Tandem mass spectra of divalent metal ion adducts of glycosyl sulfides, sulfoxides and sulfones; distinction among stereoisomers

The tandem mass spectra of the divalent metal ion (Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Ni2+, Co2+ and Zn2+) adducts of acetylated 1,2-trans-glycosyl sulfides, sulfoxides and sulfones were examined using low energy collision-induced dissociation on a Quattro II quadrupole tandem mass spectrometer. Abundant doubly charged ions, such as [3M + Met]2+ and [2M + Met]2+, were observed with alkaline earth metal chlorides. The other ions observed were [M + MetCl]+, [M + MetOAc]+, [M + MetO2SPh]+ and [2M + MetCl]+. The deprotonated metal adducts [M + Met-H]+ were seen only in the sulfones. The divalent metal ion adducts showed characteristic fragmentation pathways for the glycosyl sulfides, sulfoxides and sulfones, depending on the site of metal attachment. The doubly charged metal ion adducts dissociate to two singly charged ions, [M + MetOAc]+ and [M - OAc]+, in the sulfides and sulfoxides. In the sulfones, the adducts dissociate to [M + MetO2SPh]+ and [M - O2SPh]+. In contrast to the alkaline earth metals, which attach to the acetoxy functions, the transition metals attach to the sulfide and sulfoxide functions. The metal chloride adducts display characteristic fragmentation for the sulfides, sulfoxides and sulfones. The glucosyl, mannosyl and galactosyl sulfides, sulfoxides and sulfones could be differentiated on the basis of the stereochemically controlled MS/MS fragmentations of the metal chloride adducts.     

Collision-induced dissociation of MCl(+) adducts (M = Mg, Mn, Zn, Co, Ni and Cu) and Cu(+) and Ag(+) adducts of dithioalkyl ketene acetals

Electrospray ionization mass spectra of equimolar solutions of dithioalkyl ketene acetals 1 and 2 and metal chlorides (MgCl(2), MnCl(2), ZnCl(2), CoCl(2), NiCl(2) and CuCl(2)) produced abundant ligated metal ion adducts [1 + MCl](+) and [2 + MCl](+). In addition, CuCl(2) also gave rise to Cu(+) adducts. The ligated metal ion adducts upon collision-induced dissociation (CID) showed characteristic fragmentation pathways reflecting the favoured site of coordination. The results show that MgCl(+) prefers oxygen over sulfur, whereas the reverse is true for ZnCl(+) adducts, exemplified by the preferred fragmentation of [1 + MgCl](+) as elimination of MgCl(OH), while that of [1 + ZnCl](+) is expulsion of ZnCl(SCH(3)). Co and Ni chloride adducts tend to give stable metal coordinated species. Cleavage of the dithiolane ring followed by elimination of C(2)H(4)S is the preferred pathway during the CID of [2 + MCl](+) adducts. The CuCl(+) adducts of 1 and 2 showed reduction of Cu((I)) to Cu((0)) resulting in the M(+)(*)ions of 1 and 2. Abstraction of *CH(3) resulting in elimination of CuCH(3) was observed during CID of Cu(+) adducts of 1 and 2. A comparative study of the corresponding Ag(+) adducts revealed a similar behaviour.     

Tandem mass spectra of transition-metal ion adducts of glycosyl dithioacetals; distinction among stereoisomers

Electrospray ionization mass spectra of some glycosyl dithioacetals recorded in the presence of transition-metal chlorides, XCl2 (where X = Co, Mn and Zn), give abundant adduct ions such as [M+XCl]+ and [2M-H+X]+ and minor ions such as [M-H+X]+ and [2M+XCl]+. The tandem mass spectra of these adducts show characteristic elimination of neutral molecules such as H2O, HCl, EtSH, CH2O, C2H4O2/C2H4O. [M+XCl]+ ions fragment readily and the fragmentation appears to be stereochemically controlled as the relative abundances of the fragments are different for three stereoisomers. The added metal is lost as neutral molecules in the form of XCl(OH) and XCl(SEt). This is a predominant pathway in the ZnCl+ adducts. [2M+XCl]+ ions fragment preferentially by elimination of HCl, indicating strong metal interactions in the resulting dimeric [2M-H+X]+ ion. As there are several electron-rich centers in the molecule, the dimeric complex [2M-H+X]+ can have several structures and the observed fragmentations may reflect the sum of those of all these structures. The dimeric complexes fragment by elimination of neutral molecules leaving the dimeric interactions intact. The extent of fragmentation varies for the stereoisomers, leading to stereochemical differentiation.     

High energy collision-induced dissociation of alkali-metal ion adducts of crown ethers and acyclic analogs.

High energy collision-induced dissociation (CID) techniques were applied for structural elucidation of alkali-metal ion adducts of crown ethers. The CID of alkali-metal adducts of tetraglyme and hexaethylene glycol were also evaluated to contrast the fragmentation pathways of the cyclic ethers with those of acyclic analogs. A common fragmentation channel for alkali-metal ion adducts of all the ethers, which results in distonic radical cations, is the homolytic cleavage of carbon-carbon bonds. Additionally, dissociation by carbon-oxygen bond cleavages occurs, and these processes are analogous to the fragmentation pathways observed for simple protonated ethers. The proposed fragmentation pathways for alkali-metal ion adducts of crown ethers result mostly in odd-electron, acyclic product ions. Dissociation of the alkali-metal ion adducts of the acyclic ethers is dominated by losses of various neutral species after an initial hydride or proton transfer. The CID processes for all ethers are independent of the alkali-metal ion sizes; however, the extent of dissociation of the complexes to bare alkali-metal ions increases with the size of the metal.     

The significance of the alkene size and the nature of the metal ion in metal-alkene complexes: a theoretical study

Cation interactions with π-systems are a problem of outstanding contemporary interest and the nature of these interactions seems to be quite different for transition and main group metal ions. In this paper, we have systematically analyzed the contrast in the bonding of Cu(+) and main group metal ions. The molecular structures and energetics of the complexes formed by various alkenes (A = C(n)H(2n), n = 2-6; C(n)H(2n- 2), n = 3-8 and C(n)H(2n + 2), n = 5-10) and metal ions (M = Li(+), Na(+), K(+), Ca(2+), Mg(2+), Cu(+) and Zn(2+)) are investigated by employing ab initio post Hartree-Fock (MP2/6-311++G**) calculations and are reported in the current study. The study, which also aims to evaluate the effect of the size of the alkyl portion attached to the π-system on the complexation energy, indicates a linear relationship between the two. The decreasing order of complexation energy with various metal ion-alkene complexes follows the order Zn(2+)-A > Mg(2+)-A > Ca(2+)-A > Cu(+)-A > Li(+)-A > Na(+)-A > K(+)-A. The increased charge transfer and the electron density at (3,-1) intermolecular bond critical point corroborates well with the size of the π-system and the complexation energy. The observed deviation from the linear dependency of the Cu(+)-A complexes is attributed to the dπ→π* back bonding interaction. An energy decomposition analysis via the reduced variational space (RVS) procedure was also carried out to analyze which component among polarization, charge transfer, coulomb and exchange repulsion contributes to the increase in the complexation energy. The RVS results suggest that the polarization component significantly contributes to the increase in the complexation energy when the alkene size increases.     

A new ion sensor based on fiber optics

A fluorimetric ion sensor based on fiber optics has been developed that employs Rhodamine 6G hydrophobically and electrostatically "trapped" on a Nafion film. The sensor is based on the measurement of quenching or enhancement of the Rhodamine 6G fluorescence by various ions. It was found that ions such as Co(2+), Cr(3+), Fe(2+), Fe(3+), Cu(2+), Ni(2+) and NH(+)(4) rapidly quench the Rhodamine 6G fluorescence at an initial rate that depends on the concentration of the ion. This quenching is then readily reversed by the addition of "reverser" ions such as H(+), Li(+), Na(+), K(+), Ba(2+), Ca(2+), Mn(2+), Zn(2+) and Mg(2+). Again, the initial rate for the attainment of the original fluorescence was found to depend on the concentration of the reverser ion. Therefore, by monitoring the quenching directly the concentration of quencher ions can be determined. In addition, by loading the film with quencher and monitoring the initial rate of return towards the original baseline signal, it is possible to determine non-quenching ions.     

Universal chiral twist via metal ion induction in the organogel of terephthalic acid substituted amphiphilic L-glutamide

A newly designed terephthalic acid substituted amphiphilic L-glutamide was found to form organogels in DMSO and a broad range of metal ions, from simple Na(+), Li(+) to Cu(2+), Ni(2+), Eu(3+) and Tb(3+), could turn the self-assembled nanostructure into a uniform helical twist.     

Influence of d orbital occupation on the binding of metal ions to adenine

Threshold collision-induced dissociation of M(+)(adenine) with xenon is studied using guided ion beam mass spectrometry. M(+) includes all 10 first-row transition metal ions: Sc(+), Ti(+), V(+), Cr(+), Mn(+), Fe(+), Co(+), Ni(+), Cu(+), and Zn(+). For the systems involving the late metal ions, Cr(+) through Cu(+), the primary product corresponds to endothermic loss of the intact adenine molecule, whereas for Zn(+), this process occurs but to form Zn + adenine(+). For the complexes to the early metal ions, Sc(+), Ti(+), and V(+), intact ligand loss competes with endothermic elimination of purine and of HCN to form MNH(+) and M(+)(C(4)H(4)N(4)), respectively, as the primary ionic products. For Sc(+), loss of ammonia is also a prominent process at low energies. Several minor channels corresponding to formation of M(+)(C(x)H(x)N(x)), x = 1-3, are also observed for these three systems at elevated energies. The energy-dependent collision-induced dissociation cross sections for M(+)(adenine), where M(+) = V(+) through Zn(+), are modeled to yield thresholds that are directly related to 0 and 298 K bond dissociation energies for M(+)-adenine after accounting for the effects of multiple ion-molecule collisions, kinetic and internal energy distributions of the reactants, and dissociation lifetimes. The measured bond energies are compared to those previously studied for simple nitrogen donor ligands, NH(3) and pyrimidine, and to results for alkali metal cations bound to adenine. Trends in these results and theoretical calculations on Cu(+)(adenine) suggest distinct differences in the binding site propensities of adenine to the alkali vs transition metal ions, a consequence of s-dsigma hybridization on the latter.     

Competitive cesium-133 NMR spectroscopic study of complexation of different metal ions with dibenzo-21-crown-7 in acetonitrile-dimethylsulfoxide and nitromethane-dimethylsulfoxide mixtures

(133)Cs NMR spectroscopy was used to determine the stoichiometry and stability of the Cs(+) ion complex with dibenzo-21-crown-7 (DB21C7) in acetonitrile-dimethylsulfoxide (96.5:3.5, w/w) and nitromethane-dimethylsulfoxide (96.5:3.5, w/w) mixtures. A competitive (133)Cs NMR technique was also employed to probe the complexation of Na(+), K(+), Rb(+), Ag(+), Tl(+), NH(4)(+), Mg(2+), Ba(2+), Hg(2+), Pb(2+) and UO(2)(2+) ions with DB21C7 in the same solvent systems. All the resulting 1:1 complexes in nitromethane-dimethylsulfoxide were more stable than those in acetonitrile-dimethylsulfoxide solution. In both solvent systems, the stability of the resulting complexes was found to vary in the order Rb(+)>K(+) approximately Ba(2+)>Tl(+)>Cs(+)>NH(4)(+) approximately Pb(2+)>Ag(+)>UO(2)(2+)>Hg(2+)>Mg(2+)>Na(+).     

Effect of metal cationization on the low-energy collision-induced dissociation of loganin, epi-loganin and ketologanin studied by electrospray ionization tandem mass spectrometry

The effect of alkali metal and silver cationization on the collision-induced dissociation (CID) of loganin (1), epi-loganin (2) and ketologanin (3) is discussed. Their protonated molecular ions fragment mainly by glycosidic cleavages. The epimeric pairs (1 and 2) show differences in the abundances of the resulting fragment ions. Lithium cationization induces new dissociation pathways such as the retro-Diels-Alder (RDA) fragmentation followed by rearrangement. Unlike the dissociation of protonated molecular ions, the dissociation of lithiated molecules also provides lithiated sugar fragments. The CID of dilithiated molecules is substantially different from that of the monolithiated precursors. RDA reaction appears to be favoured by the presence of the additional lithium atom in the molecule. In addition, other ring cleavages are also induced. The abundances of the various fragment ions are different in the CID spectra of the epimeric pairs. Extensive D labelling and (6)Li labelling experiments confirmed many of the ion structures proposed. The CID spectra of the sodiated ions are generally weaker, although similar to those of the corresponding lithiated species. Higher alkali metal ion (K(+), Rb(+) and Cs(+)) adducts generated only the corresponding metal ions as products of CID. Similar fragmentations were also observed in the CID of the [M + Ag](+) ions of these compounds, the epimeric pairs showing characteristic differences in their CID behaviour. Copyright 2000 John Wiley & Sons, Ltd.     

Synthesis and photochromism of spirobenzopyrans and spirobenzothiapyran derivatives bearing monoazathiacrown ethers and noncyclic analogues in the presence of metal ions

Spirobenzopyrans bearing monoazathiacrown ethers and noncyclic analogues were synthesized, and their ion-responsive photochromism depending on the dual metal ion interaction with the crown ether and the phenolate anion moieties was examined using alkali and alkaline-earth metal ions, Ag(+), Tl(+), Pb(2+), Hg(2+), and Zn(2+). The prepared spirobenzopyrans showed a selective binding ability to Mg(2+) and Ag(+) with negative and positive photochromism, respectively. Among the metal ions, only Ag(+) facilitated photoisomerization to the corresponding merocyanine form. Depending on the ring size of the monoazathiacrown ether moieties, soft metal ions such as Hg(2+) and Ag(+) showed significant shifts in the UV-vis absorption spectra, while hard metal ions such as Mg(2+), Zn(2+), and Pb(2+) did not afford any meaningful shift. This result reflects that the monoazathiacrown ether and phenolate anion moieties prefer soft and hard metal ions, respectively. Therefore, the Mg(2+) and Ag(+) selectivities are mainly derived from the phenolate anion and monoazathiacrown ether moieties, respectively. On the other hand, a spirobenzothiapyran bearing 3,9-dithia-6-monoazaundecane showed a remarkable selectivity to Ag(+).     

Separation and evaluation of soybean protein hydrolysates prepared by immobilized metal ion affinity chromatography with different metal ions

Metal ion affinity chromatography is widely used to purify peptides on the basis of the dissimilarities of their amino acids. However, researchers are interested in the separation differences between different metal ions in this method. In our study, four kinds of commonly used metal ions are compared by the amount of immobilized metal ion on iminodiacetic acid-Sepharose and binding amount of soybean peptide to immobilized iminodiacetic acid-Mn(+) adsorbents and evaluated by high-performance liquid chromatography (HPLC) profiles. The results show that due to the different adsorption behaviors of metal ions, the binding ability order of soybean protein peptide on the column should be Fe(3+) > Cu(2+) > Zn(2+) > Ca(2+). The HPLC profiles show that peptides adsorbed by four kinds of metal ions display similar strong hydrophobic characteristics.     

Reactions of first-row transition metal ions with propargyl alcohol in the gas phase

The gas-phase reactions with propargyl alcohol (PPA) of all the singly charged ions of the first-row transition metals, generated by laser ablation in an external ion source, were studied by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS.). The reactivities of the metal ions change irregularly across the periodic table, and the reactivity of each ion is a function of its electronic configuration and corresponding metal-oxygen (M-O) bond energies. The 10 metal ions were classified into three categories according to their reactivities: Sc(+), Ti(+) and V(+) are the most reactive ions which react with PPA to give many kinds of oxygen-rich products due to stronger M-O bonds; Fe(+), Co(+) and Ni(+) are less reactive; Cr(+), Mn(+), Cu(+) and Zn(+) are the most unreactive ions, due to the half and completely occupied valence electronic configurations. The order of reactivity is Ti(+) > V(+) > Sc(+) > Co(+) > Fe(+) approximately Ni(+) > Zn(+) > Cr(+) approximately Mn(+) approximately Cu(+).     

Dissociation of gas-phase dimeric complexes of lactic acid and transition-metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Dimeric complex ions of the type [M(A-H)A]+, where M=metal ion (Co, Ni, Cu, and Zn) and A=ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]+ ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions.     

Metal ion modulated organization and function of the Langmuir-Blodgett films of amphiphilic diacetylene: photopolymerization, thermochromism, and supramolecular chirality

Some novel properties of organized molecular films of 10,12-tricosadiynoic acid (TDA), which were modulated by transition metal ions, were investigated. It was found that metal ions such as Cu(2+), Zn(2+), Ni(2+), Cd(2+), and Ag(+) in the subphase can greatly affect the monolayer formation of TDA and the properties of the subsequently deposited Langmuir-Blodgett (LB) films, particularly in the case of Ag(+), Zn(2+), and Cu(2+) ions. TDA LB film from the subphase containing Ag(+) ion could not be photopolymerized. It was suggested that both the strong chelating property to the carboxylate and the easy reduction of Ag(+) in the film disrupted the topochemical sequence of TDA and resulted in no polymerization in the film. Zinc ion coordinated TDA film could be photopolymerized into a blue polydiacetylene (PDA) film, which showed a reversible thermochromism between blue and purple color upon thermal stimulation. Fourier transform infrared spectra revealed the difference of the Zn(2+)-PDA film from those of the other ions, and the mechanism of the thermochromism was discussed. Copper ion coordinated TDA film could only be photopolymerized to a red PDA film, which showed supramolecular chirality although TDA itself was achiral. Atomic force microscopic measurements revealed the nanofiber structure in the Cu(2+)-PDA film. The supramolecular chirality of the Cu(2+)-PDA film was suggested to be due to the arrangement of the polymer backbone in a helical sense. Furthermore, it was found that the chiral assemblies from the achiral TDA molecules were very stable and the chirality could be kept even upon heating or treating with alkaline solution. While many synthetic efforts have been devoted to the functionalization of PDA films, we provided a simple method of modulating the organization and function of PDA films through metal ions.     

Effect of metal cationization on the tandem mass spectra of glycosyl dithioacetals

The effect of metal cationization on the tandem mass spectra of glycosyl dithioacetals of glucose, mannose, galactose, rhamnose, arabinose and xylose was studied by electrospray ionization mass spectrometry under ammonium and metal (Li, Na, Ag and Cu) ion cationization conditions. The ammonium-cationized glycosyl dithioacetals fragment by loss of ammonia followed by either two molecules of EtSH or one molecule of EtSH and one molecule of H2O. Lithium cationization leads to additional eliminations such as EtSEt and EtSSEt and C-C cleavages. Elimination of EtSH is not observed under sodium cationization. Silver cationization, on the other hand, leads to additional fragmentations involving the elimination of silver as AgOH and AgSEt. Copper cationization results in adducts where copper has undergone a change of oxidation state from II to I. Li+, Ag+ and Cu+ cationization seem to favour cyclization resulting in elimination of EtSH. However, the mechanisms seem to be differently affected by different metal ions. Li+ and Ag+ cationization appear to be non-specific and favour cyclization involving C2-, C4- and C5-hydroxyl hydrogens, whereas Cu+ cationization seems to favour cyclization involving C4-hydroxyl hydrogen.     

Understanding the relationship between photolysis efficiency and metal binding using ArgenCast photocages

ArgenCast-1 (1), a photocage for silver utilizing acyclic polythioether 3,6,12,15-tetrathia-9-azaheptadecane receptor and 4,5-dimethoxy-2-nitrobenzyl (DMNB) chromophore has been prepared using trimethylsilyl trifluoromethanesulfonate-assisted electrophilic aromatic substitution. Metal binding studies with ArgenCast-1 reveal interactions with Ag(+), Hg(2+) and Cu(+), but only Ag(+) coordinates in both aqueous and organic solvents. The uncaging mechanism of ArgenCast-1 metal complex involves a photoreaction that converts the nitrobenzydrol into the electron withdrawing nitrosobenzophenone that participates in a resonance interaction with a metal-bound aniline nitrogen atom. The structural change following photolysis decreases availability of the nitrogen lone pair for Ag(+) coordination, but strong interactions between Ag(+) and the thioether ligands mitigates metal ion release. A resonance interaction with a key aci-nitro intermediate reduces the photolysis quantum yield of ArgenCast-1, so several naphthyl-based nitrobenzyl groups were screened as alternatives to DMNB. The naphthyl Ag(+) photocages, ArgenCast-2 and -3, exhibit nearly identical quantum yield to ArgenCast-1 owing to the dominance of resonance between aci-nitro intermediate and the aniline nitrogen atom.     

Evaluation of the metal binding properties of a histidine-rich fusogenic peptide by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) was used to investigate metal ion interactions of the 18 amino acid peptide fragment B18 (LGLLLRHLRHHSNLLANI), derived from the membrane-associated protein bindin. The peptide sequence B18 represents the minimal membrane-binding motif of bindin and resembles a putative fusion peptide. The histidine-rich peptide has been shown to self-associate into distinct supramolecular structures, depending on the presence of Zn(2+) and Cu(2+). We examined the binding of B18 to the metal ions Cu(2+), Zn(2+), Mg(2+), Ca(2+), Mn(2+) and La(3+). For Cu(2+), we compared the metal binding affinities of the wild-type B18 peptide with those of its mutants in which one, two or three histidine residues have been replaced by serines. Upon titration of B18 with Cu(2+) ions, we found sequential binding of two Cu(2+) ions with dissociation constants of approximately 34 and approximately 725 micro M. Mutants of B18, in which one histidine residue is replaced by serine, still exhibit sequential binding of two copper ions with affinities for the first Cu(2+) ion comparable to that of wild-type B18 peptide, but with a greatly reduced affinity for the second Cu(2+) ion in mutants H112S and H113S. For mutants in which two histidines are replaced by serines, the affinity for the first Cu(2+) ion is reduced approximately 3-10 times in comparison with B18. The mutant in which all three histidine residues are replaced by serines exhibits an approximately 14-fold lower binding for the first Cu(2+) ion compared with B18. For the other metal ions under investigation (Zn(2+), Mg(2+), Ca(2+), Mn(2+) and La(3+)), a modest affinity to B18 was detected binding to the peptide in a 1 : 1 stoichiometry. Our results show a high affinity of the wild-type fusogenic peptide B18 for Cu(2+) ions whereas the Zn(2+) affinity was found to be comparable to that of other di- and trivalent metal ions.     

Double ionization and Coulomb explosion of the formic acid dimer by intense near-infrared femtosecond laser pulses

Ionization and fragmentation of formic acid dimers (HCOOH)(2) and (DCOOD)(2) by irradiation of femtosecond laser pulses (100 fs, 800 nm, ~1 × 10(14) W/cm(2)) were investigated by time-of-flight (TOF) mass spectrometry. In the TOF spectra, we observed fragment ions (HCOOH)H(+), (HCOOH)HCOO(+), and H(3)O(+), which were produced via the dissociative ionization of (HCOOH)(2). In addition, we found that the TOF signals of COO(+), HCOO(+), and HCOOH(+) have small but clear side peaks, indicating fragmentation with large kinetic energy release caused by Coulomb explosion. On the basis of the momentum matching among pairs of the side peaks, a Coulomb explosion pathway of the dimer dication, (HCOOH)(2)(2+) → HCOOH(+) + HCOOH(+), was identified with the total kinetic energy release of 3.6 eV. Quantum chemical calculations for energies of (HCOOH)(2)(2+) were also performed, and the kinetic energy release of the metastable dication was estimated to be 3.40 eV, showing good agreement with the observation. COO(+) and HCOO(+) signals with kinetic energies of 1.4 eV were tentatively assigned to be fragment ions through Coulomb explosion occurring after the elimination of a hydrogen atom or molecule from (HCOOH)(2)(2+). The present observation demonstrated that the formic acid dimer could be doubly ionized prior to hydrogen bond breaking by intense femtosecond laser fields.     

Gas Phase Chemistry of Li+ with Amides: the Observation of LiOH Loss in Mass Spectrometry

Collision-induced dissociation (CID) of Li(+) adducts of three sets of compounds that contains an amide bond, including 2-(4, 6-dimethoxypyrimidin-2-ylsulfanyl)-N-phenylbenzamide, its derivatives and simpler structures was investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Observed fragment ions include those that reflect loss of LiOH. Other product ions result from the Smiles rearrangement and direct C-S bond cleavage. MS/MS of H/D exchange products demonstrated occurrence of a 1,3-H shift from the amide nitrogen atom to the phenyl ring of these compounds. The LiOH loss from Li(+) adducts of amides was further examined by CID of [M + Li](+) ions of N-phenylbenzamide and N-phenylcinnamide. Loss of LiOH was essentially the sole fragmentation reaction observed for the former. For the latter, both losses of LiOH and H(2)O were discovered. The presence of electron-donating substituents of the phenyl ring of these compounds was found to facilitate elimination of LiOH, while that loss was retarded by electron-withdrawing substituents. Proposed fragment ion structures were supported by elemental compositions deduced from ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS) m/z value determinations. Density functional theory-based (DFT) calculations were performed to evaluate potential mechanisms for these reactions.