Triplex hydrogen bonds

Yasushi Yokoyama Yokohama National University 86.5 Supramolecular Properties Controlled by Fulgides... Crowned Fulgides Crowned Fulgenates Fulgimide with Triplex Hydrogen Bonds Fulgimides Attached to Peptides. 86-7... 

Fig. 21.—Structure of the 6-fold anhydrous curdlan III (19) helix, (a) Stereo view of a full turn of the parallel triple helix. The three strands are distinguished by thin bonds, open bonds, and filled bonds, respectively. In addition to intrachain hydrogen bonds, the triplex shows a triad of 2-OH - 0-2 interchain hydrogen bonds around the helix axis (vertical line) at intervals of 2.94 A. (b) A c-axis projection of the unit cell contents illustrates how the 6-0H - 0-4 hydrogen bonds between triple helices stabilize the crystalline lattice.

Thus, structurally similar to their respective tg g tg+ polymer analogues, the monomers in the polymer-monomer complexes, are all interlinked through 03 0 (phosphate) hydrogen bonds in the duplex and through 03 05 hydrogen bonds in the triplex (17). 

The structures of the bases of these DNA triplexes were studied, by means of B3LYP/6-31+G calculations, in terms of their interaction energies and electron densities for the different hydrogen bonds established. This is one of the interactions that determines the structure and dynamics of nucleic acid molecules, and some of them, 219 and 220, are represented in the below structure [182], A good agreement was found with the experimental results. The trends observed for the interaction energies are consistent with those observed by experimental and/or by... 

Complementary base pairs are joined by hydrogen bonds and are best represented by a centered dot dA-dT and dG-dC are the canonical pairings in double-stranded DNA, although alternate pairings, DNA-RNA hybrids, triplexes, and other variations may occur. 

The extra hydrogen-bonding sites can, however, also form further base pairs, as observed for poly(A) poly(U). In the Watson-Crick A-U pair, one of the adenine N(6)-H donors and the N(7) acceptor are still free and can form another A-U pair of the Hoogsteen type (Fig. 16.16). This is in fact observed if the Watson-Crick duplex poly(A) poly(U) is exposed to high salt conditions, it disproportionates to form a triplex poly(A)-2poly(U) and a single strand poly(A) [539] ... 

Triplex formation with natural bases is limited by several important structural requirements. Recognition of any sequence in one of the WC strands is achieved by the formation of specific sets of hydrogen bonds (Hoogsteen or reverse Hoogsteen) with complementary base pairs in the other strand (Figure 7). 

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