Schematic diagram for the opposite effects of ACN on peptide self-assembly. (a) Symbols for peptide, water, and ACN molecules (polar groups in red and nonpolar groups in green) as well as polar (red) and nonpolar (green) interactions. (b) Since water has a stronger hydrophilic interaction with peptide than ACN, hydrophilic interactions between peptide molecules in solutions with ACN are stronger than in pure water. (c) Since ACN has a stronger nonpolar interaction with peptide than water, cross-β sheets in solutions with ACN effectively have a less hydrophobic surface than in pure water, so the lateral stacking in former is weaker than in latter.