Ruthenium-catalyzed mild C-H oxyfunctionalization of cyclic steroidal ethers

Ruthenium-catalyzed site-specific C-H oxyfunctionalization of steroidal ethers with periodate or bromate as terminal oxidants in phosphate buffer provided the acid-sensitive C-16 hydroxy compounds in high yields. Phosphate buffer (pH 7.5) significantly inhibits formation of unwanted side products generated under more acidic reaction conditions. A key example is demonstrated at the 100 g scale.     

Na+-Ca2+ exchanger modulates Ca2+ content in intracellular Ca2+ stores in rat osteoblasts

Na+-Ca2+ exchanger (NCX) transports Ca2+ coupled with Na+ across the plasma membrane in a bi-directional mode. Ca2+ flux via NCX mediates osteogenic processes, such as formation of extracellular matrix proteins and bone nodules. However, it is not clearly understood how the NCX regulates cellular Ca2+ movements in osteogenic processes. In this study, the role of NCX in modulating Ca2+ content of intracellular stores ([Ca2+]ER) was investigated by measuring intracellular Ca2+ activity in isolated rat osteoblasts. Removal of extracellular Na+ elicited a transient increase of intracellular Ca2+ concentration ([Ca2+]i). Pretreatment of antisense oligodeoxynucleotide (AS) against NCX depressed this transient Ca2+ rise and raised the basal level of [Ca2+]i. In AS-pretreated cells, the expression and activity of alkaline phosphatase (ALP), an osteogenic marker, were decreased. However, the cell viability was not affected by AS-pretreatment. Suppression of NCX activity by the AS-pretreatment decreased ATP-activated Ca2+ release from intracellular stores and significantly enhanced Ca2+ influx via store operated calcium influx (SOCI), compared to those of S-pretreated or control cells. These results strongly suggest that NCX has a regulatory role in cellular Ca2+ pathways in osteoblasts by modulating intracellular Ca2+ content.     

Analysis of intracellular short organic acid-coenzyme A esters from actinomycetes using liquid chromatography-electrospray ionization-mass spectrometry

A method employing silicone oil density centrifugation, solid-phase extraction (SPE) cleanup, and LC-ESI-MS/MS analysis was developed for the rapid, selective, sensitive, and quantitative detection of an intracellular pool of short organic acid-CoA esters in actinomycetes. The detection limit was determined to be approximately 0.8 pmol (1.2 ng/ml) for each standard CoA-ester analyzed by the present LC-ESI-MS/MS method. A selected ion chromatogram for a typical fragment ion (m/z 428) specific to CoA-esters enabled the detection of eight intracellular CoA-esters involved in both primary and secondary metabolisms. The application of this method to bacterial metabolomic study is demonstrated by the profiling of the intracellular CoA-ester pools in the wild-type Streptomyces venezuelae strain producing polyketide antibiotics (methymycin and pikromycin), a polyketide synthase (PKS)-deleted S. venezuelae mutant, and a S. venezuelae mutant expressing the heterologous PKS genes. By quantifying the individual CoA-esterlevel in three different genotypes of the S. venezuela e strain, further insight could be gained into the role of CoA-estersin polyketide biosynthesis. This analytical approach can be extended to the quantification of the size and composition of in vivo CoA-ester pools in various microbes, and can provide a detailed understanding of the relationship between the in vivo CoA-ester pool and the production of pharmaceutically important polyketides.     

X-ray photoelectron spectroscopy and first principles calculation of BCN nanotubes

Multiwalled boron carbonitride (BCN) nanotubes with two different structures were synthesized via thermal chemical vapor deposition; one has 10% C atoms homogeneously doped into BN nanotubes (B0.45C0.1N0.45 NTs), and the other has BN layers sheathed with 5-nm-thick C outerlayers (BN-C NTs). The electronic structures of the B, C, and N atoms were thoroughly probed by synchrotron X-ray photoelectron spectroscopy and the X-ray absorption near-edge structure method. The B0.45C0.1N0.45 NTs contain a significant amount of B-C and C-N bonding with a pyridine-like structure (hole structure), which reduces the pi bonding states of the B and N atoms. From the XPS valence band spectrum, the band gap was estimated to be about 2.8 eV. In the BN-C NTs, the C and BN domains are separated without forming the pyridine-like structure. Using the first principles method, we investigated the relative stabilities and electronic structures of the various isomers of the double-walled (12,0)@(20,0) BCN NTs. The C-outerlayer BN nanotube structure is the most stable isomer, when there exist no defects in the tubes with B/N = 1.0 (i.e., graphite-like structure). In addition, a reasonable model, which is characterized by the motives consisted of three pyridine-like rings around a hollow site, is presented for the local structure of C atoms in the B0.45N0.45C0.1 NTs. A considerable decrease of the band gap due to the 10% C doping was predicted, which was consistent with the experimental results.     

Using atomic layer deposition to hinder solvent decomposition in lithium ion batteries: first-principles modeling and experimental studies

Passivating lithium ion (Li) battery electrode surfaces to prevent electrolyte decomposition is critical for battery operations. Recent work on conformal atomic layer deposition (ALD) coating of anodes and cathodes has shown significant technological promise. ALD further provides well-characterized model platforms for understanding electrolyte decomposition initiated by electron tunneling through a passivating layer. First-principles calculations reveal two regimes of electron transfer to adsorbed ethylene carbonate molecules (EC, a main component of commercial electrolyte), depending on whether the electrode is alumina coated. On bare Li metal electrode surfaces, EC accepts electrons and decomposes within picoseconds. In contrast, constrained density functional theory calculations in an ultrahigh vacuum setting show that, with the oxide coating, e(-) tunneling to the adsorbed EC falls within the nonadiabatic regime. Here the molecular reorganization energy, computed in the harmonic approximation, plays a key role in slowing down electron transfer. Ab initio molecular dynamics simulations conducted at liquid EC electrode interfaces are consistent with the view that reactions and electron transfer occur right at the interface. Microgravimetric measurements demonstrate that the ALD coating decreases electrolyte decomposition and corroborates the theoretical predictions.     

The Role of Water for the Phase‐Selective Preparation of Hexagonal and Cubic Cobalt Oxide Nanoparticles

A selective preparation and the formation mechanism of hexagonal and cubic CoO nanoparticles from the reaction of [Co(acac)₂] (acac=acetylacetonate) and amine have been investigated. CoO nanoparticles with a hexagonal pyramidal shape were yielded under decomposition conditions with amine. Importantly, the addition of water altered the final phase to cubic and comprehensively changed the reaction mechanism. The average sizes of the hexagonal and cubic CoO nanoparticles could be controlled either by changing the amine concentration or by using different reaction temperatures. Detailed formation mechanisms are proposed on the basis of gas chromatography–mass spectrometry data and color changes of the reaction mixture. The hexagonal CoO phase is obtained through two distinct pathways: solvolysis with C C bond cleavage and direct condensation by amine. On the other hand, the cubic CoO nanoparticles were synthesized by strong nucleophilic attack of hydroxide ions from water and subsequent C C bond breaking. The resulting caboxylate ligand can stabilize a cobalt hydroxide intermediate, leading to the generation of a thermodynamically stable CoO phase.     

Artificial photosynthesis on a chip: microfluidic cofactor regeneration and photoenzymatic synthesis under visible light

We present a microfluidic artificial photosynthetic platform that incorporates quantum dots and redox enzymes for photoenzymatic synthesis of fine chemicals under visible light. Similar to natural photosynthesis, photochemical cofactor regeneration takes place in the light-dependent reaction zone, which is then coupled with the light-independent, enzymatic synthesis in the downstream of the microchannel.     

"Bioelectronic super-taster" device based on taste receptor-carbon nanotube hybrid structures

We have developed a method to monitor the activities of human taste receptor protein in lipid membrane using carbon nanotube transistors, enabling a "bioelectronic super-taster (BST)", a taste sensor with human-tongue-like selectivity. In this work, human bitter taste receptor protein expressed in E. coli was immobilized on a single-walled carbon nanotube field effect transistor (swCNT-FET) with the lipid membrane. Then, the protein binding activity was monitored using the underlying swCNT-FET, leading to the operation as a BST device. The fabricated BST device could detect bitter tastants at 100 fM concentrations and distinguish between bitter and non-bitter tastants with similar chemical structures just like a human tongue. Furthermore, this strategy was utilized to differentiate the responses of taster or non-taster types of the bitter taste receptor proteins.     

A low-energy-consumption electroactive valveless hydrogel micropump for long-term biomedical applications

Stimuli-responsive hydrogels have attracted considerable interest in the field of microfluidics due to their ability to transform electrical energy directly into mechanical work through swelling, bending, and other deformations. In particular, electroactive hydrogels hold great promise for biomedical micropumping applications such as implantable drug delivery systems. In such applications, energy consumption rate and durability are key properties. Here, we developed a valveless micropump system that utilizes a hydrogel as the main actuator, and tested its performance over 6 months of continuous operation. The proposed micropump system, powered by a single 1.5 V commercial battery, expended very little energy (less than 750 μWs per stroke) while pumping 0.9 wt% saline solution under a low voltage (less than 1 V), and remained fully functional after 6 months. CFD simulations were conducted to improve the microchannel geometry so as to minimize the backflow caused by the valveless mechanism of the system. Based on the simulation results, an asymmetric geometry and a stop post were introduced to enhance the pumping performance. To demonstrate the feasibility of the proposed system as a drug delivery pump, an anti-cancer drug (adriamycin) was perfused to human breast cancer cells (MCF-7) using the pump. The present study showed that the proposed system can operate continuously for long periods with low energy consumption, powered by a single 1.5 V battery, making it a promising candidate for an implantable drug delivery system.