Gas-phase formation of radical cations of monomers and dimers of guanosine by collision-induced dissociation of Cu(II)-guanosine complexes

An electrosprayed water/methanol solution of guanosine and Cu(NO3)2 was observed to give rise to gas-phase copper complexed ions of [CuLn]*2+, [CuL(MeOH)n]*2+, and [CuG n(NO3)]*+, as well as the ions [L]*+, [L+H]+, [G]*+, and [G+H]+ (L=guanosine, G=guanine). The Collision-Induced Dissociation (CID) of [CuL3]*2+ and [CuL(MeOH)n]*2+ (n=2, 3) generates guanosine radical cations [L]*+, while dimeric guanosine radical cations [L2]*+ are generated in the dissociation of [CuL4]*2+. Protonated guanosine [L+H]+ is one of the main products in the primary dissociation of [CuL2]*2+, while the dissociation of the higher-order [CuG2]*2+ produces the [G]*+ radical cation. The guanosine dimer radical cation, [L2]*+ presumably arises from the interaction of two guanosine molecules via proton and hydrogen bonding and is observed to dissociate into [L+H]+ and [L-H]* at low energies. We propose that the first two ligands bind strongly with Cu(II) through N7 and O6 to form a [CuL2]*2+ complex with a four-coordinated planar structure and that a third ligand binds loosely with copper to form [CuL3]*2+. Additional ligation observed in the formation of [CuLn]*2+ (n相似文献   

Photodissociation and collision-induced dissociation of molecular ions from methylphenol and chloromethylphenol

The photodissociation of molecular ions from a series of methylphenols and chloromethylphenols was studied using Fourier transform ion cyclotron resonance mass spectrometry (FTMS). The photodissociation spectra contain both UV and visible absorption maxima. The positions of these bands correlate well with solution electronic absorption spectra and photoelectron spectra, respectively, suggesting that photodissociating populations of the molecular ions have not rearranged. The molecular ion of benzyl alcohol can be readily distinguished from the isomeric 2- and 4-methylphenol ions on the basis of the position and intensity of the photodissociation bands, and the identity of the photoproduct. The p-chlorophenol isomers, 4-chloro-2-methylphenol and 4-chloro-3-methylphenol, cannot be distinguished by their photodissociation spectra. Minor differences exist between these spectra and that of the o-chlorophenol isomer 2-chloro-5-methylphenol, suggesting that the relative positions of the chloro and hydroxy groups may have a greater effect on photodissociation than the position of the methyl group. For comparison, low-energy collision-induced dissociation using FTMS was also performed on the same ions.     

A phenoxyl radical complex of copper(II)

A new N,O-bidentate pro-ligand (HL), [ML2] (M = Cu, Zn) and [CuL2][BF4] have been synthesised; [CuL2].4DMF and [CuL2][BF4].2CH2Cl2 have been crystallographically and spectroscopically characterised; these data indicate that [CuL2]+ cations are constituted as [Cu2+(L.)(L-)]+ and involve the phenoxyl radical L..     

Formation of double and triple complexes of copper(II) with enkephalin and histidine

Complex formation between copper(II) and pentapeptide enkephalin and histidine was studied at various pH values by fast-atom bombardment (FAB) and field-desorption (FD) mass spectrometry and ESR. It was shown that a triple complex, stable over a wide range of pH and detectable in the FD mass spectrum, is formed in the solutions with the components in an equimolar ratio.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 5, pp. 634–641, September–October, 1987.     

Identification of a new fragment ion type in the collision-induced dissociation spectra of peptides: Formation of a2-16 ions

The identification of an ion observed in the high-energy collision-induced dissociation spectra of several model peptides is reported. The ion, observed at m/z 99 for the peptide pentaalanine (Ala₅) and designated a₂-16, is shown to have an elemental formula of C₅H₉NO by high-resolution peak matching. The precursor ion spectrum of the a₂-16 ion and product ion spectra of the a₂ and the a₂+ 1 ions for Ala₅ suggest that this ion is formed by the loss of 17 u (presumably NH₃) from the a₂+1 ion and, to a lesser extent, by loss of 28 u (presumably CO) from the b₂-16 ion. On the basis of the data presented and other experimental evidence, a structure and mechanism for the formation of the a₂-16 ion is proposed.     

The promotion of d-type ions during the low energy collision-induced dissociation of some cysteic acid-containing peptides

Low energy collisionally activated dissociations (CAD) of doubly protonated peptides incorporating cysteic acid and arginine residues have been studied. Deuterium labeling experiments have established that loss of the elements of H₂SO₃ occurs with cleavage of one CH bond and transfer of the hydrogen to a neutral fragment. Prominent d-type ions were observed corresponding to cleavage at the cysteic acid residue. The analysis of structural analogs suggested that the unexpectedly low energy requirement for this process is attributable to a charge-proximal process promoted by intra-ionic interaction of the arginine and cysteic acid side chains. CAD (in the collision hexapole of a tandem quadrupole instrument) of electrospray source-formed fragment ions established that the d-type ions can form via b-type ions; there was no evidence of formation via (a _n + 1) or (b _n — H₂SO₃) ions. The equivalent d-ion was observed, albeit with lesser abundance, when the cysteic acid residue was replaced by aspartic acid, but not by glutamic acid.     

Designing copper(II) ternary complexes to generate radical cations of peptides in the gas phase: role of the auxiliary ligand

A series of ternary copper(II) complexes of the type [Cu(II)(L)(M)](2+), where M represents the hexapeptides GGGFLR, YGGFLR and WGGFLR and L a set of 12 nitrogen donor ligands have been evaluated for their ability to form cationic peptide radicals, M(+)*, in the gas phase. Although the fragmentation chemistry of these ions is complex, two main conclusions emerge: (i) Complexes containing a tri- or tetra-dentate ligand were found to be more effective at producing the peptide radical because in these instances competitive loss of the ligand from the complex is inhibited; (ii) The ligands ought not possess any acidic protons in order to prevent competitive loss of the protonated peptide, [M + H](+). There is significant interaction of the N-terminal aromatic residues in YGGFLR and WGGLFR with the copper(ii) ion in several of the complexes as revealed by the formation of [Cu(I)(L)(p-quinomethide)](+) and [Cu(I)(L)(3-methyleneindoline)](+) fragment ions. Following its dissociation from the ternary complex, CID of the YGGFLR(+)* radical cation shows a dependence on the ligand in the complex from which it was formed. This 'memory effect' most likely reflects differences in the coordinated peptide structure induced by the ligand in the precursor complex which are maintained following dissociation.     

Potentiometric study of complex formation equilibria of alpha-oxooximes with copper(II) and nickel(II) and ions

Complex formation equilibria between copper(II) and nickel(II) with phenylglyoxal 2-oxime (HPGO) and 1-phenyl-1,2-propanedione 2-oxime (HPPO) have been studied in 50% (v/v) ethanol-water solution containing 0.5M sodium nitrate as constant ionic medium at 25 degrees , using glass electrode potentiometry. The emf data obtained have been analysed with MINIGLASS and SUPERQUAD programs. Formation constants for the Cu(PGO)(+), Cu(2)(PGO)(OH)(2+), Cu(2)(PGO)(2)(OH)(+), Ni(PGO)(+), Ni(2)(PGO)(3)(+), Ni(2)(PGO)(4), Ni(2)(PGO)(2)(OH)(2), Cu(2)(PPO)(OH)(+) and Cu(2)(PPO)(2)(OH)(+) complexes are reported.     

Comparison of infrared multiphoton dissociation and collision-induced dissociation of supercharged peptides in ion traps

The number and types of diagnostic ions obtained by infrared multiphoton dissociation (IRMPD) and collision-induced dissociation (CID) were evaluated for supercharged peptide ions created by electrospray ionization of solutions spiked with m-nitrobenzyl alcohol. IRMPD of supercharged peptide ions increased the sequence coverage compared with that obtained by CID for all charge states investigated. The number of diagnostic ions increased with the charge state for IRMPD; however, this trend was not consistent for CID because the supercharged ions did not always yield the greatest number of diagnostic ions. Significantly different fragmentation pathways were observed for the different charge states upon CID or IRMPD with the latter yielding far more immonium ions and often fewer uninformative ammonia, water, and phosphoric acid neutral losses. Pulsed-Q dissociation resulted in an increase in the number of internal product ions, a decrease in sequence-informative ions, and reduced overall ion abundances. The enhanced sequence coverage afforded by IRMPD of supercharged ions was demonstrated for a variety of model peptides, as well as for a tryptic digest of cytochrome c.     

Non-zwitterionic structures of aliphatic-only peptides mediated the formation and dissociation of gas phase radical cations

We have investigated how the non-zwitterionic and zwitterionic structures of aliphatic-only tripeptides affect the formation and dissociation of peptide radical cations in the gas phase. The non-zwitterionic forms of the aliphatic-only peptides in their metal complexes play an important role in determining whether the electron transfer pathway predominates. We extended this study by synthesizing permanent non-zwitterionic and zwitterionic forms of aliphatic-only peptide radical cations and exploring their reactivities in the gas phase. Collision-induced dissociation spectra demonstrated the feasibility of generating both non-zwitterionic and zwitterionic forms. Radical cations in zwitterionic forms may indeed mediate the beta and gamma carbon-carbon bond cleavages of leucine and isoleucine side chains from the GlyGlyXle radical peptides; this feature allows leucine and isoleucine residues to be distinguished unambiguously.     

Detection and characterization of methionine oxidation in peptides by collision-induced dissociation and electron capture dissociation

Electron capture dissociation (ECD) and collision-induced dissociation (CID), the two complementary fragmentation techniques, are demonstrated to be effective in the detection and localization of the methionine sulfoxide [Met(O)] residues in peptides using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The presence of Met(O) can be easily recognized in the low-energy CID spectrum showing the characteristic loss of methanesulfenic acid (CH(3)SOH, 64 Da) from the side chain of Met(O). The position of Met(O) can then be localized by ECD which is capable of providing extensive peptide backbone fragmentation without detaching the labile Met(O) side chain. We studied CID and ECD of several Met(O)-containing peptides that included the 44-residue human growth hormone-releasing factor (GRF) and the human atrial natriuretic peptide (ANP). The distinction and complementarity of the two fragmentation techniques were particularly remarkable in their effects on ANP, a disulfide bond-containing peptide. While the predominant fragmentation pathway in CID of ANP was the loss of CH(3)SOH (64 Da) from the molecular ion, ECD of ANP resulted in many sequence-informative products, including those from cleavages within the disulfide-bonded cyclic structure, to allow for the direct localization of Met(O) without the typical procedures for disulfide bond reduction followed by [bond]SH alkylation.     

Infrared multiphoton and collision-induced dissociation studies of some gaseous alkylamine ions

Collision-induced dissociation and infrared multiphoton dissociation of ions formed in di- and tri-ethylamine, di- and tri-n-propylamine, and di-isopropylamine were investigated by Fourier-transform ion-cyclotron resonance mass spectrometry. Molecular ions of all amines except di-n-propylamine produced similar fragment ions when subjected to either dissociation technique. The initial fragmentation involved C_αC_β bond cleavage, loss of an alkyl radical, and formation of an immonium ions. Subsequent fragmentations of the immonium ions produced by both dissociation mechanisms involved McLafferty-type rearrangements and loss of alkenes. The molecular ion of di-n-propylamine fragmented by a different mechanism when subjected to infrared irradiation. Protonated molecules of di- and tri-n-propylamine yielded C₃H₆ and an ammonium ion upon infrared multiphoton dissociation, while protonated molecules of the other amines did not dissociate when this technique was applied. In contrast, collision-induced dissociation produced fragmentation for all protonated molecules. Explanation of the different fragmentations observed for the two dissociation techniques is given in terms of a mechanism involving a tight transition state for protonated di- and tri-n-propylamine dissociation.     

Synthesis and study of copper(II), nickel(II), and cobalt(II) complex compounds with dihydrobenzoxazine derivatives

Complex compounds ML₂ of copper(II), nickel(II), and cobalt(II) with 2-(2-hydroxy-5-nitrophenyl)-4,4-diphenyl-1,4-dihydro-2H-3,1-benzoxazine and 2-(2-hydroxyphenyl)-4,4-diphenyl-1,4-dihydro-2H-3,1-benzoxazine (HL) were prepared by electrochemical and chemical syntheses. The complex formation involves the azomethine form of the ligand and gives a six-membered chelate cycle comprising deprotonated phenol and azomethine groups. The coordination entity has a planar structure with trans arrangement of the nitrogen and oxygen atoms.     

Formation of molecular radical cations of aliphatic tripeptides from their complexes with CuII(12-crown-4)

Molecular radical cations have proven to be difficult to generate from aliphatic peptides under electrospray ionization mass spectrometry (ESI-MS) conditions. For a family of small aliphatic peptides GGX, where X = G, A, P, I, L and V, these cations have been generated by electrospraying a mixture of Cu.2+, 12-crown-4 and GGX in methanol/water. GGX.+ is readily formed from the collision-induced dissociation (CID) of [CuII(12-crown-4)(GGX)].2+. The formation of these aliphatic peptide radical ions from these complexes, in cases where it is not possible from the corresponding complexes involving a series of amine ligands instead of 12-crown-4, is likely due to the second ionization energy of the [CuI(12-crown-4)(GGX)]+ complex being higher than that of the corresponding [CuI(amine)(GGX)]+ complex. Using these 12-crown-4 complexes, GGI can be differentiated from the isomeric GGL by comparing the CID spectra of their [a3 + H].+ ions.     

The association of hexacyanoferrate(II) ions and group IIA cations

A thermodynamic study has been made of the equilibrium $$M^{2 + } {\text{ + }}Fe(CN)_6^{4 - } {\text{ }} \rightleftharpoons {\text{ }}MFe(CN)_6^{2 - } $$ in dilute aqueous solution by a potentiometric method using a divalent-cation electrode where, M²⁺ is a group IIA cation. Ion pairing was found to be quite extensive: Thus, at 25°C, the association constants extrapolated to zero ionic strength were 5840, 4730, 4560, and 6080M ^?1 for M²⁺=Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively. In each case, ion pairing is slightly endothermic, the corresponding ΔH ^o values being 18.0, 13.0, 7.8, and 17.5 kJ-mole^?1. However, the values of ΔS ^o are larger and positive, thus favoring ion pairing: the values are 133, 115, 96, and 131 J^o-K^?1-mole^?1 for the same series of cations. There was also some indication of a small amount of ion triplet formation, M₂Fe(CN)₆. Comparisons were made with the predictions of the Fuoss theory, and these support the view that the bonding in the ion is largely electrostatic and not covalent.     

Homogeneous isotope exchange between copper(II) and bis(resacetophenone oxime)copper(II) complex

Isotope exchange behavior of bis(resacetophenone oxime)copper(II) complex with copper(II) in tri-n-butyl-phosphate and methanol medium has been studied. The studies were carried out at different temperatures varying the concentration of both metal ion and complex. The results show that the complex is labile in the kinetic sense. Increase in temperature increases the isotope exchange rate. The increase in concentration also results in enhancement of the rate of reaction.