Self-assembly combining two bioactive peptide-amphiphile molecules into nanofibers by electrostatic attraction

We describe a new approach to peptide-amphiphile (PA) nanofiber preparation that allows PAs with different bioactive amino acid sequences to be combined into a single fiber. Oppositely charged PAs are synthesized separately and then mixed to produce gels of nanofiber networks at physiological pH. Transmission electron microscopy reveals the formation of fibers approximately 7 nm in diameter and several micrometers long in these dimeric systems. On the basis of NMR and microscopy, we suggest that these nanofibers are cylindrical micelles of mixed composition, formed due to electrostatic attraction between the oppositely charged PAs. This strategy for self-assembly may be useful in cell therapies that can be implemented without invasive surgery or in in vitro tissue engineering.     

Self-assembly of well-defined structures by hydrogen bonding

The directionality and specificity of hydrogen bonds are invaluable tools in designing complex self-assembling structures. Hydrogen bonds have been used to construct defined structures ranging from reversible polymeric systems to cyclic arrays and capsules which reversibly bind guest molecules. Recent developments show the emergence of functionality in these structures and suggest future uses of well-defined assemblies in areas as diverse as catalysis and materials science. © 1999 Elsevier Science Ltd.     

Self-assembly of supramolecular complexes based on hydrogen bonding

Self-assembly of hydrogen-bonding recognition complexes—2.5-bis(alkylamino)-1,4-benzoquinones were studied, and thermotropic liquid crystalline behavior of 2.5-bis(dodecylamino)-1,4-benzoquinone was further investigated. The obtained results showed that a ribbon-like backbone in this system plays an important role in keeping the layered supramolecular structure.     

Self-assembly of an amphiphilic

The template-directed synthesis of a [2]rotaxane, in which a pi-electron deficient ring component-cyclobis(paraquat-p-phenylene)-is assembled around a pi-electron rich asymmetric monopyrrolotetrathiafulvalene unit on the rod section of an amphiphilic dumbbell component that is terminated by a hydrophilic dendritic stopper at one end and a hydrophobic tetraarylmethane stopper at the other end, is reported.     

Self-assembly of short peptide amphiphiles: the cooperative effect of hydrophobic interaction and hydrogen bonding

The interplay between hydrogen bonding, hydrophobic interaction and the molecular geometry of amino acid side-chains is crucial to the development of nanostructures of short peptide amphiphiles. An important step towards developing their practical use is to understand how different amino acid side-chains tune hydrophobic interaction and hydrogen bonding and how this process leads to the control of the size and shape of the nanostructures. In this study, we have designed and synthesized three sets of short amphiphilic peptides (I(3)K, LI(2)K and L(3)K; L(3)K, L(4)K and L(5)K; I(3)K, I(4)K and I(5)K) and investigated how I and L affected their self-assembly in aqueous solution. The results have demonstrated a strong tendency of I groups to promote the growth of β-sheet hydrogen bonding and the subsequent formation of nanofibrillar shapes. All I(m)K (m = 3-5) peptides assembled into nanofibers with consistent β-sheet conformation, whereas the nanofiber diameters decreased as m increased due to geometrical constraint in peptide chain packing. In contrast, L groups had a weak tendency to promote β-sheet structuring and their hydrophobicity became dominant and resulted in globular micelles in L(3)K assembly. However, increase in the number of hydrophobic sequences to L(5)K induced β-sheet conformation due to the cooperative hydrophobic effect and the consequent formation of long nanofibers. The assembly of L(4)K was, therefore, intermediate between L(3)K and L(5)K, similar to the case of LI(2)K within the set of L(3)K, LI(2)K and I(3)K, with a steady transition from the dominance of hydrophobic interaction to hydrogen bonding. Thus, changes in hydrophobic length and swapping of L and I can alter the size and shape of the self-assembled nanostructures from these simple peptide amphiphiles.     

Self-assembly of linear-shaped bi-dihydrazine derivative through intermolecular quadruple hydrogen bonding

A linear-shaped bi-1,3,4-oxadiazole derivative, oxalyl acid N′,N′-di(4-(2-ethylhexyloxy)benzoyl)-hydrazide (FH-Z8) was designed and synthesized. Quadruple hydrogen bonds between bi-dihydrazide units and π-π interactions cooperatively participated in forming supramolecules in chloroform at higher concentrations of FH-Z8. The association constants (K) in chloroform were 2.2×10³ and 1.8×10³ M⁻¹ based on NH1 and NH2 in FH-Z8, respectively. FH-Z8 could gel dichloroethane efficiently with the critical gelation concentration (CGC) of 0.14 wt %, while spontaneously crystallized from the gel during storage.     

Self-assembly of multilayer films containing gold nanoparticles via hydrogen bonding

Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV-vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.     

Self-assembly of main chain liquid crystalline polymers via heteromeric hydrogen bonding

Complexation between pyridines and carboxylic acids is driven by hydrogen bonding. This simple, single hydrogen bond is shown to be capable of serving concomitantly as both the agent of liquid crystallinity and as the coupling bond generating an extended linear chain structure. Three such complexes made from an aromatic diacid and three structurally different bis pyridyls were prepared. In each case the association complex self-assembles into an organized liquid crystalline phase. Discussion of this complexation as a step-growth polymerization process is presented along with an examination of the suitability of various methods for characterizing these materials.     

Effects of hydrogen bonding on the monolayer properties of amphiphilic double-decker-shaped polyhedral silsesquioxanes

"Core-corona" type amphiphiles, which comprise double-decker-shaped POSSs (DDSQs) as the core and two or four di(ethylene glycol) (DEG) units as the coronae, have recently been reported to form a stable monolayer at the air-water interface. In this paper, another core-corona amphiphile, 2DEGNH-DDSQ, which has a urethane group at the end of the coronae, was synthesized to elucidate the effects of hydrogen bonding on monolayer properties. The surface pressure-area isotherm and Brewster angle microscopy revealed that 2DEGNH-DDSQ initially formed rodlike assemblies. They subsequently coalescence to form a uniform monolayer with compression. Actually, 2DEGNH-DDSQs are well ordered in the rodlike assembly because of the strong hydrogen bonds among the urethane groups, as confirmed by FT-IR spectra. Although the monolayer was not transferred onto a solid substrate, mixing of 2DEGNH-DDSQ with 2DEG-DDSQ, which has already been reported to form a liquidlike monolayer, overcame this problem. The 1:1 molar mixture of 2DEGNH-DDSQ and 2DEG-DDSQ forms a uniform liquidlike monolayer. The mixed monolayer was transferred onto a solid substrate as a Z-type Langmuir-Blodgett film. Atomic force microscopic (AFM) images of the mixed-bilayer film showed a uniform surface with root-mean-square surface roughness of 0.21 nm. The intermolecular hydrogen bonds between the urethane groups in 2DEGNH-DDSQ and the hydroxyl groups in 2DEG-DDSQ improve the monolayer properties, which enable successful transfer of the LB film.     

Self-assembly and hydrophobic clusters of amphiphilic polysaccharides

The objective of this work was to synthesize and characterize new polymeric surfactants deriving from natural polymers and designed for membrane protein solubilization. For this purpose, a set of hydrophobically-modified pullulans (HMCMPs) of moderate molar mass and differing in hydrophobic modification ratio, charge ratio and the nature of the hydrophobic chains introduced, were prepared. Their behaviour in aqueous dilute solutions was investigated by surface tension measurement and with a polarity probe, the Coomassie Brilliant Blue dye. Two distinct critical concentrations were evidenced, demonstrating the complex behaviour of HMCMPs. Amphiphilic pullulan derivatives may indeed establish hydrophobic associations in bulk solution while adsorbing at the air  water interface. The structural parameters of the polymers influence their aqueous behaviour. Self-assembly of HMCMPs occurs at smaller concentrations when the hydrophobic modification ratio or the alkyl hydrophobic chain length increases. It seems to be governed by the concentration of hydrophobic grafts, rather than by polymer concentration. Probably because of steric hindrance, 3-phenylpropyl grafts do not favour self-assembly, and lead to HMCMPs that preferentially adsorb at the air  water interface.     

Self-assembly of azo molecules to mesogenic phasmid-like materials through inter-molecular hydrogen bonding

A series of acid-functionalised new azo compounds was synthesised and characterised. The constituent molecules self-organise to form dimers through inter-molecular hydrogen bonding, resulting in phasmid-like compounds. This was once considered to be a promising molecular architecture to form biaxial nematic phases. The mesomorphic properties of these new azo compounds were studied using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. Investigations revealed that these compounds form nematic and columnar mesophases. A few more compounds were synthesised by replacing the??N=N- linkage in these compounds with??CH=N- and??COO- to study the effect of different linkages on the mesomorphic properties in such molecular systems. All were found to be liquid crystalline. The compounds with a??N=N- linkage are more conducive to mesomorphism and are thermally very stable. The effect of number of alkoxy chains on the mesomorphic properties of this system was also studied. To the best of our knowledge, at present, only a handful of phasmid-like mesogenic compounds, formed by the intermolecular hydrogen bonding, are known.     

Self-assembly of model amphiphilic Janus particles

We apply molecular dynamics simulations to investigate the structure formation of amphiphilic Janus particles in the bulk phase. The Janus particles are modeled as (soft) spheres composed of a hydrophilic and hydrophobic part. Their orientation is described by a vector representing an internal degree of freedom. Investigating energy fluctuations and cluster size distributions, we determine the aggregation line in a temperature-density-diagram, where the reduced temperature is an inverse measure for the anisotropic coupling. Below this aggregation line clusters of various sizes depending on density and reduced temperature are found. For low densities in the range ρ? ≤ 0.3, the cluster size distribution has a broad maximum, indicating simultaneous existence of various cluster sizes between 5 and 10. We find no hint of a condensation transition of these clustered systems. In the case of higher densities (ρ? = 0.5 and 0.6), the cluster size distribution shows an extremely narrow peak at clusters of size 13. In these icosahedrons, the particles are arranged in a closed-packed manner, thereby maximizing the number of bonds. Analyzing the translational mean-square displacement we also observe indications of hindered diffusion due to aggregation.     

Self-assembly of alpha-helical coiled coil nanofibers

The alpha-helical coiled coil is one of the best-studied and most well-understood protein folding motifs. In particular, the coiled coil can be made to self-assemble into a nanofibrous architecture with many potential applications in biomimetic engineering and elsewhere. The key to the assembly of such nanofibers has been the formation of "sticky ended" dimers through careful selection of electrostatically charged amino acids. In this work, we demonstrate for the first time that sticky ended dimers are not a prerequisite for alpha-helical coiled coil nanofiber formation. In contrast, we show that blunt-ended dimers are able to form nanofibers with a uniform diameter of 4 nm while being hundreds of nanometers in length. Furthermore, the length and lateral packing can be controlled through selection of amino acids not involved in the coiled coil interface.     

Self-assembly of helical supramolecular channels from chiral aminopyrimidine hydrogen bonding motifs in the solid state

The H-bond mediated self-assembly of the chiral C₂-symmetric bis-(2-amino-4-chloro-pyrimidines) 3 and 4 allows for the molecular recognition directed generation of helical superstructures. In the former case, unoccupied channel structures defined by the cylindrical interior of the derived supramolecular helix result, as revealed by X-ray crystallographic analysis using a synchrotron source. Upon crystallization, racemic 3 spontaneously resolves to form homochiral crystals exhibiting a helical packing motif identical to that determined for optically pure 3. The data provide insight into the interplay of the different structural and interactional features of the molecular components to the generation of the channel structure and suggest design strategies toward porous organic molecular solids of variable size.     

Role of hydrogen bonding interactions in directing one-dimensional thiol-assisted growth of silver-based nanofibers

We present evidence, based on scanning and transmission electron microscopy measurements, for the formation of nanofibers from silver-thiol materials treated with water. Mercapto acetic acid, a thiol with a carboxylic acid group at one end, was employed for the experiments presented here. Nanoparticles, with diameters as large as 1 nm, fill the nanofibers and are responsible for absorption bands between 2 and 5.5 eV in UV-visible absorption spectroscopy measurements. The nanofibers disappear at pH values larger than the first pK(a) of the acid, while rods are observed for pH values between 3.6 and 7. This result is interpreted in the context of hydrogen bonding interactions playing an important role in driving the one-dimensional growth of the fibers, a proposal that is supported by the vibrational frequency of the carbonyl stretching mode in surface reflection Fourier transform infrared measurements on dry deposits of aqueous dispersions of the thiol-silver material.     

Self-assembly of facially amphiphilic dendrimers on surfaces

Facially amphiphilic dendrimers have been shown to provide significant difference in surface behavior due to subtle changes in structure. The monodendrons are capable of providing hydrophobic surfaces, while the didendrons provide superhydrophobic surfaces. This provides an example of how a molecular level change could result in significant changes in surface behavior. This difference is attributed to the conformational differences exhibited by these dendrimers on surfaces.     

Self-assembly of amphiphilic glycoconjugates into lectin-adhesive nanoparticles

This work describes the synthesis and self-assembly of carbohydrate-clicked rod-coil amphiphilic systems. Copper-catalyzed Huisgen cycloaddition was efficiently employed to functionalize the hydrophilic extremity of PEG-b-tetra(p-phenylene) conjugates by lactose and N-acetyl-glucosamine ligands. The resulting amphiphilic systems spontaneously self-assembled into nanoparticles when dissolved in aqueous media, as evidenced by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The formation of highly monodisperse micelles having a mean diameter of 10 nm was observed for systems containing a PEG 900 core, and a decrease in the hydrophilic moiety (PEG 600) led to the formation of vesicles with a broader size distribution. The presence of carbohydrate residues on the surfaces of the micelles and their ability to establish specific interactions with wheat germ agglutinin (WGA) and peanut agglutinin (PNA) were further highlighted by light-scattering measurements, thus confirming the attractive applications of such sugar micelles in biosensor devices.     

Self-assembly using dynamic coordination chemistry and hydrogen bonding: mercury(II) macrocycles, polymers and sheets

The self-assembly of extended metal-containing arrays is described based on dynamic coordination chemistry at mercury(II) with bis(amidopyridyl) ligands to form macrocycles, polymers, or sheets which can be further organized by hydrogen bonding between amide substituents. The ligands 1,2-C6H4[NHC(O)-4-C5H4N]2, 1, 1,2-C(6)H(4)[C(O)NHCH(2)-4-C(5)H(4)N](2), 2, and 1,2-C(6)H(4)[CH(2)C(O)NHCH(2)-4-C(5)H(4)N]2, 3 can adopt polar conformations and so can confer helicity in their complexes. Several macrocycles of formula [(HgX(2))(2)(micro-LL)(2)] (LL = 1, 2), with tetrahedral mercury(II) centers, were prepared in which individual molecules are further self-assembled via hydrogen bonding in the solid state to form one- or two-dimensional polymers or sheets. In one case, a one-dimensional polymer [((HgX2)-(mu-3))n] was formed. It is shown that the mercury(II) centers can be six-coordinate in forming the sheet structure [((HgX2)(mu-2)2)n], in which there are particularly large pores.