Astrobiology Science Conference 2017 (LPI Contrib. No. 1965) 3329.pdf STRUVITE (NH4MgPO4 6H2O) AS A PREBIOTIC MINERAL AND SOURCE OF AVAILABLE PHOSPHATE. C. Menor-Salvan1, B. Burcar1, M. Pasek2 and N.V. Hud1, 1School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30033 (USA), [email protected], 2School of Geosci- ences, University of South Florida, Tampa, FL (USA). Introduction: The natural occurrence of struvite is urea solution at 65 ºC, pH 5.5 to 8, in a glass vial. The uncommon and associated with the decay of putrescent solutions were left drying and diluted with a magnesi- organic matter ever since its first description [1]. Stru- um sulfate solution. The wet-dry cycles were repeated vite is also formed as a biomineral in microbial ecosys- over the course of two weeks. The solid material tems and in the kidneys of fish and mammal. The min- (Fig.1) was analyzed by Raman spectroscopy and X- eral was first discovered in the subsoil of the St. Nicho- ray diffraction. las church in Hamburg, built over an ancient deposit of manure. Struvite is unstable when exposed to our oxy- genated atmosphere, a fact that limits its natural occur- rence. Struvite gained interest among prebiotic chem- ists due to its ability to efficiently transfer phosphate in a potential prebiotic formation of nucleotides [2]. However, concerns regarding the prebiotic availability of struvite [3] and the fixation of inorganic phosphate in the form of highly insoluble minerals, the so-called ‘phosphate problem’ [4], led researchers to consider other alternatives in the prebiotic formation of organo- Fig.1: Gypsum and Newberyite formed by hydroxylap- phosphates [5]. If Earth had an active prebiotic organic atite alteration. chemistry, including in situ synthesis and/or delivery of organic precursors from meteorites or comets, it is rea- As a proof of concept, we performed the synthesis sonable to propose the existence of pools containing of struvite in model prebiotic conditions using free water-soluble organics on the prebiotic Earth that phosphate, demonstrating that the rate of non- would have been concentrated by water evaporation. enzymatic urea decomposition is sufficient for the effi- One of the organics enriched in the pools would likely cient crystallization of struvite. We also observed the have been urea, an abundant product of model prebi- fast transformation of struvite into newberyite otic reactions [6]. Living matter is not a prerequisite (Mg(PO3OH)·3H2O), a mineral that maintains the for the formation of struvite, just organic matter in an- phosphorylation ability of struvite. oxic conditions. One of the best places for the for- We found the thermodinamically favorable (K= 1059 at 298 K) reaction: mation of struvite are the manure ponds associated with + 2+ 2- agriculture, where the decomposition of urea into am- H + 1.5(NH2)2CO + 30H2O + 4.5Mg + 5SO4 + Ca5(PO4)3OH monia and CO2 is the driving reaction for the struvite formation. Interestingly, struvite is the dominant phos- 3MgNH4PO4·6H2O + 5CaSO4·2H2O + 1.5MgCO3 phate mineral in these environments, and the calcium for the secondary formation of struvite from hydro- phosphates (such as brushite) are less common, with xyapatite. This phosphate mobilization reaction in- negligible apatite formation. We hypothesized that duced by urea is directly connected with the phosphor- fresh water ponds on prebiotic Earth would have had ylation of nucleosides, linking the geochemistry of organic matter in common with modern manure ponds phosphate with the prebiotic formation of nucleotides (without the enzymatic decomposition of organics by and other organophosphates in a one-pot, evaporating bacteria), so we investigated struvite formation in these water pool scenario [6]. model prebiotic environments, a process that could References: make phosphate available for the prebiotic formation [1] Ulex G.L. (1846) Philosophical Magazine Se- of nucleotides [7]. ries, 3, 29:192, 124-128. [2] Gull M., Pasek M.A. Results and Discussion: To test the formation of (2013) Life 3, 321-330. [3] Handschuh G.J. and Orgel struvite as a potential solution to the ‘phosphate prob- L.E. (1973) Science 179, 483-484. [4] Schwartz, A.W. lem’, we used hydroxylapatite as primary phosphate (2006) Phil. Trans. R. Soc. B, 361, 1743-1749. [5] and epsomite as magnesium source. Hydroxyapatite Benner. [6] Förstel M. et al. (2015) Chem. Comm. 52, was treated with a magnesium sulfate and an aqueous 741-744. [7] Burcar, B. et al. (2016) Angew. Chem. Int. Ed. 55, 13249-13253. .