Quantitative Visualization of the Interaction between Complement Component C1 and Immunoglobulin G: The Effect of CH1 Domain Deletion

Immunoglobulin G (IgG) adopts a modular multidomain structure that mediates antigen recognition and effector functions, such as complement-dependent cytotoxicity. IgG molecules are self-assembled into a hexameric ring on antigen-containing membranes, recruiting the complement component C1q. In order to provide deeper insights into the initial step of the complement pathway, we report a high-speed atomic force microscopy study for the quantitative visualization of the interaction between mouse IgG and the C1 complex composed of C1q, C1r, and C1s. The results showed that the C1q in the C1 complex is restricted regarding internal motion, and that it has a stronger binding affinity for on-membrane IgG2b assemblages than C1q alone, presumably because of the lower conformational entropy loss upon binding. Furthermore, we visualized a 1:1 stoichiometric interaction between C1/C1q and an IgG2a variant that lacks the entire C_H1 domain in the absence of an antigen. In addition to the canonical C1q-binding site on Fc, their interactions are mediated through a secondary site on the C_L domain that is cryptic in the presence of the C_H1 domain. Our findings offer clues for novel-modality therapeutic antibodies.     

Solvent- and Light-Sensitive AIEE-Active Azo Dye: From Spherical to 1D and 2D Assemblies

Fluorescent molecular assembly systems provide an exciting platform for creating stimuli-responsive nano- and microstructured materials with optical, electronic, and sensing functions. To understand the relationship between (i) the plausible molecular structures preferentially adopted depending on the solvent polarity (such as N,N-dimethylformamide [DMF], tetrahydrofuran [THF], and toluene), (ii) the resulting spectroscopic features, and (iii) self-assembled nano-, micro-, and macrostructures, we chose a sterically crowded triangular azo dye (3Bu) composed of a polar molecular core and three peripheral biphenyl wings. The chromophore changed the solution color from yellow to pink-red depending on the solvent polarity. In a yellow DMF solution, a considerable amount of the twisted azo form could be kept stable with the help of favorable intermolecular interactions with the solvent molecules. By varying the concentration of the DMF solution, the morphology of self-assembled structures was transformed from nanoparticles to micrometer-sized one-dimensional (1D) structures such as sticks and fibers. In a pink-red toluene solution, the periphery of the central ring became more planar. The resulting significant amount of the keto-hydrazone tautomer grew into micro- and millimeter-sized 1D structures. Interestingly, when THF-H₂O (1:1) mixtures were stored at a low temperature, elongated fibers were stacked sideways and eventually developed into anisotropic two-dimensional (2D) sheets. Notably, subsequent exposure of visible-light-irradiated sphere samples to solvent vapor resulted in reversible fluorescence off↔on switching accompanied by morphological restoration. These findings suggest that rational selection of organic dyes, solvents, and light is important for developing reusable fluorescent materials.     

Bactericidal effect of cationic hydrogels prepared from hydrophilic polymers

This study investigated whether hydrogels comprising hydrophilic cationic polymers have similar bactericidal effects. Bacteria were seeded on hydrogels and agar and their viability was assessed with time. Cationic hydrogels displayed bactericidal effects upon long-term bacterial contact. Furthermore, we assessed the areal density of cationic monomer unit of the cationic hydrogels, water content, and the initial elastic modulus. We examined correlations between each factor and bacterial death ratios; consequently, the bacterial death ratios were strongly correlated with the areal density of cationic hydrogel monomers. Elastic energy (W_el) generated at the cytomembrane ion-binding region and the cationic hydrogel and the cytomembrane interfacial energy (W_f) were estimated; consequently, W_el exceeded W_f at higher contact areas. The cationic hydrogel may extract cytomembranes with a reasonable adsorption area. Therefore, cationic hydrogels may be used as probes for ultrasonic echo to sterilize medical equipment.     

Contact and friction between catheter and blood vessel

Therapeutic vascular catheterization techniques are sometimes hampered by the frictional forces between the blood vessel and the catheter, when contact points of the vessel are changing and deforming during the movement of the catheter. The goal of the present study was to characterize frictional interactions between the blood vessel wall and the catheter using experimental and numerical analysis. First, the frictional force was measured with an experimental apparatus that uses a ball and flattened porcine aorta to simulate frictional forces between the catheter and the vessel. Second, catheter motion was characterized by two-dimensional numerical calculations based on the experimental results. Experimental analysis demonstrated that slip occurred and that friction coefficient between the vessel and the catheter and the deformation of the specimen were small when the contact between the ball and the aorta occurred at a small angle. The compliance of the specimen in the normal direction obtained by the experiment was by far larger than that calculated according to the Hertzian contact theory. Numerical analysis shows that this difference of the parameter of the vessel, which must be determined accurately in surgical simulator, could affect the trajectory of the catheter.     

Poly(sulfonated phenylene)-block-poly(arylene ether sulfone) copolymer for polymer electrolyte fuel cell application

Novel poly(2-(3-sulfo)benzoyl-1,4-phenylene)-block-poly(arylene ether sulfone) copolymers (PSP-b-PAESs) were successfully synthesized by Ni(0)-catalyzed copolymerization of 2,5-dichloro-3′-sulfo-benzophenone (DCSB) and chlorobenzophenone-endcapped oligo(arylene ether sulfone). Their physical property, morphology and polymer electrolyte fuel cell (PEFC) performance were investigated compared to those of the DCSB-based random copolymers and Nafion112. PSP-b-PAES with a measured ion exchange capacity (IEC) of 1.82 meq g^?1, of which the hydrophilic/hydrophobic block lengths were evaluated as 17/8.4, showed the relatively small number of water molecules sorbed per sulfonic acid group (λ = 15) in water and the anisotropic membrane swelling with 2.4 times larger through-plane swelling than in-plane one, whereas it showed the almost isotropic proton conductivity. The PSP-b-PAES exhibited a microphase-separated structure composed of hydrophobic and hydrophilic domains, whereas the random copolymers exhibited a homogenous morphology. The PSP-b-PAES had the larger proton conductivity than the random copolymer with an IEC of 2.01 meq g^?1, especially under the low relative humidities. Even at a low humidification of 17% RH at 90 °C and 0.2 MPa, the PSP-b-PAES exhibited the high PEFC performance; namely, cell voltage of 0.69 V at load current density of 0.5 A cm^?2 and maximum output of 0.73 W cm^?2, which were much higher than those at 30% RH for the random copolymer (0.65 V and 0.51 W cm^?2) and Nafion112 (0.70 V and 0.61 W cm^?2). The PSP-b-PAES showed the fairly high durability of 750 h under PEFC operation at 90 °C in spite of the relatively low molecular weight. PSP-b-PAESs have the high potential as polymer electrolyte membrane for PEFC applications.     

Phase morphologies and mechanical properties of high‐impact polystyrene (HIPS) and polycarbonate blends compatibilized with polystyrene and polyarylate block copolymer

Phasemorphology and mechanical properties of blends of high‐impact polystyrene (HIPS) and polycarbonate (PC) blends compatibilized with a polystyrene (PS) and polyarylate (PAr) (PS–PAr) block copolymer were investigated. Over a broad range of composition from 50/50 through 30/70, HIPS/PC blends formed cocontinuous structures induced by the flow during the extrusion or injection‐molding processes. These cocontinuous phases had heterogeneity between the parallel and perpendicular directions to the flow. The micromorphology in the parallel direction to the flow consisted of stringlike phases, which were highly elongated along the flow. Their longitudinal size was long enough to be longer than 180 μm, while their lateral size was shorter than 5 μm, whereas that in the perpendicular direction to the flow showed a cocontinuous phase with regular spacing due to interconnection or blanching among the stringlike phases. The PS–PAr block copolymer was found to successfully compatibilize the HIPS/PC blends. The lateral size of the stringlike phases could be controlled both by the amount of the PS–PAr block copolymer added and by the shear rate during the extrusion or injection‐molding process without changing their longitudinal size. The HIPS/PC blend compatibilized with 3 wt % of the PS–PAr block copolymer under an average shear rate of 675 s^?1 showed a stringlike phase whose lateral size was reduced almost equal to the rubber particle size in HIPS. The tensile modulus and yield stress of the HIPS/PC blends could be explained by the addition rule of each component, while the elongation at break was almost equal to that of PC. These mechanical properties of the HIPS/PC blends can be explained by a parallel connection model independent of the HIPS and PC phases. On the other hand, the toughness factor of the HIPS/PC blends strongly depended on the lateral size of the stringlike phases and the rubber particle size in the HIPS. It was found that the size of the string phases and the rubber particle should be smaller than 1.0 μm to attain a reasonable energy absorbency by blending HIPS and PC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2347–2360, 2001     

High-Temperature Active Oxidation of Chemically Vapor-Deposited Silicon Carbide in CO─CO2 Atmosphere

Active oxidation behavior of CVD-SiC in CO─CO₂ atmospheres was investigated using a thermogravimetric technique in the temperature range between 1823 and 1923 K. The gas pressure ratio, P _CO2/ P _CO, was controlled between 10⁻⁴ and 10⁻¹ at 0.1 MPa. Active oxidation rates (mass loss rates) showed maxima at a certain value of P _CO2/ P _CO, ( P _CO2/ P _CO )^*, In a P _CO2/ P _CO region lower than the ( P _CO2/ P _CO)^* a carbon layer was formed on the SiC surface. In a P _CO2/ P _CO region higher than the ( P _CO2/ P _CO)^*, silica particles or a porous silica layer was observed on the SiC surface.     

Temperature- and pH-responsive photosensitization activity of polymeric sensitizers based on poly-N-isopropylacrylamide

We previously reported that a copolymer consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, behaves as a photosensitizer showing temperature-controlled oxygenation activity in water (J. Am. Chem. Soc.2006, 128, 8751). This polymer shows a heat-induced oxygenation enhancement at low temperature region (5-20 °C), while showing a heat-induced oxygenation suppression at high temperature region (20-60 °C), resulting in an off-on-off activity profile against the temperature window. This is driven by a heat-induced phase transition of the polymer from coil to micelle and then to globule states. In the present work, effects of adding an amine component (N-[3-(dimethylamino)propyl]acrylamide: DMAPAM) to the polymer on the sensitization activity were studied, where the relationship between the phase transition behavior and the activity was clarified by several spectroscopic analyses. The polymers, poly(NIPAM_x-co-BP_y-co-DMAPAM_z), show activity controlled by temperature and pH. The off-on-off activity profile shifts to higher temperature with a pH decrease. This is because protonation of the DMAPAM units leads to an increase in the polymer polarity and, hence, the polymer aggregates at higher temperature. In addition, increase in the DMAPAM content of the polymer leads to further shift of the activity profile. In contrast, at pH < 8, no activity enhancement is observed because complete protonation of the DMAPAM units suppresses polymer aggregation.     

Influence of electrolytes on the photovoltaic performance of organic dye-sensitized nanocrystalline TiO2 solar cells

We have studied the influence of electrolytes on the photovoltaic performance of mercurochrome-sensitized nanocrystalline TiO₂ solar cells using LiI, LiBr, and tetraalkylammonium iodides as the electrolyte. Short-circuit photocurrent density (J_sc) and open-circuit photovoltage (V_oc) depended strongly on the electrolyte. J_sc of 3.42 mA cm⁻² and V_oc of 0.52 V were obtained for the LiI electrolyte and J_sc of 2.10 mA cm⁻² and V_oc of 0.86 V were obtained for the Pr₄NI electrolyte. This difference in photovoltaic performance was due to the change in the conduction band level of the TiO₂ electrode. Large V_oc of 0.99 V was obtained for the LiBr electrolyte due to the large energy gap between the conduction band level of TiO₂ and the Br/Br₂ redox potential. Solar cell performance also depended strongly on organic solvent, suggesting that the physical properties of solvents such as Li ion conductivity and donor number affect photovoltaic performance.     

Unsteady behavior of leading-edge vortex and diffuser stall in a centrifugal compressor with vaned diffuser

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge (i.e., the leading-edge vortex (LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading- edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.