Investigation of the salting-in/-out, hydrotropic and surface-active behavior of plant-based hormone and phenolic acid salts

Abstract

Hypothesis: The role of hormones and polyphenolic acids in communication and regulation of biological processes can be linked to their physical-chemical interaction with target compounds and water. Further, the variety of polyphenolic acids suggests adjustable hydrotropic properties of these natural compounds.

Experiments: Phase transition temperature (PTT) measurements of binary water/di(propylene glycol) n-propyl ether (DPnP) or propylene glycol n-propyl ether (PnP) systems with sodium dehydroepiandrosterone sulfate (NaDHEAS), indole-3-acetate (NaIAA), indole-3-butyrate (NaIBA) - common hormones -, and sodium polyphenolates should unravel their salting-in/-out properties. Their salting-in/-out behavior was compared to the compounds' surface-active and structuring properties via surface tension, dynamic light scattering (DLS) and Nuclear magnetic resonance (NMR) experiments.

Findings: All hormone salts were revealed as salting-in agents. PTT, surface tension and DLS measurements indicated surfactant-like behavior of the hormone NaDHEAS, and hydrotropic behavior of NaIAA and NaIBA. The salting-in/-out properties of sodium polyphenolates - in an (anti-)hydrotrope range - are adjustable with functional groups. The (i) absence of nano-structuring in pure water, (ii) the reduction of the DPnP nano-structuring in water in presence of sodium polyphenolates and (iii) the absence of a slope change of the PTT curves at the critical aggregation concentration showed that the DPnP/polyphenolate interactions are of molecular hydrotropic and not of micellar/aggregative nature.

Keywords: Dynamic light scattering; Hydrotrope; Salting-in/-out; Surface tension; Surfactant; Water/DPnP.