Date of Award
Doctor of Philosophy (PhD)
The studies presented in this work relate to conformational studies of polymers and biopolymers. Polyethylene is used as a model chain to develop a general formalism to characterize helical molecules with varying degrees of flexibility. The average projection of a unit vector along the last bond onto a unit vector along the first bond is the principal quantity calculated for modeling purposes. Behavior of this average projection has been examined for helical chains in which flexibility is introduced by either of two devices: random occurrence of a configuration much different from that required for helix propagation and use of a square well potential centered at the dihedral angle utilized in a rigid helix. Essential features are modeled by coupled damped harmonic oscillators. Representative poly(L-proline) chains containing peptide bonds in the trans configuration have been generated using a conformational energy surface which successfully reproduced the unperturbed dimensions in dilute solution. Representative chains have also been generated using selected portions of that surface in order to assess the influence of various features on the local conformation. Approach of the X component of the end-to-end vector to its asymptotic limit has been characterized for these same cases. Somatostatin, a hypothalamic tetradecapeptide, possesses a disulfide bond between the two cystein residues at position three and fourteen. Experimental studies obtained the molar extinction coefficient to be equal to 6300 l/m-cm at 280.5 nm. Optical rotatory dispersion studies found that somatostatin possesses no helical content in water for both the reduced and nonreduced form. In SDS the total helical content for the nonreduced form was measured to be about 10% and the reduced form about 40%. Monte Carlo calculations were performed in which elements from rotational isomeric state theory and Zimm-Bragg theory were incorporated. In water, calculation found that somatostatin contained virtually no helical structure regardless of whether the disulfide bond was intact. Additionally, it was found that the reduced somatostatin in SDS possessed a maximum f(,h) = 0.33 and the nonreduced form yielded f(,h) = 0.22. These numbers agree qualitatively with experimental results.
Darsey, Jerome Anthony, "Studies of Helix Formation in Model Chains, Poly(l-Proline) and Somatostatin (Polyproline)." (1982). LSU Historical Dissertations and Theses. 3797.