Ruthenium coordination preferences in imidazole‐containing systems revealed by electrospray ionization mass spectrometry and molecular modeling: Possible cues for the surprising stability of the Ru (III)/tris (hydroxymethyl)‐aminomethane/imidazole complexes

Ruthenium is a platinoid that exhibits a range of unique chemical properties in solution, which are exploited in a variety of applications, including luminescent probes, anticancer therapies, and artificial photosynthesis. This paper focuses on a recently demonstrated ability of this metal in its +3 oxidation state to form highly stable complexes with tris (hydroxymethyl)aminomethane (H₂NC(CH₂OH)₃, Tris‐base or T) and imidazole (Im) ligands, where a single Ru^III cation is coordinated by two molecules of each T and Im. High‐resolution electrospray ionization mass spectrometry (ESI MS) is used to characterize Ru^III complexes formed by placing a Ru^II complex [(NH₃)₅Ru^IICl]Cl in a Tris buffer under aerobic conditions. The most abundant ionic species in ESI MS represent mononuclear complexes containing an oxidized form of the metal, ie, [X_nRu^IIIT₂ – 2H]⁺, where X could be an additional T (n = 1) or NH₃ (n = 0‐2). Di‐ and tri‐metal complexes also give rise to a series of abundant ions, with the highest mass ion representing a metal complex with an empirical formula Ru₃C₂₄O₂₁N₆H₆₆ (interpreted as cyclo(T₂RuO)₃, a cyclic oxo‐bridged structure, where the coordination sphere of each metal is completed by two T ligands). The empirical formulae of the binuclear species are consistent with the structures representing acyclic fragments of cyclo(T₂RuO)₃ with addition of various combinations of ammonia and dioxygen as ligands. Addition of histidine in large molar excess to this solution results in complete disassembly of poly‐nuclear complexes and gives rise to a variety of ionic species in the ESI mass spectrum with a general formula [Ru^IIIHis_kT_m (NH₃)_n ? 2H]⁺, where k = 0 to 2, m = 0 to 3, and n = 0 to 4. Ammonia adducts are present for all observed combinations of k and m, except k = m = 2, suggesting that [His₂Ru^IIIT₂ ? 2H]⁺ represents a complex with a fully completed coordination sphere. The observed cornucopia of Ru^III complexes formed in the presence of histidine is in stark contrast to the previously reported selective reactivity of imidazole, which interacts with the metal by preserving the RuT₂ core and giving rise to a single abundant ruthenium complex (represented by [Im₂Ru^IIIT₂ ? 2H]⁺ in ESI mass spectra). Surprisingly, the behavior of a hexa‐histidine peptide (HHHHHH) is similar to that of a single imidazole, rather than a single histidine amino acid: The RuT₂ core is preserved, with the following ionic species observed in ESI mass spectra: [HHHHHH·(Ru^IIIT₂)_m ? (3m‐1)H]⁺ (m = 1‐3). The remarkable selectivity of the imidazole interaction with the Ru^IIIT₂ core is rationalized using energetic considerations at the quantum mechanical level of theory.     

Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry

Dopamine [DA]⁺ (m/z 154), DA dimer [2DA‐H]⁺ (m/z 307) and DA quinone [DAQ]⁺ (m/z 152) are detected in positive ion mode electrospray ionization mass spectrometry (ESI MS) of dopamine in 50/1/49 (vol%) water/acetic acid/methanol. H/D exchange experiments support a covalent structure of DA dimer. Thus, ESI of DA may involve 1e^?, 1H⁺ oxidation processes followed by rapid radical dimerization. The DA quinone signal is low in ESI MS, which indicates a low efficiency of the 2e^?, 2H⁺ oxidation reaction. On‐line electrochemistry ESI MS (EC/ESI MS) with low electrochemical cell voltage floated on high ES voltage increases electrospray current and improves sensitivity for DA. The DA quinone signal increases and DA dimer signal decreases. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity of ESI and EC/ESI MS measurements. A DA quinone‐cysteine adduct [DAQ+Cys]⁺ was detected in solutions of DA with cysteine (Cys). ESI MS and EC/ESI MS indicate formation of the DA quinone‐cysteine adduct by 1e^? pathway. Oxidation pathways in ESI MS are relevant to biological reactivity of DA and Cys.     

One‐Electron Oxidation and Sensitivity of Uric Acid in On‐Line Electrochemistry and in Electrospray Ionization Mass Spectrometry

The sensitivity of detection of uric acid (H₂U) in positive ion mode electrospray ionization mass spectrometry (ESI MS) was enhanced by uric acid oxidation during electrospray ionization. With a carrier solution of pH 6.3>pK_a1=5.4 of H₂U, protonated unoxidized uric acid [H₂U+H]⁺ (m/z 169) was detected together with the protonated uric acid dimer [2H₂U+H]⁺ (m/z 337). The dimer likely forms by 1e^? oxidation of urate (HU^?) followed by rapid radical dimerization. A covalent structure of the dimer was verified by H/D exchange experiments. Efficiency of 2e^?, 2H⁺ oxidation of uric acid is low during ESI in pH 6.3 carrier solution and improves when a low on‐line electrochemical cell voltage is floated on the high voltage of the ES in on‐line electrochemistry ESI MS (EC/ESI MS). The intensity of the uric acid dimer decreases with an increase in the low applied voltage. In a carrier solution with 0.1 M KOH, pH 12.7>pK_a2=9.8 of H₂U, allantoin (Allnt) (MW 158.04), the final 2e^?, 2H⁺ oxidation product of uric acid, was detected as a potassium complex [K(Allnt)+K]⁺ (m/z 235) and the [2H₂U+H]⁺ dimer was not detected. In direct ESI MS analysis of 1000‐fold diluted urine [NaHU+H]⁺ (pK_sp NaHU=4.6) was detected in 40/60 (vol%) water/methanol, 1 mM NH₄Ac, pH ca. 6.3 carrier solution. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity in ESI and EC/ESI MS measurements of uric acid.     

Gas‐phase dissociation of ionic liquid aggregates studied by electrospray ionisation mass spectrometry and energy‐variable collision induced dissociation

Positive singly charged ionic liquid aggregates [(C_nmim)_m+1(BF₄)_m]⁺ (mim = 3‐methylimidazolium; n = 2, 4, 8 and 10) and [(C₄mim)_m+1(A)_m]⁺ (A = Cl⁻, BF₄⁻, PF₆⁻, CF₃SO₃⁻ and (CF₃SO₂)₂N⁻) were investigated by electrospray ionisation mass spectrometry and energy‐variable collision induced dissociation. The electrospray ionisation mass spectra (ESI‐MS) showed the formation of an aggregate with extra stability for m = 4 for all the ionic liquids with the exception of [C₄mim][CF₃SO₃]. ESI‐MS‐MS and breakdown curves of aggregate ions showed that their dissociation occurred by loss of neutral species ([C_nmim][A])_a with a ≥ 1. Variable‐energy collision induced dissociation of each aggregate from m = 1 to m = 8 for all the ionic liquids studied enabled the determination of E_{cm, 1/2} values, whose variation with m showed that the monomers were always kinetically much more stable than the larger aggregates, independently of the nature of cation and anion. The centre‐of‐mass energy values correlate well with literature data on ionic volumes and interaction and hydrogen bond energies. Copyright © 2008 John Wiley & Sons, Ltd.     

Elucidating Factors Manipulated the Formation of Multiply Charged Protein Homomultimeric Complexes by Electrospray Ionization

Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)_mⁿ⁺ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)_mⁿ⁺ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH₄OH also promotes the formation of (Cyt c)_mⁿ⁺. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)_mⁿ⁺ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS.     

Metal displacement and stoichiometry of protein‐metal complexes under native conditions using capillary electrophoresis/mass spectrometry

Increases in the study of protein‐metal complexes, as well as in metal displacement in protein‐metal complexes under native conditions for optimum catalytic properties in drug research and catalyst design, demands a separation/detection technology that can accurately measure metal displacement and stoichiometry in protein‐metal complexes. Both nuclear magnetic resonance (NMR) and X‐ray diffraction techniques have been used for this purpose; however, these techniques lack sensitivity. Electrospray ionization mass spectrometry (ESI‐MS) using direct infusion offers higher sensitivity than the former techniques and provides molecular distribution of various protein‐metal complexes. However, since protein‐metal complexes under native conditions usually are dissolved in salt solutions, their direct ESI‐MS analysis requires off‐line sample clean‐up prior to MS analysis to avoid sample suppression during ESI. Moreover, direct infusion of the salty solution promotes non‐specific salt adduct formation by the protein‐metal complexes under ESI‐MS, which complicates the identification and stoichiometry measurements of the protein‐metal complexes. Because of the high mass of protein‐metal complexes and lack of sufficient resolution by most mass spectrometers to separate non‐specific from specific metal‐protein complexes, accurate protein‐metal stoichiometry measurements require some form of sample clean up prior to ESI‐MS analysis. In this study, we demonstrate that capillary electrophoresis/electrospray ionization in conjunction with a medium‐resolution (～10 000) mass spectrometer is an efficient and fast method for the measurement of the stoichiometry of the protein‐metal complexes under physiological conditions (pH ～7). The metal displacement of Co²⁺ to Cd²⁺, two metal ions necessary for activation in the monomeric AHL lactonase produced by B. thuringiensis, has been used as a proof of concept. Copyright © 2010 John Wiley & Sons, Ltd.     

Complexation of late transition metal(II) ions (M = Co,Ni, Cu,and Zn) by a macrocyclic thiacrown ether studied by means of electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI‐MS) is used to probe the metal‐binding selectivity of a macrocyclic thiacrown ether (C₄₄H₃₂S₂₀) towards Co^II, Ni^II, Cu^II, and Zn^II. In homogeneous 1:1 v/v methanol/dichloromethane solutions, it is found that the thia ligand very selectively binds traces of copper even in the presence of an excess of the other metal ions. The large selectivity is ascribed to the redox‐active nature of copper which enables a reduction from Cu^II to Cu^I, occurring upon ESI‐MS, whereas Co^II, Ni^II and Zn^II cannot undergo similar redox reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of pH on the Metabolism of Aconitine under Rat Intestinal Bacteria and Analysis of Metabolites Using HPLC/MS-MSn Technique

A semi‐quantitative method of mass spectrometry (MS) has been described for the analysis of metabolites of aconitine by rat intestinal bacteria at different pH. At pH 7.0, the rat intestinal bacteria exhibit optimal activity for the metabolism of aconitine. A high‐performance liquid chromatography‐electrospray ionization multiple‐stage mass spectrometry (HPLC/ESI‐MSⁿ) method has been applied to investigate the characteristic product ions of metabolites. Then, the logical fragmentation pathways of metabolites have been proposed. By comparing the retention time (t_R) of HPLC and the ESI‐MSⁿ data with the data of standard compounds and reports from literature, ten metabolites have been identified and a distinctive metabolite (15‐deoxyaconitine) has been deduced first time. The experimental results demonstrate that HPLC/ESI‐MSⁿ is a specific and useful method for the identification of metabolites of aconitine. Also, in the present paper, the HPLC‐MS method was introduced to determine the synthetical metabolite prior to the study of the toxicity by the method of Bliss.     

LC/ESI‐MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C₁₃, C₁₄ and C₁₅ surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]⁺ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]⁺ at m/z 1478 and 1506 corresponding to C₁₇ fengycin A and C₁₇ fengycin B, respectively. Other homologues (C₁₄ to C₁₆) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization and quantification of 10‐hydroxycamptothecine in Camptotheca acuminate and its medicinal preparation by liquid chromatography–ion trap mass spectrometry

A rapid and sensitive method for the identification and quantification of 10‐hydroxycamptothecine (HCPT) in Camptotheca acuminata Decne is described. The HCPT standard solution was directly infused into the ion trap mass spectrometers (IT/MS) for collecting the MSⁿ spectra. The electrospray ionization (ESI) mass spectral fragmentation pathway of HCPT was proposed and the ESI‐MSⁿ fragmentation behavior of HCPT was deduced in detail. The major fragment ions of HCPT were confirmed by MSⁿ in both negative ion and positive ion mode. The possible main cleavage pathway of fragment ions was studied. Quantification of HCPT was assigned in negative‐ion mode at a product ion at m/z 363 → 319 by LC‐MS. The LC‐MS method was validated for linearity, sensitivity, accuracy and precision, and then used to determine the content of the HCPT. Lastly, the LC‐MS method was successfully applied to determine HCPT in real samples of Camptotheca acuminate Decne and its medicinal preparation in the first time. Copyright © 2013 John Wiley & Sons, Ltd.     

甾体磷酰胺类缀合物在电喷雾质谱中的裂解特征

Novel steroidal phosphoramidate conjugates of 3'-azido-2',3'-dideoxythymidine(AZT)and amino acid esterswere synthesized and determined by positive and negative ion electrospray ionization mass spectrometry.The MSfragmentation behaviors of the steroidal phosphoramidate conjugates have been investigated in conjunction withtandem mass spectrometry of ESI-MS/MS.There were three characteristic fragment ions in the positive ion ESImass spectra,which were the Na adduct ions with loss of steroidal moiety,amino acid ester moiety from pseudomolecular ion(M Na)~ ,and the phosphoamino acid methyl ester Na adduct ion by α-cleavage of the phosphora-midate respectively.The main fragment ions in negative ion ESI mass spectra were the ion(M-HN_3)~-,the ion(M-AZT-H)~-,and the ion(M-steroidal moiety-H)~- besides the pseudo molecular ion(M-H)~-.Thefragmentation patterns did not depend on the attached amino acid ester moiety.     

Capillary electrophoresis/mass spectrometry for the separation and characterization of bovine Cu,Zn‐superoxide dismutase

The native form of Cu,Zn‐superoxide dismutase (SOD‐1) is a homodimer that coordinates one Cu²⁺ and one Zn²⁺ per monomer. Cu²⁺ and Zn²⁺ ions play crucial roles in enzyme activity and structural stability, respectively. In addition, dimer formation is essential for SOD‐1 functionality, and in humans several SOD‐1 mutant isoforms have been associated with certain types of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder. In this paper we used capillary electrophoresis and mass spectrometry to study the different structures of bovine SOD‐1. The metal ions of the native enzyme (Cu₂,Zn₂‐dimer SOD‐1) were released in acidic medium in order to obtain apo‐SOD‐1, which is a monomer. Both substances were analyzed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) and capillary electrophoresis with ultraviolet and electrospray ionization mass spectrometry detection (CE/UV and CE/ESI‐MS, respectively). With MALDI‐TOF‐MS, using matrices of sinapinic acid (SA) or 2,5‐dihydroxybenzoic acid (DHB) with or without trifluoroacetic acid (TFA), similar mass spectra were obtained for the metalated and non‐metalated samples. In both cases, an average molecular mass corresponding to the apo‐monomer SOD‐1 was calculated. This finding indicated that the metals were released from the Cu₂,Zn₂‐dimer SOD‐1 during sample preparation or ionization. For CE/UV and CE/ESI‐MS, two background electrolytes (BGEs) potentially compatible with ESI‐MS detection were used, namely 1 M of acetic acid (pH 2.3) and 10 mM of ammonium acetate (pH 7.3). Using a sheath liquid of 2‐propanol/water (60:40 v/v), with or without 0.1% v/v of formic acid, CE/ESI‐MS sensitivity was enhanced when the acidic BGE and the acidic sheath liquid were used. However, the electrophoretic profiles and the mass spectra obtained suggested that the metals of Cu₂,Zn₂‐dimer SOD‐1 were released, which generated the apo‐monomer during the electrophoretic separation. The neutral BGE provided enhanced conditions for the detection of the native enzyme. The differences between the mass spectra obtained for the Cu₂,Zn₂‐dimer and the apo‐monomer forms were significant and the presence of formic acid in the sheath liquid affected only sensitivity. Our results highlight the importance of selecting appropriate non‐denaturing separation and detection conditions to obtain reliable structural information about non‐covalent protein complexes by CE/ESI‐MS. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies of gas-phase reactions of cationic iron complexes of 2-pyrimidinyloxy-N-arylbenzylamines by electrospray ionization tandem mass spectrometry

Electrospray ionization triple quadrupole mass spectrometry (ESI‐TSQ‐MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICR‐MS) were used to investigate the interesting gas‐phase reactions of the cationic iron (Fe) complexes of 2‐pyrimidinyloxy‐N‐arylbenzylamines (1–6), which are generated by ESI when mixing their methanolic solutions. Further studies of these Fe complexes by collision‐induced dissociation (CID) show that Fe(III) complexes undergo an interesting gas‐phase single electron transfer (SET) reaction to give 1^?+–6^?+,with loss of neutral FeCl₂, whereas Fe(II) can catalyze gas‐phase Smiles rearrangement reactions of compounds 1–6. By using different Fe(II)X₂ salts (X = Cl or Br) with a set of reactants, the role of the counterion (X^?) and the structure effect of the reactants on Fe(II)‐catalyzed gas‐phase Smiles rearrangement reactions are studied. Evidence obtained from by TSQ‐MS and FTICR‐MS experiments, hydrogen/deuterium (H/D) exchange experiments and theoretical computations supported some unique gas‐phase chemistries initiated by introduction of Fe(II) into 1. Importantly, by comparing the distinct gas‐phase reaction results of the cationic Fe(III) complexes with those of Fe(II) complexes, the charge state effects of iron on the gas‐phase chemistries of Fe complexes are revealed. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and Characterization of a Series of New Asymmetric Salphen Mono- and Binuclear Metal Complexes

Two novel asymmetric salen ligands H₂L¹ [N‐phenyl‐N‐(2‐hydroxy‐5‐methylphenyl)‐N′‐(2‐hydroxy‐3‐meth‐ oxylphenyl)‐o‐phenyldiamine] and H₂L² [N‐phenyl‐N‐(2‐hydroxy‐5‐chlorophenyl)‐N′‐(2‐hydroxy‐3‐methoxyl‐ phenyl)‐o‐phenyldiamine] and their metal complexes MLⁿ (M=Zn, Co, Ni, Cu; n=1, 2) have been prepared and characterized by elemental analyses, ¹H NMR, ESI‐MS, FT‐IR and UV‐Vis spectra. In particular, the complex ZnL¹, the binuclear monosalphen complex, was synthesized and studied in detail using ¹H NMR and ESI‐MS techniques. For other metal complexes under the same reaction conditions, only mononuclear complexes were obtained. The results are relevant to both the metal ions and the structure of ligands.     

Studies on Triterpenoids and Flavones in Glycyrrhiza uralensis Fisch. By HPLC-ESI-MSn and FT-ICR-MSn

应用高效液相色谱质谱联用方法(HPLC-ESI-MSn)研究了甘草提取物中的七种化合物,四种三萜类化合物和三种黄酮类化合物。通过多极串联质谱(ESI-MSn)和多极串联傅里叶变换回旋共振质谱(FT-ICR-MSn)法研究了它们的碎裂规律。通过比较保留时间和质谱数据对上述七种化合物进行了归属,并阐述了其可能的质谱裂解途径。以上结果显示ESI-MSn和FT-ICR-MSn是非常有效的分析三萜类化合物和黄酮类化合物结构的工具。     

Atomically Precise Alloy Nanoclusters

Metal nanoclusters (NCs) have a particle size of about one nanometer, which makes them the smallest unit that can give a function to a substance. In addition, metal NCs possess physical and chemical properties that are different from those of the corresponding bulk metals. Metal NCs with such characteristics are expected to be important for use in nanotechnology. Research on the precise synthesis of metal NCs and elucidation of their physical/chemical properties and functions is being actively conducted. When metal NCs are alloyed, it is possible to obtain further various electronic and geometrical structures and functions. Thus, research on alloy NCs has become a hot topic in the study of metal NCs and the number of publications on alloy NCs has increased explosively in recent years. Such publications have provided much insight into the effects of alloying on the electronic structure and function of metal NCs. However, the rapid increase in knowledge has made it difficult for researchers (especially those new to the field) to grasp all of it. Therefore, in this review, we summarize the reported chemical composition, geometrical structure, electronic structure, and physical and chemical properties of Au_n−xM_x(SR)_m, Ag_n−xM_x(SR)_m, Au_n−xM_x(PR₃)_l(SR)_m, and Ag_n−xM_x(PR₃)_l(SR)_m (Au=gold, Ag=silver, M=heteroatom, PR₃=phosphine, and SR=thiolate) NCs. This review is expected to help researchers understand the characteristics of alloy NCs and lead to clear design guidelines to develop new alloy NCs with intended functions.     

Gas‐phase fragmentation of protonated C60‐pyrimidine derivatives

Electrospray ionization mass spectrometry/mass spectrometry (ESI/MS/MS) and multiple stage mass spectrometry (MSⁿ, n > 2) were used in the positive ion mode, with two different types of mass spectrometers, a quadrupole time‐of‐flight and an ion trap, to characterize two sets of different types of C₆₀‐aminopyrimidine exohedral derivatives. In one set, the pyrimidine moiety bears an amino acid methyl ester residue, and in the other the pyrimidine ring is part of a nucleoside‐type moiety, the latter existing as two separated diastereoisomers. We have found that retro‐cycloaddition processes occur for the closed shell protonated species formed by electrospraying C₆₀ derivatives synthesized by Diels–Alder reactions, whereas for the C₆₀ derivatives synthesized via 1,3‐dipolar cycloadditions, these processes did not occur. Formation of diagnostic ions allowed the differentiation between the two groups of fullerene derivatives, and between the diastereoisomers of C₆₀ derivatives with a nucleoside‐type moiety. In general, the fragmentation processes are strongly dependent on the protonation sites and on the structure of the exohedral moieties. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural characterization of a vegetable oil‐based polyol through liquid chromatography multistage mass spectrometry

A commercial vegetable oil‐based polyol for rigid polyurethane foams has been characterized by liquid chromatography‐electrospray ionization‐quadrupole ion trap mass spectrometry (LC‐ESI‐QIT‐MS). The absolute molecular weight (MW = 960) was measured by gel permeation chromatography (GPC) equipped with both refractive index (RI) detector and static laser light‐scattering detector (SLSD), which allowed further analysis by LC‐MS. The oligo‐polyol mixture was first separated in two elutes and then investigated by a deep multistage mass spectrometry (MSⁿ) study and completed using NMR. The major constituents identified were regioisomers of propoxylated sucrose (n_PO = 6–12), and the related esters of C16:0, C18:1, and C18:2 fatty acids had a mass ratio of 6:3:1. A comparison of fatty acids composition between the sample and palm oil demonstrated that the sample was initially prepared from the mixture of sucrose and palm oil by direct propoxylation. The MSⁿ fragmentation studies validated the structure of propoxylated sucrose and the related fatty acids derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 255–262     

Synthesis,alkali metal picrate extraction,and alkali metal cation binding selectivities of some new cage‐annulated polyoxamacrocyclic crown ethers

Five new cage‐annulated crown ethers, i.e., 4a, 4b, 6b, 11a, and 11b, have been synthesized and their respective alkali metal picrate extraction profiles along with that of a previously synthesized host molecule, 6a, have been obtained. These results are compared with the corresponding results obtained for electrospray ionization mass spectrometric (ESI‐MS) measurements of relative binding selectivities displayed by the same hosts toward a series of alkali metal chlorides. Among the crown‐5 hosts studied, 6a displays enhanced avidity toward complexation with K⁺ picrate in liquid‐liquid extraction experiments. Among the three crown‐6 hosts, 4b proved to be the best alkali metal picrate extractant and displayed significant levels of avidity toward complexation with the larger alkali metal cations (i.e., K⁺, Rb⁺, and Cs⁺). The trends in the picrate extraction and the ESI‐MS results obtained herein show several notable similarities and some differences. The similarities generally stem from size‐selective binding properties that are intrinsic to the different cavity sizes of the cage‐annulated macrocycles, whereas the differences reflect the important influence of solvation effects on the binding properties of the macrocycles.     

MassBank: a public repository for sharing mass spectral data for life sciences

MassBank is the first public repository of mass spectra of small chemical compounds for life sciences (<3000 Da). The database contains 605 electron‐ionization mass spectrometry(EI‐MS), 137 fast atom bombardment MS and 9276 electrospray ionization (ESI)‐MSⁿ data of 2337 authentic compounds of metabolites, 11 545 EI‐MS and 834 other‐MS data of 10 286 volatile natural and synthetic compounds, and 3045 ESI‐MS² data of 679 synthetic drugs contributed by 16 research groups (January 2010). ESI‐MS² data were analyzed under nonstandardized, independent experimental conditions. MassBank is a distributed database. Each research group provides data from its own MassBank data servers distributed on the Internet. MassBank users can access either all of the MassBank data or a subset of the data by specifying one or more experimental conditions. In a spectral search to retrieve mass spectra similar to a query mass spectrum, the similarity score is calculated by a weighted cosine correlation in which weighting exponents on peak intensity and the mass‐to‐charge ratio are optimized to the ESI‐MS² data. MassBank also provides a merged spectrum for each compound prepared by merging the analyzed ESI‐MS² data on an identical compound under different collision‐induced dissociation conditions. Data merging has significantly improved the precision of the identification of a chemical compound by 21–23% at a similarity score of 0.6. Thus, MassBank is useful for the identification of chemical compounds and the publication of experimental data. Copyright © 2010 John Wiley & Sons, Ltd.