Counterion effects on the amyloid morphology of a peptide gel.

In this study we investigated amyloid hydrogels produced by a decapeptide fragment of the acyl carrier protein (ACP) in water, in the presence of different counterions: trifluoroacetate (TFA􀀀 ), SO42􀀀 , Cl􀀀 , Br􀀀 , and I􀀀 , through confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), attenuated total reflectance Fourier‑transform infrared spectroscopy (ATR-FTIR), circular dichroism (CD), fluorescence spectroscopy, rheological measurements, to understand how the nature of the counterion affects amyloid morphology across length scales, secondary structure, and the mechanical response of the gels. The results show that the nature of the counterion profoundly affects the gelation properties, amyloid morphology, and rheological properties. The results bear an important implication on the choice of post-synthesis counterion to accommodate a correct modeling of the system of interest.