Self-Assembly of α-Helical Polypeptides into Microscopic and Enantiomorphic Spirals.

Helical structures are ubiquitous in biological materials and often serve a structural purpose. Bioinspired helical materials can be challenging to synthesize and rarely reach the degree of hierarchy of their natural counterparts. Here we report the first example of particles synthesized by direct emulsification of polypeptides found to display spiral morphologies in the dry state. The polypeptides were α-helical homo- and copolypeptides of γ-benzyl glutamate and allylglycine. The chirality of the spirals was controlled by the chirality of the α-helices. Notably, right-handed α-helical polypeptides (rich in l residues) produced clockwise spirals, whereas left-handed α-helical polypeptides (rich in d residues) produced the enantiomorphs, i.e., counterclockwise spirals. The disruption of the α-helical conformation by the introduction of chiral defects led to less regular spirals and in some cases their suppression. A hypothesis for the transmission of helicity and chirality from a molecular to a higher hierarchical level, involving fibril bundling of coiled α-helices, is proposed.

Swelling of latex particles-towards a solution of the riddle.

The assumption that during emulsion polymerization, the monomer molecules simply diffuse through the aqueous phase into the latex particles is a commonplace. However, there are experimental hints that this might not be that easy. Here, simulation results are discussed based on Fick's diffusion laws regarding the swelling of latex particles. The results of quantitative application of these laws for swelling of latex particles allow the conclusion that the instantaneous replenishment of the consumed monomer during emulsion polymerization requires a close contact between the monomer and the polymer particles.

Thermosensitive polymer controlled morphogenesis and phase discrimination of calcium carbonate.

Homogeneous aragonite flowers with controlled surface structures can be synthesized by using a thermosensitive polymer, i.e. poly (ethylene glycol)-poly(N-isopropyl acrylamide)-poly(acrylamido methyl propane sulfonate) (PEG-PNIPAM-PAMPS), as a crystal growth modifier in the mineralization of calcium carbonate.

EDTA and NTA Effectively Tune the Mineralization of Calcium Phosphate from Bulk Aqueous Solution.

This study describes the effects of nitrilotriacetic acid (NTA) and ethylenediaminotetraacetic acid (EDTA) on the mineralization of calcium phosphate from bulk aqueous solution. Mineralization was performed between pH 6 and 9 and with NTA or EDTA concentrations of 0, 5, 10, and 15 mM. X-ray diffraction and infrared spectroscopy show that at low pH, mainly brushite precipitates and at higher pH, mostly hydroxyapatite forms. Both additives alter the morphology of the precipitates. Without additive, brushite precipitates as large plates. With NTA, the morphology changes to an unusual rod-like shape. With EDTA, the edges of the particles are rounded and disk-like particles form. Conductivity and pH measurements suggest that the final products form through several intermediate steps.

Stabile, thermoresponsive colloidal clusters: an unusual morphology of polymer dispersions.

A new class of colloidal polymeric particles consisting of polystyrene spheres grown in a poly(N-isopropyl acrylamide) precursor scaffold is synthesized via redox-initiated heterophase polymerization. The morphology and thermoresponsiveness of these assemblies is proven by electron microscopy investigations and temperature-dependent measurements of the change of both the speed of sound travelling through the dispersion and the hydrodynamic particle size. Electron microscopy (EM) micrographs (transmission and scanning EM as well cryo-scanning EM) prove the existence of colloidal clusters when the freeze-dried copolymer is redispersed in pure water. The clusters have a size of several micrometers, contain about 800 polystyrene particles with diameter below 100 nm, and show a highly reproducible thermoresponsive behavior with a lower critical solution temperature corresponding to that of pure poly(N-isopropyl acrylamide).

π-Conjugated polyHIPEs as highly efficient and reusable heterogeneous photosensitizers.

π-Conjugated microporous polyHIPEs are synthesized via Suzuki cross-coupling. The polymeric backbone consists of electron donor and acceptor moieties with suitable energetic characteristics to promote the efficient photosensitizing ability for the activation of singlet oxygen, showing extraordinarily high stability. The reaction can be carried out in a continuous flow reaction set-up, realizing complete conversion of α-terpinene into ascaridole.

Polymerized ionic liquid as stabilizer in aqueous emulsion polymerization enables a hydrophilic-hydrophobic transition during film formation.

Polymerized ionic liquid (PIL) nanoparticles are for the first time applied as sole stabilizers in aqueous emulsion polymerization and reveal an astonishing and unexpected behavior. In a well-dispersed state, the PIL nanoparticles serve as an unexpectedly effective stabilizer for polystyrene dispersions, enabling solids content of greater than 40%. However, the same PIL as dry powder is hydrophobic and, in accordance with Bancroft's rule, unable to stabilize aqueous dispersions. This ambivalent behavior of PIL is extremely beneficial for the application of aqueous dispersions because, as desired for decades, the hydrophilic dispersed state during synthesis turns hydrophobic in the dried state during application of the polymer.

Snowballing radical generation leads to ultrahigh molecular weight polymers.

Styrene is the classical monomer obeying zero-one kinetics in radical emulsion polymerization. Accordingly, particles that are less than 100 nm in diameter contain either one or no growing radical(s). We describe a unique photoinitiated polymerization reaction accelerated by snowballing radical generation in a continuous flow reactor. Even in comparison to classical emulsion polymerization, these unprecedented snowballing reactions are rapid and high-yielding, with each particle simultaneously containing more than one growing radical. This is a consequence of photoinitiator incorporation into the nascent polymer backbone and repeated radical generation upon photo-irradiation.

"Schizomorphic" emulsion copolymerization particles.

Cryo-electron microscopy, atomic force microscopy, and light microscopy investigations provide experimental evidence that amphiphilic emulsion copolymerization particles change their morphology in dependence on concentration. The shape of the particles is spherical at solids content above 1%, but it changes to rod-like, ring-like, and web-like structures at lower concentrations. In addition, the shape and morphology of these particles at low concentrations are not fixed but very flexible and vary with time between spheres, flexible pearl-necklace structures, and stretched rods.

Dynamics of amphiphilic diblock copolymers at the air-water interface.

Two polyisoprene-polyethyleneoxide diblock copolymers with different block length ratios adsorbed to the water surface were investigated by multiple angle of incidence ellipsometry, evanescent wave light scattering, and surface tension experiments. In a semidilute interfacial regime, the transition from a two-dimensional to a "mushroom" regime, in which polymer chains form loops and tails in the subphase, was discussed. A diffusion mechanism parallel to the interface was probed by evanescent wave dynamic light scattering. At intermediate concentrations, the interfacial diffusion coefficient D(∥) scales with the surface concentration Γ, as D(∥) ~ Γ(0.77) in agreement with the scaling observed for polymer solutions in a semidilute regime. At relatively high concentrations a decreasing of D(∥) is discussed in terms of increasing friction due to interactions between polyisoprene chains.

Functional hollow carbon nanospheres by latex templating.

A facile and sustainable synthesis of hollow carbonaceous nanospheres is presented, offering a scalable and multifunctional route to the generation of useful nanocontainers, which critically possess the stability not offered by polymeric equivalents and functionality not afforded by other nanocarbons. Carbonization temperature provides a subtle but elegant mechanism to control structure and thereby hydrophobicity, nanopartitioning, and permeation between the inner and outer space.

Randomization of amyloid-ß-peptide(1-42) conformation by sulfonated and sulfated nanoparticles reduces aggregation and cytotoxicity.

The amyloid-ß peptide (Aß) plays a central role in the mechanism of Alzheimer's disease, being the main constituent of the plaque deposits found in AD brains. Aß amyloid formation and deposition are due to a conformational switching to a ß-enriched secondary structure. Our strategy to inhibit Aß aggregation involves the re-conversion of Aß conformation by adsorption to nanoparticles. NPs were synthesized by sulfonation and sulfation of polystyrene, leading to microgels and latexes. Both polymeric nanostructures affect the conformation of Aß inducing an unordered state. Oligomerization was delayed and cytotoxicity reduced. The proper balance between hydrophilic moieties and hydrophobic chains seems to be an essential feature of effective NPs.

Polyamide capsules via soft templating with oil drops-1. Morphological studies of the capsule wall.

Poly(terephthalamide) microcapsules can be reproducibly and easily prepared by interfacial polycondensation around emulsion droplets in water. Oil drops of cyclohexane/chloroform mixture stabilized with poly(vinyl alcohol) containing terephthaloylchloride serve as soft template. The interfacial polycondensation starts immediately after addition of an amine mixture (hexamethylenediamine/diethylenetriamine). Light and scanning electron microscopy prove the formation of capsules with size distribution in the range from a few up to 100 microm depending on particular composition of the reaction mixture. The morphology of the capsule wall is characterized by precipitated particles. If instead of pure organic solvents a reactive oil phase is used as template, the capsules can serve in subsequent reactions as templates for the synthesis of composite particles. In this way, styrene can be radically polymerized inside the capsule leading to composite capsules. The capsule morphology is determined by the partition of all components between all phases.

Molecular aspects of radical polymerizations-the propagation frequency.

The product of the propagation rate constant and monomer concentration is a central issue of radical polymerization. Both quantities are strongly interrelated as the determination of a reliable value of the propagation rate constant requires exact knowledge of the monomer concentration. Even for homogeneous polymerization conditions, exact knowledge of the monomer concentration at the reaction site from the molecular perspective is not trivial. For emulsion polymerizations the situation is additionally complicated by mass transfer events and colloid-chemical effects. Molecular modeling appears as an attractive alternative or complement to the deterministic kinetic description of radical polymerizations.

Core-shell particle interconversion with di-stimuli-responsive diblock copolymers.

Core-shell reversible particle precipitation from aqueous di-stimuli-responsive diblocks is demonstrated as also is the interconversion from one core-shell combination to the other.

Separation of coherent and incoherent scattering contributions in ellipsometric light scattering experiments on latex mixtures.

Mixtures of poly(styrene) latices were used to vary the sample polydispersity for an investigation of polydispersity effects on ellipsometric light scattering (ELS) data. A procedure for high-accuracy ELS measurements is presented and the experimental distinction of coherent and incoherent scattering contributions is demonstrated. The ellipsometric parameters tan (phiQ) and delta are solely determined from coherent scattering and represent averaged ensemble properties, independent of the width of the size distribution. The change in polydispersity shows up in the parameter tan(phiI), which is affected by incoherent contributions. The average particle size detected by ELS can be estimated from the intensity-weighted size distribution. A radial local birefringence in the particles has been detected and attributed to stress birefringence due to the action of the interface tension on the particles during their growth.

Towards a consistent mechanism of emulsion polymerization-new experimental details.

The application of atypical experimental methods such as conductivity measurements, optical microscopy, and nonstirred polymerizations to investigations of the 'classical' batch ab initio emulsion polymerization of styrene revealed astonishing facts. The most important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low-molecular-weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).

The interface engine: experimental consequences.

A light microscopy study confirms spontaneous emulsification at the quiescent, thermally equilibrated interface between pure oil and pure water during the chemical equilibration period. The process is qualitatively explained within the frame of the classical nucleation theory assuming a mixed interface layer between the two liquids in contact allowing supersaturation.

Ion distribution around electrostatically stabilized polystyrene latex particles studied by ellipsometric light scattering.

The ion distribution around electrostatically stabilized polystyrene latex spheres for different ionic strengths is investigated by ellipsometric light scattering. This method is sensitive to the refractive index profile around colloidal particles, which is affected by the local salt content. At an average salt concentration of c* = 10(-4) mol L(-1), the ion concentration at the particle interface increases discontinuously, and a layer of high salt content with 20-30 nm thickness is built up. The observation cannot be explained within the framework of the Poisson-Boltzmann equation; it rather resembles a prewetting transition. Interactions that could possibly lead to a stabilization of the observed layer of high salt content are discussed.

Ellipsometric light scattering for the characterization of thin layers on dispersed colloidal particles.

The thin interface layer on colloids in a liquid can be characterized by applying nulling ellipsometry to a scattering experiment. Close to 90 degrees scattering angle the ellipsometric quantities tan(Psi) and Delta of particles smaller than the wavelength behave like at the Brewster angle of reflection ellipsometry. The minimum of tan(Psi) and the slope of Delta depend on thickness and refractive index of the layer, while the location of the minimum is sensitive to the refractive index of the particle. As an example, the swelling of a thermosensitive layer on colloidal particles has been determined from measurements at two wavelengths.