On the origin of the extremely different solubilities of polyethers in water.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31253797.
- Also identified by DOI 10.1038/s41467-019-10783-z and PMC identifier 6599002.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The solubilities of polyethers are surprisingly counter-intuitive. The best-known example is the difference between polyethylene glycol ([-CH<sub>2</sub>-CH<sub>2</sub>-O-]<sub>n</sub>) which is infinitely soluble, and polyoxymethylene ([-CH<sub>2</sub>-O-]<sub>n</sub>) which is completely insoluble in water, exactly the opposite of what one expects from the C/O ratios of these molecules. Similar anomalies exist for oligomeric and cyclic polyethers. To solve this apparent mystery, we use femtosecond vibrational and GHz dielectric spectroscopy with complementary ab initio calculations and molecular dynamics simulations. We find that the dynamics of water molecules solvating polyethers is fundamentally different depending on their C/O composition. The ab initio calculations and simulations show that this is not because of steric effects (as is commonly believed), but because the partial charge on the O atoms depends on the number of C atoms by which they are separated. Our results thus show that inductive effects can have a major impact on aqueous solubilities.