Formation Of Concentration Gradient Research Articles

Cluster formation and diffusion in supersaturated binary and ternary amino acid solutions

Indirect evidence for the existence of molecular clusters in supersaturated solutions of the binary systems glycine-water and valine-water and the ternary system glycine-valine-water is provided through measurement of diffusion coefficients and through concentration gradient formation in long columns. The binary system diffusion coefficient results show that the diffusion coefficient declines with both time and concentration in the metastable region and that this decline can be accounted for employing a theory of precritical molecular cluster evolution. The ternary system result shows that the concentration of valine seems to increase the tendency of glycine to form molecular clusters. In addition the ternary diffusion coefficient results show that the “cross term” diffusion coefficient (hence the multicomponent diffusive effect) becomes as large as the “main” term coefficient in supersaturated glycine-valine-water solutions.

Death of tumor cells in response to the use of a system of stimulated polyamine uptake from the transport of methylglyoxal bis(guanylhydrazone).

Putrescine and spermidine depletion produced by α-difluoromethylornithine, an irreversible inhibitor of omithine decarboxylase (EC 4.1.1.17) greatly enhances the uptake of the anti-cancer drug methylglyoxal bis(guanylhydrazone) by cultured Ehrlich ascites carcinoma cells. The drug was also more effectively retained in the cells previously exposed to the inhibitor of ornithine decarboxylase. When untreated Ehrlich ascites carcinoma cells were shortly exposed to methylglyoxal bis(guanylhydrazone) and then transferred into drug-free medium, they rapidly reinitiated growth, while polyamine-deprived cells were irreversibly damaged upon similar exposure to the drug. Tumor cells with greatly reduced intracellular pools of putrescine and spermidine so effectively concentrated methylglyoxal bis(guanylhydrazone) that the drug largely disappeared from the medium resulting in a formation of concentration gradient of more than 5000-fold across the cell membrane. The tumor cells tolerated high intracellular concentrations (6-9 mM) of methylglyoxal bis(guanylhydrazone) for not more than 24 h whereafter they simply disintegrated and excreted the drug back into the medium. The final destruction of the polyaminedepleted cells in response to methylglyoxal bis(guanylhydrazone) was preceded by profound inhibition of protein synthesis, which occurred before any disturbances in thymidine incorporation were obvious. The inhibition of protein synthesis by methylglyoxal bis(guanylhydrazone) was more pronounced in cells previously exposed to difluoromethylornithine than in cells with normal intracellular polyamine pools. The extent of polyamine depletion produced by difluoromethylornithine and the rate of the uptake of methylglyoxal bis(guanylhydrazone) were positively correlated to the growth rate of the tumor cells, i.e. cells dividing slowly were more resistant towards the action of difluoromethylornithine, as regards the development of intracellular polyamine depletion, and they also accumulated methylglyoxal bis(guanylhydrazone) less effectively than did rapidly dividing cells. The rate of methylglyoxal bis(guanylhydrazone) transport was likewise related to the extent of intracellular putrescine and spermidine deprivation: tumor cells with greatly reduced putrescine and spermidine pools concentrated methylglyoxal bis(guanylhydrazone) more rapidly than cells containing only moderately decreased concentrations of the polyamines. Although the uptake of exogenous spermidine by polyamine-deprived tumor cells was initially at least as rapid as that of methylglyoxal bis(guanylhydrazone), the transport of the natural polyamine was automatically halted when the intracellular spermidine pool was brought to a normal level. It thus appears that the uptake of methylglyoxal bis(guanylhydrazone) by the stimulated transport system of polyamines leads to a suicidal accumulation of the drug and to rapid cell death.

Thermoelectric Powers of Molten I2+Te Solutions

Abstract The initial and steady-state potentials of thermocells of the liquid I2+Te system were measured at temperatures 250–600°C. Cells with a vapor path were used, together with those in which a vapor transport was forbidden. The difference due to these types of cells was found in the values of not the initial thermoelectric powers but the steady-state ones for only solutions with low Te compositions. In the I2-rich region, the mechanism is discussed by using the model of charge-transfer due to I3− as in the case of conductivities and absorption spectra. The thermoelectric data in both the Te-rich and intermediate composition regions suggest that electronic contributions are highly predominant and a transition to delocalized states continuously appears with increasing Te concentration. Some experiments were carried out in order to examine the formation of concentration gradient due to the thermal effect in low Te compositions.