Non-Equilibrium Isomer Distribution of the Gas-Phase Photoactive Yellow Protein Chromophore

Almasian, Mitra; Grzetic, Josipa; Maurik, Johanne van; Steill, Jeffrey D.; Berden, Giel; Ingemann, Steen; Buma, Wybren Jan; Oomens, Jos

doi:10.1021/jz300780t

Cited by 65 publications

(71 citation statements)

References 37 publications

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“…For instance, solvent-dependent spectra attributed to (de)protonation isomers have been recorded for p-hydroxybenzoic acid,[12] PABA,[10] and p-coumaric acid. [11] Notably, IMS-MS has recently been combined with IRMPD spectroscopy to investigate the solvent-dependence of observed protonation isomers of benzocaine. [8]…”

Section: Introductionmentioning

confidence: 99%

Effects of ESI conditions on kinetic trapping of the solution-phase protonation isomer of p-aminobenzoic acid in the gas phase

Patrick

Cismesia

Tesler

et al. 2017

International Journal of Mass Spectrometry

125

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The effects of electrospray ionization (ESI) solvent and source temperature on the relative abundance of the preferred solution-phase (N-protonated; i.e. amine) versus preferred gas-phase (O-protonated; i.e., acid) isomers of p-aminobenzoic acid (PABA) were investigated. When PABA was electrosprayed from protic solvents (i.e., methanol/water), the infrared multiple photon dissociation (IRMPD) spectrum recorded was consistent with that for O-protonation, according to both calculations and previous studies. When aprotic solvent (i.e., acetonitrile) was used, a different spectrum was recorded and was assigned to the N-protonated isomer. As the amine is the preferred protonation site in solution, this suggests that an isomerization takes place under certain conditions. Photodissociation at the diagnostic band for the O-protonated isomer (NH2 stretching mode) was used to quantify the relative contributions of each isomer to ion signal as a function of ESI conditions. For mixtures of methanol and acetonitrile, the relative contribution of the O-protonated gas-phase structure increased as a function of methanol content. Yet, substituting methanol for water resulted in a marked decrease of isomerization to the O-protonated structure. The source temperature (i.e., temperature of a heated desolvation capillary) was found to play a key role in determining the extent of isomerization, with higher temperatures yielding increased presence of gas-phase structures. These results are consistent with a protic bridge mechanism, in which the ESI droplet temperatures, dependent on endothermic desolvation and radiative heating from the capillary, may determine the isomerization yield.

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Section: Introductionmentioning

confidence: 99%

Effects of ESI conditions on kinetic trapping of the solution-phase protonation isomer of p-aminobenzoic acid in the gas phase

Patrick

Cismesia

Tesler

et al. 2017

International Journal of Mass Spectrometry

125

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“…In rare cases, orthogonal separation of tautomers prior to MS analysis could be afforded by gas chromatography [4], but the vast majority of cases involve MS analysis of convolved mixtures of tautomers. As such, the probing of tautomeric systems with MS has consisted of observing the relative ratios of tautomers and their fragment ions by adjusting ionization conditions [5], adjusting the energy of a tandem mass spectrometry (MS/MS) event [6], using diagnostic ion/molecule reactions [7][8][9][10][11][12], probing with ion spectroscopy [13,14], or through the assistance of computational modeling to confirm the presence and behavior of a given tautomer [15].…”

Section: Introductionmentioning

confidence: 99%

Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

Campbell

Yang

Melo

et al. 2016

J. Am. Soc. Mass Spectrom.

125

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Abstract. In this study, we report on the use of differential mobility spectrometry (DMS) as a tool for studying tautomeric species, allowing a more in-depth interrogation of these elusive isomers using ion/molecule reactions and tandem mass spectrometry. As an example, we revisit a case study in which gas-phase hydrogendeuterium exchange (HDX)-a probe of ion structure in mass spectrometry-actually altered analyte ion structure by tautomerization. For the N-and O-protonated tautomers of 4-aminobenzoic acid, when separated using DMS and subjected to subsequent HDX with trace levels of D 2 O, the anticipated difference between the exchange rates of the two tautomers is observed. However, when using higher levels of D 2 O or a more basic reagent, equivalent and almost complete exchange of all labile protons is observed. This second observation is a result of the interconversion of the N-protonated tautomer to the Oprotonated form during HDX. We can monitor this transformation experimentally, with support from detailed molecular dynamics and electronic structure calculations. In fact, calculations suggest the onset of bulk solution phase properties for 4-aminobenzoic acid upon solvation with eight CH 3 OH molecules. These findings also underscore the need for choosing HDX reagents and conditions judiciously when separating interconvertible isomers using DMS.

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“…In negative ion mode, the carboxylic acid can be readily deprotonated, 3 or may compete with other putative sites (e.g., phenol). 4-7 In positive ion mode, some studies on metal-adducted amino acids and peptides have shown that carboxylic acids can be de-protonated, and hence act as acidic moieties. 8-10 Conversely, studies on protonated PABA have shown that the carboxylic acid site can be protonated, and thus act as a basic site.…”

Section: Introductionmentioning

confidence: 99%

Amine vs. carboxylic acid protonation in ortho-, meta-, and para-aminobenzoic acid: An IRMPD spectroscopy study

Cismesia

Nicholls

Polfer

2017

Journal of Molecular Spectroscopy

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Infrared multiple photon dissociation (IRMPD) spectroscopy and computational chemistry are applied to the ortho-, meta-, and para- positional isomers of aminobenzoic acid to investigate whether the amine or the carboxylic acid are the favored sites of proton attachment in the gas phase. The NH and OH stretching modes yield distinct patterns that establish the carboxylic acid as the site of protonation in para-aminobenzoic acid, as opposed to the amine group in ortho- and meta-aminobenzoic acid, in agreement with computed thermochemistries. The trends for para- and meta-substitutions can be rationalized simplistically by inductive effects and resonant stabilization, and will be discussed in light of computed charge distributions based from electrostatic potentials. In ortho-aminobenzoic acid, the close proximity of the amine and acid groups allow a simultaneous interaction of the proton with both groups, thus stabilizing and delocalizing the charge more effectively, and compensating for some of the resonance stabilization effects.

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Non-Equilibrium Isomer Distribution of the Gas-Phase Photoactive Yellow Protein Chromophore

Cited by 65 publications

References 37 publications

Effects of ESI conditions on kinetic trapping of the solution-phase protonation isomer of p-aminobenzoic acid in the gas phase

Effects of ESI conditions on kinetic trapping of the solution-phase protonation isomer of p-aminobenzoic acid in the gas phase

Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

Amine vs. carboxylic acid protonation in ortho-, meta-, and para-aminobenzoic acid: An IRMPD spectroscopy study

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