Measurement of the Population of Electrosprayed Deprotomers of Coumaric Acids Using UV–Vis Laser Photodissociation Spectroscopy

Abstract

The measurement of deprotonation sites in multifunctional molecules following electrospray ionization is important to better inform a wide range of spectroscopic and photophysical studies that use electrospray to prepare molecular species for study in the gas phase. We demonstrate that low-resolution UV–vis laser photodissociation spectroscopy can be applied in situ to identify the deprotomers of three coumaric acids, trans-para -coumaric acid (CMA), trans- caffeic acid (CA), and trans- ferulic acid (FA), formed via electrospray. Electronic absorption spectra of the deprotonated coumaric acids are recorded via photodepletion and photofragmentation following electrospray from solutions of ethanol and acetonitrile. By comparing the experimental spectra to wave function theory calculations, we are able to confirm the presence of phenoxide and carboxylate deprotomers upon electrospray for all three coumaric acids, when sprayed from both protic and aprotic solvents. Ratios of the phenoxide:carboxylate deprotomers are obtained by generating summed theoretical absorption spectra that reproduce the experimental spectra. We find that choice of electrospray solvent has little effect on the ratio of deprotomers obtained for deprotonated CMA and CA but has a greater impact for FA. Our results are in excellent agreement with previous work conducted on deprotonated CMA using IR spectroscopy and demonstrate that UV photodissociation spectroscopy of electrosprayed ions has potential as a diagnostic tool for identifying deprotomeric species.

Probing the electronic relaxation pathways and photostability of the synthetic nucleobase Z via laser interfaced mass spectrometry

“…Previously, significant differences have been observed in the relative energetic order of deprotomers calculated with DFT, depending on the choice of functional. 32 Overall, the relative energetic order of the protomers was consistent across all levels of theory used here, and while no significant geometric differences were found, we note that the choice of both functional and basis set in DFT can lead to quite significant variability in the relative energy and therefore the Boltzmann distribution.…”

“…Previous high-level computational calculations of the excited state potential energy surfaces have underlined the strength of combining insight from the two complementary experimental methods. 31,32 Here, we use this approach to gain fundamental insight into the ultrafast vs. non-ultrafast regimes 33,34 of the Z nucleobase.…”

Photodegradation of Riboflavin under Alkaline Conditions: What Can Gas-Phase Photolysis Tell Us about What Happens in Solution?

“…Since [RF − H] − is anionic, any photodepletion that is not associated with photofragment ion production must generally be associated with electron loss processes [ 6 , 29 , 30 ]. This is discussed further in Section S2 .…”

Virtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in Space

“…Small molecular clusters held together by weak, noncovalent interactions can be prepared in the low temperature environment of a molecular beam, and their photodissociation dynamics can be studied using the same methods developed for isolated molecules. ,, Other strategies to produce clusters of various types include electrospray of anions or cations, ,,, plasma expansion, or laser ablation from a metal or graphite target. ,, Charged clusters can be accumulated, stored, and cooled in ion traps, entrained in supersonic expansions, or separated by ion mobility through a buffer gas. Microsolvation in these clusters offers a bridge between photodissociation in the gas phase and in solution, allowing in-depth study of the impacts of intermolecular interactions on photochemical outcomes.…”