电喷雾电离质谱在化学中应用新进展

电喷雾电离质谱(ESI-MS)是本世纪发展的非常重要的质谱,具有无碎片的特点,可分析检测非挥发性的、极性的、热不稳定的化合物。评述了ESI-MS在富勒烯化学、无机配合物、簇合物、有机化学反应,金属有机化合物及超分子化学中的应用进展。     

Optimization of information content in a mass spectrometry based flow-chemistry system by investigating different ionization approaches

Current development in catalyst discovery includes combinatorial synthesis methods for the rapid generation of compound libraries combined with high-throughput performance-screening methods to determine the associated activities. Of these novel methodologies, mass spectrometry (MS) based flow chemistry methods are especially attractive due to the ability to combine sensitive detection of the formed reaction product with identification of introduced catalyst complexes. Recently, such a mass spectrometry based continuous-flow reaction detection system was utilized to screen silver-adducted ferrocenyl bidentate catalyst complexes for activity in a multicomponent synthesis of a substituted 2-imidazoline. Here, we determine the merits of different ionization approaches by studying the combination of sensitive detection of product formation in the continuous-flow system with the ability to simultaneous characterize the introduced [ferrocenyl bidentate+Ag]⁺ catalyst complexes. To this end, we study the ionization characteristics of electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), no-discharge APCI, dual ESI/APCI, and dual APCI/no-discharge APCI. Finally, we investigated the application potential of the different ionization approaches by the investigation of ferrocenyl bidentate catalyst complex responses in different solvents.     

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.     

Chemical Conversion of Hardly Ionizable Rhenium Aryl Chlorocomplexes with p-Substituted Anilines

Fast and selective analytical methods help to ensure the chemical identity and desired purity of the prepared complexes before their medical application, and play an indispensable role in clinical practice. Mass spectrometry, despite some limitations, is an integral part of these methods. In the context of mass spectrometry, specific problems arise with the low ionization efficiency of particular analytes. Chemical derivatization was used as one of the most effective methods to improve the analyte’s response and separation characteristics. The Schotten–Baumann reaction was successfully adapted for the derivatization of ESI hardly ionizable Re(VII) bis(catechol) oxochlorocomplex. Various alkyl and halogen p-substituted anilines as possible derivatization agents were tested. Unlike the starting complex, the reaction products were easily ionizable in electrospray, providing structurally characteristic molecular and fragment anions. DFT computer modeling, which proposed significant conformation changes of prepared complexes within their deprotonation, proved to have a close link to MS spectra. High-resolution MS and MS/MS measurements complemented with collision-induced dissociation experiments for detailed specification of prepared complexes’ fragmentation pathways were used. The specified fragmentation schemes were analogous for all studied derivatives, with an exception for [Re(O)(Cat)₂PIPA].     

Collision-induced dissociation of three groups of hydroxamate siderophores: ferrioxamines, ferrichromes and coprogens/fusigens

The behaviour of a series of hydroxamate siderophores--microbially produced iron complexes - was investigated using electrospray ionisation mass spectrometry (ESI-MS). Three groups of iron hydroxamate siderophores, namely the ferrioxamines, ferrichromes and coprogens/fusigens, were separated by high-performance liquid chromatography (HPLC) prior to ESI and MS(2) fragmentation. For the majority of the siderophores, both protonated molecules and sodium adducts were observed. The most abundant ion was selected for collision-induced fragmentation. Potential fragmentation mechanisms are postulated and discussed. Fragmentation patterns differed between siderophore groups; however, common fragmentation patterns were observed for siderophore ions within the groups examined. Cleavage frequently occurred at carbon-nitrogen or carbon-oxygen bonds. Fragmentation of the ions also involved cleavage of iron-oxygen bonds and transfer of the charge to iron.     

2,2-二羟甲基丙二酸二乙酯的化学电离质谱分析

化学电离(chem ical ionization,CI)是由Munson和Field[1]于1966年提出的一种质谱电离技术,其原理实际上是分子-离子反应[2,3]。在化学电离条件下,常常可以得到丰度很强的准分子离子峰,没有或很少碎片离子,能准确提供相对分子质量信息,但缺乏结构信息。我们在实验中发现,采用适     

Pseudo-MS3 in a MALDI orthogonal quadrupole-time of flight mass spectrometer

Both the matrix selected and the laser fluence play important roles in MALDI-quadrupole/time of flight (QqTOF) fragmentation processes. "Hot" matrices, such as alpha-cyano4-hydroxycinnamic acid (HCCA), can increase fragmentation in MS spectra. Higher laser fluence also increases fragmentation. Typical peptide fragment ions observed in the QqTOF are a, b, and y ion series, which resemble low-energy CID product ions. This fragmentation may occur in the high-pressure region before the first mass-analyzing quadrupole. Fragment ions can be selected by the first quadrupole (Q1), and further sequenced by conventional MS/MS. This allows pseudo-MS3 experiments to be performed. For peptides of higher molecular weight, pseudo-MS3 can extend the mass range beyond what is usually accessible for sequencing, by allowing one to sequence a fragment ion of lower molecular weight instead of the full-length peptide. Peptides that predominantly show a single product ion after MS/MS yield improved sequence information when this technique is applied. This method was applied to the analysis of an in vitro phosphorylated peptide, where the intact enzymatically-generated peptide showed poor dissociation via MS/MS. Sequencing a fragment ion from the phosphopeptide enabled the phosphorylation site to be unambiguously determined.     

Determination of glycopeptide structures by multistage mass spectrometry with low-energy collision-induced dissociation: comparison of electrospray ionization quadrupole ion trap and matrix-assisted laser desorption/ionization quadrupole ion trap reflectron time-of-flight approaches

Multistage mass spectrometry, as implemented using low-energy collision-induced dissociation (CID) analysis in three-dimensional (3D) quadrupole ion traps (QITs), has become a powerful tool for the investigation of protein glycosylation. In addition to the well-known combination of QITs with electrospray ionization (ESI), also a matrix-assisted laser desorption/ionization--quadrupole ion trap--reflectron time-of-flight (MALDI-QIT-rTOF) mass spectrometer has recently become available. This study systematically investigates the differences between these types of instrument, as applied to characterization of glycopeptides from human antithrombin. The glycopeptides were obtained by tryptic digestion followed by lectin-affinity purification. Some significant differences between the ESI-QIT and MALDI-QIT-rTOF approaches appeared, most of them are causally related to the desorption/ionization process. The combination of a vacuum MALDI source with an ion-trap analyzer accentuates some characteristic differences between MALDI and ESI due the longer time frame needed for the trapping process. In contrast to ESI, MALDI generated ions that exhibited considerable metastable fragmentation during trapping. The long time span of the QIT process (ms range) compared with that for conventional rTOF experiments (micros range) significantly magnified the extent of this metastable fragmentation. With the investigated glycopeptides, a complete depletion of the terminal sialic acids of the glycopeptides as well as a variety of other fragment ions was already found in the MS1 spectra from the MALDI-QIT-rTOF instrument. The positive ion low-energy CID spectra (MS2) of the selected glycopeptides obtained using the two different QIT equipped instruments were found to be quite similar. In both approaches, fragmentation of the glycan and peptide structures occurred sequentially, allowing unambiguous sequence determination. In the case of ESI-QIT-MS, fragmentation of the glycan structure occurred at the MS2 stage and fragmentation of the peptide structure was obtained only at the MS3 stage, which indicates the necessity of multistage CID experiments for complete structure elucidation. The MALDI-QIT-rTOF instrument yielded both kinds of fragments at the MS2 stage but without mutual interference.     

环钯化二茂铁亚胺-膦配合物的电喷雾离子阱质谱研究

采用电喷雾离子阱质谱法(ESI-MS)对10种环钯化二茂铁亚胺-膦配合物的质谱特征进行了研究, 获得了其结构碎片信息, 对其质谱裂解途径进行了解析. 结果表明, 在正离子检测方式下可以得到强的准分子离子峰[M-Cl]+簇, 它们的(+) ESI-MSn(n=1~3)质谱主要产生碳-膦键断裂的碎片, 同时也能观察到Pd—P或Pd—C键的断裂, 这些特征为此类化合物及其结构类似物的结构推断提供了依据.     

The Study on the Noncovalent Complexes of Silver Ion with Xanthone Diglycosides by Electrospray Ionization with Tandem Mass Spectrometry

Xanthones are one species of C6-C1-C6 structure flavonoids, showing the various pharmacological activities, such as hepatocytes1 and antioxidative2 etc.. As one of the softest ionization technique, atmospheric pressure ionization mass spectrometry (API-MS…     

新型环钯化二茂铁亚胺-膦配合物的质谱特征

采用电喷雾离子阱质谱法(ESI-MS)对两种环钯化二茂铁亚胺-膦配合物的质谱特征进行了研究,获得了它们的结构碎片信息,对其质谱裂解途径进行了解析.结果表明:在正离子检测方式下可以得到强的准分子离子峰[M-C l]+和[M-I]+簇,它们的(+)ESI-MSn(n=1~4)质谱主要产生碳-膦键断裂的碎片,同时也能观察到钯-磷键的断裂.这些特征为此类化合物及其结构类似物的结构推断提供了依据.     

An experimental approach to enhance precursor ion fragmentation for metabolite identification studies: application of dual collision cells in an orbital trap

Recent advancements in mass spectrometry including data-dependent scanning and high-resolution mass spectrometry have aided metabolite profiling for non-radiolabeled xenobiotics. However, narrowing down a site of metabolism is often limited by the quality of the collision-induced dissociation (CID)-based precursor ion fragmentation. An alternative dissociation technique, higher energy collisional dissociation (HCD), enriches compound fragmentation and yields 'triple-quadrupole-like fragmentation'. Applying HCD along with CID and data-dependent scanning could enhance structural elucidation for small molecules. Liquid chromatography/multi-stage mass spectrometry (LC/MS(n) ) experiments with CID and HCD fragmentation were carried out for commercially available compounds on a hybrid linear ion trap orbital trap mass spectrometer equipped with accurate mass measurement capability. The developed method included stepped normalized collision energy (SNCE) parameters to enhance MS fragmentation without tuning for individual compounds. All the evaluated compounds demonstrated improved fragmentation under HCD as compared with CID. The results suggest that an LC/MS(n) method that incorporated both SNCE HCD- and CID-enabled precursor ion fragmentation afforded comprehensive structural information for the compounds under investigation. A dual collision cell approach was remarkably better than one with only CID MS(n) in an orbital trap. It is evident that such an acquisition method can augment the identification of unknown metabolites in drug discovery by improving fragmentation efficiency of both the parent compound and its putative metabolite(s).     

Structural investigation and elucidation of new communesins from a marine‐derived Penicillium expansum Link by liquid chromatography/electrospray ionization mass spectrometry

Penicillium expansum is a ubiquitous species for which there are only few reports for chemical investigation in marine environments. Among the numerous secondary metabolites produced by this species, communesins represent a new class of cytotoxic and insecticidal indole alkaloids. In this study, we investigated a marine P. expansum strain exhibiting neuroactivity on a Diptera larvae bioassay. Bio‐guided purification led to the isolation and the identification of communesin B as the main active compound by HRMS and ¹H and ¹³C NMR. Liquid chromatography analyses with detection by electrospray ionization coupled with tandem mass spectrometry (LC/ESI‐MS/MS) and high‐resolution tandem mass spectrometry (LC/HRMS/MS) allowed the identification and characterization of four other known communesins (A, D, E and F) in the crude extract. A fragmentation model for dimethyl epoxide communesins was proposed after detailed interpretation of their MS/MS spectra. Further analyses of the extract using the modelled fragmentations led to the detection of seven new communesins found as minor compounds. Chemical structural elucidation of these new derivatives is discussed based on their fragmentation characteristics. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of metal complex azo dyes by high-performance liquid chromatography/electrospray ionization mass spectrometry and multistage mass spectrometry

Five metal complex azo compounds were analyzed using negative-ion electrospray ionization mass spectrometry (ESI-MS). Mass spectra of all compounds yield intense peaks corresponding to [M - H](-) ions without any fragmentation, where M denotes the neutral compound with a proton as the counterion. Under collision induced dissociation (CID) conditions, structurally important fragment ions were studied using the ion trap analyzer with a multistage mass spectrometry (MS(n) facility. Synthesized compounds with (15)N atoms in the azo group facilitated the fragmentation pattern recognition. A reversed-phase high-performance liquid chromatography (HPLC) method using 5 mM ammonium acetate in 70% aqueous acetonitrile as mobile phase was developed making possible the separation of all complex compounds tested. The lower detection limits of the ESI-MS method are in the range 10-20 ng of each compound. The HPLC/ESI-MS method makes possible the monitoring of ligand exchange in aqueous solutions of metal complex azo dyes, and also investigation of the stabilities of the complexes in solution. Copyright 2000 John Wiley & Sons, Ltd.     

Comparison of LID versus CID activation modes in tandem mass spectrometry of peptides

We report our contribution to the systematic investigation of peptide fragmentations performed on high‐performance Tof equipment, operating in MS and MS/MS modes, such as ESI‐QqTof and MALDI‐Tof/Tof instruments that are commonly available today in proteomic laboratories. Whereas the former analyzer's configuration provides low‐energy collision‐induced dissociations (CID), the latter allows tunable activation methods of the selected parent ion to induce either metastable laser‐induced dissociations (LID) or high‐energy CID (‘gas on spectra LID’). Fragmentation of the monoprotonated ion of 53 peptides (FW 807–2853 g/mol) was undertaken upon low‐energy CID on an ESI‐QTof mass spectrometer (Waters) as well as high‐energy CID and LID conditions on a MALDI Ultraflex mass spectrometer (Bruker). Systematic comparison of MS/MS spectra provided useful information on the performance of each piece of equipment for efficient peptide sequencing and also insights into the observed fragmentation behaviors. Copyright © 2008 John Wiley & Sons, Ltd.     

MALDI‐TOF mass spectrometry,an efficient technique for in situ detection and characterization of actinomycins

An extensive study of actinomycins was performed using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐TOF MS). Actinomycins represent a well‐known family of peptidolactone chromopeptides with potent cytostatic and antibiotic properties. Using five well‐characterized streptomycete strains, we introduced MALDI‐TOF MS as an efficient technique for rapid in situ detection of actinomycins in surface extracts of cells picked from agar plates. By this procedure, actinomycin complexes can be investigated with high sensitivity and accuracy in a minimum of time. These studies were complemented by mass spectrometric investigation of actinomycins obtained from culture filtrate extracts and purified by high‐performance liquid chromatography to detect yet unknown actinomycin species. By feeding experiments, C‐demethyl‐actinomycins from Streptomyces chrysomallus and Streptomyces parvulus as well as hemi‐actinomycins from Streptomyces antibioticus lacking one of the two pentapeptide lactone rings were isolated and characterized as novel variants for structure–activity relationship studies. Structural characterization of the investigated actinomycins was performed by post source decay MALDI‐TOF MS. The specific features of the fragmentation patterns of the protonated and cationized forms of selected actinomycins were investigated in detail. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrospray tandem mass spectrometry of beta-nitroalkenyl meso-tetraphenylporphyrins

Beta-nitroalkenyl meso-tetraphenylporphyrins [beta-TPPCHC(NO(2))R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the [M + H](+) ions are formed. The fragmentation pattern of the resulting [M + H](+) ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of beta- nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO(2), HNO(2), 2OH, RNO(2), RCNO, RCNO(2), RCH(2)NO(2), C(6)H(5) plus NO(2) and the formation of the protonated macrocycle, [TPP + H](+) or [ZnTPP + H](+). However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl group leads to a peculiar behaviour, since the main fragmentation pattern corresponds to the combined elimination of the bromine atom with the typical nitro group fragments. When R = Br, the loss of the nitro group occurs in low relative abundance (11-16%). However, when R = CH(3), the relative abundance of the ion due to the loss of HNO(2) changes drastically from 100%, observed for the free-base porphyrin, to 29% in the case of the Zn(II) complex. These variations of the relative abundance of the fragment corresponding to the loss of the nitro moiety (typically considered as a diagnostic fragment) can induce to an erroneous interpretation of their MS/MS spectra. Some fragmentations are observed only for the free-base porphyrins, namely the loss of CH(NO(2)R and HNO(2) plus C(2)H(2), while the loss of OH, H(2)O, OH plus H(2)O and RCCH plus H(2)O is observed only for the complexes. Unusual and unexpected fragmentations are also observed, namely the losses of RCNO, RCNO(2) and HNO(2) plus C(2)H(2). This work demonstrates that valuable structural information about the beta-nitroalkenyl substituents linked to meso- tetraarylporphyrins can be achieved using MS/MS. These results can also be useful for the interpretation of the mass spectra of other nitroalkenyl substituted compounds.     

Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectra of poly(butylene adipate)

Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS/MS) was employed to analyze four poly(butylene adipate) (PBAd) oligomers and to investigate their fragmentation pathways as a continuation of our work on the MALDI-TOF/TOF-MS/MS study of synthetic polymers. MALDI-TOF/TOF-MS/MS analysis was performed on oligomers terminated by carboxyl and hydroxyl groups, methyl adipate and hydroxyl groups, dihydroxyl groups, and dicarboxyl groups. The sodium adducts of these oligomers were selected as precursor ions. Different end groups do not influence the fragmentation of sodiated polyester oligomers and similar series of product ions were observed in all the MALDI-TOF/TOF-MS/MS spectra. According to the structures of the most abundant product ions identified in the present work, three fragmentation pathways have been proposed to occur most frequently in PBAd: beta-hydrogen-transfer rearrangement, leading to the selective cleavage of the --O--CH(2)-- bonds; --CH(2)--CH(2)-- (beta--beta) bond cleavage in the adipate moiety; and ester bond scission.     

Solid-phase microextraction liquid chromatography/tandem mass spectrometry for the analysis of chlorophenols in environmental samples

Liquid chromatography with atmospheric pressure chemical ionisation mass spectrometry (LC/APCI-MS), using negative ion detection in a triple quadrupole instrument, was used for the determination of chlorophenols (CPs) in environmental samples. In-source collision-induced dissociation (CID) was compared with MS/MS fragmentation. In general, less fragmentation was observed in MS/MS as compared with in-source CID, with the latter providing more intense fragment ions due to chemical ionisation. Under MS/MS conditions [M - H - HCl](-) was the main fragment ion observed for all compounds except for pentachlorophenol, which showed no fragmentation. For multiple reaction monitoring (MRM) acquisition mode, the transition from [M - H](-) to [M - H - HCl](-) was selected, leading to detection limits down to 0.3 ng injected. Direct and headspace-solid-phase microextraction (HS-SPME) were used as preconcentration procedures for the analysis of CPs in wood and in industrially contaminated soils. CPs were quantified by standard addition, which led to good reproducibility (RSD between 4 and 11%) in both SIM and MRM modes, and detection limits down to ng/g. The combination of MS/MS and in-source CID allowed confirmation of the presence of CPs in environmental samples.     

Tandem mass spectrometric sequence characterization of synthetic thymidine-rich oligonucleotides

Tandem mass spectrometry (MS/MS) can provide direct and accurate sequence characterization of synthetic oligonucleotide drugs, including modified oligonucleotides. Multiple factors can affect oligonucleotide MS/MS sequencing, including the intrinsic properties of oligonucleotides (i.e., nucleotide composition and structural modifications) and instrument parameters associated with the ion activation for fragmentation. In this study, MS/MS sequencing of a thymidine (T)-rich and phosphorothioate (PS)-modified DNA oligonucleotide was investigated using two fragmentation techniques: trap-type collision-induced dissociation (“CID”) and beam-type CID also termed as higher-energy collisional dissociation (“HCD”), preceded by a hydrophilic interaction liquid chromatography (HILIC) separation. A low to moderate charge state (−4), which predominated under the optimized HILIC-MS conditions, was selected as the precursor ion for MS/MS analysis. Comparison of the two distinctive ion activation mechanisms on the same precursor demonstrated that HCD was superior to CID in promoting higher sequence coverage and analytical sensitivity in sequence elucidation of T-rich DNA oligonucleotides. Specifically, HCD provided more sequence-defining fragments with higher fragment intensities than CID. Furthermore, the direct comparison between unmodified and PS-modified DNA oligonucleotides demonstrated a loss of MS/MS fragmentation efficiency by PS modification in both CID and HCD approaches, and a resultant reduction in sequence coverage. The deficiency in PS DNA sequence coverage observed with single collision energy HCD, however, was partially recovered by applying HCD with multiple collision energies. Collectively, this work demonstrated that HCD is advantageous to MS/MS sequencing of T-rich PS-modified DNA oligonucleotides.