- Prof. David B. Collum (Cornell University)
Masterclass in Organic Synthesis @ SNU-season2
- Prof. Daniele Leonori, Prof. Thomas Poulsen (RWTH Aachen University, Aarhus University)
Frontiers in Organic Synthesis symposium
- Matthew AB Baker (School of Biotechnology and Biomolecular Science (BABS), UNSW)
Bionanotechnology in vivo and in vitro: directing evolution of molecular motors and building them from the bottom up
Electrochemical conversion of CO2 to value-added chemicals over bimetallic Pd-based nanostructures: Recent progress and emerging trends
Electrochemical conversion of CO2 to fuels and chemicals as a sustainable solution for waste transformation has garnered tremendous interest to combat the fervent issue of the prevailing high atmospheric CO2 concentration while contributing to the generation of sustainable energy. Monometallic palladium (Pd) has been shown promising in electrochemical CO2 reduction, producing formate or CO depending on applied potentials. Recently, bimetallic Pd-based materials strived to fine-tune the binding affinity of key intermediates is a prominent strategy for the desired product formation from CO2 reduction. Herein, the recent emerging trends on bimetallic Pd-based electrocatalysts are reviewed, including fundamentals of CO2 electroreduction and material engineering of bimetallic Pd-electrocatalysts categorized by primary products. Modern analytical techniques on these novel electrocatalysts are also thoroughly studied to get insights into reaction mechanisms. Lastly, we deliberate over the challenges and prospects for Pd-based catalysts for electrochemical CO2 conversion.
Inositol polyphosphate multikinase physically binds to the SWI/SNF complex and modulates BRG1 occupancy in mouse embryonic stem cells
Inositol polyphosphate multikinase (IPMK), a key enzyme in inositol polyphosphate (IP) metabolism, is a pleiotropic signaling factor involved in major biological events, including transcriptional control. In the yeast, IPMK and its IP products promote the activity of the chromatin remodeling complex SWI/SNF, which plays a critical role in gene expression by regulating chromatin accessibility. However, the direct link between IPMK and chromatin remodelers remains unclear, raising the question of how IPMK contributes to transcriptional regulation in mammals. By employing unbiased screening approaches and in vivo/in vitro immunoprecipitation, here we demonstrate that mammalian IPMK physically interacts with the SWI/SNF complex by directly binding to SMARCB1, BRG1, and SMARCC1. Furthermore, we identified the specific domains required for IPMK-SMARCB1 binding. Notably, using CUT&RUN and ATAC-seq assays, we discovered that IPMK co-localizes with BRG1 and regulates BRG1 localization as well as BRG1-mediated chromatin accessibility in a genome-wide manner in mouse embryonic stem cells. Together, these findings show that IPMK regulates the promoter targeting of the SWI/SNF complex, thereby contributing to SWI/SNF-meditated chromatin accessibility, transcription, and differentiation in mouse embryonic stem cells.
Patch formation on diblock copolymer micelles confined in templates for inducing patch orientation and cyclic colloidal molecules
Hypothesis Chemically or physically distinct patches can be induced on the micelles of amphiphilic block copolymers, which facilitate directional binding for the creation of hierarchical structures. Hence, control over the direction of patches on the micelles is a crucial factor to attain the directionality on the interactions between the micelles, particularly for generating colloidal molecules mimicking the symmetry of molecular structures. We hypothesized that direction and combination of the patches could be controlled by physical confinement of the micelles. Experiments We first confined spherical micelles of diblock copolymers in topographic templates fabricated from nanopatterns of block copolymers by adjusting the coating conditions. Then, patch formation was conducted on the confined micelles by exposing them with a core-favorable solvent. Microscopic techniques of SEM, TEM, and AFM were employed to investigate directions of patches and structures of combined micelles in the template. Findings The orientation of the patches on the micelles was guided by the physical confinement of the micelles in linear trenches. In addition, by confining the micelles in a circular hole, we obtained a specific polygon arrangement of the micelles depending on the number of micelles in the hole, which enabled the formation of cyclic colloidal molecules consisting of micelles.
Systematic Exploration of Furoindolizine-Based Molecular Frameworks towards a Versatile Fluorescent Platform
The photophysical behaviors of fluorescent molecules largely determine their major utility in biological studies. Despite their well-defined characteristics, classical fluorophores have often been challenged by their limited synthetic methodology and tunability in adjusting intrinsic optical properties. A novel heterocyclic core equipped with modular functional groups could offer the flexibility to control its photophysical properties with a minimum synthetic effort. By conducting a systematic analysis guided by quantum calculations, we proposed the furoindolizine-based molecular framework as a unique fluorescent platform capable of providing versatile photophysical properties with minimal structural modification. A broad tunability of furoindolizine derivatives′ photophysical properties such as emission wavelength, Stokes shift, fluorescent brightness, and charge transfer characteristics was achieved through synergistic interaction between two functional moieties. Furthermore, this modular platform led to live-cell imaging probes with two distinct optical features simply by reorganizing a pair of functional moieties.
Microfluidics-Assisted Synthesis of Hierarchical Cu2O Nanocrystal as C2-Selective CO2 Reduction Electrocatalyst
Copper-based catalysts have attracted enormous attention due to their high selectivity for C2+ products during the electrochemical reduction of CO2 (CO2RR). In particular, grain boundaries on the catalysts contribute to the generation of various Cu coordination environments, which have been found essential for C—C coupling. However, smooth-surfaced Cu2O nanocrystals generally lack the ability for the surface reorganization to form multiple grain boundaries and desired Cu undercoordination sites. Flow chemistry armed with the unparalleled ability to mix reaction mixture can achieve a very high concentration of unstable reaction intermediates, which in turn are used up rapidly to lead to kinetics-driven nanocrystal growth. Herein, the synthesis of a unique hierarchical structure of Cu2O with numerous steps (h-Cu2O ONS) via flow chemistry-assisted modulation of nanocrystal growth kinetics is reported. The surface of h-Cu2O ONS underwent rapid surface reconstruction under CO2RR conditions to exhibit multiple heterointerfaces between Cu2O and Cu phases, setting the preferable condition to facilitate C—C bond formation. Notably, the h-Cu2O ONS obtained the increased C2H4 Faradaic efficiency from 31.9% to 43.5% during electrocatalysis concurrent with the morphological reorganization, showing the role of the stepped surface. Also, the h-Cu2O ONS demonstrated a 3.8-fold higher ethylene production rate as compared to the Cu2O nanocube.
Fabrication of Semiconducting Nanoribbons with Tunable Length and Width via Crystallization-Driven Self-Assembly of a Homopolymer Prepared by Cyclopolymerization Using Grubbs Catalyst
Precise control of the width and length of one-dimensional (1D) semiconducting nanostructures is a topic of attention owing to the potential applications of such nanostructures in optoelectronics. However, regulating both the length and width of the 1D nanostructures using conjugated polymers or block copolymers is a significant challenge. To solve this problem, we synthesized a unique conjugated polyacetylene homopolymer via living cyclopolymerization, which spontaneously formed 1D nanoribbons via in situ nanoparticlization. Interestingly, their widths could be controlled from 11 to 42 nm, which is directly proportional to their degree of polymerization. Furthermore, a self-seeding technique via crystallization-driven self-assembly (CDSA) was adopted to control the length of the nanoribbons up to 2.3 μm with narrow distributions. Interestingly, adding a block copolymer unimer to these nanoribbons produced triblock comicelles by the living CDSA mechanism. The nanoribbons were visualized directly by super-resolution optical fluorescence microscopy. The proposed approach allows us to tune the length and width of 1D nanoribbons up to a certain degree.
Modulating the Rate of Controlled Suzuki–Miyaura Catalyst-Transfer Polymerization by Boronate Tuning
Despite the remarkable breakthroughs in the catalyst-transfer polymerization (CTP) technology in the precision synthesis of conjugated polymers, modulating the monomer reactivity is still challenging. We report that, by boronate tuning, we can modulate the rate of the Suzuki–Miyaura CTP (SCTP) of 3-hexylthiophene with high control. First, cyclic boronate esters showed different polymerization rates depending on their diol subunit structure. Additionally, the rates of the N-coordinated boronates were differentiated by tuning their O- or N-substituents. Notably, the origin of the difference in reactivity could be explained by the N → B bond lengths. The detailed structural analysis of the resulting polymers by 1H nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry showed that the slower and more stable boronate monomers were less prone to homocoupling and protodeboronation, thereby producing poly(3-hexylthiophene) (P3HT) with higher control (i.e., molecular weight, dispersity, end-group fidelity, and yield). By rational optimizations to suppress homocoupling and protodeboronation, well-defined P3HT were prepared at various monomer-to-initiator ratios (M/I ratios).
Paper-based electrochromic glucose sensor with polyaniline on indium tin oxide nanoparticle layer as the optical readout
Surging interests in point-of-care diagnostics have led to the development of many lightweight and cost-effective paper-based sensors. Particularly, sensors using colorimetric readouts are considered highly advantageous because no additional detector or device is required for signal display. Herein, we introduce an electrochemically operated colorimetric sensor that can compensate for the disadvantages of traditional colorimetry, hence enhancing response time, reusability and color uniformity. On a single paper substrate, carbon/graphite paste was screen printed to form the working and counter electrodes, and Ag/AgCl ink was applied for the reference electrode. Prussian blue and Glucose oxidase were employed on the one of the carbon electrodes for the detection of analytes, hydrogen peroxide and glucose. For the colorimetric readout, indium tin oxide nanoparticles and polyaniline were consecutively introduced on the other carbon electrode, which is used as the counter electrode. The color change of electrochromic polyaniline could be clearly observed, and its application as a colorimetric sensor was demonstrated by the quantitative analyses of hydrogen peroxide and glucose. This paper-based electrochromic glucose sensor showed a short response time of 30 s and exhibited a detection limit of 126 μM for glucose. Along with its rapid and easy detection by incorporating the merits of electrochemical sensing and colorimetry, the paper-based electrochromic sensor could potentially contribute to the development of point-of-care devices by combination with portable power sources.
Rationally designed nanoparticle delivery of Cas9 ribonucleoprotein for effective gene editing
Programmable endonucleases such as CRISPR/Cas9 system emerge as a promising tool to treat genetic and non-genetic diseases such as hypercholesterolemia, Duchenne muscular dystrophy, and cancer. However, the lack of safe and efficient vehicles that enable intracellular delivery of CRISPR/Cas9 endonuclease is a big hurdle for its therapeutic applications. Here, we employed porous nanoparticle for the Cas9 ribonucleoprotein (RNP) delivery and achieved efficient knockout of target genes in vitro and in vivo. The porous nanoparticle, called ‘BALL’, enabled safe and direct intracellular Cas9 RNP delivery by improving bioavailability and serum stability. The BALL-mediated delivery of Cas9 RNP showed superior indel efficiency of about 40% in vitro and 20% in vivo in a model system employing green fluorescent protein (GFP). More importantly, intramuscular injection of the Cas9 RNP-BALL complex targeting the myostatin (MSTN) gene which is known to suppress muscle growth achieved successful knockout of the MSTN gene, resulting in the increase of muscle and the improved motor functions. Thus, we believe that the BALL is a promising delivery system for CRISPR-based genome editing technology, which can be applied to the treatment of various genetic diseases.
Radical-Mediated C-C Coupling of Alcohols Induced by PlasmonicHot Carriers
The C–C coupling reactions of aliphatic alcohols to aromatics and larger-mass compounds have large endothermicities and activation energies, calling for catalysts operating at high temperatures. Here, we demonstrate that plasmon-excited nanoparticles catalyze the C–C coupling of aliphatic alcohols at room temperature to produce polyaromatic hydrocarbons and graphene oxide. The conversion is quenched by radical and electron scavengers and by the surface passivation of metals, suggesting that the reaction proceeds through alkoxy, peroxyl, hydroxyalkyl, and alkyl radical intermediates created by the metal to molecule transfer of plasmonic hot carriers. Besides being the first realization of C–C coupling of aliphatic alcohols at room temperature, the result constitutes a rare example of an endothermic plasmon-induced reaction producing new bonds and a new method for photogenerating graphene derivatives. More importantly, the result demonstrates the facile generation of organic radicals directly from alcohols, which may be used as precursors for radical-based organic reactions.