Driscoll Hatcher (doubleskin7)

Large intramolecular 13C kinetic isotope effects (KIEs) for the di-π-methane rearrangement of benzobarrelene fit with statistical expectations from heavy-atom tunneling when a low-energy sensitizer is employed, but much lower KIEs are observed with higher-energy sensitizers. These results in combination with trajectory studies suggest that the excess vibrational energy available from triplet energy transfer leads to hot and nonstatistical dynamics in the rearrangement.In duplex DNA, the continuous sugar phosphate backbones prevent the double helix from significant bending, but breaks in the duplex such as nicks, gaps, and flaps present points at which significant bending is possible. The conformational dynamics of these aberrant structures remains poorly understood. Two factors can maintain the duplexlike conformation of these aberrant structures, these being the hydrophobic and aromatic stacking interactions of the nucleobases, and the electrostatic repulsion of the negatively charged backbones. Using confocal single-molecule Förster resonance energy transfer on nicked and gapped DNA structures, we compare the relative contributions of these two factors by modulating the electrostatic repulsion through mono- and divalent cation concentrations. Base stacking interactions dominate the dynamics of nicked DNA, making it behave essentially like duplex DNA. Gapped structures have weaker base stacking and thus backbone electrostatic repulsion becomes important, and shielding from cations results in an average increase in bending around the gap. This bending of gapped structures could be interpreted by increased flexibility of unstacked structures, transient unstacking events, or a combination of the two. check details Burst variance analysis (BVA) and analysis by photon-by-photon hidden Markov modeling (H2MM), methods capable of detecting submillisecond dynamics of single molecules in solution, only revealed a single state, indicating that dynamics are occurring at time scales shorter than microseconds.Structural engineering techniques such as local strain engineering and folding provide functional control over critical optoelectronic properties of 2D materials. Local strain engineering at the nanoscale level is practically achieved via permanently deformed wrinkled nanostructures, which are reported to show photoluminescence enhancement, bandgap modulation, and funneling effect. Folding in 2D materials is reported to tune optoelecronic properties via folding angle dependent interlayer coupling and symmetry variation. The accurate and efficient monitoring of local strain vector and folding angle is important to optimize the performance of optoelectronic devices. Conventionally, the accurate measurement of both strain amplitude and strain direction in wrinkled nanostructures requires the combined usage of multiple tools resulting in manufacturing lead time and cost. Here, we demonstrate the usage of a single tool, polarization-dependent second-harmonic generation (SHG), to determine the folding angle and strain vector accurately and efficiently in ultrathin WS2. The folding angle in trilayer WS2 folds exhibiting 1-9 times SHG enhancement is probed through variable approaches such as SHG enhancement factor, maxima and minima SHG phase difference, and linear dichroism. In compressive strain induced wrinkled nanostructures, strain-dependent SHG quenching and enhancement is observed parallel and perpendicular, respectively, to the direction of the compressive strain vector, allowing us to determine the local strain vector accurately using a photoelastic approach. We further demonstrate that SHG is highly sensitive to band-nesting-induced transition (C-peak), which can be significantly modulated by strain. Our results show SHG as a powerful probe to folding angle and strain vector.While X-ray crystallography routinely provides structural characterization of kinetically stable pre-catalysts and intermediates, elucidation of the structu