Seon-Mi Jin

Mitochondria localization induced self-assembly of peptide amphiphiles for cellular dysfunction

Achieving spatiotemporal control of molecular self-assembly associated with actuation of biological functions inside living cells remains a challenge owing to the complexity of the cellular environments and the lack of characterization tools. We present, for the first time, the organelle-localized self-assembly of a peptide amphiphile as a powerful strategy for controlling cellular fate. A phenylalanine dipeptide (FF) with a mitochondria-targeting moiety, triphenyl phosphonium (Mito-FF), preferentially accumulates inside mitochondria and reaches the critical aggregation concentration to form a fibrous nanostructure, which is monitored by confocal laser scanning microscopy and transmission electron microscopy. The Mito-FF fibrils induce mitochondrial dysfunction via membrane disruption to cause apoptosis. The organelle-specific supramolecular system provides a new opportunity for therapeutics and in-depth investigations of cellular functions.Spatiotemporal control of intracellular molecular self-assembly holds promise for therapeutic applications. Here the authors develop a peptide consisting of a phenylalanine dipeptide with a mitochondrial targeting moiety to form self-assembling fibrous nanostructures within mitochondria, leading to apoptosis.

Electric-Field-Assisted Assembly of Polymer-Tethered Gold Nanorods in Cylindrical Nanopores.

In this report, we demonstrate the confined assembly of polymer-tethered gold nanorods in anodic aluminum oxide (AAO) channels with the assistance of electric field (EF). Various interesting hybrid assemblies, such as single-, double-, triple-, or quadruple-helix, linear, and hexagonally packed structures are obtained by adjusting pore size in AAO channels, ligand length, and EF orientation. Correspondingly, surface plasmonic property of the assemblies can thus be tuned. This strategy, by coupling of external-field and cylindrically confined assembly, is believed to be a promising approach for generating ordered hybrid assemblies with hierarchical structures, which may find potential applications in photoelectric devices, biosensors, and data storage devices.

A Nonchlorinated Solvent-Processable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors

High carrier mobilities have recently been achieved in polymer field effect transistors (FETs). However, many of these polymer FET devices require the use of chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (DCB) during fabrication. The use of these solvents is highly restricted in industry because of health and environmental issues. Here, we report the synthesis of a low band gap (1.43 eV, 870 nm) semiconducting polymer (PDPP2DT-F2T2) having a planar geometry, which can be readily processable with nonchlorinated solvents such as toluene (TOL), o-xylene (XY), and 1,2,4-trimethylbenzene (TMB). We performed structural characterization of PDPP2DT-F2T2 films prepared from different solvents, and the electrical properties of the films were measured in the context of FETs. The devices exhibited an ambipolar behavior with hole dominant transport. Hole mobilities increased with increasing boiling point (bp) of the nonchlorinated solvents: 0.03, 0.05, and 0.10 cm2 V-1 s-1 for devices processed using TOL, XY, and TMB, respectively. Thermal annealing further improved the FET performance. TMB-based polymer FETs annealed at 200 °C yielded a maximum hole mobility of 1.28 cm2 V-1 s-1, which is far higher than the 0.43 cm2 V-1 s-1 obtained from the CF-based device. This enhancement was attributed to increased interchain interactions as well as improved long-range interconnection between fibrous domains. Moreover, all of the nonchlorinated solutions generated purely edge-on orientations of the polymer chains, which is highly beneficial for carrier transport in FET devices. Furthermore, we fabricated an array of flexible TMB-processed PDPP2DT-F2T2 FETs on the plastic PEN substrates. These devices demonstrated excellent carrier mobilities and negligible degradation after 300 bending cycles. Overall, we demonstrated that the organized assembly of polymer chains can be achieved by slow drying using high bp nonchlorinated solvents and a post thermal treatment. Furthermore, we showed that polymer FETs processed using high bp nonhalogenated solvents may outperform those processed using halogenated solvents.

Structure-Dependent Antimicrobial Theranostic Functions of Self-Assembled Short-Peptide Nanoagents

Gadolinium (Gd[III])-based nanoaggregates are potential noninvasive magnetic resonance imaging (MRI) probes with excellent spatial and temporal resolution for cancer diagnosis. Peptides conjugated with Gd3+ can aid in supramolecular scaffolding for MRI nanoagents because of their inherent biocompatibility and degradability. We report here a strategy to tune the MR relaxivity of tumor cell-targeted nanoagents and enhance the antimicrobial and anticancer activities of nanoagents based on rationally designed antimicrobial peptide (AMP) assembly. A tripeptide with glycyl-l-histidyl-l-lysine (GHK) capable of Gd3+ chelation was attached to short AMPs containing pyrazole amino acids that spontaneously assembled as a function of the number of hydrophobic amino acid residues and the peptide length of AMPs. Aqueous coassembly of GHK with tumor-targeting, cyclic arginine-glycine-aspartic acid (cRGD)-tagged AMPs resulted in the formation of micelles, fibrils, vesicles, sheets, and planar networks. Interestingly, the two-dimensional planar network nanostructure showed less antibacterial activity and tumor cell cytotoxicity but greater drug loading/delivery and magnetic resonance signaling than micelles because of its intrinsic structural characteristics. This study can provide a rational approach for the design and fabrication of clinically useful nanoagents.

Structure–Property Relationships of Semiconducting Polymers for Flexible and Durable Polymer Field-Effect Transistors

We report high-performance top-gate bottom-contact flexible polymer field-effect transistors (FETs) fabricated by flow-coating diketopyrrolopyrrole (DPP)-based and naphthalene diimide (NDI)-based polymers (P(DPP2DT-T2), P(DPP2DT-TT), P(DPP2DT-DTT), P(NDI2OD-T2), P(NDI2OD-F2T2), and P(NDI2OD-Se2)) as semiconducting channel materials. All of the polymers displayed good FET characteristics with on/off current ratios exceeding 107. The highest hole mobility of 1.51 cm2 V-1 s-1 and the highest electron mobility of 0.85 cm2 V-1 s-1 were obtained from the P(DPP2DT-T2) and P(NDI2OD-Se2) polymer FETs, respectively. The impacts of the polymer structures on the FET performance are well-explained by the interplay between the crystallinity, the tendency of the polymer backbone to adopt an edge-on orientation, and the interconnectivity of polymer fibrils in the film state. Additionally, we demonstrated that all of the flexible polymer-based FETs were highly resistant to tensile stress, with negligible changes in their carrier mobilities and on/off ratios after a bending test. Conclusively, these high-performance, flexible, and durable FETs demonstrate the potential of semiconducting conjugated polymers for use in flexible electronic applications.

Multicompartment Vesicles Formation by Emulsification-Induced Assembly of Poly(ethylene oxide)-block-poly(ε-caprolactone) and Their Dual-Loading Capability

Emulsification-induced assembly is employed to allow structural diversity in nanoaggregates of a biocompatible amphiphilic polymer, poly(ethylene oxide)-block-poly(ε-caprolactone). Onion-like vesicles are efficiently produced by tuning the interfacial instability of the oil-in-water emulsion. The increase in the polymer concentration and use of the organic solvents with a low interfacial tension between water and the oil phase lead to a strong tendency of emulsion droplets to generate the onion-like vesicles. The vesicular networks and fibers are also obtained by controlling the concentration and type of the surfactant, respectively. Interestingly, the onion-like vesicles composed of alternating walls and water channels and the vesicular networks originated from a string of vesicles show dual-loading ability for hydrophobic and hydrophilic dyes but slightly different loading capacities. This result indicates that the development of a methodology to fabricate well-defined, unique nanostructures, such as multivesicular and multilamellar nanostructures, and subsequent elucidation of their structure-property relationships can provide useful guidance in the design of novel biomedical materials.

Peroxisome-targeted Supramolecular Nanoprobes Assembled with Pyrene-labelled Peptide Amphiphiles

Despite the versatile metabolic functions of peroxisomes such as lipid synthesis and fatty acid oxidation and their relevance to genetically inherited diseases, namely, peroxisome biogenesis disorders and peroxisomal enzyme deficiency, there is not much research on peroxisome-targeting therapeutics. Herein we present supramolecular nanostructured probes based on the self-assembly of peptide amphiphiles (PAs) having peroxisome-targeting ability in mammalian cells. The PA was designed to include the peroxisome-targeting tripeptide (SKL) and a fluorescent dye (pyrene). It was revealed that the presence of the SKL-appended carboxyl terminal group of PA, the extent of α-helical nature of the peptide block, and the fibrillar morphology of nano-assemblies affected the targeting efficiency of PA supramolecular nanoprobe. The simple modification of PAs by the peroxisome-targeting strength prediction showed an enhanced peroxisome specificity, as expected. This work provides important insights into designing subcellular organelle-targeting nanoparticles for next-generation nanomedicines.

Columnar-Structured Low-Concentration Donor Molecules in Bulk Heterojunction Organic Solar Cells

We investigate the arrangement of donor molecules in vacuum-deposited bulk heterojunction (BHJ) 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane (TAPC):C70-based organic solar cells (OSCs). Even a low dose of donors (∼10%) forms columnar structures that provide pathways for efficient hole transport in the BHJ layer; however, these structures disappear at donor concentrations below 10%, generating disconnected and isolated hole pathways. The formation of columnar donor structures is confirmed by the contrast of the contact potential difference, measured by Kelvin probe force microscopy, and by the trap-assisted charge injection at low donor concentrations. The mobility of electrons and holes is well balanced in OSCs owing to the preservation of the hole mobility at such low donor concentrations, consequently maximizing the internal quantum efficiency of the OSCs. A high power conversion efficiency of 6.24% was achieved in inverted TAPC:C70 (1:9) OSCs.