Double helices, chiral

Double helix (DNA), 1103-1105 Doublet (NMR), 462 Dovvnfield (NMR), 445 Drugs, approval procedure for, 165 chiral, 320-322 origin of, 164... 

The twist angles between the terminal rungs of 141, 142 and 143 are 44.0, 63.0, and 80.3°, respectively. The double helix structures crystallize with equal amounts of left- and right-handed screw sense forms, as expected in the absence of any chiral field. Some ladder polysilanes crystallize with both helical forms in the same centrosymmetric unit cell for others, the two forms can crystallize separately. It will be interesting to carry out the crystallization in a chiral field. 

Chain Building. Both crystalline polymorphs of starch have the same fiber repeat of 1.05 nm and are built with the same unit a parallel stranded double-helix. Each strand has six glucose residues per turn in 2.1 nm and the two strands are related by a two-fold axis of symmetry this creates the apparent 1.05 nm fiber repeat. The chirality of the helices has been postulated to be either right-handed (12.13) or left-handed (14.15. ... 

Our template synthesis of knots implies that the target molecules are obtained as cationic dicopper(I) complexes. Therefore we considered the possibility of interconverting both enantiomers into a pair of diastereomeric salts [137, 138] by combining them with an optically active anion. Binaphthyl phosphate (BNP") [139] drew our attention because its chirality arises from the binaphthyl core, which is twisted. This helical structure is of the same type as that of die copper double helix, precursor of the knot. Besides, both compounds are aromatic and, thus, we could expect some potentially helpful stacking interactions [87],... 

To introduce the chiral auxiliary, a labile anion, unlike the classical BFJ or PF which cannot be exchanged, is required. Preliminary studies showed the triflate to be appropriate. We introduced it during the formation step of the double helix. One equivalent of copper ) triflate was added to the bischelating diphenolic strand in a reductive medium. H NMR showed that the dinuclear copper dou-... 

The achiral network of tetraphenylenes served as an inspiration for the design of a it-conjugated double helix. Double helical polymers, in which two polyphenylene helices are intertwined or tetraphenylenes are sequentially annelated, were recognized as the chiral building block of the network (Fig. 15.24) [107]. 

Fig. 18 Supramolecular chiral aggregates based on bis-guanidinium functional groups A chiral tetra-guanidinium units self-assemble around sulfate anions into a left-handed double helical structure B chiral bis-guanidinium unit associates with a complementary bis-anionic counterpart leading to a left-handed double helix...

Roelfes, Feringa, and Kraemer (104,105) developed a similar hybrid supramolecular catalyst, which they named DNAzyme, relating to DNA as the biomacromolecular chiral host. 9-Aminoacridine-modified Cu(II) complexes were employed as metal fragments with high DNA affinities (Figure 29). The acridine unit is likely to intercalate into the double helix of the DNA. The Cu(II) catalytic center is thus brought into close proximity to the DNA, which creates a chiral environment around the Cu(II) site. Stereoinduction can be expected in any transformation mediated by this Cu(II) center. 

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