Using small molecule probes to investigate aggregation of sunset yellow FCF: what are the concentration limits?

The assembly of small molecules into larger structures, often driven by non-covalent interactions such as hydrogen-bonding, aromatic stacking interactions and burial of hydrophobic surface, is of wide spread interest. The interaction of small molecules with aggregates also has a large range of application from fluorescence aggregation assays to gas storage in framework materials. Here we utilise nuclear magnetic resonance spectroscopy to investigate the interaction of a small molecule probe on the assembly state of sunset yellow across a wide range of relative concentrations. Information from both macroscopic (diffusion) and microscopic (chemical shifts) measurements allows the interaction to be studied and the binding mode to be interrogated. Using fluorophenol as the small molecule probe, we show that the aggregation behaviour of sunset yellow is broadly unaffected by the relative amount of fluorophenol added.