Gas phase mid-infrared spectroscopy of molecular ions can nowadays be performed with high performance mass spectrometers coupled to free electron lasers (FEL). The wide and continuous tunability of highly intense FELs in the mid-infrared region can be exploited for performing infrared multiple photon dissociation (IRMPD) spectroscopy of molecular ions. This review will focus on gas phase IRMPD spectroscopic investigations aiming at probing the structure and the reactivity of transition metal complexes. The performance of infrared spectroscopy for characterizing the coordination mode of polydentate ligands and the spin state of the metal will be illustrated. Infrared spectroscopy has also been exploited to probe the reactivity of metal complexes, and a special attention will be given to the infrared spectroscopy of reactive intermediates. # 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:583-605, 2007
The frequency-dependent gas-phase infrared multiple photon dissociation (IRMPD) spectrum for the protonbound dimer of water is reported. The present spectrum is shown to be only in fair agreement with a spectrum reported in an earlier communication but is in agreement with spectra predicted by theoretical means. Two different possible assignments of the observed infrared bands are provided. The first is based on the harmonic oscillator approximation from density functional theory calculations, and a second is based on a quantum four-dimensional model calculation of anharmonic frequencies and intensities. Both calculated spectra agree fairly well, but the density functional calculation assignments are in better agreement. This is expected despite the anharmonic nature of the asymmetric stretch due to the flat potential energy surface associated with this mode.The proton-bound dimer of water ( Figure 1) and larger protonated water clusters are of considerable importance both because of the interest in proton mobility from a biochemical point of view as well as the interest in the strong hydrogen bonding that takes place in these clusters. A normal hydrogen bond is on the order of 10-20 kJ mol -1 , whereas the protonbound water dimer is bound by some 130 kJ mol -1 . 1 Many theoretical studies of protonated water clusters have been conducted in the past. 2-7 Experimentally, the vibration-rotation spectrum has been observed for H 5 O 2 + and H 9 O 4 + in the OH stretching region (3550-3850 cm -1 ) using infrared multiplephoton dissociation spectroscopy (IRMPD). 8 Much more recently, the gas-phase vibrational spectrum of the proton-bound water dimer was measured by observing IRMPD in an ion trap using the free-electron laser for infrared experiments (FELIX) in The Netherlands. 9 The H 5 O 2 + ions were formed with an electrospray source and transferred to a linear radio frequency hexapole ion trap at 100 K where the ions were exposed to high intensity and tunable infrared light from the FEL and the dissociation products were monitored.In the present work, we present an infrared spectrum for the proton-bound water dimer also determined by observing IRMPD using a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer (MICRA, 10 a mobile ion cyclotron resonance analyzer), coupled to the FEL in Orsay, France (CLIO). The FTICR is based on the use of a permanent magnet, which is an assembly composed of two Halbach 11 cylinders producing a nominal magnetic field of 1.25 T. The ICR cell presents an open geometry derived from a cubic cell (20 × 20 × 20 mm 3 ) where the excitation electrodes have been replaced by two tunnels made of four interconnected electrodes. Gases are introduced through the combination of a leak valve and followed by a pulsed three-way valve that directs the gas flow either to the mass spectrometer or to the pump of the gas inlet system.The FEL at CLIO (Centre Laser Infrarouge d'Orsay), 12 a European facility in France, provides highly intense IR radiation from 3-120 µm. This FEL consists of a...
The gas-phase structures of protonated uracil, thymine, and cytosine are probed by using mid-infrared multiple-photon dissociation (IRMPD) spectroscopy performed at the Free Electron Laser facility of the Centre Laser Infrarouge d'Orsay (CLIO), France. Experimental infrared (IR) spectra are recorded for ions that were generated by electrospray ionization, isolated, and then irradiated in a quadrupole ion trap; the results are compared to the calculated infrared absorption spectra of the different low-lying isomers (computed at the B3LYP/6-31++G(d,p) level). For each protonated base, the global energy minimum corresponds to an enolic tautomer, whose infrared absorption spectrum matched very well with the experimental IRMPD spectrum, with the exception of a very weak IRMPD signal observed at about 1800 cm(-1) in the case of the three protonated bases. This signal is likely to be the signature of the second-energy-lying oxo tautomer. We thus conclude that within our experimental conditions, two tautomeric ions are formed which coexist in the quadrupole ion trap.
MALDI imaging mass spectrometry (MALDI-IMS) has become a powerful tool for the detection and localization of drugs, proteins, and lipids on-tissue. Nevertheless, this approach can only perform identification of low mass molecules as lipids, pharmaceuticals, and peptides. In this article, a combination of approaches for the detection and imaging of proteins and their identification directly on-tissue is described after tryptic digestion. Enzymatic digestion protocols for different kinds of tissues-formalin fixed paraffin embedded (FFPE) and frozen tissues-are combined with MALDI-ion mobility mass spectrometry (IM-MS). This combination enables localization and identification of proteins via their related digested peptides. In a number of cases, ion mobility separates isobaric ions that cannot be identified by conventional MALDI time-of-flight (TOF) mass spectrometry. The amount of detected peaks per measurement increases (versus conventional MALDI-TOF), which enables mass and time selected ion images and the identification of separated ions. These experiments demonstrate the feasibility of direct proteins identification by ion-mobility-TOF IMS from tissue. The tissue digestion combined with MALDI-IM-TOF-IMS approach allows a proteomics "bottom-up" strategy with different kinds of tissue samples, especially FFPE tissues conserved for a long time in hospital sample banks. The combination of IM with IMS marks the development of IMS approaches as real proteomic tools, which brings new perspectives to biological studies. (J Am Soc Mass Spectrom 2010, 21, 338 -347)
BackgroundHypertension is, amongst others, characterized by endothelial dysfunction and vascular remodeling. As sphingolipids have been implicated in both the regulation of vascular contractility and growth, we investigated whether sphingolipid biology is altered in hypertension and whether this is reflected in altered vascular function.Methods and FindingsIn isolated carotid arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, shifting the ceramide/S1P ratio towards ceramide dominance by administration of a sphingosine kinase inhibitor (dimethylsphingosine) or exogenous application of sphingomyelinase, induced marked endothelium-dependent contractions in SHR vessels (DMS: 1.4±0.4 and SMase: 2.1±0.1 mN/mm; n = 10), that were virtually absent in WKY vessels (DMS: 0.0±0.0 and SMase: 0.6±0.1 mN/mm; n = 9, p<0.05). Imaging mass spectrometry and immunohistochemistry indicated that these contractions were most likely mediated by ceramide and dependent on iPLA2, cyclooxygenase-1 and thromboxane synthase. Expression levels of these enzymes were higher in SHR vessels. In concurrence, infusion of dimethylsphingosine caused a marked rise in blood pressure in anesthetized SHR (42±4%; n = 7), but not in WKY (−12±10%; n = 6). Lipidomics analysis by mass spectrometry, revealed elevated levels of ceramide in arterial tissue of SHR compared to WKY (691±42 vs. 419±27 pmol, n = 3–5 respectively, p<0.05). These pronounced alterations in SHR sphingolipid biology are also reflected in increased plasma ceramide levels (513±19 pmol WKY vs. 645±25 pmol SHR, n = 6–12, p<0.05). Interestingly, we observed similar increases in ceramide levels (correlating with hypertension grade) in plasma from humans with essential hypertension (185±8 pmol vs. 252±23 pmol; n = 18 normotensive vs. n = 19 hypertensive patients, p<0.05).ConclusionsHypertension is associated with marked alterations in vascular sphingolipid biology such as elevated ceramide levels and signaling, that contribute to increased vascular tone.
Imaging mass spectrometry is currently receiving a significant amount of attention in the mass spectrometric community. It offers the potential of direct examination of biomolecular patterns from cells and tissue. This makes it a seemingly ideal tool for biomedical diagnostics and molecular histology. It is able to generate beautiful molecular images from a large variety of surfaces, ranging from cancer tissue sections to polished cross sections from old-master paintings. What are the parameters that define and control the implications, challenges, opportunities, and (im)possibilities associated with the application of imaging MS to biomedical tissue studies. Is this just another technological hype or does it really offer the hope to gain new insights in molecular processes in living tissue? In this critical insight this question is addressed through the discussion of a number of aspects of MS imaging technology and sample preparation that strongly determine the outcome of imaging MS experiments.
Infrared spectra of the protonated monomers of glycine, alanine, valine, and leucine methyl esters are presented. These protonated species are generated in the gas phase via matrix assisted laser desorption ionization (MALDI) within the cell of a Fourier transform ion cyclotron resonance spectrometer (FTICR) where they are subsequently mass selected as the only species trapped in the FTICR cell. Alternatively, they have also been generated by electrospray ionization and transferred to a Paul ion-trap mass spectrometer where they are similarly isolated. In both cases IR spectra are then derived from the frequency dependence of the infrared multiple photon dissociation (IRMPD) in the mid-infrared region (1000-2200 cm(-1)), using the free electron laser facility Centre de Laser Infrarouge d'Orsay (CLIO). IR bands are assigned by comparison with the calculated vibrational spectra of the lowest energy isomers using density functional theory (DFT) calculations. There is in general good agreement between experimental IRMPD spectra and calculated IR absorption spectra for the lowest energy conformer which provides evidence for conformational preferences. The two different approaches to ion generation and trapping yield IRMPD spectra that are in excellent agreement.
Highly parallel, active pixel detectors enable novel detection capabilities for large biomolecules in time-of-flight (TOF) based mass spectrometry imaging (MSI). In this work, a 512 × 512 pixel, bare Timepix assembly combined with chevron microchannel plates (MCP) captures time-resolved images of several m/z species in a single measurement. Mass-resolved ion images from Timepix measurements of peptide and protein standards demonstrate the capability to return both mass-spectral and localization information of biologically relevant analytes from matrix-assisted laser desorption ionization (MALDI) on a commercial ion microscope. The use of a MCP-Timepix assembly delivers an increased dynamic range of several orders of magnitude. The Timepix returns defined mass spectra already at subsaturation MCP gains, which prolongs the MCP lifetime and allows the gain to be optimized for image quality. The Timepix peak resolution is only limited by the resolution of the in-pixel measurement clock. Oligomers of the protein ubiquitin were measured up to 78 kDa.
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