Helicoidal double strand

Figure 2.10 The helicoidal double strand of DNA. In the lower part of the figure replication into two daughter double strands proceeds.

Very few structural studies have been concentrated on models of ApG adducts of cisplatin. Conformational analysis of two rotameric forms of the complex m-[Pt(NH3)2(9-MeA-A(7))(9-EtGH-A(7))]2+ has recently been described [40], One of the forms, crystallized as a PI 6 salt, can be characterized as a right-handed helicoidal model for the intrastrand ApG crosslink in double-stranded DNA. The bases in this compound assume a head-to-head orientation (Fig. 6) with the interbase dihedral angles of 81.8° and 87.5°. There are two independent complex cations in the unit cell. The left-... 

Several works have shown that the aggregation of isotactic and syndiotactic chains leads to the formation of stereoeomplexes for which the iso/syndio stoichiometry is found equal to 1/2, probably with a structure composed of a double-stranded helix of a 30/4 helicoidal isotactic chain surroxmded by a 60/4 helicoidal syndiotactic chain. Syndiotactic PMMA self-aggregates exhibit similar structures, with conformations close to extended chains. Experimental data indicate that, in self-aggregated syndiotactic PMMA in solution, some of the ester groups are close in contact, probably in a double helix slructure with solvent molecules included in the cavities of inner- and inter-helices. Isotactic PMMA self-aggregates also exhibit conformational helix structures. 

---