ABSTRACT
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. In this work, we apply temperature-cycle microscopy of single FRET-labeled polyproline and dsDNA molecules and compare their responses to resolve the conformational origin of different FRET states. We observe different steady-state FRET distributions and different temperature-cycle responses in the two samples. Our temperature-cycle results on single molecules resemble the results in steady-state measurements but reveal a dark state which could not be observed otherwise. By comparing the timescales and probabilities of different FRET states in temperature-cycle traces, we assign the conformational heterogeneity reflected by different FRET states to linker dynamics, dye-chain and dye-dye interactions. The dark state and low-FRET state are likely due to dye-dye interactions at short separations.
Subject(s)
Microscopy/methods , Molecular Conformation , Temperature , Fluorescence Resonance Energy TransferABSTRACT
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.
ABSTRACT
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.
