Determination of the anomeric configuration of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl phosphates by fast-atom bombardment tandem mass spectrometry

Collision-induced dissociation of the deprotonated molecules of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl (dolichyl and polyprenyl) phosphates results in distinct fragmentation patterns that depend on cis-trans configuration of the phosphodiester and 2″ (or 2′, respectively)-hydroxyl groups of the glycosyl residue. At the collision-offset voltage of 0. 5 V, sugar nucleotides with cis configuration produce only one very abundant fragment of nucleoside monophosphate, whereas compounds with trans configuration give weak signals for nucleoside di- and mono-phosphates and their dehydration products. These fragmentation patterns are largely preserved at higher collision energy, with the exception that, for sugar nucleotides with trans configuration, the characteristic signals are much more abundant and a novel diagnostic fragment of [ribosyl(deoxyribosyl)-5′-P₂O₅ — H]^? is generated. In the case of polyisoprenyl-P-sugars, polyisoprenyl phosphate ion is the only fragment observed for compounds with trans configuration, whereas in compounds with cis configuration, this ion is accompanied by another abundant fragment, which is derived from the cleavage across the sugar ring and corresponds to [polyisoprenyl-PO₄-(C₂H₃O)]^?. The relative intensity ratio of the latter ion to the [polyisoprenyl-HPO₄]^? ion is close to 1 for compounds with cis configuration, but it is only about 0. 01 for compounds with trans configuration. This ratio may serve, therefore, as a diagnostic value for determination of the anomeric configuration of glycosyl esters of polyisoprenyl phosphates. It is proposed that the observed differences in fragmentation patterns of cis-trans sugar nucleotides and polyisoprenyl-P-sugars could be explained in terms of kinetic stereoelectronic effect, and a speculative mechanism of fragmentation of compounds with trans configuration is presented. For compounds with cis configuration, formation of a hydrogen bond between the C-2″(2′) hydroxyl and the phosphate group could play a crucial role in directing the specific fragmentation reactions. Consequently, the described empirical rules would hold only for compounds that have a free 2″(2′)-hydroxyl group and no alternative charge location. Owing to its simplicity, sensitivity, and tolerance of impurities, fast-atom bombardment-tandem mass spectrometry represents a suitable method for determination of the anomeric linkage of glycosyl esters of nucleoside pyrophosphates and polyisoprenyl phosphates if the absolute configuration of glycosyl residue is known and the compound fulfills the above-mentioned requirements.     

Pseudochalkogen-Verbindungen. XVI. IR-spektroskopische Untersuchungen an Cyanamidomonophosphaten, [PO4−n (NCN)n]3−

Pseudochalkogen Compounds. XVI. Infrared-spectroscopic Investigations of Cyanamidomonophosphates, [PO_4?n(NCN)_n]^3? Infrared spectroscopic investigations of trisodium cyanamidomonophosphates of the general type Na₃[PO_4?n(NCN)_n] · aq (n: 1, 2, 3) are reported. The vibrational spectra of the compounds are confirming very clearly the special position of cyanamidophosphates within the group of substituted phosphates: Cyanamidophosphates are characterized by a full participation of pseudochalkogen groups representing NCN substituents into the mesomeric system of the anions and an only slight shortening of the P? O distances in comparision to [PO₄]^3?. Characteristic frequencies between 970 and 1150 cm^?1 are attributed to v(PO_4?nN_n)-stretching frequencies. A partial ¹⁵N labelling of the monocyanamidophosphate anion, [PO₃NCN]^3? leads to some splitting or shifting of frequencies being connected with vibrations of the NCN group; isolated v(P? N) stretching frequencies cannot be found.     

Fragmentation of protonated O,O-dimethyl O-aryl phosphorothionates in tandem mass spectral analysis

A study was carried out on the fragmentation of 12 protonated O,O-dimethyl O-aryl phosphorothionates by tandem quadrupole mass spectrometry. Some of the studied compounds are used in agriculture as pesticides. Energy-resolved and pressure-resolved experiments were performed on the [M + H]⁺ ions to investigate the dissociation behavior of the ions with various amounts of internal energy. On collisionally activated dissociation, the [M + H]⁺ ions decompose to yield the [M + H ? CH₃OH]⁺, (CH₃O)₂PS⁺ (m/z 125), and (CH₃O)₂PO⁺ (m/z 109) ions as major fragments. The ions [M + H ? CH₃OH]⁺ and (CH₃O)₂PS⁺ probably arise from the [M + H]⁺ ions of the O,O-dimethyl O-aryl phosphorothionates with the proton on the sulfur or on the oxygen of the phenoxy group. The origin of the hydroxy proton of the methanol fragment was in many cases, surprisingly, the phenyl group and not the reagent gas. This was confirmed by using deuterated isobutane, C₄D₁₀, as reagent gas in Cl. The fragment ions (CH₃O)₂PO⁺ and [ZPhS]⁺ are the results of thiono-thiolo rearrangement reaction. The precursor ion for the ion (CH₃O)₂PO⁺ arises from most compounds upon chemical ionization, whereas the precursor ion for the ion [ZPhS]⁺ arises only from a few compounds upon chemical ionization. The observed fragments imply that several sites carry the extra proton and that these sites get the proton usually upon ionization. The stability order and some characteristics of three protomers of O,O-dimethyl O-phenyl phosphorothionate were investigated by ab initio calculations at the RHF/3-21G* level of theory.     

Mass spectrometric characterization of a series of adenosylated peptides acting as bisubstrate analogs of protein kinases

We are currently developing strategies to synthesize bisubstrate analogs as potential inhibitors of serine and tyrosine protein kinases; several such analogs have been synthesized. The initial target proteins were the cAMP dependent protein kinase (cAPK) and the Ca⁺²/calmodulin dependent protein kinase (CaM kiiase II). These bisubstrate analogs were based on either known peptide substrates such as kemptide, a seven amino acid peptide substrate of cAPK, or on inhibitory peptides such as a seventeen amino acid peptide encompassing the autoinhibitory domain of CaM kinase II. Peptides containing a single phosphoserine group were first synthesized and then adenosine 5′-monophosphate (AMP), adenosine 5′-diphosphate (ADP), or adenosine 5′-triphosphate (ATP) was coupled through the serine phosphate with prior activation by 1,1-carbonyldiimidazole using either a solution or solid phase reaction scheme. In this current study, we report the characterization of the bisubstrate analogs by liquid secondary ionization mass spectrometry (LSIMS), matrix-assisted laser desorption mass spectrometry (MALDI), and tandem mass spectrometry (MS/MS). In the positive-ion mode, the LSIMS spectra of the bisubstrate analogs yielded a series of molecular ions containing mono-, di-, and trivalent cation adducts. Cation adducts were absent in the negative-ion mode where the dominant species were deprotonated molecular ions, [M ? H]^?, making this latter technique more useful for confirming product identity and assessing purity. Analysis of these compounds by MALDI in both the positive- and negative-ion modes yielded molecular ions which also contained metal ion adducts, although they were limited primarily to Fe⁺² adducts. Unlike LSIMS, the MALDI spectra showed no evidence for the elimination of the phosphoadenosine or other structural moieties. When these compounds were subjected to high energy collision-induced dissociation (CID), the dominant fragmentation pathways under positive-ion MS/MS conditions resulted from cleavage of the phosphate linkages to the adenosine moiety with charge retention on the peptide, although a major peak for 5′-deoxyadenosine was also seen at m/z 250. Charge retention in the negative-ion mode was most pronounced for ion fragments containing the highly acidic phosphate moieties and yielded phosphoadenosine related ions, for example, (AMP-H)^?, (AMP-H-H₂O)^?, (ADP-H)^?, etc., as well as ions originating from the phosphate linker such as PO₃ ^?, H₂PO₄ ^?, HP₂O₆ ^?, H₃P₂O₇ ^?, and H₂P₃O₉ ^?. The largest phosphoadenosine ion in the negative-ion CID spectra for each bisubstrate analog, for example, m/z 426 (ADP-H)^?, m/z 506 (ATP-H)^?, or m/z 586 (AP₄-H)^?, indicated that the desired covalent modification had been formed between the phosphoserine and AP_n moieties.     

Mechanistic Investigation of Phosphate Ester Bond Cleavages of Glycylphosphoserinyltryptophan Radical Cations under Low-Energy Collision-Induced Dissociation

Under the conditions of low-energy collision-induced dissociation (CID), the canonical glycylphosphoserinyltryptophan radical cation having its radical located on the side chain of the tryptophan residue ([G _p SW]^?+) fragments differently from its tautomer with the radical initially generated on the α-carbon atom of the glycine residue ([G^? _p SW]⁺). The dissociation of [G^? _p SW]⁺ is dominated by the neutral loss of H₃PO₄ (98 Da), with backbone cleavage forming the [b₂ – H]^?+/y₁ ⁺ pair as the minor products. In contrast, for [G _p SW]^?+, competitive cleavages along the peptide backbone, such as the formation of [G _p SW – CO₂]^?+ and the [c₂?+?2H]⁺/[z₁ – H]^?+ pair, significantly suppress the loss of neutral H₃PO₄. In this study, we used density functional theory (DFT) to examine the mechanisms for the tautomerizations of [G^? _p SW]⁺ and [G _p SW]^?+ and their dissociation pathways. Our results suggest that the dissociation reactions of these two peptide radical cations are more efficient than their tautomerizations, as supported by Rice–Ramsperger–Kassel–Marcus (RRKM) modeling. We also propose that the loss of H₃PO₄ from both of these two radical cationic tautomers is preferentially charge-driven, similar to the analogous dissociations of even-electron protonated peptides. The distonic radical cationic character of [G^? _p SW]⁺ results in its charge being more mobile, thereby favoring charge-driven loss of H₃PO₄; in contrast, radical-driven pathways are more competitive during the CID of [G _p SW]^?+.

Complexation of the [Rh(NH3)5H2O]3+ ion in aqueous solutions of H3PO4 based on 31P NMR data

The kinetics of the reaction between the [Rh(NH₃)₅H₂O]³⁺ ion and H₃PO₄ was studied by ³¹P NMR at 323?C343 K (E _a = 100.9 ± 0.3 kJ/mol, lnA = 35.7 ± 0.1). An empirical dependence of the ³¹P chemical shift on the equilibrium pH was found. The acid dissociation constants of the coordinated H₂PO ₄ ^? (3.9) and H PO ₄ ^2? ions (9.1) were estimated. The chemical shifts of the [Rh(NH₃)₅H₂PO₄]²⁺, [Rh(NH₃)₅HPO₄]⁺, and [Rh(NH₃)₅PO₄]⁰ complex ions were 8.38 ± 0.03, 10.76 ± 0.05, and 13.63 ± 0.05 ppm, respectively.     

Magneto-structural study and synthesis optimization of a phosphovanadate copper complex, [Cu(VO)2(PO4)2(H2O)4] n

The optimized synthesis of a phospho-vanadyl compound, [Cu(VO)₂(PO₄)₂(H₂O)₄] _n , is presented and its structural analysis is performed and discussed in relation to magnetic properties. The structure consists of a 2-D skeleton parallel to (100), made up by two independent VO₆ octahedra linked by phosphates. Neighboring 2-D structures stack along [100] and are connected by aqua-mediated H-bonds. The spatial disposition of paramagnetic ions gives rise to weak antiferromagnetic behavior, with J?=??17?cm^?1, which is consistent with a model of three paramagnetic centers in an irregular triangular arrangement. An optimization of the synthesis process, looking for a response surface with optimum experimental values, was performed using a multivariate analysis.     

1,2- and 3,4-rich polyisoprene synthesized by Mo(VI)-based catalyst with phosphorus ligand

Polyisoprene with relatively high content of 1,2/3,4 structure was synthesized using a novel catalyst system composed of MoO₂Cl₂ supported by phosphorus ligand and Al(OPhCH₃)(i-Bu)₂ as co-catalyst. The effects of phosphites, phosphates and phosphoric acid as ligands were investigated in the coordination polymerization of isoprene in the chosen catalyst system. The studied ligands significantly affected the catalytic activity of the Mo–Al catalytic active center without significant effect on the stereoselectivity. Mo(VI)-based catalyst system was proved to be highly effective in the polymerization of isoprene even at low [Al]/[Mo] ratio (10), affording polyisoprene with 1,2- and 3,4-% structural units in the range of 44.6–52.5%, high molecular weights M_n ~ 10⁵, and relatively broad molecular weight distributions (M_w/M_n = 3.0–4.4). The effect of molar ratio of phosphorous ligand to Mo-catalyst on catalyst activity of isoprene polymerization was discussed, and the structures of Mo–phosphite complexes were preliminarily studied by IR.     

The chemistry of the phosphates of barium and tetravalent cations in the 1:1 stoichiometry

The chemistry of phosphates of barium and tetravalent cations [BaM^IV(PO₄)₂] is reviewed. Such phosphates crystallise in the C2/m space group for M^IV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P2₁/n space group for BaTh(PO₄)₂. The existence of BaM^IV(PO₄)₂ in which M^IV=Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaM^IV(PO₄)₂ compounds and practical applications are briefly discussed.     

Fragmentation Chemistry of [Met-Gly]•+, [Gly-Met]•+, and [Met-Met]•+ Radical Cations

Radical cations [Met-Gly]^?+, [Gly-Met]^?+, and [Met-Met]^?+ have been generated through collision-induced dissociation (CID) of [Cu^II(CH₃CN)₂(peptide)]^?2+ complexes. Their fragmentation patterns and dissociation mechanisms have been studied both experimentally and theoretically using density functional theory at the UB3LYP/6-311++G(d,p) level. The captodative structure, in which the radical is located at the α-carbon of the N-terminal residue and the proton is on the amide oxygen, is the lowest energy structure on each potential energy surface. The canonical structure, with the charge and spin both located on the sulfur, and the distonic ion with the proton on the terminal amino group, and the radical on the α-carbon of the C-terminal residue have similar energies. Interconversion between the canonical structures and the captodative isomers is facile and occurs prior to fragmentation. However, isomerization to produce the distonic structure is energetically less favorable and cannot compete with dissociation except in the case of [Gly-Met]^?+. Charge-driven dissociations result in formation of [b _n – H]^?+ and a ₁ ions. Radical-driven dissociation leads to the loss of the side chain of methionine as CH₃-S-CH?=?CH₂ producing α-glycyl radicals from both [Gly-Met]^?+ and [Met-Met]^?+. For [Met-Met]^?+, loss of the side chain occurs at the C-terminal as shown by both labeling experiments and computations. The product, the distonic ion of [Met-Gly]^?+, NH₃ ⁺CH(CH₂CH₂SCH₃)CONHCH^?COOH dissociates by loss of CH₃S^?. The isomeric distonic ion NH₃ ⁺CH₂CONHC^?(CH₂CH₂SCH₃)COOH is accessible directly from the canonical [Gly-Met]^?+ ion. A fragmentation pathway that characterizes this ion (and the distonic ion of [Met-Met]^?+) is homolytic fission of the C_β–C_γ bond to lose CH₃SCH₂ ^?.      

Complexes of iron(II) with cysteine-containing peptides in the gas phase

Gas-phase interactions of peptides that contain cysteine with iron(II) atoms were examined by using fast-atom bombardment and tandem mass spectrometry. Specific and strong interactions of iron and sulfur from the thiol group of the cysteine side chain occur in the gas phase and are the basis for highly specific fragmentation to give abundant [a _n ?⁺ ions. For peptides that contain two cysteines, an internal ion, which results from the interaction of Fe and both thiol groups, is formed upon collisional activation. The mechanism for the formation of [a _n ?2H+Fe]⁺ fragment ions requires the metal to be coordinated at sulfur in close proximity to the site of reaction. Iron-bis(pentapeptide) complexes, which form under the same conditions, decompose predominantly to lose a pentapeptide molecule and, to a lesser extent, to give [a _a ?2H+Fe]⁺ ions.     

Synthesis and electrochemical properties of calix[4]arene derivatives containing ferrocene units in the cone and 1,3-alternate conformation

Two novel calix[4]arene receptors containing ferrocene units in cone (L₁) and 1,3-alternate (L₂) conformations have been synthesized from 25,27-dihydroxy-26,28-bis[(3-aminopropyl)oxy]calix[4]arene 4 or 25,26,27,28-tetra[(3-aminopropyl)oxy]calix[4]arene 6 and ferrocenecarboxaldehyde via condensation, respectively. Their structures have been characterized by ¹H, ¹³C, APT, COSY NMR, FTIR, HSMR, and UV–vis spectral data. The electrochemical behavior of L₁ and L₂ has been investigated in the presence of F^?, Cl^?, Br^?, H₂PO₄^?, CH₃COO^? anions. Electrochemical studies show that these receptors electrochemically recognize CH₃COO^?, H₂PO₄^?, and Cl^?, anions. Using an UV–vis study, the selectivity to these anions in DMSO solution was confirmed.     

Charge-remote fragmentations are energy-dependent processes

Fast atom bombardment-produced [M + Na]⁺ ions of tristearoylglycerol and [M ? H]^? ions of stearic or nervonic acid undergo charge-remote fragmentations (CRFs) to produce one series of product ions reflecting C _n H_2n+2 losses, whereas electrospray ionization-produced ions fragment to give two series of product ions reflecting C _n H_2n+2 and C _n H_2n+1 losses. These results and those from previous studies show that the mechanisms and energetics of CRFs are complex and unsettled. We demonstrate that several pathways are simultaneously involved in CRFs, and the preference for certain pathways (by C _n H_2n+1 and C _n H_2n+2 losses) is determined by the internal energy of the compound itself and the ionization and activation energies that are applied to it.     

Beiträge zur chemie des iodpentafluorids teil III. Chelatisierung und strukturisomerie bei α,β-methylierten IOD(V)-α,β-ethandiolat-fluoriden

We report metathetical reactions of IF₅ with series of α,β-trimethylsilylated ethanediolates with increasing numbers of CH₃-groups in α- and β-positions. Short lived intermediates IF₄[OC₂H_4?n(CH₃)_nO]X with X = Si(CH₃)₃ or IF₄ and stable chelates IF₃[OC₂H_4?n(CH₃)_nO] and IF[OC₂H_4?n(CH₃)_nO]₂ (n = 0–4) are observed and characterized. Time and temperature dependence of ¹⁹F-NMR-spectra in relation to degree of methylation, arrangement and stereo-chemistry are discussed referring to previously published mono- and polynuclear I(V)-compounds containing a series of monodentate alcoholates CH_3?n(CH₃)_nO^? and (CH₃)₃CCH₂O^? (n = 0,2,3) [1,2] and of bidentate alcoholates ^?O(CH₂)_nO^? (n = 2,3,4,5,6,12) [1]. In contrast to aliphatic α,β-diolates the aromatic diolates 1,2-C₆H₄(O^?)₂, 1,2-C₆Cl₄(O^?)₂ rapidly undergo redox reactions even at low temperatures.     

Iron(III) selective fluorescence probe based on perylene tetracarboxylic diimide

Responses of organic fluorophore, perylenediimide derivative N,N′-di[3-[2-(3-thienyl)ethyl]phenyl]perylene-3,4,9,10-bis-(dicarboxyimide) (PDI1) was investigated in polymer matrix of polyvinyl chloride (PVC) by emission spectrometry. Its response to Fe(III) ions was evaluated in terms of the effect of pH. The properties of time dependent response, reversibility, limit of detection, linear concentration range for the metal ion and repeatability characteristics of the sensing element also have been studied. The offered sensor exhibited remarkable fluorescence intensity quenching at pH 6.0 in the concentration range of 1 × 10^?6 to 2.5 × 10^?3 M Fe(III) ions. The reproducibility of the sensor membrane was investigated by alternately changing the solution between 1 × 10^?4 M Fe(III) in Na₂HPO₄ (4 × 10^?2 M) and NaH₂PO₄ buffer (2 × 10^?3 M).     

A comparison of the unimolecular decomposition pathways of some C7 and C8 ions in the gas phase

[CnH_2n?3]⁺ and [C_nH_2n?4]⁺·(n = 7, 8) ions have been generated in the mass spectrometer from C_nH_2n?3 Br (n = 7, 8) precursors and from two steroids. The relative abundances of competing ‘metastable transitionss’ indicate (partial) isomerization to a common structure (or mixture of structures) prior to decomposition in most examples of all four types of ions. In contrast, [C₈H₁₀O]⁺· and [C₈H₁₂O]⁺· ions, generated from different sources as molecular ions and by fragmentation of steroids, do not decompose through common-intermediates.     

Synthesis, crystal structure and spectroscopy properties of Na3AZr(PO4)3 (A=Mg, Ni) and Li2.6Na0.4NiZr(PO4)3 phosphates

Na₃AZr(PO₄)₃ (A=Mg, Ni) phosphates were prepared at 750 °C by coprecipitation route. Their crystal structures have been refined at room temperature from X-ray powder diffraction data using Rietveld method. Li_2.6Na_0.4NiZr(PO₄)₃ was synthesized through ion exchange from the sodium analog. These materials belong to the Nasicon-type structure. Raman spectra of Na₃AZr(PO₄)₃ (A=Mg, Ni) phosphates present broad peaks in favor of the statistical distribution in the sites around PO₄ tetrahedra. Diffuse reflectance spectra indicate the presence of octahedrally coordinated Ni²⁺ ions.     

Substituent effects in the mass spectra of diethyl phenyl phosphates

The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M⁺˙, and the [M? C₂H₄]⁺˙, [M – 2C₂H₄]⁺˙ and [XPhOH]⁺˙ ions. The [PO₃C₂H₆]⁺ (m/z 109) and [PO₃H₂]⁺ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC₂H₃]⁺˙ ion involves rearrangement of C₂H₃ to the position ortho to the phosphate group. Ortho effects are also observed.     

Reference standards for negative ion mass spectrometry

The negative ion mass spectra of phosphonitrile chlorides (PNCl₂)_n (n≥3) are studied. Since this series of compounds give very intense negative [M]^? and [M? Cl]^? ions, they can be used as good reference standards for negative ion mass spectrometry.     

Electron ionization mass spectrometry of systematically modified ligands in chromium(III) β-diketonates

The positive ion mass spectra of several chromium(III) β-diketonates with aliphatic α-substituents have been investigated. Metastable peaks in the spectra confirm that ions containing substituents with γ-H atoms undergo propene loss. This implies a McLafferty rearrangement of an open-chain ligand structure. Ethyl radicals are lost from n-butyl substituents; methyl groups are cleaved from the molecular ions of complexes formed from methyl-substituted ligands. The main fragment is, as expected, [ML₂]⁺; however, its further fragmentation is different from that of [ML₃]⁺. Electron donating substituents stabilize doubly charged molecular ions.