Solute equilibrated with water environment

Contaminating CO2. The ubiquitous presence of CO2 causes a great difficulty to the experiment. Normal atmosphere contains 0.03% CO2, and a 5-6 ml portion of pure water equilibrated with atmosphere contains 0.06 pmol of CO2. However, the amount of CO2 in buffers and luciferase solutions is much greater. For example, 5 ml of freshly prepared Tris-HCl buffer, pH 7.8, contained 0.13 pmol of CO2 after 20 min degassing, and the value increased to 0.23 pmol when the same buffer was tested one week later (Shimomura et al., 1977). It is strongly advised to eliminate all nonessential CO2 sources from the experimental environment. 

The proton, the smallest solute in the cellular water, illustrates particularly well the critical role of the aqueous milieu of the cell in governing macromolecular stability and function under both stable and variable thermal conditions. One of the ubiquitous features of cellular regulatory processes involves control of pH. No type of cell allows the proton activity within its cytoplasm to equilibrate with that of the external medium, whether the medium in question is the external environment or the extracellular fluids. Organelles, too, may maintain a steep proton gradient between the intra-organellar fluids, for instance, the mitochondrial matrix, and the cytoplasm. 

Membrane Diffusion in Nonaqueous Solvent Environments. Self-diffusion coefficients of Na+ and Cs+ for 1200 EW Nafion membranes in dilute methanol and acetonitrile solutions have been measured (5). Arrhenius plots of these results are shown in Figure 7 along with corresponding results for aqueous experiments activation energies of diffusion are listed in Table IV. Diffusion coefficients of Na+ in methanol and water-equilibrated membranes are very similar, and the activation energy of diffusion for the methanol system is only slightly higher than the respective value for Na+ in pure methanol solvent, 12.9 kJ mol 1 (27). Thus a solution-like diffusion mechanism is inferred for both solvent systems. Cesium ion diffusion in the methanol equilibrated membrane is much slower than sodium ion diffusion in fact the... 

The HPLC technique has certain advantages that allow partition coefficients to be determined relatively rapidly in comparison to the conventional shaking-flask method. The elution process also makes it feasible to run mixture of solutes and yield results relatively free of solute-solute or solute-impurity interactions with a column giving good separation. Basically, the precision of the method depends on whether the value of yw/7o solute in the octanol-water system [Eq. (5)] can be effectively simulated by the column composition. It is therefore important that efforts be expanded to ensure that the properties of the column environment accurately reflect the bulk solvent-water (e.g., octanol-water) characteristics. If the solute can truly be equilibrated between mobile and stationary phases during elution, its retention time is determined by the ratio of the activity coefficients (i.e., partition constant) in the mobile and stationary phases. When octanol and... 

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