On the Use of Biomarkers in the Search for Life on Mars Vera M. Kolb, Department of Chemistry E-mail: kolb@uwp.edu

Abstract We have examined a large number of chemical structures of

biomarkers including those from (poly)extremophiles and have analyzed their IR spectra, from the literature or our own. We conclude that the IR is a valuable tool for in situ measurements on Mars or on the samples returned from Mars. While characteristic bands are mostly constant, there is a problem with biosilicification and formation of organo-silicates. These can be observed in the IR, however.

Some insights about the use of biomarkers from Earth as potential biosignatures in search of life on Mars:

Flores-Martinez (2015) .“Convergent evolution and the search for biosignatures within the solar system and beyond,” Acta Astronautica, 116, 394-402:

Biomolecules will be re-discovered by nature as they are needed for life (convergent molecular evolution); “Structural universals” as convergent traits;

“The usefulness of a biosignature is determined, not only by the probability of life creating it, but also by the improbability of non-biological processes producing it.”

Selected examples of biomarkers Examples of compounds which have been studied as biomarkers for various astrobiological applications are: chlorophyll; phycoerhythorbilin(accessory pigment); menaquinone (redox coenzyme); AHLs (acyl homoserine lactone autoinducers for quorum sensing); scytonemin (UV-radiation screening pigment); DPA (dipicolinic acid found in bacterial spores); phenazines (electron acceptors); ladderane lipids; AI-2 (boron-containing autoinducer involved in quorum sensing); quinolone molecules (involved in quorum sensing); pyrrones (signaling molecules); DARs (dialkylresorcinols) and DHDs (cyclohexanediones) (signaling molecules in bacteria); cyclic dipeptides and DKPs (diketopiperazines) (they interfere with the quorum-sensing systems in various bacteria); PQS; HHQ; pyoverdine (signaling under low iron condition), and DSF (diffusible signal factor family, able to cross cell membranes by passive diffusion).

N

N

N

NMg

OH

O

N

N

N COOHHOOC

COOH

B

O

O

O

HO

HO CH3

HO

HO

NH

O

OH

IR studies of biomarkers and their molecular analogs

-IR vs Raman

-Which bands are we looking for?

-Which bands are constant, and which move?

-Silicification of alcohols and phenols in context of molecular fossils

-Must take into account Ithe R of the mineral background

-Complexation with metals and its influence on the position of the -IR bands

-Shifting of bands of an individual organic compound when found in the mixture of organic compounds .

Si

OH

HO OH

OH

O

Si

O

Si

O

Si

O

OH

HO

O

HO

OH

HO

Si

OHO

O

Si

O

Si

O

Si

O

OH O

HO

OH

O

Si

OO

O

CH2

HC

COOH

NH2

CH

HC

COOH

NH2

H3C

HHO

HHOH2C

O

O

H

H

O

Si

O

SiO

SiO

SiO

Si

O

SiO

SiO

Si

OSi

OSi

O

Si

O

Si

O Si

O

HOOH

HO

HOO

OH

OH

OH

OH

OH

OH

HO OH

HO OH

HOOH

OH

OHHOOH

HO

HOOH

HO

HOOH

Compound Si-O-Si band (cm-1)

Si-O-C band (cm-1)

Hydrocarbons in 2800-3200

cm-1 range

Mechanism of

silicification

Polydimethoxysiloxane (known organo-silicate)

1091 1197 2950, 2847 (alkyl)

NA

Acidified Na-Silicate (“plain” silica gel)

1088 –– –– Catalysis

Amino Acid (Serine)

(Proline)

1077 1060

–– ––

–– 2952, 2925, 2859 (alkyl)

Catalysis Catalysis/ Entombment

Maillard Mixture (Serine)

(Glycine)

1095

1093

––

––

2952, 2926, 2855 (alkyl)

––

Catalysis/ Entombment Catalysis

Maillard Complex (Iron (III) Sucrose Complex)

1039

––

––

Catalysis, Entombment of metal ions

Sugar & (Ribose)

Sugar Alcohol (Sorbitol)

1086 1076

–– ––

–– ––

Catalysis Catalysis

Alcohol (n-butanol) 1009 –– –– Catalysis, Covalent Bonding

Amino Alcohol (ethanolamine)

1023 1158 2963, 2890 (alkyl)

Covalent Bonding

Acid Halide 1087 1178 3107 (aryl) Covalent Bonding

Class of Organic Molecule

Notes

Amino Acids (AA): Biological AA: Meteoritic AA: (Sarcosine and 5- Aminovaleric Acid)

Mechanism: Catalysis. Entombment possible in trace amounts; low levels of organics detected in some cases. Gel formation and appearance: Immediate formation of rubbery or hard whitish opaque gels. Gels are not water-soluble. Dried gels consist of small white chunks and powder. Sol-Gel-Sol Transformation: Some transformations were seen. Gel formation and appearance: Sarcosine behaved similarly to the biological A.A. 5-Aminovaleric acid did not result in immediate gel formation. Gel isolated from 5-aminovaleric acid was water-soluble. Sol-Gel-Sol Transformation: Some transformations were seen with sarcosine.

Maillard Mixtures:

Mechanism: Catalysis. Entombment possible in trace amounts; low levels of organics detected in some cases. Gel formation and appearance: Rubbery gels quickly form, often within a minute or less. Gels are originally whitish but darken to orange and brown within days. Dried gels consist of white chunks and powder. Sol-Gel-Sol Transformation: Major transformations were seen.

Maillard-Metal Complexes:

Mechanism: Catalysis. No organics detected in the IR spectra. Gel formation and appearance: Soft gels quickly form, often within seconds, but may take up to 30 minutes to form. Gels are brownish. Dried gels from Fe-containing complexes were gray in color. All other metals resulted in whitish dried gels. Sol-Gel-Sol Transformation: Major transformations were seen. Other: The gels from Fe-containing complexes were the only ones in our laboratory that kept a distinct color after being dried.

Sugars and Sugar Alcohols:

Mechanism: Catalysis. No organics detected in the IR spectra to suggest otherwise. C-13 and Si-29 NMR studies suggest covalent bond formation occurs leading to the formation of water-soluble organosilicates. Gel formation and appearance: Soft, transparent gels form slowly and darken over hours and days. Gels partially water-soluble. Dried gels consist of small white chunks. Sol-Gel-Sol Transformation: Some transformations were seen.

Left: Polymerization of silicic acid Middle: An example of organo-silicate: ribose (bottom left), serine (bottom right), and threonine (top right), make Si-O-C bonds with silicic acid within the silica gel. Right: Models for biosilicification: Ethanol entombed in silica gel (inside, left), or reacted to make an organo-silicate (inside, right).

Table 2. Summary of the interactions of various organic compounds with sodium silicate.

Selected references:

1) Kolb, V. M., and Liesch, P. J. (2009). “Models for silicate fossils of organic materials in the astrobiological context”, in Sechbach, J., and Walsh, M., Eds, “From Fossils to Astrobiology”, Springer, Heidelberg, Germany, pp. 69-88.;2) Edwards, H. G.M., Hutchinson, I. B., Ingley, R., and Jehlicka, J. (2014). “Biomarkers and their Raman spectroscopic signatures: A spectral challenge for analytical astrobiology”, Phil. Trans., R. Soc., A 372, 20140193.;

3) Madejová, J., and Komadel, P. (2001). “Baseline studies of the clay minerals society source clays: Infrared methods”, Clays and Clay Minerals, 49, 410-432; 4) Dumas, S., Dutil, Y., and Joncas, G. (2010). “Detection of biomarkers using infrared spectroscopy”, Acta Astronautica, 67, 1356-1360.

Acknowledgments : Wisconsin Space Grant Consortium / NASA has sponsored our work on the formation and the IR study of organosilicates; University of Wisconsin-Parkside URAP grant (Undergraduate Research Apprenticeship Program) sponsored undergraduate research on a continuous basis.

Table 1. Summary of main trends of IR spectral analysis.

University of Wisconsin-Parkside, Kenosha, WI 53141