Jeremiah M. Purcell

Singlet oxygen in the coupled photochemical and biochemical oxidation of dissolved organic matter.

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 ((1)O(2)) on DOM by mass spectrometry with (18)O-labeled oxygen, to understand how (1)O(2)-mediated transformations of DOM may lead to altered DOM bioavailability. The photochemical oxygen uptake by DOM attributed to (1)O(2) 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 (1)O(2)-generating conditions (Rose Bengal and visible light), increases were observed in DOM constituents with higher oxygen content and release of H(2)O(2) was detected. Differential effects of H(2)O(2) and (1)O(2)-treated DOM showed that (1)O(2)-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.

Comprehensive characterization of marine dissolved organic matter by Fourier transform ion cyclotron resonance mass spectrometry with electrospray and atmospheric pressure photoionization

We compare the ultrahigh resolution 9.4 T Fourier transform ion cyclotron resonance (FT-ICR) mass spectra of marine dissolved organic matter (DOM) isolated from two sites in the Weddell Sea (Antarctica) obtained by complementary electrospray ionization (ESI) and atmospheric pressure photoionization (APPI). Ions produced by APPI extend to higher carbon unsaturation than those produced by ESI, indicated by higher double-bond equivalents (rings plus double bonds) minus oxygen (DBE-O) values, whereas ESI-generated ions are more oxygenated. Moreover, many sulfur-containing compounds were efficiently ionized by ESI but not detected by APPI. Because the mass spectra obtained by ESI and APPI are significantly different, both are necessary to obtain a more complete description of the molecular composition of marine DOM.

Microchip Atmospheric Pressure Photoionization for Analysis of Petroleum by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has significantly contributed to the molecular speciation of petroleum. However, a typical APPI source operates at 50 microL/min flow rate and thus causes a considerable mass load to the mass spectrometer. The recently introduced microchip APPI (microAPPI) operates at much lower flow rates (0.05-10 microL/min) providing decreased mass load and therefore decreased contamination in analysis of petroleum by FT-ICR MS. In spite of the 25 times lower flow rate, the signal response with microAPPI was only 40% lower than with a conventional APPI source. It was also shown that microAPPI provides very efficient vaporization of higher molecular weight components in petroleum analysis.

Synthesis and Structural Characterization of C70H38

Reference LSMB-ARTICLE-2008-007doi:10.1002/anie.200705450View record in Web of Science Record created on 2008-11-03, modified on 2017-05-12

Identifying bryostatins and potential precursors from the bryozoan Bugula neritina

The bryozoan species Bugula neritina contains the anticancer agent bryostatin. Bryostatin has been extracted from these sessile marine invertebrates since the late 1960s from the Gulf of California, Gulf of Mexico, as well as various locations on the eastern and western rims of the Pacific Ocean. In this work we are focusing on animals harvested in the Gulf of Mexico near Alligator Point (Florida). Using Inductively Coupled Plasma-Mass Spectrometry (ICP–MS) we measure the concentration of 70 elements in B. neritina, a sea squirt, and the sediment from the point of harvesting. This data has helped us generate an extraction process for marine natural products. Combining UV/VIS absorbance measurements with Matrix Assisted Laser Desorption Ionization–Time of Flight-Mass Spectrometer (MALDI–TOF-MS), we demonstrated that the specific form of bryostatin extracted is a function of the solvent. A 9.4 T Fourier Transform-Ion Cyclotron Resonance (FT-ICR) mass spectrometer, whose sensitivity, mass accuracy, and resolving power allowed the exact empirical formulas of potential precursors of bryostatin to be identified, was employed. Finally we examine extracts of 14 marine species of the Gulf of Mexico, from the sand trout (Cynoscion arenarius) to chicken liver sponge (Chrondrilla nucula), all recently collected, which had shown some medicinal activity thirty years ago in a National Cancer Institute study. By the MALDI–TOF-MS, we were able to identify mass spectral features that correspond to different variations of the basic bryostatin structure, which raises the question if the bryozoans are the original source of bryostatin.

Petroleomics: a test bed for ultra-high- resolution Fourier transform ion cyclotron resonance mass spectrometry

Within a relative abundance dynamic range of ~10,000: 1, the worlds most compositionally complex organic mixture is petroleum crude oil. As such, it provides the most challenging target for mass spectral resolution and identification of molecules below m/z 2000. The mass “splits” in petroleum include most of those that also appear in proteomics, metabolomics and other complex organic mixture analysis. Therefore, petroleum provides an excellent test bed for optimizing mass spectrometer performance in general. The presence of multiple elemental compositions spanning less than 1 Da in mass facilitates mapping and correction of rf phase variation across a Fourier transform ion cyclotron resonance mass spectrum, as well as exposing otherwise inaccessible systematic mass deviations, for additional improvement in mass resolving power and mass accuracy by a factor of up to 5. Internal mass calibration, combined with systematic peak assignment for successive homologous series, enables automated elemental composition assignment of tens of thousands of peaks in a single mass spectrum.

Kinetic Determination of Potassium Affinities by IRMPD: Elucidation of Precursor Ion Structures

Dissociation kinetics of the K(+) loss reaction of three potassiated tertiary amino acids (Scheme 1) were studied by infrared multiple photon dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT ICR)-MS instrument. The aim of the study was to probe if a kinetic study by IRMPD can yield useful information on the ion structure of the precursor ion species. The measured activation energy values determined by IRMPD are related to the potassium affinity, DeltaH(K(+)), of N-methyl proline determined by threshold collision-induced dissociation experiments. By appropriate scaling with this reference value, the experimentally determined activation energy values for the K(+) loss are transformed into respective potassium affinities, DeltaH(K(+))(IRMPD). These values match the calculated potassium affinity values for salt bridge (SB) structures, DeltaH(K(+))(SB), substantially better than those for canonical structures with a single formal charge site (charge solvation (CS)), thereby allowing structure identification. This conclusion is consistent with other spectroscopic data, which yielded unambiguous evidence of these tertiary amino acids adopting SB structures in the gas phase. This study demonstrates that IRMPD can be applied to determine individual ion structures in the gas phase, given that adequate reference values are available for proper scaling.

External electron ionization 7T Fourier transform ion cyclotron resonance mass spectrometer for resolution and identification of volatile organic mixtures

An external electron ionization (EI) source has been interfaced to a 7T Fourier transform ion cyclotron resonance mass spectrometer and tested for volatile complex mixture analysis. A new Sulfinert®-deactivated inlet system provides continuous stable sample flow to the EI source, leading to stable ion signal (±10% deviation) for 2h from a 200nL mixture of 15 n-alkylbenzenes. Ultrahigh-mass resolving power, m∕Δm50%≈735000, was obtained for 1-bromo-2-chlorobenzene with accurate isotopic ratio measurement. Base line resolution was observed for two of the closest commonly encountered mass doublets, C3∕SH4 (m2−m1=3.4mDa at m∕z=190) and SH3C13∕C4 (m2−m1=1.1mDa at m∕z=190). Although hydrocarbons dominate the positive-ion 18eV EI Fourier transform ion cyclotron resonance mass spectrum from diesel fuels, many sulfur-, nitrogen-, and oxygen-containing compounds were readily observed without prior fractionation. By comparing 18eV EI Fourier transform ion cyclotron resonance mass spectra of unprocessed and processed ...