Probing spatial heterogeneity in supercooled glycerol and temporal heterogeneity with single-molecule FRET in polyprolines

Abstract

This thesis presents two lines of research. On the one hand, we investigate heterogeneity in supercooled glycerol by means of rheometry, small-angle neutron scattering, and fluorescence imaging. We find from the rheological experiments that supercooled glycerol can behave like weak solids at temperatures well above the glass transition. This is very surprising because glycerol is supposed to be purely liquid-like in this temperature range. However, the structural origin of this solid-like state of glycerol still remains unclear. The preliminary results from small-angle neutron scattering show that the solidified glycerol is structurally different from both the supercooled liquid and the crystal. In addition, fluorescence imaging of a thin film of glycerol doped with fluorescent probes reveals heterogeneous patterns of the fluorescence intensity, which is related to long-lived and micrometer scale density fluctuations in supercooled glycerol. All these results will contribute to understanding heterogeneity or even glass transition of supercooled liquids. On the other hand, we study the conformational dynamics of polyprolines by single-molecule FRET (F_rster resonance energy transfer) combined with temperature-cycle microscopy, a novel technique developed in our group, and demonstrate the potential of this new method to address complex molecular dynamics, for example the dynamics of protein-folding, at the single-molecule level.