STRl'CTl'RAL 1-ACTORS IN POI.YM1.R17.ATION 5 1 



polymerization and niclanization, inasmuch as il was desired ihal a test ol matrix 

 function be carried out objectively with a model substrate selected for chemical 

 and analytical simplicity. o-Bcnzoquinone woukl be the ideal substrate il it were 

 stable, but its para-isomer was selected as a reasonably satisfactory substitute. 

 Nuclear coupling of /7-quinones to form polymers is known (6). Although experi- 

 ments with catechol and tyrosine are in progress, it was deemed advantageous to 

 avoid the complications that might arise during the initial phase of precursor 

 oxidation and restrict preliminary studies as much as possible to the polymeriza- 

 tion phase. 



The primary criteria established for recognition of directed polymerization 

 were: a) change in color and visible spectrum as related primarily to degree of 

 conjugation, hence degree of polymerization; b) change in solubility; c) minimal 

 changes and minimal differences in elementary composition. 



The basis for selection of proteins as matrix substances was essentially bio- 

 logical; namely, the comparatively greater abundance of melanins in animal tissues 

 lacking the highly developed polysaccharide products of the plant cell wall. It 

 cannot be assumed, of course, that substances such as chitin play no role in 

 melanization, and it is recognized that otherwise the criterion of distribution is 

 far from absolute. The selection of protein was justified, however, by tests made 

 with cellulose and pectic acid, neither of which had any discernible effect upon 

 the behavior of quinone solutions under any of the conditions described below. 



Oxdiative Polymerization Without Matrix. p-Quinone forms yellow solutions 

 with a single, distinct visible absorption maximum (fig. 6); solubility in water 

 corresponds to a concentration of approximately 0.02 m; p-quinone yields, on 

 analysis, C 66.8^, H 3.7%. Under moderately acid conditions (pH 4-5), it is 

 stable for approximately an hour, but darkens rapidly in alkaline media. Under 

 acid conditions solutions undergo color changes toward red-orange and red-brown 

 hues, but yield little or no NaCl-precipitable product, even after 75-100 hours; 

 under alkaline conditions ( pH 8.8), solutions develop a deep red-brown color 

 and form a brown precipitate when saturated with NaCl. Precipitates formed at 

 pH 5.5 and pH 8.8 show a slight decrease in percentages of C and a sizeable 

 decrease in percentages of H, which is indicative of polymerization with some 

 introduction of oxygen into the product molecules. Decrease in H is more pro- 

 nounced at pH 8.8 than in acid media. The products formed in these systems 

 exhibit neither the parent spectrum nor any other distinctive maxima, although 

 a certain amount of analytically useful detail is present (fig. 7, table 6). 



Effect of the Protein Matrix. When fibrin (100 mg/20 ml quinone) is incubated 

 with fresh quinone solution, evidence for its effect on behavior of the quinone 

 may be obtained by spectrophotometric examination of the supernatant (water- 

 soluble) phase also (fig. 8, table 6). Thus the comparatively undifferentiated 

 spectrum of a pH 5.5 control is modified to one with a new distinct maximum 



