PHOTOSENSFI'IZED REACTIONS 16'1 42 40 80 120 160 AREA/MOLECULE, .•' Figure 4. Surface pressure versus area per molecule for L-o•-dipalmitoyl lecithin on acetic acid- sodium acetate buffer (pH 5.9) at 25øC and ionic strength 0.1. Key: e, zero concentration of trifiuoperazine dihydrochloride, irradiated and nonirradiated l, 1 X 10-sM trifiuoperazine dihydrochloride, nonirradiated &, 1 X 10-'•M trifiuoperazine dihydrochloride, irradiated same degree as the starting compound (trifiuoperazine) or to a consider- ably greater degree (fluphenazine). The kinetic studies were conducted in the absence of a DPL film in order to determine if the observed photoinduced changes in drug-film interactions were the result of changes in the surface activity of the drugs. The same six phenothiazine drugs were used for this part of the study. However, in order to obtain a measurable surface pressure in the absence of DPI, either before or after irradiaton, the concentration of the drug in the acetate buffer had to be increased to 1 X 10-4M. Under these con- ditions the initial surface pressures of prochlorperazine, trifiupromazine, trifiuoperazine, and fiuphenazine prior to irradiation were 1.6, 4.4, 9.4, and 6.6 dynes/era, respectively. Chlorpromazine and promazine exhib- ited no initial surface pressure at this concentration. Each drug solution was irradiated for a 25-minute period during which time its surface pressure was recorded at convenient intervals. The surface pressure was also recorded periodically for approximately 25 minutes after the irradiation lamp was shut off. Chlorpromazine and prochlorperazine both exhibited a rapid initial increase in surface pressure lasting' two or three minutes, followed by a

162 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 40 80 120 160 AREA/MOLECULE, [•' Figure 5. Surface pressure versus area per molecule for L-o•-dipalmitoyl lecithin on acetic acid- sodium acetate buffer (pH 5.9) at 25øC and ionic strength 0.1. Key: O, zero concentration of fluphenazine dihydrochloride, irradiated and nonirradiated I, 1 X 10-'•M fluphenazine dihydrochloride, nonirradiated &, 1 X 10-•M fluphenazine dihydrochloride, irradiated o IO 20 3o 40 50 TIME • MINU'TES Figure 6. Surface pressure versus time of irradiation of 1 X 10-4M solutions of promazine (&) chlorpromazine HC1 (O) and prochlorperazine diHC1 (I) at 25øC, pH 5.9, and ionic strength 0.1. Dashed line (---) indicates period after irradiation was stopped