Controlling the Location of Nanoparticles in Colloidal Assemblies of Amphiphilic Polymers by Tuning Nanoparticle Surface Chemistry

Here, we report a simple method to control the location of nanoparticles in colloidal block-copolymer assemblies by using nanoparticles modified with mixed surface ligands. The binary self-assembly of amphiphilic polymers of polystyrene-<i>b</i>-poly­(acrylic acid) (PS-<i>b</i>-PAA) and gold nanoparticles (AuNPs) modified with a hydrophobic ligand, dodecanethiol (DT), led to polymer micelles with nanoparticles segregated in the core of polymer micelles. On the other hand, AuNPs modified with mixed ligands of mercaptoundecanol (MUL) and DT were distributed at the PS–PAA interface, reducing the interfacial energy between the two polymers. This result was in good agreement with the prediction by the surface energy calculations. We also showed that the AuNPs with mixed ligands can decorate preformed polymer assemblies by the interfacial self-assembly. Furthermore, we demonstrated the compartmentalization of two different types of nanoparticles in colloidal polymer assemblies based on the strategy

Low-Dimensional Nanoparticle Clustering in Polymer Micelles and Their Transverse Relaxivity Rates

One- or two-dimensional arrays of iron oxide nanoparticles were formed in colloidal assemblies of amphiphilic polymers. Electron tomography imaging revealed that nanoparticles are arranged into one-dimensional strings in magneto-micelles or two-dimensional sheets in magneto-core/shell assemblies. The distinct directional assembly behavior was attributed to the interparticle interaction relative to the nanoparticle–polymer interaction, which was modulated by varying the cosolvent used for the solution phase self-assembly. Magneto-core/shell assemblies with varying structural parameters were formed with a range of different sized as-synthesized nanoparticles. The transverse magnetic relaxivity rates (<i>r</i>₂) of a series of different assemblies were determined to examine the effect of nanoparticle arrangement on the magnetic relaxivity for their potential applications in MRI. The results indicated that the assembly structure of nanoparticles in polymer micelles significantly affects the <i>r</i>₂ of surrounding water, providing a way to control magnetic relaxivity

Low-Dimensional Nanoparticle Clustering in Polymer Micelles and Their Transverse Relaxivity Rates

One- or two-dimensional arrays of iron oxide nanoparticles were formed in colloidal assemblies of amphiphilic polymers. Electron tomography imaging revealed that nanoparticles are arranged into one-dimensional strings in magneto-micelles or two-dimensional sheets in magneto-core/shell assemblies. The distinct directional assembly behavior was attributed to the interparticle interaction relative to the nanoparticle–polymer interaction, which was modulated by varying the cosolvent used for the solution phase self-assembly. Magneto-core/shell assemblies with varying structural parameters were formed with a range of different sized as-synthesized nanoparticles. The transverse magnetic relaxivity rates (<i>r</i>₂) of a series of different assemblies were determined to examine the effect of nanoparticle arrangement on the magnetic relaxivity for their potential applications in MRI. The results indicated that the assembly structure of nanoparticles in polymer micelles significantly affects the <i>r</i>₂ of surrounding water, providing a way to control magnetic relaxivity

Low-Dimensional Nanoparticle Clustering in Polymer Micelles and Their Transverse Relaxivity Rates

One- or two-dimensional arrays of iron oxide nanoparticles were formed in colloidal assemblies of amphiphilic polymers. Electron tomography imaging revealed that nanoparticles are arranged into one-dimensional strings in magneto-micelles or two-dimensional sheets in magneto-core/shell assemblies. The distinct directional assembly behavior was attributed to the interparticle interaction relative to the nanoparticle–polymer interaction, which was modulated by varying the cosolvent used for the solution phase self-assembly. Magneto-core/shell assemblies with varying structural parameters were formed with a range of different sized as-synthesized nanoparticles. The transverse magnetic relaxivity rates (<i>r</i>₂) of a series of different assemblies were determined to examine the effect of nanoparticle arrangement on the magnetic relaxivity for their potential applications in MRI. The results indicated that the assembly structure of nanoparticles in polymer micelles significantly affects the <i>r</i>₂ of surrounding water, providing a way to control magnetic relaxivity

Polymerization-Induced Nanostructural Transitions Driven by In Situ Polymer Grafting

Polymerization-induced structural transitions have gained attention recently due to the ease of creating and modifying nanostructured materials with controlled morphologies and length scales. Here, we show that order–order and disorder–order nanostructural transitions are possible using in situ polymer grafting from the diblock polymer, poly­(styrene)-<i>block</i>-poly­(butadiene). In our approach, we are able to control the resulting nanostructure (lamellar, hexagonally packed cylinders, and disordered spheres) by changing the initial block polymer/monomer ratio. The nanostructural transition occurs by a grafting from mechanism in which poly­(styrene) chains are initiated from the poly­(butadiene) block via the creation of an allylic radical, which increases the overall molecular weight and the poly­(styrene) volume fraction. The work presented here highlights how the chemical process of converting standard linear diblock copolymers to grafted block polymers drives interesting and controllable polymerization-induced morphology transitions

Partial Purification of a Megadalton DNA Replication Complex by Free Flow Electrophoresis

<div><p>We describe a gentle and rapid method to purify the intact multiprotein DNA replication complex using free flow electrophoresis (FFE). In particular, we applied FFE to purify the human cell DNA synthesome, which is a multiprotein complex that is fully competent to carry-out all phases of the DNA replication process in vitro using a plasmid containing the simian virus 40 (SV40) origin of DNA replication and the viral large tumor antigen (T-antigen) protein. The isolated native DNA synthesome can be of use in studying the mechanism by which mammalian DNA replication is carried-out and how anti-cancer drugs disrupt the DNA replication or repair process. Partially purified extracts from HeLa cells were fractionated in a native, liquid based separation by FFE. Dot blot analysis showed co-elution of many proteins identified as part of the DNA synthesome, including proliferating cell nuclear antigen (PCNA), DNA topoisomerase I (topo I), DNA polymerase δ (Pol δ), DNA polymerase ɛ (Pol ɛ), replication protein A (RPA) and replication factor C (RFC). Previously identified DNA synthesome proteins co-eluted with T-antigen dependent and SV40 origin-specific DNA polymerase activity at the same FFE fractions. Native gels show a multiprotein PCNA containing complex migrating with an apparent relative mobility in the megadalton range. When PCNA containing bands were excised from the native gel, mass spectrometric sequencing analysis identified 23 known DNA synthesome associated proteins or protein subunits.</p></div

Separation of IZE fractions by BN gel electrophoresis.

<p>(A) The gels were stained with Coomassie. (B) Separate gels were transferred to PVDF membrane and probed with PCNA antibody. Fraction numbers are labeled on top of the figure.</p

Previously identified DNA synthesome proteins or protein subunits identified by mass spectrometry from BN gel with a relative electrophoretic mobility of 0.8–1 MDa.

<p>Previously identified DNA synthesome proteins or protein subunits identified by mass spectrometry from BN gel with a relative electrophoretic mobility of 0.8–1 MDa.</p

Fractionation of HeLa cell proteins using IZE.

<p>(A) Simplified diagram of the FFE separation chamber. (B) pH measured for every other fraction on the 96-well plate after protein separation. (C) Separation of fractions from the IZE by denaturing gel electrophoresis and detection by silver staining. Fraction numbers are labeled on top, and M represents the mol wt marker. P4 represents the protein before the IZE separation. The molecular masses of the markers are 250 kDa, 150 kDa, 100 kDa, 75 kDa, 50 kDa, 37 kDa, 25 kDa, and 20 kDa labeled A to H from top to bottom.</p

Dot blot analysis of IZE fractions.

<p>(A) Dot blot analysis of an IZE separation from the P4 fraction using antibodies that recognize PCNA, Topo I, Pol ɛ subunit 2, RPA subunit 2, Pol δ catalytic subunit, and RFC subunit 4. Recombinant PCNA (rPCNA) was analyzed following IZE separation of PCNA-FLAG expressed and purified protein. Fraction numbers are labeled at the top of the figure. (B) Dot blot quantification of PCNA. The Western blot signal of each fraction for PCNA from the P4 fraction (black circle) and PCNA-FLAG (blue square) was normalized from 0 to 1.</p