Publications

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2013
Bennett, RV, Cleaves HJ, Davis JM, Sokolov DA, Orlando TM, Bada JL, Fernandez FM.  2013.  Desorption Electrospray Ionization Imaging Mass Spectrometry as a Tool for Investigating Model Prebiotic Reactions on Mineral Surfaces. Analytical Chemistry. 85:1276-1279.   10.1021/ac303202n   AbstractWebsite

Mineral-assisted thermal decomposition of formamide (HCONH2) is a heavily studied model prebiotic reaction that has offered valuable insights into the plausible pathways leading to the chemical building blocks of primordial informational polymers. To date, most efforts have focused on the analysis of formamide reaction products released in solution, although several studies have examined the role of mineral catalysts in promoting this chemistry. We show here that the direct investigation of reactive mineral surfaces by desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) gives a new perspective on the important role of the mineral surface in the formation of reaction products. As a proof-of-principle example, we show that DESI-MSI allows interrogation of the molecular products produced on heterogeneous granite samples with minimal sample preparation. Purine and pyrimidine nucleobases and their derivatives are successfully detected by DESI-MSI, with a strong correlation of the spatial product distribution with the mineral microenvironment. To our knowledge, this study is the first application of DESI-MSI to the study of complex and porous mineral surfaces and their roles in chemical evolution. This DESI-MSI approach is generally applicable to a wide range of reactions or other processes involving minerals.

2006
Skelley, AM, Cleaves HJ, Jayarajah CN, Bada JL, Mathies RA.  2006.  Application of the mars organic analyzer to nucleobase and amine biomarker detection. Astrobiology. 6:824-837.   10.1089/ast.2006.6.824   AbstractWebsite

The Mars Organic Analyzer (MOA), a portable microfabricated capillary electrophoresis instrument being developed for planetary exploration, is used to analyze a wide variety of fluorescamine-labeled amine-containing biomarker compounds, including amino acids, mono-and diaminoalkanes, amino sugars, nucleobases, and nucleobase degradation products. The nucleobases cytosine and adenine, which contain an exocyclic primary amine, were effectively labeled, separated, and detected at concentrations < 500 nM. To test the general applicability of the MOA for biomarker detection, amino acids and mono- and diamines were extracted from bacterial cells using both hydrolysis and sublimation followed by analysis. The extrapolated limit of detection provided by the valine biomarker was similar to 4 x 10(3) cells per sample. Products of an NH4CN polymerization that simulate a prebiotic synthesis were also successfully isolated via sublimation and analyzed. Adenine and alanine/serine were detected with no additional sample cleanup at 120 +/- 13 mu M and 4.1 +/- mu M, respectively, corresponding to a reaction yield of 0.04% and 0.0003%, respectively. This study demonstrates that the MOA provides sensitive detection and analysis of low levels of a wide variety of amine-containing organic compounds from both biological and abiotic sources.

2004
Glavin, DP, Cleaves HJ, Schubert M, Aubrey A, Bada JL.  2004.  New method for estimating bacterial cell abundances in natural samples by use of sublimation. Applied and Environmental Microbiology. 70:5923-5928.   10.1128/aem.70.10.5923-5928.2004   AbstractWebsite

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500degreesC for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from similar to10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DA-PI (4,6-diamidino-2-phenylindole) staining.

1992
Chen, RF, Bada JL.  1992.  The Fluorescence of Dissolved Organic-Matter in Seawater. Marine Chemistry. 37:191-221.   10.1016/0304-4203(92)90078-o   AbstractWebsite

A total of 28 vertical profiles of seawater fluorescence was measured in the Sargasso Sea, the Straits of Florida, the Southern California Borderlands, and the central Pacific Ocean. In all cases, surface seawater fluorescence was low as a result of photochemical bleaching which occurs on the timescale of hours. Fluorescence of deep water was 2-2.5 times higher than that of surface waters, and was constant, implying a long residence time for fluorescent organic matter, possibly of the order of thousands of years. Fluorescence correlates well with nutrients (NO3-, PO43-) in mid-depth waters ( 100-1000 m) in the Sargasso Sea and the central North Pacific, consistent with results in the central Pacific and the coastal seas of Japan. This suggests that regeneration or formation of fluorescent materials accompanies the oxidation and remineralization of settling organic particles. The various sources and sinks of fluorescent organic matter in the global oceans are assessed. The major sources are particles and in situ formation; rivers, rain, diffusion from sediments, and release from organisms are minor sources. The major sink is photochemical bleaching.