Polymer conformation: 3. Rapid methods for seeking contact-free double helices

A methodology for mapping helix constraint surfaces and contact-free molecular structures, as introduced in parts 1 and 2 of the series^1,2, has been developed and extended to include investigation of stability and stereochemical feasibility of double helices. The motivation for this development was prompted by practical considerations concerning the interpretation of new X-ray fibre diffraction patterns obtained from the gelling polysaccharide agarose³, in the light of previous interpretations⁴ favouring a double helix model for this biopolymer. The method may be of use for objectively scrutinizing double helix structures the interpretation of a number of which, e.g. carrageenan^5,6, poly(methyl methacrylate)^7,10, isotactic polystyrene^11,12, xanthan gum^13,16, appear to be controversial issues.