Distribution and Effect of Water Content on Molecular Mobility in Poly(vinylpyrrolidone) Glasses: A Molecular Dynamics Simulation

Abstract

Water distribution in the PVP glass is highly heterogeneous at 10% w/w water, reflecting the formation of water strands or small clusters rather than complete phase separation. Local enhancement of mobility with increasing water content has been demonstrated using MD simulations.

Component dynamics in polyvinylpyrrolidone concentrated aqueous solutions

“…This would also support the finding in Ref. 18 that almost all available water molecules are in close contact with PVP carbonyl groups in the 10% water concentration sample. In principle, we would not expect the position of this contribution to change with water concentration, but its relative contribution to the intensity would increase with increasing water content.…”

“…Our results thus would support the existence of water strands or small clusters found by means of MD-simulations on PVP/H 2 O (Ref. 18) (note that in that case, the water concentrations investigated were even smaller (≤10%)).…”

“…In particular, we note that it is rather close to the 6.6 Å separating carbonyl oxygen atoms. 18 Therefore, this peak could correspond to correlations between PVP atoms in a side group and a water molecule forming a H-bond with the carbonyl group of a neighboring ring. This would also support the finding in Ref.…”

Correlations between Molecular Mobility and Chemical Stability During Storage of Amorphous Pharmaceuticals

“…[122][123][124] Based on molecular dynamics simulations, water distribution in PVP glasses was suggested to be highly heterogeneous at 10% w/w water content. 125 Water molecules are known to have high diffusivity even in amorphous solids. Water in solid amorphous Ficoll 126 and carbohydrates 127 was found to have diffusivity values high enough to be determined from the rate of desorption even at temperatures below T g ; the diffusion constants of water exhibited linear Arrhenius behavior around T g .…”

Effect of Antioxidants and Silicates on Peroxides in Povidone

“…Also, the uptake of water by povidone powder can cause increased plasticity, leading to higher molecular mobility. 26 This can cause increased reactivity of impurities in povidone, leading to consumption of peroxides in a downstream reaction. 27 For example, hydroperoxides can be catalytically decomposed by trace concentrations of transition metals, leading to the formation of peroxy and alkoxy radicals, 11,13 which may not be detected as peroxide impurities.…”