Surface phenomena and drug action. Diuretics. Cardiac glycosides. Other ionophoric effects

1 Surface phenomena and drug action. Diuretics. Cardiac glycosides. Other ionophoric effects 

The use of soaps to solubilize phenols in water, for use as disinfectants, depends on the formation of mixed micelles of the soap and the phenol. It has been found that variation in the proportion of soap to phenol leads to several zones, as shown in Fig. 14.2 (Berry, Cook, and Wills, 1956). The first of these exists below 0.03 m potassium laurate and is poorly bactericidal the maximal bactericidal effect is obtained when the soap reaches 0.03M, a figure which is identical with the critical micelle concentration for this soap. It was concluded that this bactericidal action is a combined attack of the phenol (mainly) and the soap on the protoplasmic membrane (see Section 14.2 for membrane damage). The next zone, up to 0.045 soap, is one of greatly diminished bactericidal effect. The interpretation is that the phenol has entered the micelles, many more of which must have formed, and hence little of it is available for disinfection. When still more soap is introduced, a final zone (vigorous disinfection) appears, due to the toxicity of the soap itself. All the phenols commonly used as disinfectants, including/ -chloro-m-xylenol, form zones like these. 

2 Bactericidal action at 20 C of 4-benzylphenol (0.0016 m) in aqueous potassium laurate (concentration varied, as shown). Organism E. coliy 2 X 10 organisms per ml. (Berry et al.y 1956). 

The anthelmintic action of phenols is similarly potentiated by soaps and again it is important to avoid excess of the soap, because micelles can retain most of the phenol and deny it to the worms (Alexander and Trim, 1946). Below the critical micelle concentration of the soap, an adjuvant effect of the soap on the phenol is observable. No soap penetrates into the worms. 

The formation of mixed micelles is well known in physical chemistry. An example potassium myristate (C ) develops micelles at one-quarter the concentration at which potassium laurate (C g) does. Because of mixed micelle formation, as little as 15 per cent of potassium myristate halves the critical micelle concentration of potassium laurate (Klevens, 1948). 

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