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See detailFast gas-phase hydrogen/deuterium exchange observed for a DNA G-quadruplex
Gabelica, Valérie ULg; Rosu, Frédéric ULg; Witt, Matthias et al

in Rapid Communications in Mass Spectrometry : RCM (2005), 19(2), 201-208

The gas-phase hydrogen/deuterium (H/D) exchange kinetics of DNA G-quadruplexes has been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The quadruplex [(TGGGGT)(4 ... [more ▼]

The gas-phase hydrogen/deuterium (H/D) exchange kinetics of DNA G-quadruplexes has been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The quadruplex [(TGGGGT)(4).3NH(4)(+)] undergoes very fast H/D exchange, in both the positive and in the negative ion modes, compared to DNA duplexes and other quadruplexes tested, and compared to the corresponding single-stranded TGGGGT. Substitution of NH4+ for K+ did not alter this fast H/D exchange, indicating that the hydrogens of the ammonium ions are not those exchanged. However, stripping of the interior cations of the quadruplex by source collision-induced dissociation (CID) in the positive ion mode showed that the presence of the inner cations is essential for the fast exchange to be possible. Molecular dynamics simulations show that the G-quadruplex is very rigid in the gas phase with NH4+ ions inside the tetrads. We suggest that the fast H/D exchange is favored by this rigid quadruplex conformation. This example illustrates that the concept that compact DNA structures exchange H for D slower than unfolded ones is a misconception. Copyright (C) 2004 John Wiley Sons, Ltd. [less ▲]

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See detailInvestigation of non-covalent interactions between paramagnetic complexes and human serum albumin by electrospray mass spectrometry
Henrotte, Virginie; Laurent, Sophie ULg; Gabelica, Valérie ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2004), 18(17), 1919-1924

Stable gadolinium(III) chelates are nowadays routinely used as contrast agents for magnetic resonance imaging (MRI). Their non-covalent binding to human serum albumin (HSA) has shown to improve their ... [more ▼]

Stable gadolinium(III) chelates are nowadays routinely used as contrast agents for magnetic resonance imaging (MRI). Their non-covalent binding to human serum albumin (HSA) has shown to improve their efficacy. Non-covalent interactions lead to complex formation that can be quantified by several techniques that are mostly tedious and time-consuming. In this study, electrospray ionization mass spectrometry (ESI-MS) was used to investigate the interaction between HSA and several gadolinium(III) complexes. The results were compared with those obtained in the liquid phase. Four gadolinium complexes were investigated: Gd-DTPA 1, Gd-C4Me-DTPA 2, Gd-EOB-DTPA 3, and MP-2269 4. Relaxometry studies show that complexes 1 and 2 have no significant affinity for HSA, while complexes 3 and 4 have increasing affinities for the protein. 1:1 and 1:2 complexes between HSA and MP-2269 were detected by ESI-MS for a twofold excess of the contrast agent, whereas a ligand/protein molar ratio of 4:1 was necessary to observe a 1:1 stoichiometry for Gd-EOB-DTPA, an observation that is in good agreement with the known weaker affinity of the contrast agent for the protein. At a fourfold molar excess, no supramolecular complex was observed for Gd-DTPA I and Gd-C4Me-DTPA 2; a tenfold molar excess was necessary to detect a 1:1 complex, confirming the very weak affinity of these contrast agents for HSA. [less ▲]

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See detailThermometer ions for matrix-enhanced laser desorption/ionization internal energy calibration
Greisch, Jean-François ULg; Gabelica, Valérie ULg; Remacle, Françoise ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2003), 17(16), 1847-1854

This work describes a method to use relative fragmentation yields to characterize the internal energy distribution of ions produced by matrix-enhanced laser desorption/ionization mass spectrometry (MELDI ... [more ▼]

This work describes a method to use relative fragmentation yields to characterize the internal energy distribution of ions produced by matrix-enhanced laser desorption/ionization mass spectrometry (MELDI-MS, see: Wright LG, Cooks RG, Wood KL. Biomed. Mass Spectrom. 1985; 12:153162). Assuming that the fragmentation proceeds statistically and that the collisions in the source lead to a Boltzmann-like distribution of the internal energy, a characteristic parameter, the effective temperature, is introduced to describe the internal energy distribution of the ions observed. The hypotheses, advantages and drawbacks of the implementation of the method that uses substituted benzylpyridinium salts as thermometer ions are discussed. Use is made of two matrices that produce no matrix cations in MELDI and are suitable for small cationic salts. The actual value of this effective temperature significantly depends on an accurate determination of the threshold dissociation energies and on the time spent in the source, in addition to the statistical hypothesis itself. The method could be applied to normalize spectra in order to compare results issued from different instruments. [less ▲]

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See detailAdvantages and drawbacks of nanospray for studying noncovalent protein-DNA complexes by mass spectrometry
Gabelica, Valérie ULg; Vreuls, Christelle ULg; Filée, Patrice ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2002), 16(18), 1723-1728

The noncovalent complexes between the BlaI protein dimer (wild-type and GM2 mutant) and its double-stranded DNA operator were studied by nanospray mass spectrometry and tandem mass spectrometry (MS/MS ... [more ▼]

The noncovalent complexes between the BlaI protein dimer (wild-type and GM2 mutant) and its double-stranded DNA operator were studied by nanospray mass spectrometry and tandem mass spectrometry (MS/MS). Reproducibility problems in the nanospray single-stage mass spectra are emphasized. The relative intensities depend greatly on the shape of the capillary tip and on the capillary-cone distance. This results in difficulties in assessing the relative stabilities of the complexes simply from MS' spectra of protein-DNA mixtures. Competition experiments using MS/MS are a better approach to determine relative binding affinities. A competition between histidine-tagged BlaIWT (BlaIWTHis) and the GM2 mutant revealed that the two proteins have similar affinities for the DNA operator, and that they co-dimerize to form heterocomplexes. The low sample consumption of nanospray allows MS/MS spectra to be recorded at different collision energies for different charge states with 1 muL of sample. The MS/MS experiments on the dimers reveal that the GM2 dimer is more kinetically stable in the gas phase than the wild-type dimer. The MS/MS experiments on the complexes shows that the two proteins require the same collision energy to dissociate from the complex. This indicates that the rate-limiting step in the monomer loss from the protein-DNA complex arises from the breaking of the protein-DNA interface rather than the protein-protein interface. The dissociation of the protein-DNA complex proceeds by the loss of a highly charged monomer (carrying about two-thirds of the total charge and one-third of the total mass). MS/MS experiments on a heterocomplex also show that the two proteins BlaIWTHis and BlaIGM2 have slightly different charge distributions in the fragments. This emphasizes the need for better understanding the dissociation mechanisms of biomolecular complexes. [less ▲]

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See detailTriplex and quadruplex DNA structures studied by electrospray mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Houssier, Claude ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2002), 16(18), 1729-1736

DNA triplex and quadruplex structures have been successfully detected by electrospray ionization mass spectrometry (ESI-MS). Circular dichroism and UV-melting experiments show that these structures are ... [more ▼]

DNA triplex and quadruplex structures have been successfully detected by electrospray ionization mass spectrometry (ESI-MS). Circular dichroism and UV-melting experiments show that these structures are stable in 150 mM ammonium acetate at pH 7 for the quadruplexes and pH 5.5 for the triplexes. The studied quadruplexes were the tetramer [d(TGGGGT)](4), the dimer [d(GGGGTTTTGGGG)](2), and the intramolecular folded strand dGGG(TTAGGG)(3), which is an analog of the human telomeric sequence. The absence of sodium contamination allowed demonstration of the specific inclusion of n-1 ammonium cations in the quadruplex structures, where n is the number of consecutive G-tetrads. We also detected the complexes between the quadruplexes and the quadruplex-specific drug mesoporphyrin IX. MS/MS spectra of [d(TGGGGT)](4) and the complex with the drug are also reported. As the drug does not displace the ammonium cations, one can conclude that the drug binds at the exterior of the tetrads, and not between them. For the triplex structure the ESI-MS spectra show the detection of the specific triplex, at m/z values typically higher than those typically observed for duplex species. Upon MS/MS the antigene strand, which is bound into the major groove of the duplex, separates from the triplex. This is the same dissociation pathway as in solution. To our knowledge this is the first report of a triplex DNA structure by electrospray mass spectrometry. [less ▲]

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See detailGas Phase Thermal Denaturation of an Oligonucleotide Duplex and Its Complexes with Minor Groove Binders
Gabelica, Valérie ULg; Rosu, Frédéric ULg; Houssier, Claude ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2000), 14(6), 464-467

Electrospray ionization with in-source collisionally induced dissociation has been used to probe the gas phase stability of an oligonucleotide duplex and its complexes with some minor groove binding drugs ... [more ▼]

Electrospray ionization with in-source collisionally induced dissociation has been used to probe the gas phase stability of an oligonucleotide duplex and its complexes with some minor groove binding drugs. On the basis of the arguments developed in detail by Drahos et al. (J. Mass Spectrom. 1999; 34:1373), this type of experiment can also be described as 'thermal denaturation in the gas phase'. We found that the gas phase denaturation curves were very similar to the solution phase denaturation curves determined by the traditional UV spectrophotometric method and, by analogy with the melting temperature T(m) which characterizes the stability in solution, we define a melting voltage V(m) to characterize the stability in the gas phase. A comparison of the T(m) and V(m) relative values suggests that the structure of the complexes is conserved during the electrospray process which transfers the ions from the solution to the gas phase. [less ▲]

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See detailStudy of the mechanism of direct laser desorption/ionisation for some small organic molecules (M < 400 daltons)
Benazouz, M.; Hakim, B.; Debrun, J. L. et al

in Rapid Communications in Mass Spectrometry : RCM (1999), 13(23), 2302-2304

Aspects of direct laser desorption/ionisation have been studied for three molecules, aminotriazole (positive ion), dinoterb and ioxynil (negative ion). The samples are deposited on metallic substrates ... [more ▼]

Aspects of direct laser desorption/ionisation have been studied for three molecules, aminotriazole (positive ion), dinoterb and ioxynil (negative ion). The samples are deposited on metallic substrates, and a nitrogen laser is used for desorption/ionisation; ion yields are measured with a time-of-flight mass spectrometer, Previous work had shown that ion yields can strongly vary from one substrate to another, and that this variation does not reflect the (calculated) metal surface temperatures. New results obtained in this work indicate that the desorption/ionisation mechanism is linked to the physical state of the substrate surface. Copyright (C) 1999 John Wiley & Sons, Ltd. [less ▲]

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See detailThree-dimensional Kinetic Energy Distributions of Ions using a Retarding Potential Analyser. Analysis of Discimination Effects by Ion Trajectory Simulations.
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg

in Rapid Communications in Mass Spectrometry : RCM (1999), 13

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were ... [more ▼]

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were performed which led to an analytical function correcting for the influence of discrimination against ions with velocity components perpendicular to the retarding field direction. The analysis of the thermal kinetic energy distribution of molecular vinyl bromide ions confirms the computed correcting factor. [less ▲]

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See detailCalibration of the Internal Energy Distribution of Ions Produced by Electrospray
Collette, Caroline ULg; De Pauw, Edwin ULg

in Rapid Communications in Mass Spectrometry : RCM (1998), 12

The internal energy deposited in the ions in the source of mass spectrometer governs their fragmentation and therefore the content of the spectra. When the ionization conditions are well defined and ... [more ▼]

The internal energy deposited in the ions in the source of mass spectrometer governs their fragmentation and therefore the content of the spectra. When the ionization conditions are well defined and reproductible, the elaboration of databases benefits the use of the method. In electrospray, however, the source conditions are not strictly defined. The elaboration of spectra databases therefore requires a calibration of internal energy of the ions. In this article, a method for the calibration of the internal energy of the ions in electrospray is presented, developed using fragmentation reactions of a set of probe ions (benzylpyridinium salts) under various conditions. [less ▲]

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See detailComparison of the Internal Energy Distributions of Ions Produced by Different Electrospray Sources
Collette, Caroline ULg; Drahos, Laszlo; De Pauw, Edwin ULg et al

in Rapid Communications in Mass Spectrometry : RCM (1998), 12

The internal energies of the emitted ions can be modulated in an electrospray source through different experimental conditions. However, the fragmentation pattern depends also on conditions that cannot be ... [more ▼]

The internal energies of the emitted ions can be modulated in an electrospray source through different experimental conditions. However, the fragmentation pattern depends also on conditions that cannot be controlled by the operator. These differences make difficult the comparison of the electrospray mass spectra obtained with different mass spectrometers. A method for the calibration of the internal energies of ions produced by an electrospray source has been presented previously to study the influence of experimental conditions on the internal energies of the ions. In this work, new results were obtained with modified values of fragmentation energy taking into account the kinetic shift of thermometer ions. [less ▲]

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See detailElectrospray Mass Spectrometry Study of Selective Complexes of Polyammonium Macrotricyclic Ligands with Dicarboxylic Acids
Collette, Caroline ULg; Meunier, Cécile; De Pauw, Edwin ULg et al

in Rapid Communications in Mass Spectrometry : RCM (1997), 11

Macrocyclic and macropolycyclic polyammonium host molecules have been shown to complex a variety of inorganic and organic anions strongly and selectively. The selectivity of the complexation depends on ... [more ▼]

Macrocyclic and macropolycyclic polyammonium host molecules have been shown to complex a variety of inorganic and organic anions strongly and selectively. The selectivity of the complexation depends on the substrate lenght and on the size of the host cavity of the macrocycle. We describe in this article the analysis of the complexation of dicarboxylic acid substrates by a macrotricyclic host using electrospray mass spectrometry. [less ▲]

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