Medieval human bones have the potential to reveal diet, mobility and treatment of diseases in the past. During the last two decades trace element chemistry has been used extensively in archaeometric investigations revealing such data. Many studies have reported the trace element inventory in only one sample from each skeleton – usually from the femur or a tooth. It cannot a priori be assumed that all bones or teeth in a skeleton will have the same trace element concentrations.
Six different bone and teeth samples from each individual were carefully decontaminated by mechanical means. Following dissolution of ca. 20 mg sample in nitric acid and hydrogen peroxide the assays were performed using inductively coupled plasma mass spectrometry (ICPMS) with quadropole detection. We describe the precise sampling technique as well as the analytical methods and parameters used for the ICPMS analysis.
The places of sampling in the human skeleton did exhibit varying trace element concentrations. Although the samples are contaminated by Fe, Mn and Al from the surrounding soil where the bones have been residing for more than 500 years, other trace elements are intact within the bones. It is shown that the elemental ratios Sr/Ca and Ba/Ca can be used as indicators of provenance.
The differences in trace element concentrations can be interpreted as indications of varying diet and provenance as a function of time in the life of the individual – a concept which can be termed chemical life history. A few examples of the results of such analyses are shown, which contains information about provenance and diagenesis. Copyright © 2013 John Wiley & Sons, Ltd.
Only a few gold tellurides are known. However, Laser Ablation Synthesis (LAS) using Laser Desorption Ionisation (LDI) time-of-flight mass spectrometry (TOF MS) has high potential for the generation of new compounds.
LDI of nanogold-Te conjugate using a nitrogen laser 337 nm was applied while the mass spectra were recorded in positive and negative ion modes using a quadrupole ion trap-TOF mass spectrometer equipped with a reflectron. Diffuse coplanar surface barrier discharge was applied for the plasma treatment of glass and silicon surfaces.
A form of nanogold-Te conjugate was prepared and found suitable for LAS of gold tellurides. Several new AumTen (m = 1–11; n = 1–4) clusters were identified. An excess of nanogold and chloride or an excess of auric acid caused the formation of mixed AumTenClx clusters. The nanogold-Te conjugate can be deposited from an aqueous suspension onto glass while the deposition is strongly enhanced if the surface is modified by plasma.
LDI of nanogold-Te conjugate is a suitable procedure for the generation of new gold telluride clusters. Treatment of borosilicate glass with a diffuse coplanar surface barrier discharge strongly enhances the deposition of gold tellurides on glass while limited adsorption on a silicon surface was observed. Copyright © 2013 John Wiley & Sons, Ltd.
The photodynamic process involves the combined use of light and a photosensitizer, which, in the presence of oxygen, originates cytotoxic species capable of oxidizing biological molecules, such as lipids. However, the effect of the photodynamic process in the bacterial phospholipid profile by a photosensitizer has never been reported. A lipidomic approach was used to study the photodynamic oxidation of membrane phospholipids of Staphylococcus warneri by a tricationic porphyrin [5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin triiodide, Tri-Py+-Me-PF].
S. warneri (108 colony forming units mL–1) was irradiated with white light (4 mW cm–2, 21.6 J cm–2) in the presence of Tri-Py+-Me-PF (5.0 μM). Non-photosensitized bacteria were used as control (irradiated without porphyrin). After irradiation, total lipids were extracted and separated by thin-layer chromatography (TLC). Isolated fractions of lipid classes were quantified by phosphorus assay and analyzed by mass spectrometry (MS): off-line TLC/ESI-MS, hydrophilic interaction (HILIC)-LC/MS and MS/MS.
The most representative classes of S. warneri phospholipids were identified as phosphatidylglycerols (PGs) and cardiolipins (CLs). Lysyl-phosphatidylglycerols (LPGs), phosphatidylethanolamines (PEs), phosphatidylcholines (PCs) and phosphatidic acids (PAs) were also identified. After photodynamic treatment, an overall increase in the relative abundance of PGs was observed as well as the appearance of new oxidized species from CLs, including hydroxy and hydroperoxy derivatives. Formation of high amounts of lipid hydroperoxides was confirmed by FOX2 assay. Photodynamic oxidation of phospholipid standards revealed the formation of hydroperoxy and dihydroperoxy derivatives, confirming the observed CL oxidized species in S. warneri.
Membrane phospholipids of S. warneri are molecular targets of the photoinactivation process induced by Tri-Py+-Me-PF. The overall modification in the relative amount of phospholipids and the formation of lipid hydroxides and hydroperoxides indicate the lethal damage caused to photosensitized bacterial cells. Copyright © 2013 John Wiley & Sons, Ltd.
In protein studies that employ tandem mass spectrometry the manipulation of protonated peptide fragmentation through exclusive dissociation pathways may be preferred in some applications over the comprehensive amide backbone fragmentation that is typically observed. In this study, we characterized the selective cleavage of the side-chain Cζ–Nε bond of peptides with ortho-hydroxybenzyl-aminated lysine residues.
Internal lysyl residues of representative peptides were derivatized via reductive amination with ortho-hydroxybenzaldehyde. The modified peptides were analyzed using collision-induced dissociation (CID) on an Orbitrap tandem mass spectrometer. Theoretical calculations using computational methods (density functional theory) were performed to investigate the potential dissociation mechanisms for the Cζ–Nε bond of the derivatized lysyl residue resulting in the formation of the observed product ions.
Tandem mass spectra of the derivatized peptide ions exhibit product peaks corresponding to selective cleavage of the side-chain Cζ–Nε bond that links the derivative to lysine. The ortho-hydroxybenzyl derivative is released either as a neutral moiety [C7H6O1] or as a carbocation [C7H7O1]+ through competing pathways (retro-Michael versus Carbocation Elimination (CCE), respectively). The calculated transition state activation barriers indicate that the retro-Michael pathway is kinetically favored over CCE and both are favored over amide cleavage.
The application of ortho-hydroxybenzyl amination is a promising peptide derivatization scheme for promoting selective dissociation pathways in the tandem mass spectrometry of protonated peptides. This can be implemented in the rational development of peptide reactive reagents for applications that may benefit from selective fragmentation paths (including crosslinking or MRM reagents). Copyright © 2013 John Wiley & Sons, Ltd.
The kinetic nature of the phosphoric acid digestion reaction enables clumped isotope analysis of carbonates using gas source isotope ratio mass spectrometry (IRMS). In most laboratories acid digestions are performed at 25°C in sealed vessels or at 90°C in a common acid bath. Here we show that different Δ47 results are obtained depending on the digestion technique employed.
Several replicates of a biogenic aragonite and NBS 19 were reacted with 104% H3PO4 in sealed vessels at 25°C and at 90°C using a common acid bath. The sample size varied between 4 mg and 14 mg. Purification methods that are standard for clumped isotope analyses were applied to the evolved CO2 before measuring the abundances of masses 44 to 49 relative to a reference gas by IRMS.
A systematic trend to lower and more consistent Δ47 values is observed for reactions at 25°C if the sample size is increased. We suggest that secondary re-equilibration of evolved CO2 or reaction intermediates with free water molecules preferentially occurs for relatively small samples (4–7 mg), finally yielding elevated Δ47 values compared with >7 mg aliquots. In contrast, no such sample size effect on Δ47 values is observed for carbonates that are digested at 90°C using the common acid bath.
The determination of Δ47 values of carbonate samples smaller than 7 mg becomes more precise and accurate if digestions are performed at 90°C. Based on our results we propose that the difference in phosphoric acid fractionation factor between 25°C and 90°C is 0.07‰ for both calcite and aragonite. Copyright © 2013 John Wiley & Sons, Ltd.
Polyethylene glycols (PEGs) are soluble molecules utilized in a wide range of applications. Mass spectrometry and fragmentation patterns of positively charged PEG oligomers are well-known, but decomposition mechanisms of the deprotonated ions have not been studied.
Deprotonated PEGs were generated by electrospray ionization of PEG in water/acetonitrile. Collision-induced dissociation (CID) experiments were carried out in a tandem mass spectrometer. The anions were studied using a tandem mass spectrometer to carry out CID experiments. A series of small PEG oligomers, with 1 to 8 monomer units, were studied in order to monitor size-dependent effects on fragmentation reactions.
Because deprotonated PEG ions have a unique charge site, their dissociation pathways can easily be monitored. The ions fragment by loss of C2H4O monomer units, with an alternating intensity pattern that suggests the loss of an even number of monomer units is favored. Smaller oligomers and oligomer fragments also yielded fragments corresponding to H2 elimination and H2O loss. H2 elimination occurs by the generation of a hydride ion which deprotonates an alcohol upon leaving, while dehydration appears to be a charge-remote process.
The fragmentation of deprotonated PEG is dominated by intramolecular SN2 reactions involving the terminal oxide anion. Copyright © 2013 John Wiley & Sons, Ltd.
High-temperature, conversion-reduction (HTC) systems convert hydrogen and oxygen in materials into H2 and CO for δ2H and δ18O measurements by isotope ratio mass spectrometry. HTC of nitrogen- and sulfur-bearing materials produces unintended byproduct gases that could affect isotope analyses by: (1) allowing isotope exchange reactions downstream of the HTC reactor, (2) creating isobaric or co-elution interferences, and (3) causing deterioration of the chromatography. This study characterizes these HTC byproducts.
A HTC system (ThermoFinnigan TC/EA) was directly connected to a gas chromatograph/quadrupole mass spectrometer in scan mode (m/z 8 to 88) to identify the volatile products generated by HTC at conversion temperatures of 1350 °C and 1450 °C for a range of nitrogen- and sulfur-bearing solids [keratin powder, horse hair, caffeine, ammonium nitrate, potassium nitrate, ammonium sulfate, urea, and three nitrated organic explosives (PETN, RDX, and TNT)].
The prominent HTC byproduct gases include carbon dioxide, hydrogen cyanide, methane, acetylene, and water for all nitrogen-bearing compounds, as well as carbon disulfide, carbonyl sulfide, and hydrogen sulfide for sulfur-bearing compounds. The 1450 °C reactor temperature reduced the abundance of most byproduct gases, but increased the significant byproduct, hydrogen cyanide. Inclusion of a post-reactor chemical trap containing Ascarite II and Sicapent, in series, eliminated the majority of byproducts.
This study identified numerous gaseous HTC byproducts. The potential adverse effects of these gases on isotope ratio analyses are unknown but may be mitigated by higher HTC reactor temperatures and purifying the products with a purge-and-trap system or with chemical traps. Published in 2013. This article is a U.S. Government work and is in the public domain in the USA.
The aim of this study was to demonstrate, and to characterize by high-resolution mass spectrometry that it is possible to preferentially induce covalent cross-links in peptides by using high-energy femtosecond ultraviolet (UV) laser pulses. The cross-link is readily formed only when aromatic amino acids are present in the peptide sequence.
Three peptides, xenopsin, angiotensin I, and interleukin, individually or in combination, were exposed to high-energy femtosecond UV laser pulses, either alone or in the presence of spin trapping molecules, the reaction products being characterized by high resolution mass spectrometry.
High-resolution mass spectrometry and spin trapping strategies showed that cross-linking occurs readily, proceeds via a radical mechanism, and is the highly dominant reaction, proceeding without causing significant photo-damage in the investigated range of experimental parameters.
High-energy femtosecond UV laser pulses can be used to induce covalent cross-links between aromatic amino acids in peptides, overcoming photo-oxidation processes, that predominate as the mean laser pulse intensity approaches illumination conditions achievable with conventional UV light sources. Copyright © 2013 John Wiley & Sons, Ltd.