Concentration-dependent activity

Arbutia [497-76-7] (67) has been suggested as a potential antitussive (96). Both oral and iatraperitoneal adrninistration of arbutia to mice ia a range of 50 to 200 mg/kg showed a concentration-dependent activity against ammonia iaduced cough. 

Whilst the fundamental driving force for crystallisation, the true thermodynamic supersaturation, is the difference in chemical potential, in practice supersaturation is generally expressed in terms of solution concentrations as given in equations 15.1-15.3. Mullin and Sohnel(19) has presented a method of determining the relationship between concentration-based and activity-based supersaturation by using concentration-dependent activity-coefficients. 

The mitotic indices observed after treatment of both cell lines with 10-fold the IC70 concentration of each congener establish that the action of the vinca binary alkaloids with this cellular target in vivo is correlated with the ability of the molecule to inhibit microtubule assembly and not with its high-concentration-dependent activities with MTP or microtubules. Based on the current understanding that neurotoxicity and neuro-ti bule damage are concerted events, the results of our structure-activity studies support the optimistic expectation that the development of a nonneurotoxic vinblastine-vincristine congener can be achieved. 

The price for this simplicity is extensive tables of concentration-dependent activity coefficients. 

At constant temperature and pressure, the concentration-dependent activity coefficient can be determined from the free excess enthalpy by differentiation through the mole fraction. These equations are the basis for the methods of Wilson and Prausnitz to calculate the activity coefficient [19, 20], The Gibbs-Duhem equation is again a convenient method for checking the obtained equilibrium data ... 

Concentration-dependent activity coefficients can be accommodated with relative ease by an added term (e.g., [see Helfferich, 1962a Brooke and Rees, 1968] and variations in diffusivities are easily included in numerical calculations (Helfferich and Petruzzelli, 1985 Hwang and Helfferich, 1986). In both instances, however, a fair amount of additional experimental information is required to establish the dependence on composition. Electro-osmotic solvent transfer and particle-size variations are more difficult to deal with, and no readily manageable models have been developed to date. A subtle difficulty here is that, as a rule, there is not only a variation in equilibrium solvent content with conversion to another ionic form, but that the transient local solvent content is a result of dynamics (electro-osmosis) and so not accessible by thermodynamic considerations (Helfferich, 1962b). Theories based on the Stefan-Maxwell equations or other forms of (hcrniodyiiainics of ir-... 

Equation (3) can be simplified through the assumption of constant activity coefficients. Under the assumption of constant activity coefficients, Eq. (3) is in harmony with a Boltzmann distribution of electrons and holes. Such an approach is valid for p/ Nv and n/Nc less than 0.1. At higher concentrations, Fermi-Dirac statistics must be used to account for the distribution of electrons and holes as functions of energy. These effects can be treated by introduction of concentration-dependent activity coefficients for... 

The relationship between these concentration-based supersaturations and the fundamental (activity-based) supersaturation may be expressed through the relevant concentration-dependent activity coefficient ratio, A = 7/7, i.e. 

Figure 5. Induction of caspase-3, -9 activity in HL-60 cells. 50 pg total cell lysate was incubated with fluorogenic substances. Emission spectra were measured by fluorescence spectrophotometer and normalized to control. (A) Concentration-dependent activation of caspase-3 by tested compounds at 24 h. (B) Kinetics of caspase-3 activation. Cells were treated with 30 pMcarnosic acid, 20 pM carnosol or 40 pM ursolic acid for different time periods. Data represent means SE of triplicate tests. (C) Kinetics of caspase-9 activity.

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