No description available.

No description available.

No description available.

In this thesis, a method is presented for studying protein adsorption on solid surfaces by Electrochemical Impedance Spectroscopy (EIS), using a model system of Bovine Serum Albumin (BSA) on platinum electrode surfaces. EIS is a commonly used analytical technique for electrochemical biosensors, particularly useful because of the ability to model the electrochemical data with Equivalent Electrical Circuits (EECs) and extract meaningful quantitative values for physical processes that are occurring in the electrochemical system (for example, double-layer capacitance Cdl or charge-transfer resistance Rct). In this thesis, a comprehensive method for EEC selection is developed by which the data are found to be Kramers-Kronig compliant, a library of possible circuits is selected, and then residual errors, parameter values, and standard deviations based on replicate measurements are used to find the circuit which best models the electrochemical system. The influence of number of factors related to experimental set-up and EIS conditions on BSA adsorption is examined, and suggestions are given as to avoid signal convolution by these factors. Most influentially, performing EIS in Phosphate Buffered Saline (PBS) before exposure to BSA results in a significant decrease in BSA film formation. BSA adsorption is strongly influenced by potential, with more positive potentials resulting in greater BSA adsorption. The application of ac vs. dc potential, however, does not influence the BSA film. Surface-Enhanced Raman Spectroscopy (SERS) experiments of BSA and Human Serum Albumin (HSA) adsorption on gold Sphere Segment Void (SSV) substrates are also presented. Finally, BSA adsorption on platinum surfaces is monitored over time using EIS. Results suggest that, after incubation, BSA desorbs from the electrode surface but the rate of desorption is dependent on the concentration gradient between the surface and the bulk solution. Results also suggest that BSA adsorption is strongly affected by concentration, with higher concentrations resulting in greater BSA adsorption on the electrode surface and greater BSA desorption upon change to a less positive potential.

No description available.

Although the native conformation of a protein is thermodynamically its most stable form, this stability is only marginal. As a consequence, globular proteins have a certain amount of flexibility in their backbones which allows for conformational changes in the course of their biological function. In the course of this thesis, we study protein models at the edge of stability in different contexts: (1) First, we use molecular dynamics to determine the force needed to rupture a chain molecule (an unfolded protein) being stretched at constant loading rate and temperature. When all energy bonds of the molecule are identical, we find that the force F depends on the pulling rate r and temperature T according to F ~ const -- T 1/3|ln(r/T)|1/3 When a single weak bond is introduced, this result is modified to F ~ const -- T2/3|ln(r/ T)|2/3 This scaling, which is model independent, can be used with force-spectroscopy experiment to quantitatively extract relevant microscopic parameters of biomolecules. (2) Second, we study the structural stability of models of proteins for which the selected folds are unusually stable to mutation, that is, designable. A two-dimensional hydrophobic-polar lattice model is used to determine designable folds and these folds were investigated under shear through Langevin dynamics. We find that the phase diagram of these proteins depends on their designability. In particular, highly designable folds are found to be weaker, i.e. easier to unfold, than low designable ones. This is argued to be related to protein flexibility. (3) Third, we study the mechanism of cold denaturation through constant-pressure simulations for a model of hydrophobic molecules in an explicit solvent. We find that the temperature dependence of the hydrophobic effect is the driving force for cold denaturation. The physical mechanism underlying this phenomenon is identified as the destabilization of hydrophobic contact in favor of solvent separated configurations, the same mechanism seen in pressure induced denaturation. A phenomenological explanation proposed for the mechanism is suggested as being responsible for cold denaturation in real proteins.

No description available.

No description available.

No description available.

No description available.