Jin-Hyun Kim

A Passive Circulator with High Isolation using a Directional Coupler for RFID

In radio-frequency identification (RFID) system, a directional coupler has been used to isolate RX from TX due to its simplicity and low cost compared with a circulator. Nevertheless, a conventional microstrip directional coupler has inherent drawback of poor isolation due to unequal phase velocity between even and odd mode. In this paper, a newly proposed circulator using a microstrip directional coupler is proposed to achieve good isolation between TX and RX. The proposed circulator is used for UHF band RFID reader with a single antenna, of which the operating frequency band is 860 MHz-960 MHz. The measurement of the fabricated circulator using a modified directional coupler exhibits excellent isolation of 64 dB and directivity of 49 dB in its frequency band. The validity of the proposed circulator is demonstrated by comparing the TX leakage at the RX port of RFID reader system with that of a conventional directional coupler

High-throughput screening system based on phenolics-responsive transcription activator for directed evolution of organophosphate-degrading enzymes

Synthetic organophosphates (OPs) have been used as nerve agents and pesticides due to their extreme toxicity and have caused serious environmental and human health problems. Hence, effective methods for detoxification and decontamination of OPs are of great significance. Here we constructed and used a high-throughput screening (HTS) system that was based on phenolics-responsive transcription activator for directed evolution of OP-degrading enzymes. In the screening system, phenolic compounds produced from substrates by OP-degrading enzymes bind a constitutively expressed transcription factor DmpR, initiating the expression of enhanced green fluorescent protein located at the downstream of the DmpR promoter. Fluorescence intensities of host cells are proportional to the levels of phenolic compounds, enabling the screening of OP-degrading enzymes with high catalytic activities by fluorescence-activated cell sorting. Methyl parathion hydrolase from Pseudomonas sp. WBC-3 and p-nitrophenyl diphenylphosphate were used as a model enzyme and an analogue of G-type nerve agents, respectively. The utility of the screening system was demonstrated by generating a triple mutant with a 100-fold higher k(cat)/K(m) than the wild-type enzyme after three rounds of directed evolution. The contributions of individual mutations to the catalytic efficiency were elucidated by mutational and structural analyses. The DmpR-based screening system is expected to be widely used for developing OP-degrading enzymes with greater potential.

A Passive Circulator for RFID Application with High Isolation using a Directional Coupler

In this paper, a newly invented circulator for T/R switch of UHF radio-frequency identification (RFID) application is proposed to overcome TX-to-RX leakage problem. A microstrip coupled-line directional coupler is used for this passive circulator and the isolation characteristic is drastically improved not by complex method such as compensating phase velocity, but by considering both directional coupler itself and imperfect input impedance of the employed antenna. The measurement result of the proposed circulator using modified microstrip coupled-line directional coupler with employed antenna shows excellent TX-to-RX leakage suppression in the 860 MHz - 960 MHz, more than 45 dB enhancement at the center frequency compared to the conventional coupler. Experimental verification using RFID system is also performed to prove the validity of the proposed circulator

Design and Evolution of Biocatalysts

Enzymes as biocatalysts offer several advantages over their chemical counterparts, and as such have attracted much attention for use in the synthesis of various organic compounds. However, despite many successes in the practical application of enzymes, the ex- tensive use of enzymes in the synthesis of organic compounds is still hindered by inadequacy in substrate specificity, catalytic activity, enantio-selectivity and stability. Enzymes with desired functions targeted for practical applications have long been a goal in pro- tein/enzyme engineering. Many approaches have been developed and employed for redesigning enzymes with desired properties, includ- ing the structure-guided rational method, directed evolution, computational methods, and combinatorial methods. This review will cover recent advances in the design and evolution of enzymes targeted for specific properties, focusing on the strategy and the applicability of each approach.

A Genetic Circuit System Based on Quorum Sensing Signaling for Directed Evolution of Quorum-Quenching Enzymes

Quorum sensing is a cell–cell communication mechanism that is involved in the regulation of biological functions such as luminescence, virulence, and biofilm formation. Quorum‐quenching enzymes, which interrupt quorum‐sensing signaling through degradation of quorum‐sensing molecules, have emerged as a new approach to controlling and preventing bacterial virulence and pathogenesis. In an effort to develop quorum‐quenching enzymes with improved catalytic activities, a genetic circuit system based on acylhomoserine‐lactone (AHL)‐mediated quorum‐sensing signaling was constructed. The genetic circuit system was composed of lux‐R, lux‐I promoter, β‐lactamase, and β‐lactamase inhibitor, and designed to confer antibiotic resistance on host cells expressing an AHL‐degrading enzyme, thereby enabling rapid screening of quorum‐quenching enzymes. To demonstrate the utility of the genetic circuit system, we attempted the directed evolution of the AHL hydrolase from Bacillus sp. The genetic circuit system was shown to be effective in screening of quorum‐quenching enzymes with high catalytic efficiency. From these results it is expected that the genetic circuit system can be widely used for the isolation and directed evolution of quorum‐quenching enzymes with greater potential.

Self-Assembled Peptide-Carbon Nitride Hydrogel as a Light-Responsive Scaffold Material

Peptide self-assembly is a facile route to the development of bioorganic hybrid materials that have sophisticated nanostructures toward diverse applications. Here, we report the synthesis of self-assembled peptide (Fmoc-diphenylalanine, Fmoc-FF)/graphitic carbon nitride (g-C3N4) hydrogels for light harvesting and biomimetic photosynthesis through noncovalent interactions between aromatic rings in Fmoc-FF nanofibers and tris-s-triazine in g-C3N4 nanosheets. According to our analysis, the photocurrent density of the Fmoc-FF/g-C3N4 hydrogel was 1.8× higher (0.82 μA cm-1) than that of the pristine g-C3N4. This is attributed to effective exfoliation of g-C3N4 nanosheets in the Fmoc-FF/g-C3N4 network, facilitating photoinduced electron transfers. The Fmoc-FF/g-C3N4 hydrogel reduced NAD+ to enzymatically active NADH under light illumination at a high rate of 0.130 mol g-1 h-1 and drove light-responsive redox biocatalysis. Moreover, the Fmoc-FF/g-C3N4 scaffold could well-encapsulate key photosynthetic components, such as electron mediators, cofactors, and enzymes, without noticeable leakage, while retaining their functions within the hydrogel. The prominent activity of the Fmoc-FF/g-C3N4 hydrogel for biomimetic photosynthesis resulted from the easy transfer of photoexcited electrons from electron donors to NAD+ via g-C3N4 and electron mediators as well as the hybridization of key photosynthetic components in a confined space of the nanofiber network.

Design of N-acyl homoserine lactonase with high substrate specificity by a rational approach

N-Acyl homoserine lactone (AHL) is a major quorum-sensing signaling molecule in many bacterial species. Quorum-quenching (QQ) enzymes, which degrade such signaling molecules, have attracted much attention as an approach to controlling and preventing bacterial virulence and pathogenesis. However, naturally occurring QQ enzymes show a broad substrate spectrum, raising the concern of unintentionally attenuating beneficial effects by symbiotic bacteria. Here we report the rational design of acyl homoserine lactonase with high substrate specificity. Through docking analysis, we identified three key residues which play a key role in the substrate preference of the enzyme. The key residues were changed in a way that increases hydrophobic contact with a substrate having a short acyl chain (C4-AHL) while generating steric clashes with that containing a long acyl chain (C12-AHL). The resulting mutants exhibited a significantly shifted preference toward a substrate with a short acyl chain. Molecular dynamics simulations suggested that the mutations affect the behavior of a flexible loop, allowing tighter binding of a substrate with a short acyl chain.

Capacitively Coupled Band-Stop Filter with an Integrated Antenna

A new antenna with a band-stop filter is presented. This device integrates a capacitively coupled band-stop filter with a printed planar monopole antenna. This new device is suitable for creating a wideband antenna with narrowband interferer rejection characteristics

Unbiased biocatalytic solar-to-chemical conversion by FeOOH/BiVO 4 /perovskite tandem structure

Redox enzymes catalyze fascinating chemical reactions with excellent regio- and stereo-specificity. Nicotinamide adenine dinucleotide cofactor is essential in numerous redox biocatalytic reactions and needs to be regenerated because it is consumed as an equivalent during the enzymatic turnover. Here we report on unbiased photoelectrochemical tandem assembly of a photoanode (FeOOH/BiVO4) and a perovskite photovoltaic to provide sufficient potential for cofactor-dependent biocatalytic reactions. We obtain a high faradaic efficiency of 96.2% and an initial conversion rate of 2.4 mM h−1 without an external applied bias for the photoelectrochemical enzymatic conversion of α-ketoglutarate to l-glutamate via l-glutamate dehydrogenase. In addition, we achieve a total turnover number and a turnover frequency of the enzyme of 108,800 and 6200 h−1, respectively, demonstrating that the tandem configuration facilitates redox biocatalysis using light as the only energy source.Photoelectrochemical (PEC) cell platforms typically need an electrical bias that drives the electron transfer from the photoanode to the photocathode. Here, the authors report a bias-free PEC tandem device for solar-driven redox biocatalysis.

Biocatalytic C=C Bond Reduction through Carbon Nanodot‐Sensitized Regeneration of NADH Analogues

Light-driven activation of redox enzymes is an emerging route for sustainable chemical synthesis. Among redox enzymes, the family of Old Yellow Enzyme (OYE) dependent on the nicotinamide adenine dinucleotide cofactor (NADH) catalyzes the stereoselective reduction of α,β-unsaturated hydrocarbons. Here, we report OYE-catalyzed asymmetric hydrogenation through light-driven regeneration of NADH and its analogues (mNADHs) by N-doped carbon nanodots (N-CDs), a zero-dimensional photocatalyst. Our spectroscopic and photoelectrochemical analyses verified the transfer of photo-induced electrons from N-CDs to an organometallic electron mediator (M) for highly regioselective regeneration of cofactors. Light triggered the reduction of NAD+ and mNAD+ s with the cooperation of N-CDs and M, and the reduction behaviors of cofactors were dependent on their own reduction peak potentials. The regenerated cofactors subsequently delivered hydrides to OYE for stereoselective conversions of a broad range of substrates with excellent biocatalytic efficiencies.