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Interactions of chiral biopolymers

Christopher B Stanley, University of Massachusetts Amherst


The self-assembly of chiral biopolymer systems involves both intra- and inter-molecular interactions. The contribution of these forces to protein hydration and stability and their influence on DNA chiral interactions is investigated. The osmotic stress technique is utilized to vary water activity in solution through the addition of a neutral osmolyte, such as poly(ethylene glycol). For the osmotic stress experiments, the osmotic pressure of the stressing solutions and its temperature dependence is needed. Since traditional methods, such as vapor pressure osmometry, static light scattering, and membrane osmometry, are not suitable for the concentration and temperature range of interest, a new method is devised using sedimentation equilibrium ultracentrifugation. We are using this method to measure the osmotic pressure of aqueous poly(ethylene glycol) solutions over a concentration range of 0 to 50 wt% and over a temperature range of 10 to 40°C. Hydration changes accompanying protein folding are investigated using the helix-coil transition in poly(glutamic acid) as a model system. Circular dichroism spectropolarimetry is used to follow this transition as a function of osmotic pressure, temperature, and pH. The energetics of the helix-coil transition allow the number of water molecules associated with the conformational change to be calculated. We find that osmotic pressure raises the helix-coil transition temperature by favoring the more compact α-helical state over the more hydrated coil state. To provide a better understanding of chiral interactions between biopolymers, measurements of short fragment (146 bp) DNA cholesteric pitch and twist angle are made as a function of DNA interaxial spacing and salt concentration. The cholesteric pitch and DNA interaxial spacing are followed by polarizing optical microscopy and X-ray scattering, respectively, and the microscopic twist angle between DNA molecules then can be calculated. Increasing ionic strength results in enhanced chiral interactions as evidenced by the increase in twist angle for a fixed interaxial spacing. In addition, we have created hybrid liquid crystals of short fragment DNA and elastin-like peptides that exhibit a cholesteric phase structure and undergo thermal contraction upon heating. These liquid crystalline systems are useful in studying chiral interactions between biopolymers and potentially could be utilized as biosensors.

Subject Area


Recommended Citation

Stanley, Christopher B, "Interactions of chiral biopolymers" (2004). Doctoral Dissertations Available from Proquest. AAI3152748.