Prof. Jaesook Yun's research team from the Department of Chemistry developed an effective synthesis method of chiral alkylboron compounds through transition metal catalysis.
The chiral alklyboron compounds are a very useful synthetic intermediary used in various fields such as natural products, medicines, and functional materials, and has received much attention not only from academia but also from the industry. Despite several important research advances have been made in this research field, the conjugate addition with a chiral secondary alkyl metal nucleophile for the C−C bond formation with two contiguous stereogenic centers has been rarely reported and represents an enormous challenge.
The team developed a CuH‐catalyzed asymmetric reductive conjugate addition of borylalkenes to α,β‐unsaturated diesters with high chemo‐, diastereo‐, and enantioselectivity. This method provides efficient and direct access to enantioenriched alkylboron compounds carrying two contiguous stereogenic centers by assembling readily available starting alkenyl reagents in a single operation without using preformed organometallic reagents or chiral auxiliaries, which greatly expands the scope of asymmetric conjugate addition. It was the first case of asymmetric conjugate addition of chiral secondary alkyl, allowing for high yield and selective synthesis of chiral alkylboron compounds with continuous stereogenic centers, which were previously inaccessible.
Moreover, the utility of the resulting products was demonstrated in the efficient synthesis of (−)‐phaseolinic acid and other derivatives. Efforts to expand the use of other chiral alkylcopper species in the asymmetric conjugate addition are currently underway. It is expected to be a very useful synthesis tool for synthesizing bones of important medicines and physiological active substances.
The first author, Dr. Won-jun Jang, conducted this study when he was a pos doc student at SKKU. He is currently serving as a post-doctoral researcher at the University of Chicago Guangbin Dong Group through the "2020 Post-doctoral Training" program organized by National Research Foundation of Korea.
This work was supported by Samsung Science and Technology Foundation under Project Number SSTF‐BA2002‐08 and was published in the world-renowned journal, 'Angewandte Chemie International Edition (ACIE; IF=12.959)' on February 23 (Tue).
※ Paper: Asymmetric Conjugate Addition of Chiral Secondary Borylalkyl Copper Species
A research collaboration team led by Prof. Jin Yong Lee (co-first author: Hao Li, Dept. of Chemistry) and Prof. Jong Seung Kim at Korea University (co-first authors: Dr. Miae Won and Dr. Seyoung Koo) announced that they have developed a new treatment for photodynamic therapy for hypoxic cancer through joint research. Since photodynamic therapy requires reactive oxygen, it has limitations in its application to hypoxic cancer. The research team proposed a new method for photodynamic therapy for hypoxic cancer by simultaneously causing reactive oxygen generation and inhibition of GST-pi.
The joint research team of Sungkyunkwan University and Korea University combines BPS, an existing photosensitizer, with EA to generate reactive oxygen and inhibits GST-pi, an enzyme that interferes with photodynamic therapy by free radicals, to improve the efficiency of photodynamic therapy for hypoxic cancer.
Currently, photodynamic therapy is clinically approved, but reactive oxygen must be present for the treatment. Therefore, there is a limit to application to hypoxic cancer that lacks oxygen around cancer cells. In order to overcome this, various attempts have been made to transport oxygen and to generate oxygen, but there were difficulties due to side reactions from excessive production of active oxygen.
To solve these difficulties, the joint research team improved the performance of photodynamic chemotherapy for hypoxic cancer by covalently binding EA to BPS, an existing photosensitizer. EA-BPS serves to scavenge glutathione (GSH) by delivering EA and reduce the activity of the GST-pi enzyme. In particular, through experiments, it was confirmed that EA-BPS lowered the activity of GST-pi by promoting lysosome decomposition and lipid peroxidation.
In addition, docking and molecular dynamics (MD) simulations were performed to reveal that five residues (chain A: F7, W37 and Y107; chain B: Y107 and A120) play an important role in the active site, and it was revealed that EA-BPS was interacting with GST-pi enzyme pocket through two subunits instead of one subunit.
Professors Lee and Kim said, "The EA-BPS developed in this study has proven its excellent therapeutic effect in a xenograft tumor mouse model, and based on this, we are looking for ways that can be applied to the clinic. It is expected to present a new path for the development of photodynamic therapy for hypoxic cancer."
The results of this study was published in the journal "Angewandte Chemie International Edition (ACIE; IF=12.959)" (Feb 8, 2021).
Prof. Baik's research team and Prof. Son's research team developed a new technique to increase the output voltage of a thermoelectric generator that does not involve material modification.
Thermoelectric energy-harvesting is a technology that produces useful energy by utilizing temperature differences at both ends of the material when heat is applied from the outside. It has attracted a great deal of research interest due to its simplicity, minimal maintenance requirements, low cost, and reliability. It provides a good solution for sustainable energy generation from ambient heat sources.
So far, various types of TE materials, including Bi2Te3, SnTe, PbTe, SnSe, etc., have been developed, and most research has been devoted to enhancing the materials' ZT values using various methods such as nanostructuring, band structure engineering, etc. However, despite recent enhancements in efficiency, major issues with TE power generation technology remain, such as ultralow output voltages and consequent low-energy conversion efficiency, which are rooted in the intrinsic properties of TE materials.
As a solution to these challenges, they created negative charges on the dielectric surface on the low temperature which caused the electric potential difference across the two electrodes to increase and achieved the highest output voltage. In addition, the team successfully demonstrated that the wind increased the output voltage without a significant decrease in wind speed through the pinwheel.
Prof. Baik said "This research is a new method of energy convergence research that can present a new direction to overcome the limitations of thermoelectric energy-harvesting."
The research team has already applied for two related patents and is developing technologies that reach commercialization through study on non-contact thermoelectric energy-harvesting.
This work was supported by the Mid-Career Researcher Program through a National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF2019R1A2C2009822), by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (2019R1A4A1029237), and by the Ministry of Trade, Industry and Energy (MOTIE, 2005721, Korea).
It was published in 'ACS Energy Letters (IF: 19.003, JCR Ranking: 1.852 %)', a world-renowned energy journal on February 2021.
※ Paper: Triboelectric Charge-Driven Enhancement of the Output Voltage of BiSbTe-Based Thermoelectric Generators
※ https://doi.org/10.1021/acsenergylett.0c02483
In recent years, numerous electronics engineers worldwide have been trying to develop new semiconductor heterostructure devices using atomically thin materials. Among the many devices that can fabricated using these materials are resonant tunnelling diodes, which typically consist of a quantum-well structure placed between two barrier layers.
Past research has shown that stacking two-dimensional (2D) layers that are twisted in relation to each other can enhance or suppress the interlayer coupling at their interface. This suppression or enhancement can in turn modulate the electronic, optical and mechanical properties of the resulting device.
For instance, some studies found that the intralayer current transport in small angle twisted bilayer graphene prompted some exotic phenomena, such as superconductivity and ferromagnetism. These observations inspired a fundamentally new approach to device engineering, known as 'twistronics' (i.e., twist electronics).
Researchers at Sungkyunkwan University in South Korea have recently carried out a study aimed at evaluating the potential of a twistronics design for developing resonant tunnelling diodes based on black phosphorus homostructures. The resulting twisted black phosphorus-based resonant tunneling diodes, presented in a paper published in Nature Electronics, exhibit a higher tunnelling conductance than resonant tunnelling diodes based on van der Waals heterostructures.
"Interlayer current transport through twisted junctions could also be an intriguing topic of research that has not yet been explored," Budhi Singh, one of the researchers who carried out the study, said. "This motivated us to investigate interlayer current-transport behavior in twisted black phosphorus-based homostructures."
In a series of laboratory experiments, Singh and his research team identified a number of valuable features that characterize black phosphorus, including its highly anisotropic nature, a thickness-dependent workfunction/2D-carrier density and a twist angle-dependent interlayer coupling. The highly anisotropic nature of black phosphorus ultimately enables a vanishing interlayer coupling strength at specific twist angles.
"Interestingly, we found that the interlayer current-transport in such twisted junctions could be controlled even at higher twist angles," Singh said. "The decoupled interface and momentum mismatch created through twisted Fermi surfaces could also affect the interlayer current-transport behavior and is a part of our primary investigation. In contrast, observation of exotic phenomena in intralayer current transport in twisted junctions is limited to smaller twist angles."
To evaluate the potential of the design strategy they devised, the researchers fabricated a black phosphorus tri-layer homojunction, by integrating a thin layer of black phosphorus between two thicker layers. The middle and thinner layer is twisted in relation to the top and bottom black phosphorus layers.
"Due to the twisted structure in our devices, the decoupled interfaces behave like a tunnel barrier for interlayer charge carrier transport," Singh explained. "If we compare this structure with the conventional double barrier resonant tunnelling diode, middle black phosphorus serves as an analogue of the quantum well."
In the device fabricated by Singh and his colleagues, the emergence of a negative differential resistance and the evolution of peak position with a varying thickness of the middle black phosphorus layer produced a signature typically associated with resonant tunnelling diodes. Resonant tunnelling occurs when the energy and momenta of the top and bottom black phosphorus layers match those of the quantum well states, due to processes of energy and momentum conservation.
"Whenever we talk about tunnelling phenomena, there has to be a physical barrier (i.e., materials with large energy bandgaps)," Singh said. "In general, this architecture is achieved in a heterostructures assembly, but we demonstrated resonant tunnelling through a homostructure without the need of any physical tunnel barrier."
The twistronics design strategy introduced by Singh and his colleagues could soon inspire the fabrication of other devices that exhibit remarkable tunnelling conductance. In the device created by the researchers, the tunnelling mechanism is dominated by a twist-controlled interlayer coupling, which results in a high tunnelling current density. Their diode device and other twist-controlled tunnel devices with high current densities could ultimately be used to realize a variety of high speed electronics, including THz oscillators and ultrafast switches.
"In the near future, we would like to perform experiments to realize twisted black phosphorus homostructures in practical applications, such as THz devices and applications in superconducting spectroscopy."
Prof. Hanyong Bae along with Prof. Benjamin List from the Max Planck Institute in Germany and Dr. Philip Kraft from Givaudan, a Swiss global fragrance and perfume company, revealed that the substance "(+)-2-epi-ziza-6(13)en-3-one" is the principle of the scent of Vetiver through organic synthesis.
Vetiver oil is one of the finest and most popular perfumery materials, appearing in over a third of all fragrances. It is a complex mixture of hundreds of molecules and the specific odorant, responsible for its characteristic suave and sweet transparent, woody-ambery has remained a mystery until today.
The research team successfully performed a high-performance asymmetric Michael addition reaction using the newly developed chiral organocatalyst and a total 11 levels of compounds characterized Pauson-Khand cyclization using cobalt metals.
Its olfactory evaluation reveals a remarkable odor threshold of 29 picograms per liter air. The odor of the compound possesses a transparent woody-ambery note vetiver character. These properties show that the synthesized compound is the main contributor to the typical note of vetiver oil. It revealed that the threshold of scent is more than 150 times stronger than a substance called khusimone, which was considered as the smelling principle of vetiver oil.
Prof. Bae said "It is expected that asymmetric synthesis method and organic synthesis-based technology using chiral catalyst can be widely used in various materials in the fragrance industries."
The study result was selected as "HOT PAPER" in February 2021 by Angewandte Chemie International Edition, a renowned journal in chemistry.
※ Paper: The Smelling Principle of Vetiver Oil, Unveiled by Chemical Synthesis. (Angew. Chem. Int. Ed. 2021, 60, 5666 –5672)
Prof. Jinkee Lee in School of Mechanical Engineering & Institute of Quantum Biophysics has developed a 3D liquid transporting diode surface using nature-inspired technology (first author Dr. MinKi Lee). This liquid transporting system has advantages for easy fabrication, cost-effectiveness, high scalability and shows the world's highest performance with novel 3D structure.
When a liquid droplet is dispensed on the surface, the liquid transports uni-directionally by the passive capillary control from the structures of the liquid diode. Up to now, diode surfaces have been manufactured using lithography processes or 3D printer, which have drawbacks of limited size with complicated manufacturing processes, and also they show low liquid transport performance. Many researchers have been investigating the diode surface but it is quite challenging to increase both the transport performance and the ease of surface manufacturing, simultaneously.
Prof. Jinkee Lee developed nature-inspired diode surface, which mimics the surface from nature such as horned lizard and pitcher plant. The 3D diode surface has a wedge structure consisting of repeating saw-like V-grooves. This surface utilizes the capillary force generated by the 3D topographical shape that pins liquid at one size and makes it flow to the other side. The fabrication of 3D diode surface is easy, fast, cost-effective and scalable because it is processed simply using a laser cutter.
Professor Jinkee Lee said, "This 3D water transport diode surface can be applied as an original technology applying to microfluidic diagnostic chips, material synthesis, heat transfer enhancement and even fog collection because of its superior performance and easy fabrication."
This study was supported by the National Research Foundation of Korea (NRF; 2020R1A2C3010568) and the Korea Environment Industry & Technology Institute (KEITI; 2019002790003), and was published online on March 20, 2021 in Advanced Functional Materials (IF=16.836).
※ Title of paper: "Enhanced Liquid Transport on a Highly Scalable, Cost‐Effective, and Flexible 3D Topological Liquid Capillary Diode"
Expecting replacement of plastics with eco-friendly materials using pollen and solution of water pollution
Prof. Joshua Jackman and Dr. Youngkyu Hwang in Department of Chemical Engineering along with Prof. Namjun Cho at Nanyang Technological University (NTU) developed a pollen sponge from natural materials including sunflower bee pollen, which can solve water pollution such as oil spills in the ocean.
Lately, as interest in the development of eco-friendly materials has increased due to the seriousness of environmental pollution, research using natural materials has been in the spotlight. Especially, pollen, as it is considered the "diamond of biopolymers", it has outstanding structural properties such as chemical and mechanical stability. However, most of pollen is discarded except for the amount used for moisture.
Hence, the research team converted pollen into microgel particles based on a simple chemical process.
By using pollen-based microgel particles, the team made a hydrophobic sponge and it exhibited that the sponge's absorption capacity is 9.7 to 29.3g/g or more. The range is comparable to commercial polypropylene absorbents (8.1-24.6 g/g), and it has been found to be able to selectively absorbs pollutants such as organic solvents, gasoline, and motor oil.
The team said, "Pollen materials, which are produced in plants and mostly discarded, will one day replace widely used plastics and help curb the global problem of plastic pollution."
The research team plans expand the size of sponge in order to meet the expectation of industries and to test it in actual environment in cooperation with non-governmental organization and international partners.
Prof. Joshua Jackman and Prof. Namjun Cho are the co-authors and Dr. Youngkyu Hwang is the first author of this study, and the result was published online in the Advanced Functional Materials (Impact Factor=16.836, JCR ranking Top 4%), a world-renowned journal on March 12 (Fri).
※ Title of paper: Colloid‐Mediated Fabrication of a 3D Pollen Sponge for Oil Remediation Applications
※ Source: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202101091
Professor Joo Sang Lee's research team (Next-Gen Medicine Lab, Department of Artificial Intelligence and School of Medicine) demonstrated that they can identify which therapies may be particularly beneficial for individual patients by only looking at the patients' molecular markup before treatment. When applied to data from a wide panel of different cancer targeted and immunotherapy clinical trials, the approach termed SELECT was successfully predictive of patient responses to these therapies in about 80 percent of the trials. These findings were reported April 13, 2021, in Cell.
The study is based on identifying synthetic lethal interactions - a functional interaction between two genes whose co-inactivation leads to cancer cell death. Over 20 years ago, synthetic lethality has been proposed to have a great potential to revolutionize cancer treatment. This is partly because these interactions provide an opportunity to selectively kill only tumor cells while sparing normal cells by targeting synthetic lethal pairs of specific genes inactivated in a tumor. It has been investigated as a means to treat cancer, with some specific treatment regimens already used in the clinic. However, it is thought that many such treatment opportunities remain to be discovered and SELECT offers a computational method for identifying such treatment options for individual patients. By analyzing tumor transcriptomics data, this approach can identify actionable tumor vulnerabilities that are not readily evident by traditional mutational - and gene fusion-based sequencing approaches.
In collaboration with Eytan Ruppin (Cancer Data Science Laboratory at National Cancer Institute), Joo Sang Lee together with his students Youngmin Chung and Dasol Kim has been leading the development of computational tools to identify synthetic lethality. In this most recent study, they assembled a broad collection of 35 published transcriptomic datasets from targeted and immunotherapy cancer clinical trials across 10 different cancer types. They applied SELECT to predict the treatment response of the patients, given their tumor molecular data, finding the SELECT signatures to be highly accurate in 80 percent of the trials.
"To the best of our knowledge, SELECT is the first approach that systematically achieves these moderate, but helpful levels of accuracy across many different therapies and cancer types," Lee says. Further investigation is now underway in collaboration with several clinical teams at the NIH Clinical Center to bring SELECT into clinic. The team hopes these prospective studies will further improve SELECT in the next few years, and if successful, establish SELECT as a complementary precision oncology approach for enhancing cancer-patient care.
The research team of professor Young-joon Kim(co-author), SKKU Advanced Institute of Nano Technology, announces that they developed high-density electrode design technology that reduces size of lithium-ion batteries through graphene (Gr) coating with Chang-won Park (first author, Ph.D. course) and other researchers.
For the existing high-nickel layered anode materials, they have limitations in increasing electrode density due to low strength of particles, and carbon-black materials used as conductive additives are an obstacle to increasing electrode density due to inefficient distribution.
As a way to overcome these problems, Gr of fine particles with excellent electronic conductivity is uniformly coated on the surface of the electrode material to effectively induce the transfer of electrons and reduce friction between particles of anode materials.
By coating on the surface of the anode materials, the use of conductive additives and binders was minimized. This secured 880mAh/cc high-energy electrode technology that overcame 700mAh/cc, which was considered the limit of capacity density of lithium-ion battery anodes, by more than 25%.
The research team announced that Gr costing with excellent electronic conductivity, which is different from the existing technology of Gr oxide coating, was implemented through its own discovered surfactant and made it with a simplified process that can be mass-produced.
Prof. Kim said, "This study suggests a new direction for the formulation of existing electrodes, we can expect innovation in electrode composition of high-density lithium-ion batteries, next-generation secondary battery material, and electrode technology in the future."
This research was published in Nature Communications, IF=12.121, the world-renowned journal on April 9 (Fri) online.
※ Title of paper: Graphene collage on Ni-rich layered oxide cathodes for advanced lithium-ion batteries
In an aging population, the frequency of patients with spine-related problems such as spinal stenosis, vertebral fractures, progressive deformities, and instability has shown a concerning increase. Due to the superior biological properties, biomimetic bone grafts have been long considered to be the reference standard for successful bone tissue regeneration and spinal fusion.
Prof. Geun Hyung Kim and his research team (Hanjun Hwangbo and Dr. Hyeongjin Lee; first author) from the department of biomechatronic engineering / biomedical institute for Convergence at SKKU (BICS) conducted joint research with Prof. In-Bo Han and his research team (Eun Ji Roh; first author) from CHA University School of medicine to develop 4D printing strategy to fabricate biomimetic microchanneled collagen/hydroxyapatite scaffold (MC- scaffold). The fabricated MC- scaffold was further analyzed in a spinal fusion model of a mouse. Consequently, the results indicate significantly higher bone regeneration and rate of spine fusion compared to the conventionally fabricated collagen/hydroxyapatite scaffold.
A major drawback of the conventionally used bone grafts is the limited vascular network causing insufficient nutrient and metabolite transfer to the surrounding tissue. To overcome this issue, Prof Geun Hyung Kim and his research team utilized a 4D printing strategy (one-way-shape-morphing) to fabricate a biomimetic microchanneled scaffold composed of collagen and hydroxyapatite (the main component of native bone) to induce a higher degree of osteogenesis and angiogenesis. These findings are owed to the synergistic effects of high infiltration of blood vessels into the microchannels and superior biophysical properties of the microchanneled collagen/hydroxyapatite scaffold.
Additionally, Prof. Geun Hyung Kim and his research team (WonJin Kim; first author) collaborated with Prof. SangJin Lee and his research team (Dr. Hyeongjin Lee; first author) from Wake Forest Institute for Regenerative Medicine (WFIRM) applied 4D printing strategy to induce cellular alignment in extracellular matrix (ECM) based scaffold. Subsequently, a significantly higher degree of muscle regeneration was observed via implantation of the 4D printed bioconstruct into a muscle defect in the rat model.
Currently, mimicking the uniaxial alignment of muscle cells as presented in the native skeletal muscle is often a challenging and difficult task to accomplish with conventional 3D printing. To overcome this issue, Prof. Geun Hyung Kim and his research team utilized developed a composite bioink composed of natural polymer (ECM) and synthetic polymer (Polyvinyl alcohol, PVA), and a 4D printing strategy to provide topographical cue in ECM-based scaffold to induce cellular alignment of primary human muscle progenitor cell (hMPC). Various process parameters such as PVA molecular weight and pneumatic pressure have been analyzed to optimized to obtain the best biological factors such as cellular alignment and differentiation of the host cells.
In addition, to conduct in vivo investigations into muscle regeneration, the bioconstruct sized 15 × 7 × 3 mm3 have been printed and implanted into the tibialis anterior (TA) muscle defect. The cell viability of the fabricated bioconstruct was measured to be around 90%. After 8 weeks of implantation, the muscle regeneration on rats that received the 4D bioprinted structure was significantly higher compared to the conventional 3D printed structure.
The presented 4D printing strategy enables versatility of designing various biological and physical factors of the implant grafts for effective tissue regeneration. Moreover, the introduced 4D printing strategy is believed to have multiple applications such as tendon, nerve, or cardiac.
These studies were supported by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology and by an NRF grant funded by the Ministry of Science and ICT for the Bioinspired Innovation Technology Development Project. In addition, both studies were published in "Applied Physics Reviews" (IF = 17.05) and were selected as a featured paper.