Visible‐Light‐Induced Photodimerization of a Photoactive Yellow Protein (PYP) Chromophore Model in a Single Crystal

Abstract

The chromophore of the photoactive yellow protein (PYP), the photoreceptor in the photomotility of the bacterium Halorhodospira halophila, is a deprotonated para-coumaric thioester linked to the side residue of a cysteine residue. The photophysics of the PYP chromophore is conveniently modeled with para-hydroxycinnamic thiophenyl esters. Herein, we report the first direct evidence, obtained with X-ray diffraction, of photodimerization of a para-hydroxycinnamic thiophenyl ester in single crystalline state. This result represents the first direct observation of [2+2] dimerization of a model PYP chromophore, and demonstrates that even very weak light in the visible region is capable of inducing parallel radical reactions in PYP from the excited state of the chromophore, in addition to the main reaction pathway (trans-cis isomerization). This PYP model system adds an interesting example to the known solid-state photodimerizations, because unlike the anhydrous crystal (which is not capable of sustaining the stress and disintegrates in the course of photodimerization), a single water molecule "dilutes" the structure to the extent sufficient for single-crystal-to-single-crystal reaction.

Following a Photoinduced Reconstructive Phase Transformation and its Influence on the Crystal Integrity: Powder Diffraction and Theoretical Study

“…Thus, tuning the reaction fashion stands at the frontiers of modern crystal engineering. The borders between the realms of SCSC and RPT reactions are not impassable, for instance dilution of the crystal packing with single water molecules can change the type of the reaction from RPT to SCSC 5b,c…”

Following a Photoinduced Reconstructive Phase Transformation and its Influence on the Crystal Integrity: Powder Diffraction and Theoretical Study

“…[5] The crystal disintegration and irreversibility of the reaction hamper the perspective applications of RPT systems in molecular machineries. Contrary, in terms of synthetic photochemistry, irreversible high-yield RPT reactions are very favorable.…”

“…[4b] When the geometrical movements during the reaction are significant (in the sense of different crystal packings, accommodated in different unit cells), the crystal cannot withstand the stress and therefore disintegrates. [5] The crystal disintegration and irreversibility of the reaction hamper the perspective applications of RPT systems in molecular machineries. Contrary, in terms of synthetic photochemistry, irreversible high-yield RPT reactions are very favorable.…”

In situ Raman monitoring of [2+2] cycloaddition of pyridine substituted olefins induced by visible laser

“…[5][6][7] For instance, a recent study demonstrated a single crystals popping phenomenon under UV light, which actually derives from a photosalient effect triggered by a [2+2] cycloaddition reaction. 8 Besides UV triggered reactions, laser induced chemical reactions have attracted more and more attention, [9][10][11] including coupling reactions, 12,13 photodimerization, 14,15 photochromic reactions. 16 Moreover, in situ Raman spectroscopy is appealing for studying photoreactions in a way that the reactions can be induced by the laser source, and simultaneously, the reaction processes (bond formation) can be monitored by the variation of the Raman fingerprints.…”

“…26,27 Using a visible laser source, some successful examples have been reported in the liquid/solid state. 14 So, it comes to the conclusion that silver or proton ion as template is essential for the cycloaddition reaction in solid/liquid.…”