Bernd 



Thus, a protein film is thinner than a hydrocarbon such as cetyl alcohol, but 

 under favorable circumstances could have smaller spacings between adjacent 

 molecular groups. Hence, because the basic dimensions of the two types of 

 films can be "roughly" the same given the proper R chains in the protein, the 

 resistance to diffusion under such conditions should be of approximately the 

 same order of magnitude. It is conceivable that various mechanical properties 

 might also be somewhat similar. The problem of course is to find proteins of 

 the proper structure. 



Film Formation from Solution 



The first experimental step was to see whether hydrocarbon films would 

 form unaided from solution, as would have to take place in nature. Some infor- 

 mation was available for proteins (19). 



Saturated solutions were used to promote film formation. They were made 

 by stirring an excess of the material at length in water, after using a wetting 

 agent. Desired was the maximum molecular weight capable of forming a film 

 within a few seconds rather than, as can be the case, minutes or hours. This 

 would then ensure that a surface film is present (in the cavitation test) from the 

 inception of a nucleus. 



Testing for the existence of a surface film was done by placing the solu- 

 tions in a Langmuir trough and highly compressing the surface to see if a film 

 had been formed. The film was then swept off the surface of the water and the 

 creation of a new film checked immediately thereafter. The Langmuir trough 

 is a device for restraining a film between barriers, compressing the film to 

 occupy a smaller surface area, and measuring the reaction of the film to 

 compression. 



Hydrocarbons — For the hydrocarbons, the molecular weights tested ranged 

 from about the minimum expected to be surfactant to the maximum readily avail- 

 able through commercial channels for the linear alcohols, fatty acids, and amines. 

 The test results are given in Table 7. The maximum molecular weights found 

 capable of rapid film formation were: cetyl alcohol (CH3(CH2)i50H), lauric 

 acid (CH3(CH2)i3CH2NH2), and pentadecylamine (CH3(CH2)i3CH2NH2). Each of 

 these materials plus a higher molecular weight in the same series was subse- 

 quently used in the cavitation test. 



Proteins — A similar procedure was followed for selecting proteins, four 

 of which were used in the cavitation test. Egg albumin was chosen because more 

 is known about its spreading than any other protein (18,19,22). Langmuir has 

 studied the film formation of the enzymes pepsin and trypsin, which are protein- 

 like in structure (19). Zein, a corn derivative, also formed films from solution. 



Various gelatins and gelling agents were also tried with some success, as 

 listed in Table 8. Gelatins are obtained from animal proteins and are composed 

 mainly of amines and carboxyls, i.e., proteins or protein fragments. Polyhall 

 is a synthetic polyacrylamide (CH2CHCOHN2). Jaguar, a plant derivative, was 

 included even though it is primarily a carbohydrate containing only 5% protein. 



100 



