Self-complementary dimers

Fig. 17 Self-complementary dimers formed by linear arrays of four hydrogen bonding sites (A acceptor, D donor), and their stability constants in CDCI3 as predicted in reference [88]. Attractive and repulsive secondary interactions are indicated by arrows...

Three corollaries arise from this. The template is likely to have C2 symmetry, to allow self-complementary dimers to form. The components will be attracted to the template molecule through complementary hydrogen bonding arrays or electrostatic dipoles. The process of templating the components brings reactive sites in close proximity to each other a general example of this is shown in Figure 5.12. 

Fig. 9 C2 operation on the special pair to produce a self-complementary dimer of imidazolyl porphyrins...

Fig. 10 a X-ray crystal structure of the dimer of self-complementary imidazolyl zinc porphyrins, b Mode of strain release in self-complementary dimer... 

Hunter [60] extended the idea of self-complementary dimer formation to higher macrocycles by adjusting the coordinating angle of the appended amidopyridyl hgands to selectively obtain the trimeric 24 and tetrameric... 

Self-complementary dimer formation of imidazolyl zinc porphyrin allowed two such units to be connected directly at their meso positions to give 51. Since the two coordination assembhes grow in opposite directions in this case, successive self-complementary coordination leads to a Unear multi-... 

Fig. 28 Formation of self-complementary dimer 66 from phthalocyanine-substituted imidazolyl zinc porphyrin 65...

A particularly intriguing kind of supramolecular self-assembly by axial coordination to metaUoporphyrins, namely self-complementary coordination, is reviewed in the second chapter by Yoshiaki Kobuke. Self-complementarity affords large stability constants. The fascinating systems described in Kobuke s contribution were prepared and investigated as models for components of photosynthetic natural systems self-complementary dimers of porphyrins mimic the special pair of the photosynthetic reaction centers, while macrocychc and three-dimensional porphyrin supramolecules were prepared as photosynthetic antenna models. 

Figure 34.1 Ureido-pyrimidinone (UPy) unit that forms a self-complementary dimer, and supramolecular polymer formed by a bifunctional UPy derivative. (Image adapted from Ref. [5] 1998, American Chemical Society.)...

Phosphorus-31 signals of self-complementary dimers (e.g., ApU and GpC) are 0.1 -0.2 ppm upheld from those of their corresponding homodimers (i.e., ApA, UpU, GpG, CpC) (Gorenstein et al., 1976b). These self-complementary dimers are apparently more constrained to the g,g conformation as a result of miniature double-helix formation, although the chemical-shift difference is small owing to the small population of the double helix present (probably < 10% at 0°C Krugh et al, 1976). 

Amino-5 -deoxy-2, 3 -0-isopropylideneadenosine was acylated at N-5 with an activated derivative of the 6-carboxy-2-naphthyl ester of Kemp s acid imide. The resulting molecule possesses self-complementary binding sites, the key feature of replicating molecules that act as templates for their own reproduction. The dimer of this molecule is, however, not very stable K = 630 L mol ). When the two initially mentioned educts are added, a small proportion of the ternary complex is also formed and undergoes a fast, template-catalysed... 

When the metalloporphyrin bears a donor group on its periphery, it can behave as a self-complementary ditopic unit capable of metal-ligand induced dimerization. Many systems have been synthesized using different metals, ligands, and spacers. The length and geometry of the spacer groups determine the stoichiometry of the assembly process. 

Wyler, R. de Mendoza, J. Rebek, J., Jr. Formation of a cavity by dimerization of a self-complementary molecule via hydrogen bonds. Angew. Chem. Int. Ed. Engl. 1993,32, 1699-1701. 

Once the viral RNA has been translated and the large polyprotein has been processed to form individual viral proteins, new viral particles begin to form. Packaged in each virion are two copies of fully unspliced viral RNA. To be packaged into the virion, the RNA dimerizes in a highly orchestrated process involving a self-complementary stem-loop interaction. Such HIV-specific RNA events may prove useful for fumre therapeutic intervention, although they have so far received relatively little attention by medicinal chemists. 

Similarly, the longer, but still self-complementary oligonucleotide d(CGCGAATTCGCG) has been observed to form a duplex via the dimerization/association reaction... 

Some of the simplest selective systems are based on hydrogen bonding interactions between molecules. Carboxylic acids hydrogen bond to form dimers (Fig. 7-24), although this process is relatively unselective in the absence of other interactions. The interaction is described as self-complementary - the carboxylic acid functionality contains both the carbonyl oxygen atom as a donor and the hydrogen atom as the acceptor. 

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