Second-shell substitution effect

Moreover, the overcrowding effect can be avoided in the cascade theory by introducing a second shell substitution effect. This was done by Gordon and Parker177. In the... 

Fig. 59. a First shell substitution effect the probability for a reaction of functionality x depends on whether y or z or both had already reacted, b Second shell substitution effect the probability of reaction for a unit Xi and x2 depends on how many of the functional groups in y and z had reacted... 

The second shell substitution effect (SSSE) is operative when the reactivity of a group depends not only on the substitution degree of the unit it belongs to, but on the substitution degree of all units that are first neighbors to that unit. Unless stated otherwise, we shall assume for simplicity that all the unreacted groups of a unit have an equal chance of reacting. 

A second-shell substitution effect (SSSE) occurs when the reactivity of a functional group is affected by the reaction of all the groups attached not only to the same monomer unit, but also to the units linked to that one. This behavior has been recognized in urea/formaldehyde formation (see Section 3.3.4.2). 

Baker HM, Anderson BF, Brodie AM, Shongwe MS, Smith CA, Baker EN. 1996. Anion binding by transferrins importance of second-shell effects revealed by the crystal structure of oxalate-substituted diferric lactoferrin. Biochemistry 35(28) 9007-9013. 

---