Sodium Adducts Research Articles

Differences in the Formation and Fragmentation of Sodium Adduct Ions between Tertiarybutoxycarbonyl-Protected Prolylproline Diastereomers in Fast Atom Bombardment Mass Spectrometry.

The effect of Na+ ions on the fragmentation of tertiarybutoxycarbonyl (Boc) protected prolylproline (Pro-Pro) diastereomers, Boc-Pro-Pro and Boc-D-Pro-Pro, was studied in positive-ion fast atom bombardment (FAB) and tandem mass spectrometry. The formaiton of the [M+Na]+ ion for Boc-D-Pro-Pro was more predominant than that for Boc-Pro-Pro on the addition of sodium chloride in positive-ion FAB mass spectrometry, suggesting that Boc-D-Pro-Pro has a stronger Na+ ion affinity than Boc-Pro-Pro. In the collisional-activated decomposition mass spectra of the [M+Na]+ ions, the abundance of the [M+Na-C(CH3)3+H]+ ion, which is due to the loss of a tertiarybutyl group from the [M+Na]+ ion for Boc-D-Pro-Pro, was higher than that for Bos-Pro-Pro. These results indicate that the interaction of the Na+ ion with Boc-Pro-Pro is different from that with Boc-D-Pro-Pro in the FAB condition, and these diastereomers are distinguished by the addition of a Na+ ion in FAB and tandem mass spectrometry.

Novel Sodium Binding Properties of Some Cyclopentapeptide Endothelin A Selective Receptor Antagonists: Electrospray and Fast-Atom-Bombardment Mass Spectrometric Studies

Electrospray ionization and fast atom bombardment mass spectrometric methods reveal novel interactions of endothelin A selective receptor antagonists, cyclo(D-Trp-D-Asp-Pro-D-Val-Leu), cyclo(D-Trp-D-Glu-Ala-D-allo-Ile-Leu) and cyclo(D-Trp-D-Asp-Pro-D-Ile-Leu) with sodium ions. The peptides have very high intrinsic affinities for sodium ions, and form multiple sodium adducts and sandwich structures: [M + Na]+, [M + 2Na − H]+, [M + 3Na − 2H]+, [M + 4Na − 3H]+, [M + 5Na − 4H]+, [2M + Na]+, [2M + 2Na − H]+, [2M + 3Na − 2H]+, [2M + 4Na − 3H]+, [2M + 5Na − 4H]+, [2M + 6Na − 5H]+, and [2M + 7Na − 6H]+. The three cyclic peptides exhibit similar sodium binding stoichiometries despite differences in their amino acids. The observed sodium binding properties may have implications in understanding their protective effects against ischemia-induced acute renal failure. Those cyclic peptides that offer protection may be those that have high affinities for multiple sodium ions.

Alkali Metal Salts of Dianions: A Theoretical and Experimental Study of (C6H4)2-M+ (M = Li and Na)

Ab initio molecular orbital calculations have been carried out on the lithium and sodium salts of doubly deprotonated benzene. Full geometry optimizations of the three isomeric bare dianions and their corresponding lithium and sodium adducts were performed at the HF/6-31+G(d) and MP2/6-311+G(d,p) levels. The resulting structures are discussed. Deprotonation energies for phenyllithium and phenylsodium are reported. Phenyllithium is more acidic than benzene, while phenylsodium is only 3 kcal/mol less acidic. Alkali metal bridging and the formation of ion triplets can be extremely stabilizing and can lead to enhanced second deprotonations. Electrospray ionization mass spectrometry of terephthalic acid (p-C6H4(CO2H)2) followed by collision-induced dissociation of the resulting alkali metal salts of the dicarboxylate (I) affords C6H42-Li+ and C6H42-Na+. Formation of these species corroborates the theoretical prediction that alkali metal salts of dianions should be stable in the gas phase.

On-line cation exchange for suppression of adduct formation in negative-ion electrospray mass spectrometry of nucleic acids.

One major difficulty in the analysis of nucleic acids by electrospray mass spectrometry is represented by the affinity of the polyanionic sugar-phosphate backbone for nonvolatile cations, especially ubiquitous sodium and potassium ions. A simple on-line sample preparation system comprising a microflow pumping system and 45 x 0.8-mm-i.d. microcolumns packed with weak or strong cation-exchange resins is described for the efficient removal of cations from nucleic acid samples. Samples were analyzed by flow injection analysis at a 3-5 microL/min flow of 10 mM triethylamine in 50% water-50% acetonitrile. After on-line desalting, mass spectra of oligonucleotides revealed no significant sodium adduct peaks. Moreover, signal-to-noise ratios were greatly enhanced compared to direct injection of the samples. Electrospray mass spectrometry with on-line sample preparation allowed accurate molecular mass determinations of picomole amounts of crude oligonucleotide preparations ranging in size from 8 to 80 nucleotides within a few minutes. The good linearity of the calibration plot (R2 = 0.9988) over at least 2 orders of magnitude and a relative standard deviation in peak areas of less than 9% permitted the sensitive quantitative measurement of oligonucleotides in a concentration range of 0.2-20 microM with selected-ion monitoring. Finally, the on-line sample preparation system was evaluated for the mass spectrometric analysis of complex oligonucleotide mixtures.

Application of gas and liquid chromatography–mass spectrometry to the evaluation of pirimiphos methyl degradation products in industrial water under ozone treatment

The organophosphorus compound pirimiphos methyl was oxidized in water under ozonolysis in the presence of formulating agents. A rapid sample handling procedure was developed based on liquid–solid extraction with nonporous carbon cartridges. This sorbent material allowed recovery of the polar degradation products (DPs). Analysis of oxidized solutions was performed with both GC–ion trap (IT)-MS using either electron impact or chemical ionization as ionization modes and LC–atmospheric pressure ionization (API)-MS using either an ionspray (ISP) or an atmospheric pressure chemical ionization (APCI) interface in order to confirm the presence of DPs. The performances of both technologies were evaluated for structure elucidation and quantitation by using pirimiphos methyl, 2,4-aminophenol and cyanuric acid as external standards of DPs. LC–API-MS techniques allowed the detection of six DPs, of which two were not detected by GC–IT-MS techniques, even after a derivatization procedure with BF 3–MeOH reagent. ISP was the most suitable ionization method for identifying the DPs, because sodium or potassium adduct ions were of great help in confirming the molecular mass of unknowns. APCI provided more fragmentation patterns than ISP. However unequivocal identification of all DPs was impossible and only a tentative degradation pathway of pirimiphos methyl in water under ozone is proposed. At the end of the reaction time, DPs accounted for between 70 and 85% of the initial concentration of methyl pirimiphos.

Influences of pH andIn-source collisional energy on the cationization of insulin

The influence of pH and in-source collisional energy variations on interactions between a model protein and sodium or cesium ions has been studied by electrospray ionization mass spectrometry. Behavioural differences regarding cationization have been observed and seem to be linked to the neutral of deprotonated form of carboxylic acids. At pH 8, cesium and sodium adducts totally disappear in the case of highest charge states. Increasing the cone voltage leads to an overall change loss that can be attributed to the loss of cesium, sodium ions and even protons.

Influences of pH and In‐source collisional energy on the cationization of insulin

The influence of pH and in-source collisional energy variations on interactions between a model protein and sodium or cesium ions has been studied by electrospray ionization mass spectrometry. Behavioural differences regarding cationization have been observed and seem to be linked to the neutral or deprotonated form of carboxylic acids. At pH 8, cesium and sodium adducts totally disappear in the case of highest charge states. Increasing the cone voltage leads to an overall charge loss that can be attributed to the loss of cesium, sodium ions and even protons. © 1998 John Wiley & Sons, Ltd.

Pitfalls for the Frozen-Core Approximation: Gaussian-2 Calculations on the Sodium Cation Affinities of Diatomic Fluorides

The Gaussian-2 (G2) total energies for species having the formula Na(FX)+ [X = H, Li → F, or Na → Cl], calculated using conventional and widely used ab initio computational program suites, show serious deficiencies which are attributable to two different effects. Firstly, for the sodium-ion adducts of almost all of the covalent fluoridesnamely HF, BF, CF, NF, OF, F2, SF, and ClFthe orbital corresponding most closely to the fluorine 2s orbital possesses a more negative eigenvalue than the set of three orbitals corresponding most closely to the sodium 2px, 2py, and 2pz orbitals, so that routine selection of the “frozen-core” option (in the single-point calculations involved in determining the G2 total energy) leads to an inappropriate correlation space. Secondly, for the sodium-ion adducts of several fluoridesmost notably, but not solely, the ionic fluorides LiF, NaF, MgF, and AlFthere is very significant mixing of the fluorine 2s and sodium 2pz orbitals, with the result that the G2 frozen-core calculations...

Electrospray Mass Spectrometric Detection of Neutral Metal Bipyridine Complexes Using Sodium Ions and Its Application in the Analysis of a Photochemical Ligand Substitution Reaction

Sodium ions can be used as efficient chemical ionization agents in electrospray mass spectrometry of a wide variety of neutral metal bipyridine complexes. This ionization method was successfully permitted the identification of a neutral metal complex generated during the photochemical ligand substitution reaction: [Re(bpy)(CO)3P(OEt)3]++Cl– ® Re(bpy)(CO)2P(OEt)3Cl+CO by sodium adduct formation to produce an electrospray-active species [Re(bpy)(CO)2P(OEt)3Cl+Na]+.

Quantitative analysis of antibiotics by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Comparative studies of the matrix-assisted laser desorption/ionization (MALDI) of 30 antibiotics were made using alpha-cyano-4-hydroxycinnamic acid (HCCA), 2,5-dihydroxybenzoic acid (DHB), 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin and meso-tetra(N-methyl-4-pyridyl)porphyrin matrices. Most antibiotics generated intense protonated molecules in HCCA and DHB matrices, and sodium or potassium adduct ions in porphyrin matrices. Using sulfonamide antibiotics as model compounds, DHB was found to be the most suitable matrix for quantitative analysis. Detection limits were about 1 picomole. Linear correlation (R2 > 0.97), between the sample quantity over the range 1 to 100 picomole and the signal response, was obtained when ratios of the sum of peak areas of protonated molecules and sodium adduct ions, with reference to that of a structurally analogous internal standard (acetaminophen), were measured. The precision was found to be in the range of 4 to 32% relative standard deviation, dependent on the type and concentration of the analyte. A simple acylation derivatization process was developed to confirm the presence of suspected antibiotic residues. It is demonstrated that MALDI is a viable technique for the quantitative analysis of low molecular weight antibiotics.

Quantitative analysis of antibiotics by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Comparative studies of the matrix-assisted laser desorption/ionization (MALDI) of 30 antibiotics were made using alpha-cyano-4-hydroxycinnamic acid (HCCA), 2,5-dihydroxybenzoic acid (DHB), 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin and meso-tetra(N-methyl-4-pyridyl)porphyrin matrices. Most antibiotics generated intense protonated molecules in HCCA and DHB matrices, and sodium or potassium adduct ions in porphyrin matrices. Using sulfonamide antibiotics as model compounds, DHB was found to be the most suitable matrix for quantitative analysis. Detection limits were about 1 picomole. Linear correlation (R2 > 0.97), between the sample quantity over the range 1 to 100 picomole and the signal response, was obtained when ratios of the sum of peak areas of protonated molecules and sodium adduct ions, with reference to that of a structurally analogous internal standard (acetaminophen), were measured. The precision was found to be in the range of 4 to 32% relative standard deviation, dependent on the type and concentration of the analyte. A simple acylation derivatization process was developed to confirm the presence of suspected antibiotic residues. It is demonstrated that MALDI is a viable technique for the quantitative analysis of low molecular weight antibiotics.

Dual parallel mass spectrometers for analysis of sphingolipid, glycerophospholipid and plasmalogen molecular species.

Analysis of phospholipids was performed using a liquid chromatographic separation with two mass spectrometers in parallel providing electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) data simultaneously from a triple quadrupole instrument and a single quadrupole instrument, respectively. The output from UV-Vis and evaporative light scattering detectors were also acquired by the two mass spectrometers, respectively, for four detectors overall. This arrangement was used to identify and calculate area percents for molecular species of dihydrosphingomyelin (DHS) and sphingomyelin (SPM) in commercially available bovine brain SPM, in human plasma extract and in porcine lens extract. Molecular species of phosphatidylethanolamine and its plasmalogen, and phosphatidylcholine and its plasmalogen were identified and semi-quantitative analysis performed. Commercially available bovine brain SPM was found to contain 11.5% DHS and 88.5% SPM. The only DHS molecular species identified in human plasma was 16:0-DHS, at or below 1% of the sphingolipid content. Porcine lens membranes were found to contain 14.4% DHS and 85.6% SPM. Other findings reported here include: (1) phospholipids were found to undergo dimerization in the electrospray source, giving masses representing combinations of species present. (2) Triacylglycerols gave usable mass spectra under electrospray ionization conditions, as well as under APCI-MS conditions. (3) Triacylglycerols gave ammonium adducts as base peaks in their APCI mass spectra, which reduced fragmentation and increased the proportions of molecular ions. (4) Mass spectra were obtained for phospholipids which underwent both protonation and sodium adduct formation in different chromatographic runs.

Electrospray ionization and collision-induced dissociation of antibiotic polyether ionophores.

A series of polyether ionophores (lasalocid, monensin-A, narasin-A and salinomycin) was investigated by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). A fast short-column liquid chromatographic (LC) method, using a ternary gradient sequence, was developed to separate the ionophores in less than 4 minutes. Several mobile phase parameters such as pH and solvent additives were investigated, and their impact on both chromatographic and mass spectrometric behavior was studied. The ionophores readily formed stable complexes with various metal cations present as impurities in the solvents. Therefore, a method was developed to convert the ionophores into only sodium adduct species prior to ESI analysis. This procedure maximized both sensitivity and specificity in the subsequent MS/MS step. Low energy collision-induced dissociation (CID) of the sodium adduct ions resulted in a number of structure-diagnostic product ions for all ionophores. The proposed interpretation of these fragment ions is presented in this work. Additionally, the fragmentation of a series of monovalent carboxylic alkali-metal ion complexes of lasalocid was investigated under CID conditions. A comparison of the CID spectra revealed a decreasing degree of fragmentation in the order [M + H]+ approximately [M + NH4]+ > [M + Li]+ > [M-H + 2Li]+ > [M + Na]+ >> [M + Cs]+. To demonstrate the analytical potential of the LC/MS/MS method, its application to the determination of salinomycin in catfood samples was investigated. Salinomycin was recovered from catfood by a microwave solvent extraction procedure, and subsequently analyzed using LC/MS/MS of the sodium adduct ions.

ChemInform Abstract: Structural Determination of Fatty Acyl Groups of Phospholipids by Fast Atom Bombardment Tandem Mass Spectrometry of Sodium Adduct Molecular Ions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Structural Systematics of 2/4-Nitrophenoxide Complexes of Closed-Shell Metal Ions. IV [Acid Salts] of the 4-Nitrophenoxides of Group 1

Room-temperature single-crystal X-ray studies are recorded for a number of ‘acid salts’ formed between Group 1 salts of 4-nitrophenol, M(4-np), and the parent ligand 4-npH, variously hydrated. The 1 : 1 salts M(4-np)(4-npH).x H2O are found for all of M = Li, Na, K, Rb and Cs. The lithium adduct (tetrahydrate) is monoclinic, C2/c, a 19·438(4), b 11·207(2), c 7·421(2) Å, β 91·38(2)°, Z = 4, conventional R on |F| being 0·043 for 1369 independent ‘observed’ (I > 3σ(I)) diffractometer reflections. The sodium adduct (dihydrate) is monoclinic, C2, a 2·174(3), b 3·674(2), c 10·358(1) Å, β 117·21(1)°, Z = 2, R 0·035 for No 1092; the potassium adduct (monohydrate) is monoclinic, C 2/c, a 22·10(1), b 3·798(3), c 21·270(6) Å, β 120·97(4)°, Z = 4, R 0·050 for No 1065. The isomorphous rubidium and caesium monohydrates are triclinic, P-1, a ≈ 11·9, b ≈ 10·2,c ≈ 6·3 Å, α ≈ 90, β ≈ 92, γ ≈ 112°, Z = 2, R 0·042, 0·028 for No 2340, 3053 respectively. For M = Rb, a 1 : 3 adduct Rb(4-np).3(4-npH) is also obtained (with an isomorphous thallium counterpart recorded elsewhere): a 12·143(5), b 11·50(1), c 11·36(1) Å, α 114·38(9), β 110·54(6), γ 96·73(6)°, Z = 2, R 0·034 for No 3945. The lithium salt may be represented as [Li(OH2)4]+ (4-npH.4-np)½-. The cation lies disposed about a crystallographic 2 axis; the anion, close to an axis, confronts its rotational image, with the associated hydrogen atom modelled as disordered between them, rather than located on the 2 axis. The sodium salt is a sheet structure, the six-coordinate sodium atoms being disposed on a crystallographic 2 axis and linked up that axis ... Na(µ-O)2Na(µ-O)2Na ... by bridging water molecule oxygen atoms, while symmetry-related trans O-nitrophenoxide moieties are bridged by confronting phenoxide oxygen atoms about an associated hydrogen atom provisionally disposed on a 2 axis also. The potassium salt structure is developed from this array, modelled with disordered potassium atoms, now lying off the 2 axis, 0·922(2) Å apart. In the rubidium/caesium structure, columns of oxygen-bridged metal ions are disposed about c, crosslinked by O-nitro-bonded phenoxide moieties, with confronting phenoxide oxygen atoms about a shared associated hydrogen.

Application of electrospray mass spectrometry to the characterisation of sulfonated and ferrocenyl phosphines

A range of ferrocenyl-containing and sulfonated triphenylphosphines have been investigated by electrospray mass spectrometry. In situ formation of hydroxymethyl phosphonium salt derivatives of the ferrocenyl phosphines and in situ formation of silver(I) adducts of both the ferrocenyl and sulfonated phosphines provided a means of characterising such compounds. Results are discussed in terms of fragmentation and aggregation of the parent molecular ion species. Sulfonated phosphines, including their sodium adducts, were easily characterised by their negative-ion spectra. Aminoalkyl-ferrocenyl phosphines form strong [M+H] + ions in their positive-ion spectra. Ferrocenyl phosphines without amino functions give weaker [M+H] + ions and may also be complicated by the existence of [M] + ions. Less complex positive-ion mass spectra of these ferrocenyl phosphines can be observed following treatment with either a solution of AgNO 3 or a mixture of formaldehyde and HCl.

MALDI mass spectrometry of biomolecules and synthetic polymers using alkali hexacyanoferrate (II) complexes and glycerol as matrix

K 4[Fe(CN) 6]/glycerol and Na 4[Fe(CN) 6]/glycerol have been investigated as liquid matrix systems for UV-MALDI MS applying a N 2 laser. Analyte molecules were detected as sodium or potassium adduct ions and, in the case of proteins, as well as protonated molecular ions. Mass accuracies were comparable to those found with standard solid matrix systems with −0.06 to +0.05% deviation in the reflectron mode and with −0.24 to +0.13% in the linear mode. Useful results could be obtained within a mass range of 15 000 Da for single-charged proteins and 8000 Da for potassium cationized polyethylene glycols. Detection limits were found for hydrophilic compounds in the low picomol range and for lipophilic compounds as triacylglycerols or peracetylated and partially benzylated carbohydrates in the low femtomol range. As shown by scanning electron microscopic investigations, the generation of a thin homogenous matrix layer was essential for a successful mass spectrometric experiment. A very careful cleaning of the target surface with glacial acid prior to matrix deposition improved the formation of such a matrix film that maximum sensitivity as well as good reproducibility of the experiments could be achieved.

Minimizing cationization effects in the analysis of complex mixtures of oligosaccharides.

We outline simple methodology for the rapid and selective analysis of 2-aminoacridone (2-AMAC) derivatised oligosaccharides by matrix-assisted laser desorption/ionization mass spectrometry. This involves the addition of small amounts of lithium chloride to the matrix before evaporation of solvent and crystallization. Signals mainly attributed to proton, sodium and potassium adducts are suppressed to a great extent, and a single signal due to (M + Li)+ is observed. This technique is rapid and is most useful for the direct analysis of complex glycan mixtures, after derivatization with 2-aminoacridone and without separation of the individual components.

Thermal stability of humic substances and their metal forms: an investigation using FTIR emission spectroscopy

The thermal decomposition of humic substances extracted from swamp water and their metal forms (Fe(III), Mn(II), Ca(II), Na(I)) in the temperature range of 50–600 °C was investigated using infrared emission spectroscopy, a technique which provides in situ information on the mechanism of thermal decomposition of the materials studied. From their IR spectrum, humic substances appear to be relatively stable up to about 300 °C. However all spectral information is lost by 600 °C. Decarboxylation is observed as the temperature is increased. Anhydrides are seen to form in the temperature range from 150 °C to 400 °C. There is also the loss of aliphatic hydrogen and the formation of aromatic hydrogen in the temperature range from 400 to 600 °C. Upon heating the metal forms of humic substances are less stable and decompose at a faster rate than humic substances, with a concomitant release of carbon monoxide. The thermal stability of the metal forms is in the order: Fe( III) < Mn( II) < Ca( II) < Na( I). The thermal stabilities of sodium and calcium ion adduct of humic substances tend to be related to the ionic radii with the divalent ion being less thermally stable than the monovalent ion. Stronger bonding of the transition metal adducts to humic substances gives metal forms of humic substances with lower thermal stability because of the effect of strain due to the formation of a metal chelate.

Gas-Phase DNA: Oligothymidine Ion Conformers

Gas-Phase DNA: Oligothymidine Ion Conformers