Aqueous self-assembly of unsymmetric Peptide bolaamphiphiles into nanofibers with hydrophilic cores and surfaces

Unsymmetric peptide bolaamphiphiles that incorporate (l-glutamyl)3glycine at one terminus and either tetraethylene glycol or aspartic acid at the other were found to form hydrogels at low wt %, presumably by self-assembling into nanofibers presenting (l-glutamyl)3glycine at their surfaces and burying the second headgroup at their cores. Transmission electron microscopy measurements on 1 wt % gels negatively stained with phosphotungstic acid and positively stained with uranyl acetate show one-dimensional objects with diameters of 5 nm and lengths in excess of 1 mum. Circular dichroism and solid-state FTIR spectra indicate the adoption of beta-sheet structure within the nanofibers.     

Self-organization of a chiral D-EAK16 designer peptide into a 3D nanofiber scaffold

Self-assembling peptide nanofiber scaffolds are an excellent material for applications such as tissue repair, tissue regeneration, instant stopping of bleeding, and slow drug release. We report a new self-assembling peptide D-EAK16 consisting purely of D-amino acids. D-EAK16 and L-EAK16 display mirror-image CD spectra at 20 degrees C. Like L-EAK16, D-EAK16 self-assembles into nanofibers, thus demonstrating that chiral self-assembling peptide nanofiber scaffolds can be made from both L- and D-amino acids. We also show that D-peptide nanofibers are resistant to natural proteases and may thus be useful in biotechnology, nanobiotechnology, tissue repair and tissue regeneration as well as other medical applications.     

Impact of C-Terminal Chemistry on Self-Assembled Morphology of Guanosine Containing Nucleopeptides

Herein, we report the design and characterization of guanosine-containing self-assembling nucleopeptides that form nanosheets and nanofibers. Through spectroscopy and microscopy analysis, we propose that the peptide component of the nucleopeptide drives the assembly into β-sheet structures with hydrogen-bonded guanosine forming additional secondary structures cooperatively within the peptide framework. Interestingly, the distinct supramolecular morphologies are driven not by metal cation responsiveness common to guanine-based materials, but by the C-terminal peptide chemistry. This work highlights the structural diversity of self-assembling nucleopeptides and will help advance the development of applications for these supramolecular guanosine-containing nucleopeptides.     

Formation of columnar mesophases by calamitic molecules: a modulated SmA phase in mixtures of amphiphilic and bolaamphiphilic biphenyl derivatives

Binary mixtures of bolaamphiphilic biphenyl derivatives with each other and with amphiphilic biphenyl derivatives were investigated by means of optical microscopy. The miscibility of the bolaamphiphiles is very sensitive to the molecular length of the components. The SmA phases of bolaamphiphiles with the same length are completely miscible. If the length difference between the two components of the binary system increases, a miscibility gap occurs. Due to their different phase structures (bilayer versus monolayer) no miscibility in the SmA phases was found for amphiphilic and bolaamphiphilic compounds with comparable molecular lengths. However, in some cases a novel mesophase was induced in the contact region. This mesophase was investigated by X-ray diffraction. It represents a two-dimensionally modulated (columnar) phase with a rectangular lattice (Col r), but the local order is similar to that of disordered smectics. Its formation is explained in terms of ribbon structures resulting from the collapse of smectic bilayers, in strong analogy to the antiphases (SmA) of terminally polar calamitic mesogens.     

Temperature-dependent self-assembly and mixing behavior of symmetrical single-chain bolaamphiphiles

The temperature-dependent self-assembly and the mixing behavior of symmetrical single-chain bolaamphiphiles with different polymethylene chain lengths and different headgroup structures were investigated in water by differential scanning calorimetry (DSC), cryo transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS). The even-numbered polymethylene-1,omega-bis(phosphocholines) (PC-C n-PC) are known to form nanofibers composed of stretched molecules with an all- trans alkyl chain conformation (Drescher, S.; Meister, A.; Blume, A.; Karlsson, G.; Almgren, M.; Dobner, B. Chem.Eur. J. 2007, 13, 5300-5307). The odd-numbered analogues were synthesized to study a possible even-odd effect of these bolaamphiphiles during their aggregation in water. In addition to these bolaamphiphiles with phosphocholine headgroups, a new series of polymethylene-1,omega-bis(phosphodimethylethanolamines) (Me2PE-Cn-Me2PE) with smaller headgroup sizes was synthesized. These bolaamphiphiles show an additional fiber-fiber transition when the alkyl chain length exceeds 26 carbon atoms. The mixing behavior of both types of bolaamphiphiles indicates that differences in the alkyl chain length up to six carbon atoms are tolerated within the fiber structure. The mixing of two Me2PE-Cn-Me2PE or PC-Cn-PC type bolaamphiphiles with different alkyl chain lengths offers the possibility to adjust the temperature, where the cross-linking of the fibers is disrupted and where the fibers break apart. As a consequence, temperature switchable hydrogels are obtained that can be fine-tuned for drug delivery applications. The comparison with dotriacontane-1,32-diyl-bis[2-(methylammonio)-ethylphosphate] (MePE-C32-MePE), a new bolaamphiphile with even smaller phosphomonomethylammonio headgroups, illustrates the importance of the headgroup size for the aggregation behavior. This bolaamphiphile self-assembles exclusively into lamellar structures, and this aggregate type persists in mixtures with the fiber forming Me2PE-C32-Me2PE.     

Enzymatically triggered self-assembly of poly(ethylene glycol)-attached oligopeptides into well-organized nanofibers

A unique and programmable peptide self-assembling system has been fabricated by using poly(ethylene glycol)-attached amphiphilic oligopeptide, which shows rapid self-assembly into well-organized beta-sheet nanofibers in response to an enzymatic reaction.     

Self-assembly of bipolar amphiphiles

Over the past 2 years, various symmetrical and unsymmetrical bipolar amphiphiles (bolaamphiphiles) have been synthesized to study their self-organizing and packing properties alone as well as in mixtures with conventional amphiphiles. This review focuses on the lyotropic properties of these bolaamphiphiles and describes their in some cases quite unusual supramolecular self-assembling properties in aqueous media and at the air–water and liquid–solid interface.     

Archaeabacteria bipolar lipid analogues: structure, synthesis and lyotropic properties

Over the past several years, various archaeal symmetrical/unsymmetrical and acyclic/macrocyclic bipolar lipid analogues have been synthesized to study, from well-defined molecules, the membrane organizing and packing properties of this new class of amphiphiles. This review focuses on the structure and the synthesis of selected bolaamphiphiles and describes their supramolecular self-assembling properties in aqueous media.     

Glycine Substitution Effects on the Supramolecular Morphology and Rigidity of Cell-Adhesive Amphiphilic Peptides

Self-assembling peptides that are capable of adopting β-sheet structures can generate nanofibers that lead to hydrogel formation. Herein, to tune the supramolecular morphologies, mechanical properties, and stimuli responses of the hydrogels, we investigated glycine substitution in a β-sheet-forming amphiphilic peptide. Glycine substitution generally enhances conformational flexibility. Indeed, glycine substitution in an amphiphilic peptide weakened the hydrogels or even inhibited the gelation. However, unexpectedly, glycine substitution at the center of the peptide molecule significantly enhanced the hydrogel stiffness. The central glycine substitution affected the molecular packing and led to twisted β-sheet structures and to nanofiber bundling, which likely led to the stiffened hydrogel. Importantly, the supramolecular structures were accurately predicted by molecular dynamics simulations, demonstrating the helpfulness of these techniques for the identification of self-assembling peptides. The hydrogel formed by the amphiphilic peptide with the central glycine substitution had cell adhesive function, and showed a reversible thermal gel-to-sol transition. Thus, glycine substitution is effective in modulating self-assembling structures, rheological properties, and dynamics of biofunctional self-assembling peptides.     

Fine-tuning the pH trigger of self-assembly

The creation of smart, self-assembling materials that undergo morphological transitions in response to specific physiological environments can allow for the enhanced accumulation of imaging or drug delivery agents based on differences in diffusion kinetics. Here, we have developed a series of self-assembling peptide amphiphile molecules that transform either isolated from molecules or spherical micelles into nanofibers when the pH is slightly reduced from 7.4 to 6.6, in isotonic salt solutions that simulate the acidic extracellular microenvironment of malignant tumor tissue. This transition is rapid and reversible, indicating the system is in thermodynamic equilibrium. The self-assembly phase diagrams show a single-molecule-to-nanofiber transition with a highly concentration-dependent transition pH. However, addition of a sterically bulky Gd(DO3A) imaging tag on the exterior periphery shifts this self-assembly to more acidic pH values and also induces a spherical micellar morphology at high pH and concentration ranges. By balancing the attractive hydrophobic and hydrogen-bonding forces, and the repulsive electrostatic and steric forces, the self-assembly morphology and the pH of transition can be systematically shifted by tenths a pH unit.     

Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers.

Design and characterization of helical ribbon assemblies of a bolaamphiphilic conjugated polymer and their color-coded transformation into nanofibers are described. An L-glutamic acid modified bolaamphiphilic diacetylene lipid was synthesized and self-assembled into right-handed helical ribbons with micron scale length and nano scale thickness under mild conditions. The ribbon structures were further stabilized by polymerizing well-aligned diacetylene units to form bisfunctional polydiacetylenes (PDAs). Transitions from flat sheets to helical ribbons and tubes were observed by transmission electron microscopy. The helical ribbons appear to originate from the rupture of flat sheets along domain edges and the peeling off between stacked lipid layers. These results point to the applicability of chiral packing theory in bolaamphiphilic supramolecular assemblies. Contact mode atomic force microscopy observations revealed that high order existed in the surface packing arrangement. Hexagonal and pseudorectangular packings were observed in flat and twisted regions of the ribbons, respectively, suggesting a correlation between microscopic morphologies and nanoscopic packing arrangements. The tricarboxylate functionalities of the bolaamphiphilic lipid provide a handle for the manipulation of the bisfunctional PDAs' morphology. Increasing solution pH caused the fraying of helical ribbons into nanofibers accompanied by a sharp blue-to-red chromatic transition. A dramatic change in circular dichroism spectra was observed during this process, suggesting the loss of chirality in packing. A model is proposed to account for the pH-induced morphological change and chromatic transition. The color-coded transition between two distinct microstructures would be useful in the design of sensors and other "smart" nanomaterials requiring defined molecular templates.     

A New Type of Deaggregators, the Bolaamphiphilic DeAgrs. Observations of the Dependence of Deaggregating Ability on Aggregator Concentration and Solvent Aggregating Power

ＩｎｔｒｏｄｕｃｔｉｏｎＡｇｇｒｅｇａｔｉｏｎｉｓａｃｏｍｍｏｎｐｈｅｎｏｍｅｎｏｎｆｏｒｍａｎｙｓｉｍ ｐｌｅｏｒｇａｎｉｃｍｏｌｅｃｕｌｅｓａｓｗｅｌｌａｓｃｏｍｐｌｅｘｍｏｌｅｃｕｌｅｓｗｉｔｈｉｍｐｏｒｔａｎｔｂｉｏｌｏｇｉｃａｌａｃｔｉｖｉｔｙ .Ｆｏｒｍａｔｉｏｎｏｆａｇｇｒｅｇａｔｅｓｍａｙｂｅｄｒｉｖｅｎｂｙｄｉｆｆｅｒｅｎｔｎｏｎ ｃｏｖａｌｅｎｔｉｎｔｅｒａｃｔｉｏｎｓ ,ｓｕｃｈａｓｈｙｄｒｏｇｅｎｂｏｎｄｉｎｇ ,1ｅｌｅｃｔｒｏｓｔａｔｉｃｉｎｔｅｒａｃｔｉｏｎ ,2 ｏｒｈｙ ｄｒ…     

Self‐Assembly of Bolaamphiphilic Molecules

The current buzzword in science and technology is self‐assembly and molecular self‐assembly is one of the most prominent fields as far as research in chemical and biological sciences is concerned. Generally, self‐assembly of molecules occurs through weak non‐covalent interactions like hydrogen bonding, π–π stacking, hydrophobic effects, etc. Inspired by many natural systems consisting of self‐assembled structures, scientists have been trying to understand their formation and mimic such processes in the laboratory to create functional “smart” materials, which respond to temperature, light, pH, electromagnetic field, mechanical stress, and/or chemical stimuli. These responses are usually manifested as remarkable changes from the molecular (e. g., conformational state, hierarchical order) to the macroscopic level (e. g., shape, surface properties). Many molecules such as peptides, viruses, and surfactants are known to self‐assemble into different structures. Among them, glycolipids are the new entries in the area of molecules that are being investigated for their self‐assembly characteristics. Among the different classes of glycolipids like rhamnolipids and trehalose lipids, owing to their biological preparations and their structural novelty, sophorolipids (SLs) are evoking greater interest among researchers. Sophorolipids are a class of asymmetric bolas bearing COOH groups at one end and sophorose (dimeric glucose linked by an unusual β(1→2) linkage). The extreme membrane stability of Archaea, attributed to the membrane‐spanning bolas (tetraether glycolipids), has inspired chemists to unravel the molecular designs that underpin the self‐assembly of bolaamphiphilic molecules. Apart from these self‐assembled structures, bolaamphiphiles find applications in many fields such as drug delivery, membrane mimicking, siRNA therapies, etc. The first part of this Personal Account presents some possible self‐assembled structures of bolaamphiphiles and their mechanism of formation. The later part covers our work on one of the typical bolaamphiphiles known as sophorolipids.     

Metal-complexed nanofiber formation in water from dicarboxylic valylvaline bolaamphiphiles

Nanofiber formation of dipeptide-based bolaamphiphiles, bis (N-alpha-amide--valyl--valine) 1,n-alkane dicarboxylate (n=6, 8, 10, and 12) in water was analyzed by TEM, SEM, IR, and XRD. The bolaamphiphiles proved to be coordinated to divalent transition-metal cations, such as Co2+, Ni2+, Cu2+, and Zn2+, giving precipitates, colloidal dispersions (loose hydrogels), and hydrogels upon self-assembly at 23 or 70 degrees C. Longer oligomethylene chains and strong interaction between the metal cations and the carboxylate anions are responsible for the hydrogel formation. Energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (EF-SEM) images revealed that the colloidal dispersions and the hydrogels consist of a large number of nanofibers with widths of 15-20 nm and lengths of several micrometers. FT-IR and powder XRD measurement supported the existence of a beta-sheet structure-based nanofibers complexing with metal cations.     

由D型氨基酸设计自组装短肽D-EAK16构建新型三维纳米纤维支架材料

采用D型氨基酸设计自组装短肽D-EAK16, 运用圆二色仪及原子力显微镜等仪器和细胞三维培养, 发现短肽D-EAK16在30 ℃时具有稳定的二级结构β-sheet, 在一定浓度下D-EAK16可形成由纳米纤维构成的透明水凝胶, 含水量高达99％, 可在细胞培养基(如PBS, DMEM)中形成支架. 细胞三维培养显示, 该水凝胶对细胞HO-8910和SPC-A-1的生长未见毒性. 比较D型氨基酸纳米支架和L型氨基酸纳米支架, 细胞的毒性未发现显著性差异. 采用D型氨基酸构建的自组装短肽, 可提供一个三维基质培养系统, 期望能广泛应用于生物医学工程等领域.     

Formation of triple helical nanofibers using self-assembling chiral benzene-1,3,5-tricarboxamides and reversal of the nanostructure's handedness using mirror image building blocks

Intertwining triple helical nanofibers with an overall handedness have been formed from self-assembling chiral benzene-1,3,5-tricarboxamides , and , whereas the achiral benzene-1,3,5-tricarboxamide upon self-association gives rise to straight nanofibers without any twist and transmission electron microscopy images of chiral compounds clearly demonstrate that the handedness of the triple helical nanofibers can be reversed by using the enantiomeric benzene-1,3,5-tricarboxamide building blocks.     

Functional self-assembling bolaamphiphilic polydiacetylenes as colorimetric sensor scaffolds

Conjugated polymers capable of responding to external stimuli by changes in optical, electrical, or electrochemical properties can be used for the construction of direct sensing devices. Polydiacetylene-based systems are attractive for sensing applications due to their colorimetric response to changes in the local environment. Here we present the design, preparation, and characterization of self-assembling functional bolaamphiphilic polydiacetylenes (BPDAs) inspired by nature's strategy for membrane stabilization. We show that by placing polar headgroups on both ends of the diacetylene lipids in a transmembranic fashion and by altering the chemical nature of the polar surface residues, the conjugated polymers can be engineered to display a range of radiation-, thermal-, and pH-induced colorimetric responses. We observed dramatic nanoscopic morphological transformations accompanying charge-induced chromatic transitions, suggesting that both side-chain disordering and main-chain rearrangement play important roles in altering the effective conjugation lengths of the poly(ene-yne). These results establish the foundation for further development of BPDA-based colorimetric sensors.     

Luminescent organic 1D nanomaterials based on bis(β-diketone)carbazole derivatives

A series of new triphenylamine-functionalized bis(β-diketone)s bridged by a carbazole (CnBDKC, n=1, 4, 8, 16) with twisted intramolecular charge-transfer emission in polar solvents has been synthesized. The length of the carbon chains has a significant effect on the self-assembling properties of the compounds. Well-defined 1D nanowires were easily generated from C1BDKC with a methyl group by a reprecipitation approach directed by π-stacking interaction, and the molecules packed into J-aggregates in the nanowires. In addition, 1D nanofibers based on C16BDKC bearing a long hexadecyl chain were prepared through the organogelation process, and H-aggregates were formed driven by the synergistic effect of π-stacking interaction and van der Waals force in the gel phase. C4BDKC and C8BDKC containing butyl and octyl side chains, respectively, cannot arrange into dispersed nanostructures, probably because π-π interaction between conjugated moieties might be disturbed by the interaction between the side chains, which is, however, not strong enough to dominate the self-assembling process. Notably, the nanowires based on C1BDKC and the gel nanofibers from C16BDKC can emit strong green light under irradiation, which suggests that these 1D nanomaterials may have potential applications in emitting materials as well as photonic devices.     

Self-assembly of phosphorylated peptide driven by Dy3+

Nature chooses phosphorylation as a key modification to modulate and program the functions of proteins. Various phosphorylated peptides (PPs) have been widely identified and investigated by biologists, but the possibility that PPs could become a building unit for artificial materials is neglected. Here we report for the first time a supramolecular assembly of PPs with the assistance of dysprosium ions (Dy³⁺). Dy³⁺ bridges multiple phosphate groups in double-phosphorylated peptides (di-PPs), and braid these peptide chains into nanofibers. The assembly occurs inside nanochannels and blocks the channels, leading to prominent “ON–OFF” switching in transmembrane ionic current. The di-PPs’ assembling process could be dynamically regulated by the addition or deletion of phosphate groups under the control of kinases or phosphatases. This study proves the huge potential of PPs being utilized as materials via self-assembling, which will promote the design of novel bio-inspired artificial materials and devices.     

Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles

Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings.