Isotopic Patterns Research Articles

Differentiation of Geographic Origin of South African Wines from Austrian Wines by IRMS and SNIF-NMR.

Geographic origin and terroir are very important parameters for wine and significantly impact price. Incorrect declarations are known to occur intentionally to increase profit, thus, measures for control are required. Accompanying paperwork has been shown to be unreliable, thus, control of the product itself is required. Here we investigate and compare the stable isotope pattern of South African (Western Cape Province) wine, and evaluate its potential for discrimination from Central European/Austrian wine. The results show that the isotope values of the investigated South African wine samples differ significantly from the values of average Austrian (Central European) wines. Thus, a differentiation of the products from these two regions by stable isotope analysis is generally straightforward. However, the data suggest that vintages from years with exceptionally hot and dry summer weather in Europe may reduce the differentiation between these regions. Therefore, this method is a potent tool for the discrimination of Austrian (Central European) and South African wines under current climatic conditions, although drier and hotter summer weather in Europe, which is likely to occur more frequently due to global climate change, may require further method adjustments in the future.

Geolocator-tracking seabird migration and moult reveal large-scale, temperature-driven isoscapes in the NE Atlantic.

By combining precision satellite-tracking with blood sampling, seabirds canbeusedto validate marine carbon and nitrogen isoscapes, but it is unclear whether a comparable approach using low-precision light-level geolocators (GLS) and feather sampling can be similarly effective. Here we used GLS to identify wintering areas of northern gannets (Morus bassanus) and sampled winter grown feathers (confirmed from image analysis of non-breeding birds) to test for spatial gradients in δ13 C and δ15 N in the NE Atlantic. By matching winter-grown feathers with the non-breeding location of tracked birds we found latitudinal gradients in δ13 C and δ15 N in neritic waters. Moreover, isotopic patterns were best explained by sea surface temperature. Similar isotope gradients were found in fish muscle sampled at local ports. Our study reveals the potential of using seabird GLS and feathers to reconstruct large-scale isotopic patterns.

Nucleosynthesis in Outflows from Black Hole–Neutron Star Merger Disks with Full GR(ν)RMHD

Along with binary neutron star mergers, the inspiral and merger of a black hole and a neutron star is a predicted site of r-process nucleosynthesis and associated kilonovae. For the right mass ratio, very large amounts of neutron-rich material (relative to the dynamical ejecta) may become unbound from the post-merger accretion disk. We simulate a suite of four post-merger disks with three-dimensional general-relativistic magnetohydrodynamics with time-dependent Monte Carlo neutrino transport. We find that within 104 GM BH/c 3 (∼200–500 ms), the outflows from these disks are very close to the threshold conditions for robust r-process nucleosynthesis. For these conditions, the detailed properties of the outflow determine whether a full r-process can or cannot occur, implying that a wide range of observable phenomena is possible. We show that on average the disk outflow lanthanide fraction is suppressed relative to the solar isotopic pattern. In combination with the dynamical ejecta, these outflows imply a kilonova with both blue and red components.

High-precision Pb isotopes of drinking water lead pipes: Implications for human exposure to industrial Pb in the United States

Millions of lead (Pb) pipes are still used in the drinking water distribution systems in many regions in the world. Human exposure to Pb from contaminated drinking water continues to be of concern in the United States (U.S.), as illustrated by the widely publicized “Flint Water Crisis” in 2015. The Pb isotopic composition of Pb-pipes potentially can be useful to identify human exposure to Pb from lead service lines (LSLs). In addition, as the LSLs were likely manufactured from similar industrial Pb sources as other Pb objects and materials in the USA, the Pb-pipes isotope data can provide information about the overall isotopic composition of the U.S. industrial Pb.In this work we present high-precision Pb isotope data from Pb-pipes excavated from different U.S. municipalities. The Pb-pipes show an extremely wide range of Pb isotopic compositions, with 206Pb/204Pb ranging from 17.004 to 22.010, 207Pb/204Pb from 15.460 to 15.921, and 208Pb/204Pb from 36.687 to 41.120. The wide isotope range is observed even in a single town, suggesting that no regional Pb isotope patterns can be expected within the continental USA. However, the high-precision MC-ICP-MS Pb data form a clear linear trend that, depending on the context, can be used to identify human Pb exposure. Furthermore, as the linear trend is a result of utilization of Pb ores from different domestic and international sources and secondary recycling of metallic Pb, it is likely representative of the overall isotopic composition of the U.S. industrial Pb pool. Therefore, the identified trend is the most accurate isotope representation of the U.S. anthropogenic Pb at present and can be used as first-order evaluation to determine if a person with elevated blood Pb levels was exposed to U.S. industrial Pb sources.

Electrospray Mass Spectrometry to Study Combinatorial iClick Reactions and Multiplexed Kinetics of [Ru(N3)(N∧N)(terpy)]PF6 with Alkynes of Different Steric and Electronic Demand.

In a combinatorial approach, a family of ruthenium(II) azido complexes [Ru(N3)(N∧N)(terpy)]PF6 with terpy = 2,2':6',2″-terpyridine and N∧N as a bidentate chelator derived from 2,2'-biypridine and its 4,4'-disubstituted derivatives, 2,2'-bipyrimidine, and 1,10-phenanthroline were reacted with different internal and terminal alkynes to give access to a total of 7 × 7 = 49 triazolato complexes in a room-temperature catalyst-free iClick reaction. The reactants were mixed in a repurposed high-performance liquid chromatography (HPLC) autosampler, and the reaction progress was monitored by direct injection into an electrospray mass spectrometer. The ratio of the peak intensities of [Ru(N3)(N∧N)(terpy)]+ and [Ru(triazolato)(N∧N)(terpy)]+ was converted to a colored heat map for facile visual inspection of the conversion ratio. By automated multiple injections of the reaction mixture in fixed time intervals and plotting peak intensities over reaction time, pseudo-first-order rate constants were easily determined. Finally, nonoverlapping isotope patterns of the azido starting materials and triazolato products enabled multiplexed parallel determination of rate constants for four different ruthenium(II) azido complexes from a single sample vial, thereby reducing experiment time by 75%.

Effects of Agricultural Large‐And Medium‐Sized Reservoirs on Hydrologic Processes in the Arid Shiyang River Basin, Northwest China

AbstractAgricultural large and medium‐sized reservoirs in arid regions increase the water stresses within local hydrologic systems, adding to pressures on aquatic ecosystems and also threatening the sustainability of water resources. Yet, there is limited research concerning how agricultural reservoirs affect the hydrology of inland river basins, which has hampered a comprehensive assessment of sustainable water use in these systems. We explore the use of stable isotopes of water to evaluate the effects of agricultural reservoirs on hydrology and the sustainable use of water in the arid Shiyang River basin. Results show that agricultural large‐ and medium‐sized reservoirs in this arid region alter local isotopic hydrologic patterns increasing water‐body evaporation and enriching the isotopic composition of water near the reservoir. As a result, evaporation losses of reservoir water can be as high as 30.7% in downstream desert reservoirs. Reservoir water also exchanges with surrounding groundwater and contributes 22% to local precipitation due to reservoir evaporation. Detailed studies of individual reservoirs show that the isotopic composition is most enriched at the surface of the reservoir and then gradually depletes toward the bottom. The cumulative effect of multiple large and medium sized reservoirs profoundly alters hydrologic processes in inland river basins, leading to an evaporation‐led water loss in these systems.

Melting and melt segregation processes controlling granitic melt composition

Abstract Several important processes in the petrogenesis of granite are still debated due to a poor understanding of complex interactions between minerals during the melting and melt segregation processes. To promote an improved understanding of the mineral-melt relationships, we present a systematic petrographic and geochemical analysis for melanosome and leucosome samples from the Triassic Jindong migmatite, South China. Petrographic observations and zircon U-Pb geochronology indicate that the Jindong migmatite was formed through water-fluxed melting of the Early Paleozoic gneissic granite (437 ± 2 Ma) during the Triassic (238 ± 1 Ma), with the production of melt dominated by the breakdown of K-feldspar, plagioclase, and quartz. The Jindong leucosomes may be divided into lenticular and net-structured types. Muscovite, plagioclase, and K-feldspar in the net-structured leucosome show higher Rb and much lower Ba and Sr contents than those in the lenticular leucosome. This may be attributed to the elevation of Rb and decreasing Ba and Sr abundances in melts during the segregation process due to early fractional crystallization of K-feldspar and plagioclase. These leucosomes show negative correlation between εNd(t) and P2O5, reflecting increasing dissolution of low-εNd(t) apatite during the melting process. The continuous dissolution of apatite caused saturation of monazite and xenotime in melt, resulting in the growth of monazite and xenotime around apatite in the melanosome. This process led to a sharp decrease of Th, Y, and REE with increasing P2O5 in the leucosome samples. This complex interplay of accessory mineral reactions in the source impacts REE geochemistry and Nd isotope ratios of granites. As the granites worldwide exhibit similar compositional and isotopic patterns to the Jindong leucosomes, we suggest that both the melting and melt segregation processes strongly control the granitic melt compositions.

Response of the North Lhasa terrane to the initial break-up of Rodinia: Evidence from the newly identified early Neoproterozoic gabbros in the Asa area, southern Tibet

Due to the less exposure of Precambrian basement, the origin of ancient continental blocks in the Tibetan plateau and their paleogeographic locations in the Rodinia supercontinent remain enigmatic. Here we first report the newly identified Precambrian basement from the Asa region of the North Lhasa terrane (NL), southern Tibet. The zircon U–Pb age and whole-rock geochemical data on gabbro intrusions (known as Tugu gabbros) in this basement reveal an important tectonic evolution process of continental-oceanic transition experienced by the North Lhasa terrane in the early Neoproterozoic (ca. 900–875 Ma), which may be the prelude to the disintegration of Rodinia in China. Tugu gabbros (ca. 876–874 Ma) belong to the series of sub-alkaline tholeiitic basalt and have N-MORB geochemical affinities. In combination, the high (87Sr/86Sr)i ratios (0.709–0.711), positive εNd(t) values (2.8–3.9) and the relatively young Nd isotopic pattern age (tDMC = 1.2–1.3 Ga) indicate that it came from a depleted mantle source and were formed in an intercontinental rift environment on the northern margin of Rodinia. According to previous studies and data provided herein, the era and nature of Precambrian magmatic-metamorphic records in North and South Lhasa terranes cannot be compared, suggesting these may have been two separate terranes in the Precambrian. We propose that the South Lhasa terrane (SL) originated from India, while the North Lhasa terrane may originate from Australia. After splitting from Australia at ca. 930–875 Ma, the North Lhasa terrane continued to drift westward owing to the break-up of Rodinia. During the process of drifting, the North Lhasa terrane received sedimentary input from India and developed Andean-type arc magmatism with the influence of oceanic subduction on the northwest margin of supercontinent.

Immuno‐Desorption Electrospray Ionization Mass Spectrometry Imaging Identifies Functional Macromolecules by Using Microdroplet‐Cleavable Mass Tags

AbstractWe present immunoassay‐based desorption electrospray ionization mass spectrometry imaging (immuno‐DESI‐MSI) to visualize functional macromolecules such as drug targets and cascade signaling factors. A set of boronic acid mass tags (BMTs) were synthesized to label antibodies as MSI probes. The boronic ester bond is employed to cross‐link the BMT with the galactosamine‐modified antibody. The BMT can be released from its tethered antibody by ultrafast cleavage of the boronic ester bond caused by the acidic condition of sprayed DESI microdroplets containing water. The fluorescent moiety enables the BMT to work in both optical and MS imaging modes. The positively charged quaternary ammonium group enhances the ionization efficiency. The introduction of the boron element also makes mass tags readily identified because of its unique isotope pattern. Immuno‐DESI‐MSI provides an appealing strategy to spatially map macromolecules beyond what can be observed by conventional DESI‐MSI, provided antibodies are available to the targeted molecules of interest.

Immuno-Desorption Electrospray Ionization Mass Spectrometry Imaging Identifies Functional Macromolecules by Using Microdroplet-Cleavable Mass Tags.

We present immunoassay-based desorption electrospray ionization mass spectrometry imaging (immuno-DESI-MSI) to visualize functional macromolecules such as drug targets and cascade signaling factors. A set of boronic acid mass tags (BMTs) were synthesized to label antibodies as MSI probes. The boronic ester bond is employed to cross-link the BMT with the galactosamine-modified antibody. The BMT can be released from its tethered antibody by ultrafast cleavage of the boronic ester bond caused by the acidic condition of sprayed DESI microdroplets containing water. The fluorescent moiety enables the BMT to work in both optical and MS imaging modes. The positively charged quaternary ammonium group enhances the ionization efficiency. The introduction of the boron element also makes mass tags readily identified because of its unique isotope pattern. Immuno-DESI-MSI provides an appealing strategy to spatially map macromolecules beyond what can be observed by conventional DESI-MSI, provided antibodies are available to the targeted molecules of interest.

Mass-independent Sn isotope fractionation and radiogenic 115Sn in chondrites and terrestrial rocks

Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In.Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures.Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth’s core.

The geochemistry of zinc and copper stable isotopes in marine hydrothermal brine pools: Perspectives from metalliferous sediments of the Atlantis II Deep, Red Sea

This study provides a zinc and copper stable isotope characterization (δ66Zn, δ68Zn, and δ65Cu) of metalliferous seafloor sediments from the Atlantis II Deep, a hydrothermally influenced brine basin in the Red Sea. Samples collected from box cores that capture the entire stratigraphy in the Deep have δ66Zn and δ65Cu values of −0.31 to 0.34 ‰ (0.02 ‰ median) and − 1.81 to 1.02 ‰ (−0.34 ‰ median) relative to the JMC-Lyon and NIST SRM 976 standards, respectively. These results suggest enrichments of light stable isotopes in sediments compared to the hydrothermal inputs to the basin, which likely overlap the mantle-like isotopic signatures of basalts beneath the Deep. Such shifts to lower δ66Zn and δ65Cu values are consistent with widespread metal sulfide deposition from the brines because sulfide anions preferentially consume the light stable isotopes of zinc and copper. However, this interpretation contrasts with observations in the open ocean, where the fractionation of zinc and copper stable isotopes is strongly influenced by biological utilization and organic matter. Previous studies proposed that metal deposition in the Atlantis II Deep is also driven by adsorption onto iron oxides/hydroxides and their weakly crystalline (Si-)Fe-OOH precursor phases within the brines. However, because this process should accumulate heavy zinc and copper stable isotopes, its influence on isotopic fractionation is likely limited. Controls by metal sulfide precipitation are also indicated by spatial covariations between δ66Zn and concentrations of zinc and copper, that is, δ66Zn values increase whereas metal contents decrease with distance away from hydrothermal venting. Comparable trends are lacking for copper isotopes, perhaps because of additional influence by redox processes or, compared to zinc, a much stronger influence by adsorption onto (Si-)Fe-OOH phases, particularly in areas distal to hydrothermal venting where reduced sulfur could be scarce. Collectively, our results from the Atlantis II Deep indicate that zinc and copper stable isotopes could provide information about base and precious metals deposits from similar paleoenvironments. Firstly, zinc and copper stable isotopes shed light on metal sourcing and accumulation processes. Secondly, mineral precipitation in hydrothermally influenced brine pools produces zinc stable isotope patterns that, at least theoretically, could be of interest in mineral exploration at sub-basin and deposit scales.

Aspartame-Sweetened Tap Water: Transformation Products and 2,6-Dichloro-1,4-Benzoquinone Formation.

Aspartame (APM), a dipeptide of aspartic acid (ASP) and phenylalanine (PHE), is a widely used artificial sweetener in beverages. It is unclear whether residual chlorine in tap water can react with APM to form disinfection byproducts (DBPs). Therefore, we investigated the formation of DBPs from the reaction of APM with residual chlorine in authentic tap water. APM and a commercial sweetener (CS) packet containing APM were studied under authentic and simulated tap water conditions. Eight chlorinated products of APM were detected using solid-phase extraction (SPE) and high performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS). These new chloro-products were tentatively identified based on accurate masses, isotopic patterns of 35,37Cl, and MS/MS spectra. Furthermore, we identified APM as a precursor to 2,6-dichloro-1,4-benzoquinone (DCBQ). DCBQ significantly increased to 2.3-12 ng/L with the addition of APM or CS in tap waters collected from different locations compared to 1.4-1.8 ng/L in the same tap water samples without sweetener. DCBQ and two of the chlorinated transformation products were identified in cold prepared tea containing APM. DCBQ formation was eliminated when the residual chlorine in tap water was reduced by ascorbic acid or boiling prior to the addition of APM or CS. This study found that eight new DBPs and DCBQ were produced by the reactions of residual chlorine with APM and CS. These findings show an unintended exposure source of emerging DBPs via APM sweetened beverages.

Seasonal Mg isotopic variation in the middle Yellow River: Sources and fractionation

In order to better understand how stable metal isotope signals in large rivers can be used to constrain present and past weathering, the seasonal riverine MgSr isotopic pattern in the middle Yellow River was systematically investigated based upon weekly collected samples for the whole year of 2013. The results demonstrate that Mg is mainly transported in the dissolved form (65%) in this river system and that 45% of the total dissolved Mg is transported during the monsoon seasons, with 2% exported over 4 days during a single storm event. Dissolved Mg in the middle Yellow River is dominantly derived from both silicate and carbonate (82–89%) in this semi-arid region, with limited evaporite contribution (∼7%). Lithological mixing is the first order control on riverine dissolved Mg and Sr isotopes, with a contribution from ∼40% carbonate dissolution and ∼ 60% from silicate dissolution in the dry seasons, and ∼ 50% carbonate and ∼ 50% silicate during the monsoon seasons according to δ26Mg signals. Furthermore, a significant role of prior calcite precipitation (PCP) can be quantified, which fractionates Mg isotopes by about 0.17‰ to 0.39‰ positively depending on the choice of elemental and isotope partition of Mg in secondary carbonates. Clay formation following the PCP further fractionates riverine Mg isotopes to the negative side. An ∼0.2‰ decrease of riverine Mg isotopes is attributable to (1) a single storm event causing carbonate dissolution and (2) delayed delivery of depleted waters to rivers (∼3 months after the storm event) because of subsurface hydrological circulation. Annually, the weighted average riverine δ26Mg (−1.05‰) in the middle Yellow River is identical to the global average (−1.09‰). Despite the significant impact of lithology on the riverine dissolved Mg isotope signature, the mixing proportions of different Mg sources remain virtually constant, even when there are huge contrast of temperature, hydrology, and precipitation seasonally along the year, providing a basis for dissolved δ26Mg response to climatic forcing on the continental scale. This means that significant changes in the sedimentary Mg isotope records would reflect extreme conditions in deep time.

Magmatic record of changing Cordilleran plate-boundary conditions—Insights from Lu-Hf isotopes in the Mojave Desert

Abstract Belts of Cordilleran arc plutons in the eastern part of the Mojave crustal province, inboard from the southwestern North American plate boundary, record major magmatic pulses at ca. 180–160 and 75 Ma and smaller pulses at ca. 100 and 20 Ma. This cyclic magmatism likely reflects evolving plate-margin processes. Zircon Lu-Hf isotopic characteristics and inherited zircons for different-age plutons may relate magma sources to evolving tectonics. Sources similar in age to the bulk of the exposed Mojave crust (1.6–1.8 Ga) dominated the magmas. Rare zircons having εHf(t) values as low as −52 indicate that Cretaceous melt sources also included more ancient crustal components, such as Archean-derived detritus in supracrustal gneisses of the Vishnu basin. Some rocks signal contributions from mantle lithosphere (in the Miocene) or asthenosphere (middle Cretaceous). Temporal shifts in isotopic pattern in this sample of the Cordillera relate to cyclic pulses of magmatic flux. Hf-isotopic pull-downs suggestive of dominantly crustal sources characterize the Jurassic and Late Cretaceous flare-ups. The Late Cretaceous flare-up, occurring near the onset of flat-slab subduction, produced abundant Proterozoic xenocrystic zircon and Hf isotopes implicating derivation largely from heterogeneous deep Mojave crust. Isotopic pull-ups characterize the lower-flux middle Cretaceous and Miocene magmatic episodes. The middle Cretaceous pulse ca. 105–95 Ma produced Mojave crust signals but also the isotopically most juvenile magmatic zircons, ranging upward to barely positive εHf values and suspected to signal an asthenosphere contribution. This may point toward transtension or slab retreat causing 105–95 Ma backarc extension in the Mojave hinterland of the Cordillera. That possibility of backarc extension raises questions about the tectonic environment of the contemporaneous main Sierra Nevada high-flux arc closer to the continental margin.

Trophic ecology of mesopelagic fishes in the northern and southern Benguela Upwelling Systems revealed through stable isotope patterns

Mesopelagic fishes are important components of marine food webs as trophic links between primary consumers and higher trophic levels, but their trophic ecology is poorly understood. We used stable isotopes (δ13C and δ15N) to compare the trophic position, trophic enrichment factor, and isotopic niche among feeding guilds of mesopelagic fishes (including myctophids, stomiids) during different seasons in the northern and southern Benguela Upwelling Systems. These subsystems are influenced by differing water masses with various physical and biological properties, which can lead to changes in the marine food web. We aimed to determine if and how the trophic ecology of mesopelagic fishes differs between seasons and subsystems. When separating fishes into guilds based on dietary preferences (zooplanktivores vs. piscivores) and migration patterns (migrating vs. non-migrating), the trophic position was highest during winter in the south for non-migrating piscivores (4.5), but the trophic positions of piscivores (3.2-4.4) were not always higher than those of zooplanktivores (3.1-4.5). This may indicate different isotopic enrichment between species or a very generalist diet from zooplanktivores such as myctophids and their prey. Trophic enrichment factors for δ15N among guilds ranged from 3.8 to 7.5‰ between the baseline and zooplanktivores and from -0.8 to 1.6‰ between zooplanktivores and piscivores. Previously, mesopelagic fishes have been incorporated into food web models in the Benguela Upwelling Systems, but only as a single entity. Elucidating the complex seasonal and regional trophodynamics of various mesopelagic feeding guilds may contribute to more accurate assessments of trophic transfer efficiencies and higher-resolution models in these systems.

Identifying Stable Isotope Patterns among Taxa, Sites, and Environmental Variables in the Eastern Mississippi Sound

Identifying Stable Isotope Patterns among Taxa, Sites, and Environmental Variables in the Eastern Mississippi Sound

Lipid oxidation induced protein scission in an oleogel as a model food

Lipid oxidation induced protein scission was investigated in oleogel using beta-lactoglobulin (whey protein isolate) as gelator. Extracted cleaved peptides were measured using high resolution mass spectrometry (FT-ICR-MS), which was provided by an automatically generated annotation list approach to identify relevant masses and sum formula using the isotopic pattern. The identified oxidized peptides were then further evaluated using partial least squares regression to relevant lipid hydroperoxide formation data, which provide the significance and importance of the peptides toward lipid induced scission. Thereby, the most important peptides are located at the surface of the protein in random coil segments and especially at the ends of the protein sequence. The most important amino acids were cysteine and aliphatic amino acids, which undergo scission mostly by the α-amidation pathway. The findings compare well with studies investigating depletion of amino acids initiated by lipid oxidation in systems containing bovine albumin or gamma-globulin.

63Cu(I) binding to human kidney 68Zn7-βα MT1A: determination of Cu(I)-thiolate cluster domain specificity from ESI-MS and room temperature phosphorescence spectroscopy.

Mammalian metallothioneins (MTs) are important proteins in Zn(II) and Cu(I) homeostasis with the Zn(II) and Cu(I) binding to the 20 cysteines in metal-thiolate clusters. Previous electrospray ionization (ESI) mass spectrometric (MS) analyses of Cu(I) binding to Zn7-MT were complicated by significant overlap of the natural abundance isotopic patterns for Zn(II) and Cu(I) leading to impossibly ambiguous stoichiometries. In this paper, isotopically pure 63Cu(I) and 68Zn(II) allowed determination of the specific stoichiometries in the 68Zn,63Cu-βα MT1A species formed following the stepwise addition of 63Cu(I) to 68Zn7-βα MT1A. These species were characterized by ESI-MS and room temperature emission spectroscopy. The key species that form and their emission band centres are Zn5Cu5-βα MT1A (λ = 684nm), Zn4Cu6-βα MT1A (λ = 750nm), Zn3Cu9-βα MT1A (λ = 750nm), Zn2Cu10-βα MT1A (λ = 750nm), and Zn1Cu14-βα MT1A (λ = 634nm). The specific domain stoichiometry of each species was determined by assessing the species forming following 63Cu(I) addition to the 68Zn3-β MT1A and 68Zn4-α MT1A domain fragments. The domain fragment emission suggests that Zn5Cu5-βα MT1A contains a Zn1Cu5-β cluster and the Zn4Cu6-βα MT1A, Zn3Cu9-βα MT1A, and Zn2Cu10-βα MT1A each contain a Cu6-β cluster. The species forming with >10mol. eq. of 63Cu(I) in βα-MT1A exhibit emission from the Cu6-β cluster and an α domain cluster. This high emission intensity is seen at the end of the titrations of 68Zn7-βα MT1A and the 68Zn4-α MT1A domain fragment suggesting that the initial presence of the Zn(II) results in clustered Cu(I) binding in the α domain.

A review of carbon isotopes and maturity determinations of paleozoic unconventional shale gases

Isotope rollover and reversal have been widely reported from unconventional shale gas systems, and importantly this phenomenon is often associated with productive and highly mature gases. Although information about thermal maturity is critical to assess potential source rocks, determining maturity is often challenging for early Paleozoic source rocks due to a lack of true vitrinite. Carbon isotopes of gas compounds have been utilized to calculate maturity (vitrinite reflectance equivalent) of conventional gases based on linear correlations between carbon isotopes and maturity. As isotope rollover and reversal commonly occur in highly mature unconventional gases (e.g., Ro > 1.5%), the relationship between carbon isotopes and maturity is no longer linear, and utilizing such calculations would underestimate maturity for highly mature gases. In order to determine gas maturity, this review integrates isotopic and chemical data with traditional maturity methods from well-studied Paleozoic unconventional gas plays in the world. These gases show a common pattern of carbon isotopes of methane and ethane varying from normal, i.e., becoming 13C enriched with maturity, to rollover and even reversing the normal trend during gas maturation. Four levels of maturity are defined as vitrinite reflectance equivalent for these Paleozoic unconventional gases based on carbon isotopes: 0.5–1.5% (I), 1.5–2.0% (II), 2.0–3.5% (III), and 3.5–5% (IV). The maturity levels and the corresponding isotope trends suggest that as gas maturity increases, carbon isotopes of gas compounds may be controlled more by maturity and affected less by source rocks (e.g., different marine facies). The implication of this study is that the isotope patterns, along with maturity levels, can be utilized to help explorationists identify sweet spots. For example, it is expected that the best liquid potential is in level I, the best gas potential is between level II and level III, and a gas in level IV is beyond its peak productivity.