1 research outputs found
Corking and Uncorking Carbon Nanotubes by Metal Nanoparticles Bearing pH-Cleavable Hydrazone Linkers. Theoretical Analysis Based on Molecular Dynamics Simulations
In this work we determine and discuss
free-energy barriers associated
with the detachment of metal (gold) nanoparticles covered by an organic
shell from carbon nanotubes functionalized by hydrazide segments.
At neutral pH, both compounds can form hydrazone bonds which in turn
lead to the chemically corked form of the nanotube. At slightly acidic
pH, the hydrazone bonds undergo hydrolysis, leading to chemically
unbonded nanotube and gold nanoparticles. We found that at this state
the dispersion interactions between the nanotube and gold nanoparticles
are still very strong and spontaneous detachment of gold nanoparticles
does not occur. Therefore, the uncorked state of the nanotube cannot
be realized at normal conditions. The presence of guest molecules
(cisplatin) in the inner cavity of the nanotube affects the energetic
balance of the system, and spontaneous uncorking can occur with some
small activation barrier. However, the uncorking is in this case related
to the shift of the nanoparticle from the nanotube tip to its sidewall.
That model system can thus realize the mechanism of pH-controlled
drug release from the inner cavities of carbon nanotubes. Determination
of the free-energy barriers in the considered systems architectures
required a special treatment. Standard application of the weighted
histogram analysis of biased probability distributions turned out
to be totally ineffective. Therefore, we developed a special version
of that method which tolerates weak overlapping of the probability
histograms. This method may be useful for fast survey of free-energy
barriers in any other system architectures