Probing mechanistic features of conventional, catalytic and living free radical polymerizations using soft ionization mass spectrometric techniques

The present feature article provides an overview on the use of state-of-the-art mass spectrometry techniques such as matrix assisted laser desorption and ionization time of flight (MALDI-TOF) mass spectrometry as well as electrospray ionization mass spectrometry (ESI-MS) for probing the mechanism of free radical polymerization processes. The article features representative examples of the application of mass spectrometry techniques to conventional free radical polymerization, nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT) as well as catalytic chain transfer (CCT) processes.     

Investigation of chemical transformations of thiophenylglycoside of muramyl dipeptide on the fumed silica surface using TPD-MS,FTIR spectroscopy and ES IT MS

In this study, chemical transformations of benzyl ester of О-(phenyl-2-acetamido-2,3-dideoxy-1-thio-β-d-glucopyranoside-3-yl)-d-lactoyl-l-alanyl-d-isoglutamine (SPhMDPOBn) on the fumed silica surface were examined, and the surface complex structure was characterized by temperature-programmed desorption mass spectrometry (TPD-MS), infrared spectroscopy (FTIR) and electrospray ion trap mass spectrometry (ES IT MS). Stages of pyrolysis of SPhMDPOBn in pristine state and on the silica surface have been determined. Probably, hydrogen-bonded complex forms between silanol surface groups and the C = O group of the acetamide moiety NH-(CH₃)-C = O…H-O-Si≡. The thermal transformations of such hydrogen-bonded complex result in pyrolysis of SPhMDPOBn immobilized on the silica surface under TPD-MS conditions. The shifts ∆ν of amide I band (measured from 1,626 to 1,639 cm^−l for SPhMDPOBn in pristine state) of 33 and 35 cm^−l which occurred when SPhMDPOBn was immobilized on the silica surface may be caused by a weakening of the intramolecular hydrogen bonding of the SPhMDPOBn because the interaction with the silica surface as hydrogen bond with silanol groups is weaker than that in associates.     

Mass spectrometric evidence for a zinc-porphyrin complex as the red pigment in dry-cured Iberian and Parma ham

Extracts containing red pigment complexes from the two types of dry-cured hams, Italian Parma and Spanish Iberian ham, were obtained using water and acetone as extraction solvents followed by a crude purification with C18 column filtration. The purified extracts were then analyzed spectroscopically by recording absorption and fluorescence spectra (λ(ex)=420nm), which both indicate the presence of chemically identical red chromophores with properties similar to a complex of transition metals and protoporphyrin IX. Electrospray ionization mass spectrometry (ESI-MS) in the positive ion mode confirms the presence of identical chemical compounds. ESI-MS in the negative ion mode detects a cluster of seven isotopologue ions (that of m/z 623.2 as the most intense) with a pattern matching that of a Zn protoporphyrin IX complex. Based on mass spectral data it is concluded that a Zn-porphyrin complex constitutes a major chromophore in dry-cured Iberian ham as well as in Parma ham.     

Polyphenol profiles of apple juices

Focusing on 17 constituents, the polyphenol profiles of juices freshly made from various dessert (n = 4) and cider apple cultivars (n = 7) as well as commercially available apple juices (n = 24) were investigated using high-performance liquid chromatography-photodiode array detection (HPLC-DAD) and (HPLC)-electrospray ionization-tandem mass spectrometry (ESI(neg)-MS/MS) analyses. Significant differences in the total polyphenol content as well as the profiles of the apple cultivars under study were observed. For dessert apples the total polyphenol content ranged from 154 to 178 mg/L, whereas for 'old' German cider apple cultivars 261-970 mg/L were determined. Boskoop showed the highest (970 mg/L) and Granny Smith the lowest (154 mg/L) polyphenol content of the freshly prepared samples under study. Hydroxycinnamic acids, with chlorogenic acid as dominating constituent, ranged from 57 to 68 mg/L as well as from 134-593 mg/L in juices made from dessert apples and that from cider apples, respectively. Dessert apple juices showed lower contents of dihydrochalcones (10-35 mg/L) and flavan-3-ols (50-95 mg/L) compared to that of cider apples (34-171 mg/L and 70-393 mg/L, respectively). Quercetin and its derivatives were found from 0.4-4 mg/L and 0.4-27 mg/L in juices made from dessert apples and that of cider apples, respectively. Compared with freshly made juices, lower contents of polyphenols were determined in the commercial samples under study. Amounts ranging from 110-459 mg/L, dominated by chlorogenic acid with concentrations from 53-217 mg/L, were determined. Information about cultivar-typical apple polyphenol content and profile is important for bioactivity studies and, consequently, essential for the development of consumer-relevant products with particular nutritional functionalities.     

Coal is a potential source of naphthenic acids in groundwater

Naphthenic acids, with the general formula C_nH_2n + ZO₂, are found in conventional petroleums and oil sands ores. These acids are toxic to aquatic life, so their discharge from petroleum processing into receiving waters must be avoided. In a previous study, naphthenic acids were putatively identified in groundwaters from two domestic wells that were distant from petroleum sources. However, coal deposits were near these wells. In this study, waters from the two wells were extracted and analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to unequivocally confirm the presence of naphthenic acids and other organic acids. In addition, distilled water was percolated through three crushed coal samples and the leachates were shown to contain a variety of organic acids, including naphthenic acids. These results clearly demonstrate that coal is a source of naphthenic acids and that the naphthenic acids can leach into groundwaters. Thus, the presence of naphthenic acids in waters cannot be solely attributed to petroleum or petroleum industry activities.     

A sensitive and selective method for the quantitative determination of fatty acid tryptamides as shell indicators in cocoa products

 Tetracosanoyl-2-(3-indolyl)ethane amide (lignocerinic acid tryptamide; LAT) and docosanoyl-2-(3-indolyl)ethane amide (behenic acid tryptamide; BAT) were identified as the most prominent tryptamides in cocoa shells based on electrospray ionisation mass spectrometry and ¹H NMR measurements. The structure of LAT, which is reported for the first time in cocoa shells, and also that of BAT were confirmed by synthesis. By using synthesised heptadecanoyl-2-(3-indolyl)ethane amide as the internal standard, a sensitive and reproducible method was developed for the quantification of LAT and BAT in the picogram range by means of HPLC/fluorescence detection. The detection limit was determined to be 30 pg/run. In authentic shell samples, 50-fold higher concentrations of both tryptamides were determined compared to the cocoa cotyledons. In 15 commercial chocolate samples, concentrations of 23.1–63.0 μg of the tryptamides (sum of both) per gram of fat were found. A first experiment attempted to correlate the tryptamide content with the amounts of shells in a model chocolate showed that the method is a promising tool to determine the shell content in the quality assessment of cocoa products. Received: 8 May 1998     

C NMR and electrospray ionization mass spectrometric study of sucrose aqueous solutions at high pH: NMR measurement of sucrose dissociation constant

The ¹³C NMR technique is used for the measurement of the first dissociation constant of sucrose (HL) in highly alkaline solutions. In 1.0 M NaCl/NaOH medium and for 25 °C, the concentration dissociation constant (pK₁) was 13.1 ± 0.3; and, for 60 °C, pK₁ = 12.30 ± 0.05. The β-d-fructofuranosyl ring was found to be responsible for dissociation. The NMR data reveal no clear evidence of the second dissociation step below pH 14, either at 25 °C or at 60 °C. In the solutions with 4–10 mol dm⁻³ NaOH content the ¹³C NMR technique indicated the chemical shift changes, treated as the second dissociation step of sucrose and a sodium complex formation. A very rough estimation, for variable ionic strength, gives the value: pK₂ ∼ 15.8 ± 0.8. The anionic species L⁻ and NaH₋₁L⁻ have been registered by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) for 0.01 M sucrose solutions with initial pH 13.     

Electrospray ionization mass spectrometric end-group analysis of PMMA produced by radical polymerization using diacyl peroxide initiators

The type and number of end groups of poly(methyl methacrylates) from free-radical polymerization with six diacyl peroxides, R-(CO)O-O(CO)-R, acting as initiators have been analyzed via electrospray ionization mass spectrometry using an ion trap and additionally Fourier transform ion cyclotron resonance for mass detection. The polymerizations were carried out in benzene solution at high initiator concentration to yield low molecular weight polymer. With R being an alkyl group, only R moieties are observed as end groups. For each oligomer size, molecules with one or two such end groups are formed, depending on whether termination occurs via disproportionation or combination. With R being an aryl type, as in di-benzoyl and di-naphthoyl peroxides, both R and R-(CO)O moieties are detected as polymeric end groups. Because of aromatic delocalization, fractions of the arylic R-(CO)O radicals are sufficiently long living at 95 °C to add to a monomer molecule prior to undergo decarboxylation.     

Study of sphingolipids oxidation by ESI tandem MS

Sphingolipids are a class of lipids that play important cellular roles both as structural components of membranes and as signaling molecules. They have also an active participation in apoptosis and inflammation processes which are associated with oxidative stress conditions. However, no studies so far accomplished the oxidative modification of sphingolipids under oxidative stress conditions. In the present study, different sphingolipids, ((d18:1/16:0) sphingomyelin (N‐palmitoyl‐D ‐erythro‐sphingosylphosphorylcholine, SM), (d18:1) sphingosylphosphorylcholine (a lysosphingolipid, SPC), and (d18:1/18:0) ceramide (Cer)) were oxidized by the hydroxyl radical, generated under Fenton reaction conditions, and the oxidation reaction was monitored by ESI‐MS in positive mode. No oxidation products were identified for Cer under the oxidative conditions used, while ESI‐MS spectra of SPC and SM after oxidation show some oxidation products that were analyzed by ESI‐MS/MS. This approach allowed identifying hydroxyl and keto derivatives of SPC and acetaldehydephosphorylcholine derivative (m/z 226). SM oxidation occurs exclusively in sphingosine backbone with formation of SPC, hydroxyl, and keto derivatives of SPC and the oxidation product at m/z 226. This study may give new insight and could help to understanding the behavior and biological roles of the sphingolipids under oxidative stress conditions.     

Monitoring of the multiple bacteriocin production by Enterococcus faecium NKR-5-3 through a developed liquid chromatography and mass spectrometry-based quantification system

Enterococcus faecium NKR-5-3 produces four antimicrobial peptides referred here as enterocins NKR-5-3A, B, C and D. A two-step electrospray ionization-liquid chromatography and mass spectrometry (ESI-LC/MS)-based quantification system was developed to monitor its multiple bacteriocin production profiles, which is essential in understanding the complex production regulation mechanism of strain NKR-5-3. The developed ESI-LC/MS-based quantification system can easily monitor the multiple bacteriocin production of this strain. Using the developed system, the production of enterocin NKR-5-3B was found to be not as variable as those of the other enterocins in different cultivation media. Production of enterocin NKR-5-3B was also found to have a wider optimum incubation temperature (20-30°C) than enterocins NKR-5-3A, C and D (25°C). Furthermore, at least 2?nM of the bacteriocin-like inducing peptide, enterocin NKR-5-3D, regulated the production of NKR-5-3 enterocins except enterocin NKR-5-3B. These findings taken together suggest that enterocin NKR-5-3B has an independent production regulation mechanism from the other NKR-5-3 enterocins. The developed system could effectively pin-point the production profiles of the multiple bacteriocins of E.?faecium NKR-5-3 under different fermentation conditions.