Publications of Emeline Hanozin
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See detailLiquid chromatography setup-dependent artefactual methionine oxidation of peptides: the importance of an adapted quality control process
Baumans, France ULiege; Hanozin, Emeline ULiege; Baiwir, Dominique ULiege et al

in Journal of Chromatography. A (2021), 1654

In both biologics quality control experiments and protein post-translational modification studies, the analytical system used is not supposed to bring any artefactual modifications which could impair the ... [more ▼]

In both biologics quality control experiments and protein post-translational modification studies, the analytical system used is not supposed to bring any artefactual modifications which could impair the results. In this work, we investigated oxidation of methionine-containing peptides during reversed-phase (RP) chromatographic separation. We first used a synthetic methionine-containing peptide to evaluate this artefactual phenomenon and then considered more complex samples (i.e., plasma and HeLa protein digests). The methionine oxidation levels of the peptides were systematically assessed and compared for the long-term use of the analytical column, the sample trapping time, the gradient length, the sample load and the nature of the stationary phase (HSS T3 from Waters, YMC Triart C18 from YMC Europe GmbH and BEH130 C18 from Waters). In addition to the oxidation of methionine in solution, we observed on the HSS T3 and the BEH130 stationary phases an additional broad peak corresponding to an on-column oxidized species. Considering the HSS T3 phase, our results highlight that the on-column oxidation level significantly increases with the age of the analytical column and the gradient length and reaches 56 % when a 1-year-old column set is used with a 180 min-long LC method. These levels go to 0 % and 18 % for the YMC Triart C18 and the BEH130 C18 phases respectively. Interestingly, the on-column oxidation proportion decreases as the injected sample load increases suggesting the presence of a discrete number of oxidation sites within the stationary phase of the analytical column. Those findings observed in different laboratories using distinct set of columns, albeit to varying degrees, strengthen the need for a standard of methionine-containing peptide that could be used as a quality control to appraise the status of the liquid chromatographic columns. [less ▲]

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See detailRadical-Pairing Interactions in a Molecular Switch Evidenced by Ion Mobility Spectrometry and Infrared Ion Spectroscopy
Hanozin, Emeline ULiege; Mignolet, Benoît ULiege; Martens, Jonathan et al

in Angewandte Chemie International Edition (2021), 60

The digital revolution sets a milestone in the progressive miniaturization of working devices and in the underlying advent of molecular machines. Foldamers involving mechanically entangled components with ... [more ▼]

The digital revolution sets a milestone in the progressive miniaturization of working devices and in the underlying advent of molecular machines. Foldamers involving mechanically entangled components with modular secondary structures are among the most promising designs for molecular switch-based applications. Characterizing the nature and dynamics of their intramolecular network following the application of a stimulus is the key to their performance. Here, we use non-dissociative electron transfers as a reductive stimulus in the gas phase and probe the consecutive co-conformational transitions of a donor-acceptor oligorotaxane foldamer using electrospray mass spectrometry interfaced with ion mobility and infrared ion spectroscopy. The comparison of collision cross section distributions for analogous closed-shell and radical molecular ions sheds light on their respective formation energetics while variations in their respective infrared absorption bands evidence different intramolecular organizations as the foldamer gets compact. These differences are compatible with the advent of radical-pairing interactions. [less ▲]

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See detailResponse to Comment on Effective Temperature and Structural Rearrangement in Trapped Ion Mobility Spectrometry
Morsa, Denis ULiege; Hanozin, Emeline ULiege; Gabelica, Valérie et al

in Analytical Chemistry (2020), 92(24), 633416337

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See detailSolvent Adducts in Ion Mobility Spectrometry: Toward an Alternative Reaction Probe for Thermometer Ions
Morsa, Denis ULiege; Hanozin, Emeline ULiege; Eppe, Gauthier ULiege et al

in Journal of the American Society for Mass Spectrometry (2020)

The fragmentation of benzylpyridinium "thermometer" ions is widely used to quantify the energetics of ions studied by mass spectrometry and other hyphenated techniques such as ion mobility. The reaction ... [more ▼]

The fragmentation of benzylpyridinium "thermometer" ions is widely used to quantify the energetics of ions studied by mass spectrometry and other hyphenated techniques such as ion mobility. The reaction pathway leads to a benzylium cation with the release of a neutral pyridine. Using trapped ion mobility spectrometry, we noticed that the addition of acetonitrile, present in the electrosprayed solvent mixture, could occur on some electrophilic benzylium cations. This process results in the formation of adducts and in the appearance of a supplementary mobility peak. We here demonstrate that the addition takes place both in the electrospray source and inside the mobility analyzer, thereby evidencing possible outflow of solvent vapors downstream the instrument. By further characterizing the initial kinetics and the resulting equilibrium linked with the addition reaction, we presently discuss these as alternative probes to calibrate ion temperature in the framework of ion mobility. [less ▲]

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See detailEffective Temperature and Structural Rearrangement in Trapped Ion Mobility Spectrometry
Morsa, Denis ULiege; Hanozin, Emeline ULiege; Eppe, Gauthier ULiege et al

in Analytical Chemistry (2020)

Modern ion mobility instrumentations are typically operated above the low field limit, which may activate the ions and cause structural rearrangement or fragmentation during the analysis. Here, we ... [more ▼]

Modern ion mobility instrumentations are typically operated above the low field limit, which may activate the ions and cause structural rearrangement or fragmentation during the analysis. Here, we quantitatively assessed the internal heating experienced by ions during trapped ion mobility spectrometry (TIMS) experiments. To this end, the fragmentation yields of fragile benzylpyridinium “thermometer” ions were monitored during both the accumulation and analysis steps inside the TIMS tunnel. The corresponding fragmentation rate constants were translated into a vibrational effective temperature Teff,vib. Our results demonstrate significant fragmentation upstream and inside the TIMS tunnel that corresponds to Teff,vib ≈ 510 K during both the accumulation and analysis steps. Broadening our scope to cytochrome c and lysozyme, we showed that although compact “native” folds can be preserved, the collision cross section distributions are highly sensitive to the transmission voltages and the analysis timescale. Our results are discussed with regard to Teff,vib data previously acquired on traveling-wave (TWIMS) ion mobility in the context of native mass spectrometry and conformational landscape exploration. [less ▲]

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See detailTwo-Parameter Power Formalism for Structural Screening of Ion Mobility Trends: Applied Study on Artificial Molecular Switches
Hanozin, Emeline ULiege; Morsa, Denis ULiege; De Pauw, Edwin ULiege

in Journal of Physical Chemistry. A (2019), 123

Recent literature provides increasing samples of structural studies relying on ion mobility coupled to mass spectrometry in view of characterizing gas-phase conformation and energetics properties of ... [more ▼]

Recent literature provides increasing samples of structural studies relying on ion mobility coupled to mass spectrometry in view of characterizing gas-phase conformation and energetics properties of biomolecular ions. A typical framework consists in experimentally monitoring the collisional cross sections for various experimental conditions and using them as references to select appropriate candidate structures issued from theoretical modeling. Although it has proved successful for structural assignment, this process is resource costly and lengthy, namely due to intricacies in the selection of appropriate input geometries. In the present work, we propose simplified methodologies dedicated to the systematic screening of ion mobility data acquired on systems built from repetitive subunits and detail their application to challenging artificial molecular switch systems. Capitalizing on coarse-grained design, we first demonstrate how the assimilation of subunits into adequately assembled building-blocks can be used for fast assignments of a system topology. Further focusing on topology-specific differential ion mobility trends, we show that the building-block assemblies can be fused into single fully convex solid figure models, i.e., sphere and cylinder, whose projected areas follow a two-parameter power formalism A × nB. We show that the fitting parameters A and B were assigned as structural descriptors respectively associated with the dimensions of each constitutive subunit, i.e., size parameter, and with their assembled tridimensional arrangement, i.e., shape parameter. The present work provides a ready-to-use method for the screening of IM-MS data sets that is expected to facilitate the eventual design of input structures whenever advanced modeling calculations are required. [less ▲]

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See detailCovalent Cross-Linking as an Enabler for Structural Mass Spectrometry
Hanozin, Emeline ULiege; Grifnée, Elodie ULiege; Gattuso, Hugo ULiege et al

in Analytical Chemistry (2019)

Studies referring to the structural elucidation of intact biomolecular systems using mass spectrometry techniques have been gradually flourishing in the post-2000s literature topics. As part of native ... [more ▼]

Studies referring to the structural elucidation of intact biomolecular systems using mass spectrometry techniques have been gradually flourishing in the post-2000s literature topics. As part of native mass spectrometry, this domain capitalizes on the kinetic trapping of physiological folds in view of probing solution-like conformational properties of isolated molecules or complexes after their electrospray transfer to the gas phase. Despite its documented efficiency for a wide array of analytes, this approach is expected to be pushed to its limits when considering highly dynamic systems or when dealing with non-ideal operating conditions. To circumvent these limitations, we challenge the adequacy of an original strategy based on cross-linkers to improve the gas-phase stability of isolated proteins and ensure the preservation of folded conformations when measuring with strong transmission voltages, by spraying from denaturing solvents or trapping for extended periods of time. Tested on cytochrome c, myoglobin and β-lactoglobulin cross-linked using BS3, we validated the process as a structurally non-intrusive in solution using far-ultraviolet circular dichroism and unraveled the preservation of folded conformations showing better resilience to denaturation on cross-linked species using ion mobility. The resulting collision cross sections were found in agreement with the native fold, and a preservation of the proteins’ secondary and tertiary structures was evidenced using molecular dynamics simulations. Our results provide new insights concerning the fate of electro-sprayed cross-linked conformers in the gas phase, while constituting promising evidence for the validation of this technique as part of tomorrow’s structural mass spectrometry workflows. [less ▲]

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See detailBenchmarking IM-MS gas-phase data based on cross-linking strategies
Hanozin, Emeline ULiege; Grifnée, Elodie ULiege; Gattuso, Hugo ULiege et al

Conference (2019)

Since the apparition of conservative soft-ionization sources in the late 80s, i.e. electrospray (ESI) and matrix-assisted laser desorption-ionization, mass spectrometry (MS) has been extensively used to ... [more ▼]

Since the apparition of conservative soft-ionization sources in the late 80s, i.e. electrospray (ESI) and matrix-assisted laser desorption-ionization, mass spectrometry (MS) has been extensively used to identify, quantify and characterize wide types of biomolecules. Especially, ESI sources make feasible the transfer of intact biomolecules and macromolecular complexes in the mass spectrometer, opening the so-called field of “native” MS. However, major questioning and inherent skepticism yet surround the native MS field concerning the ability to preserve non-bonded biological interactions during and after the molecular transfer from the physiological aqueous media to the gas-phase. Indeed, the introduction of biological structures into the gas-phase may eventually result in a reshape of their tridimensional fold, therefore leading to a misinterpretation of further derived structural data. In an effort to circumvent gas-phase unfolding scenarios, we here suggest a structural strategy relying on intra-molecular covalent cross-linkers acting as molecular scaffolds. We focused on small 10 kDa to 20 kDa proteins, such as cytochrome c, myoglobin and β-lactoglobulin, which are yet often used as model systems to gauge wide range of structural, kinetic and thermodynamics methodologies. We studied the products of “type 0” and “type 1” cross-linking reactions achieved using bissulfosuccinimidyl suberate (BS3) as a linker reagent and compared them with their non-linked counter-parts regarding their respective structural properties. The model systems were structurally investigated both in solution, through circular dichroism and thermal denaturation measurements, and in the gas-phase following ESI injection, through IM-MS and collision induced unfolding (CIU) measurements. The gas-phase data were acquired from different solvent conditions and compared with “native-compliant” benchmarks furnished by NMR spectroscopy. In general, the content in secondary structures within the proteins was found barely unaffected by the presence of the linkers when operating in physiological solution, therefore witnessing a preservation of the native fold upon linking reaction. However, after ionization and transfer into the gas-phase, we monitored significant reshapes in the conformational landscapes materialized through a shift of the collision cross-sections distribution towards lower values when linkers are present. The magnitude of the compaction effect is directly dependent on the protein charge and linker content. Altogether, the comprehension of the fate of electro-sprayed cross-linked conformers in the gas-phase and their respective correlation with the physiological fold achieved in solution constitute major steps in the validation of this technique as part of native MS workflows. [less ▲]

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See detailMulti-Enzymatic Limited Digestion: The Next-Generation Sequencing for Proteomics?
Morsa, Denis ULiege; Baiwir, Dominique ULiege; La Rocca, Raphaël ULiege et al

in Journal of proteome research (2019)

Over the past 40 years, proteomics, generically defined as the field dedicated to the identification and analysis of proteins, has tremendously gained in popularity and potency through advancements in ... [more ▼]

Over the past 40 years, proteomics, generically defined as the field dedicated to the identification and analysis of proteins, has tremendously gained in popularity and potency through advancements in genome sequencing, separative techniques, mass spectrometry, and bioinformatics algorithms. As a consequence, its scope of application has gradually enlarged and diversified to meet specialized topical biomedical subjects. Although the tryptic bottom-up approach is widely regarded as the gold standard for rapid screening of complex samples, its application for precise and confident mapping of protein modifications is often hindered due to partial sequence coverage, poor redundancy in indicative peptides, and lack of method flexibility. We here show how the synergic and time-limited action of a properly diluted mix of multiple enzymes can be exploited in a versatile yet straightforward protocol to alleviate present-day drawbacks. Merging bottom-up and middle-down ideologies, our results highlight broad assemblies of overlapping peptides that enable refined and reliable characterizations of proteins, including variant identification, and their carried modifications, including post-translational modifications, truncations, and cleavages. Beyond this boost in performance, our methodology also offers efficient de novo sequencing capabilities, in view of which we here present a dedicated custom assembly algorithm. [less ▲]

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See detailKendrick Mass Defect Approach Combined to NORINE Database for Molecular Formula Assignment of Nonribosomal Peptides
Chevalier, M.; Ricart, E.; Hanozin, Emeline ULiege et al

in Journal of the American Society for Mass Spectrometry (2019), 30(12), 2608-2616

The identification of known (dereplication) or unknown nonribosomal peptides (NRPs) produced by microorganisms is a time consuming, expensive, and challenging task where mass spectrometry and nuclear ... [more ▼]

The identification of known (dereplication) or unknown nonribosomal peptides (NRPs) produced by microorganisms is a time consuming, expensive, and challenging task where mass spectrometry and nuclear magnetic resonance play a key role. The first step of the identification process always involves the establishment of a molecular formula. Unfortunately, the number of potential molecular formulae increases significantly with higher molecular masses and the lower precision of their measurements. In the present article, we demonstrate that molecular formula assignment can be achieved by a combined approach using the regular Kendrick mass defect (RKMD) and NORINE, the reference curated database of NRPs. We observed that irrespective of the molecular formula, the addition and subtraction of a given atom or atom group always leads to the same RKMD variation and nominal Kendrick mass (NKM). Graphically, these variations translated into a vector mesh can be used to connect an unknown molecule to a known NRP of the NORINE database and establish its molecular formula. We explain and illustrate this concept through the high-resolution mass spectrometry analysis of a commercially available mixture composed of four surfactins. The Kendrick approach enriched with the NORINE database content is a fast, useful, and easy-to-use tool for molecular mass assignment of known and unknown NRP structures. [Figure not available: see fulltext.]. © 2019, American Society for Mass Spectrometry. [less ▲]

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See detailCan we correlate ion mobility mass spectrometry data with native solution structures? A crosslinking approach
Hanozin, Emeline ULiege; Grifnée, Elodie ULiege; Morsa, Denis ULiege et al

Poster (2018, June)

Introduction: The structural characterization of biomolecules is of prime importance in the understanding of biological processes at the molecular level. In this context, the development of soft ... [more ▼]

Introduction: The structural characterization of biomolecules is of prime importance in the understanding of biological processes at the molecular level. In this context, the development of soft ionization techniques, namely electrospray ionization, and the advent of ion mobility (IM) separation tools open new perspectives for the analysis of large intact molecular ions by mass spectrometry (MS). Previous (IM-)MS experiments emphasized that the solution phase structures may be (partially) preserved in the gas phase under soft ionization conditions. However, several factors (e.g. coulombic interactions, accelerating voltages) have an influence on the conformation of biomolecular ions in the gas phase and should be carefully considered. Consequently, some fundamental questions remain elusive: “Can we correlate ion mobility mass spectrometry data to native solution structures?” Methods: To bring innovative answers to these longtime debated questions, we here propose an early stage study targeting constrained “native-like” conformations in the gas phase. To this end, we capitalize on a crosslinking approach to establish chemical links between lysine residues located in close spatial proximity within the protein. The so-created covalent network is here used as a scaffold to prevent the collapsing and unfolding of biomolecular ions once desolvated in the gas phase. These “frozen” native solution conformations are then interrogated using ion mobility as implemented on the commercial SYNAPT G2 HDMS spectrometer. Preliminary data: Practically, we used cytochrome c as a model system that we crosslinked with BS3 linkers. Using ion mobility, we monitored the evolution of the collision cross section (CCS) quantity, a rotationally averaged 2D projection of the ion conformation, for each charge state as function of the number of covalent intramolecular linkers. These data were readily compared with those obtained in similar conditions for the non-crosslinked cytochrome c as well as with a benchmark corresponding to the native solution conformations as resolved by NMR spectroscopy. Our results highlight that the crosslinked cytochrome c adopts more compact conformations in the gas phase, closer to values monitored for the native solution conformation, compared to its non-crosslinked homologue. In addition, we found that a critical number of intramolecular linkers were required to prevent structural unfolding from Coulomb repulsions. Novel aspect: Bring innovative answers to the longtime debated native MS questions based on an alternative application of intramolecular covalent linkers. [less ▲]

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See detailWhere Ion Mobility and Molecular Dynamics Meet to Unravel the (Un)Folding Mechanisms of an Oligorotaxane Molecular Switch
Hanozin, Emeline ULiege; Mignolet, Benoît ULiege; Morsa, Denis ULiege et al

in ACS Nano (2017), 11(10), 10253-10263

At the interface between foldamers and mechanically interlocked molecules, oligorotaxanes exhibit a spring-like folded secondary structure with remarkable mechanical and physicochemical properties. Among ... [more ▼]

At the interface between foldamers and mechanically interlocked molecules, oligorotaxanes exhibit a spring-like folded secondary structure with remarkable mechanical and physicochemical properties. Among these properties, the ability of oligorotaxanes to act as molecular switches through controlled modulations of their spatial extension over (un)folding dynamics is of particular interest. The present study aims to assess and further characterize this remarkable feature in the gas phase using mass spectrometry tools. In this context, we focused on the [4]5NPR+12 oligorotaxane molecule complexed with PF6 - counterion and probed its co-conformational states as a function of the in-source-generated charge states. Data were interpreted in light of electronic secondary structure computations at the PM6 and DFT levels. Our results highlight two major co-conformational groups associated either with folded compact structures, notably stabilized by intramolecular π-π interactions and predominant for low charge states or with fully stretched structures resulting from significant Coulombic repulsions at high charge states. Between, the oligorotaxane adopts intermediate folded co-conformations, suggesting a stepwise unfolding pathway under increasing repulsive Coulombic constraints. The reversibility of this superstructural transition was next interrogated under electron-driven (nondissociative electron transfer) and heat-driven (collision-induced unfolding) activation stimuli. The outcomes support the feasibility to either unfold or (partially) refold the oligorotaxane foldamer on purpose in the gas phase. Our results show that the balance between the stabilizing π-π interactions and the versatile Coulomb interactions dictates the elongation state of the foldamer in the gas phase and emphasizes the adequacy of mass spectrometry tools for the superstructural characterization of desolvated prototypical artificial molecular machines. © 2017 American Chemical Society. [less ▲]

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See detailCoulombic driven multi-conformational aspects of oligorotaxane switches studied by ion mobility mass spectrometry and molecular dynamics
Hanozin, Emeline ULiege; Mignolet, Benoît ULiege; Morsa, Denis ULiege et al

Conference (2017, June)

Introduction Artificial Molecular Machines (AMMs), such as Mechanically Interlocked Molecules (MIMs) and foldamers, have recently raised tremendous interest due to their unique properties. Under the ... [more ▼]

Introduction Artificial Molecular Machines (AMMs), such as Mechanically Interlocked Molecules (MIMs) and foldamers, have recently raised tremendous interest due to their unique properties. Under the influence of an appropriate stimuli (pH, redox potential, light…), such molecules are able to reversibly switch between distinct conformational states. Scientists may capitalize on such exclusive properties to get a better understanding of the biomacromolecular level or to design innovative “smart” materials. At the interface between foldamers and MIMs, oligorotaxanes exhibit a spring-like folded secondary structure with remarkable mechanical and physicochemical properties. In the present study, we use ion mobility coupled with mass spectrometry (IM-MS) to probe the conformational states of differentially charged oligorotaxanes in the gas phase. Method Oligorotaxanes are donor-acceptor polymers composed of a π electron-donating dumbbell over which a discrete number of π electron-accepting tetracationic cyclophanes are threaded. The numerous intra-molecular interactions provide them a highly-stabilized rigid rod-like structure in solution. We use IM-MS as implemented in the Synapt G2 HDMS (Waters, Manchester, UK) to investigate the structure of the ionized oligorotaxanes. Our purposes are to probe (i) the different populations of stable conformers generated according to the charge state z and (ii) the reversibility of an electron-driven or thermal-driven conformational change in the gas phase implemented via an electron transfer or collisional activation process prior to the mobility separation. Our experimental observations are supported by electronic structure optimizations at the PM6 and DFT levels coupled with Born-Oppenheimer Molecular Dynamics simulations. Preliminary data Our results highlight a progressive elongation of the oligorotaxane structure with increasing charge numbers until it reaches a maximum extension state. Matching the experimental data with theoretical simulations, we find that the oligorotaxanes adopt an entropically-favored globular shape at low z. As z increases, coulombic repulsions occurring between the cyclophanes gradually outweigh the stabilizing π-stacking interactions and force the structure to elongate. This process occurs in a multistep fashion, each corresponding to a distinct group of helical-shaped conformers, before it eventually results in a fully stretched structure. On the other hand, our results also highlight that a charge reduction driven by a non-dissociative electron transfer process leads to a refolding of the structure so that it adopts a size similar to its electrospray-generated counterpart when the appropriate number of electrons is added. This observation may be imparted to the gradual decrease of the Coulomb repulsions between the cyclophanes mediated through increasing numbers of transferred electrons. These results suggests that the transition from one conformer to another is reversible so that the electrostatic balance between the cyclophanes may be used to further tune the structural state adopted by this artificial molecular switch. The second stimulus relied on collisional activation whose inelastic component provides a way to build up energy into the accessible vibrational degrees of freedom. The conformational landscapes of such-activated oligorotaxanes ions were found unchanged in term of collision cross section position but the repartition of population was altered with a promotion of the most elongated conformer, provided the absence of selective fragmentation. Altogether, these results highlight the feasibility of handling the elongation state of oligorotaxanes in the gas phase through appropriate inputs and underline its conformational reversibility properties. Novel aspect Stimuli-induced reversible conformational rearrangements of innovative AMMs studied by IM-MS and molecular dynamics in the gas phase. [less ▲]

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See detailFirst Results Using TIMS on Systems Requiring High IMS Resolution
Haler, Jean ULiege; Massonnet, Philippe ULiege; Morsa, Denis ULiege et al

Conference (2016, June 05)

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See detailDo pi-stacking interactions preserve the solution-state structure un the gas phase? Study of oligorotaxanes by ion mobility mass spectrometry
Hanozin, Emeline ULiege; Mignolet, Benoît ULiege; Morsa, Denis ULiege et al

Conference (2016)

The development of the so-called soft ionization techniques, namely ESI and MALDI, opened new perspectives for the analysis of large intact molecular ions by mass spectrometry (MS) and set the basis of ... [more ▼]

The development of the so-called soft ionization techniques, namely ESI and MALDI, opened new perspectives for the analysis of large intact molecular ions by mass spectrometry (MS) and set the basis of the native MS field. In this context, the conservation of nonbonded interactions maintaining the physiological conformation of an ion through the ESI process is of major interest. Among these, π-stacking interactions are ubiquitous both within biological (DNA) and synthetic (organic electronic devices) systems. In the present investigation we attempt to probe the conservation of π-stacking interactions on oligorotaxanes, a synthetic π-stacked polymers, after its transfer process to the gas phase. The foundations of native mass spectrometry still constitute a controversial topic. In this context, we here investigate this eventuality using ion mobility on electrosprayed mechanically interlocked molecules (MIMS) called oligorotaxanes. These ones are π-stacked polymers composed of a π electron-donating dumbbell over which a discrete number of π electron-accepting tetracationic cyclophanes are threaded5. The numerous intra-molecular interactions confer to these molecules a highly-stabilized rigid rod-like structure and make them ideal candidates to probe the structural fate of ions following the electrospray process. Both the effects of electrostatic repulsions and of collision-driven internal activation on the ion conformation are considered. The resulting isolated ions were then structurally interrogated by means of ion mobility directly hyphenated with MS (Synapt G2 HDMS, Manchester, UK). Dealing with different polymer lengths and charge states, our results highlight a progressive elongation of the oligorotaxane structure with increasing charge density until it reaches a plateau. Using theoretical models built around a linear assemble of monomeric units with tunable sizes as a reference tool, we show that, at low charge states, the “native” π-stacked rod-like structure of oligoratoxanes is expected to be preserved. However, as the charge density increases, coulombic repulsions occurring between the cyclophanes gradually outweigh the stabilizing π-stacking interactions and force the structure to elongate, eventually resulting in the formation of fully stretched structure. Geometries optimized at a PM6 and DFT level also support these conclusions. Meanwhile, collisional activation experiments highlight potent population shifts towards the formation of slightly elongated conformers. They however remain insufficient to promote the formation of fully extended conformations before the fragmentation occurs, emphasizing the high stability of oligorotaxanes. Altogether, our results show that the structure of strongly stabilized oligorotaxanes could be preserved from the solution to the gas phase provided that the electrostatic repulsions and the internal heating are kept minimal. Moreover, our results may also constitute a starting point to quantitatively study the strength of π-stacking interactions in the gas phase. [less ▲]

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See detailCoulombic driven multi-conformational aspects of oligorotaxane switches studied by ion mobility mass spectrometry
Hanozin, Emeline ULiege; Mignolet, Benoît ULiege; Morsa, Denis ULiege et al

Conference (2016)

Molecular machines, such as Mechanically Interlocked Molecules (MIMs) and foldamers, have recently raised tremendous interest due to their unique properties. Under the influence of an appropriate stimuli ... [more ▼]

Molecular machines, such as Mechanically Interlocked Molecules (MIMs) and foldamers, have recently raised tremendous interest due to their unique properties. Under the influence of an appropriate stimuli (pH, redox potential, light…), such molecules are able to reversibly switch between distinct conformational states. Scientists may capitalize on such exclusive properties to get a better understanding of the biomacromolecular level or to design innovative “smart” materials. At the edge of foldamers and MIMs, oligorotaxanes exhibit a spring-like folded secondary structure with remarkable mechanical and physicochemical properties. In the present study, we use ion mobility coupled with mass spectrometry (IM-MS) to probe the conformational states of differentially charged oligorotaxanes in the gas phase. Oligorotaxanes are donor-acceptor polymers composed of a π electron-donating dumbbell over which a discrete number of π electron-accepting tetracationic cyclophanes are threaded. The numerous intra-molecular interactions provide them a highly-stabilized rigid rod-like structure in solution. We presently use IM-MS as implemented in the Synapt G2 HDMS (Waters, Manchester, UK) to investigate the structure of the ionized three-ring oligorotaxane. Our purposes are to probe (i) the different populations of stable conformers generated according to the charge state z and (ii) the reversibility of an electron-driven conformational change in the gas phase implemented via an electron transfer process (ETnoD) prior to the mobility separation. Our experimental observations are supported by electronic structure optimizations at the PM6 and DFT levels coupled with Born-Oppenheimer Molecular Dynamic (BOMD) simulations. Our results highlight a progressive elongation of the oligorotaxane structure with increasing charge numbers until it reaches a plateau. Matching the experimental data with theoretical simulations, we find that the oligorotaxanes adopt an entropically-favored globular shape at low z. As z increases, coulombic repulsions occurring between the cyclophanes gradually outweigh the stabilizing π-stacking interactions and force the structure to elongate. This process occurs in a multistep fashion, each corresponding to a distinct group of conformers, before it eventually results in a fully stretched structure. On the other hand, our results also highlight that a charge reduction driven by the ETnoD process leads to a refolding of the structure so that it adopts a size similar to its electrospray-generated counterpart, therefore attesting of the conformational reversibility of olixorotaxanes in the gas phase. Altogether, our results show that the oligorotaxanes adopt different conformers associated with increasing levels of extension as a function of the charge state. The transition from one conformer to another is reversible so that the electrostatic balance between the cyclophanes may be used to further tune the structural state adopted by this switch in the gas phase. [less ▲]

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