All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nucleobases in meteorites has been debated for over 50 y. So far, the few nucleobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics. Here, we investigated the abundance and distribution of nucleobases and nucleobase analogs in formic acid extracts of 12 different meteorites by liquid chromatography-mass spectrometry. The Murchison and Lonewolf Nunataks 94102 meteorites contained a diverse suite of nucleobases, which included three unusual and terrestrially rare nucleobase analogs: purine, 2,6-diaminopurine, and 6,8-diaminopurine. In a parallel experiment, we found an identical suite of nucleobases and nucleobase analogs generated in reactions of ammonium cyanide. Additionally, these nucleobase analogs were not detected above our parts-per-billion detection limits in any of the procedural blanks, control samples, a terrestrial soil sample, and an Antarctic ice sample. Our results demonstrate that the purines detected in meteorites are consistent with products of ammonium cyanide chemistry, which provides a plausible mechanism for their synthesis in the asteroid parent bodies, and strongly supports an extraterrestrial origin. The discovery of new nucleobase analogs in meteorites also expands the prebiotic molecular inventory available for constructing the first genetic molecules.

High-resolution mass spectrometry can provide a detailed fingerprint of the composition of the nonvolatile fraction of petroleum. That analysis is typically performed using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, which offers greater mass resolution than any other mass analyzer. While high resolution is desirable for complex mixtures, such as petroleum, the high costs associated with FT-ICR limit its use to a small number of research laboratories, limiting the impact of the measurement relative to more accessible techniques. Here, we explore whether there is a role for other high-resolution mass analyzers to complement FT-ICR. One such high-resolution mass analyzer is the LTQ Orbitrap XL, which presents significantly lower costs relative to typical FT-ICR instruments. The Orbitrap mass analyzer provides mass resolution inferior to the modern FT-ICR instrument but still sufficient to assign molecular formulas to individual components present in mixtures, especially those components present in relatively high abundance. Indeed, the resolution of the LTQ Orbitrap XL is comparable to that obtained by FT-ICR instruments 1 decade ago, at which time FT-ICR was being used successfully to fingerprint petroleum. Here, we demonstrate successful application of the Orbitrap to resolve and identify >1000 of the more abundant molecular formulas in the negative ion electrospray ionization mass spectrum of a petroleum sample. These results are compared to the 9.4 T FT-ICR analysis of the same sample (published previously; Pomerantz, A. E.; Ventura, G. T.; McKenna, A. M.; Cañas, J.; Auman, J.; Koerner, K.; Curry, D.; Nelson, R. K.; Reddy, C. M.; Rodgers, R. P.; Marshall, A. G.; Peters, K. E.; Mullins, O. C. Combining biomarker and bulk compositional gradient analysis to assess reservoir connectivity. Org. Geochem. 2010, 41, 812À821), and in this analysis, both the compositional fingerprints and conclusions derived from those fingerprints are essentially the same for the FT-ICR and Orbitrap data. Setting up and operating a LTQ Orbitrap XL mass spectrometer presents significantly lower initial and continuing costs compared to setting up and operating a 9.4 T FT-ICR, and this difference may make the Orbitrap accessible to laboratories for which FT-ICR is cost-prohibitive. Although several valuable high-resolution mass spectrometric analyses require the extremely high resolution of FT-ICR, we propose Orbitrap mass spectrometry as a method for routine analysis of the composition of the more abundant species in the nonvolatile and polar fraction of petroleum. Extending the realm of high-resolution mass spectrometry from a limited research environment to routine analysis would increase the utility of the technique and the impact of fundamental research regarding mass spectrometry of petroleum.

The collision-induced dissociation (CID) mass spectra of several protonated benzylamines are described and mechanistically rationalized. Under collision-induced decomposition conditions, protonated dibenzylamine, for example, loses ammonia, thereby forming an ion of m/z 181. Deuterium labeling experiments confirmed that the additional proton transferred to the nitrogen atom during this loss of ammonia comes from the ortho positions of the phenyl rings and not from the benzylic methylene groups. A mechanism based on an initial elongation of a C--N bond at the charge center that eventually cleaves the C--N bond to form an ion/neutral complex of benzyl cation and benzylamine is proposed to rationalize the results. The complex then proceeds to dissociate in several different ways: (1) a direct dissociation to yield a benzyl cation observed at m/z 91; (2) an electrophilic attack by the benzyl cation within the complex on the phenyl ring of the benzylamine to remove a pair of electrons from the aromatic sextet to form an arenium ion, which either donates a ring proton (or deuteron when present) to the amino group forming a protonated amine, which undergoes a charge-driven heterolytic cleavage to eliminate ammonia (or benzylamine) forming a benzylbenzyl cation observed at m/z 181, or undergoes a charge-driven heterolytic cleavage to eliminate diphenylmethane and an immonium ion; and (3) a hydride abstraction from a methylene group of the neutral benzylamine to the benzylic cation to eliminate toluene and form a substituted immonium ion. Corresponding benzylamine and dibenzylamine losses observed in the spectra of protonated tribenzylamine and tetrabenzyl ammonium ion, respectively, indicate that the postulated mechanism can be widely applied. The postulated mechanisms enabled proper prediction of mass spectral fragments expected from protonated butenafine, an antifungal drug.

Collision-induced dissociation (CID) mass spectra of anions derived from several hydroxyphenyl carbaldehydes and ketones were recorded and mechanistically rationalized. For example, the spectrum of m/z 121 ion of deprotonated ortho-hydroxybenzaldehyde shows an intense peak at m/z 93 for a loss of carbon monoxide attributable to an ortho-effect mediated by a charge-directed heterolytic fragmentation mechanism. In contrast, the m/z 121 ion derived from meta and para isomers undergoes a charge-remote homolytic cleavage to eliminate an žH and form a distonic anion radical, which eventually loses CO to produce a peak at m/z 92. In fact, for the para isomer, this two-step homolytic mechanism is the most dominant fragmentation pathway. The spectrum of the meta isomer on the other hand, shows two predominant peaks at m/z 92 and 93 representing both homolytic and heterolytic fragmentations, respectively.18 O-isotope-labeling studies confirmed that the oxygen in the CO molecule that is eliminated from the anion of meta-hydroxybenzaldehyde originates from either the aldehydic or the phenolic group. In contrast, anions of ortho-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde, both of which show two consecutive CO eliminations, specifically lose the carbonyl oxygen first, followed by that of the phenolic group. Anions from 2-hydroxyphenyl alkyl ketones lose a ketene by a hydrogen transfer predominantly from the a position. Interestingly, a very significant charge-remote 1,4-elimination of a H 2 molecule was observed from the anion derived from 2,4-dihydroxybenzaldehyde. For this mechanism to operate, a labile hydrogen atom should be available on the hydroxyl group adjacent to the carbaldehyde functionality.

Fluorescent lipids are important tools for live imaging in cell culture and animal models, yet their metabolism has not been well-characterized. Here we describe a novel combined HPLC and LC-MS/MS method developed to characterize both total lipid profiles and the products of fluorescently labeled lipids. Using this approach, we found that lipids labeled with the fluorescent tags, 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza--indacene (BODIPY FL), 4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza--indacene [BODIPY(558/568)], and dipyrrometheneboron difluoride undecanoic acid (TopFluor) are all metabolized into varying arrays of polar and nonpolar fluorescent lipid products when they are fed to larval zebrafish. Quantitative metabolic labeling experiments performed in this system revealed significant effects of total dietary lipid composition on fluorescent lipid partitioning. We provide evidence that cholesterol metabolism in the intestine is important in determining the metabolic fates of dietary FAs. Using this method, we found that inhibitors of dietary cholesterol absorption and esterification both decreased incorporation of dietary fluorescent FAs into cholesterol esters (CEs), suggesting that CE synthesis in enterocytes is primarily responsive to the availability of dietary cholesterol. These results are the first to comprehensively characterize fluorescent FA metabolism and to demonstrate their utility as metabolic labeling reagents, effectively coupling quantitative biochemistry with live imaging studies.