Fraction Of Total Uptake Research Articles

Oxidative coupling and the irreversible adsorption of phenol by graphite

Uptake of phenol by graphite, and regeneration by methanol extraction, was measured to evaluate irreversible adsorption of phenols to carbon surfaces. The emphasis of this work was to identify the role of oxidative coupling, which has been invoked to explain irreversible phenol sorption by activated carbons. Graphite was chosen as a model carbon surface to eliminate potentially confounding effects of microporosity present in other types of carbonaceous sorbents. The isotherm data were well described by the Langmuir–Freundlich isotherm from pH 3 to 9. At pH 12, measured uptakes were higher than expected based on model predictions, suggesting the occurrence of an adsorption mechanism besides physisorption. One oxidative coupling product, 2,2′-dihydroxybiphenyl, was obtained exclusively after adsorption at pH values above 7, and appeared both in aqueous solution and in the methanol regenerant solution. The fraction of total uptake that was not recoverable by methanol extraction decreased with increasing phenol concentration in solution, suggesting preferential sorption by high-energy sites. However, absolute irreversible adsorption increased with phenol concentration in solution. Both fractional irreversible adsorption and 2,2′-dihydroxybiphenyl oxidative coupling product recovery as a function of pH and contact time demonstrated that irreversible sorption of phenol by graphite could not be explained by an oxidative coupling mechanism alone.

Basolateral 3-O-methylglucose transport by cultured kidney (LLC-PK1) epithelial cells.

In previous work we demonstrated the similarity of basolateral sugar transport of LLC-PK1 renal epithelia to basolateral kidney sugar transport using 2-deoxy-D-glucose as a substrate. In this study we first examine a central limitation to use of 2-deoxyglucose for basolateral sugar transport study in LLC-PK1 epithelia, namely, a shift of the rate-limiting step in uptake from transport to phosphorylation. Use of 3-O-methylglucose avoids this complication because it is not phosphorylated. However, use of 3-O-methylglucose requires much shorter incubation periods to examine linear rates of uptake (steady state is reached by 60 s at 22 degrees C for 0.1 mM 3-O-methylglucose). As was true for 2-deoxyglucose, apical uptake of 3-O-methylglucose was only a fraction of total uptake. Basolateral uptake was characteristically more sensitive to phloretin and cytochalasin B inhibition, relative to phlorizin. Inhibition studies indicate a requirement for a free hydroxyl on C-1 carbon of the pyranose ring, as is characteristic for renal basolateral sugar transport. Kinetic analysis indicates a single transport system with a Km of 10.9 mM and Vmax of 17.2 pmol.micrograms DNA-1.15 s-1. Subconfluent, undifferentiated LLC-PK1 cells show a similar Km (12.7 mM) but a ninefold higher Vmax (166.2 pmol.micrograms DNA-1.15 s-1). Stimulation of 3-O-methylglucose transport rate in confluent cultures by phorbol ester is relatively small (less than 100%) compared with effects on other somatic cells. The uptake rate of 3-O-methylglucose is not affected by glucose starvation, but subsequent refeeding with glucose-containing medium does significantly stimulate uptake.