Papers by Author: Jeong Ho Chang

Abstract: This work reported the development of the high throughput protein separation process with molecularly assembled silica-coated magnetic nanoparticles as a function of amino group numbers such as mono-, di-, and tri-aminofunctionality, in which the range of silica coating thicknesses were optimized to be interacted with protein. The protein separation efficiency was demonstrated as a function of each aminofunctional group and the particle sizes of the silica coated magnetic nanoparticles. The particles were prepared by the chemical precipitation of Fe2+ and Fe3+ salts with a molar ratio of 1:2 under basic solution. The silica coated magnetic nanoparticles were directly produced by the sol-gel reaction of a tetraethyl orthosilicate (TEOS) precursor, in which the coating layer serves as a biocompatible and versatile group for further biomolecular functionalization. To effectively capture the proteins, silica coated magnetic nanoparticles need to be functionalized reproducibly on the silica surface, and three kinds of amino functional groups were adapted as a function of number of amine using the mono-, di-, and tri-aminopropylalkoxysilanes.

Abstract: This study describes the development of a high throughput purification process of nucleic acid using amino-functionalized silica coated ferrite nanoparticles. The magnetic ferrite nanoparticles were synthesized and coated by a silica precursor in controlling the coating thicknesses and sizeses. The surface modification was performed with amino-functionalized organic silanes on silica coated magnetic nanoparticles. The spectroscopic measurements such as a FT-IR (ATR-method) and Vibrational Sample Magnetometer (VSM) were used to characterize the chemical structures and magnetic strengths. To elucidate the relationship between surface area, pore size distribution and reactivity of the materials, BET and Zeta potential were used. The use of functionalized self-assembled magnetic ferrite nanoparticles for a nucleic acid separation process provides a lot of advantages compared to the conventional silica based process.

Abstract: Selected MPEG-b-PDLLA block copolymers have been synthesized by ring-opening polymerization with systematic variation of the chain lengths of the resident hydrophilic and hydrophobic blocks. The size and shape of the micelles that spontaneously form in solution are then controlled by the characteristics of the block copolymer template. All the materials prepared in this study showed the tunable pore size of 20-80Å with the increase of hydrophobic chain lengths and up to 660m2/g of specific surface area. The formation mechanism of these nanoporous structures obtained by controlling the micelle size has been confirmed using both liquid and solid state 13C and 29Si NMR techniques. This work verifies the formation mechanism of nanoporous structures in which the pore size and wall thickness are closely dependent on the size of hydrophobic cores and hydrophilic shells of the block copolymer templates.

Abstract: This work describes an innovative approach to preparation of the highly controlled drug delivery materials that involves a self-assembly process at the molecular level based upon the silicified L3 phase silicates and thermoresponsive PNIPAm integrated L3 phase silicates. The materials designed by the integration of thermosensitive polymer have been prepared and demonstrated for the highly controlled drug releasing system over a longer period of time due to their high degree of continuity and contigunity in 3-D interconnected porous structure. This approach is suitable for long term drug delivery systems with constant release in hard tissue engineering due to nanodiffusion mechanism. The structural characterization was achieved by TEM, SEM, SAXD, solid-state 29Si NMR, and BET.

Abstract: This work describes chemically functionalized nanoporous silica as a novel catalyst for the rapid hydrolysis of a phenyl ester. Work demonstrates a very simple and flexible approach to control surface reactivity on the nanometer scale using a self-assembled organic monolayer consisting of polar, (dihydroxyl, carboxyl, ethylene-diamine, and dihydroimidazole), and non-polar (isobutyl) groups. All five functional groups are an essential requirement in preparing an enzymelike catalyst because of the synergistic effect and hydrophobic partitioning, which has been verified by a 13C CP- MAS solid-state NMR technique. Catalytic activities were obtained from the catalytic efficiency constant and specificity constant using Michaelis-Menten kinetics. Catalytic activities were close to those of a natural enzyme when 12% of the surface was covered by hydrophobic isobutyl silane. The rate of enzyme catalyzed activity was dependent on the energy of the transition state as defined in terms of an energy barrier derived from the relationship between transfer free energy and specificity constant.