Subcritical water extraction of amino acids from Atacama Desert soils

Abstract

[1] Amino acids are considered organic molecular indicators in the search for extant and extinct life in the Solar System. Extraction of these molecules from a particulate solid matrix, such as Martian regolith, will be critical to their in situ detection and analysis. The goals of this study were to optimize a laboratory amino acid extraction protocol by quantitatively measuring the yields of extracted amino acids as a function of liquid water temperature and sample extraction time and to compare the results to the standard HCl vapor-phase hydrolysis yields for the same soil samples. Soil samples from the Yungay region of the Atacama Desert (Martian regolith analog) were collected during a field study in the summer of 2005. The amino acids (alanine, aspartic acid, glutamic acid, glycine, serine, and valine) chosen for analysis were present in the samples at concentrations of 1-70 parts-per-billion. Subcritical water extraction efficiency was examined over the temperature range of 30-325°C, at pressures of 17.2 or 20.0 MPa, and for water-sample contact equilibration times of 0-30 min. None of the amino acids were extracted in detectable amounts at 30°C (at 17.2 MPa), suggesting that amino acids are too strongly bound by the soil matrix to be extracted at such a low temperature. Between 150°C and 250°C (at 17.2 MPa), the extraction efficiencies of glycine, alanine, and valine were observed to increase with increasing water temperature, consistent with higher solubility at higher temperatures, perhaps due to the decreasing dielectric constant of water. Amino acids were not detected in extracts collected at 325°C (at 20.0 MPa), probably due to amino acid decomposition at this temperature. The optimal subcritical water extraction conditions for these amino acids from Atacama Desert soils were achieved at 200°C, 17.2 MPa, and a water-sample contact equilibration time of 10 min.

Compressed fluids for the extraction of bioactive compounds

“…Even if it has been repeatedly observed that bioactive extracts might be obtained at high temperatures (maintaining the solvent's liquid state), this parameter should be studied and selected for each type of matrix/bioactive being extracted. On the other hand, possible formation of new components in the extracts, as a result of the occurrence of different reaction during the extraction process, has to be considered [73,74]. This point, that is clear shortcoming when the natural composition of a sample is sought, has been considered by some authors as an additional advantage in terms of bioactivity of the achieved extracts [75].…”

Earth as a Tool for Astrobiology—A European Perspective

“…The Yungay (Chile) and Arequipa (Peru) regions of the Atacama Desert are the driest hot places on Earth, serving as a compositional Martian analogue because of its sulphate and perchlorate mineralogy and low organic content (Catling et al 2010;Peeters et al 2009;Buch et al 2006;Amashukeli et al 2007;Meunier et al 2007;Skelley et al 2007). This is suggested to be the result of the highly oxidizing composition of the Atacama Desert soil (Sutter et al 2005;Ewing et al 2006;Navarro-González et al 2003;Lester et al 2007).…”

Capillary Electrophoresis Analysis of Organic Amines and Amino Acids in Saline and Acidic Samples Using the Mars Organic Analyzer

“…The analysis via the optimized protocol, however, allowed for identification of several amino acids and quantitation of total amino acid content at 450 mM. This result is a significant advance in the MOA capabilities because it demonstrates the potential for the direct analysis of aqueous extracts without extensive preprocessing (Kminek et al, 2000;Amashukeli et al, 2007).…”