Reduction of Nitrite and Nitrate to Ammonium on Pyrite

Abstract

An important constraint on the formation of the building blocks of life in the Hadean is the availability of small, activated compounds such as ammonia (NH(3)) relative to its inert dinitrogen source. Iron-sulfur particles and/or mineral surfaces have been implicated to provide the catalytic active sites for the reduction of dinitrogen. Here we provide a combined kinetic, spectroscopic, and computational modeling study for an alternative source of ammonia from water soluble nitrogen oxide ions. The adsorption of aqueous nitrite (NO(2)(-)) and nitrate (NO(3)(-)) on pyrite (FeS(2)) and subsequent reduction chemistry to ammonia was investigated at 22°C, 70°C, and 120°C. Batch geochemical and in situ Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR) spectroscopy experiments were used to determine the reduction kinetics to NH(3) and to elucidate the identity of the surface complexes, respectively, during the reaction chemistry of NO(2)(-) and NO(3)(-). Density functional theory (DFT) calculations aided the interpretation of the vibrational data for a representative set of surface species. Under the experimental conditions used in this study, we detected the adsorption of nitric oxide (NO) intermediate on the pyrite surface. NH(3) production from NO(2)(-) occurred at 70 and 120°C and from NO(3)(-) occurred only at 120°C.

The evolution of Earth's biogeochemical nitrogen cycle

“…Rates of up to 10 12 mol N/yr may have been achieved under high pCH 4 (1000ppmv) and <1% pCO 2 favoring the production of HCN later in the Archean (Tian et al, 2011;Zahnle, 1986), but pCH 4 would probably have been low in the Hadean under prebiotic conditions prior to the origin of methanogenic microbes, lowering this flux to 10 9 mol N/yr. Lightning and volcanism both generate NO x species which could have been reduced abiotically into the more bioavailable NH 4 + in hydrothermal vents, catalyzed by sulfide minerals or native metals (Brandes et al, 1998;Singireddy et al, 2012;Smirnov et al, 2008;Summers and Chang, 1993), provided that the reduction did not stop at N 2 (Section 2.3). Reduction of NO x to N 2 may have greatly diminished the abiotic supply of fixed nitrogen to prebiotic reactions and the earliest biosphere.…”

New insights into the evolutionary history of biological nitrogen fixation

“…Most N on Earth is in the form of dinitrogen (N 2 ), which is not bio-available. On early Earth, fixed sources of N may have been supplied by abiotic processes such as electrical (i.e., lightning) based oxidation of N 2 to nitric oxide (NO) (Yung and McElroy, 1979; Kasting and Walker, 1981) or mineral (e.g., ferrous sulfide) based reduction of N 2 (Schoonen and Xu, 2001; Summers et al, 2012), nitrous oxide (Summers et al, 2012), or nitrite (NO − 2 )/nitrate (NO − 3 ) (Summers, 2005; Singireddy et al, 2012) to NH 3 . Abiotic sources of fixed N (e.g., NO, NO − 2 , NO − 3 , NH 3 ) are thought to have become limiting to an expanding global biome (Kasting and Siefert, 2001; Navarro-González et al, 2001), which may have precipitated the innovation of biological mechanisms to reduce N 2 .…”

Nitrogenous Derivatives of Phosphorus and the Origins of Life: Plausible Prebiotic Phosphorylating Agents in Water

“…Whether such concentrations of ammonia would have been available on early earth has been a matter of debate [ 126 ] in terms of a reducing atmosphere which is important for generation of organic compounds. However, there seems to be various avenues by which ammonia could have been available on early earth for further processing [ 127 , 128 , 129 , 130 , 131 ]. There are also some mechanisms that can provide some concentration of ammonia (as ammonium species) on early earth [ 132 , 133 ].…”