DNA-templated assemblies of nickel hexacyanoferrate crystals

We report here the synthesis of nickel hexacyanoferrate (NiHCF) crystals using calf thymus DNA (CT-DNA) as a template. The double-stranded CT-DNA has been used as a template to self-assemble NiHCF crystals and to produce aggregates having different morphologies at different temperatures. The guided self-assembly behavior of DNA was studied at different temperatures by scanning electron microscopy. The cube-shaped crystals of NiHCF with an average diameter of 400 nm are observed along the DNA framework at room temperature; however, at higher temperatures, the morphology of NiHCF changed from open tubular to dendrimer. The intermediate temperatures show long chains (up to many micrometers) and spherical structures of NiHCF crystals. The micrometer long DNA template plays a key role in the formation of extended arrays of NiHCF crystals, suggesting that the templating action is retained even at the higher temperatures.     

Novel phases and colloidal assemblies in liquid crystals

New phases and colloidal assemblies have recently been observed in liquid crystalline solvents. The long-range-ordering and the topological constraints of the solvents allow controlled organization of the particles. In addition, liquid crystals have been doped with the aim of achieving new physical properties in potentially useful composite materials. © 1999 Elsevier Science Ltd.     

Single crystals and two-dimensional crystalline assemblies of block copolymers

Block copolymer single crystals (BCPSCs) have attracted widespread attentions due to their unique two-dimensional (2D) structure, good controllability, and great potential applications in recent years. In this paper, the morphology, surface structure of BCPSCs and the related influencing factors are reviewed. We also summarize the studies of 2D crystalline assemblies of block copolymers (BCPs) driven by crystallization and intermolecular π–π interaction. Moreover, the functionalization and properties of BCPSCs and 2D crystalline assemblies of BCPs are introduced. Finally, we put forward some unsolved problems in this field.     

Shear modulus of single wood pulp fibers from torsion tests

Cellulose - The shear modulus of pulp fibers is difficult to measure and only very little literature is available on this topic. In this work we are introducing a method to measure this fiber...     

Shear modulus determination in model hydrogels by means of elongated magnetic nanoprobes

The mechanical characterization of complex soft matter by quasi-static magnetometry using nanoscopic magnetic probes is demonstrated for model hydrogels doped with two types of elongated magnetic nanoparticles. Chemically crosslinked poly(acrylamide) (PAAm) hydrogels serve as the matrix in which nickel nanorods or weakly magnetized hematite (α-Fe₂O₃) ellipsoids are embedded as local probes. We investigated the swelling behavior of the ferrogels in order to verify that their equilibrium swelling degree in water is not influenced by the probes, shows a good correlation with the Frenkel–Flory–Rehner model. The proposed magnetomechanical method relies on a correlation between the shear modulus of the PAAm hydrogel matrix and the coercive fields of the corresponding isotropic ferrogels. By extending the Stoner–Wohlfarth model for single-domain blocked magnetic particles by a term for particle rotation in an elastic matrix, information on the shear modulus of the matrix can be obtained. Comparison of the results with the expected relation from rubber elasticity theory illustrates both the general potential as well as the limits of the approach. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Shear rheology of lyotropic liquid crystals: a case study

We have investigated the rheological properties of lyotropic liquid crystals (LCs) formed by self-assembled neutral lipids and water, their relationship with the topology of the structure, and their dependence on temperature and water content. The phase diagram of a representative monoglyceride-water system, determined by combining cross-polarized optical microscopy and small-angle X-ray scattering (SAXS), included four structures: lamellar, hexagonal, gyroid bicontinuous cubic (Ia3d), and double diamond bicontinuous cubic (Pn3m), as well as several regions of two-phase coexistence of some of the above structures. Rheology in the linear viscoelastic regime revealed a specific signature that was characteristic of the topology of each structure considered. The order-order transitions lamellar-to-cubic and cubic-to-hexagonal, as well as the order-disorder transitions from each LC to an isotropic fluid, were easily identified by following the development of the storage and loss moduli, G' and G', respectively. The viscoelastic properties of both bicontinuous cubic phases were shown to be strongly frequency-dependent, following a pseudo-Maxwell behavior, with multiple relaxation times. Cubic-to-cubic transitions were nicely captured by scaling the longest relaxation time, tau, with either temperature or water volume fraction. Therefore, the set of the three main parameters used to establish the rheological behavior of the structure, that is, G', G', and relaxation time, tau, constitutes a consistent ensemble to identify the structures of the liquid crystal. Finally, relaxation spectra, extracted for all liquid crystalline phases, allowed an additional possible identification criterion of the various structures considered.     

Elastic modulus of poly(isobutylene oxide) crystals parallel to the chain axis

The elastic tensile modulus of the crystalline regions parallel to the chain axis E₁ for poly(isobutylene oxide) (PIBO) was determined by an x-ray diffraction method. The stress-strain (σ—ε) curve calculated from the meridional reflection of (002) shows an inflection point at about 75 MN/m² or an extension of 0.25%. The observed moduli below and above this point are 29 and 47 GN/m², respectively, at room temperature. The initial lower modulus agrees well with the value, 29.7 GN/m², calculated on the basis of the double zigzag structure of PIBO chain determined by Kaji and Sakurada. The higher modulus may be due to an intrachain steric hindrance between the hydrogen atoms of the methylenic group in the main chain and those of the two side methyl groups.     

Calculation of the bulk modulus of simple and complex crystals with the chemical bond method

The relation between the lattice energies and the bulk moduli on binary inorganic crystals was studied, and the concept of lattice energy density is introduced. We find that the lattice energy densities are in good linear relation with the bulk moduli in the same type of crystals, the slopes of fitting lines for various types of crystals are related to the valence and coordination number of cations of crystals, and the empirical expression of calculated slope is obtained. From crystal structure, the calculated results are in very good agreement with the experimental values. At the same time, by means of the dielectric theory of the chemical bond and the calculating method of the lattice energy of complex crystals, the estimative method of the bulk modulus of complex crystals was established reasonably, and the calculated results are in very good agreement with the experimental values.     

Chain direction elastic modulus of PE crystal and interlamellar force constant of n-alkane crystals from RAMAN measurements

Spectroscopic data can deliver force constants only if the exact chain conformation is known. For the longitudinal acoustic modes (LAM), however, simple linear chain models can be used to yield the effective longitudinal chain modulus from spectroscopic data of oligomer crystals. The model of p-coupled linear chain molecules with N masses and only nearest neighbor interactions was used to investigate the longitudinal acoustic modes with s nodes. The frequencies plotted versus s/N fall onto different branches for different s. The intermolecular coupling and the heavier endmasses shift the LAM branches to higher and lower frequencies, respectively. There exists a value x₀ depending on the masses and force constants, where the branches cut the dispersion curve of the infinite molecule. For s/N ≥ x₀ the effect of endmasses dominates. Low-frequency RAMAN spectra of n-alkanes (N = 20, …, 40 C atoms) were recorded and analyzed. The LAM1 branch runs clearly above a smooth fit through all other LAM data and the origin. This fit approximates to first order the dispersion curve of the infinite PE molecule in an ideal crystal. Its curvature exceeds that of the dispersion curve of the simple linear chain, but is somewhat smaller than that of the dispersion curve of the planar zig-zag chain with rigid bonds. The slope at the origin yields the limiting elastic modulus E_c = 315 GPa in chain direction of crystalline polyethylene. From our measurements on n-alkanes we obtained the frequency shift of LAM1 due to the interlayer coupling and the heavier endmasses. Calculation of the intermolecular coupling constant of the model of a long row of linear chain molecules with the same frequency shift yield the mean value f_l = 2.5 N/m. This value decreases with increasing chain length. The relevance and applicability of the model is discussed. © 1997 John Wiley & Sons, Inc.     

Light-harvesting hybrid assemblies

Light-harvesting hybrids have gained much importance as they are considered as potential mimics for photosynthetic systems. In this Concept article we introduce the design concepts involved in the building up of light-harvesting hybrids; these resemble the well-studied organic-based assemblies for energy transfer. We have structured this article into three parts based on the strategies adopted in the synthesis of hybrid assemblies, as covalent, semicovalent, and noncovalent procedures. Furthermore, the properties and structural features of the hybrids and analogous organic assemblies are compared. We also emphasize the challenges involved in the processability of these hybrid materials for device applications and present our views and results to address this issue through the design of soft-hybrids by a solution-state, noncovalent, self-assembly process.     

Polymerization of organized polymer assemblies

Supramolecular chemistry has provided the means by which to selectively assemble small and large molecules into intricate two- and three-dimensional nanostructures. The past 2 years have witnessed considerable increase in extending such self-assembled structures into stable, single macromolecular nano-objects, through intra-assembly covalent bond formation. The selective polymerization of specific domains within organized polymer assemblies allows for the preparation of crosslinked, nanostructured bulk or particulate materials, with a variety of possible morphologies and properties.     

Hierarchical assemblies of coordination supramolecules

Hierarchical assemblies of coordination supramolecules are reviewed. These assemblies are self-organized by coordination supramolecules themselves or co-assemblies with other modules. By utilizing electrostatic interaction, the coordination supramolecules can be incorporated into films, liquid crystals, micelles, and hydrogels, etc. These coordination supramolecules-containing novel materials exhibit many switchabilities and other desired properties. The following contents are covered in this review: (1) coordination supramolecules of different architecture; (2) hierarchical molecular devices containing these coordination supramolecules; (3) short perspectives and conclusions.     

Cryo-TEM of soft molecular assemblies

Cryo-transmission electron microscopy (cryo-TEM) is a powerful method for uncovering the structure of soft nanostructured materials. The method is based on ultra-fast cooling and conversion of a liquid sample to a vitrified (glassy) specimen that can be examined in the TEM. Direct-imaging cryo-TEM discloses both the global supramolecular structure and local aggregate-specific details, at the hydrated state, and at a nanometer resolution. This placed the method as a central characterization tool in colloid, material, bio- and nano-related technologies in academia and industry. The advancement of cryo-TEM to new fields of research has been motivated also by significant improvements in instrumentation and software. In this review, we summarize the primary principles of cryo-TEM and highlight the recent contribution of this method to understanding soft-matter self-assembly. Detailed example address the origin of the viscosity peak in micellar solutions, and the nature of exotic assemblies as branched micelles, and micellar discs and ribbons. We further emphasize the strategic application of direct-imaging cryo-TEM to study fundamental biological processes and structure-function relations using the example of membrane-remodeling proteins involved in fission and fusion.     

Magnetic-field-induced assemblies of cobalt nanoparticles

Under the influence of a 0.05 T magnetic field, 15-nm diameter cobalt nanoparticles covered with surfactants in a colloidal solution assemble into highly constrained linear chains along the direction of the magnetic field. The magnetic-field-induced (MFI) chains become floppy after removal of the field, folding into three-dimensional (3D) coiled structures upon gentle agitation. The 3D structures are broken into smaller units with vigorous agitation. The nanoparticles redisperse into the solvent upon ultrasonic agitation. Optical microscopy and transmission electron microscopy (TEM) are used to characterize the morphologies of the nanoparticle assemblies at various stages of this reversible process. The hysteresis loops and zero-field cooled/field cooled (ZFC/FC) curves reveal the interparticle coupling in the assemblies. MFI assembly provides a powerful tool to manipulate magnetic nanoparticles.     

The shape of metallosupramolecular assemblies

Despite original doubts on its feasibility, the control of the stereochemistry in ligand-bridged oligonuclear assemblies based on tris(bidentate) components has seen considerable progress in the last two decades, and differences have been observed in the physical characteristics of stereoisomers of such species. This retrospective review examines the background to this "stereochemical problem" and shows how the control of the stereochemical integrity of dinuclear and trinuclear ligand-bridged complexes has been utilised in studies of intramolecular electron transfer within the oligonuclear assemblies, and in probing the sequence- and structure-selectivity of the interaction of these species with nucleic acids.     

Organized assemblies of magnetic clusters

In this work we have explored the possibilities to create layered organizations of the Mn₁₂ single-molecule magnets using the Langmuir–Blodgett technique or attaching these clusters onto a metal surface by preparing self-assembled monolayers (SAMs). In the first part we discuss the use of the Langmuir–Blodgett (LB) technique in order to obtain organized magnetic films formed by monolayers of these clusters. Two strategies have been used with this aim. The first one consists of mixing Mn₁₂ acetate or benzoate derivatives with an amphiphile, while the second procedure is based on the use of Mn₁₂ derivatives specifically designed to form LB films. An alternative method is that of preparing self-assembled monolayers (SAMs). Some preliminary results obtained with this method are reported in the second part of the work. To cite this article: M. Clemente-León et al., C. R. Chimie 6 (2003).     

Supramolecular assemblies of lipid-coated polyelectrolytes

We reveal the existence of a general class of supramolecular assemblies made up of lipid-coated polyelectrolytes including the celebrated lipid-nucleic acid complexes. With the aid of high-resolution cryo-electron microscopy, we unveil the nanoscale internal organization of assemblies generated with a wide range of synthetic and biological polyelectrolytes, several of them being investigated in this context for the first time, namely, poly(styrene sulfonic acid), carboxylmethylcellulose, and filamentous actin. Using an original coarse-grained model representing lipid-coated polyelectrolytes as semiflexible tubes, we thoroughly explored the morphologies resulting from the self-assembly process as a function of tube lengths and rigidities; the computed structures are fully consistent with the experimental observations. In particular, we found a strong extension of the correlation range of the order parameter as the rigidity of the lipid-coated polyelectrolytes increases. Electrostatic interactions provide a stabilizing mechanism leading to finite-size equilibrium assemblies. These assemblies may constitute a generic route for interfacing polyelectrolytes to living cells to perform gene delivery, for instance.