  This study presents the results of atomistic structural characterisation of
3.7 nm diameter gold nanoparticles (NP) coated with polymer polyethylene glycol
(PEG)-based ligands of different lengths (containing $2-14$ monomers) and
solvated in water. The system size and composition are selected in connection
to several experimental studies of radiosensitisation mechanisms of gold NPs.
The coating structure and water distribution near the NP surface are
characterised on the atomistic level by means of molecular dynamics
simulations. The results of simulations carried out in this study, combined
with the results of our recent study [J. Phys. Chem. A 126 (2022) 2170] and
those from the field of polymer physics, are used to calculate key structural
parameters of the coatings of radiosensitising gold NPs. On this basis,
connections between the coating structure and distribution of water are
established for different NP sizes as well as lengths and surface densities of
coating molecules. The quantitative analysis of water distribution in the
vicinity of coated metal NPs can be used to evaluate the radiosensitising
effectiveness of a particular NP system based on the proximity of water to the
NP metal core, which should impact the production of hydroxyl radicals and
reactive oxygen species in the vicinity of metal NPs exposed to ionising
radiation.
