Supramolecular assemblies formed by new L-lysine derivatives of viologens

L-Lysine derivatives of viologens form supramolecular assemblies of fibers and ribbons in some aromatic solvents, and the charge separation reaction in these self-assembling systems proceeds with a similar efficiency to the MV2+ system.     

Dissociation of tetrameric ions of noncovalent streptavidin complexes formed by electrospray ionization

The noncovalent tetrameric association of the protein streptavidin formed by electrospray ionization (ESI) mass spectrometry has been observed intact and dissociated in the gas phase. An extended mass-to-charge ratio range quadrupole mass spectrometer was employed to examine the effects of harsher conditions in the ESI atmosphere-vacuum interface region on the streptavidin tetramer. Thermally induced dissociation caused the mass spectra to exhibit a series of complementary monomer and trimer ions that correspond to decomposition of the tetrameric species. Similar results were obtained with tandem mass spectrometric experiments on a Fourier transform ion cyclotron resonance mass spectrometer by application of sustained off-resonance irradiation (SORI) on a selected tetrameric charge state. The technique of single-frequency quadrupole excitation was used to accomplish selected-ion accumulation of the 14 + charge state of the tetramer during ion injection. Subsequent low energy SORI combined with broadband quadrupole cooling produced the 7 + monomer and 7 + trimer species, as well as the 6 + monomer and 8 + trimer complementary ions. The observed asymmetric breakup of the tetramer is qualitatively explained by using physical models.     

Non-centrosymmetric tetrameric assemblies of tetramethylammonium halides with uranyl salophen complexes in the solid state

Ditopic salophen-UO(2) receptors 1-4 and 7 co-crystallize with tetramethylammonium (TMA) chloride and fluoride salts producing good quality crystals amenable for X-ray diffraction characterization. The arrangement of the receptor and salt units in the crystal lattice is such that tetrameric ball-shaped assemblies are formed, where an inner cluster of four TMA cations are surrounded by an outer shell of four UO(2)-bound anions. These elaborate architectures, which occur in all cases, regardless of a certain degree of structural modification on the receptors, lead to lattices that belong to non-centrosymmetric (NCS) space groups. Interestingly, the tetragonal symmetry of the tetrameric ball-shaped assemblies is either retained (I4?) or lost (R3c and I4?3d) at the lattice level, without compromising the NCS nature of the crystal lattices. The principal X-ray investigation on TMAX (X = Cl/F) co-crystals, that is, 1-(TMA)Cl, 2-(TMA)Cl, 3-(TMA)Cl, 4-(TMA)Cl, 7-(TMA)Cl, and 7-(TMA)F, is accompanied by NMR and electrospray ionization (ESI) mass spectrometry studies to gather additional insight on the modality of formation of the solid state structures observed. The important role of cation-π interactions in the receptor-salt recognition process is renewed and strengthened by comparison with NMR titration data with a novel reference compound, the salophen-UO(2) complex 8. Given the importance of NCS and polar crystalline solids in the development of functional materials, this study shows that this property can be introduced into elaborate host-guest systems, as those which assemble in the architectures described here, thus expanding its field of applicability.     

Virus-like supramolecular assemblies formed by cooperation of base pairing interaction and peptidic association

A peptide nucleic acid(PNA)-peptide conjugated molecule, T′_3(AKAE)_2, was designed to have both a PNA segment for oligonucleotide binding and an ionic self-complementary peptide sequence for self-association. T′_3(AKAE)_2 could co-assemble with oligoadenines(d(A)_x) to form virus-like supramolecular structures whose morphology showed dependence on the chain length and rigidity of the d(A)_x molecules. Smaller nanospheres with diameters of 13.0±2.0 nm were produced in the case of d(A)_6. Wormlike aggregates with lengths of 20–50 nm and diameters of 15.0±2.5 nm were found in the cases of d(A)_(12), d(A)_(18), d(A)_(24) and d(A)_(30). And larger spherical aggregates with diameters of 18±5 nm came into presence in the cases of d(A)_(36) and d(A)_(42). These nanostructures were suggested to be formed under a cooperative effect of base pair recognition and peptidic association. The study provides insights into the programmed assembly of a multi-components system as well as control of the size and shape of the co-assembled structures, which is of great significance in developing gene/drug delivery systems.     

Size and morphology of assemblies formed by DNA and lysozyme in dilute aqueous mixtures

Assemblies formed by a well-defined quality of DNA (4331 bp T7 DNA) and the small net-cationic protein lysozyme in dilute aqueous solutions have been characterized using cryo-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) as the main techniques. In a wide range of different DNA to lysozyme ratios in solutions of low ionic strength, dispersions of aggregates with the same general morphology and a practically constant hydrodynamic size are formed. The basic structure formed in the dispersions is that of rather flexible worm-like assemblies with a diameter of 10-20 nm, which are suggested to be made up by bundles of on the order of 10 DNA chains with an intervening matrix of lysozyme. With increased ionic strength, the worm-like appearance of the assemblies is lost and they adopt a less well-defined shape. The results suggest that the formation of the DNA-lysozyme aggregates is strongly influenced by cooperative assembly of the components and that, in addition to the electrostatic attraction between DNA and lysozyme, attractive interactions between the protein units are important in governing the behavior of the system.     

Molecular-level control of feature separation in one-dimensional nanostructure assemblies formed by biomolecular nanolithography

In this paper, we present a convenient and reliable method to organize small gold nanoparticles (d(CORE) = 1.5 nm) into linear chains with precisely controlled interparticle spacing over a range of 1.5-2.8 nm through biomolecular nanolithography. Controlling the feature separations of 1 to a few nanometers with angstrom-level precision is a key requirement in electronic and optical applications of nanostructures to tune the properties of the nanostructures and manipulate the interactions between neighboring structures. Here, chains are formed in solution by utilizing functional-group-directed self-assembly to organize ligand-stabilized gold nanoparticles onto DNA templates. The spacing between neighboring nanoparticles can be controlled chemically and tuned at the molecular level by utilizing nanoparticles possessing ligand shells of varying thickness to achieve angstrom-level resolution at spacings of 1.5, 2.1, and 2.8 nm. The small standard deviation (< or = 20%) in the values for the interparticle spacing illustrates the reproducibility of the approach. Because the interparticle spacing is enforced by the ligand shell rather than the scaffold, the spacing is uniform even in nonlinear sections of the chain. We further show that the assembly process is robust and produces extended linear nanoparticle chains of up to 1 microm in length and a total coverage of > 90%. All structures and interparticle spacings were analyzed using transmission electron microscopy. Our results demonstrate the potential of scaffold-assisted assembly approaches for patterning features with tunable dimensions on a length scale that is important for future applications of these materials in nanoscale electronics and optics.     

Enhanced mechanical rigidity of hydrogels formed from enantiomeric peptide assemblies

Chirality can be used as a design tool to control the mechanical rigidity of hydrogels formed from self-assembling peptides. Hydrogels prepared from enantiomeric mixtures of self-assembling β-hairpins show nonadditive, synergistic, enhancement in material rigidity compared to gels prepared from either pure enantiomer, with the racemic hydrogel showing the greatest effect. CD spectroscopy, TEM, and AFM indicate that this enhancement is defined by nanoscale interactions between enantiomers in the self-assembled state.     

Interfacial dilational rheology properties of films formed at the oil/water interface by reaction between tetrameric acid and calcium ion

This article aims to determine the applicability of interfacial dilational rheology to study the formation of viscoelastic film at the oil/water interface by reaction between tetrameric acids ARN and calcium ions, and to determine the influence of asphaltenes and naphthenic acids (NA) on this film. It was first found that the formation of viscoelastic film by reaction between ARN and calcium ions is easily observed by dilational rheology: Significantly high values of E′ (130?mN/m) were measured for this system at low ARN concentration (10?µM). These values are at least 5 to 10 times higher than values obtained for ARN without Ca²⁺ or other crude oil components such as asphaltenes and naphthenic acids.

The influence of asphaltenes and NA on the viscoelastic film formation has been studied. When asphaltenes or NA are present, the interfacial viscoelastic film is weakened: There is a gradual decrease of E′ and E″ when the asphaltenes or NA concentration increases. These two components can therefore inhibit the ARN/Ca²⁺ film formation. This decrease is similar to the one previously observed by shear rheology. Several explanations are proposed.     

Synthesis of poly(amino acid)s on molecular assemblies formed by functional active esters of amino acids

The new active β-alanine and glycine esters ( 6 and 7 ) of N-hydroxy-2,3-dihexadecylsuccinimide were prepared and their polycondensation was studied. The aggregation behavior of these esters was examined by an electron microscopy and an osmotic method. They formed multilamella in water and reversed micelle in nonpolar solvents. These solvents were found to be suitable for the polycondensation, which gave the corresponding poly(amino acid)s. The results of polycondensation can be explained by assuming that the aggregations, that is, multilamella in water and reversed micelle in nonpolar solvents, are playing an important role in the polycondensation.     

Nanostructured polymer assemblies formed at interfaces: applications from immobilization and encapsulation to stimuli-responsive release

In recent years, interfacial properties have been tailored with nanostructured polymer assemblies to generate materials with specific properties and functions for application in diverse fields, including biomaterials, drug delivery, catalysis, sensing, optics and corrosion. This perspective begins with a brief introduction of the assembly techniques that are commonly employed for the synthesis of nanostructured polymer materials, followed by discussions on how the interfaces influence the properties and thus the functionalities of the polymer materials prepared. Applications of the interfacial polymer nanostructures, particularly for the immobilization and encapsulation of cargo, are then reviewed, focusing on stimuli-responsive cargo release from the polymer nanostructured assemblies for controlled delivery applications. Finally, future research directions in these areas are briefly discussed.     

Theoretical study on tertiary structural elements of beta-peptides: nanotubes formed from parallel-sheet-derived assemblies of beta-peptides

Parallel or polar strands of beta-peptides spontaneously form nanotubes of different sizes in a vacuum as determined by ab initio calculations. Stability and conformational features of [CH3CO-(beta-Ala)k-NHCH3]l (1 < or = k < or = 4, 2 < or = l < or = 4) models were computed at different levels of theory (e.g., B3LYP/6-311++G(d,p)// B3LYP/6-31G(d), with consideration of BSSE). For the first time, calculations demonstrate that sheets of beta-peptides display nanotubular characteristics rather than two-dimensional extended beta-layers, as is the case of alpha-peptides. Of the configurations studied, k = l = 4 gave the most stable nanotubular structure, but larger assemblies are expected to produce even more stable nanotubes. As with other nanosystems such as cyclodextrane, these nanotubes can also incorporate small molecules, creating a diverse range of applications for these flexible, biocompatible, and highly stable molecules. The various side chains of beta-peptides can make these nanosystems rather versatile. Energetic and structural features of these tubular model systems are detailed in this paper. It is hoped that the results presented in this paper will stimulate experimental research in the field of nanostructure technology involving beta-peptides.     

Binding of inorganic oxoanions to macrocyclic ligands: effect of the degree of protonation on supramolecular assemblies formed by phosphate and [18]aneN(6)

Five macrocycle-oxoanion adducts have been isolated from aqueous solutions containing 1,4,7,10,13,16-hexaazacyclooctadecane ([18]aneN(6), L) and phosphoric acid whose pH had been adjusted to selected values in the 1-8 range. Four products, (H(6)L)(H(2)PO(4))(6).2H(3)PO(4) (1), (H(6)L)(H(2)PO(4))(6) (2), (H(4)L)(H(2)PO(4))(4).2H(2)O (4), and (H(4)L)(HPO(4))(2).7H(2)O (5) crystallized from aqueous solutions at pH 1, 3, 6, and 8, respectively, while (H(4)L)(H(2)PO(4))(4) (3) crystallized on diffusion of EtOH into an aqueous reaction mixture at pH 6. Single-crystal X-ray structure determinations enabled an examination of supramolecular interactions between protonated forms of [18]aneN(6), phosphoric acid and its conjugate bases, and water of solvation. The macrocycle adopts a variety of conformations in order to accommodate the supramolecular constructs formed by the oxoanions and solvent molecules as the relative proportions of interacting species are altered. At pH 1 and 3, the fully protonated macrocycle, [LH(6)](6+), is found with six H(2)PO(4)(-) anions. At pH 6 and 8, the tetraprotonated macrocycle, [LH(4)](4+), crystallizes with four H(2)PO(4)(-) and two HPO(4)(2)(-), respectively. Variations in the solute of crystallization are evident, with phosphoric acid being present at the lowest pH and water at pH 6 and 8. In 5, the seven unique water molecules form a string-of-pearls motif within which a new heptameric isomer, consisting of a water pentamer that uses a single water to interact with the other two unique water molecules, is found. Structures 1, 2, 4, and 5 exhibit eta-3 H-bonding of ammonium protons to a single oxygen of the guest phosphates located above and below the macrocyclic ring. In 3, two phosphate oxygens of the cavity anion interact with the macrocycle, one of which participates in eta-2 H-bonding with ammonium groups.     

Guest-controlled self-sorting in assemblies driven by the hydrophobic effect

The extent of self-sorting in systems comprised of two different deep-cavity cavitands is investigated. The nature of the guest(s) encapsulated in the resulting assemblies is shown to profoundly influence the extent of self-sorting.     

Controlling the morphology of cross beta-sheet assemblies by rational design

Low molecular weight peptidomimetics with simple amphiphilic sequences can help to elucidate the structures of cross beta-sheet assemblies, such as amyloid fibrils. The peptidomimetics described herein comprise a dibenzofuran template, two peptide strands made up of alternating hydrophilic and hydrophobic residues, and carboxyl termini, each of which can be varied to probe the structural requirements for beta-sheet self-assembly processes. The dibenzofuran template positions the strands approximately 10 A apart, allowing corresponding hydrophobic side chains in the strands to pack into a collapsed U-shaped structure. This conformation is stabilized by hydrophobic interactions, not intramolecular hydrogen bonds. Intermolecular stacking of the collapsed peptidomimetics, enabled by intermolecular hydrogen bonding and hydrophobic interactions, affords 25-27 A wide protofilaments having a cross beta-sheet structure. Association of protofilaments, mediated by the dibenzofuran substructures and driven by the hydrophobic effect, affords 50-60 A wide filaments. These widths can be controlled by changing the length of the peptide strands. Further assembly of the filaments into fibrils or ribbons can be controlled by modification of the template, C-terminus, and buffer ion composition.     

Structure and stability of the complex formed by oligonucleotides

Polycations and cationic lipids have been widely used as non-viral vectors for the delivery of plasmid DNA, siRNA and anti-sense oligonucleotides. To demonstrate that one polycation can form a complex with several types of DNA, we conducted a comparative study on the complexation of poly(L-lysine) (PLL) with 2000 bp salmon testes DNA (dsDNA), 21 bp double-stranded oligonucleotides (ds-oligo), and 21 nt single-stranded oligonucleotides (ss-oligo) in PBS buffer. The complexes are prepared by a titration method and the process is monitored by laser light scattering. It was found that in most cases, ss-oligo and ds-oligo form complexes with higher molecular weights than the complex formed by dsDNA at the same +/- ratio immediately after mixing. More importantly, the complexes formed by oligonucleotides are not stable, the scattered intensity gradually decreases to the level of the solvent in weeks. Atomic force microscopy measurements also indicate that the freshly prepared complex is subject to environmental changes and could dissociate very quickly. The behaviour of oligonucleotides cannot be predicted by the classical polyelectrolyte theories.     

Handedness inversion of chiral amphiphilic molecular assemblies evidenced by supramolecular chiral imprinting in mesoporous silica assemblies

Antipodal twisted helical ribbons with lamellar bilayer structure were obtained by self-assembly of chiral amphiphilic molecules in water and water/ethanol. The handedness inversion of the molecular arrangement in these antipodal helical ribbons was investigated by using chiroptical spectroscopy and molecular probes in their antipodal mesoporous silica assemblies synthesized through pairing interaction between the head group of the chiral amphiphilic molecules and a co-structure-directing agent. The supramolecular chirality is imprinted in the pore surface through the organic group of the co-structure-directing agent. The mirror-image diffuse-reflectance circular dichroism spectra of the conjugated discotic probing molecule introduced into their supramolecular chiral imprinted mesoporous silica demonstrated the origin of inverse chirality from the antipodal helical stacking of the molecules.     

Supramolecular assemblies through macromolecular recognition by cyclodextrins

Cyclodextrins have been found to form inclusion complexes with various polymers with high specificities to give stoichiometric compounds in crystalline states. Polyrotaxanes in which many cyclodextrins are threaded on a single chain were prepared by capping the chain ends with bulky groups.     

Hydrogen-bonding based multilayer assemblies by self-deposition of dendrimer

We reported on hydrogen-bonding directed Layer-by-Layer assemblies by self-deposition of a kind of dendrimer bearing carboxyl groups on its periphery that act as hydrogen bonding donor as well as hydrogen bonding acceptor.