peptides and proteins as biopharmaceutical candidates in the fight against many diseases and infections that share common features of membrane interactive processes.

Study on Green Nanofluid Profile Control and Displacement of Oil in a Low Permeability Reservoir

Low permeability reservoirs are characterized by low permeability, small pore throat, strong heterogeneity, and poor injection-production ability. High shale content of the reservoir, strong pressure sensitivity, micropore undersaturation, and significant water-lock effect in water injection development lead to increased fluid seepage resistance. There is an urgent need to adopt physical and chemical methods to supplement energy and improve infiltration efficiency, thereby forming effective methods for increasing the production and efficiency. Aiming at the characteristics of ultralow permeability reservoirs, in this paper, a green and environmental friendly biobased profile control and displacement agent (Bio Nano30) has been developed using noncovalent supramolecular interaction. Physical simulation experiments illustrate the profile control and displacement mechanism of Bio-Nano30. Laboratory experiments and field applications show that good results have been achieved in oil well plugging removal, water well pressure reduction and injection increase, and well group profile control and oil displacement. This research has good application prospects in low permeability heterogeneous reservoirs.

Self-Assembly, In Vitro Gene Transfection, and Antimicrobial Activity of Biodegradable Cationic Bolaamphiphiles

Bolaamphiphiles or bolaforms have drawn particular interest in drug and gene delivery, and studies of bolaforms have been growing continuously. Bolaforms, due to their unique structure, exhibit specific self-assembly behavior in water. The present work aims to develop biodegradable cationic bolaforms with a better gene transfection ability. In this work, a novel cationic bolaform (Bola-1) with head groups bearing hydroxyl (OH) functionality was designed and synthesized to investigate self-assembly and gene transfection efficiency. The self-assembly behavior of Bola-1 in water was compared with that of the hydrochloride salt (Bola-2) of its precursor molecule to investigate the effect of the -OH functionality on their solution properties. Several techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy, were employed for the physicochemical characterization of Bola-1 and Bola-2. Despite the presence of polar urea groups in the spacer chain, both bolaforms were found to form spherical or elongated micelles above a relatively low critical aggregation concentration (CAC). The presence of the OH group was found to significantly affect the CAC value. The results of calorimetric measurements suggested a thermodynamically favorable aggregate formation in salt-free water. Despite stronger binding efficiency with calf thymus DNA, in vitro gene transfection studies performed using adherent cell Hek 293 suggested that both Bola-1 and Bola-2 have gene transfection efficiency comparable to that of turbofectamine standard. Both bolaforms were found to exhibit significant in vitro cytotoxicity at higher concentrations. Also, the bolaforms showed beneficial antibacterial activity at higher concentrations.

Fast Self-Assembly Dynamics of a β-Sheet Peptide Soft Material

Peptide-based hydrogels are promising biocompatible materials for wound healing, drug delivery, and tissue engineering applications. The physical properties of these nanostructured materials depend strongly on the morphology of the gel network. However, the self-assembly mechanism of the peptides that leads to a distinct network morphology is still a subject of ongoing debate, since complete assembly pathways have not yet been resolved. To unravel the dynamics of the hierarchical self-assembly process of the model β-sheet forming peptide KFE8 (Ac-FKFEFKFE-NH₂ )_, high-speed atomic force microscopy (HS-AFM) in liquid is used. It is demonstrated that a fast-growing network, based on small fibrillar aggregates, is formed at a solid-liquid interface, while in bulk solution, a distinct, more prolonged nanotube network emerges from intermediate helical ribbons. Moreover, the transformation between these morphologies has been visualized. It is expected that this new in situ and in real-time methodology will set the path for the in-depth unravelling of the dynamics of other peptide-based self-assembled soft materials, as well as gaining advanced insights into the formation of fibers involved in protein misfolding diseases.

Self-Assembly of Short Amphiphilic Peptides and Their Biomedical Applications

A series of functional biomaterials with different sizes and morphologies can be constructed through self-assembly, among which amphiphilic peptide-based materials have received intense attention. One main possible reason is that the short amphiphilic peptides can facilitate the formation of versatile materials and promote their further applications in different fields. Another reason is that the simple structure of amphiphilic peptides can help establish the structure-function relationship. This review highlights the recent advances in the self-assembly of two typical peptide species, surfactant-like peptides (SLPs) and peptides amphiphiles (PAs). These peptides can self-assemble into diverse nanostructures. The formation of these different nanostructures resulted from the delicate balance of varied non-covalent interactions. This review embraced each non-covalent interaction and then listed the typical routes for regulating these non-covalent interactions, then realized the morphologies modulation of the self-assemblies. Finally, their applications in some biomedical fields, such as the stabilization of membrane proteins, templating for nanofabrication and biomineralization, acting as the antibacterial and antitumor agents, hemostasis, and synthesis of melanin have been summarized. Further advances in the self-assembly of SLPs and PAs may focus on the design of functional materials with targeted properties and exploring their improved properties.

Phenol-soluble modulins PSMα3 and PSMβ2 form nanotubes that are cross-α amyloids

Phenol-soluble modulins (PSMs) are peptide-based virulence factors that play significant roles in the pathogenesis of staphylococcal strains in community-associated and hospital-associated infections. In addition to cytotoxicity, PSMs display the propensity to self-assemble into fibrillar species, which may be mediated through the formation of amphipathic conformations. Here, we analyze the self-assembly behavior of two PSMs, PSMα3 and PSMβ2, which are derived from peptides expressed by methicillin-resistant Staphylococcus aureus (MRSA), a significant human pathogen. In both cases, we observed the formation of a mixture of self-assembled species including twisted filaments, helical ribbons, and nanotubes, which can reversibly interconvert in vitro. Cryo–electron microscopy structural analysis of three PSM nanotubes, two derived from PSMα3 and one from PSMβ2, revealed that the assemblies displayed remarkably similar structures based on lateral association of cross-α amyloid protofilaments. The amphipathic helical conformations of PSMα3 and PSMβ2 enforced a bilayer arrangement within the protofilaments that defined the structures of the respective PSMα3 and PSMβ2 nanotubes. We demonstrate that, similar to amyloids based on cross-β protofilaments, cross-α amyloids derived from these PSMs display polymorphism, not only in terms of the global morphology (e.g., twisted filament, helical ribbon, and nanotube) but also with respect to the number of protofilaments within a given peptide assembly. These results suggest that the folding landscape of PSM derivatives may be more complex than originally anticipated and that the assemblies are able to sample a wide range of supramolecular structural space.

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.

Tuning the shell structure of peptide nanotubes with sodium tartrate: From monolayer to bilayer

Though the function of peptide based nanotubes are well correlated with its shape and size, controlling the dimensions of nanotubes still remains a great challenge in the field of peptide self-assembly. Here, we demonstrated that the shell structure of nanotubes formed by a bola peptide Ac-KI₃VK-NH₂ (KI₃VK, in which K, I, and V are abbreviations of lysine, isoleucine, and valine) can be regulated by mixing it with the salt sodium tartrate (STA). The ratio of KI₃VK and STA had a great impact on shell structure of the nanotubes. Bilayer nanotubes can be constructed when the molar ratio of KI₃VK and STA was less than 1:2. Both the two hydroxyls and the negative charges carried by STA were proved to play important roles in the bilayer nanotubes formation. Observations of different intermediates provided obvious evidence for the varied pathway of the bilayer nanotubes formation. Based on these experimental results, the possible mechanism for bilayer nanotubes formation was proposed. Such a study provides a simple and effective way for regulating the shell structure of the nanotubes and may expand their applications in different fields.

Ordered Packing of β-Sheet Nanofibrils into Nanotubes: Multi-hierarchical Assembly of Designed Short Peptides

Although it is well-known proteins and their complexes are hierarchically organized and highly ordered structures, it remains a major challenge to replicate their hierarchical self-assembly process and to fabricate multihierarchical architectures with well-defined shapes and monodisperse characteristic sizes via peptide self-assembly. Here we describe an amphiphilic short peptide Ac-I₃GGHK-NH₂ that first preassembles into thin, left-handed β-sheet nanofibrils, followed by their ordered packing into right-handed nanotubes. The key intermediate morphology and structures featuring the hierarchical process are simultaneously demonstrated. Further mechanistic exploration with the variants Ac-I₃GGGK-NH₂, Ac-I₃GGFK-NH₂, and Ac-I₃GG^DH^DK-NH₂ reveals the vital role of multiple His-His side chain interactions between nanofibrils in mediating higher-order assembly and architectures. Altogether, our findings not only advance current understanding of hierarchical assembly of peptides and proteins but also afford a paradigm of how to take advantage of side chain interactions to construct higher-order assemblies with enhanced complexities.

Deterministic chaos in the self-assembly of β sheet nanotubes from an amphipathic oligopeptide

The self-assembly of designed peptides into filaments and other higher-order structures has been the focus of intense interest because of the potential for creating new biomaterials and biomedical devices. These peptide assemblies have also been used as models for understanding biological processes, such as the pathological formation of amyloid. We investigate the assembly of an octapeptide sequence, Ac-FKFEFKFE-NH₂, motivated by prior studies that demonstrated that this amphipathic β strand peptide self-assembled into fibrils and biocompatible hydrogels. Using high-resolution cryoelectron microscopy (cryo-EM), we are able to determine the atomic structure for two different coexisting forms of the fibrils, containing four and five β sandwich protofilaments, respectively. Surprisingly, the inner walls in both forms are parallel β sheets, while the outer walls are antiparallel β sheets. Our results demonstrate the chaotic nature of peptide self-assembly and illustrate the importance of cryo-EM structural analysis to understand the complex phase behavior of these materials at near-atomic resolution.

Mechanistic process understanding of the self-assembling behaviour of asymmetric bolaamphiphilic short-peptides and their templating for silica and titania nanomaterials

Investigation of the self-assembly of peptides is critically important to clarify certain biophysical phenomena, fulfill some biological functions, and construct functional materials. However, it is still a challenge to precisely predict the self-assembled structures of peptides because of their complicated driving forces and various assembling pathways. In this work, to elucidate the effects of noncovalent interactions including hydrogen bonding, molecular geometry, and hydrophobic and electrostatic interactions on the peptide self-assembly, a series of asymmetric bolaamphiphilic short peptides consisting of Ac-EI₃K-NH₂ (EI₃K), Ac-EI₄K-NH₂ (EI₄K), Ac-KI₃E-NH₂ (KI₃E) and Ac-KI₄E-NH₂ (KI₄E) were designed and their self-assembling behaviors at different solution pH values were investigated systematically. The peptides self-assembled into twisted nanofibers under most conditions except for EI₄K in a strongly alkaline solution and KI₄E under a strongly acidic condition, in which they self-assembled into nanotubes via helical monolayer nanosheet intermediates. In particular, KI₄E nanotubes are formed under acidic conditions, and its diameters are ∼500 nm much greater than most of the self-assembled structures from bolaamphiphilic peptides. Moreover, reversible morphological transition between the nanotubes and twisted nanofibers was observed with the change in solution pH. Such tunable self-assembled structures and switchable surface properties of the asymmetric bolaamphiphilic short-peptides allow them to be used as templates to construct advanced materials. Silica and titania nanomaterials faithful to the peptide templates in morphology were prepared at ambient temperature. This work clearly elucidates the effects of noncovalent interactions on the peptide self-assembly and also provides new insights into the design and preparation of complicated inorganic materials from tunable organic templates.

Nanocapsule designs for antimicrobial resistance

The pressing need of new antimicrobial products is growing stronger, particularly because of widespread antimicrobial resistance, endangering our ability to treat common infections. The recent coronavirus pandemic has dramatically highlighted the necessity of effective antibacterial and antiviral protection. This work explores at the molecular level the mechanism of action of antibacterial nanocapsules assembled in virus-like particles, their stability and their interaction with mammal and antimicrobial model membranes. We use Molecular Dynamics with force-fields of different granularity and protein design strategies to study the stability, self-assembly and membrane poration properties of these nanocapsules.

Effect of Stereochemistry on Chirality and Gelation Properties of Supramolecular Self-Assemblies

Although chiral nanostructures have been fabricated at various structural levels, the transfer and amplification of chirality from molecules to supramolecular self-assemblies are still puzzling, especially for heterochiral molecules. Herein, four series of C₂ -symmetrical dipeptide-based derivatives bearing various amino acid sequences and different chiralities are designed and synthesized. The transcription and amplification of molecular chirality to supramolecular assemblies are achieved. The results show that supramolecular chirality is only determined by the amino acid adjacent to the benzene core, irrespective of the absolute configuration of the C-terminal amino acid. In addition, molecular chirality also has a significant influence on the gelation behavior. For the diphenylalanine-based gelators, the homochiral gelators can be gelled through a conventional heating-cooling process, whereas heterochiral gelators form translucent stable gels under sonication. The racemic gels possess higher mechanical properties than those of the pure enantiomers. All of these results contribute to an increasing knowledge over control of the generation of specific chiral supramolecular structures and the development of new optimized strategies to achieve functional supramolecular organogels through heterochiral and racemic systems.

Ordered Nanofibers Fabricated from Hierarchical Self-Assembling Processes of Designed α-Helical Peptides

Peptide self-assembly is fast evolving into a powerful method for the development of bio-inspired nanomaterials with great potential for many applications, but it remains challenging to control the self-assembling processes and nanostrucutres because of the intricate interplay of various non-covalent interactions. A group of 28-residue α-helical peptides is designed including NN, NK, and HH that display distinct hierarchical events. The key of the design lies in the incorporation of two asparagine (Asn) or histidine (His) residues at the a positions of the second and fourth heptads, which allow one sequence to pack into homodimers with sticky ends through specific interhelical Asn-Asn or metal complexation interactions, followed by their longitudinal association into ordered nanofibers. This is in contrast to classical self-assembling helical peptide systems consisting of two complementary peptides. The collaborative roles played by the four main non-covalent interactions, including hydrogen-bonding, hydrophobic interactions, electrostatic interactions, and metal ion coordination, are well demonstrated during the hierarchical self-assembling processes of these peptides. Different nanostructures, for example, long and short nanofibers, thin and thick fibers, uniform metal ion-entrapped nanofibers, and polydisperse globular stacks, can be prepared by harnessing these interactions at different levels of hierarchy.

Temperature-Dependent Reversible Morphological Transformations in N-Oleoyl β-d-Galactopyranosylamine

Amphiphilic molecules self-assemble into supramolecular structures of various sizes and morphologies depending on their molecular packing and external factors. Transformations between various self-assembled morphologies are a matter of great fundamental interest. Recently, we reported the discovery of a novel class of single-chain galactopyranosylamide amphiphiles that self-assemble to form vesicles in water. Here, we describe how the vesicles composed of the amphiphile N-oleoyl β-d-galactopyranosylamine (GOA) undergo a morphological transition to fibers consisting of mainly flat sheet-like structures. Moreover, we show that this transformation is reversible in a temperature-dependent manner. We used several optical microscopy and electron microscopy techniques, circular dichroism spectroscopy, small-angle X-ray scattering, and differential scanning calorimetry, to fully investigate and characterize the morphological transformations of GOA and provide a structural basis for such phenomena. These studies provide significant molecular insight into the structural polymorphism of sugar-based amphiphiles and foresee future applications in rational design of self-assembled materials.

Study on the Reducing Injection Pressure Regulation of Hydrophobic Carbon Nanoparticles

The interest in the application of nanofluid in reducing injection pressure has been increasing especially for tight reservoirs. In this work, a new type of hydrophobic carbon nanofluid was prepared and the pressure-reducing performance was investigated. The results of particle size distribution, zeta potential, and transmission electron microscopy image showed that the dispersion of nanofluid was uniform and stable. In addition, the hydrophobic carbon nanofluid showed excellent antitemperature and antisalinity property. The contact angle of oil-wet glass slide can range from 45 to 89° after it adsorbs hydrophobic carbon nanoparticles (HCNPs). The atomic force microscope tests showed that the core surface roughness was reduced about 16.67%. The core flooding tests showed that the pressure-reducing rate of 0.15 wt % HCNP nanofluid can reach 17.00%. HCNPs show good performance in reducing pressure and have a broad application prospect in oil field development.

Modulation of Antimicrobial Peptide Conformation and Aggregation by Terminal Lipidation and Surfactants

The function and properties of peptide-based materials depend not only on the amino acid sequence but also on the molecular conformations. In this paper, we chose a series of peptides G_m(XXKK)_nX-NH₂ (m = 0, 3; n = 2, 3; X = I, L, and V) as the model molecules and studied the conformation regulation through N-terminus lipidation and their formulation with surfactants. The structural and morphological transition of peptide self-assemblies have also been investigated via transmission electron microscopy, atomic force microscopy, circular dichroism spectroscopy, and small-angle neutron scattering. With the terminal alkylation, the molecular conformation changed from random coil to β-sheet or α-helix. The antimicrobial activities of alkylated peptide were different. C₁₆-G₃(IIKK)₃I-NH₂ showed antimicrobial activity against Streptococcus mutans, while C₁₆-(IIKK)₂I-NH₂ and C₁₆-G₃(IIKK)₂I-NH₂ did not kill the bacteria. The surfactant sodium dodecyl sulfonate could rapidly induce the self-assemblies of alkylated peptides (C₁₆-(IIKK)₂I-NH₂, C₁₆-G₃(IIKK)₂I-NH₂, C₁₆-G₃(VVKK)₂V-NH₂) from nanofibers to micelles, along with the conformation changing from β-sheet to α-helix. The cationic surfactant hexadecyl trimethyl ammonium bromide made the lipopeptide nanofibers thinner, and nonionic surfactant polyoxyethylene (23) lauryl ether (C₁₂EO₂₃) induced the nanofibers much more intensively. Both the activity and the conformation of the α-helical peptide could be modulated by lipidation. Then, the self-assembled morphologies of alkylated peptides could also be further regulated with surfactants through hydrophobic, electrostatic, and hydrogen-bonding interactions. These results provided useful strategies to regulate the molecular conformations in peptide-based material functionalization.

Plasma Amine Oxidase-Induced Nanoparticle-to-Nanofiber Geometric Transformation of an Amphiphilic Peptide for Drug Encapsulation and Enhanced Bactericidal Activity

Patients with cancer have reduced immune function and are susceptible to bacterial infection after surgery, chemotherapy, or radiotherapy. Spherical nanoparticles formed by the self-assembled peptide V₆K₃ can be used as carriers for poorly soluble antitumor drugs to effectively deliver drugs into tumor cells. V₆K₃ was designed to achieve nanoparticle-to-nanofiber geometric transformation under induction by plasma amine oxidase (PAO). PAO is commercially available and functionally similar to lysyl oxidase (LO), which is widely present in serum. After the addition of fetal bovine serum (FBS) or PAO, the secondary structure of the peptide changed, while the spherical nanoparticles stretched and transformed into nanofibers. The conversion of the self-assembled morphology reveals the susceptibility of this amphiphilic peptide to subtle chemical modifications and may lead to promising strategies to control self-assembled architecture via enzyme induction. Enzymatically self-assembled V₆K₃ had bactericidal properties after PAO addition that were surprisingly superior to those before PAO addition, enabling this peptide to be used to prevent infection. The amphiphilic peptide V₆K₃ displayed antitumor properties and low toxicity in mammalian cells, demonstrating good biocompatibility, as well as bactericidal properties, to prevent bacterial contamination. These advantages indicate that enzymatically self-assembled V₆K₃ has great biomedical application potential in cancer therapy.

Designing stable, hierarchical peptide fibers from block co-polypeptide sequences

Here we report the pH induced self-assembly of equilibrium zwitterionically charged block co-polypeptide nanotubes into hierarchical nanotube fibers.

Natural materials, such as collagen, can assemble with multiple levels of organization in solution. Achieving a similar degree of control over morphology, stability and hierarchical organization with equilibrium synthetic materials remains elusive. For the assembly of peptidic materials the process is controlled by a complex interplay between hydrophobic interactions, electrostatics and secondary structure formation. Consequently, fine tuning the thermodynamics and kinetics of assembly remains extremely challenging. Here, we synthesized a set of block co polypeptides with varying hydrophobicity and ability to form secondary structure. From this set we select a sequence with balanced interactions that results in the formation of high-aspect ratio thermodynamically favored nanotubes, stable between pH 2 and 12 and up to 80 °C. This stability permits their hierarchical assembly into bundled nanotube fibers by directing the pH and inducing complementary zwitterionic charge behavior. This block co-polypeptide design strategy, using defined sequences, provides a straightforward approach to creating complex hierarchical peptide-based assemblies with tunable interactions.

bola-Type Ala-Ala Dipeptides: Odd-Even Effect in Molecular Packing Structures

A series of bola-type Ala-Ala dipeptides with different alkylene bridges (n = 10-15) were synthesized. In methanol, the molecules with even-numbered carbon bridges self-assembled into twisted nanoribbons, while those with odd-numbered carbon bridges self-assembled into straight belts. The morphology displays a pronounced odd-even dependence upon the number of carbons (n) in the connecting alkylene bridge. The circular dichroism spectra of the self-assemblies showed that molecules with even- and odd-numbered carbon bridges stacked in different structures. FT-IR spectra indicated that the dipeptides with even-numbered carbon bridges formed hydrogen bonds between the amide group and carboxyl ester group, while those with odd-numbered carbon bridges formed hydrogen bonds only between the amide groups. X-ray diffraction patterns revealed that molecules with odd- and even-numbered carbon bridges stacked in monoclinic and triclinic structures, respectively.

Light- and pH-Controlled Hierarchical Coassembly of Peptide Amphiphiles

The coassembly behavior of peptide amphiphiles (PAs) C₄-Bhc-EE-NH₂ and C₁₄-FKK-NH₂ has been investigated by transmission electron microscopy, atomic force microscopy, fluorescence microscopy, circular dichroism, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance. These two PAs coassembled into nanofibers by electrostatic and π-π stacking interactions at a low concentration and further aggregated into nanofiber bundles via charge complementation on the surface of nanofibers. As the charge number varied with pH, the bundles could be disassembled/assembled with pH regulation. More interestingly, as C₄-Bhc-EE-NH₂ was a photodegradable molecule, the bundles could also be responsive to both ultraviolet (UV) and near-infrared (NIR) light. In contrast to the reversible pH-dependent response, the light responses were irreversible as C₄-Bhc-EE-NH₂ broke under UV or NIR radiation. The highlight of this article is that structural changes were realized for control at the aggregate level, not only at the molecular level. With this inspiration, we hope that we can support the novel biomaterial construction and exploitation of new functions of biomaterials.

Temperature-responsive self-assembled nanostructures from lysine-based surfactants with high chain length asymmetry: from tubules and helical ribbons to micelles and vesicles

Stimuli-sensitive self-assembled nanostructures are of great relevance for the templating of nanomaterials and the design of efficient systems for the controlled delivery of molecules. Amino acid-based surfactants often display such fascinating self-assembly due to a combination of molecular features such as critical packing parameter, chirality and H-bonding interactions. Herein, we focus on a family of newly synthesized double-chained alkylcarboxylates derived from l-lysine, and designated by 8Lysn, mLys8, with n, m = 12, 14 and 16, and 12Lys16 and 16Lys12, where the numbers represent the number of C atoms in each hydrocarbon chain. The effects of the chain length asymmetry and structural isomerism of the surfactants on their interfacial properties, thermal behavior and self-assembly in water were investigated by a comprehensive toolbox, including surface tension, DSC, imaging (light microscopy, SEM, TEM and AFM) and SAXS. All the surfactants below their Krafft temperature self-organize into tubular structures of various morphologies (flat structures, twisted and coiled ribbons and hollow tubes), forming hydrogels at low surfactant concentration. Upon the solubilization phase transition, micelles or vesicles are formed depending on the surfactant structure, and the tubule-micelle or tubule-vesicle transition is thermoreversible. A molecular-level rationalization of the observed self-assembly and phase transition features is put forth.

Amino acid conformations control the morphological and chiral features of the self-assembled peptide nanostructures: Young investigators perspective

HYPOTHESIS

A variety of nanostructures with different chiral features can be self-assembled from short peptides with highly similar sequences. We hypothesize that these supramolecular nanostructures are ruled by the constituent amino acid residues which adopt their conformations under the influence of intra-/inter-molecular interactions during peptide self-assembly.

APPROACH

Through reviewing recent advances in the self-assembly of short peptides and focusing on the relationship between amino acid conformations, peptide secondary structures and intra-/inter-molecular interactions within the supramolecular architectures, we aim to rationalize the complex interactive processes involved in the self-assembly of short, designed peptides.

RESULTS

Given the highly complexing interactive processes, the adoption of amino acid conformations and their control over peptide self-assembly consist of 4 main steps: (1) Each amino acid residue adopts its unique conformation in a specific sequence; (2) The sequence exhibits its own main chain geometry and determines the propensity of the intermolecular alignment within the building block; (3) The structural propensity of the building block and the packing mode between them determine the self-assembled structural features such as twisting, growth and chirality; (4) In addition to intra-/inter-molecular interactions, inter-sheet and inter-building block interactions could also affect the residue conformations and nanostructures, causing structural readjustment.

Nanoribbons self-assembled from short peptides demonstrate the formation of polar zippers between β-sheets

Peptide self-assembly is a hierarchical process, often starting with the formation of α-helices, β-sheets or β-hairpins. However, how the secondary structures undergo further assembly to form higher-order architectures remains largely unexplored. The polar zipper originally proposed by Perutz is formed between neighboring β-strands of poly-glutamine via their side-chain hydrogen bonding and helps to stabilize the sheet. By rational design of short amphiphilic peptides and their self-assembly, here we demonstrate the formation of polar zippers between neighboring β-sheets rather than between β-strands within a sheet, which in turn intermesh the β-sheets into wide and flat ribbons. Such a super-secondary structural template based on well-defined hydrogen bonds could offer an agile route for the construction of distinctive nanostructures and nanomaterials beyond β-sheets.

Peptide self-assembly is a hierarchical process which includes forming β-sheets but the formation of high ordered structures remains largely unexplored. Here the authors report on a super-secondary structural template, based on well-defined hydrogen bonds by rational design and assembly of short peptides

Hierarchical Assembly of l-Phenylalanine-Terminated Bolaamphiphile with Porphyrin Show Tunable Nanostructures and Photocatalytic Properties

Demands related to clean energy and environmental protection promote the development of novel supramolecular assemblies for photocatalysis. Because of the distinctive aggregation behaviors, bolaamphiphiles with two hydrophilic end groups could be theoretically the right candidates for the fabrication of high-performance photocatalysis. However, photocatalytic applications based on bolaamphiphilic assemblies were still rarely investigated. Especially, the relationship between diverse assembled nanostructures and the properties for different applications is urgently needed to be studied. Herein, we demonstrate that using the hierarchical assembly of bolaamphiphiles could correctly induce the porphyrin supramolecular architectures with much better photocatalytic performances than the aggregations containing 450 times of the porphyrin molecules, even though both molecular structures as well as the J-aggregations of porphyrin building blocks are same in two different systems. Thus, the co-assembly of l-phenylalanine terminated bolaamphiphile (Bola-F) and the porphyrin containing four hydroxyl groups (tetrakis-5,10,15,20-(4-hydroxyphenyl)porphyrin) can form microtube in methanol and forms fibers/spheres in methanol/water mixture. For catalyzing the photodegradation of rhodamine B, the small amount of J-aggregated porphyrin within Bola-F microtubes show much better photocatalytic performance comparing with that of huge porphyrin J-aggregations in fibers/spheres. The supramolecular assemblies as well as the photocatalysis were thoroughly characterized by different spectroscopies and electron microscopy. It is demonstrated that the co-assembly with bolaamphiphiles could inhibit the energy transfer of porphyrin aggregation and subsequently benefit the electron transfer and corresponding photocatalysis under photo-irradiation. This work is not only useful for further understanding the hierarchically supramolecular assembly but also provides a new strategy for making novel functional supramolecular architectures based on the assembly of bolaamphiphiles and porphyrins.