MOLECULAR COMPLEMENTARINESS IN ANTIGEN-ANTIBODY SYSTEMS 



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Fig. 6. Effects of van der Waals attraction for several systems where substituent 

 is in position of attachment. 



bility on the other. The order obser\^ed in the anti-or///o-azobenzoate system is 

 CHs < Br < CI < I. Apparently, the increased tilt due to the bromine over 

 that induced by chlorine due to size is not compensated for by the greater 

 polarizability of bromine, while for iodine the greater polarizability wins out. 



Table 1 is a summary of some other para systems investigated (Pressman 

 and Siegel, 1953; Pressman, Grossberg and Pauling, 1943; Pressman and Siegel, 

 1953a; Pressman and Siegel, 1953b). Antisera were prepared against the 

 various haptens indicated. The asterisk represents the homologous charged 

 group as indicated. The values are the relative combining constants of the 

 homologous hapten with antibody. The benzene derivative has the value of 1 

 in all cases. A /?ara-methyl substituent increases the constant in all cases. 

 The methyl group tits into the part of the antibody site directed toward the 

 azo group in the position of attachment and thus, exhibits a greater van der 

 Waals attraction than the hydrogen of the benzene derivative without any 

 steric effect. The relative constants for the meta-meihyl, or///o-methyl and 

 a//>/;a-naphthyl derivatives are an indication of the tightness of lit of antibody 

 around the hapten group. For a tightly fitting antibody we would expect the 

 constant to be decreased; the tighter the fit, the greater the decrease (taking 

 into account also the tilt of the carboxylate out of the plane of the benzene 



