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.