Many biological macromolecules, including polysaccharides, undergo a cooperative conformational transition within a narrow range of temperature or other intensive variable. Cooperativity of the transition, as manifested in a narrow transitional domain, typically arises because one or both of the chain conformations connected by the transition possesses some degree of long range order. In many cases one or both of these conformations involves a helical chain conformation. Transitions of this class are often referred to as helix-random coil transitions or order-disorder transitions, even though it is not necessary that one of the conformations be random or disordered.;The biologically active fungal (1;This thesis describes an investigation of the geometric structure and the energetic stabilizing factors that characterize the ordered forms of scleroglucan and other multiple-stranded carbohydrate polymers. A systematic study of the transition between linear and circular forms of scleroglucan serves as the basis for testing theoretical models for the interactions that stabilize the helical forms and may benefit future structure-function studies. Atomic force microscopy, operating in the noncontact mode, was used to image and characterize the ordered forms of (1;In particular it has been possible to measure proportions of linear and cyclic forms in denatured/renatured scleroglucan as a function of annealing temperature, annealing time, and mean molar mass. In addition, the distributions of contour lengths and chain thicknesses have been measured for the renatured linear and cyclic forms as functions of the same variables. Differences in the measured mean contour lengths and mean chain thicknesses are described and interpreted.
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