6533b829fe1ef96bd12896fb

RESEARCH PRODUCT

Optimizing [13N]N2 radiochemistry for nitrogen-fixation in root nodules of legumes

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Here we explored the conditions for synthesizing [ 13 N]N 2 in a state that is suitable for the administration to plant root nodules enabling studies of nitrogen fixation. [ 13 N]N 2 was prepared batchwise, starting with [ 13 N]NO ― 3 from the 16 O(p,α) 13 N nuclear reaction on a liquid water target. [ 13 N]NO ― 3 was first reduced to [ 13 N]NH 3 using Devarda's alloy, and then the [ 13 N]NH 3 was oxidized to [ 13 N]N 2 by hypobromite using carrier-added NH 4 CI. The amounts of carrier NH 4 CI and hypobromite were varied to determine the effects these parameters had on the radiochemical yield, and on the radiotracer specific activity. As expected, increasing the amount of carrier NH 4 CI improved the radiochemical yield. Unexpectedly, increasing the amount of excess hypobromite from 1.6-fold to 6-fold molar equivalents (relative to NH 4 CI) improved the radiochemical yield and radiotracer specific activity under all conditions of carrier NH 4 Cl. As a comparison, we measured [ 13 N]N 2 specific activity derived from in-target production based on a 50 μA min irradiation driving the 14 N(p,pn) 13 N reaction on a gaseous N 2 target. The 'wet' radiochemistry approach afforded two advantages over the in-target approach with a ∼600-fold improvement in specific activity, and the ability to collect the tracer in a small volume of gas (∼20 mL at STP).