Hydrophobe content, collapse

Figure 11. Conceptual illustration of the collapse of the secondary structure into the tertiary structure with an increase in the hydrophobe content.

If polar sequences or short phosphopeptides fail to bind to the stationary phase upon loading, the acetonitrile content of the eluent could be reduced to 3%. A further decrease is not possible for standard Ci8-columns, as the stationary phase could collapse reducing the loading capacity and the reproducibility. Instead, TFA could be replaced by the more hydrophobic ion-pair reagent HFBA (heptafluorobutyric acid), or a stationary phase with a special coating compatible with pure aqueous eluents could be used (e.g., Aqua-column from Phenomenex). 

Fluorescence studies of volume phase transition of polyacrylamide (PAAM) in mixed acetone/ water solvent, with incorporated dansyl group and pyrenyl probe were reported by Hu and co-workers [70, 71]. They observed an increase in the fluorescence lifetime of the probe with increase of acetone content in the solvent. They reported that gradual increase of fluorescence lifetime accompanies the volume phase transition of the PAAM gels from the swollen to collapsed state with increasing hydrophobicity of the microenvironment. 

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