Crystallization of DNA‐Capped Gold Nanoparticles in High‐Concentration,Divalent Salt Environments

The multiparametric nature of nanoparticle self‐assembly makes it challenging to circumvent the instabilities that lead to aggregation and achieve crystallization under extreme conditions. By using non‐base‐pairing DNA as a model ligand instead of the typical base‐pairing design for programmability, long‐range 2D DNA–gold nanoparticle crystals can be obtained at extremely high salt concentrations and in a divalent salt environment. The interparticle spacings in these 2D nanoparticle crystals can be engineered and further tuned based on an empirical model incorporating the parameters of ligand length and ionic strength.     

An efficient synthesis of the 4'-epimer of 2-fluoronoraristeromycin

The 4'-epimer of 2-fluoronoraristeromycin was synthesized by employing bis-t-butoxycarbonyl (Boc) protected 2-fluoroadenine as a superior substrate for the Mitsunobu reaction with the appropriate cyclopentenol. Unlike the unsubstituted counterpart 2-fluoroadenine, this substrate is completely soluble in THF and resulted in a very good yield in the Mitsunobu coupling reaction as well as subsequent steps.     

Evaporation of polydispersed droplets in a highly turbulent channel flow

A model experiment for the study of evaporating turbulent two-phase flows is presented here. The study focuses on a situation where pre-atomized and dispersed droplets vaporize and mix in a heated turbulent flow. The test bench consists in a channel flow with characteristics of homogeneous and isotropic turbulence where fluctuations levels reach very high values (25% in the established zone). An ultrasonic atomizer allows the injection of a mist of small droplets of acetone in the carrier flow. The large range diameters ensure that every kind of droplet behavior with regards to turbulence is possible. Instantaneous concentration fields of the vaporized phase are extracted from fluorescent images (PLIF) of the two phase flow. The evolution of the mixing of the acetone vapor is analyzed for two different liquid mass loadings. Despite the high turbulence levels, concentration fluctuations remain significant, indicating that air and acetone vapor are not fully mixed far from the injector.     

NMR investigations into heterogeneous structures of thermosensitive microgel particles

The internal properties of submicron poly(N‐isopropylmethacrylamide) latex particles were investigated as a function of the methylene bisacrylamide (MBA) concentration used as a crosslinker. Two experimental approaches were performed. First, quasi‐electric light scattering measurements provided the size variation of the particles as a function of temperature, from which the swelling capacity of the particles as a function of MBA were estimated. In addition, the broadening and lowering effects of the volume phase transition temperature were detected from the turbidity of the solutions versus the MBA concentration. Second, observations of the transverse relaxation of protons gave evidence for heterogeneous structures inside the particles; several structural parts were discriminated from one another from different proton mobilities detected through magnetic relaxation rates. Corresponding to the concentration gradients of the crosslinker, the internal particle structures were looser and looser from the core to the shell. The state of the gelation of the polymer particles was governed by the initial amount of the crosslinker introduced into the latex recipe. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 889–898, 2000     

Measurements of vaporized and liquid fuel concentration fields in a burning spray jet of acetone using planar laser induced fluorescence

Planar LIF of acetone has been performed in the near development field of a burning spray jet. The main difficulty of such investigations comes from the large range of signal levels provided by the vapor and the size dispersed spray, which cannot be covered by the camera dynamics. The key point of the present work lies in a strong compression of the fluorescence signal dynamics as the UV laser radiation is strongly absorbed by the liquid phase. Preliminary experiments were made in homogeneous vapor and with calibrated drops to quantify the acetone fluorescence signals. Analysis of the histograms of signal level in the spray shows that a cut-off signal level can be used to reject the contribution of the liquid phase. The single shot fluorescence profiles have been processed to restore the fields of fluctuating and mean concentration of acetone vapor in the spray. The liquid concentration field was obtained by extracting the individual drops data from the single shot fluorescence images with a reduced gain of the camera. A statistical correction accounting for the discrete extinctions of the laser by the drops has been used. Analysis of the results shows the influence of the input atomization parameters on the structures of the condensed and vaporized concentration fields.     

The x-ray structure of a five-coordinate platinum(II) complex cation

[NEt₄][W₂(CO)₁₀SC₆Cl₅] has been synthesised via the mononuclear pentacarbonyl species and characterised by elemental, IR and X-ray analyses; the bridging W-S-W angle in the dinuclear anion is 132.1°     

Liquid density of biofuel mixtures: (Dibutyl ether + 1-butanol) system at pressures up to 140 MPa and temperatures from (293.15 to 393.15) K

This work reports new experimental density data (445 points) for binary mixtures of (dibutyl ether + 1-butanol) over the composition range (five compositions; 0.15 ? dibutyl ether mole fraction x ? 0.85), from (293.15 to 393.15) K (every 20 K), and for 15 pressures from (0.1 to 140) MPa (every 10 MPa).An Anton Paar vibrating tube densimeter, calibrated with an uncertainty of ±0.5 kg · m^?3 was used to perform these measurements. The experimental density data were fitted with a Tait-like equation with low standard deviations. Excess volumes have been calculated from the experimental data and fitted by the Redlich–Kister equation. In addition, the isobaric thermal expansivity and the isothermal compressibility have been derived from the Tait-like equation.     

Comparison of the safety profiles of PLA50 and Me.PEG-PLA50 nanoparticles after single dose intravenous administration to rat

We compared the safety profiles of two types of nanoparticles intravenously administered to rats, prepared from PLA₅₀ and Me.PEG-PLA₅₀ by emulsification/solvent evaporation using cholate as tensioactive agent. With PLA₅₀/Cholate nanoparticles, no signs of toxicity were noted at 75 mg kg⁻¹. At higher doses, 220 and 440 mg kg⁻¹, marked toxicity (mortality and marked clinical signs) was observed with dose-related hematological changes (decrease of thrombocytes count, increase of Prothrombine Time and Activated Partial Thromboplastin Time) and biochemical changes (increase of aminotransferases activities). All changes were transient and disappeared on Day 9. With Me.PEG-PLA₅₀/Cholate nanoparticles, no lethality and no clinical changes were observed after intravenous administration of Me.PEG-PLA₅₀/Cholate even at high dose, up to 440 mg kg⁻¹. The improved safety profile of Me.PEG-PLA₅₀/Cholate nanoparticles as compared to PLA₅₀/Cholate nanoparticles suggests that the steric repulsion owing to the high density of Me.PEG chains on the nanoparticles surface prevents the coagulation cascade and associated toxicity.     

Effect of orientation on thermoset frontal polymerization

We observed that the velocities of descending thermoset polymerization fronts were strongly affected by the orientation of the tube. The front remained approximately perpendicular to the gravitational vector but propagated almost 1.8 times as fast at 75° along the axis of the tube. We performed a study of the velocity and front‐shape dependence on orientation with propagating fronts of triethylene glycol dimethacrylate with peroxide initiator and acrylamide/bisacrylamide polymerization in dimethyl sulfoxide with persulfate initiator. The percentage increase of velocity was independent of the initiator concentration but strongly dependent on the viscosity. Convection under the front flowed away from the tube wall nearest the vertical axis and was stronger as the angle increased. The front shape also changed, becoming significantly distorted near the wall from which the convection originated. We applied a simple geometric argument to explain the angular dependence for small angles on the basis of the assumption that convection did not affect the velocity of propagation normal to the front. The increase in velocity along the tube axis could be explained by a projection of the normal velocity onto the tube axis, following a 1/cosθ dependence. For higher angles, the convection was not sufficiently strong to maintain a level front. When the difference from a 180° orientation was considered, the velocity dependence exactly followed the geometric relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3504–3508, 2002