Regular Assemblies Research Articles

Self-Assembly of Ag Nanoparticles Induced by Centrifuging and Broken by Silanization.

A novel method was developed to assemble Ag nanoparticles (NPs) into chain-like structures. The assembly of the NPs was created by suspending in an ethanol and water solution as well as centrifuging at a high speed (a force of more than 29 Kg for the NPs with an average diameter of 18 nm). The composition of solvents and centrifuged speeds of samples play important roles for the formation of regular assemblies. The number of Ag NPs in the chain-like assemblies was adjusted by changing centrifuging forces. The assemblies of the NPs were fixed by a SiO2 coating through a St6ber synthesis. In addition, the assemblies were broken through a silanization process because of partially hydrolyzed tetraethyl-orthosilicate molecules adsorbed on the surface of Ag NPs to form a SiO2 layer opposite aggregation. A slow silanization process made Ag NPs monodispersed in solutions, in which Ag/SiO2 core/shell NPs were created.

Lysine-based oligomeric surfactants with cyanuric chloride: synthesis and micellization properties

Two lysine-based oligomeric surfactants 2C12LyNa2 and 3C12LyNa3 were synthesized using cyanuric chloride and Ne-lauroyl-l-lysine. Their physicochemical properties of aqueous solutions were determined by surface tension and conductivity as well as dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. From the results of surface tension and conductivity measurements, the critical micelle concentration decreases by one order of magnitude with increasing degree of oligomerization. 3C12LyNa3 and 2C12LyNa2 tend to form premicellar aggregates in solution at a sufficiently low concentration. In addition, their interface behaviors such as adsorption and micellization are reflected by parameters such as the minimum surface area per molecule (Amin), adsorption efficiency and effectiveness (pC20), maximum surface excess concentration (Γmax), and standard free energy for micellization and adsorption (ΔGmic∘, ΔGads°). The Amin value of 2C12LyNa2 and 3C12LyNa3 is two times that of the monomeric surfactant sodium Ne-lauroyl-l-lysine (C12LyNa). With increasing degree of oligomerization, pC20 increases, which follows the reverse order for ΔGmic° and ΔGads°. TEM results showed that C12LyNa forms slightly entangled rod-like micelles. 2C12LyNa2 and 3C12LyNa2 can self-assemble into regular spherical assemblies; DLS showed that with increasing degree of oligomerization for 2C12LyNa2 and 3C12LyNa3, the diameters of the spherical aggregates decrease and the hydrophobic interaction and hydrogen bonding become stronger.

The salt‐induced crystallization behavior of potato amylose

The salt‐induced crystallization behavior of potato amylose was probed by measurement of fluorescent inversive microscope, X‐ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The crystalline patterns and granular structures of potato amylose in the presence of salt were highly dependent on the type and concentration of salt as well as the amylose content. High amylose content and low salt concentration (specifically 4% of amylose content and below 0.1 mol/L of salt in this study) favored the organization of double‐stranded helices into regular assemblies. Salt was proposed to act on the crystallization of potato amylose mainly via the cation‐starch interactions occurring between the cations of salt and the negatively charged phosphate groups and free hydroxyl groups of potato amylose. The difference in the crystalline growth mode of potato amylose with different concentrations might be attributed to different nature of cations, especially the charge density.

Regular assembly of filamentous viruses and gold nanoparticles by specific interactions and subsequent chemical crosslinking

The assembly of molecular components into regular structures is a key ambition of nanoscience and nanotechnology. In this study, we constructed regular assemblies composed of filamentous M13 phages and gold nanoparticles (GNPs). Mixed solutions of gold-binding peptide-displaying phages at the termini (A3 phages) and GNPs behaved as viscous solutions, and GNPs in the solutions were self-assembled into regularly assembled structures. Then, hydrogels composed of A3 phages and GNPs were successfully constructed by chemical crosslinking of phages. In the hydrogels, A3 phages showed liquid-crystalline properties, suggesting high orientation of phages.

Micro-macro scale instability in 2D regular granular assemblies

Instability and stress–strain behavior were investigated for 2D regular assemblies of cylindrical particles. Biaxial shear experiments were performed on three sets of assemblies with regular, albeit increasingly defective structures. These experiments revealed unique instability behavior of these assemblies. Continuum models for the assemblies were then constructed using the granular micromechanics approach. In this approach, the constitutive equations governing the behavior of inter-particle contacts are written in local or microscopic level. The behavior of the RVE is then retrieved by using either kinematic constraint or least squares (static constraint) along with the principle of virtual work to equate the work done by microscopic force–displacement conjugates to that of the macroscopic stress and strain tensor conjugates. The ability of the two continuum approaches to describe the measured stress–strain behavior was evaluated. The continuum models and the local constitutive laws were used to perform instability analyses. The onset of instability and orientation of shear band was found to be well predicted by the instability analyses with the continuum models. Further, macro-scale instability was found to correlate with the instability of inter-particle contacts, although with some variations for the two modeling approaches.

Optic neuritis in neuromyelitis optica.

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease associated with recurrent episodes of optic neuritis and transverse myelitis, often resulting in permanent blindness and/or paralysis. The discovery of autoantibodies (AQP4-IgG) that target aquaporin-4 (AQP4) has accelerated our understanding of the cellular mechanisms driving NMO pathogenesis. AQP4 is a bidirectional water channel expressed on the plasma membranes of astrocytes, retinal Müller cells, skeletal muscle, and some epithelial cells in kidney, lung and the gastrointestinal tract. AQP4 tetramers form regular supramolecular assemblies at the cell plasma membrane called orthogonal arrays of particles. The pathological features of NMO include perivascular deposition of immunoglobulin and activated complement, loss of astrocytic AQP4, inflammatory infiltration with granulocyte and macrophage accumulation, and demyelination with axon loss. Current evidence supports a causative role of AQP4-IgG in NMO, in which binding of AQP4-IgG to AQP4 orthogonal arrays on astrocytes initiates complement-dependent and antibody-dependent cell-mediated cytotoxicity and inflammation. Immunosuppression and plasma exchange are the mainstays of therapy for NMO optic neuritis. Novel therapeutics targeting specific steps in NMO pathogenesis are entering the development pipeline, including blockers of AQP4-IgG binding to AQP4 and inhibitors of granulocyte function. However, much work remains in understanding the unique susceptibility of the optic nerves in NMO, in developing animal models of NMO optic neuritis, and in improving therapies to preserve vision.

Direct Numerical Simulations of Electrophoretic Deposition of Charged Colloidal Suspensions

Motivated by applications in the field of nanomanufacturing, we perform large-scale numerical simulations of the electrophoretic deposition of suspensions of charged colloids in an electrolyte. A simulation method is developed to model the full deposition process that captures linear electrophoresis, dipolar interactions, van-der-Waals forces, steric interactions, Brownian motion, as well as electric and hydrodynamic interactions with the electrodes. Using a fast algorithm, suspensions of up to 5,000 particles are simulated, and results are reported for the final deposit microstructure as a function of field strength. The simulation results demonstrate that regular crystalline colloidal assemblies are obtained at low field strengths and volume fractions, while more random structures with frequent defects are formed in stronger fields and at higher volume fractions, in agreement with recent deposition experiments.

The C0C1 Fragment of Human Cardiac Myosin Binding Protein C Has Common Binding Determinants for Both Actin and Myosin

The N-terminal domains of cardiac myosin binding protein C (MyBP-C) play a regulatory role in modulating interactions between myosin and actin during heart muscle contraction. Using NMR spectroscopy and small-angle neutron scattering, we have determined specific details of the interaction between the two-module human C0C1 cMyBP-C fragment and F-actin. The small-angle neutron scattering data show that C0C1 spontaneously polymerizes monomeric actin (G-actin) to form regular assemblies composed of filamentous actin (F-actin) cores decorated by C0C1, similar to what was reported in our earlier four-module mouse cMyBP-C actin study. In addition, NMR titration analyses show large intensity changes for a subset of C0C1 peaks upon addition of G-actin, indicating that human C0C1 interacts specifically with actin and promotes its assembly into filaments. During the NMR titration, peaks corresponding to cardiac-specific C0 domain are the first to be affected, followed by those from the C1 domain. No peak intensity or position changes were detected for peaks arising from the disordered proline/alanine-rich (P/A) linker connecting C0 with C1, despite previous suggestions of its involvement in binding actin. Of considerable interest is the observation that the actin-interaction “hot-spots” within the C0 and C1 domains, revealed in our NMR study, overlap with regions previously identified as binding to the regulatory light chain of myosin and to myosin ΔS2. Our results suggest that C0 and C1 interact with myosin and actin using a common set of binding determinants and therefore support a cMyBP-C switching mechanism between myosin and actin.

Monodisperse Hexagonal Silver Nanoprisms: Synthesis via Thiolate-Protected Cluster Precursors and Chiral, Ligand-Imprinted Self-Assembly

Silver nanoprisms of a predominantly hexagonal shape have been prepared using a ligand combination of a strongly binding thiol, captopril, and charge-stabilizing citrate together with hydrogen peroxide as an oxidative etching agent and a strong base that triggered nanoprism formation. The role of the reagents and their interplay in the nanoprism synthesis is discussed in detail. The beneficial role of chloride ions to attain a high degree of reproducibility and monodispersity of the nanoprisms is elucidated. Control over the nanoprism width, thickness, and, consequently, plasmon resonance in the system has been demonstrated. One of the crucial factors in the nanoprism synthesis was the slow, controlled aggregation of thiolate-stabilized silver nanoclusters as the intermediates. The resulting superior monodispersity (better than ca. 10% standard deviation in lateral size and ca. 15% standard deviation in thickness (<1 nm variation)) and charge stabilization of the produced silver nanoprisms enabled the exploration of the rich diversity of the self-assembled morphologies in the system. Regular columnar assemblies of the self-assembled nanoprisms spanning 2-3 μm in length have been observed. Notably, the helicity of the columnar phases was evident, which can be attributed to the chirality of the strongly binding thiol ligand. Finally, the enhancement of Raman scattering has been observed after oxidative removal of thiolate ligands from the AgNPR surface.

Spatial distribution of enhanced optical fields in monolayered assemblies of metal nanoparticles: Effects of interparticle coupling

Near-field two-photon excitation images of assemblies of many gold nanospheres show characteristic feature that enhanced optical fields are confined at the rim parts of the assemblies. In the present report we analyzed the origin of this feature based on finite-difference time-domain (FDTD) approach as well as a simple point dipole model that incorporates the interparticle interaction with the dipole–dipole potential. It has been found that the simple point dipole model is useful for qualitative discussion on the optical field distribution in the metal nanoparticle assemblies. From the analysis, we have found that the interparticle interaction, which causes the propagation of the plasmon excitation in the assemblies, seems to be essential for the localization of the enhanced field at the rim. We propose that regular close-packed assemblies do not yield efficiently enhanced optical fields in visible to near-infrared region, and rather assemblies with large fluctuation are more advantageous to get highly enhanced fields.

Hydrophilic cyclodextrin protected Pd nanoclusters: insights into their size control and host–guest behavior

The process of formation of narrow size spherical PdNPs covered by cyclodextrins with an average size of 5.1 nm ± 0.5 nm has been investigated in aqueous solution at room-temperature. Analyses by UV-Vis spectroscopy and dynamic light scattering (DLS) at the beginning of reaction indicated a fast exchange of chloride ions with water molecules within the palladium coordination sphere. This process is followed by reduction of Pd(II) species according to the α-HPCD concentration. The hydrodynamic radii observed from both PdNPs and α-HPCD aqueous solutions suggested that regular CDs assemblies in the order of a few nanometers may direct the homogeneous NPs growth towards uniform aggregates. These scattering measurements are corroborated by 1H DOSY NMR spectroscopy in solution and AFM (atomic force microscopy) analyses which provided evidence of stable hybrid assemblies. Interestingly, by changing the cavity size, structures with distinct hydrodynamic diameters are formed. Further evidence from ECD (electronic circular dichroism) spectra reveals that the primary face of cyclodextrin is most likely associated to the metal surface.

Evaluation of Isoprene Chain Extension from PEO Macromolecular Chain Transfer Agents for the Preparation of Dual, Invertible Block Copolymer Nanoassemblies

Two RAFT-capable PEO macro-CTAs, 2 and 5 kDa, were prepared and used for the polymerization of isoprene which yielded well-defined block copolymers of varied lengths and compositions. GPC analysis of the PEO macro-CTAs and block copolymers showed remaining unreacted PEO macro-CTA. Mathematical deconvolution of the GPC chromatograms allowed for the estimation of the blocking efficiency, about 50% for the 5 kDa PEO macro-CTA and 64% for the 2 kDa CTA. Self assembly of the block copolymers in both water and decane was investigated and the resulting regular and inverse assemblies, respectively, were analyzed with DLS, AFM, and TEM to ascertain their dimensions and properties. Assembly of PEO-b-PIp block copolymers in aqueous solution resulted in well-defined micelles of varying sizes while the assembly in hydrophobic, organic solvent resulted in the formation of different morphologies including large aggregates and well-defined cylindrical and spherical structures.

Hydrostatic Optimization of Inkjet-Printed Films

In this work, we study the optimization of the geometry of inkjet-printed polymer films and develop a simple analytic framework to understand our results and establish limitations on inkjet-printed patterns. We show how drop spacing and ink concentration affect the thickness of a printed film and how hydrostatic conditions with contact angle hysteresis have to be considered to print optimized rectangular features. If advancing and receding contact angle are not taken into account, printed features will either bulge or break up into smaller beads. Thus, we provide a comprehensive analysis of the limits of film formation using regular assemblies of droplets.

Synthesis and structural features of cyclobutane-containing chiral bicyclic ureas

Abstract Efficient and stereoselective synthetic routes have been developed for the preparation of chiral N-monoprotected cyclobutane bicyclic ureas in which one of the N H groups is protected as a benzyl or tert -butyl carbamate. Ureas in both enantiomeric forms were obtained from a common chiral precursor via the selective manipulation of functional groups. These compounds have been subjected to a structural study in solution and in the solid state. NMR, IR and TEM techniques evidence a strong tendency to aggregation in solution giving regular assemblies, which is a result of intermolecular urea N– H ⋯ O C hydrogen bonding. In the solid state, X-ray analysis shows that two urea molecules interact through only one hydrogen bond yielding infinite chains. This fact and the almost complete coplanarity of both the urea and the carbamate carbonyl groups determine the crystal packing to be formed by a parallel molecular arrangement. All these structural features are well supported by theoretical calculations that allow us to conclude that the formation of a network based on hydrogen bonding is energetically favourable.

Taking multicalixarenes into the nanoworld: first third-generation calixarene dendrimer

We report the first synthesis of a dendritic multicalixarene, featuring twenty-one calixarene units, which when adsorbed onto mica, forms regular assemblies which can then further aggregate to form larger clusters.

Positive Constructs: Charges Localized on Surface-Confined Organometallic Oligomers

Assemblies with molecular-level organization based on organic chromophores and a bimetallic palladium complex are presented. A layer-by-layer strategy is employed by alternately coordinating vinylpyridine-terminated chromophores to the metal centers to form cationic oligomers. These new structures are formed from solution on quartz and silicon substrates functionalized with a covalently bound template layer. Twelve consecutive deposition steps result in structurally regular assemblies as demonstrated by linear increases in the ellipsometrically determined thickness and UV−vis optical absorption. The increase in thickness for each additional layer shows that the long-range order of the system is determined by the structure of the chromophores and by the square-planar geometry of the metal centers. Furthermore, the optical properties indicate that the conjugation length of the assembly component does not increase in the surface-bound oligomers with each additional deposition cycle. Structural communication is transferred via the system components, but they remain electronically isolated. This is supported by density functional theory (DFT) calculations.

Effectiveness of Communication on Students Discipline in Secondary Schools in Kenya.

The influence of communication on student discipline in secondary schools is an issue of continued debate in Kenya. This study was necessitated by the growing concern by education stakeholders in Kenya over the rising reports of student indiscipline in secondary schools. The study utilized qualitative approach with questionnaires, interviews and documentation as instruments of collecting data. Purposive sampling was used to identify Naivasha district as the location of the study. Stratified and simple random sampling was used to identify 8 secondary schools and 200 respondents from these schools. 20 students and 4 teachers in each sampled school were given the self administered questionnaires while all the 8 head teachers were interviewed. The data collected was analyzed descriptively. The findings of this study shows that the level of discipline in secondary schools in Kenya is very low, schools administration rarely discussed implementation of rules and regulations to students hence there are poor channels of communication. Ineffective communication results in conflict, chaos, misunderstanding and lack of confidence in school administration. Factors such as individual communication skills promoted effective communication whereas barriers to interpersonal communication hindered effective communication. This study recommends that the school administration should initiate dialogue when dealing with students to discuss discipline matters, rules and regulations. Regular meetings and morning assemblies should be used as main channels of communication. Schools should avoid ineffective channels of communication which result in conflict, chaos, misunderstanding and lack of confidence in school administration. Guidance and counselling were seen to be effective ways of communication to overcome barriers of communication (255 words). Key words: Communication, effective, channels, influence, discipline, administrators.

Language and Democracy ‘in Movement’: Multilingualism and the Case of the European Social Forum Process

In recent years new cross-European protests and movements have developed on global justice and within the loose platform of the European Social Forum (ESF). One of the major challenges for transnational communication and grassroots democracy within the Social Forums is linguistic communication problems and the ‘work of translation’ required to create a democratic setting. In the willingness to provide open access beyond linguistic communication problems, activists and organizers involved in the ESF preparatory process therefore hold their regular European preparatory assemblies to the ESF summits within a multilingual setting. Given the potential challenges of working transnationally, and of multilingual meetings, the ESF provides a good case study to test whether such processes work effectively in practice in comparison with national social movement assemblies: to what extent is democratic discussion and decision making possible in such emerging multilingual meetings compared to national meetings in which the majority of participants speak the same language? Being interested in linking the theoretical ground of discourse and deliberative democracy to the subject of the emerging Social Forums, I have studied the extent to which democratic discussion in the sense of deliberative debate might or might not take place within the multilingual and Europe-wide preparatory assemblies in the ESF process. The findings of my comparison between Europe-wide Social Forum preparatory assemblies and those taking place at the national level in Germany and the UK show that the absence of one common language within the European assemblies, contrary to what one might intuitively suppose, does not reduce the quality of democratic deliberation as compared to the national context. Therefore, informal power structures and gatekeeping mechanisms frequently rooted at the national level of Social Forum processes, together with a lack of transparency and asymmetries of information, seem to have indirectly reduced the accessibility of European meetings.

Scanning tunneling microscopy investigations of electropolymerized tetra-arylporphyrin complexes

Scanning tunneling microscopy (STM) studies on poly(Zinc-tetraphenylporphyrin) (poly( ZnTPP)) and poly(Zn- or Pt-tetradimethoxyphenylporphyrins) (poly( Zn8OMeTPP) or poly( Pt8OMeTPP)) deposited through anodic oxidation on platinum surfaces are reported. STM investigations on these metalloporphyrin films were conducted to obtain informations on the supramolecular architecture of these polymers. These STM images indicate that poly( ZnTPP) covered the metallic electrode with a layered structure. For poly( Zn8OMeTPP) and poly( Pt8OMeTPP) a tendency to form regular molecular assemblies is obvious.

DNA-based routes to semiconducting nanomaterials

The controlled preparation and assembly of opto-electronic nanoscale materials is being tackled by top-down and bottom-up approaches. The latter draws inspiration from biology, where complex hierarchical systems are assembled from simpler building blocks. One of these, DNA, is proving especially useful: its size, stability, topology; the assorted chemical functional groups; plus its capacity for self-assembly provide a powerful nanoscale toolbox for materials preparation. Here we review recent research that shows the roles DNA can play in the preparation and organisation of semiconductor nanomaterials. Studies show that both hard inorganic and soft polymer materials can be directed to grow at nanoscale lengths using DNA and its constituents. In some cases the resulting materials have been used as components in simple electrical devices and the methodology has been extended to analytical tools. Intriguingly, these DNA-semiconductor hybrid materials have been found to self-assemble themselves, forming highly regular rope-like assemblies and conducting network structures.