Doctor of Philosophy
Charged droplets involving macromolecules undergo distinct disintegration mechanisms and shape deformations as a consequence of droplet-macroion interactions. Three general classes of droplet-macroion interactions that have been identified in the Consta group are: contiguous extrusion of a linear macroion from a droplet, "pearl-necklace" droplet conformations, and "star"-shaped droplets. This dissertation probes in a systematic manner the onset and various outcomes of macroion-droplet interactions, using atomistic molecular dynamics and realistic examples of solvent and macromolecules.
When the charge-squared-to-volume ratio of a droplet is below but near a threshold value, certain flexible macromolecules, such as poly(ethylene glycol), extrude from a droplet, induced by the charging of the macromolecules. An analytical model is constructed based on the simulation data to suggest that the droplet surface electric field may play a role in the extrusion of the macroion. The effect of different solvents is studied to show that the final charge state of the macroion is determined by complicated macromolecule-ion-solvent interactions.
Beyond this threshold, the charge-induced instability evolves to certain droplet deformations that lead to new stable states. These include "pear-shaped" lobes of solvent at the termini of a linear macroion, such as unstructured proteins, and conical protrusions of dielectric solvent surrounding a macroion regardless of its shape. In the former, such droplet conformation may emerge due to the interplay of a number of factors, subject to the constraint that each sub-droplet should be below a certain charge-squared-to-volume ratio. In the latter, the overall star geometry is determined by the amount of the macroion charge.
As the next level of system complexity, different factors that affect the stability of weak transient protein complexes in droplets are examined. A multiscale approach is devised to model a protein in an evaporating droplet where its acidity constantly changes. A methodology is then developed to compute the dissociation rate and the error in the dissociation constant measured in mass spectrometry experiments. A possible charging mechanism of the macroion due to the "star" structure of solvent is also proposed.
Oh, Myong In, "Computational and Analytical Modelling of Droplet-Macroion Interactions" (2018). Electronic Thesis and Dissertation Repository. 5297.