Yoon Mo Koo

Simple Synthesis of Functionalized Superparamagnetic Magnetite/Silica Core/Shell Nanoparticles and their Application as Magnetically Separable High‐Performance Biocatalysts

Uniformly sized silica-coated magnetic nanoparticles (magnetite@silica) are synthesized in a simple one-pot process using reverse micelles as nanoreactors. The core diameter of the magnetic nanoparticles is easily controlled by adjusting the w value ([polar solvent]/[surfactant]) in the reverse-micelle solution, and the thickness of the silica shell is easily controlled by varying the amount of tetraethyl orthosilicate added after the synthesis of the magnetite cores. Several grams of monodisperse magnetite@silica nanoparticles can be synthesized without going through any size-selection process. When crosslinked enzyme molecules form clusters on the surfaces of the magnetite@silica nanoparticles, the resulting hybrid composites are magnetically separable, highly active, and stable under harsh shaking conditions for more than 15 days. Conversely, covalently attached enzymes on the surface of the magnetite@silica nanoparticles are deactivated under the same conditions.

Application of ionic liquids as mobile phase modifier in HPLC

Ionic liquids are receiving an upsurge of interest as ‘green’ solvents; primarily as replacements for conventional media in chemical processes. Although ionic liquids are rather “young” modifier, their great potential in high-performance liquids chromatography (HPLC) has already been demonstrated. This review presents an overview of the applications of ionic liquids as mobile phase modifiers in HPLC.

Highly stable trypsin-aggregate coatings on polymer nanofibers for repeated protein digestion

A stable and robust trypsin‐based biocatalytic system was developed and demonstrated for proteomic applications. The system utilizes polymer nanofibers coated with trypsin aggregates for immobilized protease digestions. After covalently attaching an initial layer of trypsin to the polymer nanofibers, highly concentrated trypsin molecules are crosslinked to the layered trypsin by way of a glutaraldehyde treatment. This process produced a 300‐fold increase in trypsin activity compared with a conventional method for covalent trypsin immobilization, and proved to be robust in that it still maintained a high level of activity after a year of repeated recycling. This highly stable form of immobilized trypsin was resistant to autolysis, enabling repeated digestions of BSA over 40u2005days and successful peptide identification by LC‐MS/MS. This active and stable form of immobilized trypsin was successfully employed in the digestion of yeast proteome extract with high reproducibility and within shorter time than conventional protein digestion using solution phase trypsin. Finally, the immobilized trypsin was resistant to proteolysis when exposed to other enzymes (i.e., chymotrypsin), which makes it suitable for use in “real‐world” proteomic applications. Overall, the biocatalytic nanofibers with trypsin aggregate coatings proved to be an effective approach for repeated and automated protein digestion in proteomic analyses.

β-Glucosidase coating on polymer nanofibers for improved cellulosic ethanol production

Abstractβ-Glucosidase (βG) can relieve the product inhibition of cellobiose in the cellulosic ethanol production by converting cellobiose into glucose. For the potential recycled uses, βG was immobilized and stabilized in the form of enzyme coating on polymer nanofibers. The βG coating (EC-βG) was fabricated by crosslinking additional βG molecules onto covalently attached βG molecules (CA-βG) via glutaraldehyde treatment. The initial activity of EC-βG was 36 times higher than that of CA-βG. After 20xa0days of incubation under shaking, CA-βG and EC-βG retained 33 and 91% of each initial activity, respectively. Magnetic nanofibers were also used for easy recovery and recycled uses of βG coating. It is anticipated that the recycled uses of highly active and stable βG coating can improve the economics of cellulosic ethanol production so long as economical materials are employed as a host of enzyme immobilization.

“Bottom-up” approach for implementing nano/microstructure using biological and chemical interactions

The “Bottom-up” approach for implementing nano/microstructure using biological self-assembled systems has been investigated with tremendous interest by many researchers in the field of medical diagnostics, material synthesis, and nano/microelectronics. As a result, the techniques for achieving these systems have been extensively explored in recent years. The developed or developing techniques are based on many interdisciplinary areas such as biology, chemistry, physics, electrical engineering, mechanical engineering, and so on. In this paper, we review the fundamentals behind the self-assembly concepts and describe the state of art in the biological and chemical self-assembled systems for the implementation of nano/microstructures. These structures described in the paper can be applied to the implementation of hybrid biosensors, biochip, novel bio-mimetic materials, and nano/microelectronic devices.

Separation of amino acids by simulated moving bed using competitive Langmuir isotherm

The separation of two amino acids, phenylalanine and tryptophan, was carried out using laboratory simulated moving bed (SMB) chromatography. The SMB process consisted of four zones, with each zone having 2 columns. The triangle theory was used to obtain the operating conditions for the SMB. The mass transfer coefficients of the two amino acids were obtained from the best-fit values by comparing simulated and experimental pulse data. The competitive adsorption isotherms of the two amino acids were obtained by single and binary frontal analyses, taking into consideration the competition between the two components. A competitive Langmuir isotherm, obtained from single-component frontal chromatography, was used in the first run, and the isotherm from binary frontal chromatography in the second, with the flow rate of zone I modified to improve the purity. Compared to the first and second runs, the competitive Langmuir isotherm from the binary frontal chromatography showed good agreement with the experimental results. Also, adjusting the flow rate in zone I increased the purity of the products. The purities of the phenylalanine in the raffinate and the tryptophan in the extract were 99.84 and 99.99%, respectively.

Effect of mobile phase additives on resolution of some nucleic compounds in high performance liquid chromatography

Here we investigate the chromatographic behavior, with reversed-phase high performance liquid chromatography (RP-HPLC) of nucleic compounds (nucleobases, nucleosides, and nucleotides) on a C18 column in several different mobile phase additives, including1-butyl-3-methylimidazolium tetrafuloroborate ([BMIm][BF4]), 1-ethyl-3-methylimidazolium methylsulfate ([EMIm][MS]) ionic liquids, ammonium formate, and potassium phosphate. The effect of the alkyl group length, the imidazolium ring, and the ionic liquids counterions on retention and resolution of the samples were tested. The results show the potential application of a used buffer system, ion pairing system, and ionic liquid as mobile phase additives in liquid chromatography resolution of nucleic compounds.

Sensitivity analysis of amino acids in simulated moving bed chromatography

We conducted a sensitivity analysis of the simulated moving bed (SMB) chromatography with the case model of the separation of two amino acids phenylalanine and tryptophan. We consider a four-zone SMB chromatography where the triangle theory is used to determine the operating conditions. Competitive Langmuir isotherm model was used to determine the adsorption isotherm. The finite difference method is used to solve nonlinear partial differential equation (PDE) systems numerically. We examined the effects of alterations in the operating conditions (feed-extract, feed-raffinate, eluent-extract, eluent-raffinate, recycle, and switching time) and the adsorption isotherm parameters (Langmuir isotherm parametersa andb) on SMB efficiency. The variation range of operating conditions and Langmuir isotherma was between −50 and 50% of original value and the variation range of the Langmuir isothermb was between 2.25−5 and 2.255 times of original value.

Single and Competitive Isotherms of Phenol and o-Cresol by Pulsed-Input Method

There is a considerable industrial interest in both the scale-up and optimization of chromatographic operations used in the purification of fine chemicals and biomolecules. One of the major factors affecting the adsorption operation is the adsorption isotherm. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used to measure the adsorption isotherm of phenol ando-cresol. From the experimental results, the retention times were decreased with increasing sample sizes, and the front of the peak was very stiff, so Langmuir adsorption isotherm was applied. Also Early-eluting component, phenol, in a mixture of the two components elutes faster than that in a pure component. Pulsed-injection method (PIM) was used to determine the two parameters of the Langmuir isotherm. The resulting parameters, a and b, were used to calculate the elution profiles of phenol ando-cresol in pure and mixed state. The agreement between the experimental data and calculated elution profiles was fairly good in a mixture as well as a pure component.

Comparing the performance of one-column process and four-zone simulated moving bed by computer simulation

A new one-column chromatography process, analogous to a four-zone simulated moving bed (SMB), was presented. The basic principle of the process was identical to that of a four-zone SMB. The process consisted of one chromatographic column and four tanks, instead of the four columns in the four-zone SMB (1-1-1-1), and has been used for the separation of two amino acids, phenylalanine and tryptophan, using an ion exchange resin. The operating parameters for the one-column process and four-zone SMB were obtained from equilibrium theory. Computer simulations were used to compare the performances of the new one column process to that of the general four-zone SMB, using Aspen Chromatography™ v 11.1. The differences between the one-column and SMB processes in terms of the purities and yields of phenylalanine and tryptophan were less than 4 and about 6%, respectively. The lower purities of the one-column process were due to the loss of the developed concentration profiles in the column when the liquid was stored in tanks. The one-column process gave great flexibility, and would be useful for reconstructing an existing conventional chromatography process to one of a SMB.