Fig. 5.

Structural transition upon confinement. The rms end-to-end distance in cylindrical confinement as a function of temperature in the bulk (black line) and in cylinders of diameter D = 3 (blue), 2 (green),1.4 (red), and 1.3 (magenta). At low temperature the peptide adopts a helical conformation (drawn in the left-hand side). At the high T limit in the bulk, the peptide samples many conformations, with either small (such as the conformation drawn in bottom right corner) or with ends far away (such as the conformation drawn in top right corner). For the confined peptide, only extended conformations are observed, signifying a random coil → stretch structural transition upon confinement. (Inset) The end-to-end distance distribution function, P(R_ee) in the bulk (black line) and in cylinders with diameter D = 3 (blue line) and D = 1.4 (red line). The fluctuations in the end-to-end distance are suppressed as D decreases, and the distributions sharpen.