Double molecules, 2-dimensional array

Figure 20. Two-dimensional arrays constructed from DAE and DAE+J motifs. Two arrays are shown, one containing two components, A and B, and a second containing four components, A, B, C, and D. Each of die starred components contains one or two hairpins perpendicular to the plane of the array. The double-crossover molecules are represented as two closed figures connected by two short lines. The helix axis of each domain is represented by a dotted line. The sticky ends are drawn schematically as complementary geometrical shapes, representing Watson-Crick complementarity. The horizontal repeat is two units in the top array and four in the bottom array the vertical repeat is a single unit in both arrays. The perpendicular hairpins are visible as stripes when this array is examined in the atomic force microscope.

Molecules containing carboxylic acid functionalities are not confined to organic systems. For example, the C=C double bond in fumaric acid can interact with a low oxidation state metal centre (see Chapter 23) to form organometallic compounds such as Fe(C0)4(r -H02CCHCHC02H) the T -prefix (see Box 18.1) indicates that the two carbon atoms of the C=C bond of the fumaric acid residue are linked to the Fe centre. Hydrogen bonding can occur between adjacent pairs of molecules as is depicted below, and such interactions extend through the solid state lattice to produce an extensive, three-dimensional array. 

Fig. 6 Two-dimensional arrays assembled from DNA components, (a) A two-component array made from a DAE and a DAE + J motif both 4 x 16 nm in this projection, where the extra domain is indicated by a filled black circle. Sticky ends are represented geometrically, (b) A four-component array, where the stripes occur every 64 nm. (c) An array made of two TX molecules (A and B), a rotated TX molecule (C). and a double helix (D). (d) A four-arm junction can also be used to produce an array, (d.l) and (d.2) show that the four-arm junction assumes a two-domain structure, where the two domains are at an angle 60° to each other. Although flexible in its own right, four of them can produce a well-structured parallelogram (d.3) that can self-assemble into a 2D array (d.4). View this art in color at www.dekker.com.)...

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