Electrospray Ionization Mass Spectrometry In Combination Research Articles

Formation and fragmentation of 2-hydroxyethylhydrazinium nitrate (HEHN) cluster ions: a combined electrospray ionization mass spectrometry, molecular dynamics and reaction potential surface study.

The 2-hydroxyethylhydrazinium nitrate ([HOCH2CH2NH2NH2]+NO3-, HEHN) ionic liquid has the potential to power both electric and chemical thrusters and provide a wider range of specific impulse needs. To characterize its capabilities as an electrospray propellant, we report the formation of HEHN cluster ions in positive electrospray ionization (ESI) and their collision-induced dissociation. The experiment was carried out using ESI guided-ion beam mass spectrometry which mimics an electrospray thruster in terms of ion emission, injection into a vacuum and fragmentation in space. Measurements include compositions of primary ions in the electrospray plume and their individual dissociation product ion cross sections and threshold energies. The results were interpreted in light of theoretical modeling. To determine cluster structures that are comprised of [HE + H]+ and NO3- constituents, classical mechanics simulations were used to create initial guesses; and for clusters that are formed by reactions between ionic constituents, quasi-classical direct dynamics trajectory simulations were used to mimic covalent bond formation and structures. All candidate structures were subject to density functional theory optimization, from which global minimum structures were identified and used for construction of reaction potential energy surface. The comparison between experimental values and calculated dissociation thermodynamics was used to verify the structures for the emitted species [(HEHN)nHE + H]+, [(HEHN)n(HE)2 + H]+, [(HE)n+1 + H]+ and [(HE)nC2H4OH]+ (n = 0-2), of which [(HE)1-2 + H]+ dominates. Due to the protic nature of HEHN, cluster fragmentation can be rationalized by proton transfer-mediated elimination of HNO3, HE and HE·HNO3, and the latter two become dominant in larger clusters. [(HE)2 + H]+ and [(HE)nC2H4OH]+ contain H-bonded water and consequently are featured by water elimination in fragmentation. These findings help to evaluate ion formation and fragmentation efficiencies and their impacts on electrospray propulsion.

Synthesis, Characterization, and Low-Toxicity Study of a Magnesium(II) Complex Containing an Isovanillate Group.

The beneficial effect of polyphenols and magnesium(II) against oxidative stress motivated our research group to explore the antioxidant activity of phenMgIso, an aqueous soluble magnesium(II) complex containing 1,10-phenanthroline (phen) and isovanillic acid (Iso) as ligands. Combined electrospray ionization–mass spectrometry and DOSY-NMR techniques identified two complexes in methanolic solution: hexacoordinated [Mg(phen)2(Iso)]+ and tetracoordinated [Mg(phen)(Iso)]+. The cyclic voltammogram of phenMgIso in the anodic region showed a cyclic process that interrupts the isovanillic acid degradation, probably by stabilization of the corresponding phenoxyl radical via complexation with Mg(II), which is interesting for antioxidant applications. phenMgIso competes with 2,2,6,6-tetramethylpiperidine by 1O2 with IC50(1O2) = 15 μg m–1 and with nitrotetrazolium blue chloride by superoxide ions (IC50(O2•–) = 3.6 μg mL–1). Exposure of both zebrafish (2 mg L–1) and wistar male rats (3 mg kg–1 day–1 dose for 21 days) to phenMgIso does not cause mortality or visual changes compared with the respective control groups, thus phenMgIso could be considered safe under the conditions of this study. Moreover, no significant changes in comparison to both control groups were observed in the biochemical parameters on the brain-acetylcholinesterase activity, digestive tract enzyme catalase, and glutathione-S-transferase. Conversely, the performance of superoxide dismutase activity in wistar male rats increased in the presence of a complex, resulting in enhanced capacity of rats for superoxide radical enzymatic scavenging. The synergistic action of phenMgIso may be explained by the strong electrostatic interaction between Mg(II) and the O,O(phenolate) group, which makes the Iso ligand easier to oxidize and deprotonate, generating a cyclic stable species under oxidative conditions.

Temperature-dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH-range

In this study the complexation of U(VI) with orthosilicic acid (H4SiO4) was investigated between pH 3.5 and 5 by combining electrospray ionization mass spectrometry (ESI-MS) and laser-induced luminescence spectroscopy. The ESI-MS experiments performed at a total silicon concentration of 5 · 10−3M (exceeding the solubility of amorphous silica at both pH-values) revealed the formation of oligomeric sodium-silicates in addition to the UO2OSi(OH)3+ species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5 · 10−6M, the silicon concentration was varied between 1.3 · 10−4–1.3 · 10−3M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO4. The results confirmed the formation of the aqueous UO2OSi(OH)3+ complex. The conditional complexation constant at 25 °C, log *β = −(0.31 ± 0.24), was extrapolated to infinite dilution using the Davies equation, which led to log *β0 = −(0.06 ± 0.24). Further experiments at different temperatures (1–25 °C) allowed the calculation of the molal enthalpy of reaction ΔrHm0 = 45.8 ± 22.5 kJ·mol−1 and molal entropy of reaction ΔrSm0 = 152.5 ± 78.8 J·K−1·mol−1 using the integrated van’t Hoff equation, corroborating an endothermic and entropy driven complexation process.

Exploration of the formation and structure characteristics of a miR-92a promoter G-quadruplex by ESI-MS and CD

Combining electrospray ionization mass spectrometry (ESI-MS) with circular dichroism (CD) spectroscopy, a G-rich sequence from miR-92a promoter region was discovered to form a parallel G-quadruplex structures in KCl or NH4OAc solution. In case of high concentration of NH4OAc, the ESI mass spectra showed peaks of a dimeric G-quadruplex structure with 4 ammonium ions. Meanwhile, palmatine, a natural alkaloid, was screened by ESI-MS to bind with the miR-92a G-quadruplex affinitively. The variable temperature experiment of CD also proved that high concentration of NH4OAc or palmatine could promote the stability of the dimeric G-quadruplex structure. To get the specific characteristics of the miR-92a G-quadruplex structure, systematic mutations of guanine were tested. Based on the number of NH4+ or ligands, the important guanines involved in the G-quadruplex could be determined. Considering the importance of involved guanines and the number of G-quartets, we speculated an interlocked dimeric parallel G-quadruplex as a possible conformation of the miR-92a promoter G-quadruplex. All results obtained from ESI-MS and CD illustrate structure characteristics of the miR-92a G-quadruplex, which is a promising method for preliminary structural analysis of G-quadruplexes. Besides, this study also provides a strategy for regulating the functions of microRNA by exploring and targeting higher-order structures of miRNAs.

Fragmentation pathways of dianionic [Pt2(μ-P2O5H2)4 + X,Y]2− (X,Y = H, K, Ag) species in an ion trap induced by collisions and UV photoexcitation

We report on the first gas phase study of dianionic species [Pt2(μ-P2O5H2)4+X,Y]2− (X,Y=H, K, Ag) derived by counterion attachment to the dimetallic [Pt2(μ-P2O5H2)4]4− complex (abbrev. Ptpop). The combined electrospray ionization mass spectrometry and laser spectroscopy investigation provides intrinsic properties and fragmentation pathways without solvent interaction in comparison to calculations by density functional theory (DFT) methods. Drastic differences between collision induced (loss of water) and UV photo-induced fragmentation (electron photodetachment or loss of Ag0) in a quadrupole ion trap are observed. The underlying fragmentation pathways are explored in detail by MSn. Upon UV photoexcitation [Ptpop+H,Ag]2− and [Ptpop+2Ag]2− exhibit dissociation of Ag0 indicating an intramolecular electron transfer, whereas mainly electron photodetachment is observed for [Ptpop+2H]2− and [Ptpop+H,K]2−. Channel specific photo-induced dissociation spectra in the range of 250–400nm reveal the main band at ∼370nm in remarkable resemblance to aqueous absorption spectra. Additional absorption features, distinct broadening and spectroscopic shifts depending on counterions and fragment channels are also observed. For the ground state structures a side-on coordination of metal counterions to the [Pt2(μ-P2O5H2)4]4− framework is deduced based on fragmentation pathways, results of geometry optimizations and calculated absorption spectra.

Breaking the Cycle: Impact of Sterically-Tailored Tetra(pyrazolyl)lutidines on the Self-Assembly of Silver(I) Complexes

A improved preparation of the pentadentate ligand alpha,alpha,alpha',alpha'-tetra(pyrazolyl)lutidine, pz(4)lut, and the syntheses of three new alkyl-substituted pyrazolyl derivatives pz(4')(4)lut (pz(4') = 4-methylpyrazolyl), pz*(4)lut (pz* = 3,5-dimethylpyrazolyl), and pz(DIP)(4)lut (pz(DIP) = 3,5-diisopropylpyrazolyl) are described. The silver(I) complexes of these ligands were studied to ascertain the impact of pyrazolyl substitution, if any, on their binding modes and on solubility issues. In the solid state, [Ag(pz(4)lut)](BF(4)) (1), [Ag(pz(4')(4)lut)](BF(4)) (2), and [Ag(pz*(4)lut)](BF(4)) (3) give cyclic dications as a result of two ligands sandwiching two silver centers where each ligand binds the metals through only pyrazolyl nitrogen donors. This cyclic motif is similar to those observed in the silver complexes of tetra(pyridyl)lutidine PY5-R derivatives (where the central pyridyl does not bind) and in related tetra(pyrazolyl)-m-xylene complexes. While suitable single crystals of [Ag(pz(DIP)(4)lut)](BF(4)) (4) could not be obtained, those of [Ag(pz(DIP)(4)lut)](OTf) (5) showed infinite polymeric chains secured via silver-bound mu-kappa(2)N(pz),kappa(2)N(pz)- ligands. The different binding mode of the latter ligand versus the former three is likely due to unfavorable steric interactions between the bulky iso-propyl (pyrazolyl) substituents and the central pyridyl rings of hypothetical cyclic architectures. The combined electrospray ionization mass spectrometry (ESI(+)-MS), variable-temperature NMR (VT NMR), and diffusion pulsed field-gradient spin-echo (PFGSE) NMR data indicate that the solid state structures of each 1-5 are neither retained nor static in CD(3)CN, rather the cations are monomeric in solution.

Determination of the degradation products of selected sulfonated phenylazonaphthol dyes treated by white rot fungus Pleurotus ostreatus by capillary electrophoresis coupled with electrospray ionization ion trap mass spectrometry

The removal of water-soluble sulphonated phenylazonaphthol dye effluents generated by textile industries is an important issue in wastewater treatment. Microbial treatment of environmental pollutants including dyes, with white rot fungi has received wide attention as a potential alternative for conventional methods in wastewater treatment. Three sulphonated phenylazonaphthol dyes with similar molecular structures Acid Orange 7, Acid Orange 8 and Mordant Violet 5 were selected and degraded by the white rot fungus Pleurotus ostreatus. Chemical instrumental analysis methods such as high-performance liquid chromatography (HPLC) and capillary electrophoresis combined with electrospray ionization mass spectrometry (CE-ESI-MS) were used to identify the degraded dyes. Mordant Violet 5 had two degradation pathways when degraded by P. ostreatus. The first degradation pathway for Mordant Violet 5 was for trans structure and the cis-Mordant Violet 5 followed the second pathway. Acid Orange 8 and Acid Orange 7 had the same degradation mechanism as the first degradation mechanism for Mordant Violet 5, that is cleavage of azo bond at the naphthalene ring side where benzenesulfonic acid and 1,2-naphthoquinone are formed.

Ligand Binding Mode to Duplex and Triplex DNA Assessed by Combining Electrospray Tandem Mass Spectrometry and Molecular Modeling

In this paper, we report the analysis of seven benzopyridoindole and benzopyridoquinoxaline drugs binding to different duplex DNA and triple helical DNA, using an approach combining electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and molecular modeling. The ligands were ranked according to the collision energy (CE(50)) necessary to dissociate 50% of the complex with the duplex or the triplex in tandem MS. To determine the probable ligand binding site and binding mode, molecular modeling was used to calculate relative ligand binding energies in different binding sites and binding modes. For duplex DNA binding, the ligand-DNA interaction energies are roughly correlated with the experimental CE(50), with the two benzopyridoindole ligands more tightly bound than the benzopyridoquinoxaline ligands. There is, however, no marked AT versus GC base preference in binding, as supported both by the ESI-MS and the calculated ligand binding energies. Product ion spectra of the complexes with triplex DNA show only loss of neutral ligand for the benzopyridoquinoxalines, and loss of the third strand for the benzopyridoindoles, the ligand remaining on the duplex part. This indicates a higher binding energy of the benzopyridoindoles, and also shows that the ligands interact with the triplex via the duplex. The ranking of the ligand interaction energies compared with the CE(50) values obtained by MS/MS on the complexes with the triplex clearly indicates that the ligands intercalate via the minor groove of the Watson-Crick duplex. Regarding triplex versus duplex selectivity, our experiments have demonstrated that the most selective drugs for triplex share the same heteroaromatic core.

Stabilization and Structure of Telomeric and c-myc Region Intramolecular G-Quadruplexes: The Role of Central Cations and Small Planar Ligands

A promising approach for anticancer strategies is the stabilization of telomeric DNA into a G-quadruplex structure. To explore the intrinsic stabilization of folded G-quadruplexes, we combined electrospray ionization mass spectrometry, ion mobility spectrometry, and molecular modeling studies to study different DNA sequences known to form quadruplexes. Two telomeric DNA sequences of different lengths and two DNA sequences derived from the NHE III1 region of the c-myc oncogene (Pu22 and Pu27) were studied. NH4+ and the ligands PIPER, TMPyP4, and the three quinacridines MMQ1, MMQ3, and BOQ1 were complexed with the DNA sequences to determine their effect on the stability of the G-quadruplexes. Our results demonstrate that G-quadruplex intramolecular folds are stabilized by NH4+ cations and the ligands listed. Furthermore, the ligands can be classified according to their ability to stabilize the quadruplexes and end stacking is shown to be the dominant mode for ligand attachment. In all cases our solvent-free experimental observations and theoretical modeling reveal structures that are highly relevant to the solution-phase structures.

Electrospray ionization mass spectrometry: a key analytical tool for the characterization of regioselectively derivatized maltooligosaccharides obtained starting from natural β‐cyclodextrin

The development of natural cyclodextrins (CDs) for various industrial applications (agroalimentary, cosmetic or pharmaceutical) constitutes a continuous challenge. For the integration of these agricultural plant products in the creation of super-absorbent biodegradable and hypoallergenic materials (water-retaining agents, cosmetic hydrating and texturing, pharmaceutical and horticultural products) to replace synthetic polymers, we have developed chemical methods to access regioselectively C-6-derivatized maltooligosaccharides starting from CDs. These compounds are highly suitable for further chemical modifications and are expected to give access to a new class of polymeric materials with potential applications such as water-retaining agents in the disposable nappies industry. For the structural analysis of carbohydrates, electrospray ionization mass spectrometry (ESI-MS) offers precise results, analytical versatility and very high sensitivity. We report herein the rapid and convenient follow-up of chemical reactions, the purity evaluation of intermediates and final products, and the structural characterization of derivatized maltooligosaccharides, obtained by acidic cleavage (acetolysis) of halogenated and esterified CDs, using ESI-MS in combination with the high-resolution (HRMS) and tandem mass spectrometry (MS/MS) capabilities of a quadrupole orthogonal time-of-flight (Q-TOF) mass spectrometer.

Gas-Phase Reactivity of Lead(II) Ions with d-Glucose. Combined Electrospray Ionization Mass Spectrometry and Theoretical Study

The gas-phase reactivity of lead(II) ions toward d-glucose has been studied by means of mass spectrometry and theoretical calculations. Electrospray mass spectra show that this reactivity mainly gives rise to [Pb(d-glucose)m − H]+ species (m = 1, 2). These ions are obtained by dissociative proton transfer within the doubly charged complexes, [Pb(d-glucose)n]2+ complexes (n = 2−12), observed in significant abundance at low cone voltage. Low-energy MS/MS experiments on [Pb(d-glucose) − H]+ (m/z 387) show that this ion essentially dissociates according to cross-ring cleavages leading mainly to the elimination of C2H4O2 and C4H8O4 neutrals and to a minor extent in the loss of C3H6O3. Use of labeled d-glucose demonstrates that the former implies specifically the elimination of C(1) and C(2) stereocenters, whereas the latter corresponds to at least two distinct fragmentations. This finding clearly suggests that several [Pb(d-glucose) − H]+ structures, characterized by different coordination schemes, coexist in the gas phase. This is confirmed by the density functional theory study carried out on both anomers, because the various coordination sites on the pyranose are close in energy. The most favorable Pb2+/d-glucopyranose association is characterized by the metallic center bonded to the deprotonated hydroxymethyl group and interacting with the hemiacetal oxygen. In such a position, the Pb2+ ion catalyzes the ring-opening process by activation of the two C−O ring bonds. This not only accounts for the fragmentation observed upon collision but also suggests that, besides fragmentation, pyranosic complexes may evolve toward energetically favored acyclic structures.

Zinc-induced conformational changes in the DNA-binding domain of the vitamin D receptor determined by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to measure conformational changes within the DNA-binding domain of the vitamin D receptor (VDR DBD) upon binding zinc (Zn2+). As increasing concentrations of Zn2+ were added to the VDR DBD, a gradual shift in the mass envelope to lower charge states was observed in the multiply charged spectrum. The shift in the charge states was correlated to changes observed in the far-ultraviolet circular dichroic (far-UV CD) spectrum of the protein as it was titrated with Zn2+. Both the multiply charged ESI and far-UV CD spectra of the Zn(2+)-titrated protein show that the binding of the first Zn2+ ion to the protein results in very little conformational change in the protein. The binding of a second Zn2+ ion resulted in a significant alteration in the structure of the protein as indicated by changes in both the multiply charged ESI and far-UV CD spectra. Much smaller changes were seen within the multiply charged ESI or far-UV CD spectra upon increasing the Zn2+ concentration beyond 2 mol/mol of protein. The results presented indicate that ESI-MS in combination with CD is a powerful method to measure gross conformational changes induced by the binding of metals to metalloproteins.