Exploring ion-ion preferences through structure-property correlations: amino acid-derived, bis(guanidinium) disiloxane salts

Sci Rep. 2020 Jan 20;10(1):646. doi: 10.1038/s41598-020-57539-0.

Abstract

In a more synthetical approach to the study of ion-specific phenomena, four dipodal bis(guanidinium) siloxanes have been synthesized starting from glycine, β-alanine, γ-aminobutanoic acid, L-proline and 1,3-bis(3-aminopropyl)tetramethyldisiloxane. Together with their non-amide progenitor they were comparatively studied in regards to their interactions with nine different anions: sulphate, chromate, molybdate, benzoate, chloride, azide, nitrite, nitrate and thiocyanate. Their aqueous solubilities, form, 1H NMR and FT-IR spectra were examined while searching for anion-specific interactions falling in- or outside of the Hofmeister series. We show that although the "chao-" and "kosmotropic" ions affect the properties of solutions in a predictable way, more selective cation-anion pairing is responsible for phase separation and crystallinity. As a prominent example, crystal structure of one of the benzoate salts was successfully obtained and reveals a synergy of hydrophobic packing, ionic and hydrogen bonding. Immobilized but still flexible siloxane bridges give rise to crystals described by P 42/n space group and neatly segregated into hydro- and lipophilic sections.

MeSH terms

  • Amino Acids / chemistry*
  • Anions / chemistry
  • Butyric Acid / chemistry
  • Crystallization
  • Glycine / chemistry
  • Guanidine / chemical synthesis*
  • Guanidine / chemistry
  • Hydrogen Bonding
  • Hydrophobic and Hydrophilic Interactions
  • Ions / chemistry*
  • Proline / chemistry
  • Silanes / chemical synthesis*
  • Silanes / chemistry
  • Solubility
  • Solutions
  • Structure-Activity Relationship
  • Water
  • beta-Alanine / chemistry

Substances

  • Amino Acids
  • Anions
  • Ions
  • Silanes
  • Solutions
  • Water
  • Butyric Acid
  • beta-Alanine
  • disiloxane
  • Proline
  • Guanidine
  • Glycine