Controlling Styrene Maleic Acid Lipid Particles through RAFT.

The ability of styrene maleic acid copolymers to dissolve lipid membranes into nanosized lipid particles is a facile method of obtaining membrane proteins in solubilized lipid discs while conserving part of their native lipid environment. While the currently used copolymers can readily extract membrane proteins in native nanodiscs, their highly disperse composition is likely to influence the dispersity of the discs as well as the extraction efficiency. In this study, reversible addition-fragmentation chain transfer was used to control the polymer architecture and dispersity of molecular weights with a high-precision. Based on Monte Carlo simulations of the polymerizations, the monomer composition was predicted and allowed a structure-function analysis of the polymer architecture, in relation to their ability to assemble into lipid nanoparticles. We show that a higher degree of control of the polymer architecture generates more homogeneous samples. We hypothesize that low dispersity copolymers, with control of polymer architecture are an ideal framework for the rational design of polymers for customized isolation and characterization of integral membrane proteins in native lipid bilayer systems.

Linearly polarized emission of an organic semiconductor nanobelt.

Linearly polarized emission has been observed for the nanobelts fabricated from a perylene diimide molecule through both solution-based and surface-supported self-assembling. The measurement of polarized emission was performed over single nanobelts with use of a near-field scanning optical microscope (NSOM) adapted with emission polarization (by putting a planar polarizer before the detector). Rotating the emission polarizer (from 0 degrees to 180 degrees) changed the emission intensity in a way depending on the relative angle between the long axis of the belt and the polarizer with a minimum of intensity detected at ca. 78 degrees, which is indicative of the tilted stacking of molecules along the belt direction.

Superparamagnetic nanoparticle-supported catalysis of Suzuki cross-coupling reactions.

Emulsion polymerization was examined as a novel route for the synthesis of core/shell superparamagnetic nanoparticles consisting of a highly crystalline gamma-Fe2O3 core and a very thin polymeric shell wall. These nanoparticles were used as soluble supports for immobilizing Pd catalysts to promote Suzuki cross-coupling reactions. Recovery of catalysts was facilely achieved by applying a permanent magnet externally. Isolated catalysts were reused for new rounds of reactions without significant loss of their catalytic activity.

Recycling of homogeneous Pd catalysts using superparamagnetic nanoparticles as novel soluble supports for Suzuki, Heck, and Sonogashira cross-coupling reactions.

Recycling of homogeneous catalysts could be achieved by using magnetic nanoparticles and solid-phase beads, but nanoparticle-supported catalysis proceeded much faster than its counterpart on resins.

Superparamagnetic nanoparticle-supported enzymatic resolution of racemic carboxylates.

Candida rugosa lipase immobilized on maghemite nanoparticles demonstrated high stereoselectivity in kinetic resolution of racemic carboxylates and improved long-term stability over its parent free enzyme, allowing the supported enzyme to be repeatedly used for a series of chiral resolution reactions.

A Corrosion Sensor for Monitoring the Early-Stage Environmental Corrosion of A36 Carbon Steel.

An innovative prototype sensor containing A36 carbon steel as a capacitor was explored to monitor early-stage corrosion. The sensor detected the changes of the surface- rather than the bulk- property and morphology of A36 during corrosion. Thus it was more sensitive than the conventional electrical resistance corrosion sensors. After being soaked in an aerated 0.2 M NaCl solution, the sensor's normalized electrical resistance (R/R0) decreased continuously from 1.0 to 0.74 with the extent of corrosion. Meanwhile, the sensor's normalized capacitance (C/C0) increased continuously from 1.0 to 1.46. X-ray diffraction result indicates that the iron rust on A36 had crystals of lepidocrocite and magnetite.

Modulation of chondrocyte behavior through tailoring functional synthetic saccharide-peptide hydrogels.

Tailoring three-dimensional (3D) biomaterial environments to provide specific cues in order to modulate function of encapsulated cells could potentially eliminate the need for addition of exogenous cues in cartilage tissue engineering. We recently developed saccharide-peptide copolymer hydrogels for cell culture and tissue engineering applications. In this study, we aim to tailor our saccharide-peptide hydrogel for encapsulating and culturing chondrocytes in 3D and examine the effects of changing single amino acid moieties differing in hydrophobicity/hydrophilicity (valine (V), cysteine (C), tyrosine (Y)) on modulation of chondrocyte function. Encapsulated chondrocytes remained viable over 21 days in vitro. Glycosaminoglycan and collagen content was significantly higher in Y-functionalized hydrogels compared to V-functionalized hydrogels. Extensive matrix accumulation and concomitant increase in mechanical properties was evident over time, particularly with the presence of Y amino acid. After 21 days in vitro, Y-functionalized hydrogels attained a modulus of 193 ± 46 kPa, compared to 44 ± 21 kPa for V-functionalized hydrogels. Remarkably, mechanical and biochemical properties of chondrocyte-laden hydrogels were modulated by change in a single amino acid moiety. This unique property, combined with the versatility and biocompatibility, makes our saccharide-peptide hydrogels promising candidates for further investigation of combinatorial effects of multiple functional groups on controlling chondrocyte and other cellular function and behavior.

Effect of side-chain substituents on self-assembly of perylene diimide molecules: morphology control.

Effect of side-chain substitutions on the morphology of self-assembly of perylene diimide molecules has been studied with two derivatives modified with distinctly different side-chains, N,N'-di(dodecyl)-perylene-3,4,9,10-tetracarboxylic diimide (DD-PTCDI) and N,N'-di(nonyldecyl)-perylene-3,4,9,10-tetracarboxylic diimide (ND-PTCDI). Due to the different side-chain interference, the self-assembly of the two molecules results in totally different morphologies in aggregate: one-dimensional (1D) nanobelt vs zero-dimensional (0D) nanoparticle. The size, shape, and topography of the self-assemblies were extensively characterized by a variety of microscopies including SEM, TEM, AFM, and fluorescence microscopy. The distinct morphologies of self-assembly have been obtained from both the solution-based processing and surface-supported solvent-vapor annealing. The nanobelts of DD-PTCDI fabricated in solution can feasibly be transferred to both polar (e.g., glass) and nonpolar (e.g., carbon) surfaces, implying the high stability of the molecular assembly (due to the strong pi-pi stacking). The side-chain-dependent molecular interaction was comparatively investigated using various spectrometries including UV-vis absorption, fluorescence, X-ray diffraction, and differential scanning calorimetry. Compared to the emission of ND-PTCDI aggregate, the emission of DD-PTCDI aggregate was significantly red-shifted (ca. 30 nm) and the emission quantum yield decreased about three times, primarily due to the more favorable molecular stacking for DD-PTCID. Moreover, the aggregate of DD-PTCDI shows a pronounced absorption band at the longer wavelength, whereas the absorption of ND-PTCDI aggregate is not significant in the same wavelength region. These optical spectral observations are reminiscent of the previous theoretical investigation on the side-chain-modulated electronic properties of PTCDI assembly.

Nanofibril self-assembly of an arylene ethynylene macrocycle.

Nanofibril structures have been fabricated from an arylene ethynylene macrocycle (AEM), which consists of a square frame corner-joined by four carbazole moieties. The fabrication was performed through a gelating process by cooling a warm, homogeneous solution in cyclohexane at high temperature (e.g., 100 degrees C) to room temperature. During the gelation, the molecules become organized, with optimal pi-pi stacking in cooperation with the side-chain association. The favorable pi-pi stacking facilitates the 1D growth of molecular assembly.