![]() Herein, we determined PPase-catalyzed O-isotope exchange rates between DIP and water over the range of typical Earth surface temperatures (3 - 37 ☌) using isotope ratio mass spectrometry (IRMS). One enzyme suggested to dominate P-cycling in nature is inorganic pyrophosphatase (PPase), a ubiquitous intracellular enzyme that catalyzes oxygen (O) isotope exchange between DIP and water. In natural aqueous systems, reactive inorganic phosphorus is dominantly present as dissolved inorganic phosphate (DIP), and reactions involving DIP are primarily carried out by microorganisms and catalyzed by enzymes. The oxygen isotope composition of phosphate ( δ 18O PO4) has been widely used as (paleo)temperature and bio-signature proxies and a tracer of biogeochemical cycling of phosphorus (P). followed by the proton transfer from N 1 and N 2 of G producing radicals HN-NO 2H.The electron transfer occurs in the 3HN-NO 2 …G complex and generates G + The reduction potential of 3HN-NO 2 is E red( 3HN-NO 2) = 1.23 V vs. The hydrogen-bonded complex is identified based on the blue shift evolvement of the absorption maximum of 3HN-NO 2 in alcoholic solutions. 3HN-NO 2 can interact with guanosine (G) to form the hydrogen-bonded 3HN-NO 2 …G complex with the rate constant k=(8.7 ± 0.3)×10 9 M −1⋅s −1. Consequently, its nitro group exhibits the hydrogen bond accepting ability. 3HN-NO 2 has increased basicity compared to its ground state. Excitation of 4-nitroindole generates the lowest triplet excited state 4-nitroindole ( 3HN-NO 2) within 10 ns in the quantum yield 0.41. The photochemical reaction of 4-nitroindole and guanosine was studied with the transient absorption spectroscopy as guanine is an effective hole trap during the charge transfer in DNA, and 4-nitroindole is a universal base. The equation presented here is thus, specific to equilibrium fractions between dissolved phosphate and water and appropriate for use in recent/future oxygen isotope studies of dissolved phosphate using similar cf-irms TC/EA analytical methods. Dissolved phosphate–water fractionations are offset by +0.9 to +2.3‰ from the earlier empirical relation for biogenic phosphate–water fractionation determined using fluorination of BiPO 4. ![]() Here, we present a new experimentally-determined equation for thermodynamic equilibrium O-isotope fractionations between dissolved phosphate and water, catalyzed by the enzyme inorganic pyrophosphatase (PPase) between 3 and 37 ☌ The new equation is slightly offset by +0.5 to +0.7‰ from recent empirically-determined fractionations based on biogenic apatite, with both based on modern cf-irms TC/EA analysis of Ag 3PO 4. In natural aqueous systems (e.g., oceans, rivers, soil/ground water) the largest reactive phosphorus pool is dissolved inorganic phosphate. The stable oxygen isotope composition of orthophosphate (δ 18O PO4) is a widely used (paleo)temperature indicator and more recently, a useful tracer of phosphorus-cycling. ![]()
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