The sodium cation-bound dimer of theophylline: IRMPD spectroscopy of a highly symmetric electrostatically bound species

et al. 2011

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The structure of the proton-bound lysine dimer has been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and electronic structure calculations. The structures of different possible isomers of the proton-bound lysine dimer have been optimized at the B3LYP/ 6-31+G(d) level of theory and IR spectra calculated using the same computational method. Based on relative Gibbs free energies (298 K) calculated at the MP2/aug-cc-pVTZ//B3LYP/6-31 +G(d) level of theory, LL-CS01, and followed closely (1.1 kJ mol -1 ) by LL-CS02 are the most stable non-zwitterionic isomers. At the MP2/aug-cc-pVTZ//6-31+G(d) and MP2/aug-cc-pVTZ//6-31+(d,p) levels of theory, isomer LL-CS02 is favored by 3.0 and 2.3 kJ mol -1 , respectively. The relative Gibbs free energies calculated by the aforementioned levels of theory for LL-CS01 and LL-CS02 are very close and strongly suggest that diagnostic vibrational signatures found in the IRMPD spectrum of the proton-bound dimer of lysine can be attributed to the existence of both isomers. LL-ZW01 is the most stable zwitterionic isomer, in which the zwitterionic structure of the neutral lysine is well stabilized by the protonated lysine moiety via a very strong intermolecular hydrogen bond. At the MP2/aug-cc-pVTZ//B3LYP/6-31+G(d), MP2/aug-cc-pVTZ//6-31+G(d) and MP2/aug-cc-pVTZ//6-31+G(d,p) levels of theory, the most stable zwitterionic isomer (LL-ZW01) is less favored than LL-CS01 by 7.3, 4.1 and 2.3 kJ mol -1 , respectively. The experimental IRMPD spectrum also confirms that the proton-bound dimer of lysine largely exists as charge-solvated isomers. Investigation of zwitterionic and charge-solvated species of amino acids in the gas phase will aid in a further understanding of structure, property, and function of biological molecules.

Section: Experimental and Electronic Structure Calculations Irmpd Expsupporting

confidence: 86%

“…B3LYP is a relatively reliable and economical computational method and is extensively employed in the investigation of biological molecules [32][33][34][35][36][37][38].…”

Section: Experimental and Electronic Structure Calculations Irmpd Expmentioning

confidence: 99%

Experimental and Theoretical Investigation of the Proton-Bound Dimer of Lysine

Marta

et al. 2011

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“…IRMPD, in combination with electronic structure calculations, is a powerful technique for structural elucidation studies such as this . IRMPD spectroscopy experiments were performed at the Centre de Laser Infrarouge d'Orsay (CLIO) and have been described in detail previously [8,12,13,24,31]. The IR-FEL beam was directed into a Bruker (Bruker; 40 Manning Road, Billerica, MA, USA 01821) Esquire 3000+ ion-trap mass spectrometer, equipped with an electrospray ionization interface.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

Consecutive Fragmentation Mechanisms of Protonated Ferulic Acid Probed by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

Marta

et al. 2012

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Protonated ferulic acid and its principle fragment ion have been characterized using infrared multiple photon dissociation spectroscopy and electronic structure calculations at the B3LYP/6-311+G(d,p) level of theory. Due to its extensively conjugated structure, protonated ferulic acid is observed to yield three stable fragment ions in IRMPD experiments. It is proposed that two parallel fragmentation pathways of protonated ferulic acid are being observed. The first pathway involves proton transfer, resulting in the loss of water and subsequently carbon monoxide, producing fragment ions m/z 177 and 149, respectively. Optimization of m/z 177 yields a species containing an acylium group, which is supported by a diagnostic peak in the IRMPD spectrum at 2168 cm −1 . The second pathway involves an alternate proton transfer leading to loss of methanol and rearrangement to a five-membered ring.

“…Interestingly, the sodiated form of the mixed dimer of TCA and taurine ( m/z 661.3) exhibited higher stability compared with the ‘pure’ PBD ( m/z 639.3). This is, of course, often observed with sodiated species undergoing CID versus protonated species of the same molecule; for PBD, it can be explained by different gas-phase conformations of the cluster ions, where the sodium cation contributes to the bonding, creating, in fact, a sodium-bound dimer [ 64 ]. Of note, some other structural factors may also play a role in the stability of the gas-phase clusters, including formation of multiple inter- and intramolecular hydrogen bonds [ 50 , 65 ], as well as different positions of the bonding hydroxyl groups at the ring [ 66 , 67 ].…”

Section: Resultsmentioning

confidence: 99%

MALDI Mass Spectral Imaging of Bile Acids Observed as Deprotonated Molecules and Proton-Bound Dimers from Mouse Liver Sections

Rzagalinski

Hainz

Meier

et al. 2018

Bile acids (BAs) play two vital roles in living organisms, as they are involved in (1) the secretion of cholesterol from liver, and (2) the lipid digestion/absorption in the intestine. Abnormal bile acid synthesis or secretion can lead to severe liver disorders. Even though there is extensive literature on the mass spectrometric determination of BAs in biofluids and tissue homogenates, there are no reports on the spatial distribution in the biliary network of the liver. Here, we demonstrate the application of high mass resolution/mass accuracy matrix-assisted laser desorption/ionization (MALDI)-Fourier-transform ion cyclotron resonance (FTICR) to MS imaging (MSI) of BAs at high spatial resolutions (pixel size, 25 μm). The results show chemical heterogeneity of the mouse liver sections with a number of branching biliary and blood ducts. In addition to ion signals from deprotonation of the BA molecules, MALDI-MSI generated several further intense signals at larger m/z for the BAs. These signals were spatially co-localized with the deprotonated molecules and easily misinterpreted as additional products of BA biotransformations. In-depth analysis of accurate mass shifts and additional electrospray ionization and MALDI-FTICR experiments, however, confirmed them as proton-bound dimers. Interestingly, dimers of bile acids, but also unusual mixed dimers of different taurine-conjugated bile acids and free taurine, were identified. Since formation of these complexes will negatively influence signal intensities of the desired [M – H]- ions and significantly complicate mass spectral interpretations, two simple broadband techniques were proposed for non-selective dissociation of dimers that lead to increased signals for the deprotonated BAs. Graphical Abstractᅟ Electronic supplementary materialThe online version of this article (10.1007/s13361-017-1886-6) contains supplementary material, which is available to authorized users.