Single-Molecule Dendrimer-Hydrocarbon Interaction
Qi Lu, Department of Physics, St. John’s College of Liberal Arts and Sciences
Karthikeyan Pasupathy, Aaron Jones and Pu Chun Ke, Laboratory of Single-Molecule Biophysics and Polymer Physics, Clemson University
John L. Lyons and Monica H. Lamm, Department of Chemical and Biological Engineering, Iowa State University
Justin Ching, former St. John’s University Student
Abstract: At high pressures and low temperatures, as is the case with oil production and deep-sea transportation, hydrates constantly occur when water hydrogen bonds with the hydrocarbons in gas and oil products. In sufficient quantities these hydrates can completely block pipelines by agglomerating to create very stable, ice-like plugs, leading to disruptive and costly production stoppages. Dendritic polymers can act as anti-agglomerants through preventing large hydrates from forming and keeping small crystals suspended in the production flow. To understand the mechanism underlying the anti-agglomerant function of dendritic polymers, we conducted a series of studies using poly(amidoamine) as the model dendrimer and squalane as the model hydrocarbon in aqueous solution. The spectrophotometry measurements indicate that the interaction between poly(amidoamine) and squalane increases with the pH of the solvent. Our simulations show that squalane resides primarily on the perimeter of the dendrimer at low to neutral pH, but becomes encapsulated in the dendrimer at high pH. Using single-molecule fluorescence microscopy, we have identified that the binding between PAMAM and squalane is a reversible process. At a pH value of 8, the approaching, binding, and dissociation constants of a single fluorescently-labeled dendrimer to squalane are 0.5 s, 7.5 s, and 0.5 s, respectively.