Interaction of beta-lactam antibiotics with H+/peptide cotransporters in rat renal brush-border membranes

Two H+/peptide cotransporters, PEPT1 and PEPT2, are expressed in the kidney, mediating the renal tubular reabsorption of oligopeptides and beta-lactam antibiotics. We examined the interactions of beta-lactam antibiotics with peptide transporters in rat renal brush-border membranes by evaluating the inhibitory potencies of the antibiotics against glycylsarcosine transport. Western blot analysis revealed that PEPT1 and PEPT2 were expressed in the renal brush-border membranes with the apparent molecular masses of 75 and 105 kDa, respectively. Using renal brush-border membrane vesicles, the uphill transport of glycylsarcosine was observed in the presence of an inward H+ gradient and an inside-negative membrane potential. Two transport systems with high affinity (Km of 50 microM) and low affinity (Km of 1.2 mM) appeared kinetically to mediate the glycylsarcosine uptake. The inhibition constants of the antibiotics for glycylsarcosine transport were more closely correlated with those in stable LLC-PK1 cells transfected with rat PEPT2 rather than PEPT1 cDNA. The beta-lactam antibiotics with an alpha-amino group showed trans-stimulation effects on the glycylsarcosine uptake, suggesting that these antibiotics and glycylsarcosine share a common peptide transporter. However, the antibiotics lacking an alpha-amino group failed to show the trans-stimulation effect. It is concluded that amino-beta-lactam antibiotics at therapeutic concentrations interact predominantly with PEPT2 localized in the brush-border membranes of rat kidney.     

Prevention of catalyst deactivation caused by coke formation in the methanation of carbon oxides

Prevention of catalyst deactivation in carbon monoxide methanation on a highly active Ni-based composite catalyst has been investigated. The composite catalyst, Ni-La₂O₃-Ru supported on silica, has greater activity than that of a Ni catalyst, but the decrease of the catalyst activity with reaction time is greater than that of the Ni catalyst, especially when the CO conversion is low. The reason for this behaviour is found in the relation between the amount of surface-carbon species and the degree of deactivation. When the CO methanation reaction is operated at above the temperature of complete CO conversion, catalyst deactivation is avoided. At such high temperatures the amount of surface-carbon species is small. The catalyst deactivation is considerably suppressed with a low concentration, e.g. 1–3 kPa, of additional CO₂ or CO₂ + H₂O. The cause of this suppression is considered to be the renewal of the covered surface with the carbon-species by the competitive adsorption of these additives.     

Fracture limits of sheet metals under stretch bending

Fracture limits in sheet stretch bending were theoretically obtained on the assumption that the fracture occurs when the stretching force reaches its maximum value. From the calculated results, a fracture criterion has been presented where limit wall stretch, L_max/L₀ (L_max: limit wall length of a sheet, L₀: initial wall length), is explicitly given as a function of the non-dimensional bending curvature, t₀/R (t₀: sheet thickness, R: bending radius) and the material's work hardening exponent (n-value). To verify this criterion, three-point stretch bending tests with various punch-radii were performed on three types of aluminum sheets (A5182-O, JIS6061-T4 and JIS6N01-T5). The predicted limit wall stretch, as well as limit forming height, were in good agreement with the experimental results.     

Effect of glass transition temperature on heat‐responsive gas bubbles formation from polymers containing tert‐butoxycarbonyl moiety

Various types of polymers containing tert‐butoxycarbonyl (BOC) moiety as the typical protecting group of functional moieties have been used for the design of stimuli‐responsive polymer materials. In this study, we investigated the heat‐responsive deprotection behavior of BOC‐containing polymers obtained by radical polymerization of 4‐(tert‐butoxycarbonyloxy)styrene (BSt) and copolymerizations of BSt with styrene and methyl acrylate. The deprotection of BOC groups accompanying the evolution of isobutene and carbon dioxide as gaseous products was monitored by thermogravimetric analyses at different temperature circumstances; that is, on heating at a rate of 10 °C/min and under isothermal conditions at various temperatures. The deprotection resulted in a significant decrease in the transmittance of visible light due to the formation of a large number of gas bubbles, that is, foaming, in the polymer films when a heating temperature was close to the glass transition temperature of the used polymer. The potential of BOC‐containing polymers was also evaluated as the heat‐responsive adhesive polymers for dismantlable adhesion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46252.     

Crosslinking of poly(vinyl alcohol) and poly(vinyl acetate) using poly(maleic anhydride‐alt−2,4‐dimethyl‐1,3‐pentadiene) as polyfunctional crosslinker and decrosslinking by ozone degradation

Crosslinking and decrosslinking reactions of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) using an alternating copolymer of maleic anhydride and 2,4‐dimethyl‐1,3‐pentadiene (PMAD) as the polyfunctional crosslinker and subsequent ozone degradation are reported. PVA and PVAc are heated at 200 °C for 0.5 to 3 h in the presence of 5 to 30 wt % of PMAD in the solid state to obtain the corresponding crosslinked polymers. The reactions of a hydroxy group of PVA and an acetate group of PVAc with an anhydride group of PMAD slowly proceed to give insoluble polymers with a loose crosslinking structure. Almost no change in the thermal decomposition temperatures and the IR spectra is observed during the crosslinking reactions. The crosslinked PVA produces hydrogels with a high swelling ratio of 500 to 1700%, which are readily degradable during a reaction with ozone in water at 0 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44229.     

Constitutive Model Considering Sand Crushing

The behavior of sand crushing will appear when the confining pressure is up to a certain value, which results in disappearing of the positive dilatancy of sand. Adopting a new hardening parameter with the crushing stress, an elastoplastic constitutive model considering sand crushing is proposed. Comparing the conventional triaxial compression test results with the model prediction, it shows that the proposed model can reasonably describe the dilatancy of sand from positive to negative.