302 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS lOO a. 50 o 1 -3-BG PG Acid Urea i-1500 1-4000 Glycerin PCA-Na (Cl 'cine Lac-Na 01 • I I I I I [ • ' i I 5 10 Concentration of Additives I I (w/v %) Figure 5. Relationship between K•K2 values of surfactants and antimicrobial activity of BP against Candida albicans and Pseudomonas aeruginosa. Figure 4. With similarity of chemical structure, the more hydrophobic the surfactants used, the larger the K1 K2 values were obtained. The relationship between this value and the antimicrobial activity of BP is shown in Figure 5. The required concentration of total BP against Candida albicans increased in proportion to the KiK2 values independently of the chemical structure of surfactant. On the other hand, for Pseudomonas aeruginosa, the effective concentration of total BP was 0.9 w/v% for Table II Required Concentration of Total BP (Ct) and Free BP (Cf) against Candida albicans and Pseudomonas aeruginosa Can. albicans Ps. aeruginosa Surfactant K•K• Ct (w/v%) Cf (ppm) Ct (w/v%) Cf (ppm) OE-525 17.64 0.31 74 0.91 201 OE-515 24.16 0.42 73 -- -- OE-510 28.41 0.49 75 -- -- DE-8 36.23 0.58 72 0.89 105 ODE-25 12.23 0.24 74 0.21 64 ODE-20 17.73 0.34 73 0.20 45 ODE-16 24.75 ....

ANTIMICROBIAL ACTIVITY OF BUTYLPARABEN 303 oleyl-ether (OE) or dodecyl-ether (DE) type surfactant, but 0.2w/v for 2-octyl- dodecyl-ether (ODE) type surfactants. Thus, in this case, the required concentration of total BP against Pseudomonas aeruginosa was governed by the chemical structure of surfactant and independent of the K•K 2 values. Table 11 summarizes the data, confirming the effects of free t31' on antimicrobial activity. EFFECT OF ADDITIVES The effect of the addition of various materials to three component systems of OE-515/BP/water on the cloud point, the concentration of free BP, and the antimicrobial activity of BP were carefully examined. Figure 6 shows the change of the cloud point under the presence of various additives. The cloud point was raised with polar oil (RA.TM-318, RA.PE-408), 1.3-BG, PG, urea, 10 0.5 Ps. aeruginosa 0E-$25 DE-8 Can. albicans ODE-25 •OE-525 .,•.•oP..s. aeruginosa ODE-25 ODE-20 O0 I I • I • i . • , • 10 20 30 40 50 K•K2 obtained from reciprocal Langmuir's Plots. Figure 6. Effect of various additives on cloud points of 3w/v% OE-515 aqueous solution containing O.4w/v% total BP. etc. where these were added into the OE-515 (3w/v%) aqueous solution containing 0.4w/v% of total BP. On the other hand, the addition of salts and amino acid such as KCI, Lac-Na, glycine, etc. depressed the cloud point. Figure 7 shows the free BP concentration in the intermicellar aqueous phase under the presence of various additives. Cw represents the concentration of free BP under the presence of additives. The addition of polyethyleneglycol and water-soluble materials such as Di-PG, Lac-Acid, 1.3-BG, etc. markedly increased Cw, while the addition of salts, amino acid such as KCI, Lac-Na, glycine, and polar oils such as RA.TM-318 and RA.PE-408 decreased Cw.