Formation of diazohydroxides ArN 2 OH in aqueous acid solution: polarographic determination of the equilibrium constant K R for the reaction of 4-substituted arenediazonium ions with H 2 O †

In aqueous acid (pH <4) solutions, in the dark, and in the absence of reductants, arenediazonium ions, ArN 2 + decompose spontaneously through the rate-limiting formation of the extremely unstable aryl cation that reacts with any nucleophile present in its solvation shell (D N + A N mechanism). However, in weak acidic and alkaline solutions, + to determine, for the first time, the equilibrium constants K R of formation of 4-substituted X-ArN 2 OH (X¼H, Me, MeO, Br, and NO 2 ), which can decompose in several ways including Z-E isomerization or further reaction with OH À to give diazoate ArN 2 O À . The technique applied was differential pulse polarography, which is very selective and sensitive. The determined pK R values are 5-6, and they are somewhat higher than those obtained for the reaction of ArN 2 + with alcohols ROH (pK DE = 3-5) under similar acidic conditions. The K R values are not very sensitive to changes in the nature of the substituent in the aromatic ring and a linear Hammett plot with a slope of ρ = 0.58 was obtained

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

Role of intermolecular interactions in assemblies of nanocontainers composed of carbon nanotubes and magnetic nanoparticles: A molecular dynamics study

10.1021/jp410736sJournal of Physical Chemistry C11821353-136

Molecular dynamics study of cisplatin release from carbon nanotubes capped by magnetic nanoparticles

10.1021/jp405593uJournal of Physical Chemistry C1173317327-1733