Predominant Binding Mode of Palmatine to DNA.

Palmatine is a protoberberine alkaloid, which may produce singlet oxygen under visible light irradiation and binds to DNA. The fact that singlet oxygen activation in palmatine may be triggered by environmental conditions, and in particular its interaction with nucleic acids, makes it a most suitable candidate for photodynamic therapy and DNA-targeted noninvasive anticancer strategies. Despite these remarkable properties, the actual binding mode between palmatine and DNA has not been resolved, yet.

Environment-Driven Coherent Population Transfer Governs the Ultrafast Photophysics of Tryptophan.

By combining UV transient absorption spectroscopy with sub-30-fs temporal resolution and CASPT2/MM calculations, we present a complete description of the primary photoinduced processes in solvated tryptophan. Our results shed new light on the role of the solvent in the relaxation dynamics of tryptophan. We unveil two consecutive coherent population transfer events involving the lowest two singlet excited states: a sub-50-fs nonadiabatic L → L transfer through a conical intersection and a subsequent 220 fs reverse L → L transfer due to solvent-assisted adiabatic stabilization of the L state.

Spectral Tuning and Photoisomerization Efficiency in Push-Pull Azobenzenes: Designing Principles.

This work demonstrates how - substitution can induce spectral tuning toward the visible range and improve the photoisomerization efficiency of azobenzene-based photoswitches, making them good candidates for technological and biological applications. The red-shifted bright ππ* state (S) behaves like the lower and more productive dark nπ* (S) state because less potential energy along the planar bending mode is available to reach higher energy unproductive nπ*/S crossing regions, which are responsible for the lower quantum yield of the parent compound. The stabilization of the bright ππ* state and the consequent increase in isomerization efficiency may be regulated the strength of - substituents.