Direct monitoring of photon induced isomerization, dissociation and electron detachment of the green fluorescent protein chromophore anion

We present the first experimental demonstration of Z↔E photoisomerization the GFP chromophore anion, HBDI−, in the gas phase. In the single photon absorption regime, the photoisomerization action spectra show two maxima at 480 nm and 455 nm. In the multiphoton absorption regime, photodissociation and photodetachment channels modify the appearance of the photoisomerization band. This work provides a new approach to characterize photoisomerization pathways in biomolecular ions

Seleniranium Ions Undergo π‑Ligand Exchange via an Associative Mechanism in the Gas Phase

Collision-induced dissociation mass spectrometry of the ammonium ions <b>4a</b> and <b>4b</b> results in the formation of the seleniranium ion <b>5</b>, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion–molecule reactions between the ion <b>5</b> (<i>m</i>/<i>z</i> = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions <b>7</b> (<i>m</i>/<i>z</i> = 225), <b>6</b> (<i>m</i>/<i>z</i> = 239), <b>8</b> (<i>m</i>/<i>z</i> = 253), and <b>9</b> (<i>m</i>/<i>z</i> = 267), respectively. Further reaction of seleniranium <b>6</b> with cyclopentene resulted in further π-ligand exchange giving seleniranium ion <b>7</b>, confirming that direct π-ligand exchange between seleniranium ion <b>5</b> and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G­(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion <b>5</b> with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively