How Hydrophobic Buckminsterfullerene Affects Surrounding Water Structure

Abstract

The hydrophobic hydration of fullerenes in water is of significant interest as the most common Buckminsterfullerene (C 60 ) is a mesoscale sphere; C 60 also has potential in pharmaceutical and nanomaterial applications. We use an all-atom molecular dynamics simulation lasting hundreds of nanoseconds to determine the behavior of a single molecule of C 60 in a periodic box of water, and compare this to methane. A C 60 molecule does not induce drying at the surface; however, unlike a hard sphere methane, a hard sphere C 60 solute does. This is due to a larger number of attractive Lennard-Jones interactions between the carbon atom centers in C 60 and the surrounding waters. In these simulations, water is not uniformly arranged but rather adopts a range of orientations in the first hydration shell despite the spherical symmetry of both solutes. There is a clear effect of solute size on the orientation of the first hydration shell waters. There is a large increase in hydrogenbonding contacts between waters in the C 60 first hydration shell. There is also a disruption of hydrogen bonds between waters in the first and second hydration shells. Water molecules in the first hydration shell preferentially create triangular structures that minimize the net water dipole near the surface near both the methane and C 60 surface, reducing the total energy of the system. Additionally, in the first and second hydration shells, the water dipoles are ordered to a distance of 8 Å from the solute surface. We conclude that, with a diameter of approximately 1 nm, C 60 behaves as a large hydrophobic solute.

Remarkable patterns of surface water ordering around polarized buckminsterfullerene

“…In our previous studies of water structure around a C 60 solute using empirical force fields, we assumed C 60 to be a smooth sphere and averaged over all azimuthal angles to get a very accurate RDF (22). Little did we expect the dramatic ordering of water structure in spherical shells as shown by the ADFs averaged over 100 ns of MD simulation (Figs.…”

“…The hydration structure of nonpolar solutes of varying size has been studied extensively in the past (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) using empirical force fields. Work from our lab has used empirical potential energy functions with popular water models to model the effect of a single molecule of benzene, cyclohexane (18,21), methane, and C 60 (22) on the structural details of water around these solutes. All these studies used force fields with nonpolarizable fixed point charge water models and analyzed water structure with a low-sensitivity method unable to detect the effect of solute surface "roughness" on water structure.…”

Communication: On the locality of Hydrogen bond networks at hydrophobic interfaces

“…28 A previously described optimized potentials for liquid simulations model for buckminsterfullerene was adapted for the 60n 2 fullerenes. 19 The functional form of the nonbonded potentials (for C-O) was U = 4 [(σ/r ) 12 − a(σ/r ) 6 ] with a = 1 for Lennard-Jones and a = 0 for purely repulsive interactions; the corresponding parameters were determined by LorentzBerthelot mixing rules. It is important to note that the typical energy of a hydrogen bond (on average 20.41 kJ/mol for SPC/E), is roughly 50 times larger than the optimal C-O Lennard-Jones interaction.…”

Can nanotechnology potentiate photodynamic therapy?

“…Andrievsky et al [218] in 2009 fi rst proposed a way to explain this seeming contradiction. They showed that the main mechanism by which hydrated C 60 can inactivate the highly reactive ROS, hydroxyl radical, was not by covalently scavenging the radicals but rather by action of the coat of " ordered water " that was associated with the fullerene nanoparticle [219] . They also claimed that the ordered water coat could slow down or trap the hydroxyl radicals for suffi cient time for two of the radicals to react with each other, thus producing the less reactive ROS, hydrogen peroxide.…”