Jimmy Yun

ZIF-derived in situ nitrogen-doped porous carbons as efficient metal-free electrocatalysts for oxygen reduction reaction

We have successfully prepared nanoporous Carbon-L and -S materials by using ZIF-7 as a precursor and glucose as an additional carbon source. Results indicate that Carbon-L and -S show an appropriate nitrogen content, high surface area, robust pore structure and excellent graphitization degree. The addition of an environmentally friendly carbon source – glucose – not only improves the graphitization degree of samples, but also plays a key role in removing residual Zn metal and zinc compound impurities, which makes the resulting materials metal-free in situ nitrogen-doped porous carbons. By further investigating the electrocatalytic performance of these nitrogen-doped porous carbons for oxygen reduction reaction (ORR), we find that Carbon-L, as a metal-free electrocatalyst, shows excellent electrocatalytic activity (the onset and half-wave potentials are 0.86 and 0.70 V vs. RHE, respectively) and nearly four electron selectivity (the electron transfer number is 3.68 at 0.3 V), which is close to commercial 20% Pt/C. Moreover, when methanol was added, the Pt/C catalyst would be poisoned while the Carbon-L and -S would be unaffected. By exploring the current-time chronoamperometric response in 25 000 s, we found that the duration stability of Carbon-L is much better than the commercial 20% Pt/C. Thus, both Carbon-L and -S exhibit excellent ability to avoid methanol crossover effects, and long-term operation stability superior to the Pt/C catalyst. This work provides a new strategy for in situ synthesis of N-doped porous carbons as metal-free electrocatalysts for ORR in fuel cells.

Stabilization of magnetic iron oxide nanoparticles in biological media by fetal bovine serum (FBS).

A facile method of stabilizing magnetic iron oxide nanoparticles (MNPs) in biological media (RPMI-1640) via surface modification with fetal bovine serum (FBS) is presented herein. Dynamic light scattering (DLS) shows that the size of the MNP aggregates can be maintained at 190 ± 2 nm for up to 16 h in an RPMI 1640 culture medium containing ≥4 vol % FBS. Under transmission electron microscopy (TEM), a layer of protein coating is observed to cover the MNP surface following treatment with FBS. The adsorption of proteins is further confirmed by X-ray photoelectron spectroscopy (XPS). Gel electrophoresis and LC-MS/MS studies reveal that complement factor H, antithrombin, complement factor I, α-1-antiproteinase, and apolipoprotein E are the proteins most strongly attached to the surface of an MNP. These surface-adsorbed proteins serve as a linker that aids the adsorption of other serum proteins, such as albumin, which otherwise adsorb poorly onto MNPs. The size stability of FBS-treated MNPs in biological media is attributed to the secondary adsorbed proteins, and the size stability in biological media can be maintained only when both the surface-adsorbed proteins and the secondary adsorbed proteins are present on the particles surface.

What is a Suitable Dissolution Method for Drug Nanoparticles

PurposeMany existing and new drugs fail to be fully utilized because of their limited bioavailability due to poor solubility in aqueous media. Given the emerging importance of using nanoparticles as a promising way to enhance the dissolution rate of these drugs, a method must be developed to adequately reflect the rate-change due to size reduction. At present, there is little published work examining the suitability of different dissolution apparatus for nanoparticles.MethodsFour commonly-used methods (the paddle, rotating basket and flow-through cell from the US Pharmacopia, and a dialysis method) were employed to measure the dissolution rates of cefuroxime axetil as a model for nanodrug particles.ResultsExperimental rate ratios between the nanoparticles and their unprocessed form were 6.95, 1.57 and 1.00 for the flow-through, basket and paddle apparatus respectively. In comparison, the model-predicted value was 7.97. Dissolution via dialysis was rate-limited by the membrane.ConclusionsThe data showed the flow-through cell to be unequivocally the most robust dissolution method for the nanoparticulate system. Furthermore, the dissolution profiles conform closely to the classic Noyes–Whitney model, indicating that the increase in dissolution rate as particles become smaller results from the increase in surface area and solubility of the nanoparticles.

Focused-ion-beam Milling: A Novel Approach to Probing the Interior of Particles Used for Inhalation Aerosols

PurposeThe current study aimed to examine the pharmaceutical applications of the focused-ion-beam (FIB) in the inhalation aerosol field, particularly to particle porosity determination (i.e. percentage of particles having a porous interior).Materials and MethodsThe interior of various spray dried particles (bovine serum albumin (BSA) with different degrees of surface corrugation, mannitol, disodium cromoglycate and sodium chloride) was investigated via FIB milling at customized conditions, followed by viewing under a high resolution field-emission scanning electron microscope. Two sets of ten particles for each sample were examined.ResultsFor the spray-dried BSA particles, a decrease in particle porosity (from 50 to 0%) was observed with increasing particle surface corrugation. Spray-dried mannitol, disodium cromoglycate and sodium chloride particles were determined to be 90–100%, 0–10% and 0% porous, respectively. The porosity in the BSA and mannitol particles thus should be considered for the aerodynamic behaviour of these particles.ConclusionsThe FIB technology represents a novel approach useful for probing the interior of particles linking to the aerosol properties of the powder. Suitable milling protocols have been developed which can be adapted to study other similar particles.

Micronization of silybin by the emulsion solvent diffusion method.

Micronized silybin particles were successfully prepared by emulsion solvent diffusion method. Uniform spherical and rod-shaped particles with a mean size of 2.48 and 0.89 microm could be obtained using sodium dodecyl sulfate (SDS) concentration of 0.1 wt% at 30 and 15 degrees C, respectively. The characterization of silybin particles by SEM and particle size distribution (PSD) indicated that with the increase of temperature from 15 to 30 degrees C, the as-prepared particles became bigger and had a tendency to turn into spherical shapes; with the increase of SDS concentration from 0.02 to 0.1 wt%, the span of PSD became narrower while the mean particle size kept almost unchanged. XRD patterns and FT-IR spectra showed that the spherical and rod-shaped silybin particles possessed decreased crystallinity; however, the chemical structure and components were similar to those of the commercial silybin powder. Dissolution tests demonstrated that both of the spherical and rod-shaped silybin particles exhibited significantly enhanced dissolution rate when compared to the commercial silybin powder.

Nanosized bicalutamide and its molecular structure in solvents

Nanosized bicalutamide particles have been obtained by anti-solvent precipitation after screened DMSO and EtOH as co-solvents. The produced nanoparticles have been characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR), X-ray diffraction (XRD) and a dissolution test. The mean particle size of bicalutamide is about 450nm with a narrow distribution. The results of the dissolution test show that dissolution rate of the produced nanoparticles are higher than that of the raw material. Besides, DFT calculations of the bicalutamide conformers have firstly been presented. It is found that the calculated geometry structure of lower-energy conformer is very similar to the experimental structure existing within the crystal lattice. The solvent effects have been taken into account based on the polarizable continuum model (PCM). The computed results appear that the introduction of dielectric medium has obvious effect on the molecular geometry of bicalutamide.

Preparation of ultrafine fenofibrate powder by solidification process from emulsion

The solidification process from emulsion, which consisted of emulsifier, water and molten drug as oil phase without use of any organic solvent, was firstly employed to prepare ultrafine fenofibrate (FF) powder. The effects of stirring speed and volume ratios of hot emulsion to cold water on the particle size and morphology were discussed as well as the impacts of different emulsifiers on emulsion. The produced ultrafine powder was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, specific surface area analysis and a dissolution test. XRD patterns and FT-IR spectra showed that the ultrafine FF was crystalline powder with the structure and the components similar to those of bulk drug. The product had a mean particle size of about 3 microm with a narrow distribution from 1 microm to 5 microm. The specific surface area reached up to 6.23 m(2)/g, which was about 25 folds as large as that of bulk FF. In the dissolution tests, about 96.1% of ultrafine FF was dissolved after 120 min, while there was only 38.1% of bulk drug dissolved, proving that the dissolution property of ultrafine FF was significantly improved when compared to commercial drug.

Micronization of gemfibrozil by reactive precipitation process

Ultrafine gemfibrozil (GEM) was prepared by reactive precipitation process in which methyl cellulose (MC) was employed to inhibit the growth and the agglomeration of particles. The impact of NaOH concentrations on bulk GEM consumption was explored. The effects of H2SO4 concentrations and the drying methods on the particle size and morphology were also discussed. The produced ultrafine powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, specific surface area analysis and dissolution test. XRD patterns and FT-IR spectra showed that the as-obtained ultrafine GEM was a crystalline powder with the structure and components similar to those of bulk GEM. The ultrafine GEM had a mean particle size of about 1.25 microm with a narrow distribution from 0.6 to 3 microm. The specific surface area reached up to 11.01 m2/g, which was about 6 times as large as that of bulk GEM. In the dissolution tests, about 91.2% of ultrafine GEM was dissolved after 120 min, while there was only 23.6% of bulk GEM dissolved, proving that the dissolution property of ultrafine GEM was significantly enhanced when compared to commercial GEM owing to a decreased particle size and an increased specific surface area.

Dissolution kinetic behavior of drug nanoparticles and their conformity to the diffusion model.

Advances in nanomedicine are expected to escalate in the coming years, particularly related to the availability and delivery of optimum dosage. It is crucial that the dissolution behavior of such novel dosage forms be adequately scrutinized to maximize their therapeutic benefits. In this work, the dissolution behavior of irregularly shaped nanoparticles was analyzed using a modified negative-two-thirds-root diffusion model (with shape factor, sigma, incorporated into the equation to describe shape evolution). The model was shown to be effective in describing the transition from peanut-shape nanoparticles (connected by bridges) to discrete spheres during the dissolution process. Due to the eventual aggregation of the discrete spheres in solution, description of the dissolution behavior was limited to the aggregate as a whole. Scanning electron microscopy, diffusion layer thickness calculations, and sonication studies provide information to show that, during dissolution, the bridges dissolve, yielding discrete spheres which then aggregate randomly in solution. Viscosity experiments reveal that the dissolution behavior was predominantly diffusion-controlled. The dissolution behavior of irregularly shaped nanoparticles in solution is described as going from bridged particles to discrete particles, to aggregates, and finally to full dissolution.

Design, preparation and characterization of cyclic RGDfK peptide modified poly(ethylene glycol)-block-poly(lactic acid) micelle for targeted delivery

Molecular targeted cancer therapy is a promising strategy to overcome the lack of specificity of anticancer drug. While the binding of c(RGDfK) (cyclic Arginine-Glycine-Aspartic acid-Phenylalanine-Lysine) to αvβ3 over-expressed on tumor cell has been validated, the underlying interaction remains poorly understood. In this work, docking calculation was applied to investigate the interactions between c(RGDfK)/c(RGDfK)-PEG and αvβ3. The calculated results indicated that c(RGDfK) interacted with αvβ3 mainly by electrostatic interaction, stabilization interaction, and hydrophobic interaction. Conjugation of PEG chain to the c(RGDfK) weakened the binding affinity of c(RGDfK) to αvβ3. Accordingly, docetaxel(DTX)-loaded target micelles (c(RGDfK)-PEG-PLA/PEG-PLA/DTX) were designed, characterized and evaluated using HeLa cells. In vitro release studies demonstrated both target and non-target micelles displayed almost the same profiles, which best fit in Ritger-Peppas model. Cellular uptake and MTT studies revealed that the target micelles with the presence of c(RGDfK) were more efficiently taken up by HeLa cells and significantly improved the cytotoxicity compared to that of non-target micelles. Cell inhibition rate of target micelles was improved by 20% after 24h. Our findings suggest that target micelles may be a potential anticancer drug delivery system in the treatment of integrin αvβ3 over-expressed on tumor cell.