Trans-Bilayer Ion Conduction by Proline Containing Cyclic Hexapeptides and Effects of Amino Acid Substitutions on Ion Conducting Properties

Several ion channel forming cyclic peptides have been reported over the past two decades and various ion conducting mechanisms have been proposed. In this article, we report on amino acid substitutions in cyclic hexapeptides and their effects on the ion conducting properties of these peptides. Cyclic hexapeptides, cyclo(Pro-Xxx-Yyy)2, containing two Pro residues, were used as the main framework. The substitution is performed at the Xxx positions with cationic/hydrophilic Lys or hydrophobic Leu. Yyy positions were substituted with D-Phe, D-Ala, or Gly. The peptides which were absent Lys residues showed ion conducting profiles with clear transitions of electric currents, whereas the peptides containing Lys residues tended to exhibit spiky or burst-like profiles. These profiles were altered single state profiles by the protection of ε-amino groups with aromatic protecting groups. The protected analogs exhibited significant decrease in ion conductance. These results indicated that peptides containing Lys conduct ions without forming ring stacked tube-like structure. Ion channel properties were also affected by conformational changes of the cyclic peptides induced by substitution of the Yyy positions. Enhancement of intramolecular β-turn structures of cyclic peptides tended to decrease their ion conductance values

Control of the incorporation and release of guest molecules by photodimerization in liposomes

In a drug-delivery system using liposomes, the use of guest molecules bearing hydrophilic moieties results in some leakage from lipid membranes. We suppressed the leakage of coumarins (used as model guest molecules in a drug-delivery system) from lipid membranes by photodimerization at 365 nm. The reason for this phenomenon could be ascribed to an increase in the hydrophobicity of the dimers of the coumarins. The formation of the dimers was detected by 1H NMR, UV-vis absorption, and mass spectra and the leakage percentages of the coumarins were determined by 1H NMR spectra based on the peak intensities. In contrast, when the dimer reverted to a monomer by ultraviolet (254 nm) irradiation, the resulting monomer was released from liposomes.This work was supported by a JSPS KAKENHI Grant-in-Aid for Scientific Research (B) (Grant No. JP16H04133) and a Grant-in-Aid for Challenging Exploratory Research (Grant No. JP16K13982)

Thermodynamic Properties of Selenium in Ag-Pb Alloy and Lead Oxide Phases at 1273 K

The distribution ratio of Se between Ag-Pb alloy and PbO phases was investigated at 1273 K. A chemical equilibrium technique was used for the measurement. The oxygen partial pressure was in equilibrium with both the phases, and it was measured by an EMF method. The distribution ratio, defined as the mole fraction of Se in PbO to the mole fraction of Se in metal, was plotted against the oxygen partial pressure. The distribution ratio decreased with an increase in the oxygen partial pressure. The slope of the plot indicates that Se dissolves in the PbO phase as oxide, which is unreasonable. The activity coefficient of Se in the Ag-Pb alloy was also measured, and it was found to decrease with an increase in the concentration of Ag. Se dissolved in the PbO phase in the non-oxide form. The activity coefficient of Se in Ag was estimated as 0.0009 at 1273 K

Determination of Low levels of Lead in Tap, River, Ground and Snow Waters using NH4H2PO4 and (NH4)2HPO4 modifiers with Tungsten-treated Pyrolytic Graphite Furnace Atomic Absorption Spectrometry

The W-treated pyrolytic graphite (PG) furnace made it possible to enhance the precision (RSD <2%), calculated limit of detection (LOD) and sensitivity of Pb by a 100 μL injection with 5 μL of modifier of 1w/v% NH4H2PO4 and 1w/v% (NH4)2HPO4. Using the phosphate modifier gave the LOD of 0.02 μg L-1 with a hollow cathode lamp as a radiation sauce. The modification effect on sulfate matrices, such as Na2SO4, K2SO4 and MgSO4 remaining a severe interference for a Pd modifier, was extended to be the upper limit to 50, 50 and 10 mg L-1 as cation concentration for each matrix, respectively. The recoveries of 1.00 μg L-1 of Pb added to tap, river and snow water samples were to be 104 ± 1 %, 105 ± 1 % and 102 ± 3 % with 1w/v% NH4H2PO4and to be 99±3 %, 99±2 % and 101±4 % with 1w/v% (NH4)2HPO4, respectively. The Pb concentration of Pb in a certified reference material of river water (MNIJ CRM 7202-a) was agreement with the certified value (1.01±0.02μg kg-1

X-ray and Optical Monitoring of State Transitions in MAXI J1820+070

We report results from the X-ray and optical monitoring of the black hole candidate MAXI J1820+070 (=ASSASN-18ey) over the entire period of its outburst from March to October 2018.In this outburst, the source exhibited two sets of `fast rise and slow decay'-type long-term flux variations. We found that the 1--100 keV luminosities at two peaks were almost the same, although a significant spectral softening was only seen in the second flux rise. This confirms that the state transition from the low/hard state to the high/soft state is not determined by the mass accretion rate alone. The X-ray spectrum was reproduced with the disk blackbody emission and its Comptonization, and the long-term spectral variations seen in this outburst were consistent with a disk truncation model. The Comptonization component, with a photon index of 1.5-1.9 and electron temperature of ~>40 keV, was dominant during the low/hard state periods, and its contribution rapidly decreased (increased) during the spectral softening (hardening). During the high/soft state period, in which the X-ray spectrum became dominated by the disk blackbody component, the inner disk radius was almost constant, suggesting that the standard disk was present down to the inner most stable circular orbit. The long-term evolution of optical and X-ray luminosities and their correlation suggest that the jets substantially contributed to the optical emission in the low/hard state, while they are quenched and the outer disk emission dominated the optical flux in the intermediate state and the high/soft state.Comment: 12 pages, 7 figures, ApJ in pres