Chang Ha Lee

Synthesis of magnetic/silica nanoparticles with a core of magnetic clusters and their application for the immobilization of His-tagged enzymes

We synthesized magnetic/silica nanoparticles with a core/shell structure. The average diameter of the spherical particles was approximately 100 nm, and the average thickness of the silica shell was 20 nm. Due to the core of the magnetic clusters, the particles exhibited strong magnetization (21 emu/g). To immobilize His-tagged lipase, copper complexes with three different ligands were anchored to the surfaces of the particles. Up to 70% of the initial activity was obtained after three uses. Differences in the enzymatic activity and ligand-dependent reusability are discussed.

Colorimetric genotyping of single nucleotide polymorphism based on selective aggregation of unmodified gold nanoparticles

We have developed a colorimetric method for genotyping of single nucleotide polymorphism (rs2131877) in 15 human DNA samples using selective aggregation of unmodified gold nanoparticles. First, we designed two different types of oligonucleotide probes with either thymine or cytosine at the end that are perfect complementary to the target allele sequence. After hybridization of the probe and target DNAs, the double-stranded DNA was added to the unmodified gold nanoparticle suspensions. By adjusting the salt concentration, we could induce aggregation of gold nanoparticles exclusively for the samples with the perfectly matched double-stranded DNAs, which resulted in a distinct color change of the suspension. This enabled us to discern samples with three different genotypes of the target sequences by naked eye: (i) the genotype with only T (thymine) alleles; (ii) that with only C (cytosine) alleles; (iii) that with both T and C alleles. We also confirmed these results by an independent direct sequencing method. These results suggest that the selective aggregation of unmodified gold nanoparticles can successfully be used to discern genotypes of single nucleotide polymorphisms.

Heparin-coated superparamagnetic nanoparticle-mediated adeno-associated virus delivery for enhancing cellular transduction

Superparamagnetic iron oxide nanoparticles (SPIONs) have been exploited as an elegant vehicle to enhance gene delivery efficiencies in gene therapy applications. We developed a magnetically guided adeno-associated virus (AAV) delivery system for enhancing gene delivery to HEK293T and PC12 cell lines. Wild-type AAV2 and a novel AAV vector, AAVr3.45, which was directly evolved in a previous study to possess diverse cell tropisms, were used as gene carriers. Additionally, the affinity of each viral vector to heparin was employed as a moiety to immobilize virus onto heparin-coated SPIONs (HpNPs). Magnetically guided AAV delivery resulted fast and efficient cellular transduction. Importantly, a short exposure of virus to target cells under a magnetic field (<180min) yielded comparable transduction produced by the conventional gene-delivery protocol (i.e., 24h-incubation of virus with target cells prior to replacing with fresh medium). Additionally, magnetic guidance of AAV encoding nerve growth factor (NGF) produced sufficient functional NGF, leading to robust neurite elongation by PC12 as compared to direct NGF protein delivery or non-magnetic delivery. The successful establishment of a magnetically guided AAV delivery system, with the ability to efficiently and rapidly infect target cells, will provide a powerful platform for a variety of gene therapy applications.

ADSORPTION AND DESORPTION CHARACTERISTICS OF AIR ON ZEOLITE 5A, 10X, AND 13X FIXED BEDS

Adsorption and desorption experiments for the binary mixture (N2/O2; 79:21 vol%) on zeolite 5A, 10X, and 13X beds were performed to study the dynamic characteristics of air separation adsorption processes. Because the breakthrough and desorption curves showed a tail by temperature variance in the beds, a nonisothermal dynamic model incorporating mass and energy balances was applied to the simulation of adsorption dynamics using the Langmuir–Freundlich model and the LDF approximation. The breakthrough and desorption results were compared among three different beds with respect to the breakthrough and desorption times, tailing effect, and temperature variation with the effects of pressure and flow rate. On the basis of the similar bed density, the order of breakthrough time and desorption time was zeolite 10X, 13X, and 5A beds. Also, the O2 MTZ of the zeolite 10X bed was slightly sharper than those of the zeolite 5A and 13X beds due to more favorable N2 isotherm of zeolite 10X. Furthermore, the breakthrough curve of the zeolite 13X bed showed a relatively long tail. In addition, the breakthrough curves of the zeolite 5A and 13X were similar to adiabatic behavior, whereas that of the zeolite 10X bed showed an isothermal behavior. The N2 desorption experiments were performed by O2 purge under the high pressure conditions. The desorption behaviors were very similar to the results of the breakthrough study, while the thermal effect on the desorption curve was negligible at the beds. The tails of the desorption curves were prominent with a change in the purge flow rate and desorption pressure. In all the beds, the feed and purge rates were more important factors for deciding the breakthrough and desorption times than the adsorption and desorption pressures in the experimental range.

High-performance strategy of a simulated moving bed chromatography by simultaneous control of product and feed streams under maximum allowable pressure drop

In this study, a novel operating strategy was developed to improve the separation performance of simulated moving bed (SMB) chromatography by the simultaneous control of product outlet streams and feed inlet stream (SimCon). The SimCon operation can achieve a high separation performance without exceeding the maximum allowable pressure drop in an SMB system. The SimCon operation consisted of three steps within a single switching period: the initial, middle, and last steps. The extract port and feed-inlet port were closed at the initial step, but the raffinate port was closed at the last step. Therefore, in the SimCon strategy, we introduce two additional operating variables in a switching period, namely the middle time and middle length. In the SimCon operation, the middle step is a key factor to achieving a good separation performance because concentration profiles can be well controlled by two new middle-step variables. The SimCon operation showed outstanding results compared with those of the corresponding conventional SMB and other stream-control strategies in terms of purity, recovery, productivity, and eluent consumption. Because the SimCon operation can be operated with smaller flow and pressure fluctuations than other flow-rate-control strategies and improves the column efficiency, it is expected that the strategy can be practically adapted to real SMB processes with a good separation performance.

Synthesis and characterization of ethosomal contrast agents containing iodine for computed tomography (CT) imaging applications

Abstract As a first step in the development of novel liver-specific contrast agents using ethosomes for computed tomography (CT) imaging applications, we entrapped iodine within ethosomes, which are phospholipid vesicular carriers containing relatively high alcohol concentrations, synthesized using several types of alcohol, such as methanol, ethanol, and propanol. The iodine containing ethosomes that were prepared using methanol showed the smallest vesicle size (392 nm) and the highest CT density (1107 HU). The incorporation of cholesterol into the ethosomal contrast agents improved the stability of the ethosomes but made the vesicle size large. The ethosomal contrast agents were taken up well by macrophage cells and showed no cellular toxicity. The results demonstrated that ethosomes containing iodine, as prepared in this study, have potential as contrast agents for applications in CT imaging.

Combined operation of outlet streams swing with partial-feed in a simulated moving bed

The operational strategy of outlet streams swing (OSS) operation combined with partial-feed (PF) operation, OSS-PF, was studied under the constraint of maximum allowable pressure and flow-rate. Its separation performance and dynamic behavior were compared with those of OSS operation and conventional simulated moving bed (SMB) chromatography. During OSS-PF operation, the switching period consisted of two steps; raffinate was produced during the closed condition of extract node and feed node in the first step, while extracts were produced and feeds were injected during the closed condition of raffinate node in the second step. As a result, OSS-PF operation could be performed under the allowable maximum flow-rate in the corresponding conventional SMB without generating an additional pressure drop at the adsorbent bed, which was different from OSS operation. OSS-PF operation successfully improved the separation performance of the conventional SMB with regard to extract purity, raffinate recovery and raffinate productivity with equivalent eluent consumption. The step ratio during a switching period worked as one of important operating variables in separation performance. The dynamic behavior of OSS-PF operation was analyzed and compared with that of OSS and conventional SMB using simulated concentration profiles in the fluid phase.

Adsorption Breakthrough Dynamics of Zeolites for Ethylene Recovery from Fluid Catalytic Cracking Fuel-gas

The adsorption dynamics of zeolite 13X, 10X and 5A beds was investigated for recovering ethylene (C2H4) from fluidized catalytic cracking fuel-gas. As a feed gas, a ternary mixture (CH4 : C2H4 : C2H6) and a model FCC fuel-gas (CH4 : C2H4 : C2H6 : C3H6 : N2 : H2) were used for breakthrough experiments. In the ternary mixture, the concentration profiles showed similar patterns in all zeolite beds. C2H4 showed higher adsorption affinity than the others in all zeolites and zeolite 5A had the highest adsorption capacity of C2H4. In the six-component mixture, the breakthrough curves in the zeolite 5A bed showed similar patterns to the results of the ternary mixture. Although weak adsorbates could be removed during the adsorption step, CH4 and N2 imparted a steric hindrance to the initial stage of C2H4 adsorption in the zeolite 5A bed. Since vacuum desorption contributed to producing a high purity of C2H4, a pressure vacuum swing adsorption process was recommended to recover C2H4.

Co-processing of heavy oil with wood biomass using supercritical m-xylene and n-dodecane solvents

Heavy oil was co-processed with wood biomass by using supercritical m-xylene and n-dodecane. The effects of the solvent, temperature, hydrogen, and catalyst on vacuum residue (VR) upgrading were evaluated using residue conversion, coke formation, and product distribution as performance parameters. VR was subjected to co-processing with microcrystalline cellulose (cellulose) or oil palm empty fruit bunch fiber (EFB), and the parameters were compared with those obtained from VR upgrading. Co-processing of VR/cellulose using a catalyst and hydrogen led to higher conversion (72.6 wt%) than co-processing of VR/EFB at 400 °C and the highest yield of light product (65.7 wt%). Using the Fe3O4 catalyst with H2 for co-processing positively influenced generation of the light product fraction. VR upgrading and co-processing using supercritical solvents could eliminate a certain amount of sulfur compounds from heavy oil. Co-processing of wood biomass with petroleum feedstocks in existing oil refineries can reduce the capital costs of bulk treatment.