BUILT-UP FILMS OF PROTEIN AND OF STEROL’ HEXRY B. BULL* Department (g’ Chemistry, Worthwestern Cninersity Medical School, Chicago. Illinois
Receiued J u n e 29, 1937
Stimulated by the work of Blodgett (1) on the deposition of fatty acid films on solid slides, the author attempted to deposit films of egg albumin directly on solid surfaces, but without success. The effort was then made to deposit a highly purified preparation of the corn protein, zein.3 This has been accomplished. Zein was dissolved in 85 per cent ethyl alcohol and spread on a paraffin waxed glass bath containing pure water. A waxed silk thread was used to separate the protein film from the castor oil which was the source of compression (15 dynes per centimeter). A highly polished chromium slide was raised slowly through the protein film by means of a windlass. Deposition was complete, but the slide emerged wet and had to be dried in an oven at a gentle heat. Deposition was again complete when the slide was lowered through the protein film. The slide had always to be dried upon being raised from the bath. Deposition of one hundred layers was accomplished in this manner. They exhibited beautiful colors which, when compared with the colors of a slide on which fatty acids had been deposited, allowed an estimate of the thickness of the protein films to be made. This was calculated to be about 14 A.U. per protein film deposited. The author is not aware of any surface balance studies done on zein but Hughes and Rideal (2) found a thickness of 12 A.U. for a gliadin film spread on a phosphate buffer a t a pH of 5.9, The most remarkable feature about the zein films is that they are strongly hydrophilic, being completely wet by water. This is especially curious when it is remembered that zein is usually considered to be one of the most hydrophobic proteins. Built-up films of cholesterol were also deposited on polished chromium. The bath was pure water, castor oil was used to compress the surface film, 1 Presented a t the Fourteenth Colloid Symposium, held a t Xnneapolis, M n n e Bots, June 10-12, 1937. 2 With the technical assistance of A b . Alvin Berman. 3 By courtesy of Dr. R . A . Gortner.
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and the cholesterol was dissolved in petroleum ether. The first film \vas dried on, and subsequent filnis deposited rapidly, both with the slide raised or lowered through the surface, and without drying. The films yielded color, but were never as clear and as brilliant as the zein or fatty acid films, being somewhat foggy. They were strongly hydrophobic. REFERESCES
(1) BLODGETT, K. B . : J. Am. Chem. Soc. 67, 1007 (1935). (2) HUGHES,A. H., AND RIDEAL,E . K.: Proc. Roy. SOC. (London) A137, 62 (1932).
