5 research outputs found
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