No abstract

Thirteen heterocyclic quinones (5 quinoline quinones, 7 isoquinoline quinones, 1 indole quinone) were tested for their effects on avian myeloblastosis virus reverse transcriptase, growth of murine lymphoblastoma L5178Ycells, respiration of rat liver mitochondria and oxidation of NADH by Clostridium kluyveri diaphorase in comparison with those of streptonigrin, in which the quinoline quinone moiety is considered to play a crucial role.Most of the quinoline quinones and isoquinoline quinones inhibited reverse transcriptase to the same extent as streptonigrin with the ID50 values ranging between 1 and 5^g/ml, whereas the ID50 value of the indole quinone derivative, 4,7-dihydro-2,3-dimethylindole-4,7-dione, was 80^g/ml. The cytotoxicities of the quinones were muchlower than that of streptonigrin; the ID50 values of the quinones were higher than 0.15^g/ml. In particular, the ID50 value of the ort/b-quinoline quinone derivative, 8-methoxy-7-methyl-5,6-dihydroquinoline-5,6-dione, was as high as 16^g/ml, while the 50% inhibition of cell growth was seen in the presence of 0.0025^g/ml streptonigrin. The membranetransport of the quinones was evaluated by comparing the effects on oxygen consumption by mitochondria and oxidation of NADHby bacterial diaphorase, being proven not to be responsible for their lower cytotoxicities.

We performed high-temperature friction experiments to investigate the effect of temperature on the frictional behavior of smectite and illite. Friction coefficients (μ) of these clay minerals increase with increasing temperature as a result of dehydration of absorbed and interstitial water. At a constant normal stress of 60 MPa, μ of Ca-smectite gouge increases from 0.27 at room temperature to 0.67 at 200°C, and μ of illite gouge increase from 0.53 at room temperature to 0.68 at 200°C. Velocity dependence of steady-state friction for smectite and illite gouges changes with temperature so that the transition from velocity-strengthening to velocity-weakening behavior occurs at 150°C at a normal stress of 60 MPa. Temperature at which this change takes place corresponds to the temperature at the updip limit of the seismogenic zone along subducting plates. Thus, the effect of temperature on the frictional behavior of these clay minerals possibly play an important role in controlling the updip limit of subduction thrust earthquakes.

Seismicity along the subducting plate interface shows regional variation, which has been explained by the seismic asperity model where large earthquakes occur at strongly coupled patches that are surrounded by weakly coupled regions. This suggests that the subduction plate interface is heterogeneous in terms of frictional properties; however, the mechanism producing the difference between strong and weak couplings remains poorly understood. Here, we propose that the heterogeneity of the fluid pathway and of the spatial distribution of clay minerals plays a key role in the formation of non-asperity at the subducting plate interface. We use laboratory measurements of frictional properties to show that clay minerals on a simulated fault interface are characterized by weak and slow recovery, whereas other materials such as quartz show relatively quick recovery and thereby strong coupling on the fault surface. Aqueous fluids change the mineralogy at the plate interface by producing clay minerals due to hydrate reactions, suggesting that the hydrated weakly coupled regions act as a non-asperity and form a barrier to rupture propagation along the plate boundary at the depths of seismogenic zone.