Studies on spermicidal activity of surfactants. I. Correlation between spermicidal effect and physicochemical...

The spermicidal activities of seven nonionic surfactants against human spermatozoa were objectively determined by a statistical method, and two types of ionic surfactants were also studied for purposes of comparison. The nonionic surfactants, p-menthanylphenyl polyoxethylene adducts used in this work were synthesized from turpentine oil. These surfactants were used in the experiment after a careful confirmation of their chemical composition and molecular weight distribution. The spermicidal activities of the surfactants in terms of minimum concentrations to accomplish irreversible immobilization of all sperms in zero time was, in decreasing order, nonionic, cationic and anionic. When the most commonly used nonionics alone were considered, the sequence of decreasing spermicidal potency was isononylphenyl polyoxyethylene (9.0) ether (nonoxynol-9), p-menthanylphenyl polyoxyethylene (8.8) ether (menfegol), isooctylphenyl polyoxyethylene (9.0) ether (octoxynol-9). The surface tension and wetting time of these surfactants were determined with a view to finding physico-chemical measures of their spermicidal activity. In the statistical analysis regarding all the nine surfactants, there was a significant correlation (p less than 0.05) between spermicidal potency and critical micelle concentration (cmc) whereas there was no significant relationship between spermicidal potency and cmc regarding the seven nonionics. There was again no significant correlation between spermicidal potency and wetting time in all but nonionics with a common hydrophobic structure. As neither surface tension nor wetting time appeared to be a valid factor, general measure of spermicidal potency of nonionic surfactants, the partition ratios between n-octanol or n-hexane and water was determined. As a result, it was revealed that there was a significant correlation (p less than 0.05) between spermicidal potency and partition coefficient, when four types of nonionic surfactants with different hydrophobic group, which were chosen from among the seven nonionics, were tested with n-hexane. The close relationship between spermical activity and partition coefficient suggests that the spermicidal activities of these surfactants are associated with their structural affinity to the lipids of spermatozoal cell membrane.