Polysorbates barbiturates

Ismail, A. A., M. W Gouda, and M. M. Motawi. 1970. Micellar solubilization of barbiturates. I. Solubilities of certain barbiturates in polysorbates of varying hydrophobic chain ledcJRtiarm. Sci. 59 220-224. 

Materials that are solubilized in polyethylene glycol can be solubilized in the polyoxyethylene chains on the surface of a nonionic micelle. Ismail, Gouda, and Motawi found that the micellar partition coefficients of barbiturates in polysorbates 20, 40, 60, and 80 is a function of the solute substituents and is proportional to the octanol-water partition coefficient of the barbiturate. Similarly, Ikeda, Kato, and Tukamoto showed that the solubilization of alkyl barbiturates by polyoxyethylene lauryl ether is not dependent upon the number of carbons in the substituents. Since the different polysorbates contain different aliphatic groups, the rather small dependence of solubilization upon polysorbate number (i.e., upon alkyl chain length) suggests that the barbiturates are not solubilized primarily in the hydrocarbon portion of the micelle. Gouda, Ismail, and Motawi showed that the solubilization of barbiturates in polyoxyethylene stearates is proportional to the number of polyoxyethylene units in the surfactant. 

A relationship between the lipophilicity of the solubilisate, expressed by the partition coefficient between octanol and water, Poctanoi (see Chapter 5), and its extent of solubilisation has been noted for the soluhilisation of substituted barbituric acids by polyoxyethylene stearates, of substituted benzoic acids by polysorbate 20, and of several steroids by polyoxyethylene nonionic surfactants. An exhaustive survey of data for the solubilisation of some 64 dmgs by bile salt micelles revealed linear relationships between log (partition coefficient between micelles and water) and log Poctanoi ach of seven bile salts... 

The search for suitable solubilizers is made necessary in the case of the barbiturates by the fact that the soluble sodium salts are unstable and less>soluble forms have therefore to be used. The increases in solubility brought about by 1 to 2% solutions of polysorbates 20-80 are not startling more water-soluble derivatives show a smaller increment in solubility in surfactant solutions (see Table 5.7, Chapter 5). 

Polysorbate 80 in concentrations of 0.01 % has no significant effect on the absorption of ethanol or other low-molecular-weight alcohols, but it increases significantly the absorption of another barbiturate, pentobarbitone. Ethanol can diffuse through pores, while the barbiturate must diffuse across the lipoidal barrier the non-ionic might have a specific effect on the lipid content of the cell... 

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