Yury Kostyukevich

Fourier transform ion cyclotron resonance (FT ICR) mass spectrometry: Theory and simulations

Fourier transform ion cyclotron resonance (FT ICR) mass spectrometer offers highest resolving power and mass accuracy among all types of mass spectrometers. Its unique analytical characteristics made FT ICR important tool for proteomics, metabolomics, petroleomics, and investigation of complex mixtures. Signal acquisition in FT ICR MS takes long time (up to minutes). During this time ion-ion interaction considerably affects ion motion and result in decreasing of the resolving power. Understanding of those effects required complicated theory and supercomputer simulations but culminated in the invention of the ion trap with dynamic harmonization which demonstrated the highest resolving power ever achieved. In this review we summarize latest achievements in theory and simulation of FT ICR mass spectrometers.

Simple atmospheric hydrogen/deuterium exchange method for enumeration of labile hydrogens by electrospray ionization mass spectrometry.

A simple method for hydrogen/deuterium exchange in a standard electrospray (ESI) ionization source is presented. In this method, a D₂O droplet is placed between the ESI needle and the entrance of the mass spectrometer and thus saturation of the atmosphere with deuterated vapor in the ESI region is achieved. It was shown that full exchange of up to 23 labile acidic hydrogens with a minimal back exchange with the surrounding atmospheric water can be performed by this method.

Conformational changes of ubiquitin during electrospray ionization as determined by in-ESI source H/D exchange combined with high- resolution MS and ECD fragmentation

In the paper, we have demonstrated the possibility of performing hydrogen/deuterium (H/D) exchange of proteins in the region of gas-phase ion formation in an electrospray ion source by saturating the electrospray ionization source with vapors of a deuterating agent (D(2)O or MeOD). In this region, charged droplets are shrinking and the protein ions transfer into the gas phase. As a model protein, we have used ubiquitin whose ion mobility spectrometry and gas-phase H/D exchange in the vacuum part of a mass spectrometer demonstrated the presence of gas-phase conformers with different cross sections and H/D exchange rates. In our experiments, we observed monomodal deuterium distributions for all solvents, charge states, desolvating capillary temperature and types of deuterating agent. Also, we found that the number of H/D exchanges increases with an increasing desolvating capillary temperature and decreasing charge state. We observed that solution composition (49 : 50 : 1 H(2)O : MeOH : formic acid or 99 : 1 H(2)O : formic acid) influences the charge-state distribution but did not change the degree of H/D exchange for the same charge state. Electron-capture dissociation fragmentation shows that higher charge states contain a segment that is protected from access by the deuterating agent.

Molecular Mapping of Sorbent Selectivities with Respect to Isolation of Arctic Dissolved Organic Matter as Measured by Fourier Transform Mass Spectrometry

The objectives of this study were to identify molecular features characteristic to arctic DOM from the Kolyma River basin and to elucidate structural imprints induced by a choice of the sorption technique. To achieve this goal, DOM was isolated from the Kolyma River basin with a use of three nonionic sorbents: Amberlite XAD-8 resin, PPL- and C18 - SPE cartridges, and one anion exchanging resin-diethylaminoethyl (DEAE) -cellulose. The structural studies were conducted with a use of electrospray ionization Fourier Transform Ion Cyclotron Resonance (ESI FT-ICR) mass spectrometry and liquid state (1)H NMR spectroscopy. The DOM isolates obtained with a use of PPL and C18 cartridges were characterized with higher content of aliphatic compounds as compared to XAD-8 and DEAE-isolates. In total, for all arctic DOM isolates we observed predominance of hydrogen saturated compounds with high H/C values of identified formulas from FT-ICR MS data. (1)H NMR spectroscopy studies have confirmed this trend and revealed high contribution of alkyl-chain protons into the spectral density of the arctic DOM reaching 43% for PPL isolates.

Enumeration of Labile Hydrogens in Natural Organic Matter by Use of Hydrogen/Deuterium Exchange Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A method to enumerate labile hydrogens in all constituents of molecular ensemble of natural organic matter (NOM) based on our previously developed simple hydrogen/deuterium (H/D) exchange (electrospray ionization (ESI) ion source (Kostyukevich et al. Anal. Chem. 2013, 85, 5330) and ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry is presented. The method was applied for analysis of Suwannee River fulvic acid (SRFA), which is an International Humic Substances Society standard, as well as Siberian crude oil; and lignosulfonate. We found that SRFA and lignosulfonate molecules contain 2-5 labile hydrogens, and their number increases with the number of oxygens in the molecule. Also, we observed that compounds of Siberian crude oil ionizing in positive-ESI mode do not have labile hydrogens, while compounds ionizing in negative-ESI mode have one labile hydrogen that detaches during ESI ionization.

In-ESI source hydrogen/deuterium exchange of carbohydrate ions.

We present the investigation of hydrogen/deuterium (H/D) exchange of carbohydrates ions occurring in the electrospray ion source. The shape of the deuterium distribution was observed to be considerably dependent on the temperature of the ion transfer tube and the solvent used. If deuterated alcohol (EtOD or MeOD) or D2O/deuterated alcohol is used as an electrospray solvent, then for high temperatures (>350 °C), intensive back exchange is observed, resulting in ∼30% depth of the deuterium exchange. At low temperatures (<150 °C), the back exchange is weaker and the depth of the deuterium exchange is ∼70%. In the intermediate temperature region (∼250 °C), the deuterium distribution is unusually wide for methanol and bimodal for ethanol. The addition of 1% formic acid results in low (∼30%) depth of the deuterium exchange for any temperature in the operating region. The bimodal distribution for the ethanol can be possibly explained by the presence of differently folded gas-phase ions of carbohydrates.

In ESI-source H/D exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66 kDa: the role of the temperature of the desolvating capillary on H/D exchange

Transition of proteins from the solution to the gas phase during electrospray ionization remains a challenging problem despite the large amount of attention it has received during the past few decades. One of the major questions relates to the extent to which proteins in the gas phase retain their condensed phase structures. We have used in-electrospray source hydrogen/deuterium exchange to determine the number of deuterium incorporations as a function of protein mass, charge state and temperature of the desolvating capillary where the reaction occurs. All experiments were performed on a Thermo LTQ FT Ultra equipped with a 7-T superconducting magnet. Ions were generated by an IonMax Electrospray ion source operated in the positive ESI mode. Deuterium exchange was performed by introducing a droplet of D2 O beneath the ESI capillary. We systematically investigated gas phase hydrogen/deuterium (H/D) exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66 kDa. We observed that almost all proteins demonstrate similar exchange rates for all charge states and that these rates increase exponentially with the temperature of the desolvating capillary. We did not observe any clear correlation of the number of H/D exchanges with the value of the cross section for a corresponding charge state. We have demonstrated the possibility of performing in-ESI source H/D exchange of large proteins under atmospheric pressure. The simplicity of the experimental setup makes it a useful experimental technique that can be applied for the investigation of gas phase conformations of proteins.

Letter: Analytical potential of the in-electrospray ionization source hydrogen/deuterium exchange for the investigation of oligonucleotides

It has previously been reported that different conformations of oligonucleotides may be detected using a gas-phase hydrogen/deuterium (H/D) exchange performed in the collision cell of a mass spectrometer. The presence of different conformers was postulated based on the bimodal shape of the deuterium distribution and on the ion mobility spectrometry data. Here we implement an in-electrospray ionization source H/D exchange to detect the different conformations of oligonucleotides in the region of ion formation. We observed that the number of H/D exchanges depends considerably on the temperature of the desolvating capillary and varies from 25% at 50°C to 80% at 450°C, but no bimodality in the shape of the deuterium distribution was observed. Such results indicate that in the region of ion formation different conformations of oligonucleotide ions rapidly interconvert one into another.

Conformations of cationized linear oligosaccharides revealed by FTMS combined with in-ESI H/D exchange

Previously (Kostyukevich et al. Anal Chem 2014, 86, 2595), we have reported that oligosaccharides anions are produced in the electrospray in two different conformations, which differ by the rate of gas phase hydrogen/deuterium (H/D) exchange reaction. In the present paper, we apply the in-electrospray ionization (ESI) source H/D exchange approach for the investigation of the oligosaccharides cations formed by attaching of metal ions (Na, K) to the molecule. It was observed that the formation of different conformers can be manipulated by varying the temperature of the desolvating capillary of the ESI interphase. Separation of the conformers was performed using gas phase H/D approach. Because the conformers have different rates of the H/D exchange reaction, the deuterium distribution spectrum becomes bimodal. It was found that the conformation corresponding to the slow H/D exchange rate dominates in the spectrum when the capillary temperature is low (~200 °C), and the conformation corresponding to the fast H/D exchange rate dominates at high (~400 °C) temperatures. In the intermediate temperature region, two conformers are present simultaneously. It was also observed that large oligosaccharide requires higher temperature for the formation of another conformer. It was found that the presence of the conformers considerably depends on the solvent used for ESI and the pH. We have compared these results with the previously performed in-ESI source H/D exchange experiments with peptides and proteins.

Letter: Observation of the 16O/18O exchange during electrospray ionization.

Isotopic exchange approach coupled to high-resolution mass spectrometry has become the power analytical approach for a wide range of analytical and bioanalytical applications. Considerable efforts have been dedicated to developing fast exchange techniques directly in the ionization source. But all such methods are limited to the hydrogen/deuterium exchange approaches. In this paper we demonstrate that certain types of oxygen atoms can also be exchanged for 18O on the time scale of the ionization process. Using HIO3 and NaIO4 and by infusing the heavy water H218O in the ESI source we have demonstrated that it is possible to obtain a high level of oxygen exchange. It was observed that the rate of this exchange depends to a large extent on the temperature of the desolvating capillary of the mass spectrometer. Several other species, such as peptides, oligonucleotides and low weight organic molecules, were subjected to in-ESI 16O/18O exchange but the exchange was not observed.