Novel des-fatty acyl-polymyxin B derivatives with Pseudomonas aeruginosa-specific antimicrobial activity

Polymyxin B (PMB) is a cationic cyclic decapeptide antibiotic with a fatty acyl (FA) modification at the α-amino group of Dab1 (Dab: L-α,γ-diaminobutyric acid). In this study, which is part of a series of PMB structure-activity relationship investigations focused on identifying clinically useful peptide antibiotics, we synthesized ten des-FA PMB derivatives whose N-terminal moieties were changed to basic or hydrophilic amino acids. The antimicrobial and lipopolysaccharide (LPS) binding activities of these synthetic analogs were tested. The analogs showed more potent antimicrobial activity against Pseudomonas aeruginosa (P. aeruginosa) compared with the PMB nonapeptide. In particular, [Ser2-Dap3]-PMB(2-10), Guanyl-[Thr2-Dab3]-PMB(2-10), Guanyl-[Dab1-Thr2-Dab3]-PMB(1-10), and N(α,γ)-diguanyl-[Dap3]-PMB(3-10) had antimicrobial activity equivalent to PMB. In LPS binding assays, the displacement curves shifted in a manner proportional to the number of positive charges available to bind to Escherichia coli (E. coli) and P. aeruginosa. Furthermore, peptides with basic side chains were comparable to PMB in binding activity assays against E. coli and P. aeruginosa. The acute toxicities of the peptides were evaluated by intravenously administering the peptides to mice through the tail vein. The toxicities of [Ser2-Dap3]-PMB(2-10), [Dap3]-PMB(3-10), and [Ser3]-PMB(3-10) were lower that of PMB (LD??, 4.8 μmol/kg).     

The effect of pressure on the phase transition behavior of tridecane, pentadecane, and heptadecane: a Fourier transform infrared spectroscopy study

The effect of pressure on the phase transition behavior of tridecane (C(13)), pentadecane (C(15)), and heptadecane (C(17)) has been investigated up to 489, 220, and 387 MPa, respectively, using Fourier transform infrared spectroscopy at 25 °C. The transition between the high pressure ordered (HPO) and high pressure rotator (HPR) phases has been observed in the pressure ranges of 270-220, 106-95, and 152-181 MPa for C(13), C(15), and C(17), respectively, and the transition between the HPR and liquid phases was observed in the pressure ranges of 171-112, 73-47, and 43-70 MPa for C(13), C(15), and C(17), respectively. The P(1)+P(3) band of the methylene rocking mode exhibits factor group splitting caused by intermolecular vibrational coupling. This was observed in both the HPO and HPR phases, while the P(1)+P(3) band did not split in the liquid phase. The separation of the peaks in the P(1)+P(3) band changed discontinuously at the HPO-HPR and HPR-liquid phase transitions, even though the separation is known to change continuously in the transition from the liquid to the high temperature rotator (HTR) phase. In the HPR phase, the ratio of the intensities of the higher and lower frequency components in the P(1)+P(3) doublet is roughly unity independent of pressure, while it is known to be much less than unity in the HTR phase. The separation of the P(1)+P(3) doublet in the HPR phase is found to be larger for longer alkanes. From the intensity ratio, a large proportion of alkane molecules is believed to participate in intermolecular vibrational coupling and possess herringbone-type short-range positional order in the HPR phase. Conversely, in the HTR phase only small proportion of alkane molecules participate in intermolecular vibrational coupling. From the pressure dependence of the separation of the doublet, intermolecular vibrational coupling and herringbone-type short-range positional order is considered to change discontinuously at the HPR-liquid phase transition, while they are reported to change continuously at the HTR-liquid phase transition. The HPR-liquid phase transition is governed by the effect of molecular packing while the HTR-liquid phase transition is predominantly governed by the difference in entropy between the herringbone-type and parallel-type packing.     

Cross Fractionation of Styrene-Butadiene Copolymer

A sample of styrene-butadiene copolymer was fractionated by successive precipitation (one-direction fractionation) in cyclohexane/isooctane and benzene/methyl ethyl ketone systems. The chemical composition and molecular weight distributions of the sample were constructed from the fractionation data. The results obtained in both systems were nearly identical for the chemical composition distribution, but were different for the molecular weight distribution. The same sample was fractionated by cross fractionation using both solvent/nonsolvent systems. Comparing the results of cross fractionation with the results of one-direction fractionation, the first gave broader molecular weight and chemical composition distribution curves than the second. However, only cross fractionation showed that the chemical composition distribution curve has a long tail not only at the right side but also at the left side of the distribution maximum.

The superiority of cross fractionation over one-direction fractionation seems clear from the present work. It is also clear that even if the chemical composition distribution curves obtained by one-direction fractionation in different systems are identical with one another, the curves do not always show the true distribution.     

Characterization of an organic field-effect thin-film transistor in operation using fluorescence-yield x-ray absorption spectroscopy

In?situ element-specific observation of electronic states of organic films beneath metal electrodes is achieved by x-ray absorption spectroscopy (XAS) in the bulk-sensitive fluorescence-yield (FY) mode. The molecular orientation in Au-covered oligo-thiophene films is confirmed by the C K-edge FY-XAS spectra and the applied bias dependence of the spectra is successfully detected for the first time. The present method can give deeper insights into the electronic-state investigation of various real-device systems under operational conditions.     

Nanosize-induced hydrogen storage and capacity control in a non-hydride-forming element: rhodium

We report the first example of nanosize-induced hydrogen storage in a metal that does not absorb hydrogen in its bulk form. Rhodium particles with diameters of <10 nm were found to exhibit hydrogen-storage capability, while bulk Rh does not absorb hydrogen. Hydrogen storage was confirmed by in situ powder X-ray diffraction, solid-state (2)H NMR, and hydrogen pressure-composition isotherm measurements. The hydrogen absorption capacity could be tuned by controlling the particle size.     

Durability enhancement and degradation of oxygen evolution anodes in seawater electrolysis for hydrogen production

For the anode composed of electrocatalyst oxide, intermediate layer and titanium substrate, the substitution of a certain amount of iridium with tin in the IrO₂ intermediate layer was remarkably effective in elongating the life of the anode in preventing oxidation of the substrate titanium during oxygen evolution. The longest life was realized by preparation of intermediate layer with uniform thickness by brush-coating of H₂IrCl₆-SnCl₄ butanol solution and subsequent calcination. The anode with the intermediate layer prepared from 0.04 M H₂IrCl₆-0.06 M SnCl₄ butanol solution showed the best performance, that is, the oxygen evolution efficiency higher than 99.8% for more than 4300 h in the electrolysis of 0.5 M NaCl solution of pH 1 at the current density of 1000 Am⁻². An increase in SnCl₄ concentration decreased the viscosity of the coating solution with a consequent enhancement of uniformity of the intermediate layer but decreased the thickness of the intermediate layer acting as a barrier to prevent oxidation of titanium. Thus, the best performance was attained at an intermediate SnCl₄ concentration. The growth of an oxide layer on titanium during electrolysis occurred and was found by the potential increase.     

Advances in Artificial Cell Membrane Systems as a Platform for Reconstituting Ion Channels

An artificial cell membrane that is composed of bilayer lipid membranes (BLMs) with transmembrane proteins incorporated within them represents a well‐defined system for the analysis of membrane proteins, especially ion channel proteins that are major targets for drug design. Because the BLM system has a high compatibility with recently developed cell‐free expression systems, it has attracted attention as a next‐generation drug screening system. However, three issues associated with BLM systems, i. e., their instability, the need for non‐volatile organic solvents and a low efficiency of ion channel incorporation, have limited their use as a drug screening platform. In this personal account, we discuss our recent approaches to address these issues based on microfabrication. We also discuss the potential for using the BLM system combined with cell‐free expression systems as a drug screening system for future personalized medicine.     

Tailoring of Deep‐Red Luminescence in Ca2SiO4:Eu2+

We report a new dicalcium silicate phosphor, Ca_2?xEu_xSiO₄, which emits red light in response to blue‐light excitation. When excited at 450 nm, deep‐red emission at 650 nm was clearly observed in Ca_1.2Eu_0.8SiO₄, the external and internal quantum efficiencies of which were 44 % and 50 %, respectively. The red emission from Ca_2?xEu_xSiO₄ was strongly related to the peculiar coordination environments of Eu²⁺ in two types of Ca sites. The red‐emitting Ca₂SiO₄:Eu²⁺ phosphors are promising materials for next‐generation, white‐light‐emitting diode applications.     

Efficient synthesis of useful heterocycles via transition metal-catalyzed cascade processes

This paper reports our recent results from synthesis of some useful heterocycles, for example oxazolidinones, indoles, and quinoxalinones, by transition metal-catalyzed cascade processes. The scope and limitations of these procedures and the reaction mechanism for formation of the heterocycles are also discussed.