Infrared multiple photon dissociation (IRMPD) spectroscopy of oxazine dyes

Abstract

The structure and energetic properties of four common oxazine dyes, Nile red, Nile blue A, Cresyl violet, and Brilliant cresyl blue, have been probed using a combination of infrared multiple-photon dissociation (IRMPD) spectroscopy and quantum chemical calculations. IRMPD spectra of the protonated dyes, as generated from an electrospray ionization (ESI) source, were collected in the range of 900-1800 cm À1 .Vibrational band assignments related to carbonyl and substituted-amine stretches were established from a comparison of the experimental spectra of these related systems as well as from a comparison with spectra generated by density functional theory (DFT) calculations. For Nile red, the thermochemical landscape for protonation at different basic sites was probed using DFT; comparison of IRMPD and calculated IR spectra reveals the site of protonation to be at the carbonyl oxygen. The structural information obtained here in the gas phase pertaining to these important fluorophores is anticipated to provide further insight into their associated intrinsic fluorescent properties in solution.

Multiband Plasmonic Sierpinski Carpet Fractal Antennas

“…The enhancement of the Raman signal attributed to the SCs at higher orders is much stronger than that of the reference Au film, thus confirming the presence of hot spots. We selected the strongest BCB vibrational mode ω = 1655 cm −1 , corresponding to the coupling of NH 2 scissor mode with the asymmetric stretch mode of C rings, 43 in order to evaluate the maximum SERS enhancement factor EF sers (see Supporting Information 8).…”

The structures and properties of proton- and alkali-bound cysteine dimers

“…While it is tempting, based on these calculated differences, to conclude that isomer 10 is not present in the sample, it is not uncommon in IRMPD spectra to observe transition intensities that are very different from those determined by electronic structure calculations. 12,[25][26][27][28][29] Given the calculated difference in relative energy between isomers 1 and 10, though, we would expect that motif H3 is (at best) a minor contributor to the observed vibrational spectrum. 3.…”

The structures and properties of anionic tryptophan complexes

“…Note that it is not uncommon in IRMPD spectra to observe intensities dissimilar to those predicted by electronic structure calculations. 52,59,60 Gaussian calculates the absorption cross-section of the molecules, whereas IRMPD monitors fragmentation efficiency (which is determined by absorption cross section and coupling efficiency to dissociative channels). Thus, one cannot directly compare intensities between IRMPD and calculation.…”

“…The peak at 1320 cm −1 is consistent with CCH/CNH bending modes of the aromatic indole moiety and methylene CH2 wagging. Note that it is not uncommon in IRMPD spectra to observe intensities dissimilar to those predicted by electronic structure calculations 52,59,60. Gaussian calculates the absorption cross-section of the molecules, whereas IRMPD monitors fragmentation efficiency (which is determined by…”