Three-strand polymers

The beta-l,3-glucans are dramatically different from the glucans described so far. This polymer is extremely flexible, and occurs in many instances in nature. The polymer goes by the names of curdlan, pachyman, laricinan, schleroglucan, paramylon, lentinan, laminarin, callose and schizophylan. The prevalent form appears to be a triple helix, with n > 6 and b 0.3 nm for each of the three strands ( ). If triacetate derivatives are made, n > 6 and h = 0.31 to 0.36 nm (10). The acetate helices are single. Of some interest is the lack of allowed 2-fold conformations on the n-b map (Figure 5). The allowed zones close up when n = 20 or so, but some small adjustments in the monomer shape could allow an infinite number of monomeric units per helix repeat. 

Polynucleotide helices are known to dissociate reversibly (Lipsett et al., 1960 Doty et al., 1959) upon heating, the melting temperature depending upon the polymers used and upon the kind and concentration of salt. By using heated solutions. Miles (1960) has followed the thermal dissociation of these three-stranded helices (Fig. 12.9 and Table 12.3) by their infrared spectra. The hot solution of tetra A -I- 2 poly U... 

Polymetallorotaxanes 7.24 (M = Zn" or Cu ) have been prepared by electropolymerization, which involved anodic oxidation of the pre-assembled metallorotaxane precursors (Scheme 7.2) [48]. Importantly, studies of these materials have allowed an evaluation of the individual contributions of the organic backbone and the metal-centered redox process to the overall conductivity measured on interdigitated microelectrodes. The Zn and Cu polymers behave quite differently. The Zn polymer behaves in a similar fashion to the metal-free material 7.25, whereas the matching of the polymer and Cu-centered redox potentials in 7.24 (M=Cu ) leads to enhancement of the communication between these two units resistance drops by a factor of 10 for the Cu polymer 7.24 relative to metal-free 7.25. In a further development in this general area, two-step electropolymerizations have been used to generate three-stranded conducting ladder polymetallorotaxanes 49]. 

Buey, J., and T.M. Swager. 2000. Three-strand conducting ladder polymers Two-step electropolymerization of metallorotaxanes. Angew Chem Int Ed Engl 39 608-612. 

J. Buey and T. M. Swager, Three-strand conducting ladder polymers two-step electropolymerization of metal-lorotaxanes, Angew. Chem. Int. Ed., 39, 608-612 (2000). 

Studies of the ionic strength dependent properties of the various polymeric complexes (Fig. 6.8) have established several important principles. All the double helical structures show ATm = 20° 2° for a tenfold increase in ionic strength (Fig. 6.8), exactly as do all double-stranded DNA s and RNA s. Three-stranded polymers generally show ATm 30°. Records (26) has discussed in great detail the thermodynamic implications of this observation. 

The activation volume of the three polymers turned out to be v 2 nm3, independent of their crosslink density. In the crosslinked polymer A the strands are short and about five of them fit into the activation volume. In contrast, one strand of polymer E requires a volume five times larger than the activation volume ... 

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