Protoisomerization of Indigo and Isoindigo Dyes Confirmed by Gas-Phase Infrared Ion Spectroscopy.

ABSTRACT: Gas-phase infrared multiple-photon dissociation (IRMPD) spectra are recorded for the protonated dye molecules indigo and isoindigo by using a quadrupole ion trap (QIT) mass spectrometer coupled to the free electron laser for infrared experiments (FELIX). From their fingerprint IR spectra (600-1800 cm^-1) and comparison with quantum-chemical calculations at the density functional level of theory (B3LYP/6-31++G(d,p)), we derive their structures. We focus particularly on the question of whether trans-to-cis isomerization occurs upon protonation and transfer to the gas phase. The trans-configuration is energetically favored in the neutral forms of the dyes in solution and in the gas phase. Instead, the cis-isomer is lower in energy for the protonated forms

SUBMITTER: Munshi MU 

PROVIDER: S-EPMC6767361 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature