PHOTOSENSITIZED REACTIONS 157 Film Studies The surface pressure of the films was determined at various areas per DPL molecule on a series of subphase solutions containing an acetate buffer (pH 5.9) alone or buffer plus 1 X 10-•M of the phenothiazine derivative. The trough area was decreased by 2.5-cm 2increments by use of the movable barrier and surface pressure readings were taken immedi- ately after each area change. Approximately 30 seconds elapsed between each reading. Irradiation was initiated at full trough area after the DPL was spread on the subphase. A two-minute irradiation period was used for all experiments. The surface pressure-surface area (•--A) curves were determined immediately after irradiation. A pure DPL film, i.e., in the absence of any phenothiazine drug, was irradiated for 30 minutes to de- termine its ultraviolet stability. The subphase containing the pheno- thiazine drug (1 X 10-•M) was irradiated for 30 minutes to determine whether any surface activity developed in the absence of the film. Kinetic Studies The effect of time of irradiation on surface pressure was determined for a series of drugs at i X i0-*M concentration in the absence of a DPI, film. The drugs were dissolved in the acetate buffer and the solution was irradiated continuously for 25 minutes. The surface pressure was determined at convenient intervals during this period of irradiation and for 25 minutes after the end of the irradiation period. RESULTS ^Nr) D•SCUSS•ON Irradiation for 30 minutes of a pure DPL film produced no detectable change in surface pressure, which demonstrated the stability of the film to the radiation. Similarly, irradiation of 1 X 10-'•M solutions of the phenothiazine compounds in the absence of the film showed no surface pressure changes, with the exception of prochlorperazine. Irradiation of the buffered solution of prochlorperazine produced a slight surface pres- sure of about 1.5 dynes/cm when the surface was compressed to the small- est allowable trough area. At larger trough areas no surface pressure was detected. No significant temperature change occurred at the film surface over the period of irradiation. DPL was found to form a mixed film with each of the phenothiazines, with the exception of promazine, as evidenced by an increase in area/ molecule of DPL in the presence of these drugs (Figs. 1-5). This ap- parently is the result of penetration of the phenothiazine molecule into

158 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 42 •o 3O r• •4 o 40 80 120 160 AREA / MOLECULE, •,z Figure l. Surface pressure versus area per molecule for L-a-dipalmitoyl lecithin on acetic acid- sodium acetate buffer (pH 5.9) at 25øC and ionic strength 0.1. Key: O, zero concentration of chlorpromazine HC1, irradiated and nonirradiated I, 1 X 10-•M chlorpromazine HC1, nonirradiated a, 1 X 10-•M chlorpromazine HCI, irradiated the DPL film (6). On compression of each of the mixed films, the =-A curves gradually approach that of the pure DPL film. At high pressures (• 30 dynes/cm) the mixed film curves coincide with the pure DPL curve, indicating ejection of the phenothiazine molecule from the film (6). Irradiation modified the =-A characteristics of most of the drug-film systems investigated. In the case of the chlorpromazine-DPL mixed film, an increase in surface presure at all areas per molecule developed on irradiation (Fig. 1). This expansion suggests an increased film interac- tion and penetration by the photoproduced species. Promazine had no influence on the •-A curve of DPL film indicating no drug-film interaction. Irradiation of this system also had no effect on the •--.4 characteristics. Thus, it appears that any photospecies produced as a result of the irradiation possesses approximately the same de•ee of •eactivity toward the DPL film as does promazine itself. Triflupromazine interacts with the DPL to form a mixed film (Fig. 2). The •--.4 characteristics of this mixed film are similar to that observed with the chlorpromazine-DPI, system. However, in contrast to the latter, ir-