Connectivity of the domains

Once proteins are divided into domains the domains are then classified hierarchically. At the top of the classification we usually find the class of a protein domain, which is generally determined from its overall composition in secondary structure elements. Three main classes of protein domains exist mainly a domains, mainly (3 domains, and mixed a p domains (the domains in the a — p class are sometimes subdivided into domains with alternating a/p secondary structures and domains with mixed a + p secondary structures). In each class, domains are clustered into folds according to their topology. A fold is determined from the number, arrangement, and connectivity of the domain s secondary structure elements. The folds are subdivided into superfamilies. A superfamily contains protein domains with similar functions, which suggests a common ancestry, often in the absence of detectable sequence similarity. Sequence information defines families, i.e., subclasses of superfamilies that regroup domains whose sequences are similar. 

However, bulk heterojunction morphologies are described by much more than just a characteristic domain size. Further morphological features which may determine the performance of a bulk heterojunction OPV include the purity of the domains, the interfaces between these domains, the connectivity of the domains, and more. Lyons et al. [18] tried to deconvolve the effects of these morphological features by comparing simulation results on a range of morphologies with different characteristics, namely impure domains with diffuse interfaces (Cl), pure domains with diffuse interfaces (DII), and pure domains with abrupt interfaces (SII), as shown in Fig. 6. 

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