Dissolved organic matter (DOM) is a significant (>700 Pg) global C pool. Transport of terrestrial DOM to the inland waters and coastal zones represents the largest flux of reduced C from land to ...water (215 Tg yr−1) (Meybeck, M. Am. J. Sci. 1983, 282, 401−450). Oxidation of DOM by interdependent photochemical and biochemical processes largely controls the fate of DOM entering surface waters. Reactive oxygen species (ROS) have been hypothesized to play a significant role in the photooxidation of DOM, because they may oxidize the fraction of DOM that is inaccessible to direct photochemical degradation by sunlight. We followed the effects of photochemically produced singlet oxygen (1O2) on DOM by mass spectrometry with 18O-labeled oxygen, to understand how 1O2-mediated transformations of DOM may lead to altered DOM bioavailability. The photochemical oxygen uptake by DOM attributed to 1O2 increased with DOM concentration, yet it remained a minority contributor to photochemical oxygen uptake even at very high DOM concentrations. When DOM samples were exposed to 1O2-generating conditions (Rose Bengal and visible light), increases were observed in DOM constituents with higher oxygen content and release of H2O2 was detected. Differential effects of H2O2 and 1O2-treated DOM showed that 1O2-treated DOM led to slower bacterial growth rates relative to unmodified DOM. Results of this study suggested that the net effect of the reactions between singlet oxygen and DOM may be production of partially oxidized substrates with correspondingly lower potential biological energy yield.
We tested a long-standing hypothesis within river ecology, predicted by the River Continuum Concept, that dissolved organic matter (DOM) diversity decreases with stream order. We measured DOM ...molecular composition across three stream orders in the headwaters of well characterized forested catchments with ultrahigh-resolution mass spectrometry to assess DOM chemogeography and chemodiversity over the spatial scales of climatic regions and fluvial networks. Stream waters with similar dissolved organic carbon (DOC) concentrations in different climatic regions had distinctive DOM compositions, but shared 69.5 % of the 3286 individual chemical formulae detected. DOM compositions common to all watersheds were characterized by abundant lignin-like and tannin-like molecules as well as carboxyl-rich alicyclic-like molecules (CRAM); 50 % of all formulae were found in all streams. Of the roughly 700 unique chemical formulae within a given fluvial network, most were outside the CRAM region within a van Krevelen diagram and 78 to 95 % were restricted to 1st-order streams where diffuse ground water sources surface, coalesce into a channel, and flow downstream. The 1st-order streams within a fluvial network also exhibited the highest formula diversity as well as the greatest numbers of formulae across a broad range of compound classes.
Although naphthenic acids are minor constituents in petroleum, their characterization is crucial because they are geochemically important tracers and play a key role in corrosion processes in ...refineries. Moreover, different isomers may exhibit different reactivity and may serve as potential biomarkers. However, determination of acid isomers in petroleum/hydrocarbon matrixes remains analytically challenging. Here, we achieve the separation and structural characterization of isomeric homologue series of naphthenic acids in petroleum samples by ion mobility time-of-flight mass spectrometry (IM-TOF MS). IM-TOF MS data processing and molecular formula assignments (for most abundant heteroatom classes), integrated with ion mobility data by PetroOrg software, expose structural differences and patterns among petroleum compounds and facilitate the identification of series of isomers. For example, a family of isomeric acids (C c H h O2) of double bond equivalents (DBE) = 5 and carbon number ranging from C28–C34 appear to correspond to steranoic acids. As another example, C c H h O2 isomers of DBE = 1 likely correspond to linear and isoprenoid acids. Ultra-high-resolution Fourier transform ion cyclotron resonance mass spectra serve to validate molecular formula assignments by IM-TOF and determine whether or not isobaric ions of different mobility are isomers. We conclude that ion mobility mass spectrometry constitutes a valuable new tool for rapid isomeric separation of polar compounds (such as naphthenic acids) in petroleum and other complex organic mixtures.
The most abundant and problematic metal compounds in crude oil exist as organic complexes of vanadium and nickel in porphyrin structures derived from biological molecules (chlorophyll and heme), the ...first petroleum biomarkers discovered by Alfred Treibs in the early 1930s. Detailed characterization of the type and structure of porphyrins is critical for development of petroleum upgrading processes, but also to link crude oil to source rock conditions. Because petroporphyrins concentrate in heavy oils, direct characterization challenges routine analytical techniques due to the increased complexity associated with heavy crudes. Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides ultrahigh resolving power (m/Δm 50% > 1 000 000 at m/z 500) and subppm mass error (<50 ppb) to identify nickel porphyrin isotopes for unambiguous elemental composition assignment. We also report the first simultaneous identification and categorization of both vanadyl and nickel porphyrins in the same sample, without prior sample preparation. More than 85 000 mass spectral peaks are resolved and identified in a single mass spectrum, and represent the most extensive molecular deconvolution of an organic mixture characterized to date.
We describe the design and current performance of a 14.5 T hybrid linear quadrupole ion trap Fourier transform ion cyclotron resonance mass spectrometer. Ion masses are routinely determined at 4-fold ...better mass accuracy and 2-fold higher resolving power than similar 7 T systems at the same scan rate. The combination of high magnetic field and strict control of the number of trapped ions results in external calibration broadband mass accuracy typically less than 300 ppb rms, and a resolving power of 200 000 (m/Δm 50% at m/z 400) is achieved at greater than 1 mass spectrum per second. Novel ion storage optics and methodology increase the maximum number of ions that can be delivered to the FTICR cell, thereby improving dynamic range for tandem mass spectrometry and complex mixture applications.
An ultimate goal in carbon nanoscience is to decipher formation mechanisms of highly ordered systems. Here, we disclose chemical processes that result in formation of high-symmetry clusterfullerenes, ...which attract interest for use in applications that span biomedicine to molecular electronics. The conversion of doped graphite into a C
cage is shown to occur through bottom-up self-assembly reactions. Unlike conventional forms of fullerene, the iconic Buckminsterfullerene cage, I
-C
, is entirely avoided in the bottom-up formation mechanism to afford synthesis of group 3-based metallic nitride clusterfullerenes. The effects of structural motifs and cluster-cage interactions on formation of compounds in the solvent-extractable C
-C
region are determined by in situ studies of defined clusterfullerenes under typical synthetic conditions. This work establishes the molecular origin and mechanism that underlie formation of unique carbon cage materials, which may be used as a benchmark to guide future nanocarbon explorations.
High resolution mass spectrometry is a key technology for in-depth protein characterization. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enables high-level ...interrogation of intact proteins in the most detail to date. However, an appropriate complement of fragmentation technologies must be paired with FTMS to provide comprehensive sequence coverage, as well as characterization of sequence variants, and post-translational modifications. Here we describe the integration of front-end electron transfer dissociation (FETD) with a custom-built 21 tesla FT-ICR mass spectrometer, which yields unprecedented sequence coverage for proteins ranging from 2.8 to 29 kDa, without the need for extensive spectral averaging (e.g., ~60% sequence coverage for apo-myoglobin with four averaged acquisitions). The system is equipped with a multipole storage device separate from the ETD reaction device, which allows accumulation of multiple ETD fragment ion fills. Consequently, an optimally large product ion population is accumulated prior to transfer to the ICR cell for mass analysis, which improves mass spectral signal-to-noise ratio, dynamic range, and scan rate. We find a linear relationship between protein molecular weight and minimum number of ETD reaction fills to achieve optimum sequence coverage, thereby enabling more efficient use of instrument data acquisition time. Finally, real-time scaling of the number of ETD reactions fills during method-based acquisition is shown, and the implications for LC-MS/MS top-down analysis are discussed.
Graphical Abstract
ᅟ
Aminoacyl-tRNA synthetases-interacting multifunctional protein3 (AIMP3/p18) is involved in the macromolecular tRNA synthetase complex via its interaction with several aminoacyl-tRNA synthetases. ...Recent reports reveal a novel function of AIMP3 as a tumor suppressor by accelerating cellular senescence and causing defects in nuclear morphology. AIMP3 specifically mediates degradation of mature Lamin A (LmnA), a major component of the nuclear envelope matrix; however, the mechanism of how AIMP3 interacts with LmnA is unclear. Here we report solution-phase hydrogen/deuterium exchange (HDX) for AIMP3, LmnA, and AIMP3 in association with the LmnA C-terminus. Reversed-phase LC coupled with LTQ 14.5 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results in high mass accuracy and resolving power for comparing the D-uptake profiles for AIMP3, LmnA, and their complex. The results show that the AIMP3-LmnA interaction involves one of the two putative binding sites and an adjacent novel interface on AIMP3. LmnA binds AIMP3 via its extreme C-terminus. Together these findings provide a structural insight for understanding the interaction between AIMP3 and LmnA in AIMP3 degradation.
One fundamental challenge with either acute or chronic oil spills is to identify the source, especially in highly polluted areas, near natural oil seeps, when the source contains more than one ...petroleum product or when extensive weathering has occurred. Here we focus on heavy fuel oil that spilled (∼200 000 L) from two suspected fuel tanks that were ruptured on the motor vessel (M/V) Cosco Busan when it struck the San Francisco-Oakland Bay Bridge in November 2007. We highlight the utility of principal component analysis (PCA) of elemental composition data obtained by high resolution FT-ICR mass spectrometry to correctly identify the source of environmental contamination caused by the unintended release of heavy fuel oil (HFO). Using ultrahigh resolution electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry, we uniquely assigned thousands of elemental compositions of heteroatom-containing species in neat samples from both tanks and then applied principal component analysis. The components were based on double bond equivalents for constituents of elemental composition, C c H h N1S1. To determine if the fidelity of our source identification was affected by weathering, field samples were collected at various intervals up to two years after the spill. We are able to identify a suite of polar petroleum markers that are environmentally persistent, enabling us to confidently identify that only one tank was the source of the spilled oil: in fact, a single principal component could account for 98% of the variance. Although identification is unaffected by the presence of higher polarity, petrogenic oxidation (weathering) products, future studies may require removal of such species by anion exchange chromatography prior to mass spectral analysis due to their preferential ionization by ESI.
PDF
