Weak base fractional composition

Different approaches have been published regarding the prediction of partition coefficients on the basis of physicochemical parameters of compounds [26-29], These authors described algorithms for the estimation of blood-air and tissue-blood partition coefficients. The most important descriptor for blood-tissue partitioning appears to be lipophilicity and can be described as a function of blood and tissue composition with regard to the lipid and water fractions. Charged molecules do not easily pass membranes passively however, weak bases appear to interact with the charges present at the hydrophilic moieties of phospholipids and can be transferred over the membranes in this way [28]. 

A weak acid or base has a small ionization constant or Ky is much less than 1. For a weak acid or base, the corresponding ionization reaction occurs to a limited extent, with a significant fraction of the acid or base not ionized. To determine the equilibrium composition of a solution of a weak acid or weak base, we need to solve an equilibrium problem, typically by using an ICE table and the value of the appropriate ionization constant, or K. Ionization constants of some weak acids and weak bases are provided in Table 16.4. A more extensive list is given in Appendix D. Ionization constants of acids and bases are determined by experiment. 

Under certain conditions, one can observe a double reentrant transition. For example, a weakly charged gel based on NIPA-sodium acrylate copolymer swollen in a water-methanol mixture undergoes reentrant phase transition two times when the methanol concentration is gradually increased. This behavior can be connected with leveling off the solvent compositions inside and outside the gel at equal volume fractions of both the solvent components in the system, which is caused by a gain in the entropy of mixing. 

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