Complexation of diazaperylene and bisisoquinoline with transition metal ions in the gas phase studied by electrospray ionization mass spectrometry

The complex formation of the ligands 1,12-diazaperylene (dap), 1,1'-bisisoquinoline (bis), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) with transition metal ions (M = Fe, Co, Ni, Cu, Zn, Ru, Os, Re, Pd, Pt, Ag and Cd) in the gas phase has been studied by electrospray ionization mass spectrometry. With the exception of Ru, Os, Fe, Ni and Cu, singly charged complexes [MLn](+) (n = 1,2) were observed. The complexes of dap and bis with Ru, Os, Fe and Ni ions, and the mixed ligand complexes with bpy and phen, are preferably of the doubly charged type [ML3]2+. In addition, collision-induced dissociation (CID) measurements were employed to evaluate the relative stabilities of these complexes. The CID experiments of mixed-ligand complexes which contain both dap and phen or dap and bpy exhibit preferential elimination of bpy, indicating that bpy is a weaker ligand than phen and dap.     

Combined effect of transition metal phosphide (MxPy,M = Ni,Co, and Cu) and intumescent flame retardant system on polypropylene

In this paper, three typical transition metal phosphide nanocrystallines (M_xP_y, M = Ni, Co, and Cu) were synthesized by a novel hydrothermal method, and their structures were characterized by X‐ray diffraction and transmission electron microscopy. Then they were used as synergistic agents with intumescent flame retardant (IFR) to improve the fire safety of polypropylene (PP). Thermogravimetry analysis (TGA) results indicated that the introduction of these synergists could improve the thermal stability and char yields of the PP/IFR system. The addition of 2 wt.% Ni₁₂P₅ and Co₂P increased the limiting oxygen index values of the PP/IFR system significantly from 28% to 36% and 34%, respectively, and the system could reach V‐0 rating. The cone calorimeter test results revealed that the combination of transition metal phosphide nanocrystallines and IFR system could result in excellent flame retardancy. The incorporation of these synergists into IFR led to a remarkable influence on charring of PP composites as revealed by TGA and cone data. The morphological structure of char residue proved that the addition of transition metal phosphide nanocrystallines was capable of forming a compact and homogeneous char on the surface, which turned out to be of most importance for the flame retardancy. Thermogravimetric analysis/infrared spectrometry results indicated that the flame retardant mechanism of PP/IFR/M_xP_y (M = Ni, Co, and Cu) system was in the condensed phase rather than in the gas phase. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural characterization of alachlor complexes with transition metal ions by electrospray ionization tandem mass spectrometry

Electrospray ionization mass (ESI-MS) spectrometry was used to investigate the nature of metal complexes of alachlor and their dissociations on activation. Ions of the first row transition metal series were employed to react with alachlor and the products were subjected to collision-induced dissociation (CID) for further structural characterization. The formation of diverse complex ions including doubly charged metal/alachlor complexes; [3L + M]²⁺ and [4L + M]²⁺ (L: alachlor and M: transition metal ions) were observed depending on the experimental conditions including the tube lens offset voltage (TLOV) and relative concentrations of alachlor and transition metal ions. It is clear that complexation with transition metal ions alters the reactive site of alachlor, promoting the loss of chlorine over the loss of CH₃OH that is the major reaction pathway in uncomplexed system. Direct elimination of chlorine from alachlor molecule was confirmed by the use of MnBr₂ instead of MnCl₂. These evidences clearly illustrate the catalytic activities of the metal ions through insertion mechanism. The function of transition metal ions in complexation was emphasized comparing the fragmentation patterns with those of protonated molecule. A change in the oxidation state of copper from + 2 to + 1 during the dissociation of metal complex was observed in company with elimination of radicals which is specific for the copper complex ions.     

Serine-phosphoric acid cluster ions studied by electrospray ionization and tandem mass spectrometry

More than 310 kinds of cluster ions of S(m) P(n) H(k) (k+) are observed in a single ESI mass spectrum of a mixed solution of serine and phosphoric acid. Some typical cluster ions are selected, activated by collision in a FT ICR cell, and the dissociation pathways were deduced in detail. For large singly protonated ions, the collisions cause the ejection of subunits of serine or phosphoric acid subsequently producing the ions of S(2) P(4) H(1) (1+) , which can be further dissociated by the loss of phosphoric acid molecules in turn and form the protonated serine dimer and monomer. However, for the doubly protonated ions, the dissociation pathways change from the loss of a protonated serine dimer for the ions of S(7) P(9) H(2) (2+) to the neutral loss of H(3) PO(4) for the ions of S(7) P(12) H(2) (2+) or the neutral loss of serine or H(3) PO(4) for the larger clusters, indicating the effect of cluster sizes on the process of dissociation. The structure of S(2) P(4) H(1) (1+) is suggested based on B3LYP/6-31G(d,p) calculations. The diversity and structural orderliness of the hetero-cluster ions are mainly attributed to the network of hydrogen bonds inside the cluster ions and the extraordinary amphotericity of the components.     

Tandem mass spectrometry of metal nitrate negative ions produced by electrospray ionization

M(NO(3))(x)(-) ions are generated by electrospray ionization (ESI) of metal solutions in nitric acid in negative ion mode. Collision-induced reactions of these ions are monitored in a tandem mass spectrometer (MS) of quadrupole-octopole-quadrupole (QoQ) geometry. For Group 1 and 2 elements, the M(NO(3))(x)(-) ions dissociate into NO(3)(-) and neutral metal nitrate molecules. These elements also form some M(x)(NO(3))x+1- clusters, especially Li(+). Metal nitrate ions from transition elements and Group 13 elements fragment into oxo products and also undergo internal electron transfer to leave the M atom in a lower oxidation state. To calibrate the collision energy, the dissociation energy of O-NO(2)(-) is found to be 5.55 eV, about 0.76 eV lower than a value derived from thermochemistry. The product ions from Fe(NO(3))(4)(-) ions have low formation thresholds of only 0.5 to 2 eV.     

Complexation of transition metals by 3-azidopropionitrile. An electrospray ionization mass spectrometry study

Most complexes of azides and transition metals involve the N(3)(-) azide anion as a ligand other than an organic azide. Complexes of organic azides with metals are involved in biological applications and in the deposition of nitrenes on metal surfaces, producing nitride layers for semi-conductors preparation; this makes the study of these interactions an important issue. This work describes a study of the complexation of nickel and cobalt by 3-azidopropionitrile by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of NiCl(2) and CoCl(2) in methanol/water. In the case of nickel, other NiX(2) salts were investigated (where X = Br or NO(3)) and other solvents were also studied (notably ethanol/water). All complexes detected were single positively charged, with various stoichiometries, some resulted from the fragmentation of the ligand, the loss of N(2), and HCN being quite common. The most abundant cations observed were [Ni(II)AzAzX](+), where X = Cl, Br, NO(3). Some of the complexes showed solvation with methanol/ethanol/water. Metal reduction was observed in complexes where a radical was lost, resulting from the homolytic cleavage of a metal-nitrogen bond. Collision induced dissociation (CID) experiments followed by tandem mass spectrometry (MS-MS) analysis were not absolutely conclusive about the coordination site. However, terminal ions observed from the fragmentation routes were explained by a proposed gas-phase mechanism. Density functional theory calculations were carried out and provided structures for some complexes, pointing to the possibility of 3-azidopropionitrile acting as a mono- or a bidentate ligand.     

Formation of positive cluster ions LinBr (n = 2–7) and ionization energies studied by thermal ionization mass spectrometry

Clusters of the type Li_nX (X = halides) can be considered as potential building blocks of cluster‐assembly materials. In this work, Li_nBr (n = 2–7) clusters were obtained by a thermal ionization source of modified design and selected by a magnetic sector mass spectrometer. Positive ions of the Li_nBr (n = 4–7) cluster were detected for the first time. The order of ion intensities was Li₂Br⁺ > Li₄Br⁺ > Li₅Br⁺ > Li₆Br⁺ > Li₃Br⁺. The ionization energies (IEs) were measured and found to be 3.95 ± 0.20 eV for Li₂Br, 3.92 ± 0.20 eV for Li₃Br, 3.93 ± 0.20 eV for Li₄Br, 4.08 ± 0.20 eV for Li₅Br, 4.14 ± 0.20 eV for Li₆Br and 4.19 ± 0.20 eV for Li₇Br. All of these clusters have a much lower ionization potential than that of the lithium atom, so they belong to the superalkali class. The IEs of Li_nBr (n = 2–4) are slightly lower than those in the corresponding small Li_n or Li_nH clusters, whereas the IEs of Li_nBr are very similar to those of Li_n or Li_nH for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of Li_nBr (n = 2–7) clusters (because their ions are thermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Complexation of silver and co-recovered metals with novel aza-crown ether macrocycles by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is used to evaluate the metal binding selectivities of an array of novel caged macrocycles for silver, gold, copper, nickel, zinc, iron, lead, manganese and alkali metal ions. It is found that five of the new compounds display silver selectivity, and their relative affinities for various metals depend on the type, number, and arrangement of heteroatoms (N, O), the cavity size, and the presence of aromatic substituents. Alkali metal cation binding studies are used to evaluate the size-selectivities of the cavities of the macrocycles. Electronic structure calculation by B3LYP density function theory methods were used to model the metal complexes. The presence of nitrogen atoms in the macrocyclic ring is essential for silver selectivity over other transition metals and alkali metal ions, and the presence of aromatic groups also enhances silver avidity. Macrocycle 3, a triaza-18-crown-6 analog modified with two phenyl groups and a cage group, is capable of selective extraction of Ag+ from aqueous solutions in the presence of other transition metal ions and the most common alkali and alkaline earth metal ions.     

Investigation on C2-ceramide complexes with transition metal ions using electrospray ionization tandem mass spectrometry

Electrospray ionization-tandem mass spectrometry (ESI-MS/MS) is applied for the investigation of C(2)-ceramide complexes with transition metal ions. Ceramide plays an important role in the regulation of various signaling pathways leading to proliferation, differentiation or apoptotic cell death. The formation and fragmentation of doubly charged cluster ions as well as singly charged cluster ions of C(2)-ceramide with transition metal ions (Mn(2+), Fe(2+), Co(2+) and Ni(2+)) are studied by ESI-MS/MS in the positive mode. Tube lens offset voltage and concentrations of C(2)-ceramide and transition metals are optimized to determine the best conditions for generating doubly charged cluster ions. The fragmentation pathways of metal ion complexes with C(2)-ceramide and the compositions of these complexes are determined by collision induced dissociation (CID). All transition metal ions (Mn(2+), Fe(2+), Co(2+) and Ni(2+) except Cu(2+)) shows similar complexation with C(2) ceramide. The unique complexation behavior of copper(II) is responsible for the different geometry of the complexes and relatively lower affinity of ceramide to copper(II) than those to other transition metals.     

Site-specifically cleavage of oxidized insulin B chain with Zn（Ⅱ） ion studied by electrospray ionization mass spectrometry

The electrospray ionization mass spectrometry and tandem mass spectrometry investigation showed that the binding sites of Zn^2＋ with oxidized insulin B chain are His 5, His 10, and Arg 22, which lead to the selective cleavages of the peptide bonds at Ash 3- Gin 4, His 5-Leu 6, Gly 8-Ser 9, and Glu 21-Arg 22 of oxidized insulin B chain.     

Interaction of angiotensin peptides and zinc metal ions probed by electrospray ionization mass spectrometry

Electrospray ionization-tandem mass spectrometry experiments were used to provide evidence regarding the sites of interactions between zinc metal ions and angiotensin peptides. The electrospray ionization mass spectra of histidine-containing human angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) and angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) in the presence of zinc show abundant multiply charged ions for the zinc-attached peptide [M + aZn²⁺ +(c ? 2a)H⁺]^c+, where a = 1, 2 and c is charge. From collisionally activated dissociation experiments, with both low energy (triple quadrupole mass spectrometry) and high energy collisions (linked scan at constant B/E with a double focusing instrument) of the [M + Zn]²⁺ and [M + Zn + H]³⁺ ions for angiotensin II, a [b ₆ + Zn]²⁺ species is produced as the most abundant product ion, suggesting that the zinc interaction site is in the vicinity of the His⁶ residue. Additionally, tandem mass spectra from the zinc-attached ions for angiotensin I show abundant [b ₆ + Zn]²⁺ and [b ₉ + Zn]²⁺ products, providing evidence that both His⁶ and His⁹ are involved in zinc coordination.     

Complexation between the fungicide tebuconazole and copper(II) probed by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the complex formation between tebuconazole (1) and copper(II) salts, which both are commonly used fungicides in agriculture. Experiments with model solutions containing 1 and CuCl(2) reveal the initial formation of the copper(II) species [(1)CuCl](+) and [(1)(2)CuCl](+) which undergo reduction to the corresponding copper(I) ions [(1)Cu](+) and [(1)(2)Cu](+) under more drastic ionization conditions in the ESI source. In additional experiments, copper/tebuconazole complexes were also detected in samples made from soil solutions of various origin and different amount of mineralization. The direct sampling of such solutions via ESI-MS is thus potentially useful for understanding of the interactions between copper(II) salts and tebuconazole in environmental samples.     

Lithium and transition metal ions enable low energy collision-induced dissociation of polyglycols in electrospray ionization mass spectrometry

Electrospray ionization tandem mass spectrometry has the potential to be widely used as a tool for polymer structural characterization. However, the backbones or molecular chains of many industrial polymers including functional polyglycols are often difficult to dissociate in tandem mass spectrometers using low energy collision-induced dissociation (CID). We present a method that uses Li+ and transition metal ions such as Ag+ as the cationization reagents for electrospray ionization in an ion trap mass spectrometer. It is shown that lithium and transition metal polyglycol adduct ions can be readily fragmented with low energy CID. Comparative results from different cationization reagents in their abilities of producing both MS spectra and CID spectra are shown. This method opens the possibility of using conventional and readily available low energy CID tandem MS to study polyglycol structures.     

Living star polymer formation (RAFT) studied via electrospray ionization mass spectrometry

A mass spectrometry analysis has been performed on complex architecture polymeric material produced during reversible addition fragmentation chain transfer (RAFT) polymerizations yielding star polymers. Para‐acetoxystyrene (AcOSty) has been polymerized at 60 °C, using azobisisobutyronitrile (AIBN) as the thermally decomposing initiator, in the presence of the R‐group approach tetrafunctional RAFT agent (1,2,4,5‐tetrakis‐(2‐phenyl‐thioacetyl‐sulfanylmethyl)‐benzene). In addition to ideal star material, a variety of products unique to this mode of polymerization have been identified. These include star–star couples, stars terminated with initiator fragments, star–star couples terminated with initiator fragments and linear polymers, supporting the notion that these species are responsible for the structured molecular‐weight distributions measured for these systems when analyzed via gel permeation chromatography. The analysis begins with a study of AcOSty polymerizing (i) in the absence of any mediating agent and (ii) in the presence of a monofunctional RAFT agent, revealing the mode of termination of propagating poly(AcOSty) radicals as combination and that some ionization biases exist among variants of poly (AcOSty). The interpretation of the mass spectrometry data has been aided by a novel kinetic model of star polymerizations, allowing the rationalization of experimental observations with theoretical expectations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1873–1892, 2008