About this Research Topic
Barrier crossing in thermally activated processes is a fundamental and ubiquitous concept in Chemistry. For example, in the study of reaction mechanisms, chemical kinetics investigations allow the determination of rate laws and the elucidation of elementary steps, while femtochemistry has sufficient time resolution to allow characterization of the transition state and reaction intermediates. Despite the large timescale difference between typical reaction rate constants and transition state lifetimes, both are crucial for understanding reaction mechanisms. Therefore, ideally one would like to integrate, conceptually and experimentally, the methods used at different timescales in order to obtain a more complete picture of how and why reactions occur. Examples where this general strategy can be applied abound, including biomolecular folding, nanocatalysis, crystal nucleation and growth, solar cells, among others.
Although timescale integration is a simple and well-known idea, and despite current efforts, it is still challenging to provide systematic structure-reactivity trends for general chemical systems from this approach. This is not entirely surprising since usually the tools employed to study fast and slow thermally activated processes are fundamentally different: stroboscopic and asynchronous methods, respectively. Within this context, we would like to tackle the Research Topic of barrier crossing from a multi-time scale perspective. To achieve this goal, we also hope to highlight the utility of learning ideas from other fields, and then suitably adapting them to the study of chemical dynamics in solution. For example, several recent advances in this area came from the integration of tools such as ultrafast time-resolved nonlinear laser spectroscopy, optical microscopy, colloid science, single-molecule spectroscopy, nanomaterials, biophysics, non-equilibrium statistical mechanics, and stochastic dynamics, among others.
Areas covered in this Research Topic include, but are not limited to, the following:
• Integrating transition path time and rate measurements in reactions with large enthalpic/entropic barriers
• Ultrafast spectroscopy characterization of fundamental timescales in reactant/product wells and transition state barrier crossing times
• Single-molecule force spectroscopy studies of transition path sampling and kinetics in biomolecular folding/unfolding
• Single-molecule fluorescence spectroscopy studies of Kramers' theory and barrier crossing in protein unfolding
• Integrating ultrafast and ultraslow studies of thermally activated processes
• Integrating stroboscopic and asynchronous measurements in molecular systems and nanomaterials
Keywords: Rare events, Long timescale processes, Ultrafast, Barrier crossing, Single molecule
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