The Geochemistry of Hydroxy- and Di-carboxylic Acids

A dissertation submitted in partial satisfaction of the
requirements for the degree of Doctor of Philosophy
in Oceanography

Edward Thomas Peltzer III
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, CA 92073

1979


ABSTRACT

A preliminary investigation of the geochemistry of the C2-C6 a-hydroxycarboxylic acids and the C2-C6 a,w-dicarboxylic acids was completed. These compounds were selected for study on the basis of their potential for revealing fundamental processes in the natural environment. In meteorites, their presence suggests that certain chemical mechanisms were active during the early phases of chemical evolution. In sediments, hydroxy and dicarboxylic acids are common products of bacterial fermentation of organic matter and are known to be suitable substrates for the growth of anaerobic bacteria. Thus, one would expect their distribution to be a reflection of in situ bacterial metabolism. In seawater, these compounds may provide important information concerning the cycling of organic carbon due to their intimate involvement in the biochemistry of living organisms.

The development of the analytical procedure was complicated by several unexpected sources of contamination, the volatility of the organic acids, and their high solubility in water. The initial extraction step usually consisted of water or acid hydrolysis. Following isolation of the organic acids by ion-exchange chromatography, they were further purified and separated into several fractions by sililca-gel chromatography. The methyl esters of the organic acids -- prepared with ethereal diazomethane -- proved to be acceptable derivatives for the identification and quantification of the compounds by gas chromatography. Combined gas chromatography-mass spectrometry was used to verify compound identifications. Diastereomeric derivatives for the estimation of the enantiomeric composition of the hydroxy acids by gas chromatography were prepared by reaction of the hydroxy acid methyl esters with N-trifluoroacetyl-L-prolyl chloride.

Several sources of routine contamination were investigated. Reagent blanks revealed that sodium hydroxide contains sufficient succinate to make it unsuitable for regeneration of the anion-exchange column. Substitution of potassium hydroxide rresulted in an acceptable procedural blank. Analysis of a human fingerprint yielded mearly pure L-lactate, some pyruvate and trace amounts of glycolate, oxalate, succinate and possibly methylsuccinate.

Analysis of the Murchinson meteorite revealed the presence of seven hydroxy acids and six dicarboxylic acids. Four of the five optically active hydroxy acids in the meteorite were shown to be racemic thereby demonstrating their probable abiotic origin. (The fifth hydroxy acid does not react with the resolving agent to form the diastereomeric derivative.) Based on previously determined rate and wquilibrium constants for the appropriate reactions, and several non-trivial assumptions, the concentrations of ammonia and hydrogen cyanide during the time of compound synthesis were estimated. Additionally, the products of an electric discharge experiment were also analyzed. Nine hydroxy acids and six carboxylic acids were found.

Box and piston cores from the Santa Barbara Basin and DSDP samples from the Cariaco Trench provided sediments representative of a variety of time scales. Four compounds were isolated and quantified: glycolic, lactic, oxalic and succinate acids. All compound concentrations tended to decrease with depth. However, in the Santa Barbara Basin sediments several sub-surface maxima were observed. Additionally, the lactic acid enantiomer composition varied substantially down core.

Surface and deep seawater samples were collected during expedition Pleiades. Four compounds were isolated: glycolic, lactic, oxalic and succinic acid. Extraction recoveries (by chelex ligand-exchange chromatography) were found to be low. Although quantitative estimates of compound concentrations were impossible, it was possible to make qualitative comparisons of compound abundances. In general, surface seawater concentrations were high in areas of high productivity, and near blank levels elsewhere. In the Panama Basin, deep water concentrations below 500 meters were not significantly above blank levels.


Acknowledgements

I would like to thank the many people who contributed to this dissertation. Without their help, I would most certainly not have been able to complete this work.

First and foremost, I thank my wife, Bev. Her love and constant support sustained me through the many hard times when my confidence and enthusiasm had waned. I would also like to thank my parents and my aunt Marnie, without their love, help and financial support my college and graduate education would never have been possible. And I especially thank my Christian friends in San Diego for their love, fellowship and prayers.

I would like to acknowledge the special contribution made by the members of my dissertation committee: Drs. G. Arrhenius, W. H. Fenical, M. Kastner, S. L. Miller, K. H. Nealson and especially Dr. J. L. Bada, whose comments and suggestions inspired and directed this research. Special thanks are also due to: Dr. D. J. Faulkner for his advice and the generous use of equipment in his laboratory; Drs. C. L. Lee and P. M. Shou for many helpful discussions and criticisms of this manuscript; Dr. P. M. Masters and Mr. M. Matthews for encouragement during those long days in the lab; and Drs. R. B. Gagosian and O. C. Zafiriou for their encouragement and patience while I finished this dissertation.

I thank Mrs. B. Stover for typing this manuscript and successfully guiding it through the many pitfalls and quagmires of the UCSD admnistration. And for their help with many things, I would like to thank Ms. S. Jorgensen and Ms. B. J. Sackville.

For technical assistance, I thank Mr. E. A. Hoopes, Ms. D. Darling, Ms. P. Snow and Mr. S. Steinberg. For assistance with the many figures and graphs, I thank Mr. M. Rolli. For his help and instructions in combined gas chromatography -- mass spectrometry, I thank Mr. R. L. LaBorde. For teching me how to pack an efficient GC column, I thank Dr. J. L. Mynderse.

I would also like to thank the many people who provided samples for analysis: Dr. S. L. Miller for samples of an electric discharge experiment; Dr. J. D. Macdougall for a sample of the Murchison meteorite; Mr. A. Soutar and Dr. J. R. Herring for Santa Barbara Basin sediment samples; Dr. W. R. Riedel for samples from DSDP cores of Cariaco Trench sediments; and Dr. R. E. McDuff for his fingerprints. I thank Dr. E. Sholkovitz for permission to re-publish some of his pore-water data for Santa Barbara Basin sediments.

For the opportunity to collect water samples on Leg I of Expedition Pleiades, I thank Drs. R. F. Weiss and P. Lonsdale. For their part in collecting these samples, I thank the captain and crew of the R/V Melville.

This work was supported in part through grants from the National Science Foundation and the Office of Naval Research to Dr. J. L. Bada.

And finally, I would like to make a special acknowledgment to Dr. W. J. H. Martinez, Mr. J. Schmidt and all the other players on the best softball team in San Diego, in spite of whom I found time to complete my research.


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