Modeling of the Permeate Flux during Microfiltration of BSA-Adsorbed Microspheres in a Stirred Cell

A study on the variation of the permeate flux was performed in a stirred cell charged with microspheres, to investigate the effects of the stirrer speeds (300, 400, and 600 rpm) and the BSA concentration (0.1, 0.2, 0.4, and 0.8 g/L) under constant pressure. The permeate flux increased over time before the saturation point, but it began to decrease after that point. An increase of the BSA concentration and the stirrer speed resulted in the rapid increase of the permeate flux. This is contrary to the observation of the conventional filtration experiments using a stirred cell. A resistance-in-series model was employed for the modeling of the permeate flux. The cake resistance (R(c), induced by the concentration polarization of microspheres) and the fouling resistance (R(f), induced by the adsorption of BSA inside the membrane pore) must be considered simultaneously for the modeling. These modeling results were in good agreement with the experimental data. These can be applied to the special system considering both R(c) and R(f) as well as the general filtration systems using a stirred cell. Copyright 2000 Academic Press.     

Electric field control of nonvolatile four-state magnetization at room temperature

We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.     

Dipeptide-assisted growth of uniform gallium oxohydroxide spindles

The catalytic dipeptide His–Ser was used as an additive in mineralizing gallium ions to form GaOOH, a solid precursor of Ga₂O₃. This dipeptide was chosen to mimic the enzyme structure of silicatein, similar to the well-known catalytic triad of chymotrypsin. The dipeptide promoted formation of spindle-structured GaOOH under acidic conditions by behaving as a heterogeneous nucleation seed. In contrast, no well-defined, structured gallium species were produced in the absence of dipeptide. The catalytic function of the dipeptide was most pronounced at pH values in the range 3–5, which are lower than the pKa of imidazole in the His side chain. These results suggest that the catalytic role of dipeptide influences the gallium hydroxide conversion and growth. This study suggests that a designed peptide with active functionality can be further exploited to produce inorganic compounds with controlled nucleation and growth.     

Thiolated dextran-coated gold nanorods for photothermal ablation of inflammatory macrophages

Thiolated dextran-coated gold nanorods (DEX-GNRs) were synthesized for targeted delivery to inflammatory macrophages and their photothermal ablation under near-infrared (NIR) light irradiation. Successful synthesis of DEX-GNRs was achieved using thiolated dextran, generated by applying mercaptopropionic acid to transform a hydroxyl group of dextran into a thiol group which has strong binding affinity with surfaces of GNRs. We confirmed both the existence of a thiol group in the functionalized dextran using Ellman's reagent in a thiol group assay and the characteristic band of DEX-GNRs using FT-IR spectrum. Furthermore, a cellular uptake study revealed that dextran showed a superior ability to bind the GNRs surface against macrophages compared to those of PEGylated GNRs with various molecular weights of polyethyleneglycol (PEG). Consequently, an in vitro photothermal irradiation experiment using NIR light indicated that DEX-GNRs exhibited a significant cell-killing efficacy, even with a lower concentration of Au and a low-power light source.     

Effects of Reaction Sequence on the Colloidal Polypyrrole Nanostructures and Conductivity

The relationship between nanoscaled morphology and macroscopic electrical conductivity of polypyrrole (PPy) nanostructures was qualitatively investigated. The PPy nanostructures were prepared via microemulsion polymerization using ionic surfactants. The morphology of PPy was influenced by both the type of ionic surfactants and reaction sequences; specifically, the PPy structures were highly influenced by the reaction sequence when anionic surfactant of SDS was used. By changing reaction sequence, a gel-like PPy was formed influencing on the macroscopic electrical conductivity. The results indicate that the macroscopic conductivity of PPy is affected by its nanoscaled structures as determined by the reaction conditions.     

Hollow silica nanocontainers as drug delivery vehicles

Novel hollow silica nanoparticles (HSNPs) for drug delivery vehicles were synthesized using silica-coated magnetic assemblies, which are composed of a number of Fe(3)O(4) nanocrystals, as templates. The core cavity was obtained by removal of Fe(3)O(4) phase with hydrochloric acid and subsequent calcination at a high temperature. HSNPs were modified by amine in order to introduce positive surface charge and further PEGylated for increased solubility in aqueous medium. Doxorubicin as a model drug was loaded into the HSNPs, and notable sustained drug release from HSNPs was demonstrated.