Collision-induced Dissociation Tandem Mass Spectrometry Research Articles

Structural characterization and bioactivity profiling of the fungal peptaibiotic tolypin reveal protective effects against influenza viruses.

In a bioprospection for new antivirals, we tested nonribosomally biosynthesized polypeptide antibiotics in MDCK II cells for their actions on influenza A and B viruses (IAV/IBV). Only tolypin, a mixture of closely related 16-residue peptaibiotics from the fungus Tolypocladium inflatum IE 1897, showed promising activity. It was selected for further investigation and structural characterization byultrahigh performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HR-MS/MS) and ultrahigh performance liquid chromatography coupled to in-source collision-induced dissociation tandem mass spectrometry (UHPLC-isCID-HR-MS/MS), revealing 12 partially co-eluting individual peptides that were fully sequenced. Since tolypin-related efrapeptins are potent inhibitors of F1/Fo-ATPase, we screened tolypin for its toxicity against MDCK II cells and larvae of the greater wax moth Galleria mellonella. We found that a nontoxic concentration of tolypin (1 µg/mL) reduced the titer of two IBV strains by 4-5 log values, and that of an H3N2 strain by 1-2 log values, but the H1N1pdm strain was not affected. The higher concentrations of tolypin were cytostatic to MDCK II cells, shifted their metabolism from oxidative phosphorylation to glycolysis, and induced paralysis in G. mellonella, supporting the inhibition of F1/Fo-ATPase as the mode of action. Our results lay the foundations for future work to investigate the interplay between viral replication and cellular energy metabolism, as well as the development of drugs that target host factors.

A spectroscopic test suggests that fragment ion structure annotations in MS/MS libraries are frequently incorrect

Modern untargeted mass spectrometry (MS) analyses quickly detect and resolve thousands of molecular compounds. Although features are readily annotated with a molecular formula in high-resolution small-molecule MS applications, the large majority of them remains unidentified in terms of their full molecular structure. Collision-induced dissociation tandem mass spectrometry (CID-MS2) provides a diagnostic molecular fingerprint to resolve the molecular structure through a library search. However, for de novo identifications, one must often rely on in silico generated MS2 spectra as reference. The ability of different in silico algorithms to correctly predict MS2 spectra and thus to retrieve correct molecular structures is a topic of lively debate, for instance in the CASMI contest. Underlying the predicted MS2 spectra are the in silico generated product ion structures, which are normally not used in de novo identification, but which can serve to critically assess the fragmentation algorithms. Here we evaluate in silico generated MSn product ion structures by comparison with structures established experimentally by infrared ion spectroscopy (IRIS). For a set of three dozen product ion structures from five precursor molecules, we find that virtually all fragment ion structure annotations in three major in silico MS2 libraries (HMDB, METLIN, mzCloud) are incorrect and caution the reader against their use for structure annotation of MS/MS ions.

OH radical-induced oxidation in nucleosides and nucleotides unraveled by tandem mass spectrometry and IRMPD spectroscopy.

OH●-induced oxidation products of DNA nucleosides and nucleotides have been structurally characterized by collision-induced dissociation tandem mass spectrometry (CID-MS2) and Infrared Multiple Photon Dissociation (IRMPD) spectroscopy. CID-MS2 results have shown that the addition of one oxygen atom occurs on the nucleobase moiety. The gas-phase geometries of +16 mass increment products of 2'-deoxyadenosine (dA(O)H+), 2'-deoxyadenosine 5'-monophosphate (dAMP(O)H+), 2'-deoxycytidine (dC(O)H+), and 2'-deoxycytidine 5'-monophosphate (dCMP(O)H+) are extensively investigated by IRMPD spectroscopy and quantum-chemical calculations. We show that a carbonyl group is formed at the C8 position after oxidation of 2'-deoxyadenosine and its monophosphate derivative. For 2'-deoxycytidine and its monophosphate derivative, the oxygen atom is added to the C5 position to form a C-OH group. IRMPD spectroscopy has been employed for the first time to provide direct structural information on oxidative lesions in DNA model systems.

Application of liquid chromatography quadrupole time-of-flight mass spectrometry for the elucidation of fenamiphos photodegradation by-products

The degradation of the insecticide fenamiphos was undertaken by using a homogeneous photocatalysis employing iron (III) aqua complex, [Fe(H2O)5(OH)]2+. The irradiation was studied by excitation at 365 nm and the generated primary by-products were elucidated by Liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry in the positive ion mode, that leads to the formation of the protonated forms of the studied compounds, [M + H+]. Collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of the protonated molecules was carried out, and the effect of the collision energy as well as the elemental compositions of the product ions were used in order to propose the chemical structures. The primary processes were then i) hydroxylation on the aromatic ring; ii) the loss of propene from the aminoisopropyl chain and iii) the loss of the methylene at the ethoxy moiety.

Electrospray Ionization Tandem Mass Spectrometric Study of Selected Phosphine-Based Ligands for Catalytically Active Organometallics.

Selected organometallic compounds are nowadays extensively used as highly efficient catalysts in organic synthesis. A great variety of different ligand systems exists, of which phosphine-based ligands are a significant subgroup. While mass spectrometry, predominantly electrospray ionization mass spectrometry (ESI-MS), is a standard analytical technique for the identification of new ligands and their metal complexes, there is little information on the behavior of phosphine-based ligands/molecules by electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) at low collision energies (<100 eV) in the literature. Here, we report a study on the identification of typical product ions occurring in tandem mass spectra of selected phosphine-based ligand systems by ESI-CID-MS/MS. The influence on the fragmentation behavior of different backbones (pyridine, benzene, triazine) as well as different spacer groups (amine, methylamine, methylene), which are directly linked to the phosphine moiety, is investigated by tandem mass spectrometry. In addition, possible fragmentation pathways are elaborated based on the assigned masses in the tandem mass spectra with high-resolution accurate mass determination. This knowledge may be particularly useful in the future for the elucidation of fragmentation pathways for coordination compounds by MS/MS, where the studied compounds serve as building blocks.

Carbene Cross-Linking in Gas-Phase Peptide Ion Scaffolds.

Scaffolds consisting of a peptide, a phthalate linker, and a 4,4-azipentyl group were synthesized and used to study intramolecular peptide-carbene cross-linking in gas-phase cations. Carbene intermediates were generated by UV-laser photodissociation at 355 nm of the diazirine ring in mass-selected ions, and the cross-linked products were detected and quantified by collision-induced dissociation tandem mass spectrometry (CID-MSn, n = 3-5). Peptide scaffolds containing Ala and Leu residues with a C-terminal Gly gave 21-26% yields of cross-linked products, while the presence of the Pro and His residues decreased the yields. Experiments using hydrogen-deuterium-hydrogen exchange, carboxyl group blocking, and analysis of CID-MSn spectra of reference synthetic products revealed that a significant fraction of cross-links involved the Gly amide and carboxyl groups. Interpretation of the cross-linking results was aided by Born-Oppenheimer molecular dynamics (BOMD) and density functional theory calculations that allowed us to establish the protonation sites and conformations of the precursor ions. Analysis of long (100 ps) BOMD trajectories was used to count close contacts between the incipient carbene and peptide atoms, and the counting statistics was correlated with the results of gas-phase cross-linking.

The DNA Radical Code. Resolution of Identity in Dissociations of Trinucleotide Codon Cation Radicals in the Gas Phase

Sixty DNA trinucleotide cation radicals covering a large part of the genetic code alphabet were generated by electron transfer in the gas phase, and their chemistry was studied by collision-induced dissociation tandem mass spectrometry and theoretical calculations. The major dissociations involved loss of nucleobase molecules and radicals, backbone cleavage, and cross-ring fragmentations that depended on the nature and position of the nucleobases. Mass identity in dissociations of symmetrical trinucleotide cation radicals of the (XXX+2H)+• and (XYX+2H)+• type was resolved by specific 15N labeling. The specific features of trinucleotide cation radical dissociations involved the dominant formation of d2+ ions, hydrogen atom migrations accompanying the formation of (w2+H)+•, (w2+2H)+, and (d2+2H)+ sequence ions, and cross-ring cleavages in the 3'- and 5'-deoxyribose moieties that depended on the nucleobase type and its position in the ion. Born-Oppenheimer molecular dynamics (BOMD) and density functional theory calculations were used to obtain structures and energies of several cation-radical protomers and conformers for (AAA+2H)+•, (CCC+2H)+•, (GGG+2H)+•, (ACA+2H)+•, and (CAA+2H)+• that were representative of the different types of backbone dissociations. The ion electronic structure, protonation and radical sites, and hydrogen bonding were used to propose reaction mechanisms for the dissociations.

Final Products of One-Electron Oxidation of Cyclic Dipeptides Containing Methionine Investigated by IRMPD Spectroscopy: Does the Free Radical Choose the Final Compound?

Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and the hydroxyl radical (•OH) have specific functions in biological processes, while their uncontrolled production and reactivity are known to be determining factors in pathophysiology. Methionine (Met) residues act as endogenous antioxidants, when they are oxidized into methionine sulfoxide (MetSO), thus depleting ROS and protecting the protein. We employed tandem mass spectrometry combined with IR multiple photon dissociation spectroscopy to study the oxidation induced by OH radicals produced by γ radiolysis on model cyclic dipeptides c(LMetLMet), c(LMetDMet), and c(GlyMet). Our aim was to characterize the geometries of the oxidized peptides in the gas phase and to understand the relationship between the structure of the 2-center 3-electron (2c-3e) free radical formed in the first step of the oxidation process and the final compound. Density functional theory calculations were performed to characterize the lowest energy structures of the final product of oxidation and to interpret the IR spectra. Collision-induced dissociation tandem mass spectrometry (CID-MS2) experiments of oxidized c(LMetLMet)H+ and c(LMetDMet)H+ led to the loss of one or two oxidized sulfenic acid molecules, indicating that the addition of one or two oxygen atoms occurs on the sulfur atom of both methionine side chains and no sulfone formation was observed. The CID-MS2 fragmentation mass spectrum of oxidized c(GlyMet)H+ showed only the loss of one oxidized sulfenic acid molecule. Thus, the final products of oxidation are the same regardless of the structure of the precursor sulfur-centered free radical.

The Good, the Bad, and the Ugly Memories of Carbohydrate Fragments in Collision-Induced Dissociation.

Collision-induced dissociation (CID) tandem mass spectrometry is commonly used for carbohydrate structural determinations. In the CID tandem mass spectrometry approach, carbohydrates are dissociated into fragments, and this is followed by the structural identification of fragments through subsequent CID. The success of the structural analysis depends on the structural correlation of fragments before and after dissociation, that is, structural memory of fragments. Fragments that completely lose the memory of their original structures cannot be used for structural analysis. By contrast, fragments with extremely strong correlations between the structures before and after fragmentation retain the information on their original structures as well as have memories of their precursors' entire structures. The CID spectra of these fragments depend on their own structures and on the remaining parts of the precursor structures, making structural analysis impractical. For effective structural analysis, the fragments produced from a precursor must have good structural memory, meaning that the structures of these fragments retain their original structure, and they must not be strongly affected by the remaining parts of the precursors. In this study, we found that most of the carbohydrate fragments produced by low-energy CID have good memory in terms of linkage position and anomericity. Fragments with ugly memory, where fragment structures change with the remaining parts of the precursors, can be attributed to C ion formation in a linear form. Fragments with ugly memory can be changed to have good memory by preventing linear C ion generation by using an alternative CID sequence, or the fragments of ugly memory can become useful in structural analysis when the contribution of linear C ions in fragmentation patterns is understood.

VUV photoprocessing of oxygen-containing polycyclic aromatic hydrocarbons: iPEPICO study of the unimolecular dissociation of ionized benzofuran

Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) are potential contributors to the 11.3 µm band in interstellar observations. To further explore their role in the interstellar medium, we investigated their fate after photoprocessing by VUV radiation; in particular, we studied the dissociative photoionization of the simplest OPAH, benzofuran, with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. Ionized benzofuran dissociates by loss of CO, followed by a sequential H-atom loss. The parallel HCO-loss channel, leading to the same bicyclic C7H5+ fragment ion, is not competitive at low excess energies above the ionization threshold. However, the collision-induced dissociation tandem mass spectrometry results suggest that CO and HCO may be formed in parallel at higher energies. A Rice–Ramsperger–Kassel–Marcus fragmentation model reproduced the iPEPICO data well, assuming the initial 1,2-H shift transition state to be rate determining to CO loss. The breakdown diagram and the measured dissociation rates agreed well at the CBS-QB3-calculated activation energy of 2.99 eV, which could be relaxed to 3.25 eV, and only a slight adjustment of the ab initio activation entropy. The model barrier to sequential H loss is larger than the computed H-loss threshold and the breakdown diagram rises less steeply than predicted, which indicates suprastatistical kinetic energy release after the tight H-transfer transition state of the first step. HCO cleavage is possible after a ring-opening transition state, which is looser than and isoenergetic with the CO-loss transition state. However, a subsequent ring formation transition state at 3.85 eV is moderately tight, which suppresses HCO loss at low excess energies.

Assessment of the similarity between in-source collision-induced dissociation (IS-CID) fragment ion spectra and tandem mass spectrometry (MS/MS) product ion spectra for seized drug identifications

The use of in-source collision-induced dissociation (IS-CID) with single-stage mass spectrometers has grown in popularity within the field of seized drug analysis as a pseudo-tandem mass spectrometry (MS/MS) analysis to gain structural information about unknown compounds. However, there is currently no statistical assessment of the similarity and thus, the comparability, of IS-CID fragment ion spectra and MS/MS product ions spectra for representative novel psychoactive substances (NPS), such as synthetic cannabinoids, synthetic cathinones, and fentanyl analogs. This study investigates the use of spectral comparisons, breakdown curves, and Pearson product-moment correlations (PPMCs) to assess the similarity between IS-CID fragment ion spectra and MS/MS product ion spectra both visually and statistically. In addition, this study also examines the repeatability of IS-CID fragment ion spectra relative to MS/MS product ion spectra to assess the short-term repeatability of IS-CID fragment ion spectra. The 95% confidence interval average PPMC for the highest pairwise comparison across this study was 0.9294 +/- 0.0106. The optimum comparison range between IS-CID fragment ion spectra and MS/MS product ion spectra was identified between a fragmentor voltage of 150–280 V and a collision energy of 0–22 eV. Similar repeatability of IS-CID fragment ion spectra (15.21%) and MS/MS product ion spectra (14.72%) was also observed. Demonstrating the achievable spectral similarity between IS-CID fragment ion spectra and MS/MS product ion spectra for representative NPS, as well as highlighting the potential deleterious effects of high activation conditions on spectral comparisons, will help inform analysts’ decisions regarding seized drug identifications based on IS-CID fragment ion spectra.

Lipid Peroxidation in Algae Oil: Antagonist Effects of Natural Antioxidants.

Tandem mass spectrometry is proposed to check lipid oxidation, a free radical-mediated phenomenon which effects oxidative deterioration in polyunsaturated fatty acids. Antioxidants are used by the food industry to delay the oxidation process. This process can be controlled by antioxidants, which may occur as natural constituents of foods or may be intentionally added to products. Synthetic antioxidants such as BHT, BHA, and propyl gallate have been extensively used as antioxidants in the industry. The worldwide tendency to avoid or minimize the use of synthetic food additives has prompted the replacement of synthetic antioxidants with natural analogues. The entire process can be supported by the detection and characterization of the reacting species by suitable application of electrospray tandem mass spectrometry under collision-induced dissociation (ESI-CID-MS/MS). Natural antioxidants were tested in this study to check the oxidative stability of algae oil when adding the natural additive. Results were observed in algae oil in situ using electrospray mass spectrometry in tandem with collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) and the POBN spin trapper. The results indicate that alpha-tocopherol is a better antioxidant.

Collision-induced dissociation of homodimeric and heterodimeric radical cations of 9-methylguanine and 9-methyl-8-oxoguanine: correlation between intra-base pair proton transfer originating from the N1-H at a Watson-Crick edge and non-statistical dissociation.

It has been shown previously in protonated, deprotonated and ionized guanine-cytosine base pairs that intra-base pair proton transfer from the N1-H at the Watson-Crick edge of guanine to the complementary nucleobase prompts non-statistical dissociation of the base-pair system, and the dissociation of a proton-transferred base-pair structure is kinetically more favored than that of the starting, conventional base-pair structure. However, the fundamental chemistry underlying this anomalous and intriguing kinetics has not been completely revealed, which warrants the examination of more base-pair systems in different structural contexts in order to derive a generalized base-pair structure-kinetics correlation. The purpose of the present work is to expand the investigation to the non-canonical homodimeric and heterodimeric radical cations of 9-methylguanine (9MG) and 9-methyl-8-oxoguanine (9MOG), i.e., [9MG·9MG]˙+, [9MOG·9MG]˙+ and [9MOG·9MOG]˙+. Experimentally, collision-induced dissociation tandem mass spectrometry coupled with an electrospray ionization (ESI) source was used for the formation of base-pair radical cations, followed by detection of dissociation product ions and cross sections in the collisions with Xe gas under single ion-molecule collision conditions and as a function of the center-of-mass collision energy. Computationally, density functional theory and coupled cluster theory were used to calculate and identify probable base-pair structures and intra-base pair proton transfer and hydrogen transfer reactions, followed by kinetics modeling to explore the properties of dissociation transition states and kinetic factors. The significance of this work is twofold: it provides insight into base-pair opening kinetics in three biologically-important, non-canonical systems upon oxidative and ionization damage; and it links non-statistical dissociation to intra-base pair proton-transfer originating from the N1-H at the Watson-Crick edge of 8-oxoguanine, enhancing understanding towards the base-pair fragmentation assisted by proton transfer.

Distinguishing between isomeric neoxanthin and violaxanthin esters in yellow flower petals using liquid chromatography/photodiode array atmospheric pressure chemical ionization mass spectrometry and tandem mass spectrometry.

RationaleLiquid chromatography/photodiode array atmospheric pressure chemical ionization mass spectrometry (LC/PDA‐APCI‐MS) is used for the analysis of various carotenoid pigments in plants. Among them, it is difficult to distinguish between the isomeric violaxanthin/neoxanthin esters.MethodsThe yellow pigments of tomato petals were extracted with acetone, and the extracts were kept at −30°C to allow the contaminating triacylglycerols to settle out physically. The supernatants were analyzed using LC/PDA‐APCI‐MS with a high‐resolution orbitrap mass spectrometer for their exact masses. The expected carotenoid esters were calculated with the combination of carotenoids and fatty acids, and they were matched with the experimental exact masses. The fatty acid structures in the carotenoid esters were also identified using collision‐induced dissociation (CID) tandem mass spectrometry (MS/MS). The isomeric violaxanthin/neoxanthin esters were distinguished using CID MS/MS from their in‐source dehydrated product ions as pseudoprecursor ions.ResultsThe in‐source dehydrated ions [M − H2O + H]+ of neoxanthin diesters predominated over their protonated molecules [M + H]+ in LC/MS. By contrast, the protonated molecules of violaxanthin diesters predominated. The 92 u loss product ions [M − H2O − C7H8 + H]+ were observed from the dehydrated violaxanthin diesters, but they were not generated from the dehydrated neoxanthin diesters in the CID MS/MS of their dehydrated pseudoprecursor ion [M − H2O + H]+.ConclusionsThe allene allyl carbocation in neoxanthin diesters was generated from dehydration after preferential protonation at the hydroxy group. The epoxide group of violaxanthin diesters opens easily after protonation; however, the dehydration did not proceed at this stage. The 92 u loss of C7H8 was explained by an intramolecular [2 + 2] cycloaddition, which proceeded preferentially in dehydrated violaxanthin diesters because the carbocations in the dehydrated species were conjugated to the polyene and those double bonds were depolarized during CID MS/MS. Therefore, the isomeric neoxanthin/violaxanthin diesters were distinguished using LC/PDA‐APCI‐MS and MS/MS. This method was a practical and useful method of profiling the carotenoid esters of the yellow petals.

Triboelectric Nanogenerator Ion Mobility-Mass Spectrometry for In-Depth Lipid Annotation.

Lipids play a critical role in cell membrane integrity, signaling, and energy storage. However, in-depth structural characterization of lipids is still challenging and not routinely possible in lipidomics experiments. Techniques such as collision-induced dissociation (CID) tandem mass spectrometry (MS/MS), ion mobility (IM) spectrometry, and ultrahigh-performance liquid chromatography are not yet capable of fully characterizing double-bond and sn-chain position of lipids in a high-throughput manner. Herein, we report on the ability to structurally characterize lipids using large-area triboelectric nanogenerators (TENG) coupled with time-aligned parallel (TAP) fragmentation IM-MS analysis. Gas-phase lipid epoxidation during TENG ionization, coupled to mobility-resolved MS3 via TAP IM-MS, enabled the acquisition of detailed information on the presence and position of lipid C═C double bonds, the fatty acyl sn-chain position and composition, and the cis/trans geometrical C═C isomerism. The proposed methodology proved useful for the shotgun lipidomics analysis of lipid extracts from biological samples, enabling the detailed annotation of numerous lipid isobars.

Top-down lignomics analysis of the French pine lignin by atmospheric pressure photoionization quadrupole time-of-flight tandem mass spectrometry: Identification of a novel series of lignin-carbohydrate complexes.

We report the top-down lignomics analysis of the virgin released lignin (VRL) extracted from French pine wood by using atmospheric pressure photoionization quadrupole time-of-flight mass spectrometry (APPI-QqTOF-MS) and low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS). We used APPI-QqTOF-MS (positive ion mode) for the analysis of the complex mixture of VRL oligomers extracted from French pine wood. Some of the major precursor ions were fished out from the complex VRL oligomeric mixture and subjected to low-energy CID-MS/MS analyses. Fourteen novel lignin-carbohydrate complexes (LCCs) were identified using APPI-QqTOF-MS/MS of the very complex mixture of virgin released lignins (VRLs), directly extracted from French pine wood without any kind of purification. The low-energy CID-MS/MS analyses allowed us to establish the fragmentation patterns of the precursor ions and to identify the complex structures of the identified LCC molecules. These novel identified series of LCCs were composed of one or two carbohydrate rings to which one, two, or three lignin units were covalently attached. In addition to the fourteen LCCs, acetyl eugenol was identified in the French pine VRL sample. The identification of acetyl eugenol indicates possible lignin degradation and modification (acetylation) during the mild extraction method developed by the Compagnie Industrielle de la Matière Végétale (CIMV). The top-down lignomics analysis of the French pine VRLs using APPI-QqTOF-MS and low energy CID-MS/MS allowed us to identify acetylated eugenol and a novel series of fourteen LCCs. These series of LCCs provide evidence that lignins are covalently linked to carbohydrates in the native wood network and act as cross-linkers between cellulose and hemicellulose components of wood.

Discrimination of common isomerides of methyl nucleosides by collision-induced dissociation tandem mass spectrometry.

The methyl-modified nucleosides (methyladenosine, methylguanosine, methylcytidine, and methyluridine) occur widely in nucleic acids and serve as biomarkers for a variety of types of diseases. Their isomers have the same parent ions in MS spectra and need further discrimination. Here, electrospray ionization mass spectrometry (ESI-MS) coupled with collision induced dissociation (CID) was used to distinguish the common isomerides of methyl-nucleosides. The various fragmentation patterns had been discussed in comparison of the different methyl modified nucleosides and were studied as a function of normalized collision energy. Then, structurally relevant fragments were obtained to efficiently identify characterization of methyl-nucleoside isomerides by collision induced dissociation. Therefore, this study provides a promising method using CID-MS for the discrimination of the isomeric methyl nucleosides, which could be useful to quantitative study of methyl nucleosides and detect of unknown methyl nucleosides.

Electron ionization mass spectrometric fragmentation and detection of autoxidation products of 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene in Arctic sediments.

Some highly branched isoprenoid (HBI) alkenes are commonly used as proxies for palaeoceanographic reconstructions. However, there is a need to identify compounds that are sufficiently stable and abundant to be used as tracers of HBI oxidation in sediments. 2,6,10,14-Tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols resulting from 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene appear to be useful for this purpose. Comparison of electron ionization (EI) mass spectra and retention times with those of standards allowed formal identification of autoxidation products of 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene. EI-MS fragmentations of TMS ethers of the main oxidation products (2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols) were deduced by gas chromatography/electron ionization mass spectrometry (GC/EI-MS), low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) and accurate mass measurements. These compounds were then quantified in Arctic sediment samples in MS/MS multiple reaction monitoring (MRM) mode using transitions based on the main fragmentation pathways elucidated. 2,6,10,14-Tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols were identified after autoxidation of the HBI alkene 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene. Low-energy CID-MS/MS analyses and accurate mass measurements allowed the EI-MS fragmentation pathways of their trimethylsilyl (TMS) derivatives to be elucidated. Some specific fragment ions and chromatographic retention times were also useful for further characterization. As an application of some of the described fragmentations, TMS derivatives of these metabolites were characterized and quantified in MRM mode in Arctic sediments. Due to their production in high proportions during autoxidation of their parent HBI diene, their apparent stability in sediments, and their specific EIMS fragmentations, (Z and E)-2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-en-4-ol TMS derivatives appeared to be useful tracers of HBI autoxidation in sediments.

Selective Bond Cleavage in Informational Poly(Alkoxyamine Phosphodiester)s.

The collision-induced dissociation (CID) of sequence-defined poly(alkoxyamine phosphodiester)s is studied by electrospray ionization mass spectrometry. These informational polymers are synthesized using three different nitroxide building blocks, namely proxyl-, SG1-, and TEMPO-derivatives. For a polymer containing TEMPO- and SG1-based main chain alkoxyamines, it is found that both types of alkoxyamines break in CID tandem mass spectrometry (MS/MS). However, SG1-sites are preferentially cleaved and this predominance can be increased by reducing collision energy, even though selective bond fragmentation is not observed. On the other hand, for a polymer containing proxyl- and SG1-alkoxyamines, selective bond cleavage is observed at all studied collision energies. The SG1-alkoxyamines can be first cleaved in MS/MS conditions and secondly the proxyl-alkoxyamines in pseudo-MS3 conditions. These results open up interesting new avenues for the design of readable, erasable or programmable informational polymers.

1,4-D-Glucan block copolymers: synthesis and comprehensive structural characterization

Multi-block glucans comprising permethylated and partially methylated blocks are compounds of interest. In order to monitor their formation by transglycosylation of corresponding starting glucans, a method has been developed and applied to model compounds. This method allows determining the average length of the blocks and the progress of incorporation of methyl blocks in partially methylated sequences with a random distribution. The method, comprising liquid chromatography mass spectrometry (LC-MS) and electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MSn) measurements of two types of peralkylated glucans representing derivatives of the target compounds, is comprehensively described and discussed. ESI-MSn allows looking into the sequences of oligomeric domains. In addition, transglycosylation is followed by attenuated total reflection FTIR and NMR spectroscopy.Graphical abstract