Engineered bacterially expressed polypeptides: assembly into polymer particles with tailored degradation profiles

In nature, the sequence of amino acids in a protein is determined by the genetic code. Biosynthesis of polypeptides by bacteria can be used to exploit this natural process to afford exact control over properties such as molecular weight, chemical functionality, and structure. It is demonstrated how control over the positioning of functional groups can be used to tune the degradation of assembled polypeptide particles (see scheme).     

Self‐assembly of polymer‐coated ferromagnetic nanoparticles into mesoscopic polymer chains

The self‐assembly of dispersed polymer‐coated ferromagnetic nanoparticles into micron‐sized one‐dimensional mesostructures at a liquid–liquid interface was reported. When polystyrene‐coated Co nanoparticles (19 nm) are driven to an oil/water interface under zero‐field conditions, long (≈ 5 μm) chain‐like assemblies spontaneously form because of dipolar associations between the ferromagnetic nanoparticles. Direct imaging of the magnetic assembly process was achieved using a recently developed platform consisting of a biphasic oil/water system in which the oil phase was flash‐cured within 1 s upon ultraviolet light exposure. The nanoparticle assemblies embedded in the crosslinked phase were then imaged using atomic force microscopy. The effects of time, temperature, and colloid concentration on the self‐assembly process of dipolar nanoparticles were then investigated. Variation of either assembly time t or temperature T was found to be an interchangeable effect in the 1D organization process. Because of the dependence of chain length on the assembly conditions, we observed striking similarities between 1D nanoparticle self‐assembly and polymerization of small molecule monomers. This is the first in‐depth study of the parameters affecting the self‐assembly of dispersed, dipolar nanoparticles into extended mesostructures in the absence of a magnetic field. © 2008 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 46: 2267–2277, 2008     

Nucleation in binary polymer blends: effects of foreign mesoscopic spherical particles

We study nucleation in binary polymer blends in the presence of mesoscopic spherical particles using self-consistent field theory, considering both heterogeneous and homogeneous nucleation mechanisms. Heterogeneous nucleation is found to be highly sensitive to surface selectivity and particle size, with rather subtle dependence on the particle size. Particles that preferentially adsorb the nucleating species generally favor heterogeneous nucleation. For sufficiently strong adsorption, barrierless nucleation is possible. By comparing the free energy barrier for homogeneous and heterogeneous nucleation, we construct a kinetic phase diagram.     

Templated assembly of sulfide nanoclusters into cubic-C3N4 type framework

Here we report a new type of nanocluster superlattice in which each four-connected cluster ([M4In16S31],6- M = Fe, Co, Zn, and Cd) alternates with a three-connected sulfur anion (S2-) to form a rare and yet theoretically important non-centrosymmetric and non-interpenetrating (3,4)-connected net topologically identical to that of the hypothetical cubic carbon nitride type net. These materials have a ring size consisting of 16 tetrahedral atoms. Because of the large cluster size and the elimination of structural intergrowth, the volume fraction of the inorganic framework is as low as 38%. A strong photoluminescent emission has also been observed.     

Polymer-coated ferromagnetic colloids from well-defined macromolecular surfactants and assembly into nanoparticle chains

A novel synthetic route to polymer-coated ferromagnetic colloids of metallic cobalt has been developed. Well-defined end-functional polystyrenes were synthesized using controlled radical polymerization and used as surfactants in the thermolysis of dicobaltoctacarbonyl to afford uniform ferromagnetic nanoparticles. The presence of the polymer shell enabled prolonged colloidal stability of dispersions in a wide range of organic solvents and formed glassy encapsulating coatings around ferromagnetic cores in the solid state. These polymer-coated colloids assembled into robust, micron-sized nanoparticle chains when cast onto supporting surfaces due to dipolar associations of magnetic cores. Hierarchical assemblies were also prepared by blending polystyrene-coated cobalt colloids with larger silica beads.     

Expeditious assembly of mesoscopic metallocycles

Very large chiral metallocycles with tunable cavities in the range of 0.9-22 nm were efficiently assembled from the requisite metal- and ligand-terminated oligomers that are built from the 2,2'-diacetoxy-1,1'-binaphthyl-3,3'-bis(ethyne) bridging ligand and trans-Pt(PEt3)2 metal connector. These unprecedented nanoscopic and mesoscopic molecular metallocycles have been characterized with 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, microanalysis, IR, UV-vis, and circular dichroism spectroscopies, MALDI-TOF MS, and size exclusion chromatography (SEC). SEC results indicated that the metallocycles appear to be much more compact and rigid than the metal- and ligand-terminated oligomers. The present molecular metallocycles provide interesting building blocks for the construction of larger functional structures that cannot be accessed from a top-down approach.     

Reversible self-assembly of patchy particles into monodisperse icosahedral clusters

We systematically study the design of simple patchy sphere models that reversibly self-assemble into monodisperse icosahedral clusters. We find that the optimal patch width is a compromise between structural specificity (the patches must be narrow enough to energetically select the desired clusters) and kinetic accessibility (they must be sufficiently wide to avoid kinetic traps). Similarly, for good yields the temperature must be low enough for the clusters to be thermodynamically stable, but the clusters must also have enough thermal energy to allow incorrectly formed bonds to be broken. Ordered clusters can form through a number of different dynamic pathways, including direct nucleation and indirect pathways involving large disordered intermediates. The latter pathway is related to a reentrant liquid-to-gas transition that occurs for intermediate patch widths upon lowering the temperature. We also find that the assembly process is robust to inaccurate patch placement up to a certain threshold and that it is possible to replace the five discrete patches with a single ring patch with no significant loss in yield.     

Encapsulating of single quantum dots into polymer particles

Single semiconductor quantum dots were embedded into polymer particles with diameters below 0.1 μm by an emulsion polymerization procedure or via a secondary dispersion approach. The photoluminescence properties of the nanocrystals are retained upon encapsulation, as demonstrated by fluorescence confocal microscopy.

Evaporation of hot mesoscopic atomic metal clusters

The evaporation times of hot mesoscopic sodium clusters are estimated using the microscopic and microcanonical statistical model of Weisskopf and the macroscopic canonical kinetic gas theory. The level density of liquid sodium clusters as function of the internal excitation energy is computed from the experimentally known thermodynamic quantities of the bulk matter. In using the known temperature dependent surface tension and standard thermodynamics, both theories are corrected to take into account finite size effects. By this method it is possible to obtain decay rates and internal level densities of mesoscopic clusters at excitations where any harmonic approximation breaks down. For clusters having more than about 200 atoms, the evaporation times obtained from the two models are practically equal.     

Templated assembly of gold nanoparticles into microscale tubules and their application in surface-enhanced Raman scattering

We report a simple procedure to assemble gold nanoparticles into hollow tubular morphology with micrometer scale, wherein the citrate molecule is used not only as a reducing and capping agent, but also as an assembling template. The nanostructure and growth mechanism of microtubes are explored via SEM, TEM, FTIR spectra, and UV-vis spectra studies. The incorporation of larger gold nanoparticles by electroless plating results in an increase in the diameter of microtubes from 900 nm to about 1.2 microm. The application of the microtubes before and after electroless plating in surface-enhanced Raman scattering (SERS) is investigated by using 4-aminothiophenol (4-ATP) as probe molecules. The results indicate that the microtubes both before and after electroless plating can be used as SERS substrates. The microtubes after electroless plating exhibit excellent enhancement ability.     

Templated assembly of a pseudorotaxane of gold rectangles

A nanoscopic pseudorotaxane (1)2 subset2 composed of the gold rectangle [Au4(mu-PAnP)2(mu-bipy)2](OTf)4 and the linear template 4,4'-bis(9'-anthryl)biphenyl was assembled (PAnP = 9,10-bis(diphenylphosphino)anthracene); bipy = 4,4'-bipyridine).     

Mixtures of interacting particles with well-defined composition field coupling chi parameters

This article proposes a systematic, quantitative treatment of the problem of associating a scalar Flory-Huggins-like chi parameter directly with the interaction potentials in a binary mixture of point particles. This work fulfills the need for a general, quantitative way to compare chi values in explicitly simulated ensembles of lattice and off-lattice polymer models with field theoretic calculations. Emphasis is placed on constructing particle models where chi is relatively well defined. In general, chi is defined through pair correlation functions, whose thermal fluctuations are coupled to local average composition and composition gradients. This implies that chi is composition dependent even in the simplest particle models. At the same time, by quantifying this effect, it is found that composition-independent chi may be defined to within a few percent for cases where the range of the potential is large relative to the interparticle distance. An explicit formula for chi in terms of interaction potentials is given.     

Shear-induced assembly of graphene oxide particles into stripes near surface

We report the shear-induced assembly of graphene oxide (GO) particles into periodic stripe-like patterns near the surface. These stripe-like patterns, which have an average periodic length of 100–250 μm, are aligned in a wavy manner along the normal to the flow direction. The self-assembled GO structures are investigated at different depths using three different analysis methods, namely, reflective microscopy observations of the photonic-crystalline GO dispersion, polarized optical microscopy, and fluorescence confocal laser scanning microscopy. The surface microstructures observed in reflection mode are different from the shear-induced band structures formed in bulk thermotropic liquid crystals and liquid crystal polymers, in terms of the shape and scale of the stripes. Further, there is also a difference in terms of the dependence of the stripe width on the shear rate. The observations suggest that the stripes are formed because of a competition between the stable surface-field-induced planar alignment of the GO particles near the surface and their relatively unstable shear-induced vertical alignment in the bulk. The findings of this study should advance our understanding of GO assembly under shear stress. Further, the proposed method is a novel one for inducing the assembly of GO particles into microstructures shaped as thread-like stripes.     

Templated synthesis and assembly with sustainable cellulose nanomaterial for functional nanostructure

Cellulose - Templated synthesis and assembly for nanostructured materials with tailored properties have received considerable attention. The powerful templates with predefined structures can guide...     

Inkjet printing of well-defined polymer dots and arrays

Inkjet printing represents a highly promising polymer deposition method, which is used for, for example, the fabrication of multicolor polyLED displays and polymer-based electronics parts. The challenge is to print well-defined polymer structures from dilute solution. We have eliminated the formation of ring stains by printing nonvolatile acetophenone-based inks on a perfluorinated substrate using different polymers. (De)pinning of the contact line of the printed droplet, as related to the choice of solvent, is identified as the key factor that determines the shape of the deposit, whereas the choice of polymer is of minor importance. Adding 10 wt % or more of acetophenone to a volatile solvent (ethyl acetate)-based polymer solution changes the shape of the deposit from ring-like to dot-like, which may be due to the establishment of a solvent composition gradient. Arrays of closely spaced dots have also been printed. The size of the dots is considerably smaller than the nozzle diameter. This may prove a potential strategy for the inkjet printing of submicrometer structures.     

Critical phenomena in particles of mesoscopic size

Anomalous optical properties of small silver particles and some silver halides are discussed as displays of critical phenomena due to particle size decreasing or to their interaction with each other in an ensemble. Special consideration is given to weak localization of conduction electrons in a small metal particle, to plasmon delocalization in ensemble of metal particles, to the effect of zero- dimensional percolation in a small dielectric particle, and to the effect of size on the superionic transition in small AgI particles and thin envelopes.     

First direct assembly of molecular helical complexes into a coordination polymer

Luminescent triple-stranded helicates, formed between Tb(iii) ions and bis-acylpyrazolones, were directly assembled into a 1-D polymeric system.     

Controlled side-by-side assembly of gold nanorods and dye molecules into polymer-wrapped SERRS-active clusters

The controlled side-by-side assembly of gold nanorods in solution together with Raman reporter dye molecules to create small SERRS-active clusters stabilised by a surrounding polymer layer is demonstrated. This promising new class of nanotags offers several advantages over spherical nanoparticles for bioimaging and is of potential importance for a wide range of plasmon-enhanced spectroscopies and can also serve as building blocks for more complex solution-phase nanostructures.     

Preparation and characterization of well-defined sterically stabilized latex particles with narrow size distribution

 The synthesis and comprehensive characterization of a purely sterically stabilized latex with narrow size distribution is reported. By use of non-ionic initiators no chemically bound surface charges are generated. Stabilization of the particles is achieved through use of a non-ionic surfactant having a double bond in the hydrophobic part which is chemically bound to the surface. Analysis of the latex particles thus generated by transmission electron microscopy, disc centrifugation, and small-angle X-ray scattering (SAXS) reveals that the size distribution is narrow (standard deviation between 6 and 10%). SAXS furthermore demonstrates that the surfactant is located in a thin layer on the surface. The interaction of the particles is purely repulsive as shown by the analysis of the turbidity of the latex. The systems obtained herein may serve as model systems of water-borne purely sterically stabilized colloid particles. Received: 23 December 1997 Accepted: 18 May 1998