156 research outputs found
Thermodynamics of micellization of oppositely charged polymers
The complexation of oppositely charged colloidal objects is considered in
this paper as a thermodynamic micellization process where each kind of object
needs the others to micellize. This requirement gives rise to quantitatively
different behaviors than the so-called mixed-micellization where each specie
can micellize separately. A simple model of the grand potential for micelles is
proposed to corroborate the predictions of this general approach.Comment: 7 pages, 2 figures. Accepted for publication in Europhysics Letter
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Synthesis and solution properties of a temperature-responsive PNIPAMâb-PDMSâb-PNIPAM triblock copolymer
In this paper, we report the synthesis and self-assembly of a novel thermoresponsive PNIPAM60âb-PDMS70âb-PNIPAM60 triblock copolymer in aqueous solution. The copolymer used a commercially available precursor modified with an atom transfer radical polymerization (ATRP) initiator to produce an ABA triblock copolymer via ATRP. Small-angle neutron scattering (SANS) was used to shed light on the structures of nanoparticles formed in aqueous solutions of this copolymer at two temperatures, 25 and 40 °C. The poly(dimethylsiloxane) block is very hydrophobic and poly(N-isopropylacrylamide) (PNIPAM) is thermoresponsive. SANS data at 25 °C indicates that the solutions of PNIPAMâb-PDMSâb-PNIPAM copolymers form well-defined aggregates with presumably coreâshell structures below cloud point temperature. The scattering curves originating from nanoparticles formed at 40 °C in 100% D2O or 100% H2O were successfully fitted with the Beaucage model describing aggregates with hierarchical structure
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PEGâpeptide conjugates
The remarkable diversity of the self-assembly behavior
of PEGâpeptides is reviewed, including self-assemblies formed by PEGâpeptides with ÎČ-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized
Ultra-Fast Oleophobic-Hydrophilic Switching Surfaces for Anti-Fogging, Self-Cleaning, and Oil-Water Separation
Smooth copolymerâfluorosurfactant complex film surfaces are found to exhibit fast oleophobicâhydrophilic switching behavior. Equilibration of the high oil contact angle (hexadecane = 80°) and low water contact angle (110°), which, when combined with the inherent ultrafast switching speed, yields oilâwater mixture separation efficiencies exceeding 98%
Unique Properties of Eukaryote-Type Actin and Profilin Horizontally Transferred to Cyanobacteria
A eukaryote-type actin and its binding protein profilin encoded on a genomic island in the cyanobacterium Microcystis aeruginosa PCC 7806 co-localize to form a hollow, spherical enclosure occupying a considerable intracellular space as shown by in vivo fluorescence microscopy. Biochemical and biophysical characterization reveals key differences between these proteins and their eukaryotic homologs. Small-angle X-ray scattering shows that the actin assembles into elongated, filamentous polymers which can be visualized microscopically with fluorescent phalloidin. Whereas rabbit actin forms thin cylindrical filaments about 100 ”m in length, cyanobacterial actin polymers resemble a ribbon, arrest polymerization at 5-10 ”m and tend to form irregular multi-strand assemblies. While eukaryotic profilin is a specific actin monomer binding protein, cyanobacterial profilin shows the unprecedented property of decorating actin filaments. Electron micrographs show that cyanobacterial profilin stimulates actin filament bundling and stabilizes their lateral alignment into heteropolymeric sheets from which the observed hollow enclosure may be formed. We hypothesize that adaptation to the confined space of a bacterial cell devoid of binding proteins usually regulating actin polymerization in eukaryotes has driven the co-evolution of cyanobacterial actin and profilin, giving rise to an intracellular entity
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