Jong-Hui Kim

OPTIMAL PRODUCTION OF L-threo-2,3-DIHYDROXYPHENYLSERINE (L-threo-DOPS) ON A LARGE SCALE BY DIASTEREOSELECTIVITY-ENHANCED VARIANT OF L-THREONINE ALDOLASE EXPRESSED IN Escherichia coli

This study examined the efficient production and optimal separation procedures for pure L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) from a mixture of diastereomers synthesized by whole-cell aldol condensation reaction, harboring diastereoselectivity-enhanced L-threonine aldolase in Escherichia coli JM109. The addition of the reducing agent sodium sulfite was found to stimulate the production of L-threo-DOPS without affecting the diastereoselectivity ratio, especially at the 50 mM concentration. The optimal pH for diastereoselective synthesis was 6.5. The addition of Triton X-100 also strongly affected the synthesis yield, showing the highest conversion yield at a 0.75% concentration; however, the diastereoselectivity of the L-threonine aldolase was not affected. Lowering the temperature to 10°C did not significantly affect the diastereoselectiviy without affecting the synthesis rate. At the optimized conditions, a mixture of L-threo-DOPS and L-erythro-DOPS was synthesized by diastereoselectivity-enhanced L-threonine aldolase from E. coli in a continuous process for 100 hr, yielding an average of 4.0 mg/mL of L-threo-DOPS and 60% diastereoselectivity (de), and was subjected to two steps of ion exchange chromatography. The optimum separation conditions for the resin and solvent were evaluated in which it was found that a two-step process with the ion-exchange resin Dowex 50 W × 8 and activated carbon by washing with 0.5 N acetic acid was sufficient to separate the L-threo-DOPS. By using two-step ion-exchange chromatography, synthesized high-purity L-threo-DOPS of up to 100% was purified with a yield of 71%. The remaining substrates, glycine and 3,4-dihydroxybenzaldehyde, were recovered successfully with a yield of 71.2%. Our results indicate this potential procedure as an economical purification process for the synthesis and purification of important L-threo-DOPS at the pharmaceutical level.

Improved supercapacitor potential and antibacterial activity of bimetallic CNFs–Sn–ZrO2 nanofibers: fabrication and characterization

The objective of our study was to develop a new class of one-dimensional Sn–ZrO2 nanocrystal decorated CNFs. The utilized CNFs–Sn–ZrO2 composite was prepared by a sol–gel electrospinning method using polyacrylonitrile, ZrO(NO3)3·2H2O and SnCl2·6H2O as precursors. The physicochemical properties of the synthesized samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The bimetallic CNFs–Sn–ZrO2 composite possessed higher electrochemical capacitance and better stability than the monometallic and pristine samples as supercapacitor electrode materials. The CNFs–Sn–ZrO2 composite also exhibited admirable antibacterial activity. From the antimicrobial kinetic test results of E. coli; it was established that the composite (CNFs–Sn–ZrO2) possessed enhanced bactericidal activity compared to monometallic ones. The obtained high supercapacitance and bactericidal potential can be attributed due to the synergistic effect of Sn and ZrO2 in the carbon nanofibrous matrix. These results suggest the applicability of the fabricated nanofibers as electrode materials for supercapacitors and as antibacterial agents for decontamination of water.

Preparation and characterization of fermented dandelion (Taraxacum officinale) beverage using Lactobacillus acidophilus F46 having cinnamoyl esterase activity

The purpose of this study was to develop probiotic functional beverage with enhanced physiochemical properties by utilizing dandelion due to its high nutritional value. Lactic acid bacteria obtained from human feces were screened based on bacterial survival ability and cinnamoyl esterase (CE) activity. Dandelion extract fermented by Lactobacillus acidophilus F-46 maintained approximately 105–106 log CFU/mL over an 8 days period. Antioxidant activity by using DPPH radical scavenging activity of the prepared fermented dandelion beverage (FDB) were significantly increased compared to that of non-fermented dandelion beverage (NFDB). Moreover, CE activity was significantly enhanced during fermentation and showed the approximately 4.3 times increased concentration of caffeic acid up to 9.91 mg/100 mL after 8 days of incubation compared to NFDB. Therefore, it concluded that dandelion can be a good source for preparing a functional beverage and fermentation by LA-F46 enhanced the food functionality with enhanced caffeic acids.