In situ neutron reflectometry investigation of gold-chemisorbed PEO layers of varying chain density: relationship of layer structure to protein resistance

In work reported previously [L.D. Unsworth, H. Sheardown, J.L. Brash, Langmuir 21 (2005) 1036] we investigated protein interactions with polyethylene oxide (PEO) layers formed by chemisorption of thiol-PEO on gold. It was shown that, as a function of surface chain density, protein adsorption passed through a minimum. In follow-on work reported here, neutron reflectometry (NR) was used to investigate the formation and properties (volume fraction and chain density) of such PEO layers in situ, i.e., in contact with water. Chain density was varied by varying solubility conditions (far from and near the cloud point) and chemisorption time. Neutron experiments were carried out using neutrons of de Broglie wavelength 2.37 A. Contrast matching techniques were used to improve sensitivity. Layers formed under high solubility conditions were found to have PEO volume fraction, layer thickness and chain density of 0.33, 28 A, and 0.56 chains/nm2, respectively, after 0.5 h chemisorption; and 0.31, 28.5 A, and 0.59 chains/nm2, respectively, after 11 h, suggesting that the layer is fully formed within 0.5 h. Both chain density and PEO volume fraction in the chemisorbed layers were significantly greater when the layers were formed under low solubility conditions. The PEO layers shown in our previous work to have maximum protein resistance were found to have a PEO volume fraction of approximately 40%. Moreover the limiting volume fraction in the PEO films formed under low solubility conditions was approximately 57%, a value similar to the solubility limit of PEO in aqueous solution, suggesting that local regions in the layers may be phase separated under these conditions. This may result in increased hydrophobicity and may explain why protein adsorption was found to increase on the layers of higher chain density.     

A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core

Oxidation of a directly meso-meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin beta-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed at slightly upfield positions. These results have been qualitatively accounted for in terms of the presence of a strong paratropic ring current around the COT core that propagates through the whole pi-electronic network of 3, hence competing with and cancelling the weak diatropic ring currents of the local zinc(II) porphyrins. This explanation was supported by DFT calculation performed at the GIAO-B3LYP/6-31G level, which indicated large positive NICS values within the COT core and small NICS values within the local zinc(II) porphyrins.     

Effect of graphene nanoplatelets as nanofiller in plasticized poly(lactic acid) nanocomposites

Plasticized PLA-based nanocomposites were prepared by melt blending of the matrix with 5 mass% of epoxidized palm oils (EPO) and different amount of graphene nanoplatelets (xGnP). Plasticized PLA (p-PLA) reinforced with 0.3 mass% xGnP resulted in an increase of up to 26.5 and 60.6 % in the tensile strength and elongation at break of the nanocomposites, respectively. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were performed to study the thermal behavior of the prepared nanocomposites. p-PLA reinforced with xGnP shows that increasing the xGnP content triggers a substantial increase in thermal stability. Crystallinity of the nanocomposites as well as cold crystallization and melting temperature did not show any significant changes upon addition of xGnP. However, there is a significant decrease of glass transition temperature up to 0.3 mass% of xGnP incorporation.     

Synthesis of palm oil-based fatty methylhydrazide

Fatty methylydrazides (FMHs) have been successfully synthesized from palm oil. Glycerol was produced as a by-product. The synthesis was carried out by reflux palm oil with methylhydrazine in hexane. FMHs have been characterized using elemental analysis, Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance technique. The results showed that a 6:1 molar ratio of palm oil to methylhydrazine, a round 78 % maximum conversion of palm oil into FMHs and a 10 h reaction time are the optimum reaction conditions.     

Temperature dependent properties and aggregation behaviour of FeCo nanoparticles produced sonoelectrochemically

The study describes synthesis of FeCo nanoparticles by using the pulsed sonoelectrochemical technique, a method which couples an electrochemical process with the employment of high power ultrasound. An ultrasonic horn is also used as the working electrode and is subjected to a pulsed galvanic current and pulsed out of phase ultrasound. Nanoparticles made of FeCo alloy were synthesized at different bath temperatures, in order to study and evaluate the influence of this parameter on process efficiency and nanoparticles’ features. Produced material was characterized by X-EDS, X-Ray diffraction, and finally by transmission electron microscopy. Moreover characterization of nanoparticles’ tendency to aggregation was performed with dynamic light scattering and by using a polyacrilate to stabilize the suspensions. Process efficiency was found to be strongly influenced by temperature, and from chemical analyses, a preferential deposition of iron was observed, due to the lower iron reduction overpotential. Structural characterization stated that FeCo nanoparticles showed a bcc structure and a mean grain size below 30 nm, which depended on synthesis temperature (T) and decreased with T to 5 nm. TEM characterization showed that nanoparticles exhibited the same mean dimensions like ones found from XRD analyses; this led to conclude that nanopowders are monocrystalline.     

Effect of water contact on the density distributions of thin supported polymer films investigated by an X-ray reflectivity method

The diffusion processes of water molecules into polymer films (PMMA/PS homopolymers and random copolymers) in contact with liquid water were investigated using gravimetric methods and X-ray reflectivity (XRR) analysis. Methods of water contact and XRR measurement were designed for studying the systems in the nonequilibrium state of diffusion. Gravimetric measurements confirmed the Fickian diffusion behavior of films in contact with water. Vertical density distributions in PMMA and methylmethacrylate-rich copolymer films demonstrate the existence of a water-rich layer at the interface. However, with further absorption of water into the film, the overall density increased throughout the film. The results suggest that the diffusion of water into the polymer film occurs to recover density uniformity with a high concentration of water molecules at the surface. Some XRR data for the PS- and styrene-rich copolymer films could not be fit and converted to a vertical density distribution because of their huge diffusion coefficients. However, the reflectivity curves for these films and the vertical density distribution after sufficient water contact suggested that the surfaces of these films were commonly diffused after water contact. Atomic force microscopy (AFM) analysis demonstrated that the surface roughness of these films actually increased with water content.     

Giant porphyrin wheels with large electronic coupling as models of light-harvesting photosynthetic antenna

Starting from a 1,3-phenylene-linked diporphyrin zinc(II) complex 2ZA, repeated stepwise Ag(I)-promoted coupling reactions provided linear oligomers 4ZA, 6ZA, 8ZA, and 12ZA. The intramolecular cyclization reaction of 12ZA under dilute conditions (1x10(-6) M) gave porphyrin ring C12ZA with a diameter of approximately 35 A in 60% yield. This synthetic strategy has been applied to a 1,3-phenylene-linked tetraporphyrin 4ZB to provide 8ZB, 12ZB, 16ZB, 24ZB, and 32ZB. The intramolecular coupling reaction of 24ZB gave a larger 24-mer porphyrin ring C24ZB with a diameter of approximately 70 A in 34% yield. These two large porphyrin rings were characterized by means of 1H NMR spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectroscopy, UV-visible spectroscopy, gel permeation chromatography (GPC) analysis, and scanning tunneling microscopy (STM) techniques. The STM images of C12ZA reveal largely circular structures, whereas those of C24ZB exhibit mostly ellipsoidal shapes, indicating more conformational flexibility of C24ZB. Similar to the case of C12ZA, the efficient excitation energy transfer along the ring has been confirmed for C24ZB by using the time-correlated single-photon counting (TCSPC) and picosecond transient absorption anisotropy (TAA) measurements, and occurs with a rate of (35 ps)(-1) for energy hops between neighboring tetraporphyrin subunits. Collectively, the present work provides an important step for the construction of large cyclic-arranged porphyrin arrays with ample electronic interactions as a model of light-harvesting antenna.     

Repeatability and reproducibility of measurements of low dissolved radiocesium concentrations in freshwater using different pre-concentration methods

Journal of Radioanalytical and Nuclear Chemistry - We assessed the repeatability and reproducibility of methods for determining low dissolved radiocesium concentrations in freshwater in Fukushima....     

Microstructural studies of nanocrystalline α-alumina powder produced from Al13-cluster

Nanocrystalline alumina powder was produced from calcinations of Al₁₃-oxalate precipitates at 1100 °C. A nearly normal distribution of agglomerated alumina powder was obtained with an average particle size of about 1 μm. XRD measurement confirmed that the alumina produced was of high purity and crystalline α-phase. Microstructural features of both the precipitates and alumina obtained were studied using the small angle neutron scattering (SANS) technique. SANS examinations show the formation of microstructures in the alumina powder of mass fractals type with dimension of ∼2.8 indicative of low intra-granular porosity.