Synthesis and preparation of nanoparticles composed of amphiphilic poly(γ-glutamic acid) with different hydrophobic side chains and their potential of membrane disruptive activity

In the development of nanoparticle-based vaccine adjuvants, the interaction between nanoparticles (NPs) and the cells is a key factor. To control them, we focused on the relationship between the hydrophobicity of the side chains and the cell membrane. In this study, amphiphilic poly(γ-glutamic acid) (γ-PGA), using various types of hydrophobic side chains, was synthesized and used to prepare NPs for evaluating the membrane disruptive activity. When leucine ethyl ester (Leu), methionine ethyl ester (Met), or tryptophan ethyl ester (Trp) was grafted, each polymer formed monodispersed NPs at physiological conditions. Significantly, NPs composed of Leu and Trp showed a membrane disruptive activity at the endosomal environment (pH 5–6.5), while NPs composed of Met did not show. This might be due to the weak hydrophobicity of Met compared to that of Leu and Trp, which demonstrated that the interaction between NPs and cells could be controlled by designing the polymer compositions.     

Selective Ablation of β‐Galactosidase‐Expressing Cells with a Rationally Designed Activatable Photosensitizer

We have developed an activatable photosensitizer capable of specifically inducing the death of β‐galactosidase‐expressing cells in response to photoirradiation. By using a selenium‐substituted rhodol scaffold bearing β‐galactoside as a targeting substituent, we designed and synthesized HMDESeR‐βGal, which has a non‐phototoxic spirocyclic structure owing to the presence of the galactoside moiety. However, β‐galactosidase efficiently converted HMDESeR‐βGal into phototoxic HMDESeR, which exists predominantly in the open xanthene form. This structural change resulted in drastic recovery of visible‐wavelength absorption and the ability to generate singlet oxygen (¹O₂). When HMDESeR‐βGal was applied to larval Drosophila melanogaster wing disks, which express β‐galactosidase only in the posterior region, photoirradiation induced cell death in the β‐galactosidase‐expressing region with high specificity.     

A solvable model of microscopic frequency modulation: I. Conventional treatment of the damping operator

A solvable model of quantum-statistical mechanical frequency modulation is proposed and is solved for the cases of boson and two-state irrelevant subsystems to obtain the intensity distribution for a certain operator of the relevant subsystem. The damping theoretical approach, which is based on the time-independent projection operator method, to the model is also investigated.     

Endpoint Strichartz estimates and global solutions for the nonlinear Dirac equation

We prove endpoint Strichartz estimates for the Klein-Gordon and wave equations in mixed norms on the polar coordinates in three spatial dimensions. As an application, global wellposedness of the nonlinear Dirac equation is shown for small data in the energy class with some regularity assumption for the angular variable.     

Further studies of the reaction kernel structure and stabilization of jet diffusion flames

The structure of axisymmetric laminar jet diffusion flames of ethane, ethylene, acetylene, and propane in quasi-quiescent air has been studied numerically in normal earth gravity (1g) and zero gravity (0g). The time-dependent full Navier–Stokes equations with buoyancy were solved using an implicit, third-order accurate numerical scheme, including a C₃-chemistry model and an optically thin-media radiation model for heat losses. Observations of the flames were also made at the NASA Glenn 2.2-Second Drop Tower. For all cases of the fuels and gravity levels investigated, a peak reactivity spot, i.e., reaction kernel, was formed in the flame base, thereby holding a trailing diffusion flame. The location of the reaction kernel with respect to the burner rim depended inversely on the reaction-kernel reactivity or velocity. In the C₂ and C₃ hydrocarbon flames, the H₂–O₂ chain reactions were important at the reaction kernel, yet the CH₃ + O → CH₂O + H reaction, a dominant contributor to the heat-release rate in methane flames studied previously, did not outweigh other exothermic reactions. Instead of the C₁-route oxidation pathway in methane flames, the C₂ and C₃ hydrocarbon fuels dehydrogenated on the fuel side and acetylene was a major hydrocarbon fragment burning at the reaction kernel. The reaction-kernel correlations between the reactivity (the heat-release or oxygen-consumption rate) and the velocity, obtained previously for methane, were developed further for various fuels in more universal forms using variables related to local Damköhler numbers and Peclet numbers.     

New approach to unravel the structure–property relationship of methylcellulose

In the present paper we suggest a new concept to overcome some of the so far unsolved problems of the structure–property relationship of methylcellulose, the most important nonionic cellulose ether industrially produced in large scale. Not only from the viewpoint of scientific understanding, but also from that of the peculiar and application-determining behavior, the aggregation in aqueous solution and phase separation on heating are the most important questions. As a part of the concept, we had prepared amphiphilic block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as structural models of typical sequences in methylcellulose chains. Now static and dynamic light scattering measurements and transmission electron microscopy (TEM) were carried out using solutions of the oligomers in water. Ellipsoidal particles with dimensions of about 50 nm for the semi-major axis and of circa 25 nm for the semi-minor one could be detected. These findings agree with the radii of gyration and the hydrodynamic radii, determined by static and dynamic light scattering. The data preliminary obtained demonstrate the strong aggregation tendency of block-like methylated cello-oligosaccharides.     

Microscopic characterisation of self-assembled colloidal particles in electrohydrodynamic convection of a low-birefringence nematic liquid crystal

Electrokinetics of small particles immersed in anisotropic fluids is attracting attention in recent years. Here we focus on microscopic appearance of single as well as self-assembled particles moving in the electrohydrodynamic convection (EHC) of a nematic liquid crystal with low birefringence. Characterisation of the birefringent properties is made by polarised light microscopy under different illumination conditions. Because of the small optical anisotropy, the director distortion around the particles clearly exhibits distinctive colours on both sides depending on the height in the cell. The observation can be explained as the change in the net phase retardation of the light. It is also found that a caterpillar-like motion is possible by tuning temperature, although the horizontal size of the EHC rolls is relatively narrow.     

Cup-burner flame structure and extinguishment by CF3Br and C2HF5 in microgravity

The effects of fire-extinguishing agents CF₃Br and C₂HF₅ on the structure and extinguishing processes of microgravity cup-burner flames have been studied numerically. Propane and a propane–ethanol–water fuel mixture, prescribed for a Federal Aviation Administration (FAA) aerosol can explosion simulator test, were used as the fuel. The time-dependent, two-dimensional numerical code, which includes a detailed kinetic model (177 species and 2986 reactions), diffusive transport, and a gray-gas radiation model, revealed unique flame structure and predicted the minimum extinguishing concentration of agent when added to the air stream. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilized a trailing flame. The calculated flame temperature along the trailing flame decreased downstream due to radiative cooling, causing local extinction at <1250 K and flame tip opening. As the mole fraction of agent in the coflow (X_a) was increased gradually: (1) the premixed-like reaction kernel weakened (i.e., lower heat release rate) (but nonetheless formed at higher temperature); (2) the flame base stabilized increasingly higher above the burner rim, parallel to the axis, until finally blowoff-type extinguishment occurred; (3) the calculated maximum flame temperature remained at nearly constant (≈1700 K) or mildly increased; and (4) the total heat release of the entire flame decreased (inhibited) for CF₃Br but increased (enhanced) for C₂HF₅. In the lifted flame base with added C₂HF₅, H₂O (formed from hydrocarbon-O₂ combustion) was converted further to HF and CF₂O through exothermic reactions, thus enhancing the heat-release rate peak. In the trailing flame, “two-zone” flame structure developed: CO₂ and CF₂O were formed primarily in the inner and outer zones, respectively, while HF was formed in both zones. As a result, the unusual (non-chain branching) reactions and the combustion enhancement (increased total heat release) due to the C₂HF₅ addition occurred primarily in the trailing diffusion flame.     

Temperature dependence of the elastic modulus of crystalline regions of Poly(ethylene terephthalate)

The temperature dependence of the elastic modulus E₁ of crystalline regions of poly(ethylene terephthalate) (PET) in the direction parallel to the chain axis has been investigated by x-ray diffraction. The axial chain contraction coefficient is constant from 25°C to 200°C, and correspondingly the value of E₁ (108 GPa) remain unchanged up to 215°C. This is in contrast with the temperature dependence of E₁ values of various polymers previously reported. It is considered for PET that the axial thermal molecular motions which cause the decrement of E₁ do not take place in the crystalline regions, and that the force constant of bond stretching and that of bond angle bending are constant over both the temperature and the stress range studied. It is reasonable to conclude that the mechanical structure of drawn PET is composed of the series model.