Temperature-cycle microscopy reveals single-molecule conformational heterogeneity.

Our previous temperature-cycle study reported FRET transitions between different states on FRET-labeled polyprolines [Yuan et al., PCCP, 2011, 13, 1762]. The conformational origin of such transitions, however, was left open.

Polymer glass transitions switch electron transfer in individual molecules.

Essentially complete photoinduced electron transfer quenching of the fluorescence of a perylene-calixarene compound occurs in poly(methyl acrylate) and poly(vinyl acetate) above their glass transition temperatures (T(g)), but the fluorescence is completely recovered upon cooling the polymer matrix to a few degrees below the T(g). The switching can be observed in an on/off fashion at the level of individual molecules.

Suppression of proton mobility by hydrophobic hydration.

Fluorescence microscopy and conductivity measurements reveal a remarkably strong effect of hydrophobic groups on the mobility of protons in water. The addition of 5 M of tetramethylurea (4 methyl groups per molecule) results in a reduction of the proton mobility by a factor of approximately 10: hydrophobic hydration strongly suppresses proton mobility. These observations demonstrate the collective nature of aqueous proton transport.