Hydrogen bonding self-complementary motifs

Fig. 31. Supramolecular (hydrogen-bonded) motifs of self-complementary molecules (196).

There are numerous cases, where identical bases, mismatched bases, and even complementary bases in protonated states are involved in hydrogen bonding. Examples are as follows Protonated adenine (HA+) has been observed in DNA mismatches as well as in RNA in pairs such as HA 1 (antl) G(syn) and HA+(anti) C(anti) (70). Poly(A) forms HA+ HA+ self-pairs in a parallel strand fashion at pH <4 (21). Protonated cytosine (HC+) exists in hemiproto-nated polyC (i-motif) (32), in HC+(anti) G(syn) (71), in a HC+ C RNA... 

Fig. 2.10 Possible self-complementary hydrogen bonding motifs for replication...

Carboxylic acids, oximes, diones and amino-pyridines can all form homomeric 0-D motifs through self-complementary and, frequently, symmetry-related hydrogen-bond interactions,... 

Amides frequently combine two unique structural motifs, dimers and catemers, into a well-known 1-D ribbon-like structure. The dimer is constructed from self-complementary N-H O hydrogen bonds, while the catemeric N-H O hydrogen bonds result from the anti-proton of the amine and the bifurcated carbonyl oxygen atom. 

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