Theoretical Study of Reactivity Indices and Rough Potential Energy Curves for the Dissociation of 59 Fullerendiols in Gas-Phase and in Aqueous Solution with an Implicit Solvent Model

TL;DR

This study extends previous gas-phase reactivity analyses of fullerendiols to aqueous solutions using implicit solvent models, confirming that their reactivity trends remain consistent across phases and exploring dipole moment changes.

Contribution

It introduces a comprehensive comparison of gas-phase and aqueous-phase reactivity indices for fullerendiols using DFT and implicit solvent models, highlighting phase effects.

Findings

Reactivity indices are similar in gas and aqueous phases.

Dipole moments of fullerendiols increase in aqueous solution.

C-O bond energies are consistent across phases.

Abstract

Buckminsterfullerene, C$_{60}$, has not only a beautiful truncated icosahedral (soccerball) shape, but simple H\"uckel calculations predict a three-fold degenerate lowest unoccupied molecular orbital (LUMO) which can accomodate up to six electrons making it a good electron acceptor. Experiments have confirmed that C60 is a radical sponge and it is now sold for use in topical cosmetics. Further medical uses require functionalization of C60 to make it soluble and one of the simplest functionalization is to make C60(OH)n fullerenols. A previous article [Adv. Quant. Chem. 8, 351 (2023)] studied reactivity indices for the successive addition of the $^\bullet$OH radical to ($^\bullet$)C$_{60}$(OH)$_n$ in gas phase. [($^\bullet$)C$_{60}$(OH)$_n$ is only a radical when n is an odd number.] This present article extends this previous work by examining various aspects of how the reaction, changes in aqueous solution. One obvious difference between C$_{60}$ and their various isomers of C$_{60}$(OH)$_2$ is the presence of a dipole. As fullerendiols are nearly spherical, their change in dipole moment in going from gas to aqueous phase may be estimated using back-of-the-envellope calculations with the Onsager model. The result is remarkably similar to what is obtained using density-functional theory (DFT) and the more sophisticated solvation model based upon the quantum mechanical density (SMD). Calculation of fullerendiol C-O bond energies and reactivity indices using with the SMD approach confirm that the general conclusions from the earlier work regarding gas-phase reactivity still hold in the aqueous phase.