Figure 5. Experimental characterization of structure of water during self-assembly of PA nanofibres.

Aggregation kinetic studies to probe the role of water during the various stages from an initial micelle to early stages of formation of PA fibres are shown in a–e. (a,b) Aggregation kinetics monitored by β-sheet formation. (a) Circular dichroism spectra of c16-AHL₃K₃-CO₂H measured in water (blue) and 100 mM ammonium hydroxide after 120 min (red). Vertical solid line at 201 nm marks where the kinetics were monitored. (b) Aggregation kinetics of β-sheet formation monitored at 201 nm in 100 mM ammonium hydroxide (blue) and 70% D₂O in 100 mM ammonium hydroxide (red). Arrows mark times wear DLS samples were monitored in the absence of β-sheets. (c) Aggregation size with respect to time. Dynamic light scattering measurements at times: 0 min, blue; 5 min, red; 10 min, green; 15 min, brown. (d,e) Fibre morphology variation with respect to time. Electron micrographs of c16-AHL₃K₃-CO₂H fibres at: (d) 5 min and (e) 120 min, scale bar, 300 nm. (f–h) Experimental infrared spectra highlighting the amide I region (f), the O–D stretching region (g) and the O–H stretching region (h). c16-AHL₃K₃-CO₂H in H₂O (blue line), 70% D₂O/30% H₂O (red line), 5 mM NaOH (green line), and 5 mM NaOH in 70% D₂O/30% H₂O (purple line). Frame (g) highlights the range of D₂O (l) from ∼2,476 cm⁻¹ to D₂O (s) ∼2,410 cm⁻¹. Frame (h) highlights the range of H₂O (l) from ∼3,425 cm⁻¹ to H₂O (s) ∼3,257 cm⁻¹. Frame (h) also shows the value for computational vibrational spectra for proximal water at ∼3,340 cm⁻¹ (vertical black line).