Sangmok Jang

Preparation of non-aggregated fluorescent nanodiamonds (FNDs) by non-covalent coating with a block copolymer and proteins for enhancement of intracellular uptake

Fluorescent nanodiamonds (FNDs) are very promising fluorophores for use in biosystems due to their high biocompatibility and photostability. To overcome their tendency to aggregate in physiological solutions, which severely limits the biological applications of FNDs, we developed a new non-covalent coating method using a block copolymer, PEG-b-P(DMAEMA-co-BMA), or proteins such as BSA and HSA. By simple mixing of the block copolymer with FNDs, the cationic DMAEMA and hydrophobic BMA moieties can strongly interact with the anionic and hydrophobic moieties on the FND surface, while the PEG block can form a shell to prevent the direct contact between FNDs. The polymer-coated FNDs, along with BSA- and HSA-coated FNDs, showed non-aggregation characteristics and maintained their size at the physiological salt concentration. The well-dispersed, polymer- or protein-coated FNDs in physiological solutions showed enhanced intracellular uptake, which was confirmed by CLSM. In addition, the biocompatibility of the coated FNDs was expressly supported by a cytotoxicity assay. Our simple non-covalent coating with the block copolymer, which can be easily modified by various chemical methods, projects a very promising outlook for future biomedical applications, especially in comparison with covalent coating or protein-based coating.

Apoptosis inducing, conformationally constrained, dimeric peptide analogs of KLA with submicromolar cell penetrating abilities.

The apoptosis inducing KLA peptide, (KLAKLAK)2, possesses an ability to disrupt mitochondrial membranes. However, this peptide has a poor eukaryotic cell penetrating potential and, as a result, it requires the assistance of other cell penetrating peptides for effective translocation in micromolar concentrations. In an effort to improve the cell penetrating potential of KLA, we have created a library in which pairs of residues on its hydrophobic face are replaced by Cys. The double Cys mutants were then transformed to bundle dimers by oxidatively generating two intermolecular disulfide bonds. We envisioned that once transported into cells, the disulfide bonds would undergo reductive cleavage to generate the monomeric peptides. The results of these studies showed that one of the mutant peptides, dimer B, has a high cell penetrating ability that corresponds to 100% of fluorescence positive cells at 250 nM. Even though dimer B induces disruption of the mitochondrial potential and cytochrome c release followed by caspase activation at submicromolar concentrations, it displays an LD50 of 1.6 μM under serum conditions using HeLa cells. Taken together, the results demonstrate that the strategy involving formation of bundle dimeric peptides is viable for the design of apoptosis inducing KLA peptide that translocate into cells at submicromolar concentrations.

Cell-Penetrating, Dimeric α-Helical Peptides: Nanomolar Inhibitors of HIV-1 Transcription†

We constructed dimeric α-helical peptide bundles based on leucine (L) and lysine (K) residues for both efficient cell penetration and inhibition of the Tat-TAR interaction. The LK dimers can penetrate nearly quantitatively into eukaryotic cells and effectively inhibit the elongation of the TAR transcript at low nanomolar concentrations. The effective inhibition of HIV-1 replication strongly suggests that the LK dimer has strong potential as an anti-HIV-1 drug.

The electronic structure of epitaxially stabilized 5d perovskite Ca1 − xSrxIrO3 (x = 0, 0.5, and 1) thin films: the role of strong spin–orbit coupling

We have investigated the electronic structure of meta-stable perovskite Ca(1 - x)Sr(x)IrO(3)(x = 0, 0.5, and 1) thin films using transport measurements, optical spectroscopy, and first-principles calculations. We artificially fabricated the perovskite phase of Ca(1 - x)Sr(x)IrO(3), which has a hexagonal or post-perovskite crystal structure in bulk form, by growing epitaxial thin films on perovskite GdScO(3) substrates using an epi-stabilization technique. The transport properties of the perovskite Ca(1 - x)Sr(x)IrO(3) films systematically change from nearly insulating (or semi-metallic) for x = 0 to weakly metallic for x = 1. Due to the extended wavefunctions, 5d electrons are usually delocalized. However, the strong spin-orbit coupling in Ca(1 - x)Sr(x)IrO(3) results in the formation of effective total angular momentum J(eff) = 1/2 and 3/2 states, which puts Ca(1 - x)Sr(x)IrO(3) in the vicinity of a metal-insulator phase boundary. As a result, the electrical properties of the Ca(1 - x)Sr(x)IrO(3) films are found to be sensitive to x and strain.

Circulatory osmotic desalination driven by a mild temperature gradient based on lower critical solution temperature (LCST) phase transition materials.

Abrupt changes in effective concentration and osmotic pressure of lower critical solution temperature (LCST) mixtures facilitate the design of a continuous desalination method driven by a mild temperature gradient. We propose a prototype desalination system by circulating LCST mixtures between low and high temperature (low T and high T) units. Water molecules could be drawn from a high-salt solution to the LCST mixture through a semipermeable membrane at a temperature lower than the phase transition temperature, at which the effective osmotic pressure of the LCST mixture is higher than the high-salt solution. After transfer of water to the high T unit where the LCST mixture is phase-separated, the water-rich phase could release the drawn water into a well-diluted solution through the second membrane due to the significant decrease in effective concentration. The solute-rich phase could be recovered in the low T unit via a circulation process. The molar mass, phase transition temperature, and aqueous solubility of the LCST solute could be tuneable for the circulatory osmotic desalination system in which drawing, transfer, release of water, and the separation and recovery of the solutes could proceed simultaneously. Development of a practical desalination system that draws water molecules directly from seawater and produces low-salt water with high purity by mild temperature gradients, possibly induced by sunlight or waste heat, could be attainable by a careful design of the molecular structure and combination of the circulatory desalination systems based on low- and high-molar-mass LCST draw solutes.

Multimeric Amphipathic α-Helical Sequences for Rapid and Efficient Intracellular Protein Transport at Nanomolar Concentrations

Abstract An amphipathic leucine (L) and lysine (K)‐rich α‐helical peptide is multimerized based on helix‐loop‐helix structures to maximize the penetrating activities. The multimeric LK‐based cell penetrating peptides (LK‐CPPs) can penetrate cells as protein‐fused forms at 100–1000‐fold lower concentrations than Tat peptide. The enhanced penetrating activity is increased through multimerization by degrees up to the tetramer level. The multimeric LK‐CPPs show rapid cell penetration through macropinocytosis at low nanomolar concentrations, unlike the monomeric LK, which have slower penetrating kinetics at much higher concentrations. The heparan sulfate proteoglycan (HSPG) receptors are highly involved in the rapid internalization of multimeric LK‐CPPs. As a proof of concept of biomedical applications, an adipogenic transcription factor, peroxisome proliferator‐activated receptor gamma 2 (PPAR‐γ 2), is delivered into preadipocytes, and highly enhanced expression of adipogenic genes at nanomolar concentrations is induced. The multimeric CPPs can be a useful platform for the intracellular delivery of bio‐macromolecular reagents that have difficulty with penetration in order to control biological reactions in cells at feasible concentrations for biomedical purposes.