Identification of the Phenol Functionality in Deprotonated Monomeric and Dimeric Lignin Degradation Products via Tandem Mass Spectrometry Based on Ion–Molecule Reactions with Diethylmethoxyborane

Molecular Basis for the Remarkably Different Gas-Phase Behavior of Deprotonated Thyroid Hormones Triiodothyronine (T3) and Reverse Triiodothyronine (rT3): A Clue for Their Discrimination?

“…In fact, the presence of two bulky electron-withdrawing (EW) substituents in both ortho-positions to the phenolate function could hinder the formation of the adduct. Such an effect is noted by Kenttämaa et al for deprotonated vanillin, where the presence of an EW aldehyde group in para - position to the phenol inhibits the formation of the adduct …”

“…[T3-H] − and [rT3-H] − were mass analyzed in the cell of an FT-ICR, which allowed measurement of the accurate mass of the anions, obtaining an m /z value of 649.78319 with a mass error of 0.66 ppm with respect to the exact mass of the formula [C 15 H 11 NO 4 I 3 ] − (649.78276 Da). [T3-H] − and [rT3-H] − were allowed to react with selected neutral molecules with appropriate volatility aiming to substantiate the different deprotonation sites of the two anions, possibly enabling characteristic ion-molecule reactions. , In this regard, Kenttämaa et al showed diethylmethoxyborane (DEMB) to react selectively with the phenolate functionality, producing the DEMB adduct, while carboxylate groups showed no reactivity . Based on this evidence, both [T3-H] − and [rT3-H] − were mass isolated and stored in the presence of DEMB introduced at a stationary pressure of 10 –7 mbar.…”

“…48 The so-obtained CCS values are reported in Table 1 and 67,68 In this regard, Kenttamaa et al showed diethylmethoxyborane (DEMB) to react selectively with the phenolate functionality, producing the DEMB adduct, while carboxylate groups showed no reactivity. 42 Based on this evidence, both [T3-H] − and [rT3-H] − were mass isolated and stored in the presence of DEMB introduced at a stationary pressure of 10 −7 mbar. Even though the reaction time spanned from 10 to 180 s, both anions showed no reactivity with DEMB.…”

“…Such an effect is noted by Kenttamaa et al for deprotonated vanillin, where the presence of an EW aldehyde group in para-position to the phenol inhibits the formation of the adduct. 42 Additional experiments were designed to obtain information on the acid properties of T3 and rT3. First, theoretical gasphase acidity (ΔG acid ) values were obtained from calculations at the B3LYP-D3 level by summing the Gibbs free energy of the proton, as reported by York et al, 69 to the one of the most stable deprotonated hormones, either T3_1 or rT3_2, and finally subtracting the Gibbs free energies of neutral T3 and rT3, respectively.…”

“…Several studies have also assessed that isomeric forms are retained from the solution to the gas phase, given the soft ionization conditions that ESI permits, − thus confirming IRMPD spectroscopy as a powerful and viable technique to assess the deprotonation sites of anions generated in solution. , Spectroscopic data are compared with results of ion-molecule reactions (IMR) in the cell of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. In particular, deprotonated T3 and rT3 were allowed to react with volatile acids and diethylmethoxyborane, which was shown to react selectively with phenoxide anions. − Finally, this work also reports on ion mobility mass spectrometry (IM-MS) analyses of [T3-H] − and [rT3-H] − with the aim to correlate the experimentally obtained collision cross section (CCS) values to the ones calculated for distinct deprotonated isomers. − On a side note, the different IM behavior of [T3-H] − and [rT3-H] − could eventually be exploited to build novel analytical methods for the detection and quantification of T3 and rT3. , …”