CRITICAL SELF-ASSEMBLY CONCENTRATION OF AN IONIC-COMPLEMENTARY PEPTIDE EAK16-I

Understanding the process of self-assembly of peptides has been important in various biomedical engineering applications. This work focuses on the effect of peptide concentration on the molecular self-assembly of an ionic-complementary peptide, EAK16-I (AEAKAEAKAEAKAEAK), in aqueous solution. The surface tension and self-assembled nanostructures were determined for a wide range of peptide concentrations using axisymmetric drop shape analysis-profile (ADSA–P) and atomic force microscopy (AFM), respectively. Surface tension measurements revealed a critical self-assembly concentration of 0.3?mg peptide/ml water, below which the surface tension decreased rapidly with increasing peptide concentration, and above which the surface tension remained at a constant, plateau value. There were two structural transitions observed with increasing peptide concentration: the first was from globular nanostructures to fibrils, and the second from the fibrils to relatively thick fibers. The second structural transition occurred at the critical self-assembly concentration as determined by the surface tension measurements. The nanostructural behavior of EAK16-I was compared with that of EAK16-II, which has the same amino acid composition but a different charge distribution. Salt effects were also examined by adding NaCl to the peptide solution. The salt addition facilitated the formation of peptide fibrils at low peptide concentrations but increased the critical self-assembly concentration, which occurred at 0.8?mg peptide/ml water in the presence of 20?mM NaCl. The structural transitions involved in the self-assembly of EAK16-I resemble those from protofibrils to fibrils observed with numerous naturally occurring peptides. An understanding of this structural transition may have relevance in the analysis and treatment of peptide/protein conformational diseases and have application in the production of self-assembled protein nanostructures.     

Chemical Reactions Directed Peptide Self-Assembly

Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.     

Charge transport in vertically aligned, self-assembled peptide nanotube junctions

The self-assembly propensity of peptides has been extensively utilized in recent years for the formation of supramolecular nanostructures. In particular, the self-assembly of peptides into fibrils and nanotubes makes them promising building blocks for electronic and electro-optic applications. However, the mechanisms of charge transfer in these wire-like structures, especially in ambient conditions, are not yet fully understood. We describe here a layer-by-layer deposition methodology of short self-assembled cyclic peptide nanotubes, which results in vertically oriented nanotubes on gold substrates. Using this novel deposition methodology, we have fabricated molecular junctions with a conductive atomic force microscopy tip as a second electrode. Studies of the junctions' current-voltage characteristics as a function of the nanotube length revealed an efficient charge transfer in these supramolecular structures, with a low current attenuation constant of 0.1 ?(-1), which indicate that electron transfer is dominated by hopping. Moreover, the threshold voltage to field-emission dominated transport was found to increase with peptide length in a manner that depends on the nature of the contact with the electrodes. The flexibility in the design of the peptide monomers and the ability to control their sequential order over the nanotube by means of the layer-by-layer assembly process, which is demonstrated in this work, can be used to engineer the electronic properties of self-assembled peptide nanotubes toward device applications.     

自组装肽基纳米材料运载药物和基因的研究进展

肽基分子自组装以其丰富的自组装驱动力、新颖的自组装体纳米结构、自组装体的特殊功能及良好的生物相容性等,在纳米生物材料、护肤和化妆产品、药物传输释放、组织工程支架材料等方面有着广泛的应用前景。由天然氨基酸组成的自组装短肽具有良好的低细胞毒性,可控的降解性能,高的运载效率及细胞摄取率,同时还具有降低药物的毒副作用等优点。因此,它在作为药物和基因的纳米载药材料方面有着巨大的发展前景。使用自组装肽基材料形成的纳米载体对疏水性抗癌药物、蛋白质药物及基因等进行传递释放已成为生物医药学领域的研究重点,因此,对近年来自组装肽基纳米材料作为药物和基因载体在生物医药学上的研究进展做了综述。     

Ultrasmall peptides self-assemble into diverse nanostructures: morphological evaluation and potential implications

In this study, we perform a morphological evaluation of the diverse nanostructures formed by varying concentration and amino acid sequence of a unique class of ultrasmall self-assembling peptides. We modified these peptides by replacing the aliphatic amino acid at the C-aliphatic terminus with different aromatic amino acids. We tracked the effect of introducing aromatic residues on self-assembly and morphology of resulting nanostructures. Whereas aliphatic peptides formed long, helical fibers that entangle into meshes and entrap >99.9% water, the modified peptides contrastingly formed short, straight fibers with a flat morphology. No helical fibers were observed for the modified peptides. For the aliphatic peptides at low concentrations, different supramolecular assemblies such as hollow nanospheres and membrane blebs were found. Since the ultrasmall peptides are made of simple, aliphatic amino acids, considered to have existed in the primordial soup, study of these supramolecular assemblies could be relevant to understanding chemical evolution leading to the origin of life on Earth. In particular, we propose a variety of potential applications in bioengineering and nanotechnology for the diverse self-assembled nanostructures.     

Self-assembly of peptide nanotubes and amyloid-like structures by charged-termini-capped diphenylalanine peptide analogues

We had recently demonstrated that the diphenylalanine peptide, the core recognition motif of the Alzheimer's ß-amyloid polypeptide, self-assembles into a novel class of peptide nanotubes. The formation of well-ordered supramolecular structures at the nanoscale by such a simple peptide was consistent with our suggestion that aromatic interactions may provide order and directionality needed for the formation of fibrillar peptide structures. Yet, we could not rule out a contribution of the charged amine and carboxyl moieties at the termini of the short peptide. In order to explore the potential role of electrostatic interaction in the assembly process we have studied a modified non-charged peptide analogue, Ac-Phe–Phe-NH₂, in which the N-terminal amine was acetylated and the C-terminal carboxyl was amidated. Scanning and transmission electron microscopy analyses demonstrated that this peptide analogue self-assembles into highly-ordered tubular structures, as observed with the NH₂-Phe–Phe-COOH. Also, infrared spectroscopy revealed an amide I absorbance pattern that is very similar to that of the non-modified peptide. Furthermore, an amidated NH₂-Phe–Phe-NH₂ peptide, which has a net positive charge, also self-assembled into ordered tubular structures. On the other hand, the amine-modified analogues Boc-Phe–Phe-COOH, Z-Phe–Phe-COOH, and Fmoc-Phe–Phe-COOH peptides formed amyloid-like structures that had a significantly smaller diameter. Taken together, the current study further supports our hypothesis regarding the role of aromatic interactions in the self-assembly of amyloid fibrils and amyloid-associated nanostructures that can be modulated by simple chemical modifications.     

Electronic Properties of Amyloid β-Based Peptide Filaments with Different Non-Natural Heterocyclic Side Chains

The incorporation of non-canonical amino acids with aromatic side chains is considered to be a promising way to improve and control the electronic properties of self-assembled peptide nanostructures. In this work, we have studied the influence of aromatic ring heteroatom on the electronic properties of amyloid β-derived peptide fiber networks. We show that the incorporation of furan instead of thiophene side chains results in only small changes in the resistivity of the peptide network, with a threefold increase in the sheet resistance and a small decrease in the contact resistance. These changes can be explained by a twofold decrease in the diameter of the self-assembled fibers. These characteristics open the way to the use of furan- instead of thiophene-based analogues as non-natural side-chain modifications of peptides for electronic applications; this makes the fibrils more biodegradable and biorenewable.     

Self/Co-Assembling Peptide,EAR8-II,as a Potential Carrier for a Hydrophobic Anticancer Drug Pirarubicin (THP)—Characterization and in-Vitro Delivery

A short ionic-complementary peptide, EAR8-II, was employed to encapsulate the hydrophobic anticancer drug pirarubicin (THP). EAR8-II was designed to inherit advantages from two previously introduced peptides, AAP8 and EAK16-II, in their self/co-assembly. This peptide is short, simple, and inexpensive to synthesize, while possessing a low critical assembly concentration (CAC). The choice of alanine (A) residues in the peptide sequence provides moderate hydrophobic interactions, causing a minimal degree of aggregation, compared with other more hydrophobic residues. EAR8-II is an ionic-complementary peptide, similar to EAK16-II, can self/co-assemble with hydrophobic compounds such as THP, and forms a stable fibular nanostructure in aqueous solution. Physiochemical properties and cellular activities of the EAR8-II and THP complexes were evaluated and show dependency on the peptide-to-drug ratio. The complex at the peptide-to-drug mass ratio of 5:1 provides a stable solution, uniform nanostructure, and highly effective anticancer activity against various cancer cell lines. This work forms the basis for detailed studies on EAR8-II and THP formulations in vitro and in vivo, for future development of peptide-based delivery systems for hydrophobic anticancer drugs.     

Supramolecular domains in mixed peptide self-assembled monolayers on gold nanoparticles

Self-organization in mixed self-assembled monolayers of small molecules provides a route towards nanoparticles with complex molecular structures. Inspired by structural biology, a strategy based on chemical cross-linking is introduced to probe proximity between functional peptides embedded in a mixed self-assembled monolayer at the surface of a nanoparticle. The physical basis of the proximity measurement is a transition from intramolecular to intermolecular cross-linking as the functional peptides get closer. Experimental investigations of a binary peptide self-assembled monolayer show that this transition happens at an extremely low molar ratio of the functional versus matrix peptide. Molecular dynamics simulations of the peptide self-assembled monolayer are used to calculate the volume explored by the reactive groups. Comparison of the experimental results with a probabilistic model demonstrates that the peptides are not randomly distributed at the surface of the nanoparticle, but rather self-organize into supramolecular domains.     

铜表面硬脂酸自组装膜的制备及耐腐蚀性能

应用自组装技术在Cu(OH)2纳米柱/CuO微花阶层结构表面制备硬脂酸自组装膜(SAM),运用电化学阻抗谱探讨了形成自组装膜的较佳浓度和自组装时间,通过极化曲线和循环伏安法考察了硬脂酸自组装膜在0.1 mol/L NaCl溶液中对铜电极的缓蚀性能.结果表明,当CuO/Cu(OH)2电极在8 mmol/L硬脂酸溶液中自组...     

Synthesis and Self-Assembly Properties of Bola-Amphiphilic Glycosylated Lipopeptide-Type Supramolecular Hydrogels Showing Colour Changes Along with Gel–Sol Transition

Supramolecular hydrogels formed by self-assembly of low-molecular-weight amphiphiles (hydrogelators) have attracted significant attention, as smart and soft materials. However, most of the observed stimuli-responsive behaviour of these supramolecular hydrogels are limited to gel–sol transitions. In this study, we present bola-amphiphilic glycosylated lipopeptide-type supramolecular hydrogelators that exhibit reversible thermochromism along with a gel–sol transition. The bola-amphiphiles have mono-, di-, tri- or tetra-phenylalanine (F) as a short peptide moiety. We investigate and discuss the effects of the number of F residues on the gelation ability and the morphology of the self-assembled nanostructures.     

Self-Assembling Peptides: From Design to Biomedical Applications

Self-assembling peptides could be considered a novel class of agents able to harvest an array of micro/nanostructures that are highly attractive in the biomedical field. By modifying their amino acid composition, it is possible to mime several biological functions; when assembled in micro/nanostructures, they can be used for a variety of purposes such as tissue regeneration and engineering or drug delivery to improve drug release and/or stability and to reduce side effects. Other significant advantages of self-assembled peptides involve their biocompatibility and their ability to efficiently target molecular recognition sites. Due to their intrinsic characteristics, self-assembled peptide micro/nanostructures are capable to load both hydrophobic and hydrophilic drugs, and they are suitable to achieve a triggered drug delivery at disease sites by inserting in their structure’s stimuli-responsive moieties. The focus of this review was to summarize the most recent and significant studies on self-assembled peptides with an emphasis on their application in the biomedical field.     

Self-Assembled Glucose and Thermo Dual-Responsive Micelles of an Amphiphilic Graft Copolymer

Amphiphilic copolymers P(PBA)-g-P(PEG) containing poly(phenylboronic acid) (PPBA) and poly(ethylene glycol) (PEG) side chains were synthesized by copolymerization of 4-vinylphenylboronic acid (PBA) and poly(ethylene glycol) methyl ether methacrylate. The surface tension results showed that the critical micelle concentration (CMC) of P(PBA)-g-P(PEG) was 0.09 g/L. TEM revealed that these copolymers self-assembled into regular sphere micelles above CMC. The photon correlation spectroscopy suggested that they had unique performance of thermo-induced self-assembly. Above critical micelle temperature, they self-assembled into monodisperse micelles with thermosensitivity. Hydrodynamic diameters of these micelles increased dramatically in the presence of glucose. The glucose-regulated drug release behavior was observed through UV-vis spectroscopy.     

pH-Responsive Self-Assembly of Designer Aromatic Peptide Amphiphiles and Enzymatic Post-Modification of Assembled Structures

Supramolecular fibrous materials in biological systems play important structural and functional roles, and therefore, there is a growing interest in synthetic materials that mimic such fibrils, especially those bearing enzymatic reactivity. In this study, we investigated the self-assembly and enzymatic post-modification of short aromatic peptide amphiphiles (PAs), Fmoc-L_nQG (n = 2 or 3), which contain an LQG recognition unit for microbial transglutaminase (MTG). These aromatic PAs self-assemble into fibrous structures via π-π stacking interactions between the Fmoc groups and hydrogen bonds between the peptides. The intermolecular interactions and morphologies of the assemblies were influenced by the solution pH because of the change in the ionization states of the C-terminal carboxy group of the peptides. Moreover, MTG-catalyzed post-modification of a small fluorescent molecule bearing an amine group also showed pH dependency, where the enzymatic reaction rate was increased at higher pH, which may be because of the higher nucleophilicity of the amine group and the electrostatic interaction between MTG and the self-assembled Fmoc-L_nQG. Finally, the accumulation of the fluorescent molecule on these assembled materials was directly observed by confocal fluorescence images. Our study provides a method to accumulate functional molecules on supramolecular structures enzymatically with the morphology control.     

Peptide and protein mimetics inhibiting amyloid beta-peptide aggregation

Protein misfolding is related to some fatal diseases including Alzheimer's disease (AD). Amyloid beta-peptide (Abeta) generated from amyloid precursor protein can aggregate into amyloid fibrils, which are known to be a major component of Abeta deposits (senile plaques). The fibril formation of Abeta is typical of a nucleation-dependent process through self-recognition. Moreover, during fibrillization, several metastable intermediates such as soluble oligomers, including Abeta-derived diffusible ligands (ADDLs) and Abeta*56, are produced, which are thought to be the most toxic species to neuronal cells. Therefore, construction of molecules that decrease the Abeta aggregates, including soluble oligomers, protofibrils, and amyloid fibrils, might further our understanding of the mechanism(s) behind fibril formation and enable targeted drug discovery against AD. To this aim, various peptides and peptide derivatives have been constructed using the "Abeta binding element" based on the structural models of Abeta amyloid fibrils and the mechanisms of self-assembly. The central hydrophobic amino acid sequence, LVFF, of Abeta is a key sequence to self-assemble into amyloid fibrils. By combination of this core sequence with a hydrophobic or hydrophilic moiety, such as cholic acid or aminoethoxy ethoxy acetic acid units, respectively, good inhibitors of Abeta aggregation can be designed and synthesized. A peptide, LF, consisting of the sequence Ac-KQKLLLFLEE-NH 2, was designed based on the core sequence of Abeta but with a simplified amino acid sequence. The LF peptide can form amyloid-like fibrils that efficiently coassemble with mature Abeta1-42 fibrils. The LF peptide was also observed to immediately transform the soluble oligomers of Abeta1-42, which are thought to pose toxicity in AD, into amyloid-like fibrils. On the other hand, two Abeta-like beta-strands with a parallel orientation were embedded in green fluorescent protein (GFP), comprised of a beta-barrel structure, to make pseudo-Abeta beta-sheets on its surface. The GFP variant P13H binds to Abeta1-42 and inhibits Abeta1-42 oligomerization effectively in a substoichiometric condition. Thus, molecules capable of binding to Abeta can be designed based on structural similarities with the Abeta molecule. The peptide and protein mimetics based on the structural features of Abeta might lead to the development of drug candidates against AD.     

季铵盐型阳离子型表面活性单体AMC16AB胶束化行为的研究

本文对季铵盐型阳离子表面活性单体2-丙烯酰胺基乙基十六烷基二甲基溴化铵（AMC16AB）的胶束化行为进行了深入的研究。使用紫外分光光度法测定了AMC16AB在水中的溶解度；同时采用表面张力法（环法）和电导滴定法测定其临界胶束浓度（CMC）及在浓度为CMC时的表面张力（γoc）。采用荧光探针法测定了不同浓度时（C〉CMC）AMC，6AB的胶束聚集数Nagg；并研究了AMC16AB浓度和外加盐浓度对Nagg的影响。实验结果表明表面活性单体AMC16AB在水中的溶解性强，但降低水表面张力的能力差，即表面活性差；与结构相同的一般表面活性单体相比，AMC16AB的CMC较低，Krafft点较低；AMC16AB的Nagg随浓度的增大而逐渐变大，随外加盐浓度增加开始时变化不大，当外加盐浓度达到临界值C★时，其胶束聚集数迅速增大。这些因素对AMC16AB胶束化行为的影响规律与普通的表面活性剂相似。     

Amyloid architecture: complementary assembly of heterogeneous combinations of three or four peptides into amyloid fibrils

The amyloid fibril is a misfolded and undesirable state for proteins that has been proposed to be a causative agent for a variety of fatal diseases known as amyloid diseases, such as Alzheimer's and prion diseases. However, the fibril has a highly ordered tertiary structure in which numerous beta-strand polypeptide chains align in a regular pattern. Thus, this kind of fibril has the potential to be engineered into proteinaceous materials. Amyloid fibrils of misfolded proteins primarily comprise a single polypeptide species, that is, the self-assembly is homogeneous. We here found that three or four designed peptides can assemble heterogeneously and cooperatively into amyloid fibrils, a process accompanied by a drastic secondary structural transition from alpha helix to beta sheet. Heterogeneous assembly into fibrils is accomplished by complementary electrostatic interactions between three or four peptide species, each of which is not able to self-assemble homogeneously. These findings will lead to a novel way to study the molecular details of amyloid formation and also to design beta-sheet peptidyl materials.     

不同NaCl浓度下十二烷基硫酸钠的理化参数和热力学行为

为了更好地研究不同NaCl浓度对阴离子表面活性剂胶束理化性质和结构稳定性的影响,以阴离子表面活性剂十二烷基硫酸钠（C₁₂H₂₅SO₄Na）在不同温度下的临界胶束浓度为基础,分别测试并得出了不同NaCl浓度与不同温度作用下溶液的表面张力、泡沫半衰期和黏度变化规律。在此基础上通过分析得出NaCl作用下溶液的黏度活化能、标准熵变、标准焓变等热力学参数及变化规律。结果表明：C₁₂H₂₅SO₄Na降低表面张力的效率由温度效应和盐效应共同控制,随着温度的升高,温度效应发挥的作用越来越大;黏度最大值所对应的表面活性剂浓度为该温度和NaCl浓度下的临界胶束浓度;C₁₂H₂₅SO₄Na胶束化过程的影响随着温度的升高由熵驱动逐渐转化为焓驱动,这种转化过程随着NaCl浓度的升高越来越提前。掌握温度和NaCl浓度的耦合作用对C₁₂H₂₅SO₄Na理化性质的影响,以期为进一步研究其热力学行为奠定基础。     

The Self-Assembled Behavior of DNA Bases on the Interface

A successful example of self-assembly in a biological system is that DNA can be an excellent agent to self-assemble into desirable two and three-dimensional nanostructures in a well-ordered manner by specific hydrogen bonding interactions between the DNA bases. The self-assembly of DNA bases have played a significant role in constructing the hierarchical nanostructures. In this review article we will introduce the study of nucleic acid base self-assembly by scanning tunneling microscopy (STM) at vacuum and ambient condition (the liquid/solid interface), respectively. From the ideal condition to a more realistic environment, the self-assembled behaviors of DNA bases are introduced. In a vacuum system, the energetic advantages will dominate the assembly formation of DNA bases, while at ambient condition, more factors such as conformational freedom and the biochemical environment will be considered. Therefore, the assemblies of DNA bases at ambient condition are different from the ones obtained under vacuum. We present the ordered nanostructures formed by DNA bases at both vacuum and ambient condition. To construct and tailor the nanostructure through the interaction between DNA bases, it is important to understand the assembly behavior and features of DNA bases and their derivatives at ambient condition. The utilization of STM offers the advantage of investigating DNA base self-assembly with sub-molecular level resolution at the surface.     

Probing the role of aromaticity in the design of dipeptide based nanostructures

Self-assembly of peptide into nanostructures is believed to be stabilized primarily by aromatic interactions. Using a minimalistic approach, we probed the importance of aromatic interactions in the self-assembly of simple model dipeptides. Our results suggest that aromaticity may not be absolutely essential for self-assembly, even though it tends to provide directionality to the assembly. We found that peptides containing cyclic/linear side chain hydrophobic residues were also capable of forming stable self-assemblies that are stabilized by hydrophobic interactions. Our observations will find relevance in the design of small peptide based nanoparticles.