Control of peroxyoxalate chemiluminescence by nitrogen-containing ligand quenching: turning off and on by ligand-metal ion host-guest interactions

The control of peroxyoxalate chemiluminescence (PO-CL) by the coordination of nitrogen-containing ligands and metal cations was investigated. Turning the CL off and on was done by PO-CL using 15-monoazacrown-5-tethered anthracene and alkali metal ions. CL quenching and regeneration was also observed in the separated molecular system of 15-monoazacrown-5 and the fluorophores. CL quenching by a number of ligands bearing dipicolylamino groups was evaluated by these PO-CL reactions and found to be closely related to their oxidation potentials, which is dependent on the Weller rate law for electron exchange and this provides strong support for the existence of the CIEEL PO-CL process. When Zn²⁺ or Cu²⁺ are added to the PO-CL system quenched by the ligand, N-[2-(2,2′-dipicolylamino)ethyl]aniline, CL was turned on because the electron donating ability of the ligands was modulated. This was controlled by the coordination of the studied metal ions and, therefore, this system results in CL because of host-guest interactions.     

Binding of metal ions by pyrimidine base pairs in DNA duplexes

Pyrimidine base pairs in DNA duplexes selectively capture metal ions to form metal ion-mediated base pairs, which can be evaluated by thermal denaturation, isothermal titration calorimetry, and nuclear magnetic resonance spectroscopy. In this critical review, we discuss the metal ion binding of pyrimidine bases (thymine, cytosine, 4-thiothymine, 2-thiothymine, 5-fluorouracil) in DNA duplexes. Thymine-thymine (T-T) and cytosine-cytosine (C-C) base pairs selectively capture Hg(II) and Ag(I) ions, respectively, and the metallo-base pairs, T-Hg(II)-T and C-Ag(I)-C, are formed in DNA duplexes. The metal ion binding properties of the pyrimidine-pyrimidine pairs can be changed by small chemical modifications. The binding selectivity of a metal ion to a 5-fluorouracil-5-fluorouracil pair in a DNA duplex can be switched by changing the pH of the solution. Two silver ions bind to each thiopyrimidine-thiopyrimidine pair in the duplexes, and the duplexes are largely stabilized. Oligonucleotides containing these bases are commercially available and can readily be applied in many scientific fields (86 references).     

Non-surface activity and micellization behavior of cationic amphiphilic block copolymer synthesized by reversible addition-fragmentation chain transfer process

Cationic amphiphilic diblock copolymers of poly(n-butylacrylate)-b-poly(3-(methacryloylamino)propyl)trimethylammonium chloride) (PBA-b-PMAPTAC) with various hydrophobic and hydrophilic chain lengths were synthesized by a reversible addition-fragmentation chain transfer (RAFT) process. Their molecular characteristics such as surface activity/nonactivity were investigated by surface tension measurements and foam formation observation. Their micelle formation behavior and micelle structure were investigated by fluorescence probe technique, static and dynamic light scattering (SLS and DLS), etc., as a function of hydrophilic and hydrophobic chain lengths. The block copolymers were found to be non-surface active because the surface tension of the aqueous solutions did not change with increasing polymer concentration. Critical micelle concentration (cmc) of the polymers could be determined by fluorescence and SLS measurements, which means that these polymers form micelles in bulk solution, although they were non-surface active. Above the cmc, the large blue shift of the emission maximum of N-phenyl-1-naphthylamine (NPN) probe and the low micropolarity value of the pyrene probe in polymer solution indicate the core of the micelle is nonpolar in nature. Also, the high value of the relative intensity of the NPN probe and the fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene (DPH) probe indicated that the core of the micelle is highly viscous in nature. DLS was used to measure the average hydrodynamic radii and size distribution of the copolymer micelles. The copolymer with the longest PBA block had the poorest water solubility and consequently formed micelles with larger size while having a lower cmc. The "non-surface activity" was confirmed for cationic amphiphilic diblock copolymers in addition to anionic ones studied previously, indicating the universality of non-surface activity nature.     

Confinement in carbon nanospace-induced production of KI nanocrystals of high-pressure phase

An outstanding compression function for materials preparation exhibited by nanospaces of single-walled carbon nanohorns (SWCNHs) was studied using the B1-to-B2 solid phase transition of KI crystals at 1.9 GPa. High-resolution transmission electron microscopy and synchrotron X-ray diffraction examinations provided evidence that KI nanocrystals doped in the nanotube spaces of SWCNHs at pressures below 0.1 MPa had the super-high-pressure B2 phase structure, which is induced at pressures above 1.9 GPa in bulk KI crystals. This finding of the supercompression function of the carbon nanotubular spaces can lead to the development of a new compression-free route to precious materials whose syntheses require the application of high pressure.     

"Click-made" biaryl-linker improving efficiency in protein labelling for the membrane target protein of a bioactive compound

We report on the design, synthesis and assessment of a novel biaryl-linked (BArL) molecular probe for the exploration of low-abundant target proteins for bioactive compounds based on the activity based protein profiling (ABPP) approach. Surprisingly, the performance of the BArL probe was better than that of the stepwise tagging approach that is considered to be the most effective method used in ABPP study.     

Image printing on the surface of anti-biofouling zwitterionic polymer brushes by ion beam irradiation

A CMB monomer was polymerized on a glass plate with a surface-confined ATRP initiator containing a 2-bromoisobutyryl group. The glass plate modified with a PCMB brush was highly hydrophilic and showed a strong resistance against non-specific adsorption of proteins and cell adhesion. Upon ion beam irradiation, furthermore, the PCMB brush was ablated and a hollow space with a designed shape could be made to which HEK293 cells (from human embryonic kidney) and Hep G2 (from human hepatoma) cells non-specifically adhered, while no adhesion of these cells to the non-treated area on the brush was observed. The present results clearly indicate the usefulness of ion beam-printed patterns of anti-biofouling zwitterionic polymer brushes in the biomedical field.     

Global existence of solutions to the compressible Navier-Stokes equation around parallel flows

The initial boundary value problem for the compressible Navier-Stokes equation is considered in an infinite layer of Rn. It is proved that if n?3, then strong solutions to the compressible Navier-Stokes equation around parallel flows exist globally in time for sufficiently small initial perturbations, provided that the Reynolds and Mach numbers are sufficiently small. The proof is given by a variant of the Matsumura-Nishida energy method based on a decomposition of solutions associated with a spectral property of the linearized operator.     

Real-space observation of local anisotropic correlation between buckled dimers on Si(100) induced by a bidentate adsorbed molecule

The anisotropic correlation between buckled dimers on Si(100) was investigated by scanning tunneling microscopy. A bidentate ligand molecule was used to pin two neighboring dimers at 300 K. The chemically pinned dimer induces antiferromagnetic interaction along the dimer rows. Observed results agree well with Monte-Carlo simulations semi-quantitatively.     

Highly clear and transparent nanoemulsion preparation under surfactant-free conditions using tandem acoustic emulsification

A new technique for the preparation of a highly clear and transparent emulsified aqueous solution containing immiscible monomer droplets with diameters of a few tens of nanometres under surfactant-free conditions using tandem acoustic emulsification is described. Highly conductive transparent polymer films were successfully prepared from such an emulsified solution.     

Hydrogen bond lifetimes in supercritical methanol–water mixtures via MD simulation

Dynamical features of hydrogen bonds in methanol–water mixtures have been analysed in terms of lifetime in the wide range of conditions, including supercritical states, using a molecular dynamics simulation with flexible potential models. Hydrogen bond characteristics in methanol–water mixtures were investigated by considering the combination of molecular species and donor–acceptor of hydrogen-bonded molecules. The hydrogen bond lifetimes mainly depend on temperature, and those in supercritical condition were about 1/10th of that at ambient condition. Focusing on the composition dependence of the hydrogen bond lifetime, the unique behaviour of that resulting from hydration structure was observed. Moreover, the molecular combination, which showed the largest hydrogen bond lifetime, was different for ambient and high temperature and high pressure conditions. The relationship between hydrogen bond lifetime and molar volume was also calculated to discuss the hydrogen bond lifetime in terms of the collision frequency of molecules and the intermolecular distance.